title: Incomplete Delta Functions

abstract:
  By applying projection operators to state vectors of coordinates we obtain
subspaces in which these states are no longer normalized according to Dirac's
delta function but normalized according to what we call "incomplete delta
functions". We show that this class of functions satisfy identities similar to
those satisfied by the Dirac delta function. The incomplete delta functions may
be employed advantageously in projected subspaces and in the link between
functions defined on the whole space and the projected subspace. We apply a
similar procedure to finite dimensional vector spaces for which we define
incomplete Kronecker deltas. Dispersion relations for the momenta are obtained
and ''sums over poles'' are defined and obtained with the aid of differences of
incomplete delta functions.


title:
Motion of a spin 1/2 particle in shape invariant scalar and magnetic
  fields

abstract:
  We study the motion of a spin 1/2 particle in a scalar as well as a magnetic
field within the framework of supersymmetric quantum mechanics(SUSYQM). We also
introduce the concept of shape invariant scalar and magnetic fields and it is
shown that the problem admits exact analytical solutions when such fields are
considered.


title: Maxwell equations as the one-photon quantum equation

abstract:
  Maxwell equations (Faraday and Ampere-Maxwell laws) can be presented as a
three component equation in a way similar to the two component neutrino
equation. However, in this case, the electric and magnetic Gauss's laws can not
be derived from first principles. We have shown how all Maxwell equations can
be derived simultaneously from first principles, similar to those which have
been used to derive the Dirac relativistic electron equation. We have also
shown that equations for massless particles, derived by Dirac in 1936, lead to
the same result. The complex wave function, being a linear combination of the
electric and magnetic fields, is a locally measurable and well understood
quantity. Therefore Maxwell equations should be used as a guideline for proper
interpretations of quantum theories.


title:
A Possible New Quantum Algorithm: Arithmetic with Large Integers via the
  Chinese Remainder Theorem

abstract:
  Residue arithmetic is an elegant and convenient way of computing with
integers that exceed the natural word size of a computer. The algorithms are
highly parallel and hence naturally adapted to quantum computation. The process
differs from most quantum algorithms currently under discussion in that the
output would presumably be obtained by classical superposition of the output of
many identical quantum systems, instead of by arranging for constructive
interference in the wave function of a single quantum computer.


title: Large Numbers, the Chinese Remainder Theorem, and the Circle of Fifths

abstract:
  This is a pedagogical article cited in the foregoing research note,
quant-ph/9911050


title: Coherent states, Yang-Mills theory, and reduction

abstract:
  This paper explains some of the ideas behind a prior joint work of the author
with Bruce Driver on the canonical quantization of Yang-Mills theory on a
spacetime cylinder. The idea is that the generalized Segal-Bargmann transform
for a compact group can be obtained from the ordinary Segal-Bargmann transform
by imposing gauge symmetry.


title: A Practical Method of Constructing Quantum Combinational Logic Circuits

abstract:
  We describe a practical method of constructing quantum combinational logic
circuits with basic quantum logic gates such as NOT and general $n$-bit Toffoli
gates. This method is useful to find the quantum circuits for evaluating logic
functions in the form most appropriate for implementation on a given quantum
computer. The rules to get the most efficient circuit are utilized best with
the aid of a Karnaugh map. It is explained which rules of using a Karnaugh map
are changed due to the difference between the quantum and classical logic
circuits.


title: Security Aspects of Practical Quantum Cryptography

abstract:
  The use of quantum bits (qubits) in cryptography holds the promise of secure
cryptographic quantum key distribution schemes. Unfortunately, the implemented
schemes can be totally insecure. We provide a thorough investigation of
security issues for practical quantum key distribution, taking into account
channel losses, a realistic detection process, and modifications of the
``qubits'' sent from the sender to the receiver. We first show that even
quantum key distribution with perfect qubits cannot be achieved over long
distances when fixed channel losses and fixed dark count errors are taken into
account. Then we show that existing experimental schemes (based on
``weak-pulse'') are usually totally insecure. Finally we show that parametric
downconversion offers enhanced performance compared to its weak coherent pulse
counterpart.


title: Unconditionally Secure Relativistic Quantum Bit Commitment

abstract:
  A new relativistic quantum protocol is proposed allowing to implement the bit
commitment scheme. The protocol is based on the idea that in the relativistic
case the field propagation to the region of space accessible to measurement
requires, contrary to the non-relativistic case, a finite non-zero time which
depends on the structure of the particular state of the field. In principle,
the secret bit can be stored for arbitrarily long time with the probability
arbitrarily close to unit.


title: Construction of quantum states with bound entanglement

abstract:
  We present a new family of bound-entangled quantum states in 3x3 dimensions.
Their density matrix depends on 7 independent parameters and has 4 different
non-vanishing eigenvalues.


title: Bell Inequalities and the Separability Criterion

abstract:
  We analyze and compare the mathematical formulations of the criterion for
separability for bipartite density matrices and the Bell inequalities. We show
that a violation of a Bell inequality can formally be expressed as a witness
for entanglement. We also show how the criterion for separability and a
description of the state by a local hidden variable theory, become equivalent
when we restrict the set of local hidden variable theories to the domain of
quantum mechanics. This analysis sheds light on the essential difference
between the two criteria and may help us in understanding whether there exist
entangled states for which the statistics of the outcomes of all possible local
measurements can be described by a local hidden variable theory.


title:
Exact Bures Probabilities that Two Quantum Bits are Classically
  Correlated

abstract:
  In previous studies, we have explored the ansatz that the volume elements of
the Bures metrics over quantum systems might serve as prior distributions, in
analogy to the (classical) Bayesian role of the volume elements ("Jeffreys'
priors") of Fisher information metrics. Continuing this work, we obtain exact
Bures probabilities that the members of certain low-dimensional subsets of the
fifteen-dimensional convex set of 4 x 4 density matrices are separable or
classically correlated. The main analytical tools employed are symbolic
integration and a formula of Dittmann (quant-ph/9908044) for Bures metric
tensors. This study complements an earlier one (quant-ph/9810026) in which
numerical (randomization) --- but not integration --- methods were used to
estimate Bures separability probabilities for unrestricted 4 x 4 or 6 x 6
density matrices. The exact values adduced here for pairs of quantum bits
(qubits), typically, well exceed the estimate (.1) there, but this disparity
may be attributable to our focus on special low-dimensional subsets. Quite
remarkably, for the q = 1 and q = 1/2 states inferred using the principle of
maximum nonadditive (Tsallis) entropy, the separability probabilities are both
equal to 2^{1/2} - 1. For the Werner qubit-qutrit and qutrit-qutrit states, the
probabilities are vanishingly small, while in the qubit-qubit case it is 1/4.

categories: quant-ph math-ph math.MP physics.data-an


title:
Generalized One-Dimensional Point Interaction in Relativistic and
  Non-relativistic Quantum Mechanics

abstract:
  We first give the solution for the local approximation of a four parameter
family of generalized one-dimensional point interactions within the framework
of non-relativistic model with three neighboring $\delta$ functions. We also
discuss the problem within relativistic (Dirac) framework and give the solution
for a three parameter family. It gives a physical interpretation for so-called
$\epsilon$ potential. It will be also shown that the scattering properties at
high energy substantially differ between non-relativistic and relativistic
cases.


title: Berry phase in magnetic systems with point perturbations

abstract:
  We study a two-dimensional charged particle interacting with a magnetic
field, in general non-homogeneous, perpendicular to the plane, a confining
potential, and a point interaction. If the latter moves adiabatically along a
loop the state corresponding to an isolated eigenvalue acquires a Berry phase.
We derive an expression for it and evaluate it in several examples such as a
homogeneous field, a magnetic whisker, a particle confined at a ring or in
quantum dots, a parabolic and a zero-range one. We also discuss the behavior of
the lowest Landau level in this setting obtaining an explicit example of the
Wilczek-Zee phase for an infinitely degenerated eigenvalue.


title:
Time dynamics in chaotic many-body systems: can chaos destroy a quantum
  computer?

abstract:
  Highly excited many-particle states in quantum systems (nuclei, atoms,
quantum dots, spin systems, quantum computers) can be ``chaotic''
superpositions of mean-field basis states (Slater determinants, products of
spin or qubit states). This is a result of the very high energy level density
of many-body states which can be easily mixed by a residual interaction between
particles. We consider the time dynamics of wave functions and increase of
entropy in such chaotic systems.
  As an example we present the time evolution in a closed quantum computer. A
time scale for the entropy S(t) increase is t_c =t_0/(n log_2{n}), where t_0 is
the qubit ``lifetime'', n is the number of qubits, S(0)=0 and S(t_c)=1. At t <<
t_c the entropy is small: S= n t^2 J^2 log_2(1/t^2 J^2), where J is the
inter-qubit interaction strength. At t > t_c the number of ``wrong'' states
increases exponentially as 2^{S(t)} . Therefore, t_c may be interpreted as a
maximal time for operation of a quantum computer, since at t > t_c one has to
struggle against the second law of thermodynamics. At t >>t_c the system
entropy approaches that for chaotic eigenstates.

categories: quant-ph chao-dyn cond-mat.mes-hall cond-mat.stat-mech nlin.CD nucl-th physics.atom-ph


title: Atomic Quantum Computer

abstract:
  The current proposals for the realization of quantum computer such as NMR,
quantum dots and trapped ions are based on the using of an atom or an ion as
one qubit. In these proposals a quantum computer consists from several atoms
and the coupling between them provides the coupling between qubits necessary
for a quantum gate. We discuss whether a {\it single} atom can be used as a
quantum computer. Internal states of the atom serve to hold the quantum
information and the spin-orbit and spin-spin interaction provides the coupling
between qubits in the atomic quantum computer. In particular one can use the
electron spin resonance (ESR) to process the information encoded in the
hyperfine splitting of atomic energy levels. By using quantum state engineering
one can manipulate the internal states of the natural or artificial (quantum
dot) atom to make quantum computations.


title: Disentanglement and Inseparability correlation : in two-qubit system

abstract:
  Started from local universal isotropic disentanglement, a threshold
inequality on reduction factors is proposed, which is necessary and sufficient
for this type of disentanglement processes. Furthermore, we give the conditions
realizing ideal disentanglement processes provided that some information on
quantum states is known. In addition, based on fully entangled fraction, a
concept called inseparability correlation is presented. Some properties on
inseparability correlation coefficient are studied.


title: Time-dependent Perturbation Theory in Quantum Mechanics

abstract:
  After revealing difficulties of the standard time-dependent perturbation
theory in quantum mechanics mainly from the viewpoint of practical calculation,
we propose a new quasi-canonical perturbation theory. In the new theory, the
dynamics of physical observables, instead of that of coefficients of
wave-function expansion, is formulated so that the gauge-invariance and
correspondence principles are observed naturally.


title: Semiclassical limit of the Dirac equation and spin precession

abstract:
  We study the Dirac equation with slowly varying external potentials. Using
matrix-valued Wigner functions we prove that the electron follows with high
precision the classical orbit and that the spin precesses according to the BMT
equation with gyromagnetic ratio g=2.


title: Nonlocal kinetic theory

abstract:
  The short time behavior of a disturbed system is influenced by off-shell
motion and best characterized by the reduced density matrix possessing high
energetic tails. We present analytically the formation of correlations due to
collisions in an interacting Fermionic system with and without initial
correlation. After this short time regime the time evolution is controlled by
small gradients. This leads to a nonlocal Boltzmann equation for the
quasiparticle distribution and a functional relating the latter one to the
reduced density matrix. The nonlocalities are presented as time and space
shifts arising from gradient expansion and are leading to virial corrections in
the thermodynamical limit.


title: Quantum theory of incompatible observations

abstract:
  Maximum likelihood principle is shown to be the best measure for relating the
experimental data with the predictions of quantum theory.


title: Reconstruction of the spin state

abstract:
  System of 1/2 spin particles is observed repeatedly using Stern-Gerlach
apparatuses with rotated orientations. Synthesis of such non-commuting
observables is analyzed using maximum likelihood estimation as an example of
quantum state reconstruction. Repeated incompatible observations represent a
new generalized measurement. This idealized scheme will serve for analysis of
future experiments in neutron and quantum optics.


title: Motional Squashed States

abstract:
  We show that by using a feedback loop it is possible to reduce the
fluctuations in one quadrature of the vibrational degree of freedom of a
trapped ion below the quantum limit. The stationary state is not a proper
squeezed state, but rather a ``squashed'' state, since the uncertainty in the
orthogonal quadrature, which is larger than the standard quantum limit, is
unaffected by the feedback action.


title:
Relativistic theory of the above-threshold multiphoton ionization of
  hydrogen-like atoms in the ultrastrong laser fields

abstract:
  The relativistic theory of above-threshold ionization (ATI) of hydrogen-like
atoms in ultrastrong radiation fields, taking into account the photoelectron
induced rescattering in the continuum spectrum is developed. It is shown that
the contribution of the latter in the multiphoton ionization probability even
in the Born approximation by Coulomb field is of the order of ATI probability
in the scope of Keldysh-Faisal-Reiss ansatz.


title: Analogy between optimal spin estimation and interferometry

abstract:
  Scheme for optimal spin state estimation is considered in analogy with phase
detection in interferometry. Recently reported coherent measurements yielding
the average fidelity (N+1)/(N+2) for N particle system corresponds to the
standard limit of phase resolution 1/\sqrt{N}. It provides the bound for
incoherent measurements when each particle is detected separately and
information is used optimally. For specific states, improvement up to the value
1/N is possible in quantum theory. The best results are obtained combining
sequentially coherent measurements on fractional groups of particles.


title:
Use of composite rotations to correct systematic errors in NMR quantum
  computation

abstract:
  We implement an ensemble quantum counting algorithm on three NMR
spectrometers with 1H resonance frequencies of 500, 600 and 750 MHz. At higher
frequencies, the results deviate markedly from naive theoretical predictions.
These systematic errors can be attributed almost entirely to off-resonance
effects, which can be substantially corrected for using fully-compensating
composite rotation pulse sequences originally developed by Tycko. We also
derive an analytic expression for generating such sequences with arbitrary
rotation angles.


title: Existence of the Schmidt decomposition for tripartite systems

abstract:
  For any bipartite quantum system the Schmidt decomposition allows us to
express the state vector in terms of a single sum instead of double sums. We
show the existence of the Schmidt decomposition for tripartite system under
certain condition. If the partial inner product of a basis (belonging to a
Hilbert space of smaller dimension) with the state of the composite system
gives a disentangled basis, then the Schmidt decomposition for a tripartite
system exists. In this case the reduced density matrix of each of the subsystem
has equal spectrum in the Schmidt basis.


title: Error Correction with Euclidean Qubits

abstract:
  In classical case there is simplest method of error correction with using
three equal bits instead of one. In the paper is shown, how the scheme fails
for quantum error correction with complex vector spaces of usual quantum
mechanics, but works in real and quaternionic cases. It is discussed also, how
to implement the three qubits scheme with using encoding of quaternionic qubit
by Majorana spinor. Necessary concepts and formulae from area of quantum error
corrections are closely introduced and proved.


title: Semiclassical wave equation and exactness of the WKB method

abstract:
  The exactness of the semiclassical method for three-dimensional problems in
quantum mechanics is analyzed. The wave equation appropriate in the
quasiclassical region is derived. It is shown that application of the standard
leading-order WKB quantization condition to this equation reproduces exact
energy eigenvalues for all solvable spherically symmetric potentials.


title:
High Efficiency Interaction-free Measurement from Continuous Wave
  Multi-beam Interference

abstract:
  A new method for high efficiency interaction-free measurement is presented.
Selective transmission of multiple beam interference is used to generate a
continuous wave target beam with an irradiance level ~1% that of a reference
beam. When the target beam is unobstructed by a potentially interposed object,
the resultant measured interference visibility of 0.86 with the reference beam
significantly exceeds the classically predicted irradiance-based visibility of
0.17 and provides a methodology for ~100% interaction-free measurement with a
continuous wave beam.


title: The stochastic limit of quantum spin systems

abstract:
  The stochastic limit for the system of spins interacting with a boson field
is investigated. In the finite volume an application of the stochastic golden
rule shows that in the limit the dynamics of a quantum system is described by a
quantum white noise equation that after taking of normal order is equivalent to
quantum stochastic differential equation (QSDE). For the quantum Langevin
equation the dynamics is well defined and is a quantum flow on the infinite
lattice system.


title: On the structure of Markov flows

abstract:
  A new infinitesimal characterization of completely positive but not
necessarily homomorphic Markov flows from a C^*-algebra to bounded operators on
the boson Fock space over L^2(R) is given. Contrarily to previous
characterizations, based on stochastic differential equations, this
characterization is universal, i.e. valid for arbitrary Markov flows. With this
result the study of Markov flows is reduced to the study of four
C_0-semigroups. This includes the classical case and even in this case it seems
to be new. The result is applied to deduce a new existence theorem for Markov
flows.


title: Minimal Entropy of States Emerging from Noisy Quantum Channels

abstract:
  In this paper, we consider the minimal entropy of qubit states transmitted
through two uses of a noisy quantum channel, which is modeled by the action of
a completely positive trace-preserving (or stochastic) map. We provide strong
support for the conjecture that this minimal entropy is additive, namely that
the minimum entropy can be achieved when product states are transmitted.
Explicitly, we prove that for a tensor product of two unital stochastic maps on
qubit states, using an entanglement that involves only states which emerge with
minimal entropy cannot decrease the entropy below the minimum achievable using
product states. We give a separate argument, based on the geometry of the image
of the set of density matrices under stochastic maps, which suggests that the
minimal entropy conjecture holds for non-unital as well as for unital maps. We
also show that the maximal norm of the output states is multiplicative for most
product maps on $n$-qubit states, including all those for which at least one
map is unital.
  For the class of {\it unital} channels on ${\bf C}^2$, we show that
additivity of minimal entropy implies that the Holevo capacity of the channel
is {\it additive} over two inputs, achievable with orthogonal states, and equal
to the Shannon capacity. This implies that superadditivity of the capacity is
possible only for non-unital channels.


title:
Hilbert space structure of a solid state quantum computer: two-electron
  states of a double quantum dot artificial molecule

abstract:
  We study theoretically a double quantum dot hydrogen molecule in the GaAs
conduction band as the basic elementary gate for a quantum computer with the
electron spins in the dots serving as qubits. Such a two-dot system provides
the necessary two-qubit entanglement required for quantum computation. We
determine the excitation spectrum of two horizontally coupled quantum dots with
two confined electrons, and study its dependence on an external magnetic field.
In particular, we focus on the splitting of the lowest singlet and triplet
states, the double occupation probability of the lowest states, and the
relative energy scales of these states. We point out that at zero magnetic
field it is difficult to have both a vanishing double occupation probability
for a small error rate and a sizable exchange coupling for fast gating. On the
other hand, finite magnetic fields may provide finite exchange coupling for
quantum computer operations with small errors. We critically discuss the
applicability of the envelope function approach in the current scheme and also
the merits of various quantum chemical approaches in dealing with few-electron
problems in quantum dots, such as the Hartree-Fock self-consistent field
method, the molecular orbital method, the Heisenberg model, and the Hubbard
model. We also discuss a number of relevant issues in quantum dot quantum
computing in the context of our calculations, such as the required design
tolerance, spin decoherence, adiabatic transitions, magnetic field control, and
error correction.


title: Relativistic semiclassical wave equation and its solution

abstract:
  The properties of relativistic particles in the quasiclassical region are
investigated. The relativistic semiclassical wave equation appropriate in the
quasiclassical region is derived. It is shown that the leading-order WKB
quantization rule is the appropriate method to solve the equation obtained.


title: A Quantum Algorithm for finding the Maximum

abstract:
  This paper describes a quantum algorithm for finding the maximum among N
items. The classical method for the same problem takes O(N) steps because we
need to compare two numbers in one step. This algorithm takes O(sqrt(N)) steps
by exploiting the property of quantum states to exist in a superposition of
states and hence performing an operation on a number of elements in one go. A
tight upper bound of 6.8(sqrt(N)) for the number of steps needed using this
algorithm was found. These steps are the number of queries made to the oracle.


title: Off-Diagonal Geometric Phases

abstract:
  We investigate the adiabatic evolution of a set of non-degenerate eigenstates
of a parameterized Hamiltonian. Their relative phase change can be related to
geometric measurable quantities that extend the familiar concept of Berry phase
to the evolution of more than one state. We present several physical systems
where these concepts can be applied, including an experiment on microwave
cavities for which off-diagonal phases can be determined from published data.


title: Dynamic Rules for Decoherence

abstract:
  In orthodox quantum theory, decoherence is presumed to be caused by
observation. In this paper, the idea of replacing observation, as the cause of
decoherence, with rules derived from the dynamics of the system is addressed.
Such rules determine the timing of decoherence and the states in the mixture
afterward. For instance, energy conservation during decohenence, for each
possible transition, leads to a timing rule. Exponetial decay and ergodic
behavior follow directly from the dynamic rules as do Boltzman's postulate of
equally probable micro-states and the Pauli rate equations. Ergodic behavior in
mesoscopic systems is predicted and those preditions are strikingly similar to
behavior observed in at least two laboratories.


title: Withdrawn paper

abstract: Only craziness I am ashamed about.


title: Deterministic Quantum State Transformations

abstract:
  We derive a necessary condition for the existence of a completely-positive,
linear, trace-preserving map which deterministically transforms one finite set
of pure quantum states into another. This condition is also sufficient for
linearly-independent initial states. We also examine the issue of quantum
coherence, that is, when such operations maintain the purity of superpositions.
If, in any deterministic transformation from one linearly-independent set to
another, even a single, complete superposition of the initial states maintains
its purity, the initial and final states are related by a unitary
transformation.


title: Radiation of a quantum localized source

abstract:
  New effective operators, describing the photons with given polarization at
given position with respect to a source are proposed. These operators can be
used to construct the near and intermediate zones quantum optics. It is shown
that the use of the conventional plane photons can lead to a wrong results for
quantum fluctuations of polarization even in the far zone.


title:
Time-of-arrival distributions from position-momentum and energy-time
  joint measurements

abstract:
  The position-momentum quasi-distribution obtained from an Arthurs and Kelly
joint measurement model is used to obtain indirectly an ``operational''
time-of-arrival (TOA) distribution following a quantization procedure proposed
by Kocha\'nski and W\'odkiewicz [Phys. Rev. A 60, 2689 (1999)]. This TOA
distribution is not time covariant. The procedure is generalized by using other
phase-space quasi-distributions, and sufficient conditions are provided for
time covariance that limit the possible phase-space quasi-distributions
essentially to the Wigner function, which, however, provides a non-positive TOA
quasi-distribution. These problems are remedied with a different quantization
procedure which, on the other hand, does not guarantee normalization. Finally
an Arthurs and Kelly measurement model for TOA and energy (valid also for
arbitrary conjugate variables when one of the variables is bounded from below)
is worked out. The marginal TOA distribution so obtained, a distorted version
of Kijowski's distribution, is time covariant, positive, and normalized.


title:
Quantum fluctuations of the angular momentum and energy of the ground
  state

abstract:
  Quasiclassical solution of the three-dimensional Schredinger's equation is
given. The existence of nonzero minimal angular momentum M_0 = \hbar /2 is
shown, which corresponds to the quantum fluctuations of the angular momentum
and contributes to the energy of the ground state.


title: Impossibility of deleting an unknown quantum state

abstract:
  A photon in an arbitrary polarization state cannot be cloned perfectly. But
suppose that at our disposal we have several copies of an unknown photon. Is it
possible to delete the information content of one or more of these photons by a
physical process? Specifically, if two photons are in the same initial
polarization state is there a mechanism that produces one photon in the same
initial state and the other in some standard polarization state. If this can be
done, then one would create a standard blank state onto which one could copy an
unknown state approximately, by deterministic cloning or exactly, by
probabilistic cloning. This might be useful in quantum computation, where one
could store some new information in an already computed state by deleting the
old information. Here we show that the linearity of quantum theory does not
allow us to delete a copy of an arbitrary quantum state perfectly. Though in a
classical computer information can be deleted against a copy, the same task
cannot be accomplished with quantum information.


title: Relativistic Quantum Computing

abstract:
  We present some informal remarks on aspects of relativistic quantum
computing.


title: Quantum chaos in small quantum networks

abstract:
  We study a 2-spin quantum Turing architecture, in which discrete local
rotations \alpha_m of the Turing head spin alternate with quantum controlled
NOT-operations. We show that a single chaotic parameter input \alpha_m leads to
a chaotic dynamics in the entire Hilbert space. The instability of periodic
orbits on the Turing head and `chaos swapping' onto the Turing tape are
demonstrated explicitly as well as exponential parameter sensitivity of the
Bures metric.


title: Schr\"odinger equations with time-dependent P^2 and X^2 terms

abstract:
  We present some general results for the time-dependent mass Hamiltonian
problem with H=-{1/2}e^{-2\nu}\partial_{xx} +h^{(2)}(t)e^{2\nu}x^2. This
Hamiltonian corresponds to a time-dependent mass (TM) Schr\"odinger equation
with the restriction that there are only P^2 and X^2 terms. We give the
specific transformations to a different quantum Schr\"odinger(TQ) equation and
to a different time-dependent oscillator (TO) equation. For each Schr\"odinger
system, we give the Lie algebra of space-time symmetries and (x,t)
representations for number states, coherent states, and squeezed states. These
general results include earlier work as special cases.


title:
The Schr\"odinger system H=-{1/2}e^{\Upsilon(t-t_o)}\partial_{xx}
  +\lfrac{1}{2}\omega^2e^{-\Upsilon(t-t_o)}x^2

abstract:
  In this paper, we attack the specific time-dependent Hamiltonian problem
H=-{1/2}e^{\Upsilon(t-t_o)}\partial_{xx}
+\lfrac{1}{2}\omega^2e^{-\Upsilon(t-t_o)}x^2. This corresponds to a
time-dependent mass (TM) Schr\"odinger equation. We give the specific
transformations to i) the more general quadratic (TQ) Schr\"odinger equation
and to ii) a different time-dependent oscillator (TO) equation. For each
Schr\"odinger system, we give the Lie algebra of space-time symmetries, the
number states, the coherent states, the squeezed-states and the time-dependent
<x>, <p>, (\Delta x)^2, (\Delta p)^2, and uncertainty product.


title:
The Schr\"odinger system H=-{1/2} (t_o/t)^a \partial_{xx} + (1/2)
  \omega^2 (t/t_o)^b x^2

abstract:
  We attack the specific time-dependent Hamiltonian problem H=-{1/2} (t_o/t)^a
\partial_{xx} + (1/2) \omega^2 (t/t_o)^b x^2. This corresponds to a
time-dependent mass (TM) Schr\"odinger equation. We give the specific
transformations to a different time-dependent quadratic Schr\"odinger equations
(TQ) and to a different time-dependent oscillator (TO) equation. For each
Schr\"odinger system, we give the Lie algebra of space-time symmetries, the
number states, the squeezed-state <x> and <p> (with their classical motion),
(\Delta x)^2, (\Delta p)^2, and the uncertainty product.


title:
The Van der Waals interaction of the hydrogen molecule - an exact local
  energy density functional

abstract:
  We verify that the van der Waals interaction and hence all dispersion
interactions for the hydrogen molecule given by: W"= -{A/R^6}-{B/R^8}-{C/R^10}-
..., in which R is the internuclear separation, are exactly soluble. The
constants A=6.4990267..., B=124.3990835 ... and C=1135.2140398... (in Hartree
units) first obtained approximately by Pauling and Beach (PB) [1] using a
linear variational method, can be shown to be obtainable to any desired
accuracy via our exact solution. In addition we shall show that a local energy
density functional can be obtained, whose variational solution rederives the
exact solution for this problem. This demonstrates explicitly that a static
local density functional theory exists for this system. We conclude with
remarks about generalising the method to other hydrogenic systems and also to
helium.

categories: quant-ph cond-mat.str-el physics.atm-clus physics.chem-ph


title:
Nonuniqueness of Canonical Ensemble Theory arising from Microcanonical
  Basis

abstract:
  Given physical systems, counting rule for their statistical mechanical
descriptions need not be unique, in general. It is shown that this
nonuniqueness leads to the existence of various canonical ensemble theories
which equally arise from the definite microcanonical basis. Thus, the Gibbs
theorem for canonical ensemble theory is not universal, and the maximum entropy
principle is to be appropriately modefied for each physical context.


title: Dynamics of Complex Quantum Systems: Dissipation and Kinetic Equations

abstract:
  We present a microscopic approach to quantum dissipation and sketch the
derivation of the kinetic equation describing the evolution of a simple quantum
system in interaction with a complex quantum system. A typical quantum complex
system is modeled by means of parametric banded random matrices coupled to the
subsystem of interest. We do not assume the weak coupling limit and allow for
an independent dynamics of the ``reservoir''. We discuss the reasons for having
a new theoretical approach and the new elements introduced by us. The present
approach incorporates known limits and previous results, but at the same time
includes new cases, previously never derived on a microscopic level. We briefly
discuss the kinetic equation and its solution for a particle in the absence of
an external field.


title: A remark on the isotropic model

abstract:
  The applicability of the so-called isotropic and anisotropic complete
photonic-band-gap (CPBG) models [S. John and J. Wang, Phys. Rev. Lett. {\bf
64}, 2418 (1990)] to capture essential features of the spontaneous emission
(SE) of a fluorescent atom or molecule near a band-gap-edge of a CPBG structure
is discussed.


title: A model independent approach to non dissipative decoherence

abstract:
  We consider the case when decoherence is due to the fluctuations of some
classical variable or parameter of a system and not to its entanglement with
the environment. Under few and quite general assumptions, we derive a
model-independent formalism for this non-dissipative decoherence, and we apply
it to explain the decoherence observed in some recent experiments in cavity QED
and on trapped ions.


title: Quantum Coins, Dice and Children: Probability and Quantum Statistics

abstract:
  We discuss counterintuitive aspects of probabilities for systems of identical
particles obeying quantum statistics. Quantum coins and children (two level
systems) and quantum dice (many level systems) are used as examples. It is
emphasized that, even in the absence of interactions, (anti)symmetrizations of
multi-particle wavefunctions destroy statistical independences and often lead
to dramatic departures from our intuitive expectations.

categories: quant-ph cond-mat.stat-mech hep-ph nucl-th physics.ed-ph


title:
A Fundamental Limit of Measurement Imposed by the Elementary
  Interactions

abstract:
  Quantum information theory is closely related to quantum measurement theory
because one must perform measurement to obtain information on a quantum system.
Among many possible limits of quantum measurement, the simplest ones were
derived directly from the uncertainty principles. However, such simple limits
are not the only limits. I here suggest a new limit which comes from the forms
and the strengths of the elementary interactions. Namely, there are only four
types of elementary interactions in nature; their forms are determined by the
gauge invariance (and symmetry breaking), and their coupling constants (in the
low-energy regime) have definite values. I point out that this leads to a new
fundamental limit of quantum measurements. Furthermore, this fundamental limit
imposes the fundamental limits of getting information on, preparing, and
controlling quantum systems.

categories: quant-ph chao-dyn cond-mat.stat-mech nlin.CD


title: Improving Detectors Using Entangling Quantum Copiers

abstract:
  We present a detection scheme which using imperfect detectors, and imperfect
quantum copying machines (which entangle the copies), allows one to extract
more information from an incoming signal, than with the imperfect detectors
alone.


title: A new PT symmetric complex Hamiltonian with a real spectra

abstract:
  We construct an isospectrum systems in terms of a real and complex potential
to show that the underlying PT symmetric Hamiltonian possesses a real spectrum
which is shared by its real partner.


title:
Quantum Information, Irreversibility and State Collapse in Some
  Microscopic Models of Measurement

abstract:
  The quantum measurement problem considered for measuring system (MS) model
which consist of measured state S (particle), detector D and information
processing device O. For spin chains and other O models the state evolution for
MS observables measurements studied. It's shown that specific O states
structure forbids the measurement of MS interference terms which discriminate
pure and mixed S states. It results in the reduction MS Hilbert space to O
representation in which MS evolution is irreversible, which in operational
formalism corresponds to S state collapse. In radiation decoherence O model
Glauber restrictions on QED field observables results in analogous irreversible
MS + field evolution. The results interpretation in Quantum Information
framework and Rovelli Relational Quantum Mechanics discussed.


title:
Quantum nondemolition measurements of a particle in an inhomogeneous
  gravitational field

abstract:
  In this work we obtain a family of quantum nondemolition variables for the
case of a particle moving in an inhomogeneous gravitational field. Afterwards,
we calculate the corresponding propagator, and deduce the probabilitites
associated with the possible measurements outputs. The comparison, with the
case in which the position is being monitored, will allow us to find the
differences with respect to the case of a quantum demolition measuring process.


title:
75 Years of Matter Wave: Louis de Broglie and Renaissance of the
  Causally Complete Knowledge

abstract:
  A physically real wave associated with any moving particle and travelling in
a surrounding material medium was introduced by Louis de Broglie in a series of
short notes in 1923 and in a more complete form in his thesis defended in Paris
on the 25th November 1924. This result, recognised by the Nobel Prize in 1929,
gave rise to a major direction of "new physics" known today as "quantum
mechanics". However, although such notions as "de Broglie wavelength" and
"wave-particle duality" form the basis of the standard quantum theory, it
actually only takes for granted (postulates) the formula for the particle
wavelength and totally ignores the underlying causal, realistic and physically
transparent picture of wave-particle dynamics outlined by Louis de Broglie in
his thesis and further considerably developed in his later works, in the form
of "double solution" and "hidden thermodynamics" theory. A price to pay for
such rough deviation from the original de Broglian realism and consistency
involves fundamental physics domination by purely abstract and mechanistically
simplified schemes of formal symbols and rules that have led to a deep
knowledge impasse justly described as "the end of science". However, a new,
independent approach of "quantum field mechanics" (quant-ph/9902015,
quant-ph/9902016, physics/0401164) created within the "universal science of
complexity" (physics/9806002) provides many-sided confirmation and natural
completion of de Broglie's "nonlinear wave mechanics", eliminating all its
"difficult points" and reconstituting the causally complete, totally consistent
and intrinsically unified picture of the real, complex micro-world dynamics
directly extendible to all higher levels of unreduced world complexity.


title: Collective variables and composite fields

abstract:
  We consider use of collective variables for description of composite fields
as collective phenomena due to the strong coupling regime. We discuss two
approaches, where identification of collective variables of complex quantum
system does not depend on knowledge of other degrees of freedom: (a) collective
variables as parameters of group transformations changing the path integral of
the system, and (b) collective variables as background fields for quantum
system. In the case (a) we briefly present an approach. In the case (b) we
consider fermions in an external scalar field, which serves as a collective
variable in a nonlinear model for composite scalar field with a finite
compositeness scale.


title: Quantum Cryptography using entangled photons in energy-time Bell states

abstract:
  We present a setup for quantum cryptography based on photon pairs in
energy-time Bell states and show its feasability in a laboratory experiment.
Our scheme combines the advantages of using photon pairs instead of faint laser
pulses and the possibility to preserve energy-time entanglement over long
distances. Moreover, using 4-dimensional energy-time states, no fast random
change of bases is required in our setup : Nature itself decides whether to
measure in the energy or in the time base.


title:
Comment on the "Maxwell Equations as the One-Photon Quantum Equation" by
  A. Gersten [Found. Phys. Lett. 12, pp. 291-298 (1999)]

abstract:
  We show that the Gersten derivation of Maxwell equations can be generalized.
It actually leads to additional solutions of `S=1 equations'. They follow
directly from previous considerations by Majorana, Oppenheimer, Weinberg and
Ogievetskii and Polubarinov. Therefore, {\it generalized} Maxwell equations
should be used as a guideline for proper interpretations of quantum theories.


title: Temperature Variation of Ultra Slow Light in a Cold Gas

abstract:
  A model is developed to explain the temperature dependence of the group
velocity as observed in the experiments of Hau et al (Nature {\bf397}, 594
(1999)). The group velocity is quite sensitive to the change in the spatial
density. The inhomogeneity in the density and its temperature dependence are
primarily responsible for the observed behavior.


title:
Analysis of radiatively stable entanglement in a system of two
  dipole-interacting three-level atoms

abstract:
  We explore the possibilities of creating radiatively stable entangled states
of two three-level dipole-interacting atoms in a $\Lambda$ configuration by
means of laser biharmonic continuous driving or pulses. We propose three
schemes for generation of entangled states which involve only the lower states
of the $\Lambda$ system, not vulnerable to radiative decay. Two of them employ
coherent dynamics to achieve entanglement in the system, whereas the third one
uses optical pumping, i.e., an essentially incoherent process.


title:
How Events Come Into Being: EEQT, Particle Tracks, Quantum Chaos, and
  Tunneling Time

abstract:
  In sections 1 and 2 we review Event Enhanced Quantum Theory (EEQT). In
section 3 we discuss applications of EEQT to tunneling time, and compare its
quantitative predictions with other approaches, in particular with
B\"uttiker-Larmor and Bohm trajectory approach. In section 4 we discuss quantum
chaos and quantum fractals resulting from simultaneous continuous monitoring of
several non-commuting observables. In particular we show self-similar,
non-linear, iterated function system-type, patterns arising from quantum jumps
and from the associated Markov operator. Concluding remarks pointing to
possible future development of EEQT are given in section 5.


title:
Ladder operator formalisms and generally deformed oscillator algebraic
  structures of quantum states in Fock space

abstract:
  We show that various kinds of one-photon quantum states studied in the field
of quantum optics admit ladder operator formalisms and have the generally
deformed oscillator algebraic structure. The two-photon case is also
considered. We obtain the ladder operator formalisms of two general states
defined in the even/odd Fock space. The two-photon states may also have a
generally deformed oscillator algebraic structure. Some interesting examples of
one-photon and two-photon quantum states are given.


title: Time scales in quantum mechanics by a scattering map

abstract:
  Inside quantum mechanics the problem of decoherence for an isolated, finite
system is linked to a coarse-grained description of its dynamics.


title: Shape invariant potentials with PT symmetry

abstract:
  Suitable complexification of the well known solvable oscillators in one
dimension is shown to give the four exactly solvable models which combine the
shape- and PT-invariance.
  In version v2 the result is extended of the s-wave shape-invariant forces.


title: A Schmidt number for density matrices

abstract:
  We introduce the notion of a Schmidt number of a bipartite density matrix,
characterizing the minimum Schmidt rank of the pure states that are needed to
construct the density matrix. We prove that Schmidt number is nonincreasing
under local quantum operations and classical communication. We show that
$k$-positive maps witness Schmidt number, in the same way that positive maps
witness entanglement. We show that the family of states which is made from
mixing the completely mixed state and a maximally entangled state have
increasing Schmidt number depending on the amount of maximally entangled state
that is mixed in. We show that Schmidt number {\it does not necessarily
increase} when taking tensor copies of a density matrix $\rho$; we give an
example of a density matrix for which the Schmidt numbers of $\rho$ and $\rho
\otimes \rho$ are both 2.


title: Variational analysis for a generalized spiked harmonic oscillator

abstract:
  A variational analysis is presented for the generalized spiked harmonic
oscillator Hamiltonian operator H, where H = -(d/dx)^2 + Bx^2+ A/x^2 +
lambda/x^alpha, and alpha and lambda are real positive parameters. The
formalism makes use of a basis provided by exact solutions of Schroedinger's
equation for the Gol'dman and Krivchenkov Hamiltonian (alpha = 2), and the
corresponding matrix elements that were previously found. For all the discrete
eigenvalues the method provides bounds which improve as the dimension of the
basis set is increased. Extension to the N-dimensional case in arbitrary
angular-momentum subspaces is also presented. By minimizing over the free
parameter A, we are able to reduce substantially the number of basis functions
needed for a given accuracy.


title: Ordering States with Entanglement Measures

abstract:
  We demonstrate that all good asymptotic entanglement measures are either
identical or place a different ordering on the set of all quantum states.


title: Classical Capacity of A Quantum Multiple Access Channel

abstract:
  We consider the transmission of classical information over a quantum channel
by two senders. The channel capacity region is shown to be a convex hull bound
by the Von Neumann entropy and the conditional Von Neumann entropy. We discuss
some possible applications of our result. We also show that our scheme allows a
reasonable distribution of channel capacity over two senders.


title: Born-Oppenheimer Approximation near Level Crossing

abstract:
  We consider the Born-Oppenheimer problem near conical intersection in two
dimensions. For energies close to the crossing energy we describe the wave
function near an isotropic crossing and show that it is related to generalized
hypergeometric functions 0F3. This function is to a conical intersection what
the Airy function is to a classical turning point. As an application we
calculate the anomalous Zeeman shift of vibrational levels near a crossing.

categories: quant-ph math-ph math.MP physics.chem-ph


title: Quantum states as generalized classical ensembles

abstract: Only craziness I am ashamed about.


title:
Quantum entanglement and information processing via excitons in
  optically-driven quantum dots

abstract:
  We show how optically-driven coupled quantum dots can be used to prepare
maximally entangled Bell and Greenberger-Horne-Zeilinger states. Manipulation
of the strength and duration of the selective light-pulses needed for producing
these highly entangled states provides us with crucial elements for the
processing of solid-state based quantum information. Theoretical predictions
suggest that several hundred single quantum bit rotations and Controlled-Not
gates could be performed before decoherence of the excitonic states takes
place.


title: The query complexity of order-finding

abstract:
  We consider the problem where P is an unknown permutation on {0,1,...,2^n -
1}, y is an element of {0,1,...,2^n - 1}, and the goal is to determine the
minimum r > 0 such that P^r(y) = y (where P^r is P composed with itself r
times). Information about P is available only via queries that yield P^x(y)
from any x in {0,1,...,2^m - 1} and y in {0,1,...,2^n - 1} (where m is
polynomial in n). The main resource under consideration is the number of these
queries. We show that the number of queries necessary to solve the problem in
the classical probabilistic bounded-error model is exponential in n. This
contrasts sharply with the quantum bounded-error model, where a constant number
of queries suffices.


title: Rapid sampling through quantum computing

abstract:
  This paper extends the quantum search class of algorithms to the multiple
solution case. It is shown that, like the basic search algorithm, these too can
be represented as a rotation in an appropriately defined two dimensional vector
space. This yields new applications - an algorithm is presented that can create
an arbitrarily specified quantum superposition on a space of size N in
O(sqrt(N)) steps. By making a measurement on this superposition, it is possible
to obtain a sample according to an arbitrarily specified classical probability
distribution in O(sqrt(N)) steps. A classical algorithm would need O(N) steps.


title:
Comment on `Counterfactual entanglement and non-local correlations in
  separable states'

abstract:
  The arguments of Cohen [Phys. Rev. A {\bf 60}, 80 (1999)] against the
`ignorance interpretation' of mixed states are questioned. The physical
arguments are shown to be inconsistent and the supporting example illustrates
the opposite of the original statement. The operational difference between two
possible definitions of mixed states is exposed and the inadequacy of one of
them is stressed.


title: Novel Scheme for Universal Quantum Computation

abstract:
  A scenario for realization of a quantum computer is proposed consisting of
spatially distributed q-bits fabricated in a host structure where nuclear
spin-spin coupling is mediated by laser pulse controlled electron-nuclear
transferred hyperfine (superhyperfine) Fermi contact interaction. Operations
illustrating entanglement, nonlocality, and quantum control logic operations
are presented and discussed. The notion of universality of quantum computation
is introduced and the irreducible conditions are presented. It is demonstrated
that the proposed generic scenario for realization of a quantum computer
fulfills these conditions.


title: Driving Atoms Into Decoherence-Free States

abstract:
  We describe the decoherence-free subspace of N atoms in a cavity, in which
decoherence due to the leakage of photons through the cavity mirrors is
suppressed. We show how the states of the subspace can be entangled with the
help of weak laser pulses, using the high decay rate of the cavity field and
strong coupling between the atoms and the resonator mode. The atoms remain
decoherence-free with a probability which can, in principle, be arbitrarily
close to unity.


title: Convergences in the Measurement Problem in Quantum Mechanics

abstract:
  This paper presents arguments purporting to show that von Neumann's
description of the measurement process in quantum mechanics has a modern day
version in the decoherence approach. We claim that this approach and the de
Broglie-Bohm theory emerges from Bohr's interpretation and are therefore
obliged to deal with some obscures ideas which were antecipated, explicitly or
implicitly and carefully circumvented, by Bohr.


title: On the Staruszkiewicz Modification of the Schroedinger Equation

abstract:
  We discuss Staruszkiewicz's nonlinear modification of the Schr\"{o}dinger
equation. It is pointed out that the expression for the energy functional for
this modification is not unique as the field-theoretical definition of energy
does not coincide with the quantum-mechanical one. As a result, this
modification can be formulated in three different ways depending on which
physically relevant properties one aims to preserve. Some nonstationary
one-dimensional solutions for suitably chosen potentials, including a KdV
soliton, are presented, and the question of finding stationary solutions is
also discussed. The analysis of physical and mathematical features of the
modification leads to the conclusion that the Staruszkiewicz modification is a
very subtle modification of the fundamental equation of quantum mechanics.


title: Burgers Turbulence and the Continuous Spontaneous Localization Model

abstract:
  There is a striking convergence between Burgers turbulence and the continuous
spontaneous localization [CSL] model of quantum mechanics. In this paper, we
exploit this analogy showing the similarities in the physics of these two
apparently unrelated problems. It is hoped that the kind of analogy we
introduce here may lead to important developments in both areas.


title: Quantum Logic with a Single Trapped Electron

abstract:
  We propose the use of a trapped electron to implement quantum logic
operations. The fundamental controlled-NOT gate is shown to be feasible. The
two quantum bits are stored in the internal and external (motional) degrees of
freedom.


title:
Classical Communication Cost in Distributed Quantum Information
  Processing - A generalization of Quantum Communication Complexity

abstract:
  We study the amount of classical communication needed for distributed quantum
information processing. In particular, we introduce the concept of "remote
preparation" of a quantum state. Given an ensemble of states, Alice's task is
to help Bob in a distant laboratory to prepare a state of her choice. We find
several examples of an ensemble with an entropy S where the remote preparation
can be done with a communication cost lower than the amount (2S) required by
standard teleportation. We conjecture that, for an arbitrary N-dimensional pure
state, its remote preparation requires 2log_2 N bits of classical
communication, as in standard teleportation.


title: Separability in 2xN composite quantum systems

abstract:
  We analyze the separability properties of density operators supported on
$\C^2\otimes \C^N$ whose partial transposes are positive operators. We show
that if the rank of $\rho$ equals N then it is separable, and that bound
entangled states have rank larger than N. We also give a separability criterion
for a generic density operator such that the sum of its rank and the one of its
partial transpose does not exceed 3N. If it exceeds this number we show that
one can subtract product vectors until decreasing it to 3N, while keeping the
positivity of $\rho$ and its partial transpose. This automatically gives us a
sufficient criterion for separability for general density operators. We also
prove that all density operators that remain invariant after partial
transposition with respect to the first system are separable.


title:
Will Quantum Cryptography ever become a successful technology in the
  marketplace?

abstract:
  We assess the potential of quantum cryptography as a technology. We highlight
the fact that academia and real world have rather different perspectives and
interests. Then, we describe the various real life forces (different types of
users, vendors of crypto-systems, conventional cryptographers, governments)
behind the decision of the adoption (or rejection) of quantum cryptography and
their different interests. Various roadblocks to the widespread application of
quantum cryptography are discussed. Those roadblocks can be fundamental,
technological, psychological, commercial or political and many of them have
nothing to do with the security of quantum key distribution. We argue that the
future success of quantum cryptography as a technology in the marketplace lies
in our ability to appreciate and to overcome those roadblocks and to answer
real world criticisms on the subject.


title: Some relations between quantum Turing machines and Turing machines

abstract:
  For quantum Turing machines we present three elements: Its components, its
time evolution operator and its local transition function. The components are
related with the components of deterministic Turing machines, the time
evolution operator is related with the evolution of reversible Turing machines
and the local transition function is related with the transition function of
probabilistic and reversible Turing machines.


title:
Angular momentum and energy structure of the coherent state of a 2D
  isotropic harmonic oscillator

abstract:
  The angular momentum structure and energy structure of the coherent state of
a 2D isotropic harmonic oscillator were investigated. Calculations showed that
the average values of angular momentum and energy (except the zero point
energy) of this nonspreading 2D wave packet are identical to those of the
corresponding classical oscillator moving along a circular or an elliptic
orbit.


title: Quantum Memory for Light

abstract:
  We propose an efficient method for mapping and storage of a quantum state of
propagating light in atoms. The quantum state of the light pulse is stored in
two sublevels of the ground state of a macroscopic atomic ensemble by
activating a synchronized Raman coupling between the light and atoms. We
discuss applications of the proposal in quantum information processing and in
atomic clocks operating beyond quantum limits of accuracy. The possibility of
transferring the atomic state back on light via teleportation is also
discussed.


title:
Derivation of the wave function collapse in the context of Nelson's
  stochastic mechanics

abstract:
  The von Neumann collapse of the quantum mechanical wavefunction after a
position measurement is derived by a purely probabilistic mechanism in the
context of Nelson's stochastic mechanics.


title: Quantum-defect Electron States Near a Helium Surface

abstract:
  Isolated electrons resting near a helium surface have a spectrum close to
that of a quantum-defect atom. A precisely solvable model with Rydberg spectrum
is sugguested and discussed.


title: Entanglement purification of Gaussian continuous variable quantum states

abstract:
  We describe an entanglement purification protocol to generate maximally
entangled states with high efficiencies from two-mode squeezed states or from
mixed Gaussian continuous entangled states. The protocol relies on a local
quantum non-demolition measurement of the total excitation number of several
continuous variable entangled pairs. We propose an optical scheme to do this
kind of measurement using cavity enhanced cross--Kerr interactions.


title: An obstruction based approach to the Kochen-Specker theorem

abstract:
  In [1] it was shown that the Kochen Specker theorem can be written in terms
of the non-existence of global elements of a certain varying set over the
partially ordered set of boolean subalgebras of projection operators on some
Hilbert space. In this paper, we show how obstructions to the construction of
such global elements arise, and how this provides a new way of looking at
proofs of the theorem.


title: Quantum Mechanics as Information Fusion

abstract:
  We provide evidence that quantum mechanics can be interpreted as a rational
algorithm for finding the least complex description for the correlations in the
outputs of sensors in a large array. In particular, by comparing the
self-organization approach to solving the Traveling Salesman Problem with a
solution based on taking the classical limit of a Feynman path integral, we are
led to a connection between the quantum mechanics of motion in a magnetic field
and self-organized information fusion.


title:
A Quantum Logic Gate Representation of Quantum Measurement: Reversing
  and Unifying the Two Steps of von Neumann's Model

abstract:
  In former work, quantum computation has been shown to be a problem solving
process essentially affected by both the reversible dynamics leading to the
state before measurement, and the logical-mathematical constraints introduced
by quantum measurement (in particular, the constraint that there is only one
measurement outcome). This dual influence, originated by independent initial
and final conditions, justifies the quantum computation speed-up and is not
representable inside dynamics, namely as a one-way propagation. In this work,
we reformulate von Neumann's model of quantum measurement at the light of above
findings. We embed it in a broader representation based on the quantum logic
gate formalism and capable of describing the interplay between dynamical and
non-dynamical constraints. The two steps of the original model, namely (1)
dynamically reaching a complete entanglement between pointer and quantum object
and (2) enforcing the one-outcome-constraint, are unified and reversed. By
representing step (2) right from the start, the same dynamics of step (1)
yields a probability distribution of mutually exclusive measurement outcomes.
This appears to be a more accurate and complete representation of quantum
measurement. PACS: 03.67.-a, 03.67.Lx, 03.65.Bz


title: Overview of "Structure behind Mechanics"

abstract:
  This letter proposes a new scenario to solve the structural or conceptual
problems remained in quantum mechanics, and gives an overview of the theory
proposed in quant-ph/9906130 (including quant-ph/9909025 and quant-ph/0001015).


title:
How to Trap Photons? Storing Single-Photon Quantum States in Collective
  Atomic Excitations

abstract:
  We show that it is possible to ``store'' quantum states of single-photon
fields by mapping them onto {\it collective} meta-stable states of an optically
dense, coherently driven medium inside an optical resonator. An adiabatic
technique is suggested which allows to transfer non-classical correlations from
traveling-wave single-photon wave-packets into atomic states and vise versa
with nearly 100% efficiency. In contrast to previous approaches involving
single atoms, the present technique does not require the strong coupling regime
corresponding to high-Q micro-cavities. Instead, intracavity
Electromagnetically Induced Transparency is used to achieve a strong coupling
between the cavity mode and the atoms.


title: Input-Output Relations in Optical Cavities: a Simple Point of View

abstract:
  In this work we present a very simple approach to input-output relations in
optical cavities, limiting ourselves to one- and two-photon states of the
field.
  After field quantization, we derive the non-unitary transformation between
{\em Inside} and {\em Outside} annihilation and creation operators. Then we
express the most general two-photon state generated by {\em Inside} creation
operators, through base states generated by {\em Outside} creation operators.
After renormalization of coefficients of inside two-photon state, we calculate
the outside photon-number probability distribution in a general case. Finally
we treat with some detail the single mode and symmetrical cavity case.


title: Strong coupling theory for driven tunneling and vibrational relaxation

abstract:
  We investigate on a unified basis tunneling and vibrational relaxation in
driven dissipative multistable systems described by their N lowest lying
unperturbed levels. By use of the discrete variable representation we derive a
set of coupled non-Markovian master equations. We present analytical treatments
that describe the dynamics in the regime of strong system-bath coupling. Our
findings are corroborated by ``ab-initio'' real-time path integral
calculations.


title: Effect of Aharonov-Bohm Phase on Spin Tunneling

abstract:
  The role of Aharonov-Bohm effect in quantum tunneling is examined when a
potential is defined on the $S^1$ and has $N$-fold symmetry. We show that the
low-lying energy levels split from the $N$-fold degenerate ground state
oscillate as a function of the Aharonov-Bohm phase, from which general
degeneracy conditions depending on the magnetic flux is obtained. We apply
these results to the spin tunneling in a spin system with $N$-fold rotational
symmetry around a hard axis.


title:
On stimulated transitions between the self-trapped states of the
  nonlinear Schrodinger equation

abstract:
  The studied model describes a particle that obeys a one-dimensional nonlinear
Schr\"odinger equation in the potential of a double-well. Transitions between
the two lowest self-trapped states of this system under the influence of the
external time-dependent perturbation are studied in the two-mode approximation.
If the perturbation dependence on time is harmonic with the frequency $\omega$,
then transitions between the states become possible if the amplitude of the
perturbation $F$ exceeds some threshold value $F_c(\omega)$; above the
threshold motion of the system becomes chaotic. If the perturbation is a
broadband noise, then transitions between the states are possible at
arbitrarily small $F$ and occur in the process of the system's energy
diffusion.


title: PT-symetrically regularized Eckart,Poeschl-Teller and Hulthen potentials

abstract:
  Version 1: The well known Eckart's singular s-wave potential is
PT-symmetrically regularized and continued to the whole real line. The new
model remains exactly solvable and its bound states remain proportional to
Jacobi polynomials. Its real and discrete spectrum exhibits several unusual
features.
  Version 2: Parity times time-reversal symmetry of complex Hamiltonians with
real spectra is usually interpreted as a weaker mathematical substitute for
Hermiticity. Perhaps an equally important role is played by the related
strengthened analyticity assumptions. In a constructive illustration we
complexify a few potentials solvable only in s-wave. Then we continue their
domain from semi-axis to the whole axis and get the new exactly solvable
models. Their energies come out real as expected. The new one-dimensional
spectra themselves differ quite significantly from their s-wave predecessors.


title: Higher-order mutual coherence of optical and matter waves

abstract:
  We use an operational approach to discuss ways to measure the higher-order
cross-correlations between optical and matter-wave fields. We pay particular
attention to the fact that atomic fields actually consist of composite
particles that can easily be separated into their basic constituents by a
detection process such as photoionization. In the case of bosonic fields, that
we specifically consider here, this leads to the appearance in the detection
signal of exchange contributions due to both the composite bosonic field and
its individual fermionic constituents. We also show how time-gated counting
schemes allow to isolate specific contributions to the signal, in particular
involving different orderings of the Schr\"odinger and Maxwell fields.


title: Bell Theorem for Nonclassical Part of Quantum Teleportation Process

abstract:
  The quantum teleportation process is composed of a joint measurement
performed upon two subsystems A and B (uncorrelated), followed by a unitary
transformation (parameters of which depend on the outcome of the measurement)
performed upon a third subsystem C (EPR correlated with system B). The
information about the outcome of the measurement is transferred by classical
means. The measurement performed upon the systems A and B collapses their joint
wavefunction into one of the four {\it entangled} Bell states. It is shown here
that this measurement process plus a possible measurement on the third
subsystem (with classical channel switched off - no additional unitary
transformation performed) cannot be described by a local realistic theory.


title: Comment on the Adiabatic Condition

abstract:
  The experimental observation of effects due to Berry's phase in quantum
systems is certainly one of the most impressive demonstrations of the
correctness of the superposition principle in quantum mechanics. Since Berry's
original paper in 1984, the spin 1/2 coupled with rotating external magnetic
field has been one of the most studied models where those phases appear. We
also consider a special case of this soluble model. A detailed analysis of the
coupled differential equations and comparison with exact results teach us why
the usual procedure (of neglecting nondiagonal terms) is mathematically sound.


title: Decoherent Histories and Realism

abstract:
  We reconsider the Decoherent Histories approach to Quantum Mechanics and we
analyze some problems related to its interpretation which, according to us,
have not been adequately clarified by its proponents. We put forward some
assumptions which, in our opinion, are necessary for a realistic interpretation
of the probabilities that the formalism attaches to decoherent histories. We
prove that such assumptions, unless one limits the set of the decoherent
families which can be taken into account, lead to a logical contradiction. The
line of reasoning we will follow is conceptually different from other arguments
which have been presented and which have been rejected by the supporters of the
Decoherent Histories approach. The conclusion is that the Decoherent Histories
approach, to be considered as an interesting realistic alternative to the
orthodox interpretation of Quantum Mechanics, requires the identification of a
mathematically precise criterion to characterize an appropriate set of
decoherent families which does not give rise to any problem.


title: Functional inversion for potentials in quantum mechanics

abstract:
  Let E = F(v) be the ground-state eigenvalue of the Schroedinger Hamiltonian H
= -Delta + vf(x), where the potential shape f(x) is symmetric and monotone
increasing for x > 0, and the coupling parameter v is positive.
  If the 'kinetic potential' bar{f}(s) associated with f(x) is defined by the
transformation: bar{f}(s) = F'(v), s = F(v)-vF'(v),then f can be reconstructed
from F by the sequence: f^{[n+1]} = bar{f} o bar{f}^{[n]^{-1}} o f^{[n]}.
Convergence is proved for special classes of potential shape; for other test
cases it is demonstrated numerically. The seed potential shape f^{[0]} need not
be 'close' to the limit f.


title: Mixedness and teleportation

abstract:
  We show that on exceeding a certain degree of mixedness (as quantified by the
von Neumann entropy), entangled states become useless for teleporatation. By
increasing the dimension of the entangled systems, this entropy threshold can
be made arbitrarily close to maximal. This entropy is found to exceed the
entropy threshold sufficient to ensure the failure of dense coding.


title: Classicality Criteria

abstract:
  We present two possible criteria quantifying the degree of classicality of an
arbitrary (finite dimensional) dynamical system. The inputs for these criteria
are the classical dynamical structure of the system together with the quantum
and the classical data providing the two alternative descriptions of its
initial time configuration. It is proved that a general quantum system
satisfying the criteria up to some extend displays a time evolution consistent
with the classical predictions up to some degree and thus it is argued that the
criteria provide a suitable measure of classicality. The features of the
formalism are illustrated through two simple examples.


title: Quantum secret sharing using pseudo-GHZ states

abstract:
  We present a setup for quantum secret sharing using pseudo-GHZ states based
on energy-time entanglement. In opposition to true GHZ states, our states do
not enable GHZ-type tests of nonlocality, however, they bare the same quantum
correlations. The relatively high coincidence count rates found in our setup
enable for the first time an application of a quantum communication protocoll
based on more than two qubits.


title: Quantum Computer Using Coupled Quantum Dot Molecules

abstract:
  We propose a method for implementation of a quantum computer using artificial
molecules. The artificial molecule consists of two coupled quantum dots stacked
along z direction and one single electron. One-qubit and two-qubit gates are
constructed by one molecule and two coupled molecules, respectively.The ground
state and the first excited state of the molecule are used to encode the |0>
and |1> states of a qubit. The qubit is manipulated by a resonant
electromagnetic wave that is applied directly to the qubit through a microstrip
line. The coupling between two qubits in a quantum controlled NOT gate is
switched on (off) by floating (grounding) the metal film electrodes. We study
the operations of the gates by using a box-shaped quantum dot model and
numerically solving a time-dependent Schridinger equation, and demonstrate that
the quantum gates can perform the quantum computation. The operating speed of
the gates is about one operation per 4ps. The reading operation of the output
of the quantum computer can be performed by detecting the polarization of the
qubits.


title:
The Emergence of Hydrodynamic Equations from Quantum Theory: A
  Decoherent Histories Analysis

abstract:
  The most general description of the classical world is in terms of local
densities (such as number, momentum, energy), and these typically evolve
according to evolution equations of hydrodynamic form. To explain the emergent
classicality of these variables from an underlying quantum theory, it is
therefore necessary to show, firstly, that these variables exhibit negligible
interference, and secondly, that the probabilities for histories of them are
peaked around hydrodynamic evolution. The implementation of this programme in
the context of the decoherent histories approach to quantum theory is
described. It is argued that, for a system of weakly interacting particles, the
eigenstates of local densities (averaged over a sufficiently large volume)
remain approximate eigenstates under time evolution. This is a consequence of
their close connection with the corresponding exactly conserved (and so exactly
decoherent) quantities. The subsequent derivation of hydrodynamic equations
from decoherent histories is discussed.


title: A Remark on the Optimal Cloning of An N-Level Quantum System

abstract:
  We study quantum cloning machines (QCM) that act on an unknown N-level
quantum state and make M copies. We give a formula for the maximum of the
fidelity of cloning and exhibit the unitary transformations that realize this
optimal fidelity. We also extend the results to treat the case of M copies from
$N^\prime$ ($M>N^\prime$) identical N-level quantum systems.


title: Reversibility of local transformations of multiparticle entanglement

abstract:
  We consider the transformation of multisystem entangled states by local
quantum operations and classical communication. We show that, for any
reversible transformation, the relative entropy of entanglement for two parties
must remain constant. This shows, for example, that it is not possible to
convert 2N three party GHZ states into 3N singlets, even in an asymptotic
sense. Thus there is true three-party non-locality (i.e., not all three-party
entanglement is equivalent to two-party entanglement). Our results also allow
us to make {\em quantitative} statements about concentrating multi-particle
entanglement. Finally, we show that there is true n-party entanglement for all
n.


title: Robust quantum computation by simulation

abstract:
  Simulation of quantum systems that provide intrinsically fault-tolerant
quantum computation is shown to preserve fault tolerance. Errors committed in
the course of simulation are eliminated by the natural error-correcting
features of the systems simulated. Two examples are explored, toric codes and
non-abelian anyons. The latter is shown to provide universal robust quantum
computation via simulation.


title: Local/Non-Local Complementarity in Topological Effects

abstract:
  In certain topological effects the accumulation of a quantum phase shift is
accompanied by a local observable effect. We show that such effects manifest a
complementarity between non-local and local attributes of the topology, which
is reminiscent but yet different from the usual wave-particle complementarity.
This complementarity is not a consequence of non-commutativity, rather it is
due to the non-canonical nature of the observables. We suggest that a
local/non-local complementarity is a general feature of topological effects
that are ``dual'' to the AB effect.


title: Wave packet scattering from an attractive well

abstract:
  Wave packet scattering off an attractive well is investigated in two spatial
dimensions numerically. The results confirm what was found previously for the
one dimensional case. The wave scattered at large angles is a polychotomous
(multiple peak) coherent train. Large angle scattering is extremely important
for low impinging velocities and at all impact parameters. The effect
disappears for packets more extended than the well. Experiments to detect the
polychotomous behavior are suggested.


title: Quantum non-demolition (QND) modulation of quantum interference

abstract:
  We propose an experiment where quantum interference between two different
paths is modulated by means of a QND measurement on one or both the arm of the
interferometer. The QND measurement is achieved in a Kerr cell. We illustrate a
scheme for the realisation of this experiment and some further developments.


title: A defense of Hellwig-Kraus reductions

abstract:
  Aharonov and Albert analyze a thought experiment which they believe shows
that quantum mechanical state reductions occur along temporal hypersurfaces in
Minkowski space. They conclude that the covariant state reduction theory of
Hellwig and Kraus does not apply. In Part I of this paper we disagree with this
interpretation of the A-A experiment, and show the adequacy of the H-K theory.
In Part II we examine the belief that H-K reductions produce self contradicting
causal loops, and/or give rise to absurd boundary conditions. These objections
to the theory are shown to be unfounded.


title: Quantum Particle-Trajectories and Geometric Phase

abstract:
  "Particle"-trajectories are defined as integrable $dx_\mu dp^\mu = 0$ paths
in projective space.
  Quantum states evolving on such trajectories, open or closed, do not
delocalise in $(x, p)$ projection, the phase associated with the trajectories
being related to the geometric (Berry) phase and the Classical Mechanics
action. High Energy Physics properties of states evolving on
"particle"-trajectories are discussed.


title: Entanglement of Atomic Ensembles by Trapping Correlated Photon States

abstract:
  We describe a general technique that allows for an ideal transfer of quantum
correlations between light fields and metastable states of matter. The
technique is based on trapping quantum states of photons in coherently driven
atomic media, in which the group velocity is adiabatically reduced to zero. We
discuss possible applications such as quantum state memories, generation of
squeezed atomic states, preparation of entangled atomic ensembles and quantum
information processing.


title: Multiqubit Spin

abstract:
  It is proposed that the state space of a quantum object with a complicated
discrete spectrum can be used as a basis for multiqubit recording and
processing of information in a quantum computer. As an example, nuclear spin
3/2 is considered. The possibilities of writing and reading two quantum bits of
information, preparation of the initial state, implementation of the "rotation"
and "controlled negation" operations, which are sufficient for constructing any
algorithms, are demonstrated.


title: Symplectic Cuts and Projection Quantization

abstract:
  The recently proposed projection quantization, which is a method to quantize
particular subspaces of systems with known quantum theory, is shown to yield a
genuine quantization in several cases. This may be inferred from exact results
established within symplectic cutting.


title: Continuous Spectra of Generalized Kronig-Penney Model

abstract:
  The standard Kronig-Penney model with periodic $\delta$ potentials is
extended to the cases with generalized contact interactions. The eigen equation
which determines the dispersion relation for one-dimensional periodic array of
the generalized contact interactions is deduced with the transfer matrix
formalism. Numerical results are presented which reveal unexpected band spectra
with broader band gap in higher energy region for generic model with
generalized contact interaction.


title: Quantization and Time

abstract:
  Starting from a functional formulation of classical mechanics, we show how to
perform its quantization by freezing to zero two Grassmannian partners of time.


title: Monte Carlo Hamiltonian from Stochastic Basis

abstract:
  In order to extend the recently proposed Monte Carlo Hamiltonian to many-body
systems, we suggest to concept of a stochastic basis. We apply it to the chain
of $N_s=9$ coupled anharmonic oscillators. We compute the spectrum of excited
states in a finite energy window and thermodynamical observables free energy,
average energy, entropy and specific heat in a finite temperature window.
Comparing the results of the Monte Carlo Hamiltonian with standard Lagrangian
lattice calculations, we find good agreement. However, the Monte Carlo
Hamiltonian results show less fluctuations under variation of temperature.


title:
Quantum Interferometric Optical Lithography: Exploiting Entanglement to
  Beat The Diffraction Limit

abstract:
  Classical, interferometric, optical lithography is diffraction limited to
writing features of a size lambda/2 or greater, where lambda is the optical
wavelength. Using nonclassical photon number states, entangled N at a time, we
show that it is possible to write features of minimum size lambda/(2N) in an
N-photon absorbing substrate. This result surpasses the usual classical
diffraction limit by a factor of N. Since the number of features that can be
etched on a two-dimensional surface scales inversely as the square of the
feature size, this allows one to write a factor of N^2 more elements on a
semiconductor chip. A factor of N = 2 can be achieved easily with entangled
photon pairs generated from optical parametric downconversion. It is shown how
to write arbitrary 2D patterns by using this method.


title: A Proof of the Security of Quantum Key Distribution

abstract:
  We prove the security of quantum key distribution against the most general
attacks which can be performed on the channel, by an eavesdropper who has
unlimited computation abilities, and the full power allowed by the rules of
classical and quantum physics. A key created that way can then be used to
transmit secure messages in a way that their security is also unaffected in the
future.


title: Holomorphic Methods in Mathematical Physics

abstract:
  This set of lecture notes gives an introduction to holomorphic function
spaces as used in mathematical physics. The emphasis is on the Segal-Bargmann
space and the canonical commutation relations. Later sections describe more
advanced topics such as the Segal-Bargmann transform for compact Lie groups and
the infinite-dimensional theory.


title: Quantum properties of classical Fisher information

abstract:
  The Fisher information of a quantum observable is shown to be proportional to
both (i) the difference of a quantum and a classical variance, thus providing a
measure of nonclassicality; and (ii) the rate of entropy increase under
Gaussian diffusion, thus providing a measure of robustness. The joint
nonclassicality of position and momentum observables is shown to be
complementary to their joint robustness in an exact sense.


title:
Reparametrization Invariance of Perturbatively Defined Path Integrals.
  II. Integrating Products of Distributions

abstract:
  We show how to perform integrals over products of distributions in coordinate
space such as to reproduce the results of momentum space Feynman integrals in
dimensional regularization. This ensures the invariance of path integrals under
coordinate transformations. The integrals are uniquely defined by expressing
the propagators in 1- epsilon dimensions in terms of modified Bessel functions.


title: Permutation Symmetry For Many Particles

abstract:
  We consider the implications of the Revised Symmetrization Postulate (see
quant-ph/9908078) for states of more than two particles. We show how to create
permutation symmetric state vectors and how to derive alternative state vectors
that may be asymmetric for any pair by creating asymmetric interdependencies in
their state descriptions. Because we can choose any pair to create such an
asymmetry, the usual generalized exclusion rules which result, apply
simultaneously to any pair. However, we distinguish between simultaneous
pairwise exclusion rules and the simultaneous pairwise anti-symmetry of the
conventional symmetrization postulate. We show how to construct a variety of
state vectors with multiple interdependencies in their state descriptions and
various exchange asymmetries - including one which is anti-symmetric under
exchange of two bosons - all without violating the spin-statistics theorem. We
conjecture that it is possible to construct state vectors for arbitrary mixes
of bosons and fermions that emulate the conventional symmetrization postulate
in a limited way and give examples. We also prove that it is not possible to
define a single state vector that simultaneously obeys the conventional
symmetrization postulate in its standard form (in which the exchange phase does
not depend on the spins of additional particles that are present) for every
pair that can be interchanged.


title: Subdynamics as a mechanism for objective description

abstract:
  The relationship between microsystems and macrosystems is considered in the
context of quantum field formulation of statistical mechanics: it is argued
that problems on foundations of quantum mechanics can be solved relying on this
relationship. This discussion requires some improvement of non-equilibrium
statistical mechanics that is briefly presented.


title:
On the theory of the relativistic cross sections for stimulated
  bremsstrahlung on an arbitrary electrostatic potential in the strong
  electromagnetic field

abstract:
  On the base of relativistic generalized eikonal approximation wave function
the multiphoton cross sections of a Dirac particle bremsstrahlung on an
arbitrary electrostatic potential and strong laser radiation field are
presented. In the limit of the Born approximation the ultimate analytical
formulas for arbitrary polarization of electromagnetic wave have been obtained.


title: Relativistic Time of Arrival

abstract:
  We propose a covariant algorithm for relativistic ideal measurements and for
relativistic continuous measurements, its non-relativistic limit results the
algorithm of the Event-Enhanced Quantum Theory. Therefore an additional
intrinsic parameter, the proper time, is used. As an application we compute the
time of arrival of a particle at a detector and find good agreement between the
expected values of the time of arrival for weak detectors and the results of
the relativistic point-mechanic over a wide range. For very high momentums
there is a small probability for a negative time of arrival, so the expected
times are a bit smaller than the results of the relativistic mechanics.


title: Teleportation of entanglement for continuous variables

abstract:
  Teleportation of a pure two particle entangled state of continuous variables
by triplet of the Greenberger-Horne-Zeilinger form is considered.
  The three-particle basis needed for a joint measurement is found. It
describes a measurement of momentum one of single particle and total moment and
relative position of the two others. Optical realization using squeezed state
of the light is discussed.


title:
Generation of continuous-wave THz radiation by use of quantum
  interference

abstract:
  We propose a scheme for generation of continuous-wave THz radiation. The
scheme requires a medium where three discrete states in a $\Lambda $
configuration can be selected, with the THz-frequency transition between the
two lower metastable states. We consider the propagation of three-frequency
continuous-wave electromagnetic (e.m.) radiation through a $\Lambda $ medium.
Under resonant excitation, the medium absorption can be strongly reduced due to
quantum interference of transitions, while the nonlinear susceptibility is
enhanced. This leads to very efficient energy transfer between the e.m. waves
providing a possibility for THz generation. We demonstrate that the photon
conversion efficiency is approaching unity in this technique.


title: Efficient microwave-induced optical frequency conversion

abstract:
  Frequency conversion process is studied in a medium of atoms with a $\Lambda$
configuration of levels, where transition between two lower states is driven by
a microwave field. In this system, conversion efficiency can be very high by
virtue of the effect of electromagnetically induced transparency (EIT).
Depending on intensity of the microwave field, two regimes of EIT are realized:
''dark-state'' EIT for the weak field, and Autler-Townes-type EIT for the
strong one. We study both cases via analytical and numerical solution and find
optimum conditions for the conversion.


title: Two-photon Franson-type experiments and local realism

abstract:
  The two-photon interferometric experiment proposed by Franson [Phys. Rev.
Lett. 62, 2205 (1989)] is often treated as a "Bell test of local realism".
However, it has been suggested that this is incorrect due to the 50%
postselection performed even in the ideal gedanken version of the experiment.
Here we present a simple local hidden variable model of the experiment that
successfully explains the results obtained in usual realizations of the
experiment, even with perfect detectors. Furthermore, we also show that there
is no such model if the switching of the local phase settings is done at a rate
determined by the internal geometry of the interferometers.


title:
About the Notion of Truth in the Decoherent Histories Approach: a reply
  to Griffiths

abstract:
  Griffiths claims that the ``single family rule'', a basic postulate of the
decoherent histories approach, rules out our requirement that any decoherent
history has a unique truth value, independently from the decoherent family to
which it may belong. Here we analyze the reasons which make our requirement
indispensable and we discuss the consequences of rejecting it.


title: Supersymmetric derivation of the hard core deuteron's bound state

abstract:
  A supersymmetric construction of potentials describing the hard core
interaction of the neutron-proton system for low energies is proposed. It
considers only the binding energy case and uses the approximation of the Yukawa
potential given by Hulthen. Recent experimental data for the binding energy of
the deuteron are used to give the involved orders of magnitude.


title: Evaluating capacities of Bosonic Gaussian channels

abstract:
  We show how to compute or at least to estimate various capacity-related
quantities for Bosonic Gaussian channels. Among these are the coherent
information, the entanglement assisted classical capacity, the one-shot
classical capacity, and a new quantity involving the transpose operation, shown
to be a general upper bound on the quantum capacity, even allowing for finite
errors. All bounds are explicitly evaluated for the case of a one-mode channel
with attenuation/amplification and classical noise.


title: Comparison of two models for bridge-assisted charge transfer

abstract:
  Based on the reduced density matrix method, we compare two different
approaches to calculate the dynamics of the electron transfer in systems with
donor, bridge, and acceptor. In the first approach a vibrational substructure
is taken into account for each electronic state and the corresponding states
are displaced along a common reaction coordinate. In the second approach it is
assumed that vibrational relaxation is much faster than the electron transfer
and therefore the states are modeled by electronic levels only. In both
approaches the system is coupled to a bath of harmonic oscillators but the way
of relaxation is quite different. The theory is applied to the electron
transfer in ${\rm H_2P}-{\rm ZnP}-{\rm Q}$ with free-base porphyrin (${\rm
H_2P}$) being the donor, zinc porphyrin (${\rm ZnP}$) being the bridge and
quinone (${\rm Q}$) the acceptor. The parameters are chosen as similar as
possible for both approaches and the quality of the agreement is discussed.


title:
Quasiclassical Analysis of the Three-dimensional Shredinger's Equation
  and its Solution

abstract:
  The three-dimensional Schredinger's equation is analyzed with the help of the
correspondence principle between classical and quantum-mechanical quantities.
Separation is performed after reduction of the original equation to the form of
the classical Hamilton-Jacobi equation. Each one-dimensional equation obtained
after separation is solved by the conventional WKB method. Quasiclassical
solution of the angular equation results in the integral of motion $\vec
M^2=(l+\frac 12)^2\hbar^2$ and the existence of nontrivial solution for the
angular quantum number $l=0$. Generalization of the WKB method for
multi-turning-point problems is given. Exact eigenvalues for solvable and some
"insoluble" spherically symmetric potentials are obtained. Quasiclassical
eigenfunctions are written in terms of elementary functions in the form of a
standing wave.


title: Quantum dissipation and neural net dynamics

abstract:
  Inspired by the dissipative quantum model of brain, we model the states of
neural nets in terms of collective modes by the help of the formalism of
Quantum Field Theory. We exhibit an explicit neural net model which allows to
memorize a sequence of several informations without reciprocal destructive
interference, namely we solve the overprinting problem in such a way last
registered information does not destroy the ones previously registered.
Moreover, the net is able to recall not only the last registered information in
the sequence, but also anyone of those previously registered.

categories: quant-ph cond-mat.other hep-th physics.bio-ph q-bio.OT


title: Half Quantization

abstract:
  A general dynamical system composed by two coupled sectors is considered. The
initial time configuration of one of these sectors is described by a set of
classical data while the other is described by standard quantum data. These
dynamical systems will be named half quantum. The aim of this paper is to
derive the dynamical evolution of a general half quantum system from its full
quantum formulation. The standard approach would be to use quantum mechanics to
make predictions for the time evolution of the half quantum initial data. The
main problem is how can quantum mechanics be applied to a dynamical system
whose initial time configuration is not described by a set of fully quantum
data. A solution to this problem is presented and used, as a guideline to
obtain a general formulation of coupled classical-quantum dynamics. Finally, a
quantization prescription mapping a given classical theory to the correspondent
half quantum one is presented.


title:
Nonclassical correlations of photon number and field components in the
  vacuum state

abstract:
  It is shown that the quantum jumps in the photon number n from zero to one or
more photons induced by backaction evasion quantum nondemolition measurements
of a quadrature component x of the vacuum light field state are strongly
correlated with the quadrature component measurement results. This correlation
corresponds to the operator expectation value <xnx> which is equal to one
fourth for the vacuum even though the photon number eigenvalue is zero. Quantum
nondemolition measurements of a quadrature component can thus provide
experimental evidence of the nonclassical operator ordering dependence of the
correlations between photon number and field components in the vacuum state.


title: Operator Methods of the Parabolic Potential Barrier

abstract:
  The one-dimensional parabolic potential barrier dealt with in an earlier
paper is re-examined from the point of view of operator methods, for the
purpose of getting generalized Fock spaces.


title: Noised based cipher system

abstract:
  A computationally secure noised based cipher system is proposed. The
advantage of this cipher system is that it operates above noise level.
Therefore computationally secure communication can be done when error
correction code fails. Another feature of this system is that minimum number of
exhaustive key search can be made fixed.


title:
Consistent histories and relativistic invariance in the modal
  interpretation of quantum mechanics

abstract:
  Modal interpretations of quantum mechanics assign definite properties to
physical systems and specify single-time joint probabilities of these
properties. We show that a natural extension, applying to properties at several
times, can be given if a decoherence condition is satisfied. This extension
defines "consistent histories" of modal properties. We suggest a new form of
the modal scheme, that offers prospects of a more general applicability of the
histories concept. Finally, we discuss a possible way of applying these ideas
to relativistic quantum field theory.