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The past few years have seen a growing interest in quantum mechanical systems with moving boundaries. One of its manifestations was the First International Workshop on Problems with Moving Boundaries organized by Professor J Dittrich in Prague in October 2003. Another event in this series will be the (first) International Workshop on the Dynamical Casimir Effect in Padua in June 2004, organized by Professor G Carugno (see webpagewww.pd.infn.it/casimir/ for details).

As Guest Editors we invite researchers working in any area related to moving boundaries to contribute to a Topical Issue of Journal of Optics B: Quantum and Semiclassical Optics on the nonstationary Casimir effect and quantum systems with moving boundaries. Our intention is to cover a wide range of topics. In particular, we envisage possible contributions in the following areas:

Theoretical and experimental studies on quantum fields in cavities with moving boundaries and time-dependent media. This area includes, in particular, various manifestations of the nonstationary (dynamical) Casimir effect, such as creation of quanta and modifications of Casimir force due to the motion of boundaries. Other relevant subjects are: generation and evolution of nonclassical states of fields and moving mirrors; interaction between quantized fields and atoms in cavities with moving boundaries; decoherence and entanglement due to the motion of boundaries; field quantization in nonideal cavities with moving boundaries taking into account losses and dispersion; nano-devices with moving boundaries.

Quantum particles in domains confined with moving boundaries. This area includes: new exact and approximate solutions of the evolution equations (Schrödinger, Klein–Gordon, Dirac, Fokker–Planck, etc); quantum carpets and revivals; escape and tunnelling through moving barriers; evolution of quantum packets in the presence of moving boundaries; ultracold atoms (ions) in traps with moving boundaries.

The topical issue is scheduled for publication in March 2005 and the deadline for submission of contributions is 1 August 2004. The Editorial Division of Institute of Physics Publishing at the P. N. Lebedev Physical Institute in Moscow will oversee editorial procedures in association with the main Publishing Office in Bristol. All contributions will be peer-reviewed in accordance with the normal refereeing procedures and standards ofJournal of Optics B: Quantum and Semiclassical Optics. Submissions should preferably be in either standard LaTeX form or Microsoft Word. Advice on publishing your work in the journal may be found at www.iop.org/journals/authors/jopb. There are no page charges for publication.

Contributions to the topical issue, quoting `Topical Issue/NCE', should be submitted by e-mail toIOPP@sci.lebedev.ru or as hard copy (enclosing the electronic code) to IOPP Division, P. N. Lebedev Physical Institute, Leninskii Prospect 53, Moscow 119991 Russia.

This special issue of Journal of Optics B: Quantum and Semiclassical Optics is composed mainly of extended versions of talks and papers presented at the Eighth International Conference on Squeezed States and Uncertainty Relations held in Puebla, Mexico on 9–13 June 2003. The Conference was hosted by Instituto de Astrofísica, Óptica y Electrónica, and the Universidad Nacional Autónoma de México.

This series of meetings began at the University of Maryland, College Park, USA, in March 1991. The second and third workshops were organized by the Lebedev Physical Institute in Moscow, Russia, in 1992 and by the University of Maryland Baltimore County, USA, in 1993, respectively. Afterwards, it was decided that the workshop series should be held every two years. Thus the fourth meeting took place at the University of Shanxi in China and was supported by the International Union of Pure and Applied Physics (IUPAP). The next three meetings in 1997, 1999 and 2001 were held in Lake Balatonfüred, Hungary, in Naples, Italy, and in Boston, USA, respectively. All of them were sponsored by IUPAP. The ninth workshop will take place in Besançon, France, in 2005.

The conference has now become one of the major international meetings on quantum optics and the foundations of quantum mechanics, where most of the active research groups throughout the world present their new results. Accordingly this conference has been able to align itself to the current trend in quantum optics and quantum mechanics.

The Puebla meeting covered most extensively the following areas: quantum measurements, quantum computing and information theory, trapped atoms and degenerate gases, and the generation and characterization of quantum states of light. The meeting also covered squeeze-like transformations in areas other than quantum optics, such as atomic physics, nuclear physics, statistical physics and relativity, as well as optical devices. There were many new participants at this meeting, particularly from Latin American countries including, of course, Mexico.

There were many talks on the subjects traditionally covered in this conference series, including quantum fluctuations, different forms of squeezing, unlike kinds of nonclassical states of light, and distinct representations of the quantum superposition principle, such as even and odd coherent states. The entanglement phenomenon, frequently in the form of the EPR paradox, is responsible for the main advantages of quantum engineering compared with classical methods. Even though entanglement has been known since the early days of quantum mechanics, its properties, such as the most appropriate entanglement measures, are still under current investigation. The phenomena of dissipations and decoherence of the initial pure states are very important because the fast decoherence can destroy all the advantages of quantum processes in teleportation, quantum computing and image processing. Due to this, methods of controlling the decoherence, such as by the use of different kinds of nonlinearities and deformations, are also under study. From the very beginning of quantum mechanics, the uncertainty relations were basic inequalities distinguishing the classical and quantum worlds.

Among the theoretical methods for quantum optics and quantum mechanics, this conference covered phase space and group representations, such as the Wigner and probability distribution functions, which provide an alternative approach to the Schr\"odinger or Heisenberg picture. Different forms of probability representations of quantum states are important tools to be applied in studying various quantum phenomena, such as quantum interference, decoherence and quantum tomography. They have been established also as a very useful tool in all branches of classical optics. From the mathematical point of view, it is well known that the coherent and squeezed states are representations of the Lorentz group. It was noted throughout the conference that another form of the Lorentz group, namely, the 2 x 2 representation of the SL(2,c) group, is becoming more prominent while providing the mathematical basis for the Poincaré sphere, entanglement, qubits and decoherence, as well as classical ray optics traditionally based on 2 x 2 `ABCD' matrices.

The contributions of this special issue cover the most recent trends in all areas of quantum optics and the foundations of quantum mechanics.

It has been almost 100 years since Einstein formulated his special theory of relativity in 1905. He showed that the basic space–time symmetry is dictated by the Lorentz group. It is shown that this group of Lorentz transformations is not only applicable to special relativity, but also constitutes the scientific language for optical sciences. It is noted that coherent and squeezed states of light are representations of the Lorentz group. The Lorentz group is also the basic underlying language for classical ray optics, including polarization optics, interferometers, the Poincaré sphere, one-lens optics, multi-lens optics, laser cavities, as well multilayer optics.

We investigate the possibility of characterizing two-party entanglement by measuring correlations of Stokes operators in polarized bright light beams. We adapt a general separability criterion to such operators. We then show that entanglement purification can only be singled out for a particular protocol.

We discuss when the use of entangled photon pairs in an imaging system can be simulated with a classically correlated source. In particular, we consider two recently proposed schemes with 'bucket detection' of one of the photons. We argue that these schemes give identical results for entangled states as for appropriately prepared classically correlated states.

Nonclassical light generation at self-frequency halving in periodically poled active nonlinear crystals is studied. The squeezing spectra of fundamental radiation and its subharmonic are investigated for a periodically poled Nd:Mg:LiNbO₃ crystal.

Informationally complete measurements on a quantum system allow one to estimate the expectation value of any arbitrary operator by just averaging functions of the experimental outcomes. We show that such kinds of measurement can be achieved through positive-operator valued measures (POVMs) related to unitary irreducible representations of a group on the Hilbert space of the system. With the help of frame theory we provide a constructive way to evaluate the data-processing function for arbitrary operators.

We investigate some examples of quantum Zeno dynamics, when a system undergoes very frequent (projective) measurements that ascertain whether it is within a given spatial region. In agreement with previously obtained results, the evolution is found to be unitary and the generator of the Zeno dynamics is the Hamiltonian with hard-wall (Dirichlet) boundary conditions. By using a new approach to this problem, this result is found to be valid in an arbitrary N-dimensional compact domain. We then propose some preliminary ideas concerning the algebra of observables in the projected region and finally look at the case of a projection onto a lower-dimensional space: in such a situation the Zeno ansatz turns out to be a procedure to impose constraints.

For the two-mode fermionic squeezing operators we find that their coherent state projection operator representation make up a loyal representation, which is homomorphic to an SO(4) group, though the fermionic coherent states are not mutual orthogonal. Thus the result of successively operating with many fermionic squeezing operators on a state can be equivalent to a single operation. The fermionic squeezing operators are mappings of orthogonal transformations in Grassmann number pseudo-classical space in the fermionic coherent state representation.

A which-way measurement destroys the twin-slit interference pattern. Bohr argued that this can be attributed to the Heisenberg uncertainty relation: distinguishing between two slits a distance s apart gives the particle a random momentum transfer of order h/s. This was accepted for more than 60 years, until Scully, Englert and Walther (SEW) proposed a which-way scheme that, they claimed, entailed no momentum transfer. Storey, Tan, Collett and Walls (STCW), on the other hand, proved a theorem that, they claimed, showed that Bohr was right. This work reviews and extends a recent proposal (Wiseman 2003 Phys. Lett. A 311 285) to resolve the issue using a weak-valued probability distribution for momentum transfer, . We show that must be nonzero for some . However, its moments can be identically zero, such as in the experiment proposed by SEW. This is possible because is not necessarily positive definite. Nevertheless, it is measurable experimentally in a way understandable to a classical physicist. The new results in this paper include the following. We introduce a new measure of spread for : half the length of the unit-confidence interval. We conjecture that it is never less than h/4s, and find numerically that it is approximately h/1.59s for an idealized version of the SEW scheme with infinitely narrow slits. For this example, the moments of , and of the momentum distributions, are undefined unless a process of apodization is used. However, we show that by considering successively smoother initial wavefunctions, successively more moments of both and the momentum distributions become defined. For this example the moments of are zero, and these moments are equal to the changes in the moments of the momentum distribution. We prove that this relation also holds for schemes in which the moments of are nonzero, but it holds only for the first two moments. We also compare these moments to the moments of two other momentum-transfer distributions that have previously been considered, and with the moments of (which is defined in the Heisenberg picture). We find agreement between all of these, but again only for the first two moments. Our results reconcile the seemingly opposing views of SEW and STCW.

We present a series of experiments measuring intensity fluctuations and correlations of laser beams after propagation through an atomic vapour at room temperature in situations where coherent effects play a major role. In particular, we investigate these properties in the condition of electromagnetically induced transparency (EIT) in three-level lambda systems and in degenerate two-level systems. In a similar way, we also study the Hanle-EIT effect and electromagnetically induced absorption (EIA) in degenerate two-level systems. These results show the great influence of coherent interaction with the atomic system over the noise properties of the macroscopic laser fields, and indicate new sensitive ways of probing an atomic sample.

Stochastic cooling of trapped atoms is considered for a laser-beam configuration with beam waists equal to or smaller than the extent of the atomic cloud. It is shown that various effects appear due to this transverse confinement, among them heating of transverse kinetic energy. Analytical results of the cooling in dependence on size and location of the laser beam are presented for the case of a non-degenerate vapour.

We report on the generation of non-separable beams produced via the interaction of a linearly polarized beam with a cloud of cold caesium atoms placed in an optical cavity. We convert the squeezing of the two linear polarization modes into quadrature entanglement and show how to find the best entanglement generated in a two-mode system using the inseparability criterion for continuous variables (Duan et al 2000 Phys. Rev. Lett. 84 2722). We verify this method experimentally with a direct measurement of the inseparability using two homodyne detectors. We then map this entanglement into a polarization basis and achieve polarization entanglement.

Based on the observation that polarization phenomena of EM waves are geometric rather than quantum mechanical in nature, it is argued that experiments involving 'entangled polarization' do not address the issues brought up by EPR. A fully classical explanation is offered for a recent experiment of this type, and a fully classical (local and realistic) photoelectron-by-photoelectron simulation is described of ordinary two-fold experiments thought to prove Bell's 'theorem'.

We have found traditional statistics for two disjoint time intervals of a measurement that little disturbs the dynamics of a two-level system. The second-quantized formulation has partly been restored for models where the two-level system is a photon.

I propose an iterative expectation maximization algorithm for reconstructing the density matrix of an optical ensemble from a set of balanced homodyne measurements. The algorithm applies directly to the acquired data, bypassing the intermediate step of calculating marginal distributions. The advantages of the new method are made manifest by comparing it with the traditional inverse Radon transformation technique.

A scheme for an atomic beam quantum self-eraser is presented. The proposal is based on time reversal invariance on a quantum optical Ramsey fringe experiment, where a realization of complementarity for atomic coherence can be achieved. It consists of two high-finesse resonators that are pumped and probed by the same atom. This property relates quantum erasing to time reversal symmetry, allowing for a full quantum erasing of the which-way information stored in the cavity fields. The outlined scheme also prepares and observes a non-local state in the fields of the resonators: a coherent superposition between correlated states of macroscopically separated quantum systems. The proposed scheme emphasizes the role of entanglement swapping in delayed-choice experiments.

The present work deals with how the quantum properties of a light beam are teleported, such as quadrature fluctuations and antibunching. We consider a variable gain at Bob's end as well as the improvement of the teleportation process via a conditional measurement of one photon addition and substraction at the EPR source.

Higher-order correlations of the radiation field improve resolution in stellar interferometers, as in the Hanbury-Brown–Twiss effect. It is also possible to improve microscopic resolution beyond the Rayleigh limit by using quantum light fields composed of entangled photons. Focusing on two photons, we distinguish two types of entanglement: frequency entanglement, where the photons in different paths are correlated in frequency, and path entanglement, where the correlation between paths is in photon number. Two paradigms of quantum microscopy are discussed: spectral microscopy, where path- and frequency-entangled photons produced in cascade decay of two atoms make possible sub-natural linewidth resolution of atomic levels, and spatial microscopy, where path-entangled photons emitted by an atomic array produce sub-wavelength diffraction resolution as compared to an equivalent classical grating. These scenarios require two-photon correlation or coincidence measurements. The connection between the two paradigms, and the two types of entanglement, highlights the link between the temporal and spatial aspects of quantum interferometry.

We develop a new approach to the quantum phase in a Hilbert space of finite dimension which is based on the relation between the physical concept of phase locking and mathematical concepts such as cyclotomy and the Ramanujan sums. As a result, the phase variability looks quite similar to its classical counterpart, having peaks at dimensions equal to a power of a prime number. Squeezing of the phase noise is allowed for specific quantum states. The concept of phase entanglement for Kloosterman pairs of phase-locked states is introduced.

We address the evolution of cat-like states in general Gaussian noisy channels, by considering superpositions of coherent and squeezed coherent states coupled to an arbitrarily squeezed bath. The phase space dynamics is solved and decoherence is studied, keeping track of the purity of the evolving state. The influence of the choice of the state and channel parameters on purity is discussed and optimal working regimes that minimize the decoherence rate are determined. In particular, we show that squeezing the bath to protect a non-squeezed cat state against decoherence is equivalent to orthogonally squeezing the initial cat state while letting the bath be phase insensitive.

The characterization of nonclassicality of quantum states in terms of measurable quadrature distributions is studied, on the basis of recently derived necessary and sufficient conditions for the failure of the Glauber–Sudarshan P-function to be a probability density. When the noise-subtracted quadrature distribution, that is the marginal of the P-function, is not a probability density, the same is true for the Glauber–Sudarshan P-function. Inversely, for a complete characterization of a nonclassical P-function one needs phase-sensitive criteria that connect quadrature distributions for different phases. Even for phase-insensitive quantum states, phase-sensitive nonclassicality conditions are needed, as is illustrated for one-photon added thermal states.

It is shown that some assumptions about the concentration behaviour of free photons in an entangled multi-photon quantum state, published in recent literature, were too optimistic. This is of fundamental interest and adversely affects the performance of quantum lithography schemes.

A system of two two-level atoms interacting with a squeezed vacuum field can exhibit stationary entanglement associated with nonclassical two-photon correlations characteristic of the squeezed vacuum field. The amount of entanglement present in the system is quantified by the well known measure of entanglement called concurrence. We find analytical formulae describing the concurrence for two identical and nonidentical atoms and show that it is possible to obtain a large degree of steady-state entanglement in the system. Necessary conditions for the entanglement are nonclassical two-photon correlations and nonzero collective decay. It is shown that nonidentical atoms are a better source of stationary entanglement than identical atoms. We discuss the optimal physical conditions for creating entanglement in the system; in particular, it is shown that there is an optimal and rather small value of the mean photon number required for creating entanglement.

We analyse the problem of a trapped ion with time-dependent frequency interacting with a laser field. By using a set of unitary time-dependent transformations we show that this system is equivalent to the interaction between a quantized field and a double level with time-dependent interaction parameters. In passing, we show that in the on-resonance case different vibrational transitions may be achieved by using time-dependent parameters.