title: Toward a More Natural Expression of Quantum Logic with Boolean Fractions

abstract:
  The fundamental algebraic concepts of quantum mechanics, as expressed by many
authors, are reviewed and translated into the framework of the relatively new
non-distributive system of Boolean fractions (also called conditional events or
conditional propositions). This system of ordered pairs (A|B) of events A, B,
can express all of the non-Boolean aspects of quantum logic without having to
resort to a more abstract formulation like Hilbert space. Such notions as
orthogonality, superposition, simultaneous verifiability, compatibility,
orthoalgebras, orthocomplementation, modularity, and the Sasaki projection
mapping are translated into this conditional event framework and their forms
exhibited. These concepts turn out to be quite adequately expressed in this
near-Boolean framework thereby allowing more natural, intuitive interpretations
of quantum phenomena. Results include showing that two conditional propositions
are simultaneously verifiable just in case the truth of one implies the
applicability of the other. Another theorem shows that two conditional
propositions (a|b) and (c|d) reside in a common Boolean sub-algebra of the
non-distributive system of conditional propositions just in case b=d, that
their conditions are equivalent. Some concepts equivalent in standard
formulations of quantum logic are distinguishable in the conditional event
algebra, indicating the greater richness of expression possible with Boolean
fractions. Logical operations and deductions in the linear subspace logic of
quantum mechanics are compared with their counterparts in the conditional event
realm. Disjunctions and implications in the quantum realm seem to correspond in
the domain of Boolean fractions to previously identified implications with
respect to various naturally arising deductive relations.


title: Quantum channels with a finite memory

abstract:
  In this paper we study quantum communication channels with correlated noise
effects, i.e., quantum channels with memory. We derive a model for correlated
noise channels that includes a channel memory state. We examine the case where
the memory is finite, and derive bounds on the classical and quantum
capacities. For the entanglement-assisted and unassisted classical capacities
it is shown that these bounds are attainable for certain classes of channel.
Also, we show that the structure of any finite memory state is unimportant in
the asymptotic limit, and specifically, for a perfect finite-memory channel
where no nformation is lost to the environment, achieving the upper bound
implies that the channel is asymptotically noiseless.


title:
Measurement-induced decoherence and Gaussian smoothing of the Wigner
  distribution function

abstract:
  We study the problem of measurement-induced decoherence using the phase-space
approach employing the Gaussian-smoothed Wigner distribution function. Our
investigation is based on the notion that measurement-induced decoherence is
represented by the transition from the Wigner distribution to the
Gaussian-smoothed Wigner distribution with the widths of the smoothing function
identified as measurement errors. We also compare the smoothed Wigner
distribution with the corresponding distribution resulting from the classical
analysis. The distributions we computed are the phase-space distributions for
simple one-dimensional dynamical systems such as a particle in a square-well
potential and a particle moving under the influence of a step potential, and
the time-frequency distributions for high-harmonic radiation emitted from an
atom irradiated by short, intense laser pulses.


title:
Wigner distributions and quantum mechanics on Lie groups: the case of
  the regular representation

abstract:
  We consider the problem of setting up the Wigner distribution for states of a
quantum system whose configuration space is a Lie group. The basic properties
of Wigner distributions in the familiar Cartesian case are systematically
generalised to accommodate new features which arise when the configuration
space changes from $n$-dimensional Euclidean space ${\cal R}^n$ to a Lie group
$G$. The notion of canonical momentum is carefully analysed, and the meanings
of marginal probability distributions and their recovery from the Wigner
distribution are clarified. For the case of compact $G$ an explicit definition
of the Wigner distribution is proposed, possessing all the required properties.
Geodesic curves in $G$ which help introduce a notion of the `mid point' of two
group elements play a central role in the construction.


title: Universal control of quantum subspaces and subsystems

abstract:
  We describe a broad dynamical-algebraic framework for analyzing the quantum
control properties of a set of naturally available interactions. General
conditions under which universal control is achieved over a set of
subspaces/subsystems are found. All known physical examples of universal
control on subspaces/systems are related to the framework developed here.


title: Generation and Evolution of Spin Entanglement in NRQED

abstract:
  A complete analysis on the generation of spin entanglement from NRQED is
presented. The results of entanglement are obtained with relativistic
correction to the leading order of (v/c)^2. It is shown that to this order the
degree of entanglement of a singlet state does not change under time evolution
whereas the triplet state can change.


title:
One-dimensional scattering problem, self-adjoint extensions,
  renormalizations and point $\delta$-interactions for Coulomb potential

abstract:
  In the paper the one-dimensional one-center scattering problem with the
initial potential $\alpha |x|^{-1}$ on the whole axis is treated and reduced to
the search for allowable self-adjoint extensions. Using the laws of
conservation as necessary conditions in the singular point alongside with
account of the analytical structure of fundamental solutions, it allows us to
receive exact expressions for the wave functions (i.e. for the boundary
conditions), scattering coefficients and the singular corrections to the
potential, as well as the corresponding bound state spectrum. It turns out that
the point $\delta$-shaped correction to the potential should be present without
fail at any choice of the allowable self-adjoint extension, moreover a form of
these corrections corresponds to the form of renormalization terms obtained in
quantum electrodynamics. Thus, the proposed method shows the unequivocal
connection among the boundary conditions, scattering coefficients and
$\delta$-shaped additions to the potential. Taken as a whole, the method
demonstrates the opportunities which arise at the analysis of the self-adjoint
extensions of the appropriate Hamilton operator. And as it concerns the
renormalization theory, the method can be treated as a generalization of the
Bogoliubov, Parasiuk and Hepp method of renormalizations.


title:
Partially separable criterion and classification of states in
  multipartite systems with an arbitrary finite number of qubits

abstract:
  After introducing the partially separable concept, we proved the equivalence
between the partial separability of a given $m$-partite subsystem with $m$
qubits and the purity of states of this $m$-partite subsystem for a pure state
in multipartite systems with arbitrary finite $n(>m)$ qubits. Furthermore, we
give out the operational realizations (corollaries) of our theorem, which are
the sufficient and necessary criterions of partial separability of states and
can be used to classification of states. Our results are helpful to understand
and describe quantum entanglement in multipartite systems.


title: Quantum computer: an appliance for playing market games

abstract:
  Recent development in quantum computation and quantum information theory
allows to extend the scope of game theory for the quantum world. The authors
have recently proposed a quantum description of financial market in terms of
quantum game theory. The paper contain an analysis of such markets that shows
that there would be advantage in using quantum computers and quantum
strategies.


title: Tomographic Quantum Cryptography

abstract:
  We present a protocol for quantum cryptography in which the data obtained for
mismatched bases are used in full for the purpose of quantum state tomography.
Eavesdropping on the quantum channel is seriously impeded by requiring that the
outcome of the tomography is consistent with unbiased noise in the channel. We
study the incoherent eavesdropping attacks that are still permissible and
establish under which conditions a secure cryptographic key can be generated.
The whole analysis is carried out for channels that transmit quantum systems of
any finite dimension.


title: Quantum measurement of the degree of polarization of a light beam

abstract:
  We demonstrate a coherent quantum measurement for the determination of the
degree of polarization (DOP). This method allows to measure the DOP in the
presence of fast polarization state fluctuations, difficult to achieve with the
typically used polarimetric technique. A good precision of the DOP measurements
is obtained using 8 type II nonlinear crystals assembled for spatial walk-off
compensation.


title:
Reply to: Comment on "Bohmian prediction about a two double-slit
  experiment and its disagreement with SQM"

abstract:
  In a recent paper, Struyve et al. [Struyve W, De Baere W, De Neve J and De
Weirdt S 2003 J. Phys. A 36 1525] attempted to show that the thought experiment
proposed in [Golshani M and Akhavan O 2001 J. Phys. A 34 5259,
quant-ph/0103101] cannot distinguish between standard and Bohmian quantum
mechanics. Here, we want to show that, in spite of their objection, our
conclusion still holds out.


title: Space-Filling Curves for Quantum Control Parameters

abstract:
  We consider the use of space-filling curves (SFC) in scanning control
parameters for quantum chemical systems. First we show that a formally exact
SFC must be singular in the control parameters, but a finite discrete
generalization can be used with no problem. We then make general observations
about the relevance of SFCs in preference to linear scans of the parameters.
Finally we present a simple magnetic field example relevant in NMR and show
from the calculated autocorrelations that a SFC Peano-Hilbert curve gives a
smoother sequence than a linear scan.


title: Distributed construction of quantum fingerprints

abstract:
  Quantum fingerprints are useful quantum encodings introduced by Buhrman,
Cleve, Watrous, and de Wolf (Physical Review Letters, Volume 87, Number 16,
Article 167902, 2001; quant-ph/0102001) in obtaining an efficient quantum
communication protocol. We design a protocol for constructing the fingerprint
in a distributed scenario. As an application, this protocol gives rise to a
communication protocol more efficient than the best known classical protocol
for a communication problem.


title: A subsystem-independent generalization of entanglement

abstract:
  We introduce a generalization of entanglement based on the idea that
entanglement is relative to a distinguished subspace of observables rather than
a distinguished subsystem decomposition. A pure quantum state is entangled
relative to such a subspace if its expectations are a proper mixture of those
of other states. Many information-theoretic aspects of entanglement can be
extended to the general setting, suggesting new ways of measuring and
classifying entanglement in multipartite systems. By going beyond the
distinguishable-subsystem framework, generalized entanglement also provides
novel tools for probing quantum correlations in interacting many-body systems.


title:
Quantum information isomorphism: beyond the dillemma of Scylla of
  ontology and Charybdis of instrumentalism

abstract:
  In order to have the most safe way of dealing with unanalysable quantum whole
the Copenhagen interpretation takes as a "frame of reference" the preparation
parameters and outcomes of the measurements. It represents {\it passive}
Ptolemean-like instrumentalism directly related to "what we see in the sky"
i.e. to the "surface" of the things. However the notion of quantum information
leads to {\it active} Copernican-like realism which involves (intrinsic)
ordering principle and thinking about the whole as being analysable. One dares
then to consider subsystems as localised in space, controlled individually, and
communicated. This makes natural treating quantum information (quantum states)
as by no means merely knowledge. Moreover it involves complementarity between
local and nonlocal information. To avoid dilemma between Scylla of ontology and
Charybdis of instrumentalism, the concept of {\it quantum information
isomorphism} is proposed according to which quantum description of Nature and
their mathematical representation. By definition it is not only just one-to-one
mapping, but it preserves the structure. It allows, in particular, to treat the
"wave function" as isomorphic image of what we are processing in laboratories
implying that quantum information is indeed carried by the quantum systems.


title: Decoherence, Control, and Symmetry in Quantum Computers

abstract:
  In this thesis we describe methods for avoiding the detrimental effects of
decoherence while at the same time still allowing for computation of the
quantum information. The philosophy of the method discussed in the first part
of this thesis is to use a symmetry of the decoherence mechanism to find robust
encodings of the quantum information. Stability, control, and methods for using
decoherence-free information in a quantum computer are presented with a
specific emphasis on decoherence due to a collective coupling between the
system and its environment. Universal quantum computation on such collective
decoherence decoherence-free encodings is demonstrated. Rigorous definitions of
control and the use of encoded universality in quantum computers are addressed.
Explicit gate constructions for encoded universality on ion trap and exchange
based quantum computers are given. In the second part of the thesis we examine
physical systems with error correcting properties. We examine systems that can
store quantum information in their ground state such that decoherence processes
are prohibited via energetics. We present the theory of supercoherent systems
whose ground states are quantum error detecting codes and describe a spin
ladder whose ground state has both the error detecting and correcting
properties. We conclude by discussing naturally fault-tolerant quantum
computation.


title: What is random about a quantum random walk?

abstract:
  We use simple deterministic dynamical systems as coins in studying quantum
walks. These dynamical systems can be chosen to display, in the classical
limit, a range of behaviors from the integrable to chaotic, or
deterministically random. As an example of an integrable coin we study the
Fourier walk that generalizes the Hadamard walk and show that the walker slows
down with coin dimensionality, which controls the effective Planck constant.
Introducing multi-Harper maps as deterministic models of random walks we study
the effect of coin chaos on the quantum walk. We also demonstrate that breaking
time-reversal symmetry in the coin dynamics effectively slows down the walk.


title: The Stark effect in the charge-dyon system

abstract:
  The linear Stark effect in the MIC-Kepler problem describing the interaction
of charged particle with Dirac's dyon is considered. It is shown that constant
homogeneous electric field completely removes the degeneracy of the energy
levels on azimuth quantum number


title: Polynomial degree vs. quantum query complexity

abstract:
  The degree of a polynomial representing (or approximating) a function f is a
lower bound for the number of quantum queries needed to compute f. This
observation has been a source of many lower bounds on quantum algorithms. It
has been an open problem whether this lower bound is tight.
  We exhibit a function with polynomial degree M and quantum query complexity
\Omega(M^{1.321...}). This is the first superlinear separation between
polynomial degree and quantum query complexity. The lower bound is shown by a
new, more general version of quantum adversary method.


title: Quantum Computational Logics. A Survey

abstract:
  Quantum computation has suggested new forms of quantum logic, called quantum
computational logics. The basic semantic idea is the following: the meaning of
a sentence is identified with a quregister, a system of qubits, representing a
possible pure state of a compound quantum system. The generalization to mixed
states, which might be useful to analyse entanglement-phenomena, is due to
Gudder. Quantum computational logics represent non standard examples of unsharp
quantum logic, where the non-contradiction principle is violated, while
conjunctions and disjunctions are strongly non-idempotent. In this framework,
any sentence of the language gives rise to a quantum tree: a kind of quantum
circuit that transforms the quregister associated to the atomic subformulas of
the sentence into the quregister associated to the sentence.


title: Quantum Approximation I. Embeddings of Finite Dimensional L_p Spaces

abstract:
  We study approximation of embeddings between finite dimensional L_p spaces in
the quantum model of computation. For the quantum query complexity of this
problem matching (up to logarithmic factors) upper and lower bounds are
obtained. The results show that for certain regions of the parameter domain
quantum computation can essentially improve the rate of convergence of
classical deterministic or randomized approximation, while there are other
regions where the best possible rates coincide for all three settings. These
results serve as a crucial building block for analyzing approximation in
function spaces in a subsequent paper.


title: Quantum Approximation II. Sobolev Embeddings

abstract:
  A basic problem of approximation theory, the approximation of functions from
the Sobolev space W_p^r([0,1]^d) in the norm of L_q([0,1]^d), is considered
from the point of view of quantum computation. We determine the quantum query
complexity of this problem (up to logarithmic factors). It turns out that in
certain regions of the domain of parameters p,q,r,d quantum computation can
reach a speedup of roughly squaring the rate of convergence of classical
deterministic or randomized approximation methods. There are other regions were
the best possible rates coincide for all three settings.


title: Deformed Heisenberg algebra: origin of q-calculus

abstract:
  The intimate connection between q-deformed Heisenberg uncertainty relation
and the Jackson derivative based on q-basic numbers has been noted in the
literature. The purpose of this work is to establish this connection in a clear
and self-consistent formulation and to show explicitly how the Jackson
derivative arises naturally. We utilize a holomorphic representation to arrive
at the correct algebra to describe q-deformed bosons. We investigate the
algebra of q-fermions and point out how different it is from the theory of
q-bosons. We show that the holomorphic representation for q-fermions is indeed
feasible in the framework of the theory of generalized fermions. We also
examine several different q-algebras in the context of the modified Heisenberg
equation of motion.


title: Observation of Lasing Mediated by Collective Atomic Recoil

abstract:
  We observe the buildup of a frequency-shifted reverse light field in a
unidirectionally pumped high-$Q$ optical ring cavity serving as a dipole trap
for cold atoms. This effect is enhanced and a steady state is reached, if via
an optical molasses an additional friction force is applied to the atoms. We
observe the displacement of the atoms accelerated by momentum transfer in the
backscattering process and interpret our observations in terms of the
collective atomic recoil laser. Numerical simulations are in good agreement
with the experimental results.


title: Generation of inequivalent generalized Bell bases

abstract:
  The notion of equivalence of maximally entangled bases of bipartite
d-dimensional Hilbert spaces is introduced. An explicit method of inequivalent
bases construction is presented.


title: Equivalence of Additivity Questions in Quantum Information Theory

abstract:
  We reduce the number of open additivity problems in quantum information
theory by showing that four of them are equivalent. We show that the
conjectures of additivity of the minimum output entropy of a quantum channel,
additivity of the Holevo expression for the classical capacity of a quantum
channel, additivity of the entanglement of formation, and strong
superadditivity of the entanglement of formation, are either all true or all
false.


title:
Spectral Dependence of Coherent Backscattering of Light in a
  Narrow-Resonance Atomic System

abstract:
  We report a combined theoretical and experimental study of the spectral and
polarization dependence of near resonant radiation coherently backscattered
from an ultracold gas of 85Rb atoms. Measurements in an approximately 6 MHz
range about the 5s^{2}S_{1/2}- 5p^{2}P_{3/2}, F=3 - F'=4 hyperfine transition
are compared with simulations based on a realistic model of the experimental
atomic density distribution. In the simulations, the influence of heating of
the atoms in the vapor, magnetization of the vapor, finite spectral bandwidth,
and other nonresonant hyperfine transitions are considered. Good agreement is
found between the simulations and measurements.


title: Exclusion of Time in Mermin's Proof of Bell-Type Inequalities

abstract:
  Mermin states that his nontechnical version of Bell's theorem stands and is
not invalidated by time and setting dependent instrument parameters as claimed
in one of our previous papers. We identify deviations from well-established
protocol in probability theory as well as mathematical contradictions in
Mermin's argument and show that Mermin's conclusions are therefore not valid:
his proof does not go forward if certain possible time dependencies are taken
into account.


title:
Quantum phase estimation algorithms with delays: effects of dynamical
  phases

abstract:
  The unavoidable finite time intervals between the sequential operations
needed for performing practical quantum computing can degrade the performance
of quantum computers. During these delays, unwanted relative dynamical phases
are produced due to the free evolution of the superposition wave-function of
the qubits. In general, these coherent "errors" modify the desired quantum
interferences and thus spoil the correct results, compared to the ideal
standard quantum computing that does not consider the effects of delays between
successive unitary operations. Here, we show that, in the framework of the
quantum phase estimation algorithm, these coherent phase "errors", produced by
the time delays between sequential operations, can be avoided by setting up the
delay times to satisfy certain matching conditions.


title:
Effects of dynamical phases in Shor's factoring algorithm with
  operational delays

abstract:
  Ideal quantum algorithms usually assume that quantum computing is performed
continuously by a sequence of unitary transformations. However, there always
exist idle finite time intervals between consecutive operations in a realistic
quantum computing process. During these delays, coherent "errors" will
accumulate from the dynamical phases of the superposed wave functions. Here we
explore the sensitivity of Shor's quantum factoring algorithm to such errors.
Our results clearly show a severe sensitivity of Shor's factorization algorithm
to the presence of delay times between successive unitary transformations.
Specifically, in the presence of these {\it coherent "errors"}, the probability
of obtaining the correct answer decreases exponentially with the number of
qubits of the work register. A particularly simple phase-matching approach is
proposed in this paper to {\it avoid} or suppress these {\it coherent errors}
when using Shor's algorithm to factorize integers. The robustness of this
phase-matching condition is evaluated analytically or numerically for the
factorization of several integers: $4, 15, 21$, and 33.


title: Fast Non-Adiabatic Two Qubit Gates for the Kane Quantum Computer

abstract:
  In this paper we apply the canonical decomposition of two qubit unitaries to
find pulse schemes to control the proposed Kane quantum computer. We explicitly
find pulse sequences for the CNOT, swap, square root of swap and controlled Z
rotations. We analyze the speed and fidelity of these gates, both of which
compare favorably to existing schemes. The pulse sequences presented in this
paper are theoretically faster, higher fidelity, and simpler than existing
schemes. Any two qubit gate may be easily found and implemented using similar
pulse sequences. Numerical simulation is used to verify the accuracy of each
pulse scheme.


title:
Broadband Geodesic Pulses for Three Spin Systems: Time-Optimal
  Realization of Effective Trilinear Coupling Terms and Indirect SWAP Gates

abstract:
  Broadband implementations of time-optimal geodesic pulse elements are
introduced for the efficient creation of effective trilinear coupling terms for
spin systems consisting of three weakly coupled spins 1/2. Based on these pulse
elements, the time-optimal implementation of indirect SWAP operations is
demonstrated experimentally. The duration of indirect SWAP gates based on
broadband geodesic sequence is reduced by 42.3% compared to conventional
approaches.


abstract:
  Comment on "Quantum Interferometric Optical Lithography: Exploiting
Entanglement to Beat the Diffraction Limit"
  The effective absorption rates in quantum lithography are very low.


title: Degree of entanglement for two qutrits in a pure state

abstract:
  In this paper, a new measure of entanglement for general pure bipartite
states of two qutrits is formulated.


title: Output state in multiple entanglement swapping

abstract:
  The technique of quantum repeaters is a promising candidate for sending
quantum states over long distances through a lossy channel. The usual
discussions of this technique deals with only a finite dimensional Hilbert
space. However the qubits with which one implements this procedure will "ride"
on continuous degrees of freedom of the carrier particles. Here we analyze the
action of quantum repeaters using a model based on pulsed parametric down
conversion entanglement swapping. Our model contains some basic traits of a
real experiment. We show that the state created, after the use of any number of
parametric down converters in a series of entanglement swappings, is always an
entangled (actually distillable) state, although of a different form than the
one that is usually assumed. Furthermore, the output state always violates a
Bell inequality.


title: Quantum Computation explained to my Mother

abstract:
  There are many falsely intuitive introductions to quantum theory and quantum
computation in a handwave. There are also numerous documents which teach those
subjects in a mathematically sound manner. To my knowledge this paper is the
shortest of the latter category. The aim is to deliver a short yet rigorous and
self-contained introduction to Quantum Computation, whilst assuming the reader
has no prior knowledge of anything but the fundamental operations on real
numbers. Successively I introduce complex matrices; the postulates of quantum
theory and the simplest quantum algorithm. The document originates from a fifty
minutes talk addressed to a non-specialist audience, in which I sought to take
the shortest mathematical path that proves a quantum algorithm right.


title: Entangling power of the quantum baker's map

abstract:
  We investigate entanglement production in a class of quantum baker's maps.
The dynamics of these maps is constructed using strings of qubits, providing a
natural tensor-product structure for application of various entanglement
measures. We find that, in general, the quantum baker's maps are good at
generating entanglement, producing multipartite entanglement amongst the qubits
close to that expected in random states. We investigate the evolution of
several entanglement measures: the subsystem linear entropy, the concurrence to
characterize entanglement between pairs of qubits, and two proposals for a
measure of multipartite entanglement. Also derived are some new analytical
formulae describing the levels of entanglement expected in random pure states.


title:
The non-Markovian stochastic Schr\"odinger equation for the position
  unraveling

abstract:
  An important and well established area of quantum optics is the theory of
Markovian stochastic Schr\"odinger equations (or by another name quantum
trajectory theory). Recently stochastic Schr\"odinger equations have been
developed for non-Markovian systems. In this paper we extend the current known
stochastic Schr\"odinger equations for non-Markovian systems to include the
position unraveling. We also discuss and illustrate that this stochastic
Schr\"odinger equation can have an interpretation under both the orthodox and
the de Broglie-Bohm hidden variable interpretation of quantum mechanics. We
conclude that only the de Broglie-Bohm hidden variable theory provides a
continuous-in-time interpretation of the non-Markovian stochastic Schr\"odinger
equation.


title:
Entanglement formation and violation of Bell's inequality with a
  semiconductor single photon source

abstract:
  We report the generation of polarization-entangled photons, using a quantum
dot single photon source, linear optics and photodetectors. Two photons created
independently are observed to violate Bell's inequality. The density matrix
describing the polarization state of the postselected photon pairs is also
reconstructed, and agrees well with a simple model predicting the quality of
entanglement from the known parameters of the single photon source. Our scheme
provides a method to generate no more than one entangled photon pair per cycle,
a feature useful to enhance quantum cryptography protocols using entangled
photons.


title: Remarks on the Theory of Angular Momenta

abstract:
  A rigorous application of the correspondence rules shows that the operator of
the angular momentum of a quantum particle---corresponding to the classical
magnitude $\mathbf{l}= m \mathbf{r} \wedge \mathbf{v}$---is given by
$\mathbf{\hat{l}}=\mathbf{r}\wedge(-i\hbar\mathbf{\nabla}
-\frac{e}{c}\mathbf{A})$ in the presence of an electromagnetic field. Thus,
despite the general opinion on the corresponding rules of quantization, the
eigenvalues of the angular momentum depend on the configuration of the
electromagnetic field. The usual rules of commutation
$[{\hat{l}}_i,{\hat{l}}_j]=i\hbar\epsilon_{ijk}{\hat{l}}_k$, that are at the
foundation of the calculus of angular momentum and of the theory of
\emph{spin}---and Bohm's example of the EPR argument---are not valid in the
presence of an electromagnetic field. The expected value of the operator
$\mathbf{\hat{l}}=-i\hbar\mathbf{r}\wedge\mathbf{\nabla}$ is not gauge
invariant, it depends on the calibration of the electrodynamic potentials.


title: Identity check is QMA-complete

abstract:
  We define the problem identity check: Given a classical description of a
quantum circuit, determine whether it is almost equivalent to the identity.
Explicitly, the task is to decide whether the corresponding unitary is close to
a complex multiple of the identity matrix with respect to the operator norm. We
show that this problem is QMA-complete.
  A generalization of this problem is equivalence check: Given two descriptions
of quantum circuits and a description of a common invariant subspace, decide
whether the restrictions of the circuits to this subspace almost coincide. We
show that equivalence check is also in QMA and hence QMA-complete.


title:
Temperature inversion symmetry in the Casimir effect with an
  antiperiodic boundary condition

abstract:
  We present explicitly another example of a temperature inversion symmetry in
the Casimir effect for a nonsymmetric boundary condition. We also give an
interpretation for our result.


title:
Implementation of controlled multi-qudit operations for a solid-state
  quantum computer based on charge qudits

abstract:
  We consider a mechanism to generate controllable qudit-qudit interactions in
a charge-position paradigm for a quantum computer, through the use of auxiliary
states. By controlling the tunneling rates onto these auxiliaries from the
qudits proper, we can controllably switch the entangling operations. We
consider a practical architecture in which to realize such a computer and
examine the associated Hilbert space dimension.


title: Introduction to Quantum Computers and Quantum Algorithms

abstract:
  This is a short introduction to Quantum Computing intended for physicists.
The basic idea of a quantum computer is introduced. Then we concentrate on
Shor's integer factoring algorithm.


title:
An experimental observation of geometric phases for mixed states using
  NMR interferometry

abstract:
  Examples of geometric phases abound in many areas of physics. They offer both
fundamental insights into many physical phenomena and lead to interesting
practical implementations. One of them, as indicated recently, might be an
inherently fault-tolerant quantum computation. This, however, requires to deal
with geometric phases in the presence of noise and interactions between
different physical subsystems. Despite the wealth of literature on the subject
of geometric phases very little is known about this very important case. Here
we report the first experimental study of geometric phases for mixed quantum
states. We show how different they are from the well understood, noiseless,
pure-state case.


title:
Autler-Townes spectroscopy of the $5S_{1/2}-5P_{3/2}-44D$ cascade of
  cold $^{85}$Rb atoms

abstract:
  We study nonlinear optical effects in the laser excitation of Rydberg states.
$5S_{1/2}$ and $5P_{3/2}$ levels of $^{85}$Rb are strongly coupled by a strong
laser field and probed by a weak laser tuned to the $5P_{3/2} - 44D$ Rydberg
resonance. We observe high contrast Autler-Townes spectra which are dependent
on the pump polarization, intensity and detuning. The observed behavior agrees
with calculations, which include the effect of optical pumping.


title:
Strong superadditivity of the entanglement of formation follows from its
  additivity

abstract:
  The additivity of both the entanglement of formation and the classical
channel capacity is known to be a consequence of the strong superadditivity
conjecture. We show that, conversely, the strong superadditivity conjecture
follows from the additivity of the entanglement of formation; this means that
the two conjectures are equivalent and that the additivity of the classical
channel capacity is a consequence of them.


title:
Exact solutions to the time-dependent supersymmetric muliphoton
  Jaynes-Cummings model and the Chiao-Wu model

abstract:
  By using both the Lewis-Riesenfeld invariant theory and the invariant-related
unitary transformation formulation, the present paper obtains the exact
solutions to the time-dependent supersymmetric two-level multiphoton
Jaynes-Cummings model and the Chiao-Wu model that describes the propagation of
a photon inside the optical fiber. On the basis of the fact that the two-level
multiphoton Jaynes-Cummings model possesses the supersymmetric structure, an
invariant is constructed in terms of the supersymmetric generators by working
in the sub-Hilbert-space corresponding to a particular eigenvalue of the
conserved supersymmetric generators (i.e., the time-independent invariant). By
constructing the effective Hamiltonian that describes the interaction of the
photon with the medium of the optical fiber, it is further verified that the
particular solution to the Schr\"{o}dinger equation is the eigenfunction of the
second-quantized momentum operator of photons field. This, therefore, means
that the explicit expression (rather than the hidden form that involves the
chronological product) for the time-evolution operator of wave function is
obtained by means of the invariant theories.


title: Quantum two and three person duels

abstract:
  In game theory, a popular model of a struggle for survival among three
competing agents is a truel, or three person generalization of a duel. Adopting
the ideas recently developed in quantum game theory, we present a quantum
scheme for the problems of duels and truels. In the classical case, the outcome
is sensitive to the precise rules under which the truel is performed and can be
counter intuitive. These aspects carry over into our quantum scheme, but
interference amongst the players' strategies can arise, leading to game
equilibria different from the classical case.


title: Bounds on general entropy measures

abstract:
  We show how to determine the maximum and minimum possible values of one
measure of entropy for a given value of another measure of entropy. These
maximum and minimum values are obtained for two standard forms of probability
distribution (or quantum state) independent of the entropy measures, provided
the entropy measures satisfy a concavity/convexity relation. These results may
be applied to entropies for classical probability distributions, entropies of
mixed quantum states and measures of entanglement for pure states.


title:
Quantum computing with an inhomogeneously broadened ensemble of ions:
  Suppression of errors from detuning variations by specially adapted pulses
  and coherent population trapping

abstract:
  The proposal for quantum computing with rare-earth-ion qubits in inorganic
crystals makes use of the inhomogeneous broadening of optical transitions in
the ions to associate individual qubits with ions responding to radiation in
selected frequency channels. We show that a class of Gaussian composite pulses
and complex sech pulses provide accurate qubit pi-rotations, which are at the
same time channel selective on a 5 MHz frequency scale and tolerant to 0.5 MHz
deviations of the transition frequency of ions within a single channel.
Rotations in qubit space of arbitrary angles and phases are produced by
sequences of pi-pulses between the excited state of the ions and coherent
superpositions of the qubit states.


title: Classical trajectories and quantum tunneling

abstract:
  The problem of inter-band tunneling in a semiconductor (Zener breakdown) in a
nonstationary and homogeneous electric field is solved exactly. Using the exact
analytical solution, the approximation based on classical trajectories is
studied. A new mechanism of enhanced tunneling through static
non-one-dimensional barriers is proposed in addition to well known normal
tunneling solely described by a trajectory in imaginary time. Under certain
conditions on the barrier shape and the particle energy, the probability of
enhanced tunneling is not exponentially small even for non-transparent
barriers, in contrast to the case of normal tunneling.


title: Renyi extrapolation of Shannon entropy

abstract:
  Relations between Shannon entropy and Renyi entropies of integer order are
discussed. For any N-point discrete probability distribution for which the
Renyi entropies of order two and three are known, we provide an lower and an
upper bound for the Shannon entropy. The average of both bounds provide an
explicit extrapolation for this quantity. These results imply relations between
the von Neumann entropy of a mixed quantum state, its linear entropy and
traces.


title: A New Quantization Map

abstract:
  In this paper we find a simple rule to reproduce the algebra of quantum
observables using only the commutators and operators which appear in the
Koopman-von Neumann (KvN) formulation of classical mechanics. The usual Hilbert
space of quantum mechanics becomes embedded in the KvN Hilbert space: in
particular it turns out to be the subspace on which the quantum positions Q and
momenta P act irreducibly.


title: Fano resonances in the overlapping regime

abstract:
  The line shape of resonances in the overlapping regime is studied by using
the eigenvalues and eigenfunctions of the effective Hamiltonian of an open
quantum system. A generalized expression $\tilde q_k(E)$ for the Fano parameter
of the resonance state $k$ is derived that contains the interaction of the
state $k$ with neighboured states $l\ne k$ via the continuum. It is energy
dependent since the coupling coefficients between the state $k$ and the
continuum show a resonance-like behaviour at the energies of the neighboured
states $l\ne k$. Under certain conditions, the energy dependent $\tilde q_k(E)$
are equivalent to the generalized complex energy independent Fano parameters
that are introduced by Kobayashi et al. in analyzing experimental data.
Long-lived states appear mostly isolated from one another in the cross section,
also when they are overlapped by short-lived resonance states. The $\tilde
q_k(E)$ of narrow resonances allow therefore to study the complicated interplay
between different time scales in the regime of overlapping resonance states by
controlling them as a function of an external parameter.


title: Comment on Repulsive Casimir Forces

abstract:
  A recent theoretical calculation shows that the Casimir force between two
parallel plates can be repulsive for plates with nontrivial magnetic properties
(O. Kenneth et al., Phys. Rev. Lett. 89, 033001 (2002)). According to the
authors, the effect may be observed with known materials, such as ferrites and
garnets, and it might be possible to engineer micro- or nanoelectromechanical
systems (MEMS or NEMS) that could take advantage of a short range repulsive
force. Here we show that on the contrary the Casimir force between two parallel
plates in vacuum at micron and submicron distance is always attractive.


title: Relations between bosonic quadrature squeezing and atomic spin squeezing

abstract:
  We study relations between bosonic quadrature squeezing and atomic spin
squeezing, and find that the latter reduces to the former in the limit of a
large number of atoms for even and odd states. We demonstrate this reduction by
treating even and odd spin coherent states, for which analytical solutions are
readily obtained, and prove that even spin coherent states always exhibit spin
squeezing, whereas odd spin coherent states do not, analogous to the squeezing
characteristic of even and odd bosonic coherent states. Finally, we examine the
squeezing transfer between photons and atoms via the Dicke Hamiltonian, where a
perfect transfer of squeezing is demonstrated in the limit of a large number of
atoms.


title: Fabrication of micro-magnetic traps for cold neutral atoms

abstract:
  Many proposals for quantum information processing require precise control
over the motion of neutral atoms, as in the manipulation of coherent matter
waves or the confinement and localization of individual atoms. Patterns of
micron-sized wires, fabricated lithographically on a flat substrate, can
conveniently produce large magnetic-field gradients and curvatures to trap cold
atoms and to facilitate the production of Bose-Einstein condensates. This paper
describes tools and techniques for the construction of such devices.


title: The Schrodinger-HJW Theorem

abstract:
  A concise presentation of Schrodinger's ancilla theorem (1936 Proc. Camb.
Phil. Soc. 32, 446) and its several recent rediscoveries.


title:
Reply to the Comment on ``On the uncertainty relations and squeezed
  states for the quantum mechanics on a circle''

abstract:
  In the preceding Comment (quant-ph/0209032) Trifonov disputes our recently
proposed uncertainty relations for a quantum particle on a circle. He states
that (i) the quantity $\Delta^2(\hat\phi)$ introduced by us representing the
uncertainty of the angle is not a proper measure of the position uncertainty
and therefore the proposed inequalities can hardly be qualified as a relevant
uncertainty relations on a circle; and that (ii) the most suitable uncertainty
relations on a circle are those based on the Gram-Robertson matrix. It is shown
by examples that both points are erroneous.


title: Decoherence of cold atomic gases in magnetic micro-traps

abstract:
  We derive a model to describe decoherence of atomic clouds in atom-chip traps
taking the excited states of the trapping potential into account. We use this
model to investigate decoherence for a single trapping well and for a pair of
trapping wells that form the two arms of an atom interferometer. Including the
discrete spectrum of the trapping potential gives rise to a decoherence
mechanism with a decoherence rate $\Gamma$ that scales like $\Gamma \sim
1/r_0^4$ with the distance $r_0$ from the trap minimum to the wire.


title:
Bell's inequality violation due to misidentification of spatially non
  stationary random processes

abstract:
  Correlations for the Bell gedankenexperiment are constructed using
probabilities given by quantum mechanics, and nonlocal information. They
satisfy Bell's inequality and exhibit spatial non stationarity in angle.
Correlations for three successive local spin measurements on one particle are
computed as well. These correlations also exhibit non stationarity, and satisfy
the Bell inequality. In both cases, the mistaken assumption that the underlying
process is wide-sense-stationary in angle results in violation of Bell's
inequality. These results directly challenge the wide-spread belief that
violation of Bell's inequality is a decisive test for nonlocality.


title: A neural-network-like quantum information processing system

abstract:
  The Hopfield neural networks and the holographic neural networks are models
which were successfully simulated on conventional computers. Starting with
these models, an analogous fundamental quantum information processing system is
developed in this article. Neuro-quantum interaction can regulate the
"collapse"-readout of quantum computation results. This paper is a
comprehensive introduction into associative processing and memory-storage in
quantum-physical framework.


title: The Signals and Systems Approach to Quantum Computation

abstract:
  In this note we point out the fact that the proper conceptual setting of
quantum computation is the theory of Linear Time Invariant systems. To convince
readers of the utility of the approach, we introduce a new model of computation
based on the orthogonal group. This makes the link to traditional electronics
engineering clear. We conjecture that the speed up achieved in quantum
computation is at the cost of increased circuit complexity.


title:
Two Photon Anti-Coalescence Interference: the Signature of Two Photon
  Entanglement

abstract:
  We study a general theory on the interference of two-photon wavepacket in a
beam splitter. We find that the symmetry of two-photon spectrum plays an
important role in the manners of interference. We distinguish the coalescence
and anti-coalescence interferences, and prove that the anti-coalescence
interference is the signature of photon entanglement.


title:
Optimal atomic detection by control of detuning and spatial dependence
  of laser intensity

abstract:
  Atomic detection by fluorescence may fail because of reflection from the
laser or transmission without excitation. The detection probability for a given
velocity range may be improved by controlling the detuning and the spatial
dependence of the laser intensity. A simple optimization method is discussed
and exemplified.


title: Vulnerabilities in Quantum Key Distribution Protocols

abstract:
  Recently proposed quantum key distribution protocols are shown to be
vulnerable to a classic man-in-the-middle attack using entangled pairs created
by Eve. It appears that the attack could be applied to any protocol that relies
on manipulation and return of entangled qubits to create a shared key. The
protocols that are cryptanalyzed in this paper were proven secure with respect
to some eavesdropping approaches, and results reported here do not invalidate
these proofs. Rather, they suggest that quantum cryptographic protocols, like
conventional protocols, may be vulnerable to methods of attack that were not
envisaged by their designers.


title:
Improved scheme for generation of vibrational trio coherent states of a
  trapped ion

abstract:
  We improve a previously proposed scheme (Phys. Rev. A 66 (2002) 065401) for
generating vibrational trio coherent states of a trapped ion. The improved
version is shown to gain a double advantage: (i) it uses only five, instead of
eight, lasers and (ii) the generation process can be made remarkably faster.


title: Qubit Disentanglement and Decoherence via Dephasing

abstract:
  We consider whether quantum coherence in the form of mutual entanglement
between a pair of qubits is susceptible to decay that may be more rapid than
the decay of the coherence of either qubit individually. An instance of
potential importance for solid state quantum computing arises if embedded
qubits (spins, quantum dots, Cooper pair boxes, etc.) are exposed to global and
local noise at the same time. Here we allow separate phase-noisy channels to
affect local and non-local measures of system coherence. We find that the time
for decay of the qubit entanglement can be significantly shorter than the time
for local dephasing of the individual qubits.


title: Pathways to non-sequential multiple ionization in strong laser fields

abstract:
  The outgoing electrons in non-sequential multiple ionization in intense laser
fields are strongly correlated. The correlations can be explained within a
classical model for interacting electrons in the presence of the external
field. Here we extend the previous analysis for two and three electrons to
cases with up to eight electrons and identify the saddle configurations that
guard the channels for non-sequential multiple ionization. For four and fewer
electrons the electrons in the dominant configuration are equivalent, for six
and more electrons this is no longer the case. The case of five electrons is
marginal, with two almost degenerate transition configurations. The total
number of configurations increases rapidly, from 2 configurations for three
electrons up to 26 configurations for eight electrons.


title:
Separability of rank two quantum states on multiple quantum spaces with
  different dimensions

abstract:
  We consider the separability of rank two quantum states on multiple quantum
spaces with different dimensions. The sufficient and necessary conditions for
separability of these multiparty quantum states are explicitly presented. A
nonseparability inequality is also given, for the case where one of the
eigenvectors corresponding to nonzero eigenvalues of the density matrix is
maximally entangled.


title: Quantum Mechanics in a Rotating Frame

abstract:
  The rotating frame is considered in quantum mechanics on the basis of the
position dependent boost relating this frame to the non rotating inertial
frame. We derive the Sagnac phase shift and the spin coupling with the rotation
in the non relativistic limit by a simple treatment. By taking the low energy
limit of the Dirac equation with a spin connection, we obtain the Hamiltonian
for the rotating frame, which gives rise to all the phase shifts discussed
before. Furthermore, we obtain a new phase shift due to the spin-orbit
coupling.


title: Measurement-induced Nonlinearity in Linear Optics

abstract:
  We investigate the generation of nonlinear operators with single photon
sources, linear optical elements and appropriate measurements of auxiliary
modes. We provide a framework for the construction of useful single-mode and
two-mode quantum gates necessary for all-optical quantum information
processing. We focus our attention generally on using minimal physical
resources while providing a transparent and algorithmic way of constructing
these operators.


title:
Measuring Pancharatnam's relative phase for SO(3) evolutions using spin
  polarimetry

abstract:
  In polarimetry, a superposition of internal quantal states is exposed to a
single Hamiltonian and information about the evolution of the quantal states is
inferred from projection measurements on the final superposition. In this
framework, we here extend the polarimetric test of Pancharatnam's relative
phase for spin$-{1/2}$ proposed by Wagh and Rakhecha [Phys. Lett. A {\bf 197},
112 (1995)] to spin $j\geq 1$ undergoing noncyclic SO(3) evolution. We
demonstrate that the output intensity for higher spin values is a polynomial
function of the corresponding spin$-{1/2}$ intensity. We further propose a
general method to extract the noncyclic SO(3) phase and visibility by rigid
translation of two $\pi /2$ spin flippers. Polarimetry on higher spin states
may in practice be done with spin polarized atomic beams.


title:
Decoherence of Histories and Hydrodynamic Equations for a Linear
  Oscillator Chain

abstract:
  We investigate the decoherence of histories of local densities for linear
oscillators models. It is shown that histories of local number, momentum and
energy density are approximately decoherent, when coarse-grained over
sufficiently large volumes. Decoherence arises directly from the proximity of
these variables to exactly conserved quantities (which are exactly decoherent),
and not from environmentally-induced decoherence. We discuss the approach to
local equilibrium and the subsequent emergence of hydrodynamic equations for
the local densities.


title: Teleportation Protocols Requiring Only One Classical Bit

abstract:
  The standard protocol for teleportation of a quantum state requires an
entangled pair of particles and the use of two classical bits of information.
Here, we present two protocols for teleportation that require only one
classical bit. In the first protocol, chained XOR operations are performed on
the particles before one of them is removed to the remote location where the
state is being teleported. In the second protocol, three entangled particles
are used.


title: On the Emergence of Nonextensivity at the Edge of Quantum Chaos

abstract:
  We explore the border between regular and chaotic quantum dynamics,
characterized by a power law decrease in the overlap between a state evolved
under chaotic dynamics and the same state evolved under a slightly perturbed
dynamics. This region corresponds to the edge of chaos for the classical map
from which the quantum chaotic dynamics is derived and can be characterized via
nonextensive entropy concepts.


title:
About entanglement properties of kaons and tests of hidden variables
  models

abstract:
  In this letter we discuss entanglement properties of neutral kaons systems
and their use for testing local realism. In particular we show that, as
previous proposals, also a scheme recently suggested for performing a test of
hidden variable theories against standard quantum mechanics cannot be
conclusive.


title: Copenhagen Computation: How I Learned to Stop Worrying and Love Bohr

abstract:
  To celebrate the 60th birthday of Charles H.Bennett I (1) publicly announce
my referee reports for the original dense coding and teleportation papers, (2)
present a very economical solution to the Bernstein-Vazirani problem that does
not even hint at interference between multiple universes, and (3) describe how
I inadvertently reinvented the Copenhagen interpretation in the course of
constructing a simple, straightforward, and transparent introduction to quantum
mechanics for computer scientists.


title: What Connects Different Interpretations of Quantum Mechanics?

abstract:
  We investigate the idea that different interpretations of quantum mechanics
can be seen as restrictions of the consistent (or decoherent) histories quantum
mechanics of closed systems to particular classes of histories,together with
the approximations and descriptions of these histories that the restrictions
permit. (Talk at the the workshop Quo Vadis Quantum Mechanics, Center for
Frontier Sciences, Temple University, Philadelphia, PA, September 24--27,
2002.)


title: Two QCMA-complete problems

abstract:
  QMA and QCMA are possible quantum analogues of the complexity class NP. In
QCMA the verifier is a quantum program and the proof is classical. In contrast,
in QMA the proof is also a quantum state.
  We show that two known QMA-complete problems can be modified to QCMA-complete
problems in a natural way:
  (1) Deciding whether a 3-local Hamiltonian has low energy states (with energy
smaller than a given value) that can be prepared with at most k elementary
gates is QCMA-complete, whereas it is QMA-complete when the restriction on the
complexity of preparation is dropped.
  (2) Deciding whether a (classically described) quantum circuit acts almost as
the identity on all basis states is QCMA-complete. It is QMA-complete to decide
whether it acts on all states almost as the identity.


title: A criterion for testing multi-particle NPT entanglement

abstract:
  We revisit the criterion of multi-particle entanglement based on the overlaps
of a given quantum state $\rho$ with maximally entangled states. For a system
of $m$ particles, each with $N$ distinct states, we prove that $\rho$ is
$m$-particle negative partial transpose (NPT) entangled, if there exists a
maximally entangled state $|{\rm MES}>$, such that $<{\rm MES}|\rho|{\rm
MES}>>{1}/{N}$. While this sufficiency condition is weaker than the
Peres-Horodecki criterion in all cases, it applies to multi-particle systems,
and becomes especially useful when the number of particles ($m$) is large. We
also consider the converse of this criterion and illustrate its invalidity with
counter examples.


title:
A high-flux source of polarization-entangled photons from a
  periodically-poled KTP parametric downconverter

abstract:
  We have demonstrated a high-flux source of polarization-entangled photons
using a type-II phase-matched periodically-poled KTP parametric downconverter
in a collinearly propagating configuration. We have observed quantum
interference between the single-beam downconverted photons with a visibility of
99% and a measured coincidence flux of 300/s/mW of pump. The
Clauser-Horne-Shimony-Holt version of Bell's inequality was violated with a
value of 2.711 +/- 0.017.


title:
Rotating frames and gauge invariance in two-dimensional many-body
  quantum systems

abstract:
  We study the quantization of many-body systems in two dimensions in rotating
coordinate frames using a gauge invariant formulation of the dynamics. We
consider reference frames defined by linear and quadratic gauge conditions. In
both cases we discuss their Gribov ambiguities and commutator algebra. We
construct the momentum operators, inner-product and Hamiltonian in both types
of gauges, for systems with and without translation invariance. The analogy
with the quantization of QED in non-covariant gauges is emphasized. Our results
are applied to quasi-rigid systems in the Eckart frame.


title:
An observable measure of entanglement for pure states of multi-qubit
  systems

abstract:
  Recently, Meyer and Wallach [D.A. Meyer and N.R. Wallach (2002), J. of Math.
Phys., 43, pp. 4273] proposed a measure of multi-qubit entanglement that is a
function on pure states. We find that this function can be interpreted as a
physical quantity related to the average purity of the constituent qubits and
show how it can be observed in an efficient manner without the need for full
quantum state tomography. A possible realization is described for measuring the
entanglement of a chain of atomic qubits trapped in a 3D optical lattice.


title: Is the end in sight for theoretical pseudophysics?

abstract:
  The question of what ontological message (if any) is encoded in the formalism
of contemporary physics is, to say the least, controversial. The reasons for
this state of affairs are psychological and neurobiological. The processes by
which the visual world is constructed by our minds, predispose us towards
concepts of space, time, and substance that are inconsistent with the
spatiotemporal and substantial aspects of the quantum world. In the first part
of this chapter, the latter are extracted from the quantum formalism. The
nature of a world that is fundamentally and irreducibly described by a
probability algorithm is determined. The neurobiological processes responsible
for the mismatch between our "natural" concepts of space, time, and substance
and the corresponding aspects of the quantum world are discussed in the second
part. These natural concepts give rise to pseudoproblems that foil our attempts
to make ontological sense of quantum mechanics. If certain psychologically
motivated but physically unwarranted assumptions are discarded (in particular
our dogged insistence on obtruding upon the quantum world the intrinsically and
completely differentiated spatiotemporal background of classical physics), we
are in a position to see why our fundamental physical theory is a probability
algorithm, and to solve the remaining interpretational problems.


title: Quantum-mechanical motion and the stillness of experimental records

abstract:
  Experimenting with metastability in recording devices leads us to wonder
about an interface between equations of motion and the stillness of
experimental records. Here we delineate an interface between wave functions as
language to describe motion and Turing tapes as language to describe
experimental records. After extending quantum formalism to make this interface
explicit, we report on constraints and freedoms in choosing quantum-mechanical
equations to model experiments with devices. We prove that choosing equations
of wave functions and operators to achieve a fit between calculated
probabilities and experimental records requires reaching beyond both logic and
the experimental records. Although informed by experience, a "reach beyond" can
fairly be called a guess.
  Recognizing that particles as features of wave functions depend on guesswork,
we introduce their use not as objects of physical investigation but as elements
of thought in quantum-mechanical models of devices. We make informed guesses to
offer a quantum-mechanical model of a 1-bit recording device in a metastable
condition. Probabilities calculated from the model fit an experimental record
of an oscillation in a time-varying probability, showing a
temperature-independent role for Planck's constant in what heretofore was
viewed as a "classical" electronic device.


title:
Numerical Analysis of Boosting Scheme for Scalable NMR Quantum
  Computation

abstract:
  Among initialization schemes for ensemble quantum computation beginning at
thermal equilibrium, the scheme proposed by Schulman and Vazirani [L. J.
Schulman and U. V. Vazirani, in Proceedings of the 31st ACM Symposium on Theory
of Computing (STOC'99) (ACM Press, New York, 1999), pp. 322-329] is known for
the simple quantum circuit to redistribute the biases (polarizations) of qubits
and small time complexity. However, our numerical simulation shows that the
number of qubits initialized by the scheme is rather smaller than expected from
the von Neumann entropy because of an increase in the sum of the binary
entropies of individual qubits, which indicates a growth in the total classical
correlation. This result--namely, that there is such a significant growth in
the total binary entropy--disagrees with that of their analysis.


title:
Relaxation and dephasing in a many-fermion generalization of the
  Caldeira-Leggett model

abstract:
  We analyze a model system of fermions in a harmonic oscillator potential
under the influence of a fluctuating force generated by a bath of harmonic
oscillators. This represents an extension of the well-known Caldeira-Leggett
model to the case of many fermions. Using the method of bosonization, we
calculate Green's functions and discuss relaxation and dephasing of a single
extra particle added above the Fermi sea. We also extend our analysis to a more
generic coupling between system and bath, that results in complete
thermalization of the system.


title: Covariant description of spin 1/2 particles in self--action

abstract:
  The bispinor wave function finds its fundamental application in the study of
electrons, neutrinos and protons as particles bound by their own potentials.
Classical electromagnetism and the Dirac electron theory appear to be natural
extensions of the physics that rules the electron itself. However, the charge
density and the negative energy eigenvalues are two concepts which cannot
survive further scrutiny. The electron and the proton resemble minute planetary
systems where the bispinor terms defining their physical properties revolve
with definite angular momentum around the singular point of the particles'
potentials. The mass of the electron--neutrino in relation to the electron's
and the mass of the latter in relation to the proton's are determined under
particular assumptions. The most important feature of the new approach is the
faithful representation of free particles at rest with respect to inertial
systems of reference. This certainly enhances the foundation of physics;
precisely in the realm of Quantum Mechanics, where the customary description of
free electrons is a confusing consequence of the limited scope of the
Schr\"{o}dinger and Dirac equations.


title: Polynomial time quantum computation with advice

abstract:
  Advice is supplementary information that enhances the computational power of
an underlying computation. This paper focuses on advice that is given in the
form of a pure quantum state and examines the influence of such advice on the
behaviors of an underlying polynomial-time quantum computation with
bounded-error probability.


title: Transfer of an unknown quantum state, quantum networks, and memory

abstract:
  We present a protocol for transfer of an unknown quantum state. The protocol
is based on a two-mode cavity interacting dispersively in a sequential manner
with three-level atoms in $\Lambda$ configuration. We propose a scheme for
quantum networking using an atomic channel. We investigate the effect of cavity
decoherence in the entire process. Further, we demonstrate the possibility of
an efficient quantum memory for arbitrary superposition of two modes of a
cavity contaning one photon.


title: Statistical Effects in the Multistream Model for Quantum Plasmas

abstract:
  A statistical multistream description of quantum plasmas is formulated, using
the Wigner-Poisson system as dynamical equations. A linear stability analysis
of this system is carried out, and it is shown that a Landau-like damping of
plane wave perturbations occurs due to the broadening of the background Wigner
function that arises as a consequence of statistical variations of the wave
function phase. The Landau-like damping is shown to suppress instabilities of
the one- and two-stream type.


title: Quantum Complexity of Parametric Integration

abstract:
  We study parametric integration of functions from the class
C^r([0,1]^{d_1+d_2}) to C([0,1]^{d_1}) in the quantum model of computation. We
analyze the convergence rate of parametric integration in this model and show
that it is always faster than the optimal deterministic rate and in some cases
faster than the rate of optimal randomized classical algorithms.


title: Estimation of unitary quantum operations

abstract:
  The problem of optimally estimating an unknown unitary quantum operation with
the aid of entanglement is addressed. The idea is to prepare an entangled pair,
apply the unknown unitary to one of the two parts and then measure the joint
output state. This measurement could be an entangled one or it could be
separable (e.g., LOCC). A comparison is made between these possibilities and it
is shown that by using non-separable measurements one can improve the accuracy
of the estimation by a factor of $2(d+1)/d$ where $d$ is the dimension of the
Hilbert space on which $U$ acts.


title:
Long-Distance Quantum Communication with Entangled Photons using
  Satellites

abstract:
  The use of satellites to distribute entangled photon pairs (and single
photons) provides a unique solution for long-distance quantum communication
networks. This overcomes the principle limitations of Earth-bound technology,
i.e. the narrow range of some 100 km provided by optical fiber and terrestrial
free-space links.


title: Information-Theoretic Comparison of Quantum Many-Body Systems

abstract:
  An information measure inspired by Onicescu's information energy and Uffink's
information measure (recently discussed by Brukner and Zeilinger) are
calculated as functions of the number of particles $N$ for fermionic systems
(nuclei and atomic clusters) and correlated bosonic systems (atoms in a trap).
Our results are compared with previous ones obtained for Shannon's information
entropy, where a universal property was derived for atoms, nuclei, atomic
clusters and correlated bosons. It is indicated that Onicescu's and Uffink's
definitions are finer measures of information entropy than Shannon's.


title:
Translational Entanglement of Dipole-Dipole Interacting Atoms in Optical
  Lattices

abstract:
  We propose and investigate a realization of the position- and
momentum-correlated Einstein-Podolsky-Rosen (EPR) states [Phys. Rev. 47, 777
(1935)] that have hitherto eluded detection. The realization involves atom
pairs that are confined to adjacent sites of two mutually shifted optical
lattices and are entangled via laser-induced dipole-dipole interactions. The
EPR "paradox" with translational variables is then modified by
lattice-diffraction effects, and can be verified to a high degree of accuracy
in this scheme.


title: Entanglement and correlation in anisotropic quantum spin systems

abstract:
  Analytical expressions for the entanglement measures concurrence,
i-concurrence and 3-tangle in terms of spin correlation functions are derived
using general symmetries of the quantum spin system. These relations are
exploited for the one-dimensional XXZ-model, in particular the concurrence and
the critical temperature for disentanglement are calculated for finite systems
with up to six qubits. A recent NMR quantum error correction experiment is
analyzed within the framework of the proposed theoretical approach.


title: Proper magnetic fields for nonadiabatic geometric quantum gates in NMR

abstract:
  In a scheme of nonadiabatic purely geometric quantum gates in nuclear
magnetic resonance(NMR) systems we propose proper magnitudes of magnetic fields
that are suitable for an experiment. We impose a natural condition and reduce
the degree of freedom of the magnetic fields to the extent. By varying the
magnetic fields with essentially one-dimensional degree of freedom, any spin
state can acquire arbitrary purely geometric phase
\phi_{g}=-2\pi(1-cos{theta}), 0 < cos{\theta} < 1. This is an essential
ingredient for constructing universal geometric quantum gates.


title:
On The Relevance Of Fair Sampling Assumption In The Recent Bell Photonic
  Experiments

abstract:
  In the experimental verification of Bell's inequalities in real photonic
experiments, it is generally believed that the so-called fair sampling
assumption (which means that a small fraction of results provide a fair
statistical sample) has an unavoidable role. Here, we want to show that the
interpretation of these experiments could be feasible, if some different
alternative assumptions other than the fair sampling were used. For this
purpose, we derive an efficient Bell-type inequality which is a CHSH-type
inequality in real experiments. Quantum mechanics violates our proposed
inequality, independent of the detection-efficiency problems.


title: Quantum Limits of Stochastic Cooling of a Bosonic Gas

abstract:
  The quantum limits of stochastic cooling of trapped atoms are studied. The
energy subtraction due to the applied feedback is shown to contain an
additional noise term due to atom-number fluctuations in the feedback region.
This novel effect is shown to dominate the cooling efficiency near the
condensation point. Furthermore, we show first results that indicate that
Bose--Einstein condensation could be reached via stochastic cooling.


title: Quantum Fingerprinting with a Single Particle

abstract:
  We show that the two slit experiment in which a single quantum particle
interferes with itself can be interpreted as a quantum fingerprinting protocol:
the interference pattern exhibited by the particle contains information about
the environment it encountered in the slits which would require much more
communication to learn classically than is required quantum mechanically. An
extension to the case where the particle has many internal degrees of freedom
is suggested and its interpretation is discussed in detail. A possible
experimental realization is proposed.


title:
Operationalistic Orthogonality Condition for Single-Mode Biphotons
  (Qutrits)

abstract:
  An arbitrary polarization state of a single-mode biphoton is considered. The
operationalistic criterion is formulated for the orthogonality og these states.
It can be used to separate a biphoton with an arbitrary degree of polarization
from a set of biphotons orthogonal to it. This is necessary fro the
implementation of quantum cryptography protocol based on three-level systems.
The experimental test of this criterion amounts to the observation of the
anticorrelation effect for a biphoton with an arbitraty polarization state.


title: Illustrating the concept of quantum information

abstract:
  Over the past decade quantum information theory has developed into a vigorous
field of research despite the fact that quantum information, as a precise
concept, is undefined. Indeed the very idea of viewing quantum states as
carriers of some kind of information (albeit unknowable in classical terms),
leads naturally to interesting questions that might otherwise never have been
asked, and corresponding new insights. We will discuss some illustrative
examples, including a strengthening of the well known no-cloning theorem
leading to a property of permanence for quantum information, and considerations
arising from information compression that reflect on fundamental issues.


title:
Practical Realization of the Quantum Cryptography Protocol Exploiting
  Polarization Encoding in the Qutrits

abstract:
  We propose and discuss a specific scheme allowing to realize a Quantum
Cryptography qutrit protocol. This protocol exploits the polarization
properties of single frequency and single spatial mode biphotons.


title: Entangled state preparation via dissipation-assisted adiabatic passages

abstract:
  The main obstacle for coherent control of open quantum systems is decoherence
due to different dissipation channels and the inability to precisely control
experimental parameters. To overcome these problems we propose to use
dissipation-assisted adiabatic passages. These are relatively fast processes
where the presence of spontaneous decay rates corrects for errors due to
non-adiabaticity while the system remains in a decoherence-free state and
behaves as predicted for an adiabatic passage. As a concrete example we present
a scheme to entangle atoms by moving them in and out of an optical cavity.


title: Why can states and measurement outcomes be represented as vectors?

abstract:
  It is shown how, given a "probability data table" for a quantum or classical
system, the representation of states and measurement outcomes as vectors in a
real vector space follows in a natural way. Some properties of the resulting
sets of these vectors are discussed, as well as some connexions with the
quantum-mechanical formalism.


title: Quantum dense coding by spatial state entanglement

abstract:
  We have presented a theoretical extended version of dense coding protocol
using entangled position state of two particles shared between two parties. A
representation of Bell states and the required unitary operators are shown
utilizing symmetric normalized Hadamard matrices. In addition, some explicit
and conceivable forms for the unitary operators are presented by using some
introduced basic operators. It is shown that, the proposed version is
logarithmically efficient than some other multi-qubit dense coding protocols.


title: Probability representation of kinetic equation for open quantum system

abstract:
  The tomographic probability distribution is used to decribe the kinetic
equations for open quantum systems. Damped oscillator is studied. Purity
parameter evolution for different damping regime is considered.


title: Comparing the states of many quantum systems

abstract:
  We investigate how to determine whether the states of a set of quantum
systems are identical or not. This paper treats both error-free comparison, and
comparison where errors in the result are allowed. Error-free comparison means
that we aim to obtain definite answers, which are known to be correct, as often
as possible. In general, we will have to accept also inconclusive results,
giving no information. To obtain a definite answer that the states of the
systems are not identical is always possible, whereas, in the situation
considered here, a definite answer that they are identical will not be
possible. The optimal universal error-free comparison strategy is a projection
onto the totally symmetric and the different non-symmetric subspaces, invariant
under permutations and unitary transformations. We also show how to construct
optimal comparison strategies when allowing for some errors in the result,
minimising either the error probability, or the average cost of making an
error. We point out that it is possible to realise universal error-free
comparison strategies using only linear elements and particle detectors, albeit
with less than ideal efficiency. Also minimum-error and minimum-cost strategies
may sometimes be realised in this way. This is of great significance for
practical applications of quantum comparison.


title: A footnote to Nelson's interpretation of the two-slit experiment

abstract:
  We seek to complement Nelson's work on the two-slit experiment by showing
that the two-slit process, whose density exhibits the characteristic
interference pattern, may be obtained as the model after the beam has reached
the screen by means of a variational mechanism. The one-slit process, modeling
the beam before it reaches the screen, plays the role of a reference model.


title: Optomechanical characterization of acoustic modes in a mirror

abstract:
  We present an experimental study of the internal mechanical vibration modes
of a mirror. We determine the frequency repartition of acoustic resonances via
a spectral analysis of the Brownian motion of the mirror, and the spatial
profile of the acoustic modes by monitoring their mechanical response to a
resonant radiation pressure force swept across the mirror surface. We have
applied this technique to mirrors with cylindrical and plano-convex geometries,
and compared the experimental results to theoretical predictions. We have in
particular observed the gaussian modes predicted for plano-convex mirrors.


title: Quasi-Hermiticity in infinite-dimensional Hilbert spaces

abstract:
  In infinite-dimensional Hilbert spaces, the application of the concept of
quasi-Hermiticity to the description of non-Hermitian Hamiltonians with real
spectra may lead to problems related to the definition of the metric operator.
We discuss these problems by examining some examples taken from the recent
literature and propose a formulation that is free of these difficulties.


title:
A second rank divergence-free tensor, constructed as a second order
  polynomial in Riemann

abstract: Preprint is withdrawn, since result isn't new.


title:
Cooperative fluorescence effects for dipole-dipole interacting systems
  with experimentally relevant level configurations

abstract:
  The mutual dipole-dipole interaction of atoms in a trap can affect their
fluorescence. Extremely large effects were reported for double jumps between
different intensity periods in experiments with two and three Ba^+ ions for
distances in the range of about ten wave lengths of the strong transition while
no effects were observed for Hg^+ at 15 wave lengths. In this theoretical paper
we study this question for configurations with three and four levels which
model those of Hg^+ and Ba^+, respectively. For two systems in the Hg^+
configuration we find cooperative effects of up to 30% for distances around one
or two wave lengths, about 5% around ten wave lengths, and, for larger
distances in agreement with experiments, practically none. This is similar for
two V systems. However, for two four-level configurations, which model two Ba^+
ions, cooperative effects are practically absent, and this latter result is at
odds with the experimental findings for Ba^+.


title: General Probabilistic Framework of Randomness

abstract:
  We introduce a new mathematical framework for the probabilistic description
of an experiment upon a system of any type in terms of initial information
representing this system. Based on the notions of an information state, an
information state space and a generalized observable, this general framework
covers the description of a wide range of experimental situations including
those where, with respect to a system, an experiment is perturbing. We prove
that, to any experiment upon a system, there corresponds a unique generalized
observable on a system initial information state space, which defines the
probability distribution of outcomes under this experiment. We specify the case
where initial information on a system provides "no knowledge" for the
description of an experiment. Incorporating in a uniform way the basic notions
of conventional probability theory and the non-commutativity aspects and the
basic notions of quantum measurement theory, our framework clarifies the
principle difference between Kolmogorov's model in probability theory and the
statistical model of quantum theory. Both models are included into our
framework as particular cases. We show that the phenomenon of "reduction" of a
system initial information state is inherent, in general, to any
non-destructive experiment and upon a system of any type. Based on our general
framework, we introduce the probabilistic model for the description of
non-destructive experiments upon a quantum system and prove that positive
bounded linear mappings on the Banach space of trace class operators, arising
in the description of experiments upon a quantum system, are completely
positive.


title: Wigner distributions for non Abelian finite groups of odd order

abstract:
  Wigner distributions for quantum mechanical systems whose configuration space
is a finite group of odd order are defined so that they correctly reproduce the
marginals and have desirable transformation properties under left and right
translations. While for the Abelian case we recover known results, though from
a different perspective, for the non Abelian case, our results appear to be
new.


title: Spectrum of One-Dimensional Anharmonic Oscillators

abstract:
  We use a power-series expansion to calculate the eigenvalues of anharmonic
oscillators bounded by two infinite walls. We show that for large finite values
of the separation of the walls, the calculated eigenvalues are of the same high
accuracy as the values recently obtained for the unbounded case by the
inner-product quantization method. We also apply our method to the Morse
potential. The eigenvalues obtained in this case are in excellent agreement
with the exact values for the unbounded Morse potential.


title: Quantum measurements and new concepts for experiments with trapped ions

abstract:
  Experiments with individual trapped ions are ideally suited to investigate
fundamental issues of quantum mechanics such as the measurement process. At the
same time electrodynamically trapped ions have been used with great success to
demonstrate quantum logic operations and are a candidate for scalable quantum
computing. In this article a brief introduction is given to the basic steps
that constitute a quantum measurement; in particular, measurements on single
quantum systems are considered. Then experiments with single Yb+ are reviewed
demonstrating the quantum Zeno paradox, as well as an experiment where an
adaptive algorithm for quantum state estimation of qubits was implemented. In
the last section of this article -- devoted to experiments and new ideas
related to quantum information processing (QIP) with trapped ions -- the
realization of various quantum channels using a hyperfine qubit of Yb+ is
briefly discussed. Then a concept for QIP with trapped ions is reviewed where
rf or microwave radiation is used instead of laser light for coherent
manipulation of a collection of ions. In a suitably modified trap the ions form
an artificial ion "molecule" to which the techniques developed in nuclear
magnetic resonance and electron spin resonance experiments can be directly
applied. Finally, coherent excitation of optical electric quadrupole
transitions in Yb+ and Ba+ is reported. In addition, robust Raman cooling of a
pair of Ba+ ions is reviewed.


title:
Efficient scheme for quantum entanglement, quantum information transfer,
  and quantum gate with three-level SQUID qubits in cavity QED

abstract:
  A novel scheme is proposed for realizing quantum entanglement, quantum
information transfer and a set of universal quantum gates with
superconducting-quantum-interference-device (SQUID) qubits in cavity QED. In
the scheme, the two logical states of a qubit are the two lowest levels of the
SQUID. An intermediate level of the SQUID is utilized to facilitate coherent
control and manipulation of quantum states of the qubits. The method presented
here does not create finite intermediate-level population or cavity-photon
population during the operations. Thus, decoherence due to spontaneous decay
from the intermediate levels is minimized and the requirement on the quality
factor of the cavity is greatly loosened.


title: On compatibility of Bohmian mechanics with standard quantum mechanics

abstract:
  It is shown that the apparent incompatibility of Bohmian mechanics with
standard quantum mechanics, found by Akhavan and Golshani quant-ph/0305020, is
an artefact of the fact that the initial wavefunction they use, being
proportional to a $\delta$-function, is not a regular wavefunction.


title: Noncyclic mixed state phase in SU(2) polarimetry

abstract:
  We demonstrate that Pancharatnam's relative phase for mixed spin$-{1/2}$
states in noncyclic SU(2) evolution can be measured polarimetrically.


title: Two-component Fermi gas in a Harmonic Trap

abstract:
  We consider a mixture of two-component Fermi gases at low temperature. The
density profile of this degenerate Fermi gas is calculated under the
semiclassical approximation. The results show that the fermion-fermion
interactions make a large correction to the density profile at low temperature.
The phase separation of such a mixture is also discussed for both attractive
and repulsive interatomic interactions, and the numerical calculations
demonstrate the exist of a stable temperature region $T_{c1}<T<T_{c2}$ for the
mixture. In addition, we give the critical temperature of the BCS-type
transition in this system beyond the semiclassical approximation.


title: Representation of Boolean Quantum Circuits as Reed-Muller Expansions

abstract:
  In this paper we show that there is a direct correspondence between quantum
Boolean operations and certain forms of classical (non-quantum) logic known as
Reed-Muller expansions. This allows us to readily convert Boolean circuits into
their quantum equivalents. A direct result of this is that the problem of
synthesis and optimization of quantum Boolean logic can be tackled within the
field of Reed-Muller logic.


title: Bell inequality, nonlocality and analyticity

abstract:
  The Bell and the Clauser-Horne-Shimony-Holt inequalities are shown to hold
for both the cases of complex and real analytic nonlocality in the setting
parameters of Einstein-Podolsky-Rosen-Bohm experiments for spin 1/2 particles
and photons, in both the deterministic and stochastic cases. Therefore, the
theoretical and experimental violation of the inequalities by quantum mechanics
excludes all hidden variables theories with that kind of nonlocality. In
particular, real analyticity leads to negative definite correlations, in
contradiction with quantum mechanics.


title: Key Disclosing in Multiphotons with Quantum Cloning

abstract:
  Multiphoton state in quantum cryptography decreases its security. Key
disclosing with universal quantum cloning machine (UQCM) is considered in
explicit manner. Although UQCM cannot make perfect clones, there is some
invariant quantity between the original photon and the imperfect clones. The
invariant quantity, the direction of Stokes parameters, tells us the auxiliary
information leading into key information. The attack, then, corresponds to some
kind of quantum non-demolition measurement. Its application to recent
high-performance quantum cryptography, Y-00 protocol, is also studied.


title: An Explanation of Spin Based on Classical Mechanics and Electrodynamics

abstract:
  It is proved that, according to Classical Mechanics and Electrodynamics, the
trajectory of the center of mass of a neutral system of electrical charges can
be deflected by an inhomogeneous magnetic field, even if its internal angular
momentum is zero. This challenges the common view about the function of the
Stern-Gerlach apparatus, as resolving the eigen-states of an intrinsic angular
momentum. Doubts are cast also on the supposed failure of Schrodinger's theory
to explain the properties of atoms in presence of magnetic fields without
introducing spin variables.

categories: quant-ph hep-ph physics.atom-ph physics.class-ph


title: Single-Step Distillation Protocol with Generalized Beam Splitters

abstract:
  We develop a distillation protocol for multilevel qubits (qudits) using
generalized beam splitters like in the proposal of Pan et al. for ordinary
qubits. We find an acceleration with respect to the scheme of Bennet et al.
when extended to qudits. It is also possible to distill entangled pairs of
photons carrying orbital angular momenta (OAM) states that conserves the total
angular momenta as those produced in recent experiments.


title:
Comment on ``Polynomial-Time Simulation of Pairing Models on a Quantum
  Computer''

abstract:
  Comment on the Letter ``Polynomial-Time Simulation of Pairing Models on a
Quantum Computer'', L. A. Wu, M. S. Byrd and D. A. Lidar, Phys. Rev. Lett. 89,
057904 (2002).


title: The quantum way to diagonalize hermitean matrices

abstract:
  An entirely quantum mechanical approach to diagonalize hermitean matrices has
been presented recently. Here, the genuinely quantum mechanical approach is
considered in detail for (2x2) matrices. The method is based on the measurement
of quantum mechanical observables which provides the computational resource. In
brief, quantum mechanics is able to directly address and output eigenvalues of
hermitean matrices. The simple low-dimensional case allows one to illustrate
the conceptual features of the general method which applies to (NxN) hermitean
matrices.


title:
Gauge equivalence classes of flat connections in the Aharonov-Bohm
  effect

abstract:
  In this note we present a simplified derivation of the fact that the moduli
space of flat connections in the abelian Aharonov-Bohm effect is isomorphic to
the circle. The length of this circle is the electric charge.


title:
A simple unconditionally secure quantum bit commitment protocol via
  quantum teleportation

abstract:
  By using local quantum teleportation of a fixed state to one qubit of an
entangled pair sent from the other party, it is shown how one party can commit
a bit with only classical information as evidence that results in an
unconditionally secure protocol. The well-known ``impossibility proof'' does
not cover such protocols due to its different commitment and opening
prescriptions, which necessitate actual quantum measurements among different
possible systems that cannot be entangled as a consequence.


title:
Another simple unconditionally secure quantum bit commitment protocol --
  beating entanglement with entanglement

abstract:
  It is shown how the evidence state space in quantum bit commitment may be
made to depend on the bit value 0 or 1 with split entangled pairs. As a
consequence, one can obtain a protocol that is perfectly concealing, but is
also $\epsilon$-binding because the bit-value dependent evidence space prevents
the committing party from cheating by means of a local transformation that is
independent of the part of evidence state space that has never been in his
possession.


title: How to Build Unconditionally Secure Quantum Bit Commitment Protocols

abstract:
  The ``impossibility proof'' on unconditionally secure quantum bit commitment
is critically analyzed. Many possibilities for obtaining a secure bit
commitment protocol are indicated, purely on the basis of two-way quantum
communications, which are not covered by the impossibility proof formulation.
They are classified under six new types of protocols, with security proofs for
specific examples on four types. Reasons for some previously failed attempts at
obtaining secure protocols are also indicated.


title: Quantum deleting and Signalling

abstract:
  It is known that if we can clone an arbitrary state we can send signal faster
than light. Here, we show that deletion of unknown quantum state against a copy
can lead to superluminal signalling. But erasure of unknown quantum state does
not imply faster than light signalling.


title:
From quantum theory to classical dynamics under spontaneous wave-packet
  reduction

abstract:
  A quantum master equation of the Lindblad form is obtained in this paper by
considering the spontaneous wave-packet reduction. Different classical
equations can be derived after exactly mapping such a quantum master equation
to a continuous time random walk (CTRW). Although this CTRW is a quasiclassical
walk, the effects due to the quantum interference can still be important in
such a walk. Macroscopically, we shall consider the uncertainty of the
potential and determine the effective transition probability by a family of
Schr\"{o}dinger equations (or operators).


title: Dynamics of the entanglement rate in the presence of decoherence

abstract:
  The dynamics of the entanglement rate are investigated in this paper for
pairwise interaction and two special sets of initial states. The results show
that for the given interaction and the decoherence scheme, the competitions
between decohering and entangling lead to two different results--some initial
states may be used to prepare entanglement while the others do not. A criterion
on decohering and entangling is also presented and discussed.


title: Unusual Properties of Superoscillating Particles

abstract:
  It has been found that functions can oscillate locally much faster than their
Fourier transform would suggest is possible - a phenomenon called
superoscillation. Here, we consider the case of superoscillating wave functions
in quantum mechanics. We find that they possess rather unusual properties which
raise measurement theoretic, thermodynamic and information theoretic issues. We
explicitly determine the wave functions with the most pronounced
superoscillations, together with their scaling behavior. We also address the
question how superoscillating wave functions could be produced.


title: Global causality in space-time universe

abstract:
  The problems connected with a causality of space-time universe and with the
paradox of Einstein, Podolsky, and Rosen are considered. A main philosophical
problem and its possible solutions are briefly discussed. A concept of unified
local field theory is considered. It is shown that in the framework of such
theory there are nonlocal correlations between space separate events. These
correlations are predicted by quantum mechanics and they are confirmed by
Aspect type experiments for testing of Bell inequality. The presence of these
nonlocal correlations in the framework of a local field theory is connected
with the fact that its solution is nonlocal in character. Prospects for
possible applications of an unified local field theory are considered.


title: Particle and Field Symmetries and Noncommutative Geometry

abstract:
  The development of Noncommutative Geometry is creating a reworking and new
possibilities in physics. This paper identifies some of the commutation and
derivation structures that arise in particle and field interactions and
fundamental symmetries. The requirements of coexisting structures, and their
consistency, produce a mathematical framework that underlies a fundamental
physics theory. Among other developments in Quantum theory of particles and
fields are the symmetries of gauge fields and the Fermi-Bose symmetry of
particles. These involve a gauge covariant derivation and the action
functionals; and commutation algebras and Bogoliubov transforms. The non
commutative Theta form introduces an additional and fundamental structure. This
paper obtains the interrelations of various structures, and the conditions for
the symmetries of Fermionic/Bosonic particles interacting with Yang Mills gauge
fields. Many example physical systems are being solved, and the mathematical
formalism is being created to understand the fundamental basis of physics.


title:
Phase space interference and the WKB approximation for squeezed number
  states

abstract:
  Squeezed number states for a single mode Hamiltonian are investigated from
two complementary points of view. Firstly the more relevant features of their
photon distribution are discussed using the WKB wave functions. In particular
the oscillations of the distribution and the parity behavior are derived and
compared with the exact results. The accuracy is verified and it is shown that
for high photon number it fails to reproduce the true distribution. This is
contrasted with the fact that for moderate squeezing the WKB approximation
gives the analytical justification to the interpretation of the oscillations as
the result of the interference of areas with definite phases in phase space. It
is shown with a computation at high squeezing using a modified prescription for
the phase space representation which is based on Wigner-Cohen distributions
that the failure of the WKB approximation does not invalidate the area overlap
picture.


title:
Conditional linear-optical measurement schemes generate effective photon
  nonlinearities

abstract:
  We provide a general approach for the analysis of optical state evolution
under conditional measurement schemes, and identify the necessary and
sufficient conditions for such schemes to simulate unitary evolution on the
freely propagating modes. If such unitary evolution holds, an effective photon
nonlinearity can be identified. Our analysis extends to conditional measurement
schemes more general than those based solely on linear optics.