title: Efficient quantum processing of 3-manifold topological invariants

abstract:
  A quantum algorithm for approximating efficiently 3--manifold topological
invariants in the framework of SU(2) Chern-Simons-Witten (CSW) topological
quantum field theory at finite values of the coupling constant k is provided.
The model of computation adopted is the q-deformed spin network model viewed as
a quantum recognizer in the sense of Wiesner and Crutchfield, where each basic
unitary transition function can be efficiently processed by a standard quantum
circuit.
  This achievement is an extension of the algorithm for approximating
polynomial invariants of colored oriented links found in Refs 2,3. Thus all the
significant quantities - partition functions and observables - of quantum CSW
theory can be processed efficiently on a quantum computer, reflecting the
intrinsic, field-theoretic solvability of such theory at finite k.
  The paper is supplemented by a critical overview of the basic conceptual
tools underlying the construction of quantum invariants of links and
3-manifolds and connections with algorithmic questions that arise in geometry
and quantum gravity models are discussed.


title: Robust Weak Measurements on Finite Samples

abstract:
  A new weak measurement procedure is introduced for finite samples which
yields accurate weak values that are outside the range of eigenvalues and which
do not require an exponentially rare ensemble. This procedure provides a unique
advantage in the amplification of small non-random signals by minimizing
uncertainties in determining the weak value and by minimizing sample size. This
procedure can also extend the strength of the coupling between the system and
measuring device to a new regime.


title:
Implications for a spatially discrete transition amplitude in the
  twin-slit experiment

abstract:
  A discrete path integral formalism is used to obtain the transition amplitude
between 'sources' (slits and detector) in the twin-slit experiment of quantum
mechanics. This method explicates the normally tacit construct of dynamic
entities with temporal duration. The resulting amplitude is compared to that of
Schrodinger dynamics in order to relate 'source' dynamics and spatial
separation. The implied metric embodies non-separability, in stark contrast to
the metric of general relativity. Thus, this approach may have implications for
quantum gravity.


title:
Quantum Superposition State Production by Continuous Observations and
  Feedback

abstract:
  We present a protocol for generation of superpositions of states with
distinguishable field amplitudes in an optical cavity by quantum nondemolition
photon number measurements and coherent feeding of the cavity.


title:
The Implications of a Cosmological Information Bound for Complexity,
  Quantum Information and the Nature of Physical Law

abstract:
  The finite age of the universe and the existence of cosmological horizons
provides a strong argument that the observable universe represents a finite
causal region with finite material and informational resources. A similar
conclusion follows from the holographic principle. In this paper I address the
question of whether the cosmological information bound has implications for
fundamental physics. Orthodox physics is based on Platonism: the laws are
treated as infinitely precise, perfect, immutable mathematical relationships
that transcend the physical universe and remain totally unchanged by physical
processes, however extreme. If instead the laws of physics are regarded as akin
to computer software, with the physical universe as the corresponding hardware,
then the finite computational capacity of the universe imposes a fundamental
limit on the precision of the laws and the specifiability of physical states.
That limit depends on the age of the universe. I examine how the imprecision of
the laws impacts on the evolution of highly entangled states and on the problem
of dark energy.


title:
Exact solutions of the pseudo-Coulomb potential plus ring-shaped
  potential in the D-dimensional Schrodinger equation by the Nikiforov-Uvarov
  method

abstract:
  We present analytically the exact energy bound-states solutions of the
Schrodinger equation in D-dimensions for an alternative (often used)
pseudo-Coulomb potential-plus- ring-shaped potential of the form $V(r)=-%
\frac{a}{r}+\frac{b}{r^{2}}+\frac{\beta \cos ^{2}\theta}{r^{2}\sin ^{2}\theta
}+c$ by means of the conventional Nikiforov-Uvarov method. We give a clear
recipe of how to obtain an explicit solution to the radial and angular parts of
the wave functions in terms of orthogonal polynomials. The total energy of the
system is different from the pseudo-Coulomb potential because of the
contribution of the angular part. The general results obtained in this work can
be reduced to the standard forms given in literature.


title:
Entanglement in the bimodal Jaynes-Cummings model with the two-mode
  squeezed vacuum state

abstract:
  In this paper, we study the interaction between the two-level atom and a
bimodal cavity field, namely, two-mode Jaynes-Cummings model when the atom and
the modes are initially in the atomic superposition state and two-mode squeezed
vacuum state, respectively. For this system we investigate the atomic
inversion, linear entropy and atomic Wehrl entropy. We show that there is a
connection between all these quantities. Also we prove that the atomic Wehrl
entropy exhibits behaviors similar to those of the linear entropy and the von
Neumann entropy. Moreover, we show that the bipartite exhibits periodical
disentanglement and derive the explicit forms of the states of the atom and the
modes at these values of the interaction times.


title: Entanglement in Many-Body Systems

abstract:
  The recent interest in aspects common to quantum information and condensed
matter has prompted a prosperous activity at the border of these disciplines
that were far distant until few years ago. Numerous interesting questions have
been addressed so far. Here we review an important part of this field, the
properties of the entanglement in many-body systems. We discuss the zero and
finite temperature properties of entanglement in interacting spin, fermionic
and bosonic model systems. Both bipartite and multipartite entanglement will be
considered. At equilibrium we emphasize on how entanglement is connected to the
phase diagram of the underlying model. The behavior of entanglement can be
related, via certain witnesses, to thermodynamic quantities thus offering
interesting possibilities for an experimental test. Out of equilibrium we
discuss how to generate and manipulate entangled states by means of many-body
Hamiltonians.


title:
Cluster state preparation using gates operating at arbitrary success
  probabilities

abstract:
  Several physical architectures allow for measurement-based quantum computing
using sequential preparation of cluster states by means of probabilistic
quantum gates. In such an approach, the order in which partial resources are
combined to form the final cluster state turns out to be crucially important.
We determine the influence of this classical decision process on the expected
size of the final cluster. Extending earlier work, we consider different
quantum gates operating at various probabilites of success. For finite
resources, we employ a computer algebra system to obtain the provably optimal
classical control strategy and derive symbolic results for the expected final
size of the cluster. We identify two regimes: When the success probability of
the elementary gates is high, the influence of the classical control strategy
is found to be negligible. In that case, other figures of merit become more
relevant. In contrast, for small probabilities of success, the choice of an
appropriate strategy is crucial.


title: Entropic security in Quantum Cryptography

abstract:
  We present two new definitions of security for quantum ciphers which are
inspired by the definition of entropic security and entropic
indistinguishability defined by Dodis and Smith. We prove the equivalence of
these two new definitions. We also propose a generalization of a cipher
described by Dodis and Smith and show that it can actually encrypt n qubits
using less than n bits of key under reasonable conditions and yet be secure in
an information theoretic setting. This cipher also totally closes the gap
between the key requirement of quantum ciphers and classical ciphers.


title: Quantum Brachistochrone for Mixed States

abstract:
  We present a general formalism based on the variational principle for finding
the time-optimal quantum evolution of mixed states governed by a master
equation, when the Hamiltonian and the Lindblad operators are subject to
certain constraints. The problem reduces to solving first a fundamental
equation (the {\it quantum brachistochrone}) for the Hamiltonian, which can be
written down once the constraints are specified, and then solving the
constraints and the master equation for the Lindblad and the density operators.
As an application of our formalism, we study a simple one-qubit model where the
optimal Lindblad operators control decoherence and can be simulated by a
tunable coupling with an ancillary qubit. It is found that the evolution
through mixed states can be more efficient than the unitary evolution between
given pure states. We also discuss the mixed state evolution as a finite time
unitary evolution of the system plus an environment followed by a single
measurement. For the simplest choice of the constraints, the optimal duration
time for the evolution is an exponentially decreasing function of the
environment's degrees of freedom.


title: Modeling heat transport through completely positive maps

abstract:
  We investigate heat transport in a spin-1/2 Heisenberg chain, coupled locally
to independent thermal baths of different temperature. The analysis is carried
out within the framework of the theory of open systems by means of appropriate
quantum master equations. The standard microscopic derivation of the
weak-coupling Lindblad equation in the secular approximation is considered, and
shown to be inadequate for the description of stationary nonequilibrium
properties like a non-vanishing energy current. Furthermore, we derive an
alternative master equation that is capable to describe a stationary energy
current and, at the same time, leads to a completely positive dynamical map.
This paves the way for efficient numerical investigations of heat transport in
larger systems based on Monte Carlo wave function techniques.


title:
Geometric phases induced in auxiliary qubits by many-body systems near
  its critical points

abstract:
  The geometric phase induced in an auxiliary qubit by a many-body system is
calculated and discussed. Two kinds of coupling between the auxiliary qubit and
the many-body system are considered, which lead to dephasing and dissipation in
the qubit, respectively. As an example, we consider the XY spin-chain
dephasingly couple to a qubit, the geometric phase induced in the qubit is
presented and discussed. The results show that the geometric phase might be
used to signal the critical points of the many-body system, and it tends to
zero with the parameters of the many-body system going away from the critical
points.


title: Faster annealing schedules for quantum annealing

abstract:
  New annealing schedules for quantum annealing are proposed based on the
adiabatic theorem. These schedules exhibit faster decrease of the excitation
probability than a linear schedule. To derive this conclusion, the asymptotic
form of the excitation probability for quantum annealing is explicitly obtained
in the limit of long annealing time. Its first-order term, which is inversely
proportional to the square of the annealing time, is shown to be determined
only by the information at the initial and final times. Our annealing schedules
make it possible to drop this term, thus leading to a higher order (smaller)
excitation probability. We verify these results by solving numerically the
time-dependent Schrodinger equation for small size systems


title: Nonprobabilistic teleportation of field state via cavity QED

abstract:
  In this article we discuss a teleportation scheme of coherent states of
cavity field. The experimental realization proposed makes use of cavity quatum
electrodynamics involving the interaction of Rydberg atoms with micromaser and
Ramsey cavities. In our scheme the Ramsey cavities and the atoms play the role
of auxiliary systems used to teleport the state from a micromaser cavity to
another. We show that, even if the correct atomic detection fails in the first
trials, one can succeed in teleportating the cavity field state if the proper
measurement occurs in a later atom.


title: Photovoltaic Probe of Cavity Polaritons in a Quantum Cascade Structure

abstract:
  The strong coupling between an intersubband excitation in a quantum cascade
structure and a photonic mode of a planar microcavity has been detected by
angle-resolved photovoltaic measurements. A typical anticrossing behavior, with
a vacuum-field Rabi splitting of 16 meV at 78K, has been measured, for an
intersubband transition at 163 meV. These results show that the strong coupling
regime between photons and intersubband excitations can be engineered in a
quantum cascade opto-electronic device. They also demonstrate the possibility
to perform angle-resolved mid-infrared photodetection and to develop active
devices based on intersubband cavity polaritons.


title: Boundary Effects in Non-Uniform Spin Chains

abstract:
  We give an explicit comparison of eigenvalues and eigenvectors of XY
Hamiltonians of an open linear spin-1/2 chain and a closed spin-1/2 ring with
periodic in space coefficients. It is shown that the Hamiltonian of a
k-periodic chain with nk-1 sites has (n-1)k multiplicity one eigenvalues which
are eigenvalues of multiplicity two for a Hamiltonian of a k-periodic ring with
2kn sites. For the corresponding eigenvectors in the case of a chain an
explicit expression in terms of eigenvectors of the ring Hamiltonian is given.
The remaining k-1 eigenvalues of the chain Hamiltonian and 2k eigenvalues of
the ring Hamiltonian, together with the corresponding eigenvectors, are
responsible for the difference between chain and ring models which displays in
the boundary effects at the ends of the chain and translation invariance of the
periodic ring.


title: Dynamics of decoherence without dissipation in a squeezed thermal bath

abstract:
  We study a generic open quantum system where the coupling between the system
and its environment is of an energy-preserving quantum nondemolition (QND)
type. We obtain the general master equation for the evolution of such a system
under the influence of a squeezed thermal bath of harmonic oscillators. From
the master equation it can be seen explicitly that the process involves
decoherence or dephasing without any dissipation of energy. We work out the
decoherence-causing term in the high and zero temperature limits and check that
they match with known results for the case of a thermal bath. The decay of the
coherence is quantified as well by the dynamics of the linear entropy of the
system under various environmental conditions. We make a comparison of the
quantum statistical properties between QND and dissipative types of evolution
using a system of two-level atom and a harmonic oscillator.


title: Phase diffusion pattern in quantum nondemolition systems

abstract:
  We quantitatively analyze the dynamics of the quantum phase distribution
associated with the reduced density matrix of a system, as the system evolves
under the influence of its environment with an energy-preserving quantum
nondemolition (QND) type of coupling. We take the system to be either an
oscillator (harmonic or anharmonic) or a two-level atom (or equivalently, a
spin-1/2 system), and model the environment as a bath of harmonic oscillators,
initially in a general squeezed thermal state. The impact of the different
environmental parameters is explicitly brought out as the system starts out in
various initial states. The results are applicable to a variety of physical
systems now studied experimentally with QND measurements.


title: Quantic Superpositions and the Geometry of Complex Hilbert Spaces

abstract:
  The concept of a superposition is a revolutionary novelty introduced by
Quantum Mechanics. If a system may be in any one of two pure states x and y, we
must consider that it may also be in any one of many superpositions of x and y.
An in-depth analysis of superpositions is proposed, in which states are
represented by one-dimensional subspaces, not by unit vectors as in Dirac's
notation. Superpositions must be considered when one cannot distinguish between
possible paths, i.e., histories, leading to the current state of the system. In
such a case the resulting state is some compound of the states that result from
each of the possible paths. States can be compounded, i.e., superposed in such
a way only if they are not orthogonal. Since different classical states are
orthogonal, the claim implies no non-trivial superpositions can be observed in
classical systems. The parameter that defines such compounds is a proportion
defining the mix of the different states entering the compound. Two quantities,
p and theta, both geometrical in nature, relate one-dimensional subspaces in
complex Hilbert spaces: the first one is a measure of proximity relating two
rays, the second one is an angle relating three rays. The properties of the
operation of superposition are very different from those that govern linear
combination of vectors.


title: Statistical bounds on the dynamical production of entanglement

abstract:
  We present a random-matrix analysis of the entangling power of a unitary
operator as a function of the number of times it is iterated. We consider
unitaries belonging to the circular ensembles of random matrices (CUE or COE)
applied to random (real or complex) non-entangled states. We verify numerically
that the average entangling power is a monotonic decreasing function of time.
The same behavior is observed for the "operator entanglement" --an alternative
measure of the entangling strength of a unitary. On the analytical side we
calculate the CUE operator entanglement and asymptotic values for the
entangling power. We also provide a theoretical explanation of the time
dependence in the CUE cases.


title: Weakly bound electrons in external magnetic field

abstract:
  The effect of the uniform magnetic field on the electron in the spherically
symmetric square-well potential is studied. A transcendental equation that
determines the electron energy spectrum is derived. The approximate value of
the lowest (bound) energy state is found. The approximate wave function and
probability current density of this state are constructed.


title:
Quantum communication without alignment using multiple-qubit
  single-photon states

abstract:
  We propose a scheme for encoding logical qubits in a subspace protected
against collective rotations around the propagation axis using the polarization
and transverse spatial degrees of freedom of single photons. This encoding
allows for quantum key distribution without the need of a shared reference
frame. We present methods to generate entangled states of two logical qubits
using present day down-conversion sources and linear optics, and show that the
application of these entangled logical states to quantum information schemes
allows for alignment-free tests of Bell's inequalities, quantum dense coding
and quantum teleportation.


title:
A Topos Foundation for Theories of Physics: I. Formal Languages for
  Physics

abstract:
  This paper is the first in a series whose goal is to develop a fundamentally
new way of constructing theories of physics. The motivation comes from a desire
to address certain deep issues that arise when contemplating quantum theories
of space and time. Our basic contention is that constructing a theory of
physics is equivalent to finding a representation in a topos of a certain
formal language that is attached to the system. Classical physics arises when
the topos is the category of sets. Other types of theory employ a different
topos. In this paper we discuss two different types of language that can be
attached to a system, S. The first is a propositional language, PL(S); the
second is a higher-order, typed language L(S). Both languages provide deductive
systems with an intuitionistic logic. The reason for introducing PL(S) is that,
as shown in paper II of the series, it is the easiest way of understanding, and
expanding on, the earlier work on topos theory and quantum physics. However,
the main thrust of our programme utilises the more powerful language L(S) and
its representation in an appropriate topos.


title:
Remarks on the Fact that the Uncertainty Principle Does Not Determine
  the Quantum State

abstract:
  We discuss the relation between density matrices and the uncertainty
principle; this allows us to justify and explain a recent statement by Man'ko
et al. We thereafter use Hardy's uncertainty principle to prove a new result
for Wigner distributions dominated by a Gaussian and we relate this result to
the coarse-graining of phase-space by "quantum blobs".


title:
A Topos Foundation for Theories of Physics: II. Daseinisation and the
  Liberation of Quantum Theory

abstract:
  This paper is the second in a series whose goal is to develop a fundamentally
new way of constructing theories of physics. The motivation comes from a desire
to address certain deep issues that arise when contemplating quantum theories
of space and time. Our basic contention is that constructing a theory of
physics is equivalent to finding a representation in a topos of a certain
formal language that is attached to the system. Classical physics arises when
the topos is the category of sets. Other types of theory employ a different
topos. In this paper, we study in depth the topos representation of the
propositional language, PL(S), for the case of quantum theory. In doing so, we
make a direct link with, and clarify, the earlier work on applying topos theory
to quantum physics. The key step is a process we term `daseinisation' by which
a projection operator is mapped to a sub-object of the spectral presheaf--the
topos quantum analogue of a classical state space. In the second part of the
paper we change gear with the introduction of the more sophisticated local
language L(S). From this point forward, throughout the rest of the series of
papers, our attention will be devoted almost entirely to this language. In the
present paper, we use L(S) to study `truth objects' in the topos. These are
objects in the topos that play the role of states: a necessary development as
the spectral presheaf has no global elements, and hence there are no
microstates in the sense of classical physics. Truth objects therefore play a
crucial role in our formalism.


title:
Quantum States and Hardy's Formulation of the Uncertainty Principle : a
  Symplectic Approach

abstract:
  We express the condition for a phase space Gaussian to be the Wigner
distribution of a mixed quantum state in terms of the symplectic capacity of
the associated Wigner ellipsoid. Our results are motivated by Hardy's
formulation of the uncertainty principle for a function and its Fourier
transform. As a consequence we are able to state a more general form of Hardy's
theorem.


title:
A Topos Foundation for Theories of Physics: III. The Representation of
  Physical Quantities With Arrows

abstract:
  This paper is the third in a series whose goal is to develop a fundamentally
new way of viewing theories of physics. Our basic contention is that
constructing a theory of physics is equivalent to finding a representation in a
topos of a certain formal language that is attached to the system. In paper II,
we studied the topos representations of the propositional language PL(S) for
the case of quantum theory, and in the present paper we do the same thing for
the, more extensive, local language L(S). One of the main achievements is to
find a topos representation for self-adjoint operators. This involves showing
that, for any physical quantity A, there is an arrow
$\breve{\delta}^o(A):\Sig\map\SR$, where $\SR$ is the quantity-value object for
this theory. The construction of $\breve{\delta}^o(A)$ is an extension of the
daseinisation of projection operators that was discussed in paper II. The
object $\SR$ is a monoid-object only in the topos, $\tau_\phi$, of the theory,
and to enhance the applicability of the formalism, we apply to $\SR$ a topos
analogue of the Grothendieck extension of a monoid to a group. The resulting
object, $\kSR$, is an abelian group-object in $\tau_\phi$. We also discuss
another candidate, $\PR{\mathR}$, for the quantity-value object. In this
presheaf, both inner and outer daseinisation are used in a symmetric way.
Finally, there is a brief discussion of the role of unitary operators in the
quantum topos scheme.


title:
Cavity-enhanced superradiant Rayleigh scattering with ultra-cold and
  Bose-Einstein condensed atoms

abstract:
  We report on the observation of collective atomic recoil lasing and
superradiant Rayleigh scattering with ultracold and Bose-Einstein condensed
atoms in an optical ring cavity. Both phenomena are based on instabilities
evoked by the collective interaction of light with cold atomic gases. This
publication clarifies the link between the two effects. The observation of
superradiant behavior with thermal clouds as hot as several tens of
$\mu\textrm{K}$ proves that the phenomena are driven by the cooperative
dynamics of the atoms, which is strongly enhanced by the presence of the ring
cavity.


title: A Topos Foundation for Theories of Physics: IV. Categories of Systems

abstract:
  This paper is the fourth in a series whose goal is to develop a fundamentally
new way of building theories of physics. The motivation comes from a desire to
address certain deep issues that arise in the quantum theory of gravity. Our
basic contention is that constructing a theory of physics is equivalent to
finding a representation in a topos of a certain formal language that is
attached to the system. Classical physics arises when the topos is the category
of sets. Other types of theory employ a different topos. The previous papers in
this series are concerned with implementing this programme for a single system.
In the present paper, we turn to considering a collection of systems: in
particular, we are interested in the relation between the topos representation
for a composite system, and the representations for its constituents. We also
study this problem for the disjoint sum of two systems. Our approach to these
matters is to construct a category of systems and to find a topos
representation of the entire category.


title: Dynamics of Quantum Dot Photonic Crystal Lasers

abstract:
  Quantum dot photonic crystal membrane lasers were fabricated and the large
signal modulation characteristics were studied. We find that the modulation
characteristics of quantum dot lasers can be significantly improved using
cavities with large spontaneous emission coupling factor. Our experiments show,
and simulations confirm, that the modulation rate is limited by the rate of
carrier capture into the dots to around 30GHz in our present system.


title:
The entanglement character between atoms in the non-degenerate two
  photons Tavis-Cummings model

abstract:
  The entanglement character including the so-called sudden death effect
between atoms in the non-degenerate two photons Tavis-Cummings model is studied
by means of concurrence. The results show that the so-called sudden death
effect occurs only for some kind of initial states. In other words, the
phenomenon is sensitive to the initial conditions. One can expect the
resurrection of the original entanglement to occur in a periodic way following
each sudden death event. The length of the time interval for the zero
entanglement is dependent on not only the degree of entanglement of the initial
state but also the initial state. And the influence of dipole-dipole
interaction and different atomic initial states on entanglement between atoms
are discussed. The sudden death effect can be weakened by the introducing of
dipole-dipole interaction.


title: Symmetry implies independence

abstract:
  Given a quantum system consisting of many parts, we show that symmetry of the
system's state, i.e., invariance under swappings of the subsystems, implies
that almost all of its parts are virtually identical and independent of each
other. This result generalises de Finetti's classical representation theorem
for infinitely exchangeable sequences of random variables as well as its
quantum-mechanical analogue. It has applications in various areas of physics as
well as information theory and cryptography. For example, in experimental
physics, one typically collects data by running a certain experiment many
times, assuming that the individual runs are mutually independent. Our result
can be used to justify this assumption.


title:
Non-relativistic Schroedinger theory on q-deformed quantum spaces I,
  Mathematical framework and equations of motion

abstract:
  The aim of these three papers (I, II, and III) is to develop a q-deformed
version of non-relativistic Schroedinger theory. Paper I introduces the
fundamental mathematical and physical concepts. The braided line and the
three-dimensional q-deformed Euclidean space play the role of position space.
For both cases the algebraic framework is extended by a time element. A short
review of the elements of q-deformed analysis on the spaces under consideration
is given. The time evolution operator is introduced in a consistent way and its
basic properties are discussed. These reasonings are continued by proposing
q-deformed analogs of the Schroedinger and the Heisenberg picture.


title: Quantum nonlocality without hidden variables: An algorithmic approach

abstract:
  Is quantum mechanics (QM) local or nonlocal? Different
formulations/interpretations (FI) of QM, with or without hidden variables,
suggest different answers. Different FI's can be viewed as different
algorithms, which leads us to propose an algorithmic definition of locality
according to which a theory is local if and only if there exists at least one
FI in which all irreducible elements of that FI are local. The fact that no
such FI of QM is known strongly supports quantum nonlocality.


title:
Non-relativistic Schroedinger theory on q-deformed quantum spaces II,
  The free non-relativistic particle and its interactions

abstract:
  This is the second part of a paper about a q-deformed analog of
non-relativistic Schroedinger theory. It applies the general ideas of part I
and tries to give a description of one-particle states on q-deformed quantum
spaces like the braided line or the q-deformed Euclidean space in three
dimensions. Hamiltonian operators for the free q-deformed particle in one as
well as three dimensions are introduced. Plane waves as solutions to the
corresponding Schroedinger equations are considered. Their completeness and
orthonormality relations are written down. Expectation values of position and
momentum observables are taken with respect to one-particle states and their
time-dependence is discussed. A potential is added to the free-particle
Hamiltonians and q-analogs of the Ehrenfest theorem are derived from the
Heisenberg equations of motion. The conservation of probability is proved.


title:
Non-relativistic Schroedinger theory on q-deformed quantum spaces III,
  Scattering theory

abstract:
  This is the third part of a paper about non-relativistic Schroedinger theory
on q-deformed quantum spaces like the braided line or the three-dimensional
q-deformed Euclidean space. Propagators for the free q-deformed particle are
derived and their basic properties are discussed. A time-dependent formulation
of scattering is proposed. In this respect, q-analogs of the Lippmann-Schwinger
equation are given. Expressions for their iterative solutions are written down.
It is shown how to calculate S-matrices and transition probabilities.
Furthermore, attention is focused on the question what becomes of unitarity of
S-matrices in a q-deformed setting. The examinations are concluded by a
discussion of the interaction picture and its relation to scattering processes.


title: Laser-induced ultrafast electron emission from a field emission tip

abstract:
  We show that a field emission tip electron source that is triggered with a
femtosecond laser pulse can generate electron pulses shorter than the laser
pulse duration (~100 fs). The emission process is sensitive to a power law of
the laser intensity, which supports an emission mechanism based on multiphoton
absorption followed by over-the-barrier emission. Observed continuous
transitions between power laws of different orders are indicative of field
emission processes. We show that the source can also be operated so that
thermionic emission processes become significant. Understanding these different
emission processes is relevant for the production of sub-cycle electron pulses.


title:
Single-atom entropy squeezing for two two-level atoms interacting with a
  single-mode radiation field

abstract:
  In this paper we consider a system of two two-level atoms interacting with a
single-mode quantized electromagnetic field in a lossless resonant cavity via
$l$-photon-transition mechanism. The field and the atoms are initially prepared
in the coherent state and the excited atomic states, respectively. For this
system we investigate the entropy squeezing, the atomic variances, the von
Neumann entropy and the atomic inversions for the single-atom case. We show
that the more the number of the parties in the system the less the amounts of
the nonclassical effects exhibited in the entropy squeezing.
  The entropy squeezing can give information on the corresponding von Neumann
entropy. Also the nonclassical effects obtained form the asymmetric atoms are
greater than those obtained form the symmetric atoms. Finally, the entropy
squeezing gives better information than the atomic variances only for the
asymmetric atoms.


title: Balanced homodyne detectors in QFT

abstract:
  Within the dipole approximation we describe the interaction of a photodiode
with the quantum electric field. The diode is modelled by an electron in a
bound state which upon interaction, treated perturbatively in the paper, can
get excited to one of the scattering states. We furthermore analyze a balanced
homodyne detector (BHD) with a local oscillator (LO) consisting of two
photodiodes illuminated by a monochromatic coherent state. We show, that to the
leading order the BHD's output measures the expectation value of the quantum
electric field, in the state without the LO, restricted to the frequency of the
LO. The square of the output measures the two-point function of the quantum
field. This shows that the BHDs provide tools for measurements of sub-vacuum
(negative) expectation values of the squares quantum fields and thus for test
of Quantum Energy Inequality - like bounds, or other QFT effects under the
influence of external conditions.


title: Sudden death and long-lived entanglement of two three-level trapped ions

abstract:
  The dynamical properties of quantum entanglement in two three-level trapped
ions interacting with a laser field are studied in terms of the negative
eigenvalues of the partial transposition of the density operator. In contrast
to the usual belief that destroying the entanglement can be observed due to the
environment, it is found that the Stark shift can also produce sudden death of
entanglement and long-lived entanglement between the qubits that are prepared
initially in separable states or mixed states.


title:
Energy-levels crossing and radial Dirac equation: Supersymmetry and
  quasi-parity spectral signatures

abstract:
  The (3+1)-dimensional Dirac equation with position dependent mass in 4-vector
electromagnetic fields is considered. Using two over-simplified examples (the
Dirac-Coulomb and Dirac-oscillator fields), we report energy-levels crossing as
a spectral property or as an effect of the hidden supersymmetric quantum
mechanical language and/or quasi-parity signatures. Under different settings of
the related interactions' way-of-coupling into Dirac equation, it is observed
that the two ultimate/effective descendents, Dirac-Coulomb and
Dirac-oscillator, exhibit different conditions on the energy-levels crossings.


title: Phase-covariant cloning of coherent states

abstract:
  We consider the problem of phase-covariant cloning for coherent states. We
show that an experimental scheme based on ideal phase measurement and
feedforward outperforms the semiclassical procedure of ideal phase measurement
and preparation in terms of fidelity. A realistic scheme where the ideal phase
measurement is replaced with double-homodyne detection is shown to be unable to
overcome the semiclassical cloning strategy. On the other hand, such a
realistic scheme is better than semiclassical cloning based on double-homodyne
phase measurement and preparation.


title:
Quantum bit string commitment protocol using polarization of mesoscopic
  coherent states

abstract:
  In this work, we propose a quantum bit string commitment protocol using
polarization of mesoscopic coherent states. The protocol is described and its
security against brute force and quantum cloning machine attack is analyzed.


title:
Decoherence-free quantum-information processing using dipole-coupled
  qubits

abstract:
  We propose a quantum-information processor that consists of decoherence-free
logical qubits encoded into arrays of dipole-coupled qubits. High-fidelity
single-qubit operations are performed deterministically within a
decoherence-free subsystem without leakage via global addressing of bichromatic
laser fields. Two-qubit operations are realized locally with four physical
qubits, and between separated logical qubits using linear optics. We show how
to prepare cluster states using this method. We include all
non-nearest-neighbor effects in our calculations, and we assume the qubits are
not located in the Dicke limit. Although our proposal is general to any system
of dipole-coupled qubits, throughout the paper we use nitrogen-vacancy (NV)
centers in diamond as an experimental context for our theoretical results.


title: On the Quantum Circuit Complexity Equivalence

abstract:
  Nielsen \cite{Nielsen05} recently asked the following question: "What is the
minimal size quantum circuit required to exactly implement a specified $%
\mathit{n}$-qubit unitary operation $U$, without the use of ancilla qubits?"
Nielsen was able to prove that a lower bound on the minimal size circuit is
provided by the length of the geodesic between the identity $I$ and $U$, where
the length is defined by a suitable Finsler metric on $SU(2^{n})$. We prove
that the minimum circuit size that simulates $U$ is in linear relation with the
geodesic length and simulation parameters, for the given Finsler structure $F$.
As a corollary we prove the highest lower bound of $O(\frac{%
n^{4}}{p}d_{F_{p}}^{2}(I,U)L_{F_{p}}(I,\tilde{U})) $and the lowest upper bound
of $\Omega (n^{4}d_{F_{p}}^{3}(I,U))$, for the standard simulation technique.
Therefore, our results show that by standard simulation one can not expect a
better then $n^{2}$ times improvement in the upper bound over the result from
Nielsen, Dowling, Gu and Doherty \cite{Nielsen06}. Moreover, our equivalence
result can be applied to the arbitrary path on the manifold including the one
that is generated adiabatically.


title: Negative Entanglement Measure, and What It Implies

abstract:
  In this paper, we extract from concurrence its variable part, denoted
$\Lambda$, and use $\Lambda$ as a time-dependent measure of "distance", either
postive or negative, from the separability boundary. We use it to investigate
entanglement dynamics of two isolated but initially entangled qubits, each
coupled to its own environment.


title:
Phase Controlled Continuously Entangled Two-Photon Laser with Double
  $\Lambda$ Scheme

abstract:
  We show that an absolute coherent phase of a laser can be used to manipulate
the entanglement of photon pairs of two-photon laser. Our focus is on the
generation of a continuous source of entangled photon pairs in the double
$\Lambda $ (or Raman) scheme. We study the dependence of steady state
entanglement on the phase and laser parameters. We obtain a relationship
between entanglement and two-photon correlation. We derive conditions that give
steady state entanglement for the Raman-EIT scheme and use it to identify
region of steady state macroscopic entanglement. No entanglement is found for
the double resonant Raman scheme for any laser parameters.


title: Discrete squeezed states for finite-dimensional spaces

abstract:
  We show how discrete squeezed states in an $N^{2}$-dimensional phase space
can be properly constructed out of the finite-dimensional context. Such
discrete extensions are then applied to the framework of quantum tomography and
quantum information theory with the aim of establishing an initial study on the
interference effects between discrete variables in a finite phase-space.
Moreover, the interpretation of the squeezing effects is seen to be direct in
the present approach, and has some potential applications in different branches
of physics.


title: Wick's theorem for q-deformed boson operators

abstract:
  In this paper combinatorial aspects of normal ordering arbitrary words in the
creation and annihilation operators of the q-deformed boson are discussed. In
particular, it is shown how by introducing appropriate q-weights for the
associated ``Feynman diagrams'' the normally ordered form of a general
expression in the creation and annihilation operators can be written as a sum
over all q-weighted Feynman diagrams, representing Wick's theorem in the
present context.


title: Determining the equivalence for 1-way quantum finite automata

abstract:
  In this paper, we focus on determining the equivalence for {\it 1-way quantum
finite automata with control language} (CL-1QFAs) defined by Bertoni et al and
{\it measure-many 1-way quantum finite automata} (MM-1QFAs) introduced by
Kondacs and Watrous. More specifically, we obtain that: \begin{enumerate}
  \item[(i)] Two CL-1QFAs ${\cal A}_1$ and ${\cal A}_2$ with control languages
(regular languages) ${\cal L}_1$ and ${\cal L}_2$, respectively, are equivalent
if and only if they are $(c_1n_1^2+c_2n_2^2-1)$-equivalent. Furthermore, if
${\cal L}_1$ and ${\cal L}_2$ are given in the form of DFAs, with $m_1$ and
$m_2$ states, respectively, then there exists a polynomial-time algorithm
running in time $O ((m_1n_1^2+m_2n_2^2)^4)$ that takes as input ${\cal A}_1$
and ${\cal A}_2$ and determines whether they are equivalent. \item[(ii)] Two
MM-1QFAs ${\cal A}_1$ and ${\cal A}_2$ with $n_1$ and $n_2$ states,
respectively, are equivalent if and only if they are
$(3n_1^2+3n_2^2-1)$-equivalent. Furthermore, there is a polynomial-time
algorithm running in time $O ((3n_1^2+3n_2^2)^4)$ that takes as input ${\cal
A}_1$ and ${\cal A}_2$ and determines whether ${\cal A}_1$ and ${\cal A}_2$ are
equivalent.


title:
Exact Master Equation and Quantum Decoherence of Two Coupled Harmonic
  Oscillators in a General Environment

abstract:
  In this paper we derive an exact master equation for two coupled quantum
harmonic oscillators interacting via bilinear coupling with a common
environment at arbitrary temperature made up of many harmonic oscillators with
a general spectral density function. We first show a simple derivation based on
the observation that the two-harmonic oscillator model can be effectively
mapped into that of a single harmonic oscillator in a general environment plus
a free harmonic oscillator. Since the exact one harmonic oscillator master
equation is available [Hu, Paz and Zhang, Phys. Rev. D \textbf{45}, 2843
(1992)], the exact master equation with all its coefficients for this two
harmonic oscillator model can be easily deduced from the known results of the
single harmonic oscillator case. In the second part we give an influence
functional treatment of this model and provide explicit expressions for the
evolutionary operator of the reduced density matrix which are useful for the
study of decoherence and disentanglement issues. We show three applications of
this master equation: on the decoherence and disentanglement of two harmonic
oscillators due to their interaction with a common environment under Markovian
approximation, and a derivation of the uncertainty principle at finite
temperature for a composite object, modeled by two interacting harmonic
oscillators. The exact master equation for two, and its generalization to $N$,
harmonic oscillators interacting with a general environment are expected to be
useful for the analysis of quantum coherence, entanglement, fluctuations and
dissipation of mesoscopic objects towards the construction of a theoretical
framework for macroscopic quantum phenomena.


title:
Generating entanglement between quantum dots with different resonant
  frequencies based on Dipole Induced Transparency

abstract:
  We describe a method for generating entanglement between two spatially
separated dipoles coupled to optical micro-cavities.
  The protocol works even when the dipoles have different resonant frequencies
and radiative lifetimes.
  This method is particularly important for solid-state emitters, such as
quantum dots, which suffer from large inhomogeneous broadening. We show that
high fidelities can be obtained over a large dipole detuning range without
significant loss of efficiency. We analyze the impact of higher order photon
number states and cavity resonance mismatch on the performance of the protocol.


title:
Simple unconventional geometric scenario of one-way quantum computation
  with superconducting qubits inside a cavity

abstract:
  We propose a simple unconventional geometric scenario to achieve a kind of
nontrivial multi-qubit operations with superconducting charge qubits placed in
a microwave cavity. The proposed quantum operations are insensitive not only to
the thermal state of cavity mode but also to certain random operation errors,
and thus may lead to high-fidelity quantum information processing. Executing
the designated quantum operations, a class of highly entangled cluster states
may be generated efficiently in the present scalable solid-state system,
enabling one to achieve one-way quantum computation.


title: Quantum estimation of a damping constant

abstract:
  We discuss an interferometric approach to the estimation of quantum
mechanical damping. We study specific classes of entangled and separable probe
states consisting of superpositions of coherent states. Based on the assumption
of limited quantum resources we show that entanglement improves the estimation
of an unknown damping constant.


title: Thermodynamics of Pseudo-Hermitian Systems in Equilibrium

abstract:
  In study of pseudo(quasi)-hermitian operators, the key role is played by the
positive-definite metric operator. It enables physical interpretation of the
considered systems. In the article, we study the pseudo-hermitian systems with
constant number of particles in equilibrium. We show that the explicit
knowledge of the metric operator is not essential for study of thermodynamic
properties of the system. We introduce a simple example where the physically
relevant quantities are derived without explicit calculation of either metric
operator or spectrum of the Hamiltonian.


title:
Generalized measurement of the non-normal two-boson operator $Z_\gamma =
  a_1 + \gamma a_2^\dag$

abstract:
  We address the generalized measurement of the two-boson operator $Z_\gamma=
a_1 + \gamma a_2^\dag$ which, for $|\gamma|^2 \neq 1$, is not normal and cannot
be detected by a joint measurement of quadratures on the two bosons. We
explicitly construct the minimal Naimark extension, which involves a single
additional bosonic system, and present its decomposition in terms of two-boson
linear SU(2) interactions. The statistics of the measurement and the added
noise are analyzed in details. Results are exploited to revisit the
Caves-Shapiro concept of generalized phase observable based on heterodyne
detection.


title: Laser theory in manifest Lindblad form

abstract:
  We discuss the laser theory for a single-mode laser with nonlinear gain. We
focus in particular on a micromaser which is pumped with a dilute beam of
excited atoms crossing the laser cavity. In the weak-coupling regime, an
expansion in the coupling strength is developed that preserves the Lindblad
form of the master equation, securing the positivity of the density matrix.
This expansion breaks rapidly down above threshold. This can be improved with
an alternative approach, not restricted to weak coupling: the Lindblad
operators are expanded in orthogonal polynomials adapted to the probability
distribution for the atom-laser interaction time. Results for the photon
statistics and the laser linewidth illustrate the theory.


title: Entanglement-swapping boxes and their communication properties

abstract:
  We pose the fundamental question of communication properties of primitives
irrespectively of their implementation. To illustrate the idea we introduce the
concept of entanglement-swapping boxes, i.e. we consider any quantum operations
which perform entanglement swapping, not necessarily via simple quantum
teleportation. We ask a question about the properties of such boxes., i.e. what
local operations and how much classical communication are needed to perform
them. We also ask if any box which performs entanglement swapping can be used
to establish classical communication. We show that each box needs at least two
bits of classical communication to perform it. It is also shown that each box
can be used for classical communication and, most importantly, that there exist
boxes which allow to communicate at most one bit. Surprisingly we find basic
irreversibility in the process of entanglement swapping with respect to its
communication properties.


title: Ultracompact Generation of Continuous-Variable Cluster States

abstract:
  We propose an experimental scheme that has the potential for large-scale
realization of continuous-variable (CV) cluster states for universal quantum
computation. We do this by mapping CV cluster-state graphs onto two-mode
squeezing graphs, which can be engineered into a single optical parametric
oscillator (OPO). The desired CV cluster state is produced directly from a
joint squeezing operation on the vacuum using a multi-frequency pump beam. This
method has potential for ultracompact experimental implementation. As an
illustration, we detail an experimental proposal for creating a four-mode
square CV cluster state with a single OPO.


title: Separability in terms of a single entanglement witness

abstract:
  The separability problem is formulated in terms of a characterization of a
single entanglement witness. More specifically, we show that any (in general
multipartite) state \varrho is separable if and only if a specially constructed
entanglement witness W_{\varrho} is weakly optimal, i.e., its expectation value
vanishes on at least one product vector. Interestingly, the witness can always
be chosen to be decomposable. Our result changes the conceptual aspect of the
separability problem and rises some questions about properties of positive
maps.


title:
Multipartite quantum correlation and entanglement in four-qubit pure
  states

abstract:
  Based on the quantitative complementarity relations, we analyze thoroughly
the properties of multipartite quantum correlations and entanglement in
four-qubit pure states. We find that, unlike the three-qubit case, the single
residual correlation, the genuine three- and four-qubit correlations are not
suited to quantify entanglement. More interestingly, from our qualitative and
numerical analysis, it is conjectured that the sum of all the residual
correlations may constitute a good measure for the total multipartite
entanglement in the system.


title: Dilemma that cannot be resolved by biased quantum coin flipping

abstract:
  We show that a biased quantum coin flip (QCF) cannot provide the performance
of a black-boxed biased coin flip, if it satisfies some fidelity conditions.
Although such a QCF satisfies the security conditions of a biased coin flip, it
does not realize the ideal functionality, and therefore, does not fulfill the
demands for universally composable security. Moreover, through a comparison
within a small restricted bias range, we show that an arbitrary QCF is
distinguishable from a black-boxed coin flip unless it is unbiased on both
sides of parties against insensitive cheating. We also point out the difficulty
in developing cheat-sensitive quantum bit commitment in terms of the
uncomposability of a QCF.


title: Time Dependent Entropy of Constant Force Motion

abstract:
  Time dependent entropy of constant force motion is investigated. Their joint
entropy so called Leipnik's entropy is obtained. The main purpose of this work
is to calculate Leipnik's entropy by using time dependent wave function which
is obtained by the Feynman path integral method. It is found that, in this
case, the Leipnik's entropy increase with time and this result has same
behavior free particle case.


title:
Analytical Solutions to the Hulthen and the Morse Potentials by using
  the Asymptotic Iteration Method

abstract:
  We present the exact analytical solution of the radial Schr\"{o}dinger
equation for the deformed Hulth\'{e}n and the Morse potentials within the
framework of the Asymptotic Iteration Method. The bound state energy
eigenvalues and corresponding wave functions are obtained explicitly. Our
results are in excellent agreement with the findings of the other methods.


title:
The Energy Eigenvalues of the Two Dimensional Hydrogen Atom in a
  Magnetic Field

abstract:
  In this paper, the energy eigenvalues of the two dimensional hydrogen atom
are presented for the arbitrary Larmor frequencies by using the asymptotic
iteration method. We first show the energy eigenvalues for the no magnetic
field case analytically, and then we obtain the energy eigenvalues for the
strong and weak magnetic field cases within an iterative approach for $n=2-10$
and $m=0-1$ states for several different arbitrary Larmor frequencies. The
effect of the magnetic field on the energy eigenvalues is determined precisely.
The results are in excellent agreement with the findings of the other methods
and our method works for the cases where the others fail.


title: "Quantumness" versus "Classicality" of Quantum States

abstract:
  Entanglement is one of the pillars of quantum mechanics and quantum
information processing, and as a result the quantumness of nonentangled states
has typically been overlooked and unrecognized. We give a robust definition for
the classicality versus quantumness of a single multipartite quantum state, a
set of states, and a protocol using quantum states. We show a variety of
nonentangled (separable) states that exhibit interesting quantum properties,
and we explore the ``zoo'' of separable states; several interesting subclasses
are defined based on their diagonalizing bases, and their non-classical
behavior is investigated.


title: Semiclassical analysis of Wigner $3j$-symbol

abstract:
  We analyze the asymptotics of the Wigner $3j$-symbol as a matrix element
connecting eigenfunctions of a pair of integrable systems, obtained by lifting
the problem of the addition of angular momenta into the space of Schwinger's
oscillators. A novel element is the appearance of compact Lagrangian manifolds
that are not tori, due to the fact that the observables defining the quantum
states are noncommuting. These manifolds can be quantized by generalized
Bohr-Sommerfeld rules and yield all the correct quantum numbers. The geometry
of the classical angular momentum vectors emerges in a clear manner. Efficient
methods for computing amplitude determinants in terms of Poisson brackets are
developed and illustrated.


title: A bird's eye view of quantum computers

abstract:
  Quantum computers are discussed in the general framework of computation, the
laws of physics and the foundations of quantum mechanics.


title:
Bell-states diagonal entanglement witnesses for relativistic and
  non-relativistic multispinor systems in arbitrary dimensions

abstract:
  Two kinds of Bell-states diagonal (BSD) entanglement witnesses (EW) are
constructed by using the algebra of Dirac $\gamma$ matrices in the space-time
of arbitrary dimension $d$, where the first kind can detect some BSD
relativistic and non-relativistic $m$-partite multispinor bound entangled
states in Hilbert space of dimension $2^{m\lfloor d/2\rfloor}$, including the
bipartite Bell-type and iso-concurrence type states in the four-dimensional
space-time ($d=4$). By using the connection between Hilbert-Schmidt measure and
the optimal EWs associated with states, it is shown that as far as the spin
quantum correlations is concerned, the amount of entanglement is not a
relativistic scalar and has no invariant meaning. The introduced EWs are
manipulated via the linear programming (LP) which can be solved exactly by
using simplex method. The decomposability or non-decomposability of these EWs
is investigated, where the region of non-decomposable EWs of the first kind is
partially determined and it is shown that, all of the EWs of the second kind
are decomposable. These EWs have the preference that in the bipartite systems,
they can determine the region of separable states, i.e., bipartite
non-detectable density matrices of the same type as the EWs of the first kind
are necessarily separable. Also, multispinor EWs with non-polygon feasible
regions are provided, where the problem is solved by approximate LP, and in
contrary to the exactly manipulatable EWs, both the first and second kind of
the optimal approximate EWs can detect some bound entangled states.
  Keywords: Relativistic entanglement, Entanglement Witness, Multispinor,
Linear Programming, Feasible Region. PACs Index: 03.65.Ud


title: Quantum Key Distribution with Classical Bob

abstract:
  Secure key distribution among two remote parties is impossible when both are
classical, unless some unproven (and arguably unrealistic)
computation-complexity assumptions are made, such as the difficulty of
factorizing large numbers. On the other hand, a secure key distribution is
possible when both parties are quantum.
  What is possible when only one party (Alice) is quantum, yet the other (Bob)
has only classical capabilities? We present a protocol with this constraint,
and prove its robustness against attacks: we prove that any attempt of an
adversary to obtain information (and even a tiny amount of information)
necessarily induces some errors that the legitimate users could notice.


title: State reconstruction for composite systems of two spatial qubits

abstract:
  Pure entangled states of two spatial qudits have been produced by using the
momentum transverse correlation of the parametric down-converted photons [Phys.
Rev. Lett. \textbf{94} 100501]. Here we show a generalization of this process
to enable the creation of mixed states of spatial qudits and by using the
technique proposed we generate mixed states of spatial qubits. We also report
how the process of quantum tomography is experimentally implemented to
characterize these states. This tomographic reconstruction is based on the free
evolution of spatial qubits, coincidence detection and a filtering process. The
reconstruction method can be generalized for the case of two spatial qudits.


title:
Signatures of non-locality in the first-order coherence of the scattered
  light

abstract:
  The spatial coherence of an atomic wavepacket can be detected in the
scattered photons, even when the center-of-mass motion is in the quantum
coherent superposition of two distant, non-overlapping wave packets. Spatial
coherence manifests itself in the power spectrum of the emitted photons, whose
spectral components can exhibit interference fringes as a function of the
emission angle. The contrast and the phase of this interference pattern provide
information about the quantum state of the center of mass of the scattering
atom.


title:
Realization of continuous-outcome measurements on finite dimensional
  quantum systems

abstract:
  This note contains the complete mathematical proof of the main Theorem of the
paper "How continuous measurements in finite dimension are actually discrete"
(quant-ph/0702068), thus showing that in finite dimension any measurement with
continuous set of outcomes can be simply realized by randomizing some classical
parameter and conditionally performing a measurement with finite outcomes.


title:
Strong low-frequency quantum correlations from a four-wave mixing
  amplifier

abstract:
  We show that a simple scheme based on nondegenerate four-wave mixing in a hot
atomic vapor behaves like a near-perfect phase-insensitive optical amplifier,
which can generate bright twin beams with a measured quantum noise reduction in
the intensity difference of more than 8 dB, close to the best optical
parametric amplifiers and oscillators. The absence of a cavity makes the system
immune to external perturbations, and the strong quantum noise reduction is
observed over a large frequency range.


title: Graphs, Quadratic Forms, and Quantum Codes

abstract:
  We show that any stabilizer code over a finite field is equivalent to a
graphical quantum code. Furthermore we prove that a graphical quantum code over
a finite field is a stabilizer code. The technique used in the proof
establishes a new connection between quantum codes and quadratic forms. We
provide some simple examples to illustrate our results.


title: Quantum Convolutional BCH Codes

abstract:
  Quantum convolutional codes can be used to protect a sequence of qubits of
arbitrary length against decoherence. We introduce two new families of quantum
convolutional codes. Our construction is based on an algebraic method which
allows to construct classical convolutional codes from block codes, in
particular BCH codes. These codes have the property that they contain their
Euclidean, respectively Hermitian, dual codes. Hence, they can be used to
define quantum convolutional codes by the stabilizer code construction. We
compute BCH-like bounds on the free distances which can be controlled as in the
case of block codes, and establish that the codes have non-catastrophic
encoders.


title: Geometric Phase for degenerate states of spin-1 and spin-1/2 pair

abstract:
  The geometric phase of a bi-particle model is discussed. For different
initial states, especially when the initial state is pure or mixed, the
geometric phase will show different properties. The relationship between the
geometric phase and the entanglement or mixedness of the initial state is
considered.


title:
Control of photon propagation via electromagnetically induced
  transparency in lossless media

abstract:
  We study the influence of a lossless material medium on the coherent storage
and quantum state transfer of a quantized probe light in an ensemble of
$\Lambda $-type atoms. The medium is modeled as uniformly distributed two-level
atoms with same energy level spacing, coupling to a probe light. This coupled
system can be simplified to a collection of two-mode polaritons which couple to
one transition of the $\Lambda$-type atoms. We show that, when the other
transition of $\Lambda$-type atoms is controlled by a classical light, the
electromagnetically induced transparency can also occur for the polaritons. In
this case the coherent storage and quantum transfer for photon states are
achievable through the novel dark states with respect to the polaritons. By
calculating the corresponding dispersion relation, we find the ensemble of the
three-level atoms with $\Lambda$-type transitions may serve as quantum memory
for it slows or even stops the light propagation through the mechanism of
electromagnetically induced transparency. the corresponding dispersion
relation, we find the ensemble of the three-level atoms with $\Lambda$-type
transitions may serve as quantum memory for it slows or even stops the light
propagation through the mechanism of electromagnetically induced transparency.


title:
Efficient and High-Fidelity Generation of Atomic Cluster State with
  Cavity-QED and Linear Optics

abstract:
  We propose a scheme to generate cluster states of atomic qubits by using
cavity quantum electrodynamics (QED) and linear optics, in which each atom is
confined in a resonant optical cavity with two orthogonally polarized modes.
Our scheme is robust to imperfect factors such as dissipation, photon loss, and
detector inefficiency. Discussions are made for experimental feasibility of our
scheme.


title: Hyperentangled Bell-state analysis

abstract:
  It is known that it is impossible to unambiguously distinguish the four Bell
states encoded in pairs of photon polarizations using only linear optics.
However, hyperentanglement, the simultaneous entanglement in more than one
degree of freedom, has been shown to assist the complete Bell analysis of the
four Bell states (given a fixed state of the other degrees of freedom). Yet
introducing other degrees of freedom also enlarges the total number of
Bell-like states. We investigate the limits for unambiguously distinguishing
these Bell-like states. In particular, when the additional degree of freedom is
qubit-like, we find that the optimal one-shot discrimination schemes are to
group the 16 states into 7 distinguishable classes, and that an unambiguous
discrimination is possible with two identical copies.


title:
Complementarity and the nature of uncertainty relations in Einstein-Bohr
  recoiling slit experiment

abstract:
  A model of the Einstein-Bohr double-slit experiment is formulated in a fully
quantum theoretical setting. In this model, the state and dynamics of a movable
wall that has the double slits in it, as well as the state of a particle
incoming to the double slits, are described by quantum mechanics. Using this
model, we analyzed complementarity between exhibiting the interference pattern
and distinguishing the particle path. Comparing the Kennard-Robertson type and
the Ozawa-type uncertainty relations, we conclude that the uncertainty relation
involved in the double-slit experiment is not the Ozawa-type uncertainty
relation but the Kennard-type uncertainty relation of the position and the
momentum of the double-slit wall. A possible experiment to test the
complementarity relation is suggested. It is also argued that various phenomena
which occur at the interface of a quantum system and a classical system,
including distinguishability, interference, decoherence, quantum eraser, and
weak value, can be understood as aspects of entanglement.


title:
Quantum-Noise Power Spectrum of Fields with Discrete Classical
  Components

abstract:
  We present an algorithmic approach to calculate the quantum-noise spectral
density of photocurrents generated by optical fields with arbitrary discrete
classical spectrum in coherent or squeezed states. The measurement scheme may
include an arbitrary number of demodulations of the photocurrent. Thereby, our
method is applicable to the general heterodyne detection scheme which is
implemented in many experiments. For some of these experiments, e.g. in
laser-interferometric gravitational-wave detectors, a reliable prediction of
the quantum noise of fields in coherent and squeezed states plays a decisive
role in the design phase and detector characterization. Still, our
investigation is limited in two ways. First, we only consider coherent and
squeezed states of the field and second, we demand that the photocurrent
depends linearly on the field's vacuum amplitudes which means that at least one
of the classical components is comparatively strong.


title:
Comment on "A local realist model for correlations of the singlet
  state'' (De Raedt et al., Eur. Phys. J. B 53: 139-142, 2006)

abstract:
  De Raedt et al. (Eur. Phys. J. B 53: 139-142, 2006) have claimed to provide a
local realist model for correlations of the singlet state in the familiar
Einstein-Podolsky-Rosen-Bohm (EPRB) experiment when time-coincidence is used to
decide which detection events should count in the analysis, and furthermore
that this suggests that it is possible to construct local realistic models that
can reproduce the quantum mechanical expectation values. In this letter we show
that these conclusions cannot be upheld since their model exploits the
so-called coincidence-time loophole. When this is properly taken into account
no startling conclusions can be drawn about local realist modelling of quantum
mechanics.


title: The Geometry of Entanglement Sudden Death

abstract:
  In open quantum systems, entanglement can vanish faster than coherence. This
phenomenon is usually called sudden death of entanglement. In this paper sudden
death of entanglement is discussed from a geometrical point of view, in the
context of two qubits. A classification of possible scenarios is presented,
with important known examples classified. Theoretical and experimental
construction of other examples is suggested as well as large dimensional and
multipartite versions of the effect.


title: Quantum key distribution with entangled photon sources

abstract:
  A parametric down-conversion (PDC) source can be used as either a triggered
single photon source or an entangled photon source in quantum key distribution
(QKD). The triggering PDC QKD has already been studied in the literature. On
the other hand, a model and a post-processing protocol for the entanglement PDC
QKD are still missing. In this paper, we fill in this important gap by
proposing such a model and a post-processing protocol for the entanglement PDC
QKD. Although the PDC model is proposed to study the entanglement-based QKD, we
emphasize that our generic model may also be useful for other non-QKD
experiments involving a PDC source. Since an entangled PDC source is a basis
independent source, we apply Koashi-Preskill's security analysis to the
entanglement PDC QKD. We also investigate the entanglement PDC QKD with two-way
classical communications. We find that the recurrence scheme increases the key
rate and Gottesman-Lo protocol helps tolerate higher channel losses. By
simulating a recent 144km open-air PDC experiment, we compare three
implementations -- entanglement PDC QKD, triggering PDC QKD and coherent state
QKD. The simulation result suggests that the entanglement PDC QKD can tolerate
higher channel losses than the coherent state QKD. The coherent state QKD with
decoy states is able to achieve highest key rate in the low and medium-loss
regions. By applying Gottesman-Lo two-way post-processing protocol, the
entanglement PDC QKD can tolerate up to 70dB combined channel losses (35dB for
each channel) provided that the PDC source is placed in between Alice and Bob.
After considering statistical fluctuations, the PDC setup can tolerate up to
53dB channel losses.


title: The effect of self-affine fractal roughness of wires on atom chips

abstract:
  Atom chips use current flowing in lithographically patterned wires to produce
microscopic magnetic traps for atoms. The density distribution of a trapped
cold atom cloud reveals disorder in the trapping potential, which results from
meandering current flow in the wire. Roughness in the edges of the wire is
usually the main cause of this behaviour. Here, we point out that the edges of
microfabricated wires normally exhibit self-affine roughness. We investigate
the consequences of this for disorder in atom traps. In particular, we consider
how closely the trap can approach the wire when there is a maximum allowable
strength of the disorder. We comment on the role of roughness in future
atom--surface interaction experiments.


title:
Immeasurability of Zero-point Energy in the Cosmological Constant
  problem

abstract:
  A huge discrepancy between the zero-point energy calculated from quantum
theory and the observed quantity in the Universe has been one of the most
illusive problems in physics. In order to examine the measurability of
zero-point energy, we construct reference frames in a given measurement using
observables. Careful and explicit construction of the reference frames
surprisingly reveals that not only is the harmonic oscillator fluctuating at
the ground level, but so is the reference frame when the measurement is
realized. The argument is then extended to examine the measurability of vacuum
energy for a quantized electromagnetic field, and it is shown that while
zero-point energy calculated from quantum theory diverges to infinity, it is
not measurable.


title: Hidden Variables and Quantum Statistics Nature

abstract:
  It is shown that the nature of quantum statistics can be clarified by
assuming the existence of a background of random gravitational fields and
waves, distributed isotropically in the space. This background is responsible
for correlating phases of oscillations of identical microobjects. If such a
background of random gravitational fields and waves is considered as hidden
variables then taking it into account leads to the Bell-type inequalities that
are fairly consistent with the experimental data.


title: Quantum interference with slits

abstract:
  In the experiments considered here, we measure the y-component of momentum
for a particle passing through a system of slits. The source-slit system is the
preparation apparatus that determines the state vector. Recognizing that a
system of slits is a position-measuring device allows us to ascertain that the
state vector is a position state. Then, writing the state vector in momentum
space provides a straightforward calculation for the probability amplitude and
its corresponding probability function. Interference effects, if any, are
inherent in the probability function We determine the statistical distribution
of scattered particles for four different slit systems. The results are in
agreement with the well-known interference patterns obtained in classical wave
optics.


title: Three-Body Recombination in One Dimension

abstract:
  We study the three-body problem in one dimension for both zero and finite
range interactions using the adiabatic hyperspherical approach. Particular
emphasis is placed on the threshold laws for recombination, which are derived
for all combinations of the parity and exchange symmetries. For bosons, we
provide a numerical demonstration of several universal features that appear in
the three-body system, and discuss how certain universal features in three
dimensions are different in one dimension. We show that the probability for
inelastic processes vanishes as the range of the pair-wise interaction is taken
to zero and demonstrate numerically that the recombination threshold law
manifests itself for large scattering length.


title:
Coherent State Distinguishability in Continuous Variable Quantum
  Cryptography

abstract:
  We use the probability of error as a measure of distinguishability between
two pure and two mixed symmetric coherent states in the context of continuous
variable quantum cryptography. We show that the two mixed symmetric coherent
states (in which the various components have the same real part) never give an
eavesdropper more information than two pure coherent states.


title: When Do Superfluidity and Long Range Order Imply Entanglement?

abstract:
  We investigate tacitly assumed relationships between the concepts of
super-fluidity (-conductivity), long range order and entanglement. We prove
that the three are by no means equivalent, but that notwithstanding, some
rigorous implication can be established between them. This leads to three
different, albeit frequently related, notions of "criticality", all of which
are exemplified within the Hubbard model in the low density regime. We use
Peierls' method of twisted Hamiltonians to link the existence of entanglement
to superfluidity and (quasi)-long range order. As an application of our
formalism, we show that recent experiments with cold atoms already prove the
existence of the field theoretic, spatial entanglement in two dimensions. More
interestingly, the appearance of entanglement in these experiments seems to be
intimately related to the phase transition of the Kosterlitz Thouless type.


title:
Upper bound on our knowledge about noncommuting observables for a qubit
  system

abstract:
  A trade-off relation on our knowledge about two noncommuting observables of a
qubit system in simultaneous measurement is formulated. The obtained inequality
offers a quantitative information-theoretic representation of Bohr's principle
of complementarity, and can be interpreted as a trade-off relation on the
asymptotic accuracy of the maximum-likelihood estimation of the probability
distributions of observables.


title:
Exact solutions of the Schrodinger equation in D-dimensions for the
  pseudoharmonic potential plus ring-shaped potential

abstract:
  We present analytically the exact energy bound-states solutions of the
Schrodinger equation in $D$-dimensions for a pseudoharmonic potential plus
ring-shaped potential of the form $V(r,\theta)=D_{e}(\frac{r}{%
r_{e}}-\frac{r_{e}}{r}) ^{2}+\frac{\beta \cos ^{2}\theta}{r^{2}\sin
^{2}\theta}$ by means of the conventional Nikiforov-Uvarov method. We also give
a clear recipe of how to obtain an explicit solution to the radial and angular
parts of the wave functions in terms of orthogonal polynomials. The total
energy of the system is different from the pseudoharmonic potential because of
the contribution of the angular part. The general results obtained in this work
can be reduced to the standard forms given in the literature.


title: Nonlocality improves Deutsch algorithm

abstract:
  Recently, [{arXiv:0810.3134}] is accepted and published. We show that the
Bell inequalities lead to a new type of linear-optical Deutsch algorithms. We
have considered a use of entangled photon pairs to determine simultaneously and
probabilistically two unknown functions. The usual Deutsch algorithm determines
one unknown function and exhibits a two to one speed up in a certain
computation on a quantum computer rather than on a classical computer. We found
that the violation of Bell locality in the Hilbert space formalism of quantum
theory predicts that the proposed {\it probabilistic} Deutsch algorithm for
computing two unknown functions exhibits at least a $2\sqrt{2}(\simeq 2.83)$ to
one speed up.


title:
Nonclassical correlation in a multipartite quantum system: two measures
  and evaluation

abstract:
  There is a commonly recognized paradigm in which a multipartite quantum
system described by a density matrix having no product eigenbasis is considered
to possess nonclassical correlation. Supporting this paradigm, we define two
entropic measures of nonclassical correlation of a multipartite quantum system.
One is defined as the minimum uncertainty about a joint system after we collect
outcomes of particular local measurements. The other is defined by taking the
maximum over all local systems about the minimum distance between a genuine set
and a mimic set of eigenvalues of a reduced density matrix of a local system.
The latter measure is based on an artificial game to create mimic eigenvalues
of a reduced density matrix of a local system from eigenvalues of a density
matrix of a global system. Numerical computation of these measures for several
examples is performed.


title:
Local commutativity versus Bell inequality violation for entangled
  states and versus non-violation for separable states

abstract:
  By introducing a quantitative `degree of commutativity' in terms of the angle
between spin-observables we present two tight quantitative trade-off relations
in the case of two qubits: First, for entangled states, between the degree of
commutativity of local observables and the maximal amount of violation of the
Bell inequality: if both local angles increase from zero to \pi/2 (i.e., the
degree of local commutativity decreases), the maximum violation of the Bell
inequality increases. Secondly, a converse trade-off relation holds for
separable states: if both local angles approach \pi/2 the maximal value
obtainable for the correlations in the Bell inequality decreases and thus the
non-violation increases. As expected, the extremes of these relations are found
in the case of anti-commuting local observables where respectively the bounds
of 2\sqrt{2} and \sqrt{2} hold for the expectation of the Bell operator. The
trade-off relations show that non-commmutativity gives ``a more than classical
result" for entangled states, whereas "a less than classical result" is
obtained for separable states. The experimental relevance of the trade-off
relation for separable states is that it provides an experimental test for two
qubit entanglement. Its advantages are twofold: in comparison to violations of
Bell inequalities it is a stronger criterion and in comparison to entanglement
witnesses it needs to make less strong assumptions about the observables
implemented in the experiment.


title: Non Thermal Equilibrium States of Closed Bipartite Systems

abstract:
  We investigate a two-level system in resonant contact with a larger
environment. The environment typically is in a canonical state with a given
temperature initially. Depending on the precise spectral structure of the
environment and the type of coupling between both systems, the smaller part may
relax to a canonical state with the same temperature as the environment (i.e.
thermal relaxation) or to some other quasi equilibrium state (non thermal
relaxation). The type of the (quasi) equilibrium state can be related to the
distribution of certain properties of the energy eigenvectors of the total
system. We examine these distributions for several abstract and concrete (spin
environment) Hamiltonian systems, the significant aspect of these distributions
can be related to the relative strength of local and interaction parts of the
Hamiltonian.


title:
Joint Entropy of the Harmonic Oscillator with Time Dependent Mass and
  Frequency

abstract:
  Time dependent entropy of harmonic oscillator with time dependent mass and
frequency are investigated. The joint entropy so called Leipnik's entropy is
calculated by using time dependent wave function obtained by the Feynman path
integral method. It is shown that, Leipnik's entropy fluctuates with time.
However in constant mass and time dependent frequency case, entropy increases
monotonically with time.


title: Generation of Symmetric Dicke States of Remote Qubits with Linear Optics

abstract:
  We propose a method for generating all symmetric Dicke states, either in the
long-lived internal levels of N massive particles or in the polarization
degrees of freedom of photonic qubits, using linear optical tools only. By
means of a suitable multiphoton detection technique, erasing Welcher-Weg
information, our proposed scheme allows the generation and measurement of an
important class of entangled multiqubit states.


title: Entanglement and its dynamics in open, dissipative systems

abstract:
  Quantum mechanical entanglement can exist in noisy open quantum systems at
high temperature. A simple mechanism, where system particles are randomly reset
to some standard initial state, can counteract the deteriorating effect of
decoherence, resulting in an entangled steady state far from thermodynamical
equilibrium. We present models for both gas-type systems and for strongly
coupled systems. We point out in which way the entanglement resulting from such
a reset mechanism is different from the entanglement that one can find in
thermal states. We develop master equations to describe the system and its
interaction with an environment, study toy models with two particles (qubits),
where the master equation can often be solved analytically, and finally examine
larger systems with possibly fluctuating particle numbers. We find that in
gas-type systems, the reset mechanism can produce an entangled steady state for
an arbitrary temperature of the environment, while this is not true in strongly
coupled systems. But even then, the temperature range where one can find
entangled steady states is typically much higher with the reset mechanism.


title:
Kramers-Kronig relations for plasma-like permittivities and the Casimir
  force

abstract:
  The Kramers-Kronig relations are derived for the permittivity of the usual
plasma model which neglects dissipation and of a generalized model which takes
into account the interband transitions. The generalized plasma model is shown
to be consistent with all precision experiments on the measurement of the
Casimir force.


title: Effects of many-electron atom polarization in electron-hole formalism

abstract:
  The method has been developed to calculate effects of polarization not only
for a atomic core in a field of valent electron, but also polarization of atom
as a whole in the electron-hole formalism. A secondary quantized density matrix
for many-electron system was used to find the Green function of a quasiparticle
and its effective mass due to many-particle effects.


title:
Semidefinite programming characterization and spectral adversary method
  for quantum complexity with noncommuting unitary queries

abstract:
  Generalizing earlier work characterizing the quantum query complexity of
computing a function of an unknown classical ``black box'' function drawn from
some set of such black box functions, we investigate a more general quantum
query model in which the goal is to compute functions of N by N ``black box''
unitary matrices drawn from a set of such matrices, a problem with applications
to determining properties of quantum physical systems. We characterize the
existence of an algorithm for such a query problem, with given error and number
of queries, as equivalent to the feasibility of a certain set of semidefinite
programming constraints, or equivalently the infeasibility of a dual of these
constraints, which we construct. Relaxing the primal constraints to correspond
to mere pairwise near-orthogonality of the final states of a quantum computer,
conditional on black-box inputs having distinct function values, rather than
bounded-error determinability of the function value via a single measurement on
the output states, we obtain a relaxed primal program the feasibility of whose
dual still implies the nonexistence of a quantum algorithm. We use this to
obtain a generalization, to our not-necessarily-commutative setting, of the
``spectral adversary method'' for quantum query lower bounds.


title: Correlated errors can lead to better performance of quantum codes

abstract:
  A formulation for evaluating the performance of quantum error correcting
codes for a general error model is presented. In this formulation, the
correlation between errors is quantified by a Hamiltonian description of the
noise process. We classify correlated errors using the system-bath interaction:
local versus nonlocal and two-body versus many-body interactions. In
particular, we consider Calderbank-Shor-Steane codes and observe a better
performance in the presence of correlated errors depending on the timing of the
error recovery. We also find this timing to be an important factor in the
design of a coding system for achieving higher fidelities.


title: Topological fault-tolerance in cluster state quantum computation

abstract:
  We describe a fault-tolerant version of the one-way quantum computer using a
cluster state in three spatial dimensions. Topologically protected quantum
gates are realized by choosing appropriate boundary conditions on the cluster.
We provide equivalence transformations for these boundary conditions that can
be used to simplify fault-tolerant circuits and to derive circuit identities in
a topological manner. The spatial dimensionality of the scheme can be reduced
to two by converting one spatial axis of the cluster into time. The error
threshold is 0.75% for each source in an error model with preparation, gate,
storage and measurement errors. The operational overhead is poly-logarithmic in
the circuit size.


title:
Generating and Revealing a Quantum Superposition of Electromagnetic
  Field Binomial States in a Cavity

abstract:
  We introduce the $N$-photon quantum superposition of two orthogonal
generalized binomial states of electromagnetic field. We then propose, using
resonant atom-cavity interactions, non-conditional schemes to generate and
reveal such a quantum superposition for the two-photon case in a single-mode
high-$Q$ cavity. We finally discuss the implementation of the proposed schemes.


title: Efficient atomic quantum memory for photonic qubits in cavity QED

abstract:
  We investigate a scheme of atomic quantum memory to store photonic qubits of
polarization in cavity QED. It is observed that the quantum-state swapping
between a single-photon pulse and a $ \Lambda $-type atom can be made via
scattering in an optical cavity [T. W. Chen, C. K. Law, P. T. Leung, Phys. Rev.
A {\bf 69} (2004) 063810]. This swapping operates limitedly in the strong
coupling regime for $ \Lambda $-type atoms with equal dipole couplings. We
extend this scheme in cavity QED to present a more feasible and efficient
method for quantum memory combined with projective measurement. This method
works without requiring such a condition on the dipole couplings. The fidelity
is significantly higher than that of the swapping, and even in the moderate
coupling regime it reaches almost unity by narrowing sufficiently the
photon-pulse spectrum. This high performance is rather unaffected by the atomic
loss, cavity leakage or detunings, while a trade-off is paid in the success
probability for projective measurement.


title: Probabilistic Simulation of Quantum Computation

abstract:
  Special stochastic representation of the wave function in Quantum Mechanics
(QM), based on soliton realization of extended particles, is suggested with the
aim to model quantum states via classical computer. Entangled solitons
construction being introduced in the nonlinear spinor field model, the
Einstein, Podolsky, Rosen (EPR) spin correlation is calculated and shown to
coincide with the quantum mechanical one for the spin-1/2 particles in the
singlet state. The concept of stochastic qubits is used for quantum computing
modelling.


title:
Variable-frequency-controlled coupling in charge qubit circuits: Effects
  of microwave field on qubit-state readout

abstract:
  To implement quantum information processing, microwave fields are often used
to manipulate superconuducting qubits. We study how the coupling between
superconducting charge qubits can be controlled by variable-frequency magnetic
fields. We also study the effects of the microwave fields on the readout of the
charge-qubit states. The measurement of the charge-qubit states can be used to
demonstrate the statistical properties of photons.


title:
Kicked Bose-Hubbard systems and kicked tops -- destruction and
  stimulation of tunneling

abstract:
  In a two-mode approximation, Bose-Einstein condensates (BEC) in a double-well
potential can be described by a many particle Hamiltonian of Bose-Hubbard type.
We focus on such a BEC whose interatomic interaction strength is modulated
periodically by $\delta$-kicks which represents a realization of a kicked top.
In the (classical) mean-field approximation it provides a rich mixed phase
space dynamics with regular and chaotic regions. By increasing the
kick-strength a bifurcation leads to the appearance of self-trapping states
localized on regular islands. This self-trapping is also found for the many
particle system, however in general suppressed by coherent many particle
tunneling oscillations. The tunneling time can be calculated from the
quasi-energy splitting of the corresponding Floquet states. By varying the
kick-strength these quasi-energy levels undergo both avoided and even actual
crossings. Therefore stimulation or complete destruction of tunneling can be
observed for this many particle system.


title:
Open-Loop Control of Quantum Particle Motion: Effective Splitting in
  Momentum Space

abstract:
  In this paper an effective quantum particle beam-splitter in the momentum
space is realized in the frame of open-loop control scheme. We demonstrate for
small interaction time that the splitting effect $\pm40\hbar k$ with summarized
relative intensity in both main components is about 50 per cent from initial
intensity of the atomic beam.


title: H-Infinity Control of Linear Quantum Stochastic Systems

abstract:
  The purpose of this paper is to formulate and solve a H-infinity controller
synthesis problem for a class of non-commutative linear stochastic systems
which includes many examples of interest in quantum technology. The paper
includes results on the class of such systems for which the quantum commutation
relations are preserved (such a requirement must be satisfied in a physical
quantum system). A quantum version of standard (classical) dissipativity
results are presented and from this a quantum version of the Strict Bounded
Real Lemma is derived. This enables a quantum version of the two Riccati
solution to the H-infinity control problem to be presented. This result leads
to controllers which may be realized using purely quantum, purely classical or
a mixture of quantum and classical elements. This issue of physical
realizability of the controller is examined in detail, and necessary and
sufficient conditions are given. Our results are constructive in the sense that
we provide explicit formulas for the Hamiltonian function and coupling operator
corresponding to the controller.


title:
Nonlocal properties of entangled two-photon generalized binomial states
  in two separate cavities

abstract:
  We consider entangled two-photon generalized binomial states of the
electromagnetic field in two separate cavities. The nonlocal properties of this
entangled field state are analyzed by studying the electric field correlations
between the two cavities. A Bell's inequality violation is obtained using an
appropriate dichotomic cavity operator, that is in principle measurable.


title: Quantum thermodynamic functions for an oscillator coupled to a heat bath

abstract:
  Small systems (of interest in the areas of nanophysics, quantum information,
etc.) are particularly vulnerable to environmental effects. Thus, we determine
various thermodynamic functions for an oscillator in an arbitrary heat bath at
arbitrary temperatures. Explicit results are presented for the most commonly
discussed heat bath models: Ohmic, single relaxation time and blackbody
radiation.


title:
Decoherence in the dynamical quantum phase transition of the transverse
  Ising chain

abstract:
  For the prototypical example of the Ising chain in a transverse field, we
study the impact of decoherence on the sweep through a second-order quantum
phase transition. Apart from the advance in the general understanding of the
dynamics of quantum phase transitions, these findings are relevant for
adiabatic quantum algorithms due to the similarities between them. It turns out
that (in contrast to first-order transitions studied previously) the impact of
decoherence caused by a weak coupling to a rather general environment increases
with system size (i.e., number of spins/qubits), which might limit the
scalability of the system.


title: Pauli graph and finite projective lines/geometries

abstract:
  The commutation relations between the generalized Pauli operators of N-qudits
(i. e., N p-level quantum systems), and the structure of their maximal sets of
commuting bases, follow a nice graph theoretical/geometrical pattern. One may
identify vertices/points with the operators so that edges/lines join commuting
pairs of them to form the so-called Pauli graph P_{p^N} . As per two-qubits (p
= 2, N = 2) all basic properties and partitionings of this graph are embodied
in the geometry of the symplectic generalized quadrangle of order two, W(2).
The structure of the two-qutrit (p = 3, N = 2) graph is more involved; here it
turns out more convenient to deal with its dual in order to see all the
parallels with the two-qubit case and its surmised relation with the geometry
of generalized quadrangle Q(4, 3), the dual of W(3). Finally, the generalized
adjacency graph for multiple (N > 3) qubits/qutrits is shown to follow from
symplectic polar spaces of order two/three. The relevance of these mathematical
concepts to mutually unbiased bases and to quantum entanglement is also
highlighted in some detail.


title:
Trapping cold atoms near carbon nanotubes: thermal spin flips and
  Casimir-Polder potential

abstract:
  We investigate the possibility to trap ultracold atoms near the outside of a
metallic carbon nanotube (CN) which we imagine to use as a miniaturized
current-carrying wire. We calculate atomic spin flip lifetimes and compare the
strength of the Casimir-Polder potential with the magnetic trapping potential.
Our analysis indicates that the Casimir-Polder force is the dominant loss
mechanism and we compute the minimum distance to the carbon nanotube at which
an atom can be trapped.


title:
Deterministic loading of individual atoms to a high-finesse optical
  cavity

abstract:
  Individual laser cooled atoms are delivered on demand from a single atom
magneto-optic trap to a high-finesse optical cavity using an atom conveyor.
Strong coupling of the atom with the cavity field allows simultaneous cooling
and detection of individual atoms for time scales exceeding 15 s. The single
atom scatter rate is studied as a function of probe-cavity detuning and probe
Rabi frequency, and the experimental results are in good agreement with
theoretical predictions. We demonstrate the ability to manipulate the position
of a single atom relative to the cavity mode with excellent control and
reproducibility.


title: Cavity cooling of internal molecular motion

abstract:
  We predict that it is possible to cool rotational, vibrational and
translational degrees of freedom of molecules by coupling a molecular dipole
transition to an optical cavity. The dynamics is numerically simulated for a
realistic set of experimental parameters using OH molecules. The results show
that the translational motion is cooled to few $\mu$K and the internal state is
prepared in one of the two ground states of the two decoupled rotational
ladders in few seconds. Shorter cooling times are expected for molecules with
larger polarizability.


title:
Fidelity criterion for quantum-domain transmission and storage of
  coherent states beyond unit-gain constraint

abstract:
  We generalize the experimental success criterion for quantum
teleportation/memory in continuous-variable quantum systems to be suitable for
non-unit-gain condition by considering attenuation/amplification of the
coherent-state amplitude. The new criterion can be used for a non-ideal quantum
memory and long distance quantum communication as well as quantum devices with
amplification process. It is also shown that the framework to measure the
average fidelity is capable of detecting all Gaussian channels in quantum
domain.