title:
Do the precise measurements of the Casimir force agree with the
  expectations?

abstract:
  An upper limit on the Casimir force is found using the dielectric functions
of perfect crystalline materials which depend only on well defined material
constants. The force measured with the atomic force microscope is larger than
this limit at small separations between bodies and the discrepancy is
significant. The simplest modification of the experiment is proposed allowing
to make its results more reliable and answer the question if the discrepancy
has any relation with the existence of a new force.


title: Bohmian mechanics contradicts quantum mechanics

abstract:
  It is shown that, for a harmonic oscillator in the ground state, Bohmian
mechanics and quantum mechanics predict values of opposite sign for certain
time correlations.
  The discrepancy can be explained by the fact that Bohmian mechanics has no
natural way to accomodate the Heisenberg picture, since the local expectation
values that define the beables of the theory depend on the Heisenberg time
being used to define the operators.
  Relations to measurement are discussed, too, and shown to leave no loophole
for claiming that Bohmian mechanics reproduces all predictions of quantum
mechanics exactly.


title: Evidence for a dynamic origin of charge

abstract:
  The fundamental equations of particle motion lead to a modified Poisson
equation including dynamic charge. This charge derives from density
oscillations of a particle; it is not discrete, but continuous. Within the
dynamic model of hydrogen it accounts for all features of electron proton
interactions, its origin are density oscillations of the proton. We propose a
new system of electromagnetic units, based on meter, kilogram, and second,
bearing on these findings. The system has none of the disadvantages of
traditional three-unit systems. On the basis of our theoretical model we can
genuinely derive the scaling factor between electromagnetic and mechanic
variables, which is equal, within a few percent, to Planck's constant h. The
implications of the results in view of unifying gravity and quantum theory are
discussed. It seems that the hypothetical solar gravity waves, in the low
frequency range of the electromagnetic spectrum, are open to experimental
detection.


title: Effects of Dicke superradiance in context of the one-atom maser

abstract:
  We consider a micromaser model to study the influence of Dicke superradiance
in the context of the one-atom maser. The model involves a microwave cavity
into which two-level Rydberg atoms are pumped in pairs. We consider a random
pump mechanism which allows the presence of at most one pair of atoms in the
cavity at any time. We analyze the differences between the present system,
called the Dicke micromaser, and an equivalently pumped conventional one-atom
micromaser. These differences are attributed to the Dicke cooperativity in the
two-atom system. We also show that the two-atom Dicke micromaser is equivalent
to a one-atom cascade two-photon micromaser. With the introduction of a
one-photon detuning, the present theory further describes a true two-photon
micromaser. We discuss in detail the role of one-photon detuning in the
mechanism of a one-atom two-photon micromaser. This leads us to point out that
the two-atom cavity dynamics can be verified by a proper scaling of the results
from an equivalent one-atom two-photon micromaser.


title: Separability and Fourier representations of density matrices

abstract:
  Using the finite Fourier transform, we introduce a generalization of
Pauli-spin matrices for $d$-dimensional spaces, and the resulting set of
unitary matrices $S(d) $ is a basis for $d\times d$ matrices. If $N=d_{1}\times
d_{2}\times...\times d_{b}$ and $H^{[ N]}=\bigotimes H^{% [ d_{k}]}$, we give a
sufficient condition for separability of a density matrix $\rho $ relative to
the $H^{[ d_{k}]}$ in terms of the $L_{1}$ norm of the spin coefficients of
$\rho >.$ Since the spin representation depends on the form of the tensor
product, the theory applies to both full and partial separability on a given
space $H^{[ N]}$% . It follows from this result that for a prescribed form of
separability, there is always a neighborhood of the normalized identity in
which every density matrix is separable. We also show that for every prime $p$
and $n>1$ the generalized Werner density matrix $W^{[ p^{n}]}(s) $ is fully
separable if and only if $s\leq (1+p^{n-1}) ^{-1}$.


title: Structure behind Mechanics II: Deduction

abstract:
  This paper proves that protomechanics, previously introduced in
quant-ph/9909025, deduces both quantum mechanics and classical mechanics. It
does not only solve the problem of the arbitrariness on the operator ordering
for the quantization procedure, but also that of the analyticity at the exact
classical-limit of $\hbar =0 $. In addition, proto-mechanics proves valid also
for the description of a half-spin.


title:
Antiparticle in Light of Einstein-Podolsky-Rosen Paradox and Klein
  Paradox

abstract:
  The original version of Einstein-Podolsky-Rosen (EPR) paradox and the Klein
paradox of Klein-Gordon (KG) equation are discussed to show the necessity of
existence of antiparticle with its wavefunction being fixed unambiguously. No
concept of "hole" is needed.


title: Some conceptual issues involving probability in quantum mechanics

abstract:
  We discuss some issues about probability in quantum mechanics, with
particular emphasis on the GHZ theorem. We propose the usage of nonmonotonic
upper probabilities as a tool to derive consistent joint upper probabilities
for systems where only contextual hidden variables are possible.


title: Quantum computation with mesoscopic superposition states

abstract:
  We present a strategy to engineer a simple cavity-QED two-bit universal
quantum gate using mesoscopic distinct quantum superposition states. The
dissipative effect on decoherence and amplitude damping of the quantum bits are
analyzed and the critical parameters are presented.


title: What does Psi tell us in hell?

abstract: This paper was removed by arXiv admin due to metadata abuse.


title:
Influence of measurement on the life-time and the line-width of unstable
  systems

abstract:
  We investigate the quantum Zeno effect in the case of electron tunneling out
of a quantum dot in the presence of continuous monitoring by a detector. It is
shown that the Schr\"odinger equation for the whole system can be reduced to
Bloch-type rate equations describing the combined time-development of the
detector and the measured system. Using these equations we find that continuous
measurement of the unstable system does not affect its exponential decay to a
reservoir with a constant density of states. The width of the energy
distribution of the tunneling electron, however, is not equal to the inverse
life-time -- it increases due to the decoherence generated by the detector. We
extend the analysis to the case of a reservoir described by an energy dependent
density of states, and we show that continuous measurement of such quantum
systems affects both the exponential decay rate and the energy distribution.
The decay does not always slow down, but might be accelerated. The energy
distribution of the tunneling electron may reveal the lines invisible before
the measurement.


title: Hidden assumptions in decoherence theory

abstract:
  The role of implicit assumptions in current decoherence theory is pointed out
and clarified.


title: Modification of relative entropy of Entanglement

abstract:
  We present the modified relative entropy of entanglement (MRE) in order to
both improve the computability for the relative entropy of entanglement and
avoid the problem that the entanglement of formation seems to be greater than
entanglement of distillation. For two qubit system we derive out an explicit
and "weak" closed expression of MRE that depends on the pure state
decompositions in the case of mixed states. For more qubit system, we obtain an
algorithm to calculate MRE in principle. MRE significantly improves the
computability of relative entropy of entanglement and decreases the dependence
and sensitivity on the pure state decompositions. Moreover it is able to
inherit most of the important physical features of the relative entropy of
entanglement. In addition, a kind of states, as an extension of Werner's
states, is discussed constructively.


title: Incompatibility of the de Broglie-Bohm Theory with Quantum Mechanics

abstract:
  t is shown that although the de Broglie-Bohm quantum theory of motion is
equivalent to standard quantum mechanics when averages of dynamical variables
are taken over a Gibbs ensemble of Bohmian trajectories, the equivalence breaks
down for ensembles built over clearly separated short intervals of time in
special multi-particle systems. This feature is exploited to propose a
realistic experiment to distinguish between the two theories.


title: Quantum Mechanics As A Limiting Case of Classical Mechanics

abstract:
  In spite of its popularity, it has not been possible to vindicate the
conventional wisdom that classical mechanics is a limiting case of quantum
mechanics. The purpose of the present paper is to offer an alternative point of
view in which quantum mechanics emerges as a limiting case of classical
mechanics in which the classical system is decoupled from its environment.


title:
Generalized Affine Coherent States: A Natural Framework for Quantization
  of Metric-like Variables

abstract:
  Affine variables, which have the virtue of preserving the positive-definite
character of matrix-like objects, have been suggested as replacements for the
canonical variables of standard quantization schemes, especially in the context
of quantum gravity. We develop the kinematics of such variables, discussing
suitable coherent states, their associated resolution of unity, polarizations,
and finally the realization of the coherent-state overlap function in terms of
suitable path-integral formulations.


title: New nonlinear coherent states and some of their nonclassical properties

abstract:
  We construct a displacement operator type nonlinear coherent state and
examine some of its properties. In particular it is shown that this nonlinear
coherent state exhibits nonclassical properties like squeezing and
sub-Poissonian behaviour.


title: Generalized intelligent states and SU(1,1) and SU(2) squeezing

abstract:
  A sufficient condition for a state |\psi> to minimize the
Robertson-Schr\"{o}dinger uncertainty relation for two observables A and B is
obtained which for A with no discrete spectrum is also a necessary one. Such
states, called generalized intelligent states (GIS), exhibit arbitrarily strong
squeezing (after Eberly) of A and B. Systems of GIS for the SU(1,1) and SU(2)
groups are constructed and discussed. It is shown that SU(1,1) GIS contain all
the Perelomov coherent states (CS) and the Barut and Girardello CS while the
Bloch CS are subset of SU(2) GIS.


title: From time inversion to nonlinear QED

abstract:
  In Minkowski flat space-time, it is perceived that time inversion is unitary
rather than antiunitary, with energy being a time vector changing sign under
time inversion. The Dirac equation, in the case of electromagnetic interaction,
is not invariant under unitary time inversion, giving rise to a ``Klein
paradox''. To render unitary time inversion invariance, a nonlinear wave
equation is constructed, in which the ``Klein paradox'' disappears. In the case
of Coulomb interaction, the revised nonlinear equation can be linearized to
give energy solutions for Hydrogen-like ions without singularity when nuclear
number $Z>137$, showing a reversed energy order pending for experimental tests
such as Zeeman effects. In non-relativistic limit, this nonlinear equation
reduces to nonlinear schr\"odinger equation with soliton-like solutions.
Moreover, particle conjugation and electron-proton scattering with a
nonsingular current-potential interaction are discussed. Finally the explicit
form of gauge function is found, the uniqueness of Lorentz gauge is proven and
the Lagrangian density of quantum electrodynamics (QED) is revised as well. The
implementation of unitary time inversion leads to the ultimate derivation of
nonlinear QED.

categories: quant-ph gr-qc hep-th nlin.PS physics.atom-ph


title:
Hardy-type experiment for the maximally entangled state: Illustrating
  the problem of subensemble postselection

abstract:
  By selecting a certain subensemble of joint detection events in a
two-particle interferometer arrangement, a formal nonlocality contradiction of
the Hardy type is derived for an ensemble of particle pairs configured in the
maximally entangled state. It is argued, however, that the class of experiments
exhibiting this kind of contradiction does not rule out the assumption of local
realism.


title: Bound states of neutral particles in external electric fields

abstract:
  Neutral fermions of spin $\frac 12$ with magnetic moment can interact with
electromagnetic fields through nonminimal coupling. The Dirac--Pauli equation
for such a fermion coupled to a spherically symmetric or central electric field
can be reduced to two simultaneous ordinary differential equations by
separation of variables in spherical coordinates. For a wide variety of central
electric fields, bound-state solutions of critical energy values can be found
analytically. The degeneracy of these energy levels turns out to be numerably
infinite. This reveals the possibility of condensing infinitely many fermions
into a single energy level. For radially constant and radially linear electric
fields, the system of ordinary differential equations can be completely solved,
and all bound-state solutions are obtained in closed forms. The radially
constant field supports scattering solutions as well. For radially linear
fields, more energy levels (in addition to the critical one) are infinitely
degenerate. The simultaneous presence of central magnetic and electric fields
is discussed.


title: Scattering theory from microscopic first principles

abstract:
  We sketch a derivation of abstract scattering theory from the microscopic
first principles defined by Bohmian mechanics. We emphasize the importance of
the flux-across-surfaces theorem for the derivation, and of randomness in the
impact parameter of the initial wave function---even for an, inevitably
inadequate, orthodox derivation.


title: Adiabatic Output Coupling of a Bose Gas at Finite Temperatures

abstract:
  We develop a general theory of adiabatic output coupling from trapped atomic
Bose-Einstein Condensates at finite temperatures. For weak coupling, the output
rate from the condensate, and the excited levels in the trap, settles in a time
proportional to the inverse of the spectral width of the coupling to the output
modes. We discuss the properties of the output atoms in the quasi-steady-state
where the population in the trap is not appreciably depleted. We show how the
composition of the output beam, containing condensate and thermal component,
may be controlled by changing the frequency of the output coupler. This
composition determines the first and second order coherence of the output beam.
We discuss the changes in the composition of the bose gas left in the trap and
show how nonresonant output coupling can stimulate either the evaporation of
thermal excitations in the trap or the growth of non-thermal excitations, when
pairs of correlated atoms leave the condensate.


title:
Inequalities for dealing with detector inefficiencies in
  Greenberger-Horne-Zeilinger-type experiments

abstract:
  In this article we show that the three-particle GHZ theorem can be
reformulated in terms of inequalities, allowing imperfect correlations due to
detector inefficiencies. We show quantitatively that taking into accout those
inefficiencies, the published results of the Innsbruck experiment support the
nonexistence of local hidden variables that explain the experimental result.


title: Bound entanglement and continuous variables

abstract:
  We introduce the definition of generic bound entanglement for the case of
continuous variables. We provide some examples of bound entangled states for
that case, and discuss their physical sense in the context of quantum optics.
We rise the question of whether the entanglement of these states is generic. As
a byproduct we obtain a new many parameter family of bound entangled states
with positive partial transpose. We also point out that the ``entanglement
witnesses'' and positive maps revealing the corresponding bound entanglement
can be easily constructed.


title:
Antibunching effect of the radiation field in a microcavity with a
  mirror undergoing heavily damping oscillation

abstract:
  The interaction between the radiation field in a microcavity with a mirror
undergoing damping oscillation is investigated. Under the heavily damping
cases, the mirror variables are adiabatically eliminated.
  The the stationary conditions of the system are discussed. The small
fluctuation approximation around steady values is applied to analysis the
antibunching effect of the cavity field. The antibunching condition is given
under two limit cases.


title:
Hybrid exciton-polaritons in a bad microcavity containing the organic
  and inorganic quantum wells

abstract:
  We study the hybrid exciton-polaritons in a bad microcavity containing the
organic and inorganic quantum wells. The corresponding polariton states are
given. The analytical solution and the numerical result of the stationary
spectrum for the cavity field are finished


title: Anharmonic oscillators energies via artificial perturbation method

abstract:
  A new pseudoperturbative (artificial in nature) methodical proposal [15] is
used to solve for Schrodinger equation with a class of phenomenologically
useful and methodically challenging anharmonice oscillator potentials
V(q)=\alpha_o q^2 + \alpha q^4. The effect of the [4,5] Pade' approximant on
the leading eigenenergy term is studied. Comparison with results from numerical
(exact) and several eligible (approximation) methods is made.


title: Time dependence of evanescent quantum waves

abstract:
  The time dependence of quantum evanescent waves generated by a point source
with an infinite or a limited frequency band is analyzed. The evanescent wave
is characterized by a forerunner (transient) related to the precise way the
source is switched on. It is followed by an asymptotic, monochromatic wave
which at long times reveals the oscillation frequency of the source. For a
source with a sharp onset the forerunner is exponentially larger than the
monochromatic solution and a transition from the transient regime to the
asymtotic regime occurs only at asymptotically large times. In this case, the
traversal time for tunneling plays already a role only in the transient regime.
To enhance the monochromatic solution compared to the forerunner we investigate
(a) frequency band limited sources and (b) the short time Fourier analysis (the
spectrogram) corresponding to a detector which is frequency band limited.
Neither of these two methods leads to a precise determination of the traversal
time. However, if they are limited to determine the traversal time only with a
precision of the traversal time itself both methods are successful: In this
case the transient behavior of the evanescent waves is at a time of the order
of the traversal time followed by a monochromatic wave which reveals the
frequency of the source.


title: First Single Bubble Sonoluminescence in Dubna

abstract:
  At the Institute in Physical-Technical Problems experiments on
sonoluminescence was started by our group at the beginning of 1998. The study
was focused at properties of the SBSL, and the aim was to find more optimum
conditions for a search for some recently predicted rare effects in SBSL-
process.


title: CSL Collapse Model And Spontaneous Radiation: An Update

abstract:
  A brief review is given of the Continuous Spontaneous Localization (CSL)
model in which a classical field interacts with quantized particles to cause
dynamical wavefunction collapse. One of the model's predictions is that
particles "spontaneously" gain energy at a slow rate. When applied to the
excitation of a nucleon in a Ge nucleus, it is shown how a limit on the
relative collapse rates of neutron and proton could be obtained, and a rough
estimate is made from data. When applied to the spontaneous excitation of 1s
electrons in Ge, by a more detailed analysis of more accurate data than
previously given, an updated limit is obtained on the relative collapse rates
of the electron and proton, suggesting that the coupling of the field to
electrons and nucleons is mass proportional.


title: Is Supersymmetric Quantum Mechanics compatible with Duality

abstract:
  Supersymmetry applied to quantum mechanics has given new insights in various
topics of theoretical physics like analytically solvable potentials, WKB
approximation or KdV solitons. Duality plays a central role in many
supersymmetric theories such as Yang-Mills theories or strings models. We
investigate the possible existence of some duality within supersymmetric
quantum mechanics.


title: Quantization of Soliton Cellular Automata

abstract:
  A method of quantization of classical soliton cellular automata (QSCA) is put
forward that provides a description of their time evolution operator by means
of quantum circuits that involve quantum gates from which the associated
Hamiltonian describing a quantum chain model is constructed.
  The intrinsic parallelism of QSCA, a phenomenon first known from quantum
computers, is also emphasized.


title: Quantum key distribution based on Greenberger-Horne-Zeilinger state

abstract:
  An unsymmetrical quantum key distribution scheme is proposed, its security is
guaranteed by the correlation of the Greenberger-Horne-Zeilinger triplet state.
In the proposed protocol, the distribution of quantum states are unsymmetrical.
This unsymmetrical characteristic makes the transmission qubits (except the
loss qubits) be useful. Sequentially the proposed protocol has excellent
efficiency and security which are very useful in the practical application.


title: Quantum key distribution relied on trusted information center

abstract:
  Quantum correlation between two particles and among three particles show
nonclassic properties that can be used for providing secure transmission of
information. In this paper, we propose two quantum key distribution schemes for
quantum cryptographic network, which use the correlation properties of two and
three particles. One is implemented by the Greenberger-Horne-Zeilinger state,
and another is implemented by the Bell states. These schemes need a trusted
information center like that in the classic cryptography. The optimal
efficiency of the proposed protocols are higher than that in the previous
schemes.


title: Quantum authentication protocol

abstract:
  In this letter, we proposed a quantum authentication protocol. The
authentication process is implemented by the symmetric cryptographic scheme
with quantum effects.


title: Quantum Diffusions and Appell Systems

abstract:
  Within the algebraic framework of Hopf algebras, random walks and associated
diffusion equations (master equations) are constructed and studied for two
basic operator algebras of Quantum Mechanics i.e the Heisenberg-Weyl algebra
(hw) and its q-deformed version hw_q. This is done by means of functionals
determined by the associated coherent state density operators. The ensuing
master equations admit solutions given by hw and hw_q-valued Appell systems.


title: Brownian motion on a smash line

abstract:
  Brownian motion on a smash line algebra (a smash or braided version of the
algebra resulting by tensoring the real line and the generalized paragrassmann
line algebras), is constructed by means of its Hopf algebraic structure.
Further, statistical moments, non stationary generalizations and its diffusion
limit are also studied. The ensuing diffusion equation posseses triangular
matrix realizations.


title:
A Generalized Jaynes-Cummings Hamiltonian and Supersymmetric
  Shape-Invariance

abstract:
  A class of shape-invariant bound-state problems which represent two-level
systems are introduced. It is shown that the coupled-channel Hamiltonians
obtained correspond to the generalization of the Jaynes-Cummings Hamiltonian.

categories: quant-ph math-ph math.MP nucl-th physics.atom-ph


title: Quantum nonlinear lattices and coherent state vectors

abstract:
  Quantized nonlinear lattice models are considered for two different classes,
boson and fermionic ones. The quantum discrete nonlinear Schroedinger model
(DNLS) is our main objective, but its so called modified discrete nonlinear
(MDNLS) version is also included, together with the fermionic polaron (FP)
model. Based on the respective dynamical symmetries of the models, a method is
put forward which by use of the associated boson and spin coherent state
vectors (CSV) and a factorization ansatz for the solution of the Schroedinger
equation, leads to quasiclassical Hamiltonian equations of motion for the CSV
parameters. Analysing the geometrical content of the factorization ansatz made
for the state vectors invokes the study of the Riemannian and symplectic
geometry of the CSV manifolds as generalized phase spaces. Next, we investigate
analytically and numerically the behavior of mean values and uncertainties of
some physically interesting observables as well as the modifications in the
quantum regime of processes such as the discrete self trapping (DST), in terms
of the Q-function and the distribution of excitation quanta of the lattice
sites. Quantum DST in the symmetric ordering of lattice operators is found to
be relatively enhanced with respect to the classical DST. Finally, the meaning
of the factorization ansatz for the lattice wave function is explained in terms
of disregarded quantum correlations, and as a quantitative figure of merit for
that ansatz a correlation index is introduced.


title:
Spin dynamics of wave packets evolving with the Dirac Hamiltonian in
  atoms with high Z

abstract:
  The motion of circular WP for one electron in central Coulomb field with high
Z is calculated. The WP is defined in terms of solutions of the Dirac equation
in order to take into account all possible relevant effects in particular the
spin-orbit potential. A time scale is defined within which spin dynamics must
be taken into account mainly in the atoms with high Z. Within this time scale
there exists a mechanism of collapses and revivals of the spin already shown by
the authors for harmonic oscillator potential and called the 'spin-orbit
pendulum'. However this effect has not the exact periodicity of the simpler
model, but the WP's spatial motion is nevertheless quite similar.


title: Canonical Quantum Teleportation

abstract:
  Canonically conjugated observables such as position-momentum and phase-number
are found to play a 3-fold role in the drama of the quantum teleportation.
Firstly, the common eigenstate of two commuting canonical observables like
phase-difference and number-sum provides the quantum channel between two
systems. Secondly, a similar pair of canonical observables from another two
systems is measured in the Bell operator measurements.


title: Positive Maps Which Are Not Completely Positive

abstract:
  The concept of the {\em half density matrix} is proposed. It unifies the
quantum states which are described by density matrices and physical processes
which are described by completely positive maps. With the help of the
half-density-matrix representation of Hermitian linear map, we show that every
positive map which is not completely positive is a {\em difference} of two
completely positive maps. A necessary and sufficient condition for a positive
map which is not completely positive is also presented, which is illustrated by
some examples.


title:
An Approach to Measurement by Quantum-Stochastic-Parameter Averaged
  Bohmian Mechanics

abstract:
  A coarse-grained quantum operator technique is used along with the formalism
of Bohmian mechanics endowed with stochastic character at the quantum level in
order to address some central issues in the quantum theory of measurement. A
surprisingly simple picture of decoherence and EPR correlations emerges from
its use.


title:
Comment on "Giant absorption cross section of ultracold neutrons in
  Gadolinium"

abstract:
  Rauch et al (PRL 83, 4955, 1999) have compared their measurements of the Gd
cross section for Ultra-cold neutrons with an exptrapolation of the cross
section for thermal neutrons and interpreted the discrepancy in terms of
coherence properties of the neutron. We show the extrapolation used is based on
a misunderstanding and that coherence properties play no role in absorption.


title:
Sensitivity to measurement perturbation of single atom dynamics in
  cavity QED

abstract:
  We consider continuous observation of the nonlinear dynamics of single atom
trapped in an optical cavity by a standing wave with intensity modulation. The
motion of the atom changes the phase of the field which is then monitored by
homodyne detection of the output field. We show that the conditional Hilbert
space dynamics of this system, subject to measurement induced perturbations,
depends strongly on whether the corresponding classical dynamics is regular or
chaotic. If the classical dynamics is chaotic the distribution of conditional
Hilbert space vectors corresponding to different observation records tends to
be orthogonal. This is a characteristic feature of hypersensitivity to
perturbation for quantum chaotic systems.


title: Discussion: Byrne and Hall on Everett and Chalmers

abstract:
  Byrne and Hall (1999) criticized the argument of Chalmers (1996) in favor of
the Everett-style interpretation. They claimed to show ``the deep and
underappreciated flaw in ANY Everett-style interpretation''. I will argue that
it is possible to interpret Chalmers's writing in such a way that most of the
criticism by Byrne and Hall does not apply. In any case their general criticism
of the many-worlds interpretation is unfounded. The recent recognition that the
Everett-style interpretations are good (if not the best) interpretations of
quantum mechanics has, therefore, not been negated.


title: Freezing Light via hot gases

abstract:
  We prove that it is possible to freeze a light pulse (i.e., to bring it to a
full stop) or even to make its group velocity negative in a coherently driven
Doppler broadened atomic medium via electromagnetically induced transparency
(EIT). This remarkable phenomenon of the ultra-slow EIT polariton is based on
the spatial dispersion of the refraction index $n(\w,k)$, i.e., its wavenumber
dependence, which is due to atomic motion and provides a negative contribution
to the group velocity. This is related to, but qualitatively different from,
the recently observed light slowing caused by large temporal (frequency)
dispersion.


title:
Geometric Phase, Curvature, and Extrapotentials in Constrained Quantum
  Systems

abstract:
  We derive an effective Hamiltonian for a quantum system constrained to a
submanifold (the constraint manifold) of configuration space (the ambient
space) by an infinite restoring force. We pay special attention to how this
Hamiltonian depends on quantities which are external to the constraint
manifold, such as the external curvature of the constraint manifold, the
(Riemannian) curvature of the ambient space, and the constraining potential. In
particular, we find the remarkable fact that the twisting of the constraining
potential appears as a gauge potential in the constrained Hamiltonian. This
gauge potential is an example of geometric phase, closely related to that
originally discussed by Berry. The constrained Hamiltonian also contains an
effective potential depending on the external curvature of the constraint
manifold, the curvature of the ambient space, and the twisting of the
constraining potential. The general nature of our analysis allows applications
to a wide variety of problems, such as rigid molecules, the evolution of
molecular systems along reaction paths, and quantum strip waveguides.


abstract:
  We construct a Universal Quantum Entanglement Concentration Gate (QEC-Gate).
Special times operations of QEC-Gate can transform a pure 2-level bipartite
entangled state to nearly maximum entanglement. The transformation can attain
any required fidelity with optimal probability by adjusting concentration step.
We also generate QEC-Gate to the Schmidt decomposable multi-partite system.


title: Causality and probabilistic interpretation of quantum mechanics

abstract:
  It is shown that probabilistic treatment of quantum mechanics can be
coordinated with causality of all physical processes. The physical
interpretation of quantum-mechanical phenomena such as process of measurement
and collapse of quantum state is given.


title:
Canonical pairs, Spatially Confined Motion and the Quantum Time of
  Arrival Problem

abstract:
  It has always been believed that no self-adjoint and canonical time of
arrival operator can be constructed within the confines of standard quantum
mechanics. In this Letter we demonstrate the otherwise. We do so by pointing
out that there is no a priori reason in demanding that canonical pairs form a
system of imprimitivities. We then proceed to show that a class of self-adjoint
and canonical time of arrival (TOA) operators can be constructed for a
spatially confined free particle. And then discuss the relatiobship between the
non-self-adjointess of the TOA operator for the unconfined particle and the
self-adjointness of the confined one.


title:
Multiparticle SUSY quantum mechanics and the representations of
  permutation group

abstract:
  The method of multidimensional SUSY Quantum Mechanics is applied to the
investigation of supersymmetrical N-particle systems on a line for the case of
separable center-of-mass motion. New decompositions of the superhamiltonian
into block-diagonal form with elementary matrix components are constructed.
Matrices of coefficients of these minimal blocks are shown to coincide with
matrices of irreducible representations of permutations group S_N, which
correspond to the Young tableaux (N-M,1^M). The connections with known
generalizations of N-particle Calogero and Sutherland models are established.


title: Quantum interfaces

abstract:
  Rational agents acting as observers use ``knowables'' to construct a vision
of the outside world. Thereby, they are bound by the information exchanged with
what they consider to be objects. The cartesian cut or, in modern terminology,
the interface mediating this exchange, is again a construction. It serves as a
``scaffolding,'' an intermediate construction capable of providing the
necessary conceptual means. An attempt is made to formalize the interface, in
particular the quantum interface and quantum measurements, by a symbolic
information exchange. A principle of conservation of information is reviewed
and a measure of information flux through the interface is proposed.


title: Optical Fock-state synthesizer

abstract:
  We suggest a tunable optical device to synthesize Fock states and their
superpositions starting from a coherent source. The scheme involves an
avalanche triggering photodetector and a ring cavity coupled to a traveling
wave through a cross-Kerr medium. Low quantum efficiency at the photodetector
improves the synthesizing quality at the expense of reducing the synthesizing
rate.


title:
Efficient factorization with a single pure qubit and $log N$ mixed
  qubits

abstract:
  It is commonly assumed that Shor's quantum algorithm for the efficient
factorization of a large number $N$ requires a pure initial state. Here we
demonstrate that a single pure qubit together with a collection of $log_2 N$
qubits in an arbitrary mixed state is sufficient to implement Shor's
factorization algorithm efficiently.


title:
Approach to the semiconductor cavity QED in high-Q regimes with
  q-deformed boson

abstract:
  The high density Frenkel exciton which interacts with a single mode
microcavity field is dealed with in the framework of the q-deformed boson. It
is shown that the q-defomation of bosonic commutation relations is satisfied
naturally by the exciton operators when the low density limit is deviated. An
analytical expression of the physical spectrum for the exciton is given by
using of the dressed states of the cavity field and the exciton. We also give
the numerical study and compare the theoretical results with the experimental
results


title: Quantum Decoherence from Adiabatic Entanglement

abstract:
  In order to understand quantum decoherence of a quantum system due to its
interaction with a large system behaving classically, we introduce the concept
of adiabatic quantum entanglement based on the Born-Oppenhemeir approximation.
In the adiabatic limit, it is shown that the wave function of the total system
formed by the quantum system plus the large system can be factorized as an
entangled state with correlation between adiabatic quantum states and
quasi-classical motion configurations of the large system. In association with
a novel viewpoint about quantum measurement, which has been directly verified
by most recent experiments [e.g, S. Durr et.al, Nature 33, 359 (1998)], it is
shown that the adiabatic entanglement is indeed responsible for the quantum
decoherence and thus it can be regarded as a "clean" quantum measurement when
the large system behaves as a classical object. The large system being taken
respectively to be a macroscopically distinguishable spatial variable, a high
spin system and a harmonic oscillator with a coherent initial state, three
illustrations are present with their explicit solutions in this paper.


title: Comment on "Hidden assumptions in decoherence theory"

abstract:
  It is shown that the conclusion of the paper "Hidden assumptions in
decoherence theory" (quant-ph/0001021) is the result of a misunderstanding of
the concept of pointer states. It is argued that pointer states are selected by
the interaction of quantum systems with the environment, and are not based on
any measurement by a conscious observer.


title:
The Phenomenological Preparation - Registration Arrow of Time and its
  Semigroup Representation in the RHS Quantum Theory

abstract:
  The observed probabilities of quantum mechanics possess a time asymmetry
which is based on the truism that a state must be prepared before an observable
can be measured in it. While Hilbert space quantum theory cannot incorporate
this arrow of time, the Rigged Hilbert Space (RHS) formulation of quantum
mechanics provides a theory of time symmetric as well as time asymmetric
quantum physics.


title: Simulation of topological field theories by quantum computers

abstract:
  Quantum computers will work by evolving a high tensor power of a small (e.g.
two) dimensional Hilbert space by local gates, which can be implemented by
applying a local Hamiltonian H for a time t. In contrast to this quantum
engineering, the most abstract reaches of theoretical physics has spawned
topological models having a finite dimensional internal state space with no
natural tensor product structure and in which the evolution of the state is
discrete, H = 0. These are called topological quantum filed theories (TQFTs).
These exotic physical systems are proved to be efficiently simulated on a
quantum computer. The conclusion is two-fold: 1. TQFTs cannot be used to define
a model of computation stronger than the usual quantum model BQP. 2. TQFTs
provide a radically different way of looking at quantum computation. The rich
mathematical structure of TQFTs might suggest a new quantum algorithm.


title: Quantum limit of optical magnetometry in the presence of ac-Stark shifts

abstract:
  We analyze systematic (classical) and fundamental (quantum) limitations of
the sensitivity of optical magnetometers resulting from ac-Stark shifts. We
show that in contrast to absorption-based techniques, the signal reduction
associated with classical broadening can be compensated in magnetometers based
on phase measurements using electromagnetically induced transparency (EIT).
However due to ac-Stark associated quantum noise the signal-to-noise ratio of
EIT-based magnetometers attains a maximum value at a certain laser intensity.
This value is independent on the quantum statistics of the light and defines a
standard quantum limit of sensitivity. We demonstrate that an EIT-based optical
magnetometer in Faraday configuration is the best candidate to achieve the
highest sensitivity of magnetic field detection and give a detailed analysis of
such a device.


abstract:
  Entangled SU(2) and SU(1,1) coherent states are developed as superpositions
of multiparticle SU(2) and SU(1,1) coherent states. In certain cases, these are
coherent states with respect to generalized su(2) and su(1,1) generators, and
multiparticle parity states arise as a special case. As a special example of
entangled SU(2) coherent states, entangled binomial states are introduced and
these entangled binomial states enable the contraction from entangled SU(2)
coherent states to entangled harmonic oscillator coherent states. Entangled
SU(2) coherent states are discussed in the context of pairs of qubits. We also
introduce the entangled negative binomial states and entangled squeezed states
as examples of entangled SU(1,1) coherent states. A method for generating the
entangled SU(2) and SU(1,1) coherent states is discussed and degrees of
entanglement calculated. Two types of SU(1,1) coherent states are discussed in
each case: Perelomov coherent states and Barut-Girardello coherent states.


title: An Epistemological Derivation of Quantum Logic

abstract:
  This paper deals with the foundations of quantum mechanics. We start by
outlining the characterisation, due to Birkhoff and Von Neumann, of the logical
structures of the theories of classical physics and quantum mechanics, as
boolean and modular lattices respectively. We then derive these descriptions
from what we claim are basic properties of any physical theory - i.e. the
notion that a quantity in such a theory may be analysed into parts and that the
results of this analysis may be treated in languages with an underlying boolean
structure. We shall see that in the course of constructing a model of a theory
with these properties different indistinguishable possibilities will arise for
how the elements of the model may be named, that is to say different
possibilities arise for how they can be associated with points from Set. Taking
a particular collection of possibilities gives the usual boolean lattice of the
propositions of classical physics. Taking all possibilities - in a sense, the
set of all things that may be described by physical theories - gives the
lattice of quantum mechanical propositions. This gives an interpretation of
quantum mechanics as the complete set of such possible descriptions, the
complete physical description of the world.


title: Qudit Entanglement

abstract:
  We consider the separability of various joint states of D-dimensional quantum
systems, which we call "qudits." We derive two main results: (i) the
separability condition for a two-qudit state that is a mixture of the maximally
mixed state and a maximally entangled state; (ii) lower and upper bounds on the
size of the neighorhood of separable states surrounding the maximally mixed
state for N qudits.


title: Covariance, correlation and entanglement

abstract:
  Some new identities for quantum variance and covariance involving commutators
are presented, in which the density matrix and the operators are treated
symmetrically. A measure of entanglement is proposed for bipartite systems,
based on covariance. This works for two- and three-component systems but
produces ambiguities for multicomponent systems of composite dimension. Its
relationship to angular momentum dispersion for symmetric symmetric spin states
is described.


title: Poly-locality in quantum computing

abstract:
  A polynomial depth quantum circuit effects, by definition a poly-local
unitary transformation of tensor product state space. It is a physically
reasonable belief [Fy][L][FKW] that these are precisely the transformations
which will be available from physics to help us solve computational problems.
The poly-locality of discrete Fourier transform on cyclic groups is at the
heart of Shor's factoring algorithm. We describe a class of poly-local
transformations, including all the discrete orthogonal wavelet transforms in
the hope that these may be helpful in constructing new quantum algorithms. We
also observe that even a rather mild violation of poly-locality leads to a
model without one-way functions, giving further evidence that poly-locality is
an essential concept.


title:
Physical model of Schrodinger electron. Feynman convenient way in
  mathematical description of its quantum behaviour

abstract:
  The physical model of a nonrelativistic quantized Schrodinger's electron (SE)
is offered. The behaviour of the SE well spread elementary electric charge had
been understood by means of two independent and different in a frequency and
size motions. The description of this resultant motion may be done by
substitution of the classical Wiener continuous integral with the quantized
Feynmam continuous integral. There are possibility to show by means of the
existent not only formal but substantial analogy between the quadratic
differential wave equation in partial derivatives of Schrodinger and quadratic
differential particle equation in partial derivatives of Hamilton-Jacoby that
the addition of a kinetic energy of the stochastic harmonic oscillation of some
quantized micro particles to the kinetic energy of classical motion of the same
micro particles formally determines their wave behaviour.It turns out the
stochastic motion of the quantized micro particles powerfully to break up the
smooth thin line of the classical motion of the same micro particle in many
broad cylindrically spread path. The SE participate in stochastically roughly
determined circumferences within different flats and with different radii, with
centres which are successively arranjed over short and very disorderly
orientated lines. Therefore the quantized motion of some micro particle cannot
be descripted by smooth thin well contured (focused) line, describing the
classical motion of the macro particle.


title:
The Physical Model of Schrodinger Electron. Schrodinger Convenient Way
  for Description of its Quantum Behaviour

abstract:
  The physical model (PhsMdl) of a Schrodinger nonrelativistic quantized
electron (ShEl) is built by means of a transition of the quadratic differential
particle equation of Hamilton-Jacoby into the quadratic differential wave
equation of Schrodinger in this work, which interprets the physical reason of
its quantum (wave and stochastic) behaviour by explanation of the physical
reason, which forces the classical Lorentz electron (LrEl) to participate in
Furthian quantized stochastic oscillation motion, which turn it into quantum
ShEl. It is performed that this transition is realized by my consideration the
Bohm's quantum potential as a kinetic energy of the forced Furthian quantized
stochastic oscillation motion of the ShEl's well spread elementary electric
charge close to a smooth thin trajectory of a classical LrEl. There exist as an
essential analogy between the Furthian quantum stochastic trembling oscillation
motion and the Brownian classical stochastic trembling motion so and between
the description of their behaviours.


title: Limitations on the Creation of Maximal Entanglement

abstract:
  We study a limited set of optical circuits for creating near maximal
polarisation entanglement {\em without} the usual large vacuum contribution.
  The optical circuits we consider involve passive interferometers,
feed-forward detection, down-converters and squeezers. For input vacuum fields
we find that the creation of maximal entanglement using such circuits is
impossible when conditioned on two detected auxiliary photons. So far, there
have been no experiments with more auxiliary photons. Thus, based on the
minimum complexity of the circuits required, if near maximal polarisation
entanglement is possible it seems unlikely that it will be implemented
experimentally with the current resources.


title: Probabilistic quantum cloning via Greenberger-Horne-Zeilinger states

abstract:
  We propose a probabilistic quantum cloning scheme using
Greenberger-Horne-Zeilinger states, Bell basis measurements, single-qubit
unitary operations and generalized measurements, all of which are within the
reach of current technology. Compared to another possible scheme via Tele-CNOT
gate [D. Gottesman and I. L. Chuang, Nature 402, 390 (1999)], the present
scheme may be used in experiment to clone the states of one particle to those
of two different particles with higher probability and less GHZ resources.


title: Quantum Diagonalization of Hermitean Matrices

abstract:
  To measure an observable of a quantum mechanical system leaves it in one of
its eigenstates and the result of the measurement is one of its eigenvalues.
This process is shown to be a computational resource. It allows one, in
principle, to diagonalize hermitean (N by N) matrices by quantum mechanical
measurements only. To do so, one considers the given matrix as an observable of
a single spin with appropriate length s=(N-1)/2, which can be measured using a
generalized Stern-Gerlach apparatus. Then, each run provides one eigenvalue of
the observable. As it is based on the `collapse of the wave function'
associated with a measurement, the procedure is neither a digital nor an analog
calculation--it defines thus a new quantum mechanical method of computation.


title: Quantum cryptography with 3-state systems

abstract:
  We consider quantum cryptographic schemes where the carriers of information
are 3-state particles. One protocol uses four mutually unbiased bases and
appears to provide better security than obtainable with 2-state carriers.
Another possible method allows quantum states to belong to more than one basis.
The security is not better, but many curious features arise.


title: Distillation of GHZ states by selective information manipulation

abstract:
  Methods for distilling maximally entangled tripartite (GHZ) states from
arbitrary entangled tripartite pure states are described. These techniques work
for virtually any input state. Each technique has two stages which we call
primary and secondary distillation. Primary distillation produces a GHZ state
with some probability, so that when applied to an ensemble of systems, a
certain percentage is discarded. Secondary distillation produces further GHZs
from the discarded systems. These protocols are developed with the help of an
approach to quantum information theory based on absolutely selective
information, which has other potential applications.


title: Nonadditive conditional entropy and its significance for local realism

abstract:
  Based on the form invariance of the structures given by Khinchin's axiomatic
foundations of information theory and the pseudoadditivity of the Tsallis
entropy indexed by q, the concept of conditional entropy is generalized to the
case of nonadditive (nonextensive) composite systems. The proposed nonadditive
conditional entropy is classically nonnegative but can be negative in the
quantum context, indicating its utility for characterizing quantum
entanglement. A criterion deduced from it for separability of density matrices
for validity of local realism is examined in detail by employing a bipartite
spin-1/2 system. It is found that the strongest criterion is obtained in the
limit q going to infinity.


title: Decoherence in QED at finite temperature

abstract:
  We consider a wave packet of a charged particle passing through a cavity
filled with photons at temperature T and investigate its localization and
interference properties. It is shown that the wave packet becomes localized and
the interference disappears with an exponential speed after a sufficiently long
path through the cavity.


title: Quantum secret sharing for general access structures

abstract:
  We explore the conversion of classical secret-sharing schemes to quantum
ones, and how this can be used to give efficient QSS schemes for general
adversary structures. Our first result is that quantum secret-sharing is
possible for any structure for which no two disjoint sets can reconstruct the
secret (this was also proved, somewhat differently, by D. Gottesman). To obtain
this we show that a large class of linear classical SS schemes can be converted
into quantum schemes of the same efficiency.
  We also give a necessary and sufficient condiion for the direct conversion of
classical schemes into quantum ones, and show that all group homomorphic
schemes satisfy it.


title: Daylight quantum key distribution over 1.6 km

abstract:
  Quantum key distribution (QKD) has been demonstrated over a point-to-point
$\sim1.6$-km atmospheric optical path in full daylight. This record
transmission distance brings QKD a step closer to surface-to-satellite and
other long-distance applications.


title: A Remark on One-Dimensional Many-Body Problems with Point Interactions

abstract:
  The integrability of one dimensional quantum mechanical many-body problems
with general contact interactions is extensively studied. It is shown that
besides the pure (repulsive or attractive) $\delta$-function interaction there
is another singular point interactions which gives rise to a new one-parameter
family of integrable quantum mechanical many-body systems. The bound states and
scattering matrices are calculated for both bosonic and fermionic statistics.


title:
Four Atomic Optical Energy Levels as a Two Qubit Quantum Computer
  Register

abstract:
  It is proposed to use four atomic optical energy levels as a two qubit
quantum register. A single Pr3+ atom in a monocrystal LaF3 subjected to
resonant laser irradiation is used as an example to illustrate the
implementation of the universal set of quantum gates. The equilibrium state of
this physical system is a desirable input state for quantum computation and
therefore there is no need for its special preparation procedure.


title: Local symmetry properties of pure 3-qubit states

abstract:
  Entanglement types of pure states of 3 qubits are classified by means of
their stabilisers in the group of local unitary operations. It is shown that
the stabiliser is generically discrete, and that a larger stabiliser indicates
a stationary value for some local invariant. We describe all the exceptional
states with enlarged stabilisers.


title:
Quantum network architecture of tight-binding models with substitution
  sequences

abstract:
  We study a two-spin quantum Turing architecture, in which discrete local
rotations \alpha_m of the Turing head spin alternate with quantum controlled
NOT-operations. Substitution sequences are known to underlie aperiodic
structures. We show that parameter inputs \alpha_m described by such sequences
can lead here to a quantum dynamics, intermediate between the regular and the
chaotic variant. Exponential parameter sensitivity characterizing chaotic
quantum Turing machines turns out to be an adequate criterion for induced
quantum chaos in a quantum network.


title: Consistent Quantum Realism: A Reply to Bassi and Ghirardi

abstract:
  A recent claim by Bassi and Ghirardi that the consistent (decoherent)
histories approach cannot provide a realistic interpretation of quantum theory
is shown to be based upon a misunderstanding of the single-framework rule: they
have replaced the correct rule with a principle which directly contradicts it.
It is their assumptions, not those of the consistent histories approach, which
lead to a logical contradiction.


title: Dark-State Polaritons in Electromagnetically Induced Transparency

abstract:
  We identify form-stable coupled excitations of light and matter (``dark-state
polaritons'') associated with the propagation of quantum fields in
Electromagnetically Induced Transparency. The properties of the dark-state
polaritons such as the group velocity are determined by the mixing angle
between light and matter components and can be controlled by an external
coherent field as the pulse propagates. In particular, light pulses can be
decelerated and ``trapped'' in which case their shape and quantum state are
mapped onto metastable collective states of matter. Possible applications of
this reversible coherent-control technique are discussed.


title: Stochastic Resonance and Nonlinear Response by NMR Spectroscopy

abstract:
  We revisit the phenomenon of quantum stochastic resonance in the regime of
validity of the Bloch equations. We find that a stochastic resonance behavior
in the steady-state response of the system is present whenever the
noise-induced relaxation dynamics can be characterized via a single relaxation
time scale. The picture is validated by a simple nuclear magnetic resonance
experiment in water.


title:
Noncommutative analysis and quantum physics I. Quantities, ensembles and
  states

abstract:
  A unified conceptual foundation of classical and quantum physics is given,
free of undefined terms.
  Ensembles are defined by extending the `probability via expectation' approach
of Whittle to noncommuting quantities. This approach carries no connotations of
unlimited repeatability; hence it can be applied to unique systems such as the
universe. Precise concepts and traditional results about complementarity,
uncertainty and nonlocality follow with a minimum of technicalities.
Probabilities are introduced in a generality supporting so-called effects
(i.e., fuzzy events).
  States are defined as partial mappings that provide reference values for
certain quantities. An analysis of sharpness properties yields well-known no-go
theorems for hidden variables. By dropping the sharpness requirement, hidden
variable theories such as Bohmian mechanics can be accommodated, but so-called
ensemble states turn out to be a more natural realization of a realistic state
concept. The weak law of large numbers explains the emergence of classical
properties for macroscopic systems.


title: Quantum mechanics and the continuum problem(II)

abstract:
  In one-dimensional case, it is shown that the basic principles of quantum
mechanics are properties of the set of intermediate cardinality.


title: A Heuristic Approach to the Relativistic Angular Momentum

abstract:
  The relativistic angular momentum is introduced as an extension of the
non-relativistic analysis of allowed states in the phase space for a quantum
particle. The paper shows the conceptual basis of the approach. An interesting
feature of the present point of view is that the indistinguishability of
identical particles and the Pauli principle are found as corollaries.


title:
Physical model of Schrodinger's electron. Heisenberg convenient way for
  description of its quantum behaviour

abstract:
  The object of this paper is to discuss the physical interpretation of quantum
behaviour of Schrodinger electron (SchEl) and bring to light on the cause for
the Heisenberg convenient operator way of its describing, using the
nonrelativistic quantum mechanics laws and its mathematical results. We
describe the forced stochastically diverse circular oscillation motion, created
by force of the electrical interaction of the SchEl's elementary electric
charge with the electric intensity of the resultant quantum electromagnetic
field of the existing StchVrtPhtns, as a solution of Abraham-Lorentz equation.
By dint of this equation we obtain that the smooth thin line of a classical
macro particle is rapidly broken of many short and disorderly orientated lines,
owing the continuous dispersion of the quantum micro particle (QntMicrPrt) on
the StchVrtPhtns. Between two successive scattering the centers of diverse
circular oscillations with stochastically various radii are moving along this
short disordered line. These circular oscillations lie within the flats,
perpendicular to same disordered short line, along which are moving its
centers. In a result of same forced circular oscillation motion the smooth thin
line of the LrEl is roughly spread and turned out into some cylindrically wide
path of the SchEl. Hence the dispersions of different dynamical parameters,
determining the state of the SchEl, which are results of its continuously
interaction with the resultant quantum electromagnetic field of the
StchVrtPhtns. The absence of the smooth thin line trajectory at the circular
oscilation moving of the QntMicrPrt forces us to use the matrix elements
(Fourier components) of its roughly spread wide cylindrical path for its
description.


title: Algebra, Logic and Qubits: Quantum Abacus

abstract:
  The canonical anticommutation relations (CAR) for fermion systems can be
represented by finite-dimensional matrix algebra, but it is impossible for
canonical commutation relations (CCR) for bosons. After description of more
simple case with representation of CAR and (bounded) quantum computational
networks via Clifford algebras in the paper are discussed CCR. For
representation of the algebra it is not enough to use quantum networks with
fixed number of qubits and it is more convenient to consider Turing machine
with essential operation of appending new cells for description of infinite
tape in finite terms --- it has straightforward generalization for quantum
case, but for CCR it is necessary to work with symmetrized version of the
quantum Turing machine. The system is called here quantum abacus due to
understanding analogy with the ancient counting devices (abacus).


title: Globally singularity-free semi-classical wave functions in closed form

abstract:
  We use a factorization technique and representation of canonical
transformations to construct globally valid closed form expressions without
singularities of semi-classical wave functions for arbitrary smooth potentials
over a one-dimensional position space.


title: Quantum Stochastic Resonance in Electron Shelving

abstract:
  Stochastic resonance shows that under some circumstances noise can enhance
the response of a system to a periodic force. While this effect has been
extensively investigated theoretically and demonstrated experimentally in
classical systems, there is complete lack of experimental evidence within the
purely quantum mechanical domain. Here we demonstrate that stochastic resonance
can be exhibited in a single ion and would be experimentally observable using
well mastered experimental techniques. We discuss the use of this scheme for
the detection of the frequency difference of two lasers to demonstrate that
stochastic resonance may have applications in precision measurements at the
quantum limit.


title: Husimi Transform of an Operator Product

abstract:
  It is shown that the series derived by Mizrahi, giving the Husimi transform
(or covariant symbol) of an operator product, is absolutely convergent for a
large class of operators. In particular, the generalized Liouville equation,
describing the time evolution of the Husimi function, is absolutely convergent
for a large class of Hamiltonians. By contrast, the series derived by
Groenewold, giving the Weyl transform of an operator product, is often only
asymptotic, or even undefined. The result is used to derive an alternative way
of expressing expectation values in terms of the Husimi function. The advantage
of this formula is that it applies in many of the cases where the anti-Husimi
transform (or contravariant symbol) is so highly singular that it fails to
exist as a tempered distribution.


title: Pulse propagation in three-level medium

abstract:
  We investigate propagation of a pulse pair in a three-level medium under the
adiabatic following condition for the general case of unequal oscillator
strengths. Exact analytical solutions to the propagation equations have been
obtained. It is shown that propagation dynamics strongly depends on the
relationship between oscillator strengths. The adiabaticity criterion for the
interaction of pulses with three-level media has been derived and analyzed in
detail.


title: Quantum Anti-Cloning

abstract:
  We derive the transformation for the optimal universal quantum anti-cloner
which produces two anti-parallel outputs for a single input state. The fidelity
is shown to be 2/3 which is same as the measurement fidelity. We consider a
probabilistic quantum anti-cloner and show quantum states can be anti-cloned
exactly with non-zero probability and its efficiency is higher than the
efficiency of distinguishing between the two states.


title: Quantum Computation by Adiabatic Evolution

abstract:
  We give a quantum algorithm for solving instances of the satisfiability
problem, based on adiabatic evolution. The evolution of the quantum state is
governed by a time-dependent Hamiltonian that interpolates between an initial
Hamiltonian, whose ground state is easy to construct, and a final Hamiltonian,
whose ground state encodes the satisfying assignment. To ensure that the system
evolves to the desired final ground state, the evolution time must be big
enough. The time required depends on the minimum energy difference between the
two lowest states of the interpolating Hamiltonian. We are unable to estimate
this gap in general. We give some special symmetric cases of the satisfiability
problem where the symmetry allows us to estimate the gap and we show that, in
these cases, our algorithm runs in polynomial time.


title: Entanglement and Open Systems in Algebraic Quantum Field Theory

abstract:
  Entanglement has long been the subject of discussion by philosophers of
quantum theory, and has recently come to play an essential role for physicists
in their development of quantum information theory. In this paper we show how
the formalism of algebraic quantum field theory (AQFT) provides a rigorous
framework within which to analyze entanglement in the context of a fully
relativistic formulation of quantum theory. What emerges from the analysis are
new practical and theoretical limitations on an experimenter's ability to
perform operations on a field in one spacetime region that can disentangle its
state from the state of the field in other spacelike-separated regions. These
limitations show just how deeply entrenched entanglement is in relativistic
quantum field theory, and yield a fresh perspective on the ways in which the
theory differs conceptually from both standard nonrelativistic quantum theory
and classical relativistic field theory.


title: A modular functor which is universal for quantum computation

abstract:
  We show that the topological modular functor from Witten-Chern-Simons theory
is universal for quantum computation in the sense a quantum circuit computation
can be efficiently approximated by an intertwining action of a braid on the
functor's state space. A computational model based on Chern-Simons theory at a
fifth root of unity is defined and shown to be polynomially equivalent to the
quantum circuit model. The chief technical advance: the density of the
irreducible sectors of the Jones representation, have topological implications
which will be considered elsewhere.


title: Covariance Systems on the Projective Line

abstract:
  We study the positive-operator-valued measures on the projective real line
covariant with respect to the projective group, assuming that the energy is a
positive operator. This problem is similar to the more complicated problem of
finding the positive-operator-valued measures on the compactified Minkowski
space-time covariant with respect to the conformal group. It also describes a
time-of-arrival observable for a free particle covariant with respect to linear
canonical transformations.


title: Note on Separability of the Werner states in arbitrary dimensions

abstract:
  Great progress has been made recently in establishing conditions for
separability of a particular class of Werner densities on the tensor product
space of $n$ $d$--level systems (qudits). In this brief note we complete the
process of establishing necessary and sufficient conditions for separability of
these Werner densities by proving the sufficient condition for general n and d.


title: Noether Theorem and the quantum mechanical operators

abstract:
  We show that the quantum mechanical momentum and angular momentum operators
are fixed by the Noether theorem for the classical Hamiltonian field theory we
proposed.


title:
There is no spooky action-at-a-distance in quantum correlations:
  Resolution of the EPR nonlocality puzzle

abstract:
  The long-standing puzzle of the nonlocal Einstein-Podolsky-Rosen correlations
is resolved. The correct quantum mechanical correlations arise for the case of
entangled particles when strict locality is assumed for the probability
amplitudes instead of locality for probabilities. Locality of amplitudes
implies that measurement on one particle does not collapse the companion
particle to a definite state.


title:
Actual computational time-cost of the Quantum Fourier Transform in a
  quantum computer using nuclear spins

abstract:
  We found that the actual computational time-cost of the QFT is O(n 2^n) for
large n in a quantum computer using nuclear spins. The computational cost of a
quantum algorithm has usually been estimated as the sum of the universal gates
required in such ideal mathematical models as the Quantum Turing Machine(QTM)
and the quantum circuit. This cost is proportional to an actual time-cost in
the physical implementation where all quantum operations can be achieved in the
same time. However, if the implementation takes a different time for each
quantum gate, there is a possibility that the actual time-cost will have a
different behavior from the ideal cost. So we estimated the actual time-cost of
the QFT in these implementations by considering the gating time. The actual
time-cost is drastically different from O(n^2) estimated by complexity
analysis.


title: Entangled Chains

abstract:
  Consider an infinite collection of qubits arranged in a line, such that every
pair of nearest neighbors is entangled: an "entangled chain." In this paper we
consider entangled chains with translational invariance and ask how large one
can make the nearest neighbor entanglement. We find that it is possible to
achieve an entanglement of formation equal to 0.285 ebits between each pair of
nearest neighbors, and that this is the best one can do under certain
assumptions about the state of the chain.


title: The space of local equivalence classes of mixed two-qubit states

abstract:
  This paper is withdrawn by the author. It is superseded by Makhlin's paper
quant-ph/0002045.


title: On local invariants of pure three-qubit states

abstract:
  We study invariants of three-qubit states under local unitary
transformations, i.e. functions on the space of entanglement types, which is
known to have dimension 6. We show that there is no set of six independent
polynomial invariants of degree less than or equal to 6, and find such a set
with maximum degree 8. We describe an intrinsic definition of a canonical state
on each orbit, and discuss the (non-polynomial) invariants associated with it.


title: Motional effects of single trapped atomic/ionic qubit

abstract:
  We investigate theoretical decoherence effects of the motional degrees of
freedom of a single trapped atomic/ionic electronically coded qubit. For single
bit rotations from a resonant running wave laser field excitation, we found the
achievable fidelity to be determined by a single parameter characterized by the
motional states. Our quantitative results provide a useful realistic view for
current experimental efforts in quantum information and computing.


title: Induced coherence with and without induced emission

abstract:
  We analyze signal coherence in the setup of Wang, Zou and Mandel, where two
optical downconverters have indistinct idler modes. Quantum interference,
caused by indistinguishability of paths, has a visibility proportional to the
transmission amplitude between idlers. Classical interference, caused by
induced emission, may be complete for any finite transmission.


title: Quantum tunneling dynamics using hydrodynamic trajectories

abstract:
  In this paper we compute quantum trajectories arising from Bohm's causal
description of quantum mechanics. Our computational methodology is based upon a
finite-element moving least-squares method (MWLS) presented recently by Wyatt
and co-workers (Lopreore and Wyatt, Phys. Rev. Lett. {\bf 82}, 5190 (1999)).
This method treats the "particles" in the quantum Hamilton-Jacobi equation as
Lagrangian fluid elements which carry the phase, $S$, and density,
  $\rho$, required to reconstruct the quantum wavefunctions. Here, we compare
results obtained via the MWLS procedure to exact results obtained either
analytically or by numerical solution of the time dependent Schr\"odinger
equation. Two systems are considered: firstly, dynamics in a harmonic well and
secondly tunneling dynamics in a double well potential. In the case of
tunneling in the double well potential, the quantum potential acts to lower the
barrier separating the right and left hand sides of the well permitting
trajectories to pass from one side to another.
  However, as probability density passes from one side to the other, the
effective barrier begins to rise and eventually will segregate trajectories in
one side from the other. We note that the MWLS trajectories exhibited long time
stability in the purely harmonic cases. However, this stability was not evident
in the barrier crossing dynamics. Comparisons to exact trajectories obtained
via wave packet calculations indicate that the MWLS trajectories tend to
underestimate the effects of constructive and destructive interference effects.


title:
Optimal States for Bell inequality Violations using Quadrature Phase
  Homodyne Measurements

abstract:
  We identify what ideal correlated photon number states are to required to
maximize the discrepancy between local realism and quantum mechanics when a
quadrature homodyne phase measurement is used. Various Bell inequality tests
are considered.


title:
Upper Bound on the region of Separable States near the Maximally Mixed
  State

abstract:
  A lower bound on the amount of noise that must be added to a GHZ-like
entangled state to make it separable (also called the random robustness) is
found using the transposition condition. The bound is applicable to arbitrary
numbers of subsystems, and dimensions of Hilbert space, and is shown to be
exact for qubits. The new bound is compared to previous such bounds on this
quantity, and found to be stronger in all cases. It implies that increasing the
number of subsystems, rather than increasing their Hilbert space dimension is a
more effective way of increasing entanglement. An explicit decomposition into
an ensemble of separable states, when the state is not entangled,is given for
the case of qubits.


title:
(Noncanonical) field quantization by means of a single harmonic
  oscillator

abstract:
  The paper is an extension of quant-ph/9912102. The new framework is tested on
the 2-photon spontaneous emission and blackbody radiation. The new effects are
rather subtle. The probability of the 2-photon emission is shown to consist of
a product of several terms: One which is identical to this from standard
quantum optics and the remaining ones formally resembling detector
inefficiencies (here arising from nontrivial vacuum structure). The blackbody
distribution is indistinguishable from the Planck law for T<T_{critical} but
for T>T_{critical} the maximum of the distribution gets lowered and shifts
towards higher frequencies. T_{critical} is a parameter that, in principle,
should be observable. No normal ordering of operators is needed and vacuum
energy is nonzero but finite. Vacuum is represented by a subspace spanned by
ground states of the oscillators and is not equivalent to the cyclic vector of
the GNS construction. The non-CCR algebra is discussed in more detail.

categories: quant-ph cond-mat hep-th physics.atom-ph


title:
All Optical Cellular Quantum Computer having Ancilla Bits for Operations
  in Each Cell

abstract:
  A quantum cellular network with a qubit and ancilla bits in each cell is
proposed. The whole circuit works only with the help of external optical pulse
sequences. In the operation, some of the ancilla bits are activated, and
autonomous single- and two-qubit operations are made. In the sleep mode of a
cell, the decoherence of the qubit is negligibly small. Since only two cells at
most are active at once, the coherence can be maintained for a sufficiently
long time for practical purposes. A device structure using a quantum dot array
with possible operation and measurement schemes is also proposed.


title: Discrete Phase Measurements and the Bell inequality

abstract:
  We present a formulation of the Bell inequalities using simple correlated
photon number states and phase measurements. Such tests generally require
binning of the information, and this effect is closely examined. Our proposal
opens up the opportunity for a new novel test of quantum mechanics versus local
realism. Some insight in entanglement in such systems may be achieved.


title:
Quantum computation by optically coupled steady atoms/quantum-dots
  inside a quantum electro-dynamic cavity

abstract:
  We present a model for quantum computation using n steady 3-level atoms or
3-level quantum dots, kept inside a quantum electro-dynamics (QED) cavity. Our
model allows one-qubit operations and the two-qubit controlled-NOT gate as
required for universal quantum computation. The n quantum bits are described by
two energy levels of each atom/dot. An external laser and n separate pairs of
electrodes are used to address a single atom/dot independent of the others, via
Stark effect. The third level of each system and an additional common-mode
qubit (a cavity photon) are used for realizing the controlled-NOT operation
between any pair of qubits. Laser frequency, cavity frequency, and energy
levels are far off-resonance, and they are brought to resonance by modifying
the energy-levels of a 3-level system using the Stark effect, only at the time
of operation.


title:
Coexistence of thermal noise and squeezing in the intensity fluctuations
  of small laser diodes

abstract:
  The intensity fluctuations of laser light are derived from photon number rate
equations. In the limit of short times, the photon statistics for small laser
devices such as typical semiconductor laser diodes show thermal characteristics
even above threshold. In the limit of long time averages represented by the low
frequency component of the noise, the same devices exhibit squeezing. It is
shown that squeezing and thermal noise can coexist in the multi-mode output
field of laser diodes. This result implies that the squeezed light generated by
regularly pumped semiconductor laser diodes is qualitatively different from
single mode squeezed light. In particular, no entanglement between photons can
be generated using this type of collective multi-mode squeezing.


title:
Global Derivation of the Fluctuation Determinant from Group Property of
  Time Evolution

abstract:
  The Van Vleck-Pauli-Morette fluctuation determinant is derived from the
global group property of the time evolution amplitude in a continuous
formulation of path integrals.


title: Information - the Fundamental Notion of Quantum Theory

abstract:
  In this article a notion of information is presented which stresses the
contextuality of quantum objects and their measurement. Mathematically this is
reached by a quantification of the quantum mechanical surplus knowledge which
has been introduced by Weizsacker. This new formulation gives insight into
relation between single quantum objects and ensembles of quantum objects. The
goal is to provide an explanatory concept for teaching purposes, the
description of quantum processes and measurement with aid of information.


title: Inverse Time-Dependent Quantum Mechanics

abstract:
  Using a new Bayesian method for solving inverse quantum problems, potentials
of quantum systems are reconstructed from coordinate measurements in
non-stationary states. The approach is based on two basic inputs: 1. a
likelihood model, providing the probabilistic description of the measurement
process as given by the axioms of quantum mechanics, and 2. additional "a
priori" information implemented in form of stochastic processes over
potentials.


title: Time of arrival in the presence of interactions

abstract:
  We introduce a formalism for the calculation of the time of arrival t at a
space point for particles traveling through interacting media. We develop a
general formulation that employs quantum canonical transformations from the
free to the interacting cases to construct t in the context of the Positive
Operator Valued Measures. We then compute the probability distribution in the
times of arrival at a point for particles that have undergone reflection,
transmission or tunneling off finite potential barriers. For narrow Gaussian
initial wave packets we obtain multimodal time distributions of the reflected
packets and a combination of the Hartman effect with unexpected retardation in
tunneling. We also employ explicitly our formalism to deal with arrivals in the
interaction region for the step and linear potentials.


title:
To the question of a nonrelativistic wave equation for a system of
  interacting particles

abstract:
  It is shown that the Schr\"{o}dinger nonrelativistic equation of a system of
interacting particles is not a rigorously nonrelativistic equation since it is
based on the implicit assumption of finiteness of the interaction propagation
velocity. For a system of interacting particles, a fully nonrelativistic
nonlinear system of integro-differential equations is proposed. In the case
where the size of the system of particles is of the same order as the Compton
wavelength associated with particles, certain essential differences are shown
to exist as compared with traditional consequences of the nonrelativistic
Schr\"{o}dinger equation.


title: Perspectives on Nonlinearity in Quantum Theory

abstract:
  An enlarged group G of nonlinear transformations, modeled on the general
linear group GL(2,R), leads to a beautiful, apparently unremarked symmetry
between the wave function's phase and the logarithm of its amplitude. Equations
Doebner and I earlier proposed are embedded in a wider, natural family of
nonlinear time-evolution equations, on which G acts as a gauge group (leaving
physical observations invariant). There exist G-invariant quantities that
reduce to the usual probability density and flux for linearizable quantum
theories in a particular gauge.


title:
Formation and life-time of memory domains in the dissipative quantum
  model of brain

abstract:
  We show that in the dissipative quantum model of brain the time-dependence of
the frequencies of the electrical dipole wave quanta leads to the dynamical
organization of the memories in space (i.e. to their localization in more or
less diffused regions of the brain) and in time (i.e. to their longer or
shorter life-time). The life-time and the localization in domains of the memory
states also depend on internal parameters and on the number of links that the
brain establishes with the external world. These results agree with the
physiological observations of the dynamic formation of neural circuitry which
grows as brain develops and relates to external world.

categories: quant-ph cond-mat hep-ph math-ph math.MP physics.bio-ph q-bio.NC


title:
Reply to "Comment on 'Quantum Phase Shift Caused by Spatial
  Confinement'" by Murray Peshkin

abstract:
  We describe a force-free phase shift due only to temporal geometric boundary
conditions placed on a neutron deBroglie wave packet.


title: Three-Qubit Gate Realization Using Single Quantum Particle

abstract:
  Using virtual spin formalism it is shown that a quantum particle with eight
energy levels can store three qubits. The formalism allows to realize a
universal set of quantum gates. Feasible formalism implementation is suggested
which uses nuclear spin-7/2 as a storage medium and radio frequency pulses as
the gates. One pulse realization of all universal gates has been found,
including three-qubit Toffoli gate.


title: Quantum Field Symbolic Analog Computation: Relativity Model

abstract:
  It is natural to consider a quantum system in the continuum limit of
space-time configuration. Incorporating also, Einstein's special relativity,
leads to the quantum theory of fields. Non-relativistic quantum mechanics and
classical mechanics are special cases. By studying vacuum expectation values
(Wightman functions W(n; z) where z denotes the set of n complex variables) of
products of quantum field operators in a separable Hilbert space, one is led to
computation of holomorphy domains for these functions over the space of several
complex variables, C^n. Quantum fields were reconstructed from these functions
by Wightman. Computer automation has been accomplished as deterministic exact
analog computation (computation over "cells" in the continuum of C^n) for
obtaining primitive extended tube domains of holomorphy. This is done in a one
dimensional space plus one dimensional time model. By considering boundary
related semi-algebraic sets, some analytic extensions of these domains are
obtained by non-deterministic methods. The novel methods of computation raise
interesting issues of computability and complexity. Moreover, the computation
is independent of any particular form of Lagrangian or dynamics, and is uniform
in n, qualifying for a universal quantum machine over C^infinity.


title: Stochastic quantization of the dynamics of interacting qubit systems

abstract: Only craziness I am ashamed about.


title:
Physical model of Dirac electron. Calculation of its mass at rest and
  own electric and magnetic intensities on its moment location

abstract:
  The physical model (PhsMdl) of the relativistic quantized Dirac's electron
(DrEl) is proposed. The DrEl is regarded as a point-like (PntLk) elementary
electric charge (ElmElcChrg), taking simultaneously part in following four
disconnected different motions: a/ in Einstein's random trembling harmonic
shudders as a result of momentum recoils (impulse kicks), forcing the DrEl's
PntLk ElmElcChrg at its continuous emission and absorption of high energy
stochastic virtual photons (StchVrtPhtns) by its PntLk ElmElcChrg ; b/ in
Schrodinger's fermion vortical harmonic oscillations of DrEl's fine spread
(FnSpr) ElmElcChrg, who minimizes the self-energy at a rest of is an
electromagnetic self-action between its continuously moving FnSpr ElmElcChrg
and proper magnetic dipole moment (MgnDplMmn) and the corresponding potential
and vector-potential; All the relativistic dynamical properties of the DrEl are
results of the participate of its FnSpr ElmElcChrg in the Schrodinger's fermion
vortical harmonic oscillations. c/ in Furthian quantized stochastic boson
circular harmonic oscillations as a result of the permanent electric or
magnetic interaction of its well spread (WllSpr) ElmElcChrg or proper MgnDplMmn
with the electric intensity (ElcInt) or the magnetic intensity (MgnInt) of the
resultant quantized electromagnetic field (QntElcMgnFld) of all the
StchVrtPhtns within the fluctuating vacuum (FlcVcm); All the quantized
dualistic dynamical properties of the SchEl are results of the participate of
its WllSpr ElmElcChrg in the Furth's stochastic boson circular harmonic
oscillations. d/ in Nweton's classical motion along a clear-cut smooth thin
line as a result of some interaction of its over spread (OvrSpr) ElmElcChrg,
MgnDplMmn or bare mass with the intensities of some classical fields.


title: Quantum Interleaver: Quantum Error Correction for Burst Error

abstract:
  The concept of quantum interleaver and a simple method of quantum burst-error
correction is proposed. By using the quantum interleaver, any quantum
burst-errors that have occurred spread over the interleaved code word, so that
we can construct good quantum burst-error correcting codes without increasing
the redundancy of the code. We also discuss the general method of constructing
the quantum circuit for the quantum interleaver and the quantum network.


title:
On balance of information in bipartite quantum communication systems:
  entanglement-energy analogy

abstract:
  We adopt the view according to which information is the primary physical
entity that posseses objective meaning. Basing on two postulates that (i)
entanglement is a form of quantum information corresponding to internal energy
(ii) sending qubits corresponds to work, we show that in the closed bipartite
quantum communication systems the information is conserved. We also discuss
entanglement-energy analogy in context of the Gibbs-Hemholtz-like equation
connecting the entanglement of formation, distillable entanglement and bound
entanglement. Then we show that in the deterministic protocols of distillation
the information is conserved. We also discuss the objectivity of quantum
information in context of information interpretation of quantum states and
alghoritmic complexity.


title:
Superluminal effects for quantum tunneling through two successive
  barriers

abstract:
  We study the phenomenon of one-dimensional non-resonant tunnelling through
two successive potential barriers, separated by an intermediate free region R,
by analyzing the relevant solutions to the Schroedinger equation. We find that
the total traversal time is INDEPENDENT not only of the barrier widths (the
so-called "Hartman effect"), but also of the R-width: so that the effective
velocity in the region R, between the two barriers, can be regarded as
infinite. This agrees with the results known from the corresponding waveguide
experiments, which simulated the tunnelling experiment herein considered
because of the formal identity between the Schroedinger and the Helmholtz
equation [PACS numbers: 73.40.Gk; 03.65.-w; 03.30.+p; 41.20.Jb; 84.40.Az].


title:
Tailoring of vibrational state populations with light-induced potentials
  in molecules

abstract:
  We propose a method for achieving highly efficient transfer between the
vibrational states in a diatomic molecule. The process is mediated by strong
laser pulses and can be understood in terms of light-induced potentials. In
addition to describing a specific molecular system, our results show how, in
general, one can manipulate the populations of the different quantum states in
double well systems.


title: Entanglement and quantum computation with ions in thermal motion

abstract:
  With bichromatic fields it is possible to deterministically produce entangled
states of trapped ions. In this paper we present a unified analysis of this
process for both weak and strong fields, for slow and fast gates. Simple
expressions for the fidelity of creating maximally entangled states of two or
an arbitrary number of ions under non-ideal conditions are derived and
discussed.


title:
First experimental test of Bell inequalities performed using a
  non-maximally entangled state

abstract:
  We report on the realisation of a new test of Bell inequalities using the
superposition of type I parametric down conversion produced in two different
non-linear crystals pumped by the same laser, but with different polarisation.
The produced state is non-maximally entangled. We discuss the advantages and
the possible developments of this configuration.


title: A separability criterion for density operators

abstract:
  We give a necessary and sufficient condition for a mixed quantum mechanical
state to be separable. The criterion is formulated as a boundedness condition
in terms of the greatest cross norm on the tensor product of trace class
operators.


title:
Preparation information and optimal decompositions for mixed quantum
  states

abstract:
  Consider a joint quantum state of a system and its environment. A measurement
on the environment induces a decomposition of the system state. Using
algorithmic information theory, we define the preparation information of a pure
or mixed state in a given decomposition. We then define an optimal
decomposition as a decomposition for which the average preparation information
is minimal. The average preparation information for an optimal decomposition
characterizes the system-environment correlations. We discuss properties and
applications of the concepts introduced above and give several examples.


title: Activating bound entanglement in multi-particle systems

abstract:
  We analyze the existence of activable bound entangled states in
multi-particle systems. We first give a series of examples which illustrate
some different ways in which bound entangled states can be activated by letting
some of the parties to share maximally entangled states. Then, we derive
necessary conditions for a state to be distillable as well as to be activable.
These conditions turn out to be also sufficient for a certain family of
multi-qubit states. We use these results to explicitely to construct states
displaying novel properties related to bound entanglement and its activation.


title: Quantum entanglement using trapped atomic spins

abstract:
  We propose an implementation for quantum logic and computing using trapped
atomic spins of two different species, interacting via direct magnetic
spin-spin interaction. In this scheme, the spins (electronic or nuclear) of
distantly spaced trapped neutral atoms serve as the qubit arrays for quantum
information processing and storage, and the controlled interaction between two
spins, as required for universal quantum computing, is implemented in a three
step process that involves state swapping with a movable auxiliary spin.


title: On Fine's resolution of the EPR-Bell problem

abstract:
  In the real spin-correlation experiments the detection/emission inefficiency
is usually ascribed to independent random detection errors, and treated by the
"enhancement hypothesis". In Fine's "prism model" the detection inefficiency is
an effect not only of the random errors in the analyzer + detector equipment,
but is also the manifestation of a pre-settled (hidden) property of the
particles.


title:
Experimental Test of Relativistic Quantum State Collapse with Moving
  Reference Frames

abstract:
  An experimental test of relativistic wave-packet collapse is presented. The
tested model assumes that the collapse takes place in the reference frame
determined by the massive measuring detectors. Entangled photons are measured
at 10 km distance within a time interval of less than 5 ps. The two apparatuses
are in relative motion so that both detectors, each in its own inertial
reference frame, are first to perform the measurement. The data always
reproduces the quantum correlations and thus rule out a class of collapse
models. The results also set a lower bound on the "speed of quantum
information" to 0.66 x 10^7 and 1.5 x 10^4 times the speed of light in the
Geneva and the background radiation reference frames, respectively. The very
difficult and deep question of where the collapse takes place - if it takes
place at all - is considered in a concrete experimental context.


title: Teleportation and Secret Sharing with Pure Entangled States

abstract:
  We present two optimal methods of teleporting an unknown qubit using any pure
entangled state. We also discuss how such methods can also have succesful
application in quantum secret sharing with pure multipartite entangled states.


title: Multi-valued Logic Gates for Quantum Computation

abstract:
  We develop a multi-valued logic for quantum computing for use in multi-level
quantum systems, and discuss the practical advantages of this approach for
scaling up a quantum computer. Generalizing the methods of binary quantum
logic, we establish that arbitrary unitary operations on any number of d-level
systems (d > 2) can be decomposed into logic gates that operate on only two
systems at a time. We show that such multi-valued logic gates are
experimentally feasible in the context of the linear ion trap scheme for
quantum computing. By using d levels in each ion in this scheme, we reduce the
number of ions needed for a computation by a factor of log d.


title:
A model for ensemble NMR quantum computer using antiferromagnetic
  structure

abstract:
  The one-dimensional homonuclear periodic array of nuclear spins I = 1/2,
owing to hyperfine interaction of nuclear spins with electronic magnetic
moments in antiferromagnetic structure, is considered. The neighbor nuclear
spins in such array are opposite oriented and have resonant frequencies
determined by hyperfine interaction constant, applied magnetic field value and
interaction with the left and right nuclear neighbor spins. The resonant
frequencies difference of nuclear spins, when the neighbor spins have different
and the same states, is used to control the spin dynamics by means of selective
resonant RF-pulses both for single nuclear spins and for ensemble of nuclear
spins with the same resonant frequency.
  A model for the NMR quantum computer of cellular-automata type based on an
one-dimensional homonuclear periodic array of spins is proposed. This model may
be generalized to a large ensemble of parallel working one-dimensional arrays
and to two-dimensional and three-dimensional structures.


title:
Controlling Decoherence in Bose-Einstein Condensation by Light
  Scattering far off Resonance

abstract:
  It is shown that, through a super-radiant Rayleigh scattering, a strong far
off-resonant pump laser applied to a Bose-Einstein condensates(BEC) can induce
a non-demolition coupling of the many-mode quantized vacuum field to the BEC.
This effective interaction will force the total system of the BEC plus the
light field to evolve from a factorized initial state to an ideal entangled
state and thus result in the quantum decoherence in the BEC. Since the
effective coupling coefficients are mainly determined by the Rabi frequency of
the pump laser, the quantum decoherence process can be controlled by adjusting
the intensity of the pump laser. To study the physical influence of decoherence
on the BEC, we investigate how the coherent tunneling of BEC in a
well-separated tight double wall is suppressed by the effectively-entangled
vacuum modes.


title: Entanglement measures and the Hilbert-Schmidt distance

abstract:
  In order to construct a measure of entanglement on the basis of a
``distance'' between two states, it is one of desirable properties that the
``distance'' is nonincreasing under every completely positive trace preserving
map. Contrary to a recent claim, this letter shows that the Hilbert-Schmidt
distance does not have this property.