title:
Non-local quantum evolution of entangled ensemble states in neural nets
  and its significance for brain function and a theory of consciousness

abstract:
  Current quantum theories of consciousness suggest a configuration space of an
entangled ensemble state as global work space for conscious experience. This
study will describe a procedure for adjustment of the singlet evolution of a
quantum computation to a classical signal input by action potentials. The
computational output of an entangled state in a single neuron will be selected
in a network environment by "survival of the fittest" coupling with other
neurons. Darwinian evolution of this coupling will result in a binding of
action potentials to a convoluted orbit of phase-locked oscillations with
harmonic, m-adic, or fractal periodicity. Progressive integration of signal
inputs will evolve a present memory space independent from the history of
construction. Implications for mental processes, e.g., associative memory,
creativity, and consciousness will be discussed. A model for the generation of
quantum coherence in a single neuron will be suggested.


title:
Quantum tunneling with dissipation in smoothly joined parabolic
  potential

abstract:
  This paper is devoted to the study of quantum dissipation in cluster decay
phenomena in the frame of the Lindblad approach to quantum open systems. The
tunneling of a metastable state across a piecewise quadratic potential is
envisaged for two cases : one and two harmonic wells smoothly joined to an
inverted parabola which simulates the barrier. The width and depth of the
second harmonic oscillator well was varied over a wide range of values in order
to encompass particular cases of tunneling such as the double well potential
and the cluster decay. The evolution of the averages and covariances of the
quantum sub-system is studied in both under- and overdamped regimes. For a
gaussian intial wave-packet we compute the tunneling probability for different
values of the friction coefficient and fixed values of the diffusion
coefficients.


title:
Empirical State Determination of Entangled Two-Level Systems and its
  Relation to Information Theory

abstract:
  Theoretical methods for empirical state determination of entangled two-level
systems are analyzed in relation to information theory. We show that hidden
variable theories would lead to a Shannon index of correlation between the
entangled subsystems which is larger that that predicted by quantum mechanics.
Canonical representations which have maximal correlations are treated by the
use of Schmidt decomposition of the entangled states, including especially the
Bohm singlet state and the GHZ entangled states. We show that quantum mechanics
does not violate locality, but does violate realism.


title: Science and Paranormal Phenomena

abstract:
  In order to ground my approach to the study of paranormal phenomena, I first
explain my operational approach to physics, and to the ``historical'' sciences
of cosmic, biological, human, social and political evolution. I then indicate
why I believe that ``paranormal phenomena'' might --- but need not --- fit into
this framework. I endorse the need for a new theoretical framework for the
investigation of this field presented by Etter and Shoup at this meeting. I
close with a short discussion of Ted Bastin's contention that paranormal
phenomena should be {\it defined} as contradicting physics.


title: Quantum Theory of Probability and Decisions

abstract:
  The probabilistic predictions of quantum theory are conventionally obtained
from a special probabilistic axiom. But that is unnecessary because all the
practical consequences of such predictions follow from the remaining,
non-probabilistic, axioms of quantum theory, together with the
non-probabilistic part of classical decision theory.


title: Maxwell Duality, Lorentz Invariance, and Topological Phase

abstract:
  We discuss the Maxwell electromagnetic duality relations between the
Aharonov-Bohm, Aharonov-Casher, and He-McKellar-Wilkens topological phases,
which allows a unified description of all three phenomena. We also elucidate
Lorentz transformations that allow these effects to be understood in an
intuitive fashion in the rest frame of the moving quantum particle. Finally, we
propose two experimental schemes for measuring the He-McKellar-Wilkens phase.


title:
Dipole Emission In Finite Photonic Band-Gap Structures: an Exactly
  Solvable One-Dimensional Model

abstract:
  I consider an exact model of atomic spontaneous dipole emission and classical
dipole radiation in a finite photonic band-gap structure. The full 3D or 2D
problem is reduced to a finite 1D model, and then this is solved for
analytically using algebraic matrix transfer techniques. The results give
insight to the electromagnetic emission process in periodic dielectrics,
quantitative predictions for emission in 1D dielectric stacks, and qualitative
formulas for the 2D and 3D problem.


title: On the Teleportation of Continuous Variable

abstract:
  The measurement procedures used in quantum teleportation are analyzed from
the viewpoint of the general theory of quantum-mechanical measurements. It is
shown that to find the teleported state one should only know the identity
resolution (positive operator-valued measure) generated by the corresponding
instrument (quantum operation describing the system state change caused by the
measurement) rather than the instrument itself. A quantum teleportation
protocol based on a measurement associated with a non-orthogonal identity
resolution is proposed for a system with non-degenerate continuous spectrum.


title: Steep anomalous dispersion in coherently prepared Rb vapor

abstract:
  Steep dispersion of opposite signs in driven degenerate two-level atomic
transitions have been predicted and observed on the D2 line of 87Rb in an
optically thin vapor cell. The intensity dependence of the anomalous dispersion
has been studied. The maximum observed value of anomalous dispersion [dn/dnu ~=
-6x10^{-11}Hz^{-1}] corresponds to anegative group velocity V_g ~= -c/23000.


title: Phase matching in quantum searching

abstract:
  Each iteration in Grover's original quantum search algorithm contains 4
steps: two Hadamard-Walsh transformations and two amplitudes inversions. When
the inversion of the marked state is replaced by arbitrary phase rotation
\theta and the inversion for the prepared state |\gamma> is replaced by
rotation through \phi, we found that these phase rotations must satisfy a
matching condition \theta=\phi. Approximate formula for the amplitude of the
marked state after an arbitrary number of iterations are also derived. We give
also a simple explanation of the phase matching requirement.


title:
Multipartite entanglement for continuous variables: A quantum
  teleportation network

abstract:
  We show that {\it one} single-mode squeezed state distributed among $N$
parties using linear optics suffices to produce a truly $N$-partite entangled
state for any nonzero squeezing and arbitrarily many parties. From this
$N$-partite entangled state, via quadrature measurements of $N-2$ modes,
bipartite entanglement between any two of the $N$ parties can be `distilled',
which enables quantum teleportation with an experimentally determinable
fidelity better than could be achieved in any classical scheme.


title:
Quantum Decoherence and Higher Order Corrections to the Large Time
  Exponential Behaviour

abstract:
  There exists the well known approximate expression describing the large time
behaviour of matrix elements of the evolution operator in quantum theory:
<U(t)>=exp(at)+... This expression plays the crucial role in considerations of
problems of quantum decoherence, radiation, decay, scattering theory,
stochastic limit, derivation of master and kinetic equations etc. This
expression was obtained in the Weisskopf-Wigner approximation and in the van
Hove (stochastic) limit. We derive the exact general formula which includes the
higher order corrections to the above approximate expression:
<U(t)>=exp(At+B+C(t)). The constants A and B and the oscillating function C(t)
are computed in perturbation theory. The method of perturbation of spectra and
renormalized wave operators is used. The formula is valid for a general class
of Hamiltonians used in statistical physics and quantum field theory.


title: Classical interventions in quantum systems. I. The measuring process

abstract:
  The measuring process is an external intervention in the dynamics of a
quantum system. It involves a unitary interaction of that system with a
measuring apparatus, a further interaction of both with an unknown environment
causing decoherence, and then the deletion of a subsystem. This description of
the measuring process is a substantial generalization of current models in
quantum measurement theory. In particular, no ancilla is needed. The final
result is represented by a completely positive map of the quantum state $\rho$
(possibly with a change of the dimensions of $\rho$). A continuous limit of the
above process leads to Lindblad's equation for the quantum dynamical semigroup.


title:
Stochastic wave function method for non-Markovian quantum master
  equations

abstract:
  A generalization of the stochastic wave function method to quantum master
equations which are not in Lindblad form is developed. The proposed stochastic
unravelling is based on a description of the reduced system in a doubled
Hilbert space and it is shown, that this method is capable of simulating
quantum master equations with negative transition rates. Non-Markovian effects
in the reduced systems dynamics can be treated within this approach by
employing the time-convolutionless projection operator technique. This ansatz
yields a systematic perturbative expansion of the reduced systems dynamics in
the coupling strength. Several examples such as the damped Jaynes Cummings
model and the spontaneous decay of a two-level system into a photonic band gap
are discussed. The power as well as the limitations of the method are
demonstrated.


title:
Coupling nanocrystals to a high-$Q$ silica microsphere: entanglement in
  quantum dots via photon exchange

abstract:
  Coupling nanocrystals (quantum dots) to a high-$Q$ whispering gallery mode
(WGM) of a silica microsphere, can produce a strong coherent interaction
between the WGM and the electronic states of the dots. Shifting the resonance
frequencies of the dots, for instance by placing the entire system in an
electric potential, then allows this interaction to be controlled, permitting
entangling interactions between different dots. Thus, this system could
potentially be used to implement a quantum computer.


title: Nonperiodic Orbit Sums in Weyl's Expansion for Billiards

abstract:
  Weyl's expansion for the asymptotic mode density of billiards consists of the
area, length, curvature and corner terms. The area term has been associated
with the so-called zero-length orbits. Here closed nonperiodic paths
corresponding to the length and corner terms are constructed.


title:
Implementing quantum logic operations, pseudo-pure states and the
  Deutsch-Jozsa algorithm using non-commuting selective pulses in NMR

abstract:
  We demonstrate experimentally the usefulness of selective pulses in NMR to
perform quantum computation. Three different techniques based on selective
pulse excitations have been proposed to prepare a spin system in a pseudo-pure
state. We describe the design of novel ``portmanteau'' gates using the
selective manipulation of level populations. A selective pulse implementation
of the Deutsch-Jozsa algorithm for a two-qubit and a three-qubit quantum
computer is demonstrated.


title: Path Integral Solution to Non-central Potential

abstract:
  We have studied the path integral solution of a system of particle moving in
certain class of non-central potential without using Kustannheimo-Stiefel
transformation. The Hamiltonian of the system has been converted to a separable
Hamiltonian of Liouville type in parabolic coordinates and has further reduced
to a Hamiltonian corresponding to two 2- dimensional simple harmonic
oscillators. The energy spectrum for this system is calculated analytically.
Hartmann ring-shaped potential and compound Coulomb plus Aharanov- Bohm
potential have also been studied as special cases.


title:
Non-Hermitian matrix description of the PT symmetric anharmonic
  oscillators

abstract:
  Schroedinger equation H \psi=E \psi with PT - symmetric differential operator
H=H(x) = p^2 + a x^4 + i \beta x^3 +c x^2+i \delta x = H^*(-x) on
L_2(-\infty,\infty) is re-arranged as a linear algebraic diagonalization at
a>0. The proof of this non-variational construction is given. Our Taylor series
form of \psi complements and completes the recent terminating solutions as
obtained for certain couplings \delta at the less common negative a.


title: ``Weighing'' a closed system and the time-energy uncertainty principle

abstract:
  A gedanken-experiment is proposed for `weighing'' the total mass of a closed
system from within the system. We prove that for an internal observer the time
$\tau$, required to measure the total energy with accuracy $\Delta E$, is
bounded according to $\tau \Delta E >\hbar $. This time-energy uncertainty
principle for a closed system follows from the measurement back-reaction on the
system. We generally examine what other conserved observables are in principle
measurable within a closed system and what are the corresponding uncertainty
relations.


title: Quantum dynamics of a damped deformed oscillator

abstract:
  The interaction of a quantum deformed oscillator with the environment is
studied deriving a master equation whose form strongly depends on the type of
deformation.


title: Stochastic control of quantum dynamics for a single trapped system

abstract:
  A stochastic control of the vibrational motion for a single trapped ion/atom
is proposed. It is based on the possibility to continously monitor the motion
through a light field meter. The output from the measurement process should be
then used to modify the system's dynamics.


title:
Complete roughness and conductivity corrections for the recent Casimir
  force measurement

abstract:
  We consider detailed roughness and conductivity corrections to the Casimir
force in the recent Casimir force measurement employing an Atomic Force
Microscope. The roughness of the test bodies-a metal plate and a sphere- was
investigated with the Atomic Force Microscope and the Scanning Electron
Microscope respectively. It consists of separate crystals of different heights
and a stochastic background. The amplitude of roughness relative to the zero
roughness level was determined and the corrections to the Casimir force were
calculated up to the fourth order in a small parameter (which is this amplitude
divided by the distance between the two test bodies). Also the corrections due
to finite conductivity were found up to the fourth order in relative
penetration depth of electromagnetic zero point oscillations into the metal.
The theoretical result for the configuration of a sphere above a plate taking
into account both corrections is in excellent agreement with the measured
Casimir force.


title: Classical interventions in quantum systems. II. Relativistic invariance

abstract:
  If several interventions performed on a quantum system are localized in
mutually space-like regions, they will be recorded as a sequence of ``quantum
jumps'' in one Lorentz frame, and as a different sequence of jumps in another
Lorentz frame. Conditions are specified that must be obeyed by the various
operators involved in the calculations so that these two different sequences
lead to the same observable results. These conditions are similar to the
equal-time commutation relations in quantum field theory. They are sufficient
to prevent superluminal signaling. (The derivation of these results does not
require most of the contents of the preceding article. What is needed is
briefly summarized here, so that the present article is essentially
self-contained.)


title: The Generalized Quantum Statistics

abstract:
  The concept of wavefunction reduction should be introduced to standard
quantum mechanics in any physical processes where effective reduction of
wavefunction occurs, as well as in the measurement processes. When the overlap
is negligible, each particle obey Maxwell-Boltzmann statistics even if the
particles are in principle described by totally symmetrized wavefunction
[P.R.Holland, The Quantum Theory of Motion, Cambridge Unversity Press, 1993,
p293]. We generalize the conjecture. That is, particles obey some generalized
statistics that contains the quantum and classical statistics as special cases,
where the degree of overlapping determines the statistics that particles should
obey among continuous generalized statistics. We present an example consistent
with the conjecture.


title:
Begging the Signalling Question: Quantum Signalling and the Dynamics of
  Multiparticle Systems

abstract:
  Many authors state that quantum nonlocality could not involve any
controllable superluminal transmission of momentum-energy, signals, or
information. We claim that most or all no-signalling proofs to date are
question-begging, in that they depend upon assumptions about the locality of
the measurement process that needed to be established in the first place. We
analyse no-signalling arguments by Bohm and Hiley, and Shimony, which
illustrate the problem in an especially striking way.


title: Quantum Measured Information

abstract:
  A framework for a quantum information theory is introduced that is based on
the measure of quantum information associated with probability distribution
predicted by quantum measuring of state. The entanglement between states of
measured system and "pointer" states of measuring apparatus, which is generated
by dynamical process of quantum measurement, plays a dominant role in
expressing quantum characteristics of information theory. The quantum mutual
information of transmission and reception of quantum states along a noisy
quantum channel is given by the change of quantum measured information. In our
approach, it is not necessary to purify the transmitted state by means of the
reference system. It is also clarified that there exist relations between the
approach given in this letter and those given by other authors.


title:
Quasi-set-theoretical foundations of statistical mechanics: a research
  program

abstract:
  Quasi-set theory provides us a mathematical background for dealing with
collections of indistinguishable elementary particles. In this paper, we show
how to obtain the usual statistics (Maxwell-Boltzmann, Bose-Einstein, and
Fermi-Dirac) into the scope of quasi-set theory. We also show that, in order to
derive Maxwell-Boltzmann statistics, it is not necessary to assume that the
particles are distinguishable. In other words, Maxwell-Boltzmann statistics is
possible even in an ensamble of indistinguishable particles, at least from the
theoretical point of view. The main goal of this paper is to provide the
mathematical grounds of a quasi-set-theoretical framework for statistical
mechanics.


title: Teleportation via generalized measurements, and conclusive teleportation

abstract:
  In this work we show that teleportation is a special case of a generalized
Einstein, Podolsky, Rosen (EPR) non-locality. Based on the connection between
teleportation and generalized measurements we define conclusive teleportation.
We show that perfect conclusive teleportation can be obtained with any pure
entangled state, and it can be arbitrarily approached with a particular mixed
state.


title:
Degenerate space-time paths and the non-locality of quantum mechanics in
  a Clifford substructure of space-time

abstract:
  The quantized canonical space-time coordinates of a relativistic point
particle are expressed in terms of the elements of a complex Clifford algebra
which combines the complex properties of SL(2.C) and quantum mechanics. When
the quantum measurement principle is adapted to the generating space of the
Clifford algebra we find that the transition probabilities for twofold
degenerate paths in space-time equals the transition amplitudes for the
underlying paths in Clifford space. This property is used to show that the
apparent non-locality of quantum mechanics in a double slit experiment and in
an EPR type of measurement is resolved when analyzed in terms of the full paths
in the underlying Clifford space. We comment on the relationship of this model
to the time symmetric formulation of quantum mechanics and to the
Wheeler-Feynman model.


title:
Experimental Implementaton of Dense Coding Using Nuclear Magnetic
  Resonance

abstract:
  Quantum dense coding has been demonstrated experimentally in terms of quantum
logic gates and circuits in quantum computation and NMR technique. Two bits of
information have been transmitted through manipulating one of the maximally
entangled two-state quantum pair, which is completely consistent with the
original ideal of Bennett-Wiesner proposal. Although information transmission
happens between spins over inter-atomic distance, the scheme of entanglement
transformation and measurement can be used in other processes of quantum
information and quantum computing.


title: Spectral Comparison Theorem for the Dirac Equation

abstract:
  We consider a single particle which is bound by a central potential and obeys
the Dirac equation. We compare two cases in which the masses are the same but
Va < Vb, where V is the time-component of a vector potential. We prove
generally that for each discrete eigenvalue E whose corresponding (large and
small) radial wave functions have no nodes, it necessarily follows that Ea <
Eb. As an illustration, this general relativistic comparison theorem is applied
to approximate the Dirac spectrum generated by a screened-Coulomb potential.


title: Vectors and Operators For Spin 1 Derived From First Principles

abstract:
  In this paper, we extend to the case of spin 1 the method we have devised for
deriving generalized spin quantities from first principles, and which we
illustrated using the spin-1/2 case. Again, we not only derive from first
principles the standard results but we obtain new generalized results as well.
Our success in doing this shows that our method is of general validity and can
be applied to any value of J.


title: New Solvable and Quasi Exactly Solvable Periodic Potentials

abstract:
  Using the formalism of supersymmetric quantum mechanics, we obtain a large
number of new analytically solvable one-dimensional periodic potentials and
study their properties. More specifically, the supersymmetric partners of the
Lame potentials ma(a+1)sn^2(x,m) are computed for integer values a=1,2,3,....
For all cases (except a=1), we show that the partner potential is distinctly
different from the original Lame potential, even though they both have the same
energy band structure. We also derive and discuss the energy band edges of the
associated Lame potentials pm sn^2(x,m)+qm cn^2(x,m)/ dn^2(x,m), which
constitute a much richer class of periodic problems. Computation of their
supersymmetric partners yields many additional new solvable and quasi exactly
solvable periodic potentials.


title:
The Influence of Superpositional Wave Function Oscillations on Shor's
  Quantum Algorithm

abstract:
  We investigate the influence of superpositional wave function oscillations on
the performance of Shor's quantum algorithm for factorization of integers. It
is shown that the wave function oscillations can destroy the required quantum
interference. This undesirable effect can be routinely eliminated using a
resonant pulse implementation of quantum computation, but requires special
analysis for non-resonant implementations.


title: Derivation of the Pauli exchange principle

abstract:
  Wave functions are generally written with arguments consisting of sets of
``particle'' coordinates and quantum numbers. Pauli derived a principle
governing the exchange of pairs of sets that differ only in their spatial and
spin component $(m_s)$ coordinates. This principle states that an exchange of
two of these sets produces the same wave function except for its being
multiplied by a factor of $(-1)^{2s}$. Pauli's proof is based upon quantum
field operators and is difficult to understand. A much simpler proof, making
use of properties of wave functions, is presented here.


title: The Best Copenhagen Tunneling Times

abstract:
  Recently, people have caculated tunneling's characteristic times within
Bohmian mechanics. Contrary to some characteristic times defined within the
framework of the standard interpretation of quantum mechanics, these have
reasonable values. Here, we introduce one of available definitions for
tunnelling's characteristic times within the standard interpretation as the
best definition that can be accepted for the tunneling times. We show that, due
to experimental limitations, Bohmian mechanics leads to same tunneling times.


title:
Unsharpness in the Stern-Gerlach device via stochastic perturbation in
  the Hamiltonian

abstract:
  This paper has been withdrawn by the author(s), due a crucial i-number error
in Eqn. 18.


title:
Bell inequality and the locality loophole: Active versus passive
  switches

abstract:
  All experimental tests of the violation of Bell's inequality suffer from some
loopholes. We show that the locality loophole is not independent of the
detection loophole: in experiments using low efficient detectors, the locality
loophole can be closed equivalently using active or passive switches.


title:
Pulse-order invariance of the initial-state population in multistate
  chains driven by delayed laser pulses

abstract:
  This paper shows that under certain symmetry conditions the probability of
remaining in the initial state (the probability of no transition) in a
chainwise-connected multistate system driven by two or more delayed laser
pulses does not depend on the pulse order.


title: Measuring a coherent superposition

abstract:
  We propose a simple method for measuring the populations and the relative
phase in a coherent superposition of two atomic states. The method is based on
coupling the two states to a third common (excited) state by means of two laser
pulses, and measuring the total fluorescence from the third state for several
choices of the excitation pulses.


title: Properties of pulsed entangled two-photon fields

abstract:
  The dependence of one- and two-photon characteristics of pulsed entangled
two-photon fields generated in spontaneous parametric down-conversion on the
pump-pulse properties (shape of the pump-pulse spectrum and its internal
structure) is examined. It is shown that entangled two-photon fields with
defined properties can be generated. A general relation between the spectra of
the down-converted fields is established. As a special case interference of two
partially overlapping pulsed two-photon fields is studied. Fourth-order
interference pattern of entangled two-photon fields is investigated in the
polarization analog of the Hong-Ou-Mandel interferometer.


title:
Calculation of the Deflection of Light Ray near the Sun with
  Quantum-corrected Newton's Gravitation Law

abstract:
  The deflection of light ray passing near the Sun is calculated with
quantum-corrected Newton's gravitation law. The satisfactory result suggests
that there may exist other theoretical possibilities besides the theory of
relativity.


title: On Universal and Fault-Tolerant Quantum Computing

abstract:
  A novel universal and fault-tolerant basis (set of gates) for quantum
computation is described. Such a set is necessary to perform quantum
computation in a realistic noisy environment. The new basis consists of two
single-qubit gates (Hadamard and ${\sigma_z}^{1/4}$), and one double-qubit gate
(Controlled-NOT). Since the set consisting of Controlled-NOT and Hadamard gates
is not universal, the new basis achieves universality by including only one
additional elementary (in the sense that it does not include angles that are
irrational multiples of $\pi$) single-qubit gate, and hence, is potentially the
simplest universal basis that one can construct. We also provide an alternative
proof of universality for the only other known class of universal and
fault-tolerant basis proposed by Shor and by Kitaev.


title: Coulomb-oscillator duality in spaces of constant curvature

abstract:
  In this paper we construct generalizations to spheres of the well known
Levi-Civita, Kustaanheimo-Steifel and Hurwitz regularizing transformations in
Euclidean spaces of dimensions 2, 3 and 5. The corresponding classical and
quantum mechanical analogues of the Kepler-Coulomb problem on these spheres are
discussed.


title: Let the New Experiments Tell the Quantum Theory

abstract:
  Several new physics experiments in 1998 were performed and analyzed to show
the subtlety of quantum theory, including the "wave-particle duality" and the
non-separability of two-particle entangled state. Here it is shown that the
measurement is bound to change the object by destroying the original quantum
coherence between the object and its environment. So the "physical reality"
should be defined at two levels, the "thing in itself" and the "thing for us".
The wave function in quantum mechanics is just playing the role for connecting
the two levels of matter via the fictitious measurement.


title: Complex Square Well --- A New Exactly Solvable Quantum Mechanical Model

abstract:
  Recently, a class of PT-invariant quantum mechanical models described by the
non-Hermitian Hamiltonian $H=p^2+x^2(ix)^\epsilon$ was studied. It was found
that the energy levels for this theory are real for all $\epsilon\geq0$. Here,
the limit as $\epsilon\to\infty$ is examined. It is shown that in this limit,
the theory becomes exactly solvable. A generalization of this Hamiltonian,
$H=p^2+x^{2M}(ix)^\epsilon$ (M=1,2,3,...) is also studied, and this
PT-symmetric Hamiltonian becomes exactly solvable in the large-\epsilon limit
as well. In effect, what is obtained in each case is a complex analog of the
Hamiltonian for the square well potential. Expansions about the large-\epsilon
limit are obtained.

categories: quant-ph cond-mat hep-th math-ph math.MP


title: The Role of Inert Objects in Quantum Mechanical Phase

abstract:
  Quantum mechanical foundations of the polarized neutron phase shift
experiment are discussed. The fact that the neutron retains its ground state
throughout the experiment is shown to be crucial for the phase shift obtained.


title: Implementation of the Quantum Fourier Transform

abstract:
  The quantum Fourier transform (QFT) has been implemented on a three bit
nuclear magnetic resonance (NMR) quantum computer, providing a first step
towards the realization of Shor's factoring and other quantum algorithms.
Implementation of the QFT is presented with fidelity measures, and state
tomography. Experimentally realizing the QFT is a clear demonstration of NMR's
ability to control quantum systems.


title: Quantum chaos induced by measurements

abstract:
  We study the dynamics of a "kicked" quantum system undergoing repeated
measurements of momentum. A diffusive behavior is obtained for a large class of
Hamiltonians, even when the dynamics of the classical counterpart is not
chaotic. These results can be interpreted in classical terms by making use of a
"randomized" classical map. We compute the transition probability for the
action variable and consider the semiclassical limit.


title: Causation & Physics

abstract:
  Philosophical analyses of causation take many forms but one major difficulty
they all aim to address is that of the spatio-temporal continuity between
causes and their effects. Bertrand Russell in 1913 brought the problem to its
most transparent form and made it a case against the notion of causation in
physics. In this essay, I focus on this subject of causal continuity and its
related issues in classical and quantum physics.


title: Improved Precision Measurement of the Casimir Force

abstract:
  We report an improved precision measurement of the Casimir force. The force
is measured between a large Al coated sphere and flat plate using an Atomic
Force Microscope. The primary experimental improvements include the use of
smoother metal coatings, reduced noise, lower systematic errors and independent
measurement of surface separations. Also the complete dielectric spectrum of
the metal is used in the theory. The average statistical precision remains at
the same 1% of the forces measured at the closest separation.


title:
Interrelations Between the Neutron's Magnetic Interactions and the
  Magnetic Aharonov-Bohm Effect

abstract:
  It is proved that the phase shift of a polarized neutron interacting with a
spatially uniform time-dependent magnetic field, demonstrates the same physical
principles as the magnetic Aharonov-Bohm effect. The crucial role of inert
objects is explained, thereby proving the quantum mechanical nature of the
effect. It is also proved that the nonsimply connectedness of the field-free
region is not a profound property of the system and that it cannot be regarded
as a sufficient condition for a nonzero phase shift.


title: On the observation of decoherence with a movable mirror

abstract:
  Following almost a century of debate on possible `independent of measurement'
elements of reality, or `induced' elements of reality - originally invoked as
an ad-hoc collapse postulate, we propose a novel line of interference
experiments which may be able to examine the regime of induced elements of
reality. At the basis of the proposed experiment, lies the hypothesis that all
models of 'induced' elements of reality should exhibit symmetry breaking within
quantum evolution. The described {\em symmetry experiment} is thus aimed at
being able to detect and resolve symmetry breaking signatures.


title: Quantization Ambiguity, Ergodicity, and Semiclassics

abstract:
  A simple argument shows that eigenstates of a classically ergodic system are
individually ergodic on coarse-grained scales. This has implications for the
quantization ambiguity in ergodic systems: the difference between alternative
quantizations is suppressed compared with the $O(\hbar^2)$ ambiguity in the
integrable case. For two-dimensional ergodic systems in the high-energy regime,
individual eigenstates are independent of the choice of quantization procedure,
in contrast with the regular case, where even the ordering of eigenlevels is
ambiguous. Surprisingly, semiclassical methods are shown to be much more
precise for chaotic than for integrable systems.


title: Entanglement swapping using continuous variables

abstract:
  We investigate the efficacy with which entanglement can be teleported using a
continuous measurement scheme. We show that by using the correct gain for the
classical channel the degree of violation of locality that can be demonstrated
(using a CH type inequality) is {\it not} a function of the level of
entanglement squeezing used in the teleportation. This is possible because a
gain condition can always be choosen such that passage through the teleporter
is equivalent to pure attenuation of the input field.


title: Quantum tomography of the GHZ state

abstract:
  We present a method of generation of the Greenberger-Horne-Zeilinger state
involving type II and type I parametric downconversion, and triggering
photodetectors. The state generated by the proposed experimental set-up can be
reconstructed through multi-mode quantum homodyne tomography. The feasibility
of the measurement is studied on the basis of Monte-Carlo simulations.


title: Zeno effect preventing Rabi transitions onto an unstable energy level

abstract:
  We consider a driven 2-level system with one level showing spontaneous decay
to an otherwise uncoupled third level. Rabi transitions to the unstable level
are strongly damped. This simple configuration can be used to demonstrate and
to explore the quantum Zeno effect leading to a freezing of the system to the
initial level. A comparison with repeated projection measurements is given. A
treatment within a phenomenological theory of continuous measurements is
sketched. The system visualizes the important role of null measurements
(negative result measurements) and may serve as a good example for a truly
continuous measurement.


title:
Natural capacity of a system of two two-level atoms as a quantum
  information channel

abstract:
  A system of two closely spaced atoms interacting through a vacuum
electromagnetic field is considered. It is demonstrated that radiative decay in
such a system resulting from photon exchange gives rise to a definite amount of
information related to interatomic communication. Joint distributions of
detection probabilities of atomic quanta and the corresponding amount of
communication information are calculated.


title:
Collisional effects on the collective laser cooling of trapped bosonic
  gases

abstract:
  We analyse the effects of atom-atom collisions on collective laser cooling
scheme. We derive a quantum Master equation which describes the laser cooling
in presence of atom-atom collisions in the weak-condensation regime. Using such
equation, we perform Monte Carlo simulations of the population dynamics in one
and three dimensions. We observe that the ground-state laser-induced
condensation is maintained in the presence of collisions. Laser cooling causes
a transition from a Bose-Einstein distribution describing collisionally induced
equilibrium,to a distribution with an effective zero temperature. We analyse
also the effects of atom-atom collisions on the cooling into an excited state
of the trap.


title: On Multistep Bose-Einstein Condensation in Anisotropic Traps

abstract:
  Multistep Bose-Einstein condensation of an ideal Bose gas in anisotropic
harmonic atom traps is studied. In the presence of strong anisotropy realized
by the different trap frequency in each direction, finite size effect dictates
a series of dimensional crossovers into lower-dimensional excitations. Two-step
condensation and the dynamical reduction of the effective dimension can appear
in three separate steps. When the multistep behavior occurs, the occupation
number of atoms excited in each dimension is shown to behave similarly as a
function of the temperature.


title: The Mach-Zehnder and the Teleporter

abstract:
  We suggest a self-testing teleportation configuration for photon q-bits based
on a Mach-Zehnder interferometer. That is, Bob can tell how well the input
state has been teleported without knowing what that input state was. One could
imagine building a "locked" teleporter based on this configuration. The
analysis is performed for continuous variable teleportation but the arrangement
could equally be applied to discrete manipulations.


title: Quantum memory in quantum cryptography

abstract:
  [Shortened abstract:] This thesis investigates the importance of quantum
memory in quantum cryptography, concentrating on quantum key distribution
schemes.
  In the hands of an eavesdropper -- a quantum memory is a powerful tool,
putting in question the security of quantum cryptography; Classical privacy
amplification techniques, used to prove security against less powerful
eavesdroppers, might not be effective when the eavesdropper can keep quantum
states for a long time. In this work we suggest a possible direction for
approaching this problem. We define strong attacks of this type, and show
security against them, suggesting that quantum cryptography is secure. We start
with a complete analysis regarding the information about a parity bit (since
parity bits are used for privacy amplification). We use the results regarding
the information on parity bits to prove security against very strong
eavesdropping attacks, which uses quantum memories and all classical data
(including error correction codes) to attack the final key directly.
  In the hands of the legitimate users, a quantum memory is also a useful tool.
We suggest a new type of quantum key distribution scheme where quantum memories
are used instead of quantum channels. This scheme is especially adequate for
networks of many users. The use of quantum memory also allows reducing the
error rate to improve large scale quantum cryptography, and to enable the
legitimate users to work with reasonable error rate.


title: Quantum cryptography via parametric downconversion

abstract:
  The use of quantum bits (qubits) in cryptography holds the promise of secure
cryptographic quantum key distribution schemes. It is based usually on
single-photon polarization states. Unfortunately, the implemented ``qubits'' in
the usual weak pulse experiments are not true two-level systems, and quantum
key distribution based on these imperfect qubits is totally insecure in the
presence of high (realistic) loss rate. In this work, we investigate another
potential implementation: qubits generated using a process of parametric
downconversion. We find that, to first (two-photon) and second (four-photon)
order in the parametric downconversion small parameter, this implementation of
quantum key distribution is equivalent to the theoretical version.
  Once realistic measurements are taken into account, quantum key distribution
based on parametric downconversion suffers also from sensitivity to extremely
high (nonrealistic) losses. By choosing the small parameter of the process
according to the loss rates, both implementations of quantum key distribution
can in principle become secure against the attack studied in this paper.
However, adjusting the small parameter to the required levels seems to be
impractical in the weak pulse process. On the other hand, this can easily be
done in the parametric downconversion process, making it a much more promising
implementation.


title: Unconditional teleportation of continuous-variable entanglement

abstract:
  We give a protocol and criteria for demonstrating unconditional teleportation
of continuous-variable entanglement (i.e., entanglement swapping). The initial
entangled states are produced with squeezed light and linear optics. We show
that any nonzero entanglement (any nonzero squeezing) in both of two
entanglement sources is sufficient for entanglement swapping to occur. In fact,
realization of continuous-variable entanglement swapping is possible using only
{\it two} single-mode squeezed states.


title: Several remarks on ``Comments'' by A. Moroz

abstract:
  We make a couple of remarks on ``Comments'' due to A. Moroz which were
addressed to our recent letter "Differential cross section for Aharonov-Bohm
effect with non standard boundary conditions", Europhys. Lett. 44 (1998) 403.


title: State preparation by photon filtering

abstract:
  We propose a setup capable of generating Fock states of a single mode
radiation field. The scheme is based on coupling the signal field to a ring
cavity through cross-Kerr phase modulation, and on conditional ON-OFF
photodetection at the output cavity mode. The same setup allows to prepare
selected superpositions of Fock states and entangled two-mode states.
Remarkably, the detector's quantum efficiency does not affect the reliability
of the state synthesis.


title:
Measurement as Absorption of Feynman Trajectories: Collapse of the Wave
  Function Can be Avoided

abstract:
  We define a measuring device (detector) of the coordinate of quantum particle
as an absorbing wall that cuts off the particle's wave function. The wave
function in the presence of such detector vanishes on the detector. The trace
the absorbed particles leave on the detector is identifies as the absorption
current density on the detector. This density is calculated from the solution
of Schr\"odinger's equation with a reflecting boundary at the detector. This
current density is not the usual Schr\"odinger current density. We define the
probability distribution of the time of arrival to a detector in terms of the
absorption current density. We define coordinate measurement by an absorbing
wall in terms of 4 postulates. We postulate, among others, that a quantum
particle has a trajectory. In the resulting theory the quantum mechanical
collapse of the wave function is replaced with the usual collapse of the
probability distribution after observation. Two examples are presented, that of
the slit experiment and the slit experiment with absorbing boundaries to
measure time of arrival. A calculation is given of the two dimensional
probability density function of a free particle from the measurement of the
absorption current on two planes.


title: Symmetry of Quantum Phase Space in a Degenerate Hamiltonian System

abstract:
  Using Husimi function approach, we study the ``quantum phase space'' of a
harmonic oscillator interacting with a plane monochromatic wave. We show that
in the regime of weak chaos, the quantum system has the same symmetry as the
classical system. Analytical results agree with the results of numerical
calculations.


title: Building multiparticle states with teleportation

abstract:
  We describe a protocol which can be used to generate any N-partite pure
quantum state using Einstein-Podolsky-Rosen (EPR) pairs. This protocol employs
only local operations and classical communication between the N parties
(N-LOCC). In particular, we rely on quantum data compression and teleportation
to create the desired state. This protocol can be used to obtain upper bounds
for the bipartite entanglement of formation of an arbitrary N-partite pure
state, in the asymptotic limit of many copies. We apply it to a few
multipartite states of interest, showing that in some cases it is not optimal.
Generalizations of the protocol are developed which are optimal for some of the
examples we consider, but which may still be inefficient for arbitrary states.


title: Improved Dirac quantization of a free particle

abstract:
  In the framework of Dirac quantization with second class constraints, a free
particle moving on the surface of a $(d-1)-$dimensional sphere has an ambiguity
in the energy spectrum due to the arbitrary shift of canonical momenta. We
explicitly show that this spectrum obtained by the Dirac method can be
consistent with the result of the Batalin-Fradkin-Tyutin formalism, which is an
improved
  Dirac method, at the level of the first-class constraint by fixing the
ambiguity, and discuss its physical consequences.


title: Classical behaviour of many-body systems in Bohmian Quantum Mechanics

abstract:
  The classical behaviour of a macroscopic system consisting of a large number
of microscopic systems is derived in the framework of the Bohmian
interpretation of quantum mechanics. Under appropriate assumptions concerning
the localization and factorization of the wavefunction it is shown explicitly
that the center of mass motion of the system is determined by the classical
equations of motion.


title:
Linear canonical transformations and quantum phase:a unified canonical
  and algebraic approach

abstract:
  The algebra of generalized linear quantum canonical transformations is
examined in the prespective of Schwinger's unitary-canonical basis. Formulation
of the quantum phase problem within the theory of quantum canonical
transformations and in particular with the generalized quantum action-angle
phase space formalism is established and it is shown that the conceptual
foundation of the quantum phase problem lies within the algebraic properties of
the quantum canonical transformations in the quantum phase space. The
representations of the Wigner function in the generalized action-angle unitary
operator pair for certain Hamiltonian systems with the dynamical symmetry are
examined. This generalized canonical formalism is applied to the quantum
harmonic oscillator to examine the properties of the unitary quantum phase
operator as well as the action-angle Wigner function.


title: A Foundation of Programming a Multi-Tape Quantum Turing machine

abstract:
  The notion of quantum Turing machines is a basis of quantum complexity
theory. We discuss a general model of multi-tape, multi-head Quantum Turing
machines with multi final states that also allow tape heads to stay still.


title: Information Content for Quantum States

abstract:
  A method of representing probabilistic aspects of quantum systems is
introduced by means of a density function on the space of pure quantum states.
In particular, a maximum entropy argument allows us to obtain a natural density
function that only reflects the information provided by the density matrix.
This result is applied to derive the Shannon entropy of a quantum state. The
information theoretic quantum entropy thereby obtained is shown to have the
desired concavity property, and to differ from the the conventional von Neumann
entropy. This is illustrated explicitly for a two-state system.


title: Geometric Quantum Mechanics

abstract:
  The manifold of pure quantum states is a complex projective space endowed
with the unitary-invariant geometry of Fubini and Study. According to the
principles of geometric quantum mechanics, the detailed physical
characteristics of a given quantum system can be represented by specific
geometrical features that are selected and preferentially identified in this
complex manifold. Here we construct a number of examples of such geometrical
features as they arise in the state spaces for spin-1/2, spin-1, and spin-3/2
systems, and for pairs of spin-1/2 systems. A study is undertaken on the
geometry of entangled states, and a natural measure is assigned to the degree
of entanglement of a given state for a general multi-particle system. The
properties of this measure are analysed for the entangled states of a pair of
spin-1/2 particles. With the specification of a quantum Hamiltonian, the
resulting Schrodinger trajectory induces a Killing field, which is quasiergodic
on a toroidal subspace of the energy surface. When the dynamical trajectory is
lifted orthogonally to Hilbert space, it induces a geometric phase shift on the
wave function. The uncertainty of an observable in a given state is the length
of the gradient vector of the level surface of the expectation of the
observable in that state, a fact that allows us to calculate higher order
corrections to the Heisenberg relations. A general mixed state is determined by
a probability density function on the state space, for which the associated
first moment is the density matrix. The advantage of a general state is in its
applicability in various attempts to go beyond the standard quantum theory.


title: Diffractive orbits in an open microwave billiard

abstract:
  We demonstrate the existence and significance of diffractive orbits in an
open microwave billiard, both experimentally and theoretically. Orbits that
diffract off of a sharp edge strongly influence the conduction spectrum of this
resonator, especially in the regime where there are no stable classical orbits.
On resonance, the wavefunctions are influenced by both classical and
diffractive orbits. Off resonance, the wavefunctions are determined by the
constructive interference of multiple transient, nonperiodic orbits.
Experimental, numerical, and semiclassical results are presented.


title: Nonlinear manipulation and control of matter waves

abstract:
  This paper reviews some of our recent results in nonlinear atom optics. In
addition to nonlinear wave-mixing between matter waves, we also discuss the
dynamical interplay between optical and matter waves. This new paradigm, which
is now within experimental reach, has the potential to impact a number of
fields of physics, including the manipulation and applications of atomic
coherence, and the preparation of quantum entanglement between microscopic and
macroscopic systems. Possible applications include quantum information
processing, matter-wave holography, and nanofabrication.


title: Efficient Algorithm for Optimal Control of Mixed-State Quantum Systems

abstract:
  In [1] Zhu and Rabitz presented a rapidly convergent iterative algorithm for
optimal control of the expectation value of a positive definite observable in a
pure-state quantum system. In this paper we generalize this algorithm to a
quantum statistical mechanics setting and show that it is both efficient in the
mixed-state case and effective in achieving the control objective of maximizing
the ensemble average of arbitrary observables in the cases studied.


title: Strong Converse and Stein's Lemma in the Quantum Hypothesis Testing

abstract:
  The hypothesis testing problem of two quantum states is treated. We show a
new inequality between the error of the first kind and the second kind, which
complements the result of Hiai and Petz to establish the quantum version of
Stein's lemma. The inequality is also used to show a bound on the first kind
error when the power exponent for the second kind error exceeds the quantum
relative entropy, and the bound yields the strong converse in the quantum
hypothesis testing. Finally, we discuss the relation between the bound and the
power exponent derived by Han and Kobayashi in the classical hypothesis
testing.


title:
On the theory of the anomalous photoelectric effect stemming from a
  substructure of matter waves

abstract:
  The two opposite concepts - multiphoton and effective photon - readily
describing the photoelectric effect under strong irradiation in the case that
the energy of the incident light is essentially smaller than the ionisation
potential of gas atoms and the work function of the metal are treated. Based on
the submicroscopic construction of quantum mechanics developed in the previous
papers by the author [Phys. Essays vol. 6, 554 (1993); vol. 10, 407 (1997)] the
analysis of the reasons of the two concepts discrepancies is led. Taking into
account the main hypothesis of those works, i.e., that the electron is an
extended object that is not point-like, the study of the interaction between
the electron and a photon flux is carried out in detail. A comparison with
numerous experiments is performed.


title: Continuous Quantum Measurement and the Emergence of Classical Chaos

abstract:
  We formulate the conditions under which the dynamics of a continuously
measured quantum system becomes indistinguishable from that of the
corresponding classical system. In particular, we demonstrate that even in a
classically chaotic system the quantum state vector conditioned by the
measurement remains localized and, under these conditions, follows a trajectory
characterized by the classical Lyapunov exponent.


title: The influence of density of modes on dark lines in spontaneous emission

abstract:
  We study two distinct multi-level atomic models in which one transition is
coupled to a Markovian reservoir, while another linked transition is coupled to
a non-Markovian reservoir. We show that by choosing appropriately the density
of modes of the non-Markovian reservoir the spontaneous emission to the
Markovian reservoir is greatly altered. The existence of `dark lines' in the
spontaneous emission spectrum in the Markovian reservoir due to the coupling to
specific density of modes of the non-Markovian reservoir is also predicted.


title: Universal Control of Decoupled Quantum Systems

abstract:
  It is shown that if one can perform a restricted set of fast manipulations on
a quantum system, one can implement a large class of dynamical evolutions by
effectively removing or introducing selected Hamiltonians. The procedure can be
used to achieve universal noise-tolerant control based on purely unitary
open-loop transformations of the dynamics. As a result, it is in principle
possible to perform noise-protected universal quantum computation using no
extra space resources.


title:
Computational Complexity of Uniform Quantum Circuit Families and Quantum
  Turing Machines

abstract:
  Deutsch proposed two sorts of models of quantum computers, quantum Turing
machines (QTMs) and quantum circuit families (QCFs). In this paper we explore
the computational powers of these models and re-examine the claim of the
computational equivalence of these models often made in the literature without
detailed investigations. For this purpose, we formulate the notion of the codes
of QCFs and the uniformity of QCFs by the computability of the codes. Various
complexity classes are introduced for QTMs and QCFs according to constraints on
the error probability of algorithms or transition amplitudes. Their
interrelations are examined in detail. For Monte Carlo algorithms, it is proved
that the complexity classes based on uniform QCFs are identical with the
corresponding classes based on QTMs. However, for Las Vegas algorithms, it is
still open whether the two models are equivalent. We indicate the possibility
that they are not equivalent. In addition, we give a complete proof of the
existence of a universal QTM simulating multi-tape QTMs efficiently. We also
examine the simulation of various types of QTMs such as multi-tape QTMs, single
tape QTMs, stationary, normal form QTMs (SNQTMs), and QTMs with the binary
tapes. As a result, we show that these QTMs are computationally equivalent one
another as computing models implementing not only Monte Carlo algorithms but
exact (or error-free) ones.


title: Book Review: Bohmian Mechanics and Quantum Theory: An Appraisal

abstract:
  A review of "Bohmian Mechanics and Quantum Theory: An Appraisal" (James
Cushing, Arthur Fine and Sheldon Goldstein, Eds.), an extensive collection of
articles on Bohmian mechanics. In addition to broad, critical overviews of
Bohmian mechanics, the reviewed collection contains extensions and hybrid
versions of the theory and several detailed applications to practical
situtations.


title: Quantum state diffusion, measurement and second quantization

abstract:
  Realistic dynamical theories of measurement based on the diffusion of quantum
states are nonunitary, whereas quantum field theory and its generalizations are
unitary. This problem in the quantum field theory of quantum state diffusion
(QSD) appears already in the Lagrangian formulation of QSD as a classical
equation of motion, where Liouville's theorem does not apply to the usual field
theory formulation. This problem is resolved here by doubling the number of
freedoms used to represent a quantum field. The space of quantum fields is then
a classical configuration space, for which volume need not be conserved,
instead of the usual phase space, to which Liouville's theorem applies. The
creation operator for the quantized field satisfies the QSD equations, but the
annihilation operator does not satisfy the conjugate eqation. It appears only
in a formal role.


title:
Entanglement quantification and purification in continuous variable
  systems

abstract:
  We develop theoretical and numerical tools for the quantification of
entanglement in systems with continuous degrees of freedom. Continuous variable
entanglement swapping is introduced and based on this idea we develop methods
of entanglement purification for continuous variable systems. The success of
these entanglement purification methods is then assessed using these tools.


title: Discrete Q- and P-symbols for spin s

abstract:
  Non-orthogonal bases of projectors on coherent states are introduced to
expand hermitean operators acting on the Hilbert space of a spin s. It is shown
that the expectation values of a hermitean operator A in a family of
(2s+1)(2s+1) spin-coherent states determine the operator unambiguously. In
other words, knowing the Q-symbol of A at (2s+1)(2s+1) points on the unit
sphere is already sufficient in order to recover the operator. This provides a
straightforward method to reconstruct the mixed state of a spin since its
density matrix is explicitly parametrized in terms of expectation values.
Furthermore, a discrete P-symbol emerges naturally which is related to a basis
dual to the original one.


title:
SU(2) coherent state path integrals based on arbitrary fiducial vectors
  and geometric phases

abstract:
  We develop the formulation of the spin(SU(2)) coherent state path integrals
based on arbitrary fiducial vectors. The resultant action in the path integral
expression extensively depends on the vector; It differs from the conventional
one in that it has a generalized form having some additional terms. We also
study, as physical applications, the geometric phases associated with the
coherent state path integrals to find that new effects of the terms may appear
in experiments. We see that the formalism gives a clear insight into geometric
phases.


title:
Non-Orthomodular Models for Both Quantum Logic and Standard Classical
  Logic: Repercussions for Quantum Computers

abstract:
  It is shown that propositional calculuses of both quantum and classical
logics are non-categorical. We find that quantum logic is in addition to an
orthomodular lattice also modeled by a weakly orthomodular lattice and that
classical logic is in addition to a Boolean algebra also modeled by a weakly
distributive lattice. Both new models turn out to be non-orthomodular. We prove
the soundness and completeness of the calculuses for the models. We also prove
that all the operations in an orthomodular lattice are five-fold defined. In
the end we discuss possible repercussions of our results to quantum
computations and quantum computers.


title: Realistic Interaction-Free Detection of Objects in a Resonator

abstract:
  We propose a realistic device for detecting objects almost without
transferring a single quantum of energy to them. The device can work with an
efficiency close to 100% and relies on two detectors counting both presence and
absence of the objects. Its possible usage in performing fundamental
experiments as well as possible applications are discussed.


title:
Secure Classical Bit Commitment using Fixed Capacity Communication
  Channels

abstract:
  If mutually mistrustful parties A and B control two or more appropriately
located sites, special relativity can be used to guarantee that a pair of
messages exchanged by A and B are independent. In earlier work, we used this
fact to define a relativistic bit commitment protocol, RBC1, in which security
is maintained by exchanging a sequence of messages whose transmission rate
increases exponentially in time. We define here a new relativistic protocol,
RBC2, which requires only a constant transmission rate and could be practically
implemented. We prove that RBC2 allows a bit commitment to be indefinitely
maintained with unconditional security against all classical attacks. We
examine its security against quantum attacks, and show that it is immune from
the class of attacks shown by Mayers and Lo-Chau to render non-relativistic
quantum bit commitment protocols insecure.


title:
Metrical Separability of the Spin Systems Energetic Surfaces and Quantum
  Jumps Hypothesis

abstract:
  Metrical separability of the spin systems energetic surfaces is shown. The
irreversibility of the spin system evolution is considered as the consequence
of random quantum jumps on energy surfaces.


title: Classical Teleportation of a Quantum Bit

abstract:
  Classical teleportation is defined as a scenario where the sender is given
the classical description of an arbitrary quantum state while the receiver
simulates any measurement on it. This scenario is shown to be achievable by
transmitting only a few classical bits if the sender and receiver initially
share local hidden variables. Specifically, a communication of 2.19 bits is
sufficient on average for the classical teleportation of a qubit, when
restricted to von Neumann measurements. The generalization to
positive-operator-valued measurements is also discussed.


title:
Single Spin State Detection for the Kane Model of Silicon-Based Quantum
  Computer

abstract:
  The scheme for measurement of the state of a single spin (or a few spin
system) based on the single-electron turnstile and injection of spin polarized
electrons from magnetic metal contacts is proposed. Applications to the recent
proposal concerning the spin gates based on a silicon matrix (B.Kane, Nature,
{\bf 393}, 133 (1998)) are discussed.


title: Unravelling quantum carpets: a travelling wave approach

abstract:
  Quantum carpets are generic spacetime patterns formed in the probability
distributions P(x,t) of one-dimensional quantum particles, first discovered in
1995. For the case of an infinite square well potential, these patterns are
shown to have a detailed quantitative explanation in terms of a travelling-wave
decomposition of P(x,t). Each wave directly yields the time-averaged structure
of P(x,t) along the (quantised)spacetime direction in which the wave
propagates. The decomposition leads to new predictions of locations, widths
depths and shapes of carpet structures, and results are also applicable to
light diffracted by a periodic grating and to the quantum rotator. A simple
connection between the waves and the Wigner function of the initial state of
the particle is demonstrated, and some results for more general potentials are
given.


title: States, Symmetries and Superselection

abstract:
  The process of dynamical decoherence may cause apparent superselection rules,
which are sometimes called `environmentally induced' or `soft'. A natural
question is whether such dynamical processes are eventually also responsible
for at least some of the superselection rules which are usually presented as
fundamentally rooted in the kinematical structure of the theory (so called
`hard' superselection rules). With this question in mind, I re-investigate two
well known examples where superselection rules are usually argued to rigorously
exist within the given mathematical framework. These are (1) the Bargmann
superselection rule for the total mass in Galilei invariant quantum mechanics
and (2) the charge superselection rule in quantum electrodynamics. I argue
that, for various reasons, the kinematical arguments usually given are not
physically convincing unless they are based on an underlying dynamical process.


title:
Influence of Non-Resonant Effects on the Dynamics of Quantum Logic Gates
  at Room Temperature

abstract:
  We study numerically the influence of non-resonant effects on the dynamics of
a single $\pi$-pulse quantum CONTROL-NOT (CN) gate in a macroscopic ensemble of
fo ur-spin molecules at room temperature. The four nuclear spins in each
molecule r epresent a four-qubit register. The qubits are ``labeled'' by the
characteristic frequencies, $\omega_k$, ($k=0$ to 3) due to the Zeeman
interaction of the nuclear spins with the magnetic field. The qubits interact
with each other through an Ising interaction of strength $J$. T he paper
examines the feasibility of implementing a single-pulse quantum CN gate in an
ensemble of quantum molecules at room temperature. We determine a paramet er
region, $\omega_k$ and $J$, in which a single-pulse quantum CN gate can be i
mplemented at room temperature. We also show that there exist characteristic
cri tical values of parameters,
$\Delta\omega_{cr}\equiv|\omega_{k^\prime}-\omega_k|_{cr}$ and $J_{cr}$, such
that for $J<J_{cr}$ and
$\Delta\omega_k\equiv|\omega_{k^\prime}-\omega_k|<\Delta\omega_{cr}$,
non-resonant effects are sufficient to d estroy the dynamics required for
quantum logic operations.


title: Quantum teleportation of EPR pair by three-particle entanglement

abstract:
  Teleportation of an EPR pair using triplet in state of the
Horne-Greenberger-Zeilinger form to two receivers is considered. It needs a
three-particle basis for joint measurement. By contrast the one qubit
teleportation the required basis is not maximally entangled. It consists of the
states corresponding to the maximally entanglement of two particles only. Using
outcomes of measurement both receivers can recover an unknown EPR state however
one of them can not do it separately. Teleportation of the N-particle
entanglement is discussed.


title: An Introduction to Quantum Complexity Theory

abstract:
  We give a basic overview of computational complexity, query complexity, and
communication complexity, with quantum information incorporated into each of
these scenarios. The aim is to provide simple but clear definitions, and to
highlight the interplay between the three scenarios and currently-known quantum
algorithms.


title: Quantum algorithms which accept hot qubit inputs

abstract:
  Realistic physical implementations of quantum computers can entail tradeoffs
which depart from the ideal model of quantum computation. Although these
tradeoffs have allowed successful demonstration of certain quantum algorithms,
a crucial question is whether they fundamentally limit the computational
capacity of such machines. We study the limitations of a quantum computation
model in which only ensemble averages of measurement observables are
accessible. Furthermore, we stipulate that input qubits may only be prepared in
highly random, ``hot'' mixed states. In general, these limitations are believed
to dramatically detract from the computational power of the system. However, we
construct a class of algorithms for this limited model, which, surprisingly,
are polynomially equivalent to the ideal case. This class includes the well
known Deutsch-Jozsa algorithm.


title: Quantum superluminal communication does not result in the causal loop

abstract:
  We show that the quantum superluminal communication based on the quantum
nonlocal influence, if exists, will not result in the causal loop, this
conclusion is essentially determined by the peculiarity of the quantum nonlocal
influence itself, according to which there must exist a preferred Lorentz frame
for consistently describing the quantum nonlocal process.


title: Pauli Exchange Errors in Quantum Computation

abstract:
  In many physically realistic models of quantum computation, Pauli exchange
interactions cause a subset of two-qubit errors to occur as a first order
effect of couplings within the computer, even in the absence of interactions
with the computer's environment. We give an explicit 9-qubit code that corrects
both Pauli exchange errors and all one-qubit errors.


title: Non dissipative decoherence of Rabi oscillations

abstract:
  We present a simple theoretical description of two recent experiments where
damping of Rabi oscillations, which cannot be attributed to dissipative
decoherence, has been observed. This is obtained considering the evolution time
or the Hamiltonian as random variables and then averaging the usual unitary
evolution on a properly defined, model-independent, probability distribution.


title: How to realize quantum superluminal communication?

abstract:
  We deeply analyze the possibility to achieve quantum superluminal
communication beyond the domain of special relativity and present quantum
theory, and show that when using the conscious object as one part of the
measuring device, quantum superluminal communication may be a natural thing.


title: Non-linear Schroedinger Equations, Separation and Symmetry

abstract:
  We investigate the symmetry properties of hierarchies of non-linear
Schroedinger equations (introduced by Doebner and Goldin, and Goldin and
Svetlichny), which describe non-interacting systems in which tensor product
wave-functions evolve by independent evolution of the factors (the separation
property). We show that there are obstructions to lifting symmetries existing
at a certain number of particles to higher numbers. Such obstructions vanish
for particles without internal degrees of freedom and the usual space-time
symmetries. For particles with internal degrees of freedom, such as spin, these
obstructions are present and their circumvention requires a choice of a new
term in the equation for each particle number. A Lie-algebra approach for
non-linear theories is developed.


title: Decoherence vs entropy in neutron interferometry

abstract:
  We analyze the coherence properties of polarized neutrons, after they have
interacted with a magnetic field or a phase shifter undergoing different kinds
of statistical fluctuations. We endeavor to probe the degree of disorder of the
distribution of the phase shifts by means of the loss of quantum mechanical
coherence of the neutron. We find that the notion of entropy of the shifts and
that of decoherence of the neutron do not necessarily agree. In some cases the
neutron wave function is more coherent, even though it has interacted with a
more disordered medium.


title: Non-Markovian dynamics in pulsed and continuous wave atom lasers

abstract:
  The dynamics of atom lasers with a continuous output coupler based on
two-photon Raman transitions is investigated. With the help of the
time-convolutionless projection operator technique the quantum master equations
for pulsed and continuous wave (cw) atom lasers are derived. In the case of the
pulsed atom laser the power of the time-convolutionless projection operator
technique is demonstrated through comparison with the exact solution. It is
shown that in an intermediate coupling regime where the Born-Markov
approximation fails the results of this algorithm agree with the exact
solution. To study the dynamics of a continuous wave atom laser a pump
mechanism is included in the model. Whereas the pump mechanism is treated
within the Born-Markov approximation, the output coupling leads to
non-Markovian effects. The solution of the master equation resulting from the
time-convolutionless projection operator technique exhibits strong oscillations
in the occupation number of the Bose-Einstein condensate. These oscillations
are traced back to a quantum interference which is due to the non-Markovian
dynamics and which decays slowly in time as a result of the dispersion relation
for massive particles.


title: Noise effects on One-Pauli Channels

abstract:
  The possibility of stochastic resonance of a quantum channel and hence the
noise enhanced quantum channel capacity is explored by considering one-Pauli
channels which are more classical like. The fidelity of the channel is also
considered.


title:
The hyperfine structure of highly charged $^{238}_{92}$U ions with
  rotationally excited nuclei

abstract:
  The hyperfine structure (hfs) of electron levels of $^{238}_{92}$U ions with
the nucleus excited in the low-lying rotational $2^+$ state with an energy
$E_{2^+} = 44.91$ keV is investigated. In hydrogenlike uranium, the hfs
splitting for the $1s_{1/2}$-ground state of the electron constitutes 1.8 eV.
The hyperfine-quenched (hfq) lifetime of the $1s2p ^3P_0$ state has been
calculated for heliumlike $^{238}_{92}$U and was found to be two orders of
magnitude smaller than for the ion with the nucleus in the ground state. The
possibility of a precise determination of the nuclear $g_r$ factor for the
rotational $2^+$ state by measurements of the hfq lifetime is discussed.


title: Dynamical Casimir effect at finite temperature

abstract:
  Thermal effects on the creation of particles under the influence of
time-dependent boundary conditions are investigated. The dominant temperature
correction to the energy radiated by a moving mirror is derived by means of
response theory. For a resonantly vibrating cavity the thermal effect on the
number of created photons is obtained non-perturbatively. Finite temperatures
can enhance the pure vacuum effect by several orders of magnitude. The
relevance of finite temperature effects for the experimental verification of
the dynamical Casimir effect is addressed.


title: Disentangling Nonlocality and Teleportation

abstract:
  Quantum entanglement can be used to demonstrate nonlocality and to teleport a
quantum state from one place to another. The fact that entanglement can be used
to do both these things has led people to believe that teleportation is a
nonlocal effect. In this paper it is shown that teleportation is conceptually
independent of nonlocality. This is done by constructing a toy local theory in
which cloning is not possible (without a no-cloning theory teleportation makes
limited sense) but teleportation is. Teleportation in this local theory is
achieved in an analogous way to the way it is done with quantum theory. This
work provides some insight into what type of process teleportation is.


title: Quantum-mechanical probability from the symmetries of two-state systems

abstract:
  In 1989, Deutsch gave a basic physical explanation of why quantum-mechanical
probabilities are squares of amplitudes. Essentially, a general state vector is
transformed into a highly symmetric equal-amplitude superposition. The argument
was recently elaborated and publicised by DeWitt. It has remained incomplete,
however, inasmuch as both authors anticipate the usual normalization (sum of
amplitudes squared) of state vectors. In the present paper, a thought
experiment is devised in which Deutsch's idea is demonstrated independently of
the normalization, exploiting further symmetries instead.


title:
Atom lasers, coherent states, and coherence: I. physically realizable
  ensembles of pure states

abstract:
  A laser, be it an optical laser or an atom laser, is an open quantum system
that produces a coherent beam of bosons. Far above threshold, the stationary
state $\rho_{ss}$ of the laser mode is a mixture of coherent field states with
random phase, or, equivalently, a Poissonian mixture of number states. This
paper answers the question: can descriptions such as these, of $\rho_{ss}$ as a
stationary ensemble of pure states, be physically realized? An ensemble of pure
states for a particular system can be physically realized if, without changing
the dynamics of the system, an experimenter can (in principle) know at any time
that the system is in one of the pure-state members of the ensemble. Such
knowledge can be obtained by monitoring the baths to which the system is
coupled, provided that coupling is describable by a Markovian master equation.
Using a family of master equations for the (atom) laser, we solve for the
physically realizable (PR) ensembles. We find that for any finite self-energy
$\chi$ of the bosons in the laser mode, the coherent state ensemble is not PR;
the closest one can come to it is an ensemble of squeezed states. This is
particularly relevant for atom lasers, where the self-energy arising from
elastic collisions is expected to be large. By contrast, the number state
ensemble is always PR. As $\chi$ increases, the states in the PR ensemble
closest to the coherent state ensemble become increasingly squeezed.
Nevertheless, there are values of $\chi$ for which states with well-defined
coherent amplitudes are PR, even though the atom laser is not coherent (in the
sense of having a Bose-degenerate output). We discuss the physical significance
of this anomaly in terms of conditional coherence (conditional Bose
degeneracy).


title: Quantum Error Detection I: Statement of the Problem

abstract:
  I. This paper is devoted to the problem of error detection with quantum
codes. In the first part we examine possible problem settings for quantum error
detection. Our goal is to derive a functional that describes the probability of
undetected error under natural physical assumptions concerning transmission
with error detection over the depolarizing channel. We discuss possible
transmission protocols with stabilizer and unrestricted quantum codes. The set
of results proved in Part I shows that in all the cases considered the average
probability of undetected error for a given code is essentially given by one
and the same function of its weight enumerators. This enables us to give a
consistent definition of the undetected error event.


title:
Emergent measure-dependent probabilities from modified quantum dynamics
  without state-vector reduction

abstract:
  Counting outcomes is the obvious algorithm for generating probabilities in
quantum mechanics without state-vector reduction (i.e. many-worlds). This
procedure has usually been rejected because for purely linear dynamics it gives
results in disagreement with experiment. Here it is shown that if non-linear
decoherence effects (previously proposed by other authors) are combined with an
exponential time dependence of the scale for the non-linear effects, the
correct measure-dependent probabilities can emerge via outcome counting,
without the addition of any stochastic fields or metaphysical hypotheses.


title: Loss and heating of particles in small and noisy traps

abstract:
  We derive the life time and loss rate for a trapped particle that is coupled
to fluctuating fields in the vicinity of a room-temperature metallic and/or
dielectric surface. Our results indicate a clear predominance of near field
effects over ordinary blackbody radiation. We develop a theoretical framework
for both charged and neutral particles with and without spin. Loss processes
that are due to a transition to an untrapped internal state are included.


title: Fault-Tolerant Quantum Computation With Constant Error Rate

abstract:
  This paper proves the threshold result, which asserts that quantum
computation can be made robust against errors and inaccuracies, when the error
rate, $\eta$, is smaller than a constant threshold, $\eta_c$. The result holds
for a very general, not necessarily probabilistic noise model, for quantum
particles with any number of states, and is also generalized to one dimensional
quantum computers with only nearest neighbor interactions. No measurements, or
classical operations, are required during the quantum computation. The
proceeding version was very succinct, and here we fill all the missing details,
and elaborate on many parts of the proof. In particular, we devote a section
for a discussion of universality issues and proofs that the sets of gates that
we use are universal. Another section is devoted to a rigorous proof that fault
tolerance can be achieved in the presence of general non probabilistic noise.
The systematic structure of the fault tolerant procedures for polynomial codes
is explained in length. The proof that the concatenation scheme works is
written in a clearer way. The paper also contains new and significantly simpler
proofs for most of the known results which we use. For example, we give a
simple proof that it suffices to correct bit and phase flips, we significantly
simplify Calderbank and Shor's original proof of the correctness of CSS codes.
We also give a simple proof of the fact that two-qubit gates are universal. The
paper thus provides a self contained and complete proof for universal fault
tolerant quantum computation.


title: Structure behind Mechanics

abstract:
  This paper proposes a basic theory on physical reality, and a new foundation
for 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 clarifies how the classical-limit occurs. It further
compares the new theory with the known quantization methods, and proposes a
self-consistent interpretation for quantum mechanics. It also provides the
internal structure inducing half-integer spin of a particle, the sense of the
regularization in the quantum field theory, the quantization of a
phenomenological system, the causality in quantum mechanics and the origin of
the thermodynamic irreversibility under the new insight.


title: Quantum Error Detection II: Bounds

abstract:
  In Part II we show that there exist quantum codes whose probability of
undetected error falls exponentially with the length of the code and derive
bounds on this exponent.The lower (existence) bound for stabilizer codes is
proved by a counting argument for classical self-orthogonal quaternary codes.
Upper bounds for any quantum codes are proved by linear programming. We present
two general solutions of the LP problem. Together they give an upper bound on
the exponent of undetected error. The upper and lower asymptotic bounds
coincide for a certain interval of code rates close to 1.


title: Optimal Cloning and No Signaling

abstract:
  It is shown that no signaling constraint generates the whole class of 1
$\rightarrow$ 2 optimal quantum cloning machines of single qubits.


title: Coherent two-field spectroscopy of degenerate two-level systems

abstract:
  Spectroscopic features revealing the coherent interaction of a degenerate
two-level atomic system with two optical fields are examined. A model for the
numerical calculation of the response of a degenerate two-level system to the
action of an arbitrarily intense resonant pump field and a weak probe in the
presence of a magnetic field is presented. The model is valid for arbitrary
values of the total angular momentum of the lower and upper levels and for any
choice of the polarizations of the optical waves. Closed and open degenerate
two-level systems are considered. Predictions for probe absorption and
dispersion, field generation by four-wave-mixing, population modulation and
Zeeman optical pumping are derived. On all these observables, sub-natural-width
coherence resonances are predicted and their spectroscopic features are
discussed. Experimental spectra for probe absorption and excited state
population modulation in the D2 line of Rb vapor are presented in good
agreement with the calculations


title: NMR Quantum Logic Gates for Homonuclear Spin Systems

abstract:
  If NMR systems are to be used as practical quantum computers, the number of
coupled spins will need to be so large that it is not feasible to rely on
purely heteronuclear spin systems. The implementation of a quantum logic gate
imposes certain constraints on the motion of those spins not directly involved
in that gate, the so-called "spectator" spins; they must be returned to their
initial states at the end of the sequence. As a result, a homonuclear spin
system where there is appreciable coupling between every pair of spins would
seem to require a refocusing scheme that doubles in complexity and duration for
every additional spectator spin. Fortunately, for the more realistic practical
case where long-range spin-spin couplings can be neglected, simpler refocusing
schemes can be devised where the overall duration of the sequence remains
constant and the number of soft pulses increases only linearly with the number
of spectator spins. These ideas are tested experimentally on a six qubit
system: the six coupled protons of inosine.


title: Quantum Probability from Decision Theory?

abstract:
  Deutsch has recently (in quant-ph/9906015) offered a justification, based
only on the non-probabilistic axioms of quantum theory and of classical
decision theory, for the use of the standard quantum probability rules. In this
note, this justification is examined.


title:
Randomly Walking 1D Quantum Harmonic Oscillator. Averaged Transition
  Probabilities

abstract:
  One-dimensional problem for quantum harmonic oscillator with "regular+random"
frequency subjected to the external "regular+random" force is considered.
Averaged transition probabilities are found.


title: Optical Quantum Random Number Generator

abstract:
  A physical random number generator based on the intrinsic randomness of
quantum mechanics is described. The random events are realized by the choice of
single photons between the two outputs of a beamsplitter. We present a simple
device, which minimizes the impact of the photon counters' noise, dead-time and
after pulses.


title: Counterfactual Computation

abstract:
  Suppose that we are given a quantum computer programmed ready to perform a
computation if it is switched on. Counterfactual computation is a process by
which the result of the computation may be learnt without actually running the
computer. Such processes are possible within quantum physics and to achieve
this effect, a computer embodying the possibility of running the computation
must be available, even though the computation is, in fact, not run. We study
the possibilities and limitations of general protocols for the counterfactual
computation of decision problems (where the result r is either 0 or 1). If p(r)
denotes the probability of learning the result r ``for free'' in a protocol
then one might hope to design a protocol which simultaneously has large p(0)
and p(1). However we prove that p(0)+p(1) never exceeds 1 in any protocol and
we derive further constraints on p(0) and p(1) in terms of N, the number of
times that the computer is not run. In particular we show that any protocol
with p(0)+p(1)=1-epsilon must have N tending to infinity as epsilon tends to 0.
These general results are illustrated with some explicit protocols for
counterfactual computation. We show that "interaction-free" measurements can be
regarded as counterfactual computations, and our results then imply that N must
be large if the probability of interaction is to be close to zero. Finally, we
consider some ways in which our formulation of counterfactual computation can
be generalised.


title: Variational Ansatz for PT-Symmetric Quantum Mechanics

abstract:
  A variational calculation of the energy levels of a class of PT-invariant
quantum mechanical models described by the non-Hermitian Hamiltonian H= p^2 -
(ix)^N with N positive and x complex is presented. Excellent agreement is
obtained for the ground state and low lying excited state energy levels and
wave functions. We use an energy functional with a three parameter class of
PT-symmetric trial wave functions in obtaining our results.


title: The importance of quantum decoherence in brain processes

abstract:
  Based on a calculation of neural decoherence rates, we argue that that the
degrees of freedom of the human brain that relate to cognitive processes should
be thought of as a classical rather than quantum system, i.e., that there is
nothing fundamentally wrong with the current classical approach to neural
network simulations. We find that the decoherence timescales ~10^{-13}-10^{-20}
seconds are typically much shorter than the relevant dynamical timescales
(~0.001-0.1 seconds), both for regular neuron firing and for kink-like
polarization excitations in microtubules. This conclusion disagrees with
suggestions by Penrose and others that the brain acts as a quantum computer,
and that quantum coherence is related to consciousness in a fundamental way.

categories: quant-ph cond-mat.dis-nn cs.NE physics.bio-ph q-bio


title: Qubit assisted Conclusive Teleportation

abstract:
  We present an optimal method for teleporting an unknown qubit using any pure
entangled state.


title: Quantum mechanical modeling of the CNOT (XOR) gate

abstract:
  We consider the CNOT quantum gate as a physical action, i.e. as unitary in
time evolution of the two-qubit system. This points to the modeling of the
interaction Hamiltonian of the two-qubit system which would correspond to the
CNOT transformation; the analysis naturally generalizes to the Toffoli gate.
Despite nonuniqueness of the model of the interaction Hamiltonian, the analysis
distinguishes that the interaction Hamiltonian does not posses any global
(rotational) symmetry. This forces us to conclude that the direct
(non-mediated) interaction in the two-qubit system does not suffice for
implementing the CNOT gate. I.e., so as to be able succesfully to implement the
CNOT transformation, a mediator (i.e. an external physical system interacting
with both of the qubits) is required.


title: Rotation Representations and e, $pi$, p Masses

abstract:
  Mass is proportional to phase gain per unit time; for e, $\pi$, and p the
quantum frequencies are 0.124, 32.6, and 227 Zhz, respectively. By explaining
how these particles acquire phase at different rates, we explain why these
particles have different masses. Any free particle spin 1/2 wave function is a
sum of plane waves with spin parallel to velocity. Each plane wave, a pair of
2-component rotation eigenvectors, can be associated with a 2x2 matrix
representation of rotations in a Euclidean space without disturbing the plane
wave's space-time properties. In a space with more than four dimensions, only
rotations in a 4d subspace can be represented. So far all is well known. Now
consider that unrepresented rotations do not have eigenvectors, do not make
plane waves, and do not contribute phase. The particles e, $\pi,$ and p are
assigned rotations in a 4d subspace of 16d, rotations in an 8d subspace of 12d,
and rotations in a 12d subspace of 12d, respectively. The electron 4d subspace,
assumed to be as likely to align with any one 4d subspace as with any other,
produces phase when aligned with the represented 4d subspace in 16d. Similarly,
we calculate the likelihood that a 4d subspace of the pion's 8d space aligns
with the represented 4d subspace in 12d. The represented 4d subspace is
contained in the proton's 12d space, so the proton always acquires phase. By
the relationship between mass and phase, the resulting particle phase ratios
are the particle mass ratios and these are coincident with the measured mass
ratios, within about one percent. 1999 PACS number(s): 03.65.Fd
Keywords:Algebraic methods; particle masses; rotation group


title:
Heterodyne Detection of Gravitational Waves in a Michelson
  Interferometer with a Vibrating Mirror

abstract:
  A new heterodyne detection method is suggested for detecting gravitational
waves in a Michelson Interferometer. The method is based on interference
between phase changes which are induced by a vibrating mirror with phase
changes which are due to the gravitational waves. The advantage of using a
second order correlation function in the present analysis is discussed.


title: q-Symmetries in DNLS-AL chains and exact solutions of quantum dimers

abstract:
  Dynamical symmetries of Hamiltonians quantized models of discrete non-linear
Schroedinger chain (DNLS) and of Ablowitz-Ladik chain (AL) are studied. It is
shown that for $n$-sites the dynamical algebra of DNLS Hamilton operator is
given by the $su(n)$ algebra, while the respective symmetry for the AL case is
the quantum algebra su_q(n). The q-deformation of the dynamical symmetry in the
AL model is due to the non-canonical oscillator-like structure of the raising
and lowering operators at each site.
  Invariants of motions are found in terms of Casimir central elements of su(n)
and su_q(n) algebra generators, for the DNLS and QAL cases respectively.
Utilizing the representation theory of the symmetry algebras we specialize to
the $n=2$ quantum dimer case and formulate the eigenvalue problem of each dimer
as a non-linear (q)-spin model. Analytic investigations of the ensuing
three-term non-linear recurrence relations are carried out and the respective
orthonormal and complete eigenvector bases are determined.
  The quantum manifestation of the classical self-trapping in the QDNLS-dimer
and its absence in the QAL-dimer, is analysed by studying the asymptotic
attraction and repulsion respectively, of the energy levels versus the strength
of non-linearity. Our treatment predicts for the QDNLS-dimer, a
phase-transition like behaviour in the rate of change of the logarithm of
eigenenergy differences, for values of the non-linearity parameter near the
classical bifurcation point.


title: "Haunted" quantum contextuality

abstract:
  Two entangled particles in threedimensional Hilbert space (per particle) are
considered in an EPR-type arrangement. On each side the Kochen-Specker
observables $\{J_1^2,J_2^2,J_3^2\}$ and $\{\bar J_1^2, \bar J_2^2,J_3^2\}$ with
$[J_1^2,\bar J_1^2]\neq 0$ are measured. The outcomes of measurements of
$J_3^2$ (via $J_1^2,J_2^2$) and $J_3^2$ (via $\bar J_1^2,\bar J_2^2$) are
compared. Although formally $J_3^2$ is associated with the same projection
operator, a strong form of quantum contextuality states that an outcome depends
on the complete disposition of the measurement apparatus, in particular whether
$J_1^2$ or $\bar J_1^2$ is measured alongside. It is argued that in this case
it is impossible to measure contextuality directly, a necessary condition being
a non-operational counterfactuality of the argument.


title:
Comment on `Experimental Entanglement Swapping: Entangling Photons That
  Never Interacted'

abstract:
  We comment on the experimental realisation of entanglement swapping by Pan et
al. [Phys. Rev. Lett. 80, 3891 (1998)].


title: Single-particle Bell-type Inequality

abstract:
  It is generally believed that Bell's inequality holds for the case of
entangled states, including two correlated particles or special states of a
single particle. Here, we derive a single-particle Bell's inequality for two
correlated spin states at two successive times, appealing to the statistical
independence condition in an ideal experiment, for a locally causal hidden
variables theory. We show that regardless of the locality assumption, the
inequality can be violated by some quantum predictions.


title: Information and noise in quantum measurement

abstract:
  Even though measurement results obtained in the real world are generally both
noisy and continuous, quantum measurement theory tends to emphasize the ideal
limit of perfect precision and quantized measurement results. In this article,
a more general concept of noisy measurements is applied to investigate the role
of quantum noise in the measurement process. In particular, it is shown that
the effects of quantum noise can be separated from the effects of information
obtained in the measurement. However, quantum noise is required to ``cover up''
negative probabilities arising as the quantum limit is approached. These
negative probabilities represent fundamental quantum mechanical correlations
between the measured variable and the variables affected by quantum noise.


title: Quantum Channels and Simultaneous ID Coding

abstract:
  This paper is on identification of classical information by the use of
quantum channels. We focus on simultaneous ID codes which use measurements
being useful to identify an arbitrary message. We give a direct and a converse
part of the appropriate coding theorem.


title: Quantum Probabilistic Subroutines and Problems in Number Theory

abstract:
  We present a quantum version of the classical probabilistic algorithms
$\grave{a}$ la Rabin. The quantum algorithm is based on the essential use of
Grover's operator for the quantum search of a database and of Shor's Fourier
transform for extracting the periodicity of a function, and their combined use
in the counting algorithm originally introduced by Brassard et al. One of the
main features of our quantum probabilistic algorithm is its full unitarity and
reversibility, which would make its use possible as part of larger and more
complicated networks in quantum computers. As an example of this we describe
polynomial time algorithms for studying some important problems in number
theory, such as the test of the primality of an integer, the so called 'prime
number theorem' and Hardy and Littlewood's conjecture about the asymptotic
number of representations of an even integer as a sum of two primes.


title: Classical information and distillable entanglement

abstract:
  We establish a quantitative connection between the amount of lost classical
information about a quantum state and the concomitant loss of entanglement.
Using methods that have been developed for the optimal purification of mixed
states we find a class of mixed states with known distillable entanglement.
These results can be used to determine the quantum capacity of a quantum
channel which randomizes the order of transmitted signals.