Table of contents

Quantum dense coding via a two-mode squeezed-vacuum state is proposed, where classical information is encoded in two quadrature components of one mode of a two-mode squeezed-vacuum state. Decoding at a receiver side is performed by simultaneous measurement of two quadrature components of the two-mode state. Since a two-mode squeezed-vacuum state is partially entangled, the information can only be transmitted without error in the strong-squeezing limit.

The generalized inverse of q-boson operators are introduced via their action on the q-number states. The q-analogy of photon-added and photon-depleted coherent states are constructed via the generalized inverse of q-boson operator actions on the q-coherent states. Their mathematical and quantum statistical properties are discussed in detail analytically and numerically.

We study the correlation between photons in the fluorescence light scattered from an atom driven by an intense bichromatic field having one strong and one weak component, with or without the use of frequency filters in front of the photodetectors. Depending on the filters used and on the spectral components selected, we predict signals corresponding either to bunching or to antibunching, and modulations at the driving field Rabi frequencies as well as at their sum and difference. In contrast with the case of monochromatic driving, the antibunching can occur between photons emitted into different (as well as the same) lines of the fluorescence spectrum.

We present an experimental and theoretical analysis of the mechanical Hanle effect, i.e., the modification of the atomic trajectories following the interaction with laser fields in the Hanle configuration. The case of open transitions is examined. In our experiment a thermal sodium atomic beam is crossed perpendicularly by a single-mode linearly polarized laser beam. The laser field is tuned to resonance with an F_gF_e transition of the sodium D₁ line. A static magnetic field B is applied collinear to the laser light propagation direction. The atomic beam flux at the position corresponding to its maximum in the absence of laser light is studied as a function of the applied magnetic field. For the F_g = FF_e = F,F-1 transitions the atomic flux shows a sharp increase at B = 0, as a result of the coherent trapping of the population into the ground state. For the F_g = 1F_e = 2 transition this effect is absent and no significant variation of the atomic flux with the magnetic field is observed. A theoretical description of the mechanical Hanle effect in open transitions is given and it is clarified why in our experiment the mechanical Hanle/CPT-resonances associated to different hyperfine transitions have different contrasts.

For a general class of two-mode lasers, simple analytic expressions are derived for the magnitude of, and the correlation between, the intensity fluctuations in the two modes. The mode-partition fluctuations and overall intensity dynamics are demonstrated to be almost decoupled, so that the former can be treated as a small perturbation to the standard description of intensity squeezing in a single-mode laser. An example is formed by polarization partition noise in vertical-cavity surface-emitting lasers (VCSELs). Mode-partition noise in general, and polarization fluctuations in VCSELs in particular, are thus predicted to have only a limited deteriorating effect on the attainable intensity squeezing.

We study a vertical-cavity surface-emitting laser with external feedback through a quarter-wavelength plate. We show that the effect of a rotation of the quarter-wavelength plate is to shift one comb of modes with respect to the other one. The dependence of the frequency on the rotation angle is calculated and shown to be in good agreement with experimental results.

We propose the reconstruction of a smoothed Wigner function from quadrature distributions instead of the Wigner function itself to avoid the problems with the inverse Radon transformation. Starting from the well known relation between s-parametrized quasiprobability distributions W(x,p,s) and quadrature component distributions w(x,), we show that the sampling function needed to determine a smoothed Wigner function W(x,p,-|s|) is basically a shifted and scaled version of the well known pattern function necessary to reconstruct the probability of finding no photon in the signal field. An analogous result has been recently found in the literature. Here we obtain this result in a very concise and alternative way.

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

A two-step interaction scheme involving ⁽²⁾ and ⁽³⁾ nonlinear media is suggested for the generation of Schrödinger cat-like states of a single-mode optical field. In the first step, a weak coherent signal undergoes a self-Kerr phase modulation in a ⁽³⁾ crystal, leading to a Kerr kitten, namely a microscopic superposition of two coherent states with opposite phases. In the second step, such a Kerr kitten enters a ⁽²⁾ crystal and, in turn, plays the role of a quantum seed for stimulated phase-sensitive amplification. The output state in the above-threshold regime consists in a quantum superposition of mesoscopically distinguishable squeezed states, i.e. an optical cat-like state. The whole setup does not rely on conditional measurements, and is robust against decoherence, as only weak signals interact with the Kerr medium.

Welcher Weg (which-path) detectors where complementarity is enforced without altering the interfering beams are analysed in terms of the quantum relative phase. In such a case, the measurement disturbs the interference via random classical phase shifts. This applies when the interfering particles are atoms or photons. In the case of photons, the quantum relative phase coincides with the field phase difference.

The European Optical Society awarded its prestigious EOS Prize, on the occasion of the EOS General Meeting on 27 May 1999 in Berlin, Germany.

The winner was selected by the EOS Prize committee, consisting of Professor M Hutley (UK), Professor J J Stamnes (Norway) and Professor H A Ferwerda (Netherlands), based on the selection criteria of high professionalism, academic and technical quality. Following the EOS Prize rules, the conditions for eligibility are that the work was performed in Europe and that it is published under the auspices of the EOS. This year, the committee has received 18 serious nominations for the EOS Prize 1998.

The winner of the European Optics Prize 1998 is the research group consisting of;

Franco Gori, Massimo Santarsiero, Silvia Vicalvi, Riccardo Borghi and Giorgio Guattari

from the Universita degli studi Roma Tre and Istituto Nazionale per la Fisica della Materia, Universita La Sapienza, Roma, Italy for their joint paper `Beam-coherence-polarization matrix', published in Pure and Applied Optics7 941-51 (September 1998), the Journal of the European Optical Society Part A, in a special issue on physical optics and coherence theory published in honour of Professor Emil Wolf's 75th birthday.

The representative of EOS, Mike Hutley, had the great pleasure to welcome Massimo Santarsiero, who accepted the prize on behalf of his co-authors. In the name of his colleagues, Massimo Santarsiero gave the audience an excellent review of the work done in this collaboration.

The EOS Prize 1998 consists of a sum of 1500 ECU and the following certificate:

The EUROPEAN OPTICAL SOCIETY presents the

EUROPEAN OPTICS PRIZE 1998 to Franco Gori, Massimo Santarsiero, Silvia Vicalvi, Riccardo Borghi and Giorgio Guattari Universita degli studi Roma Tre and Istituto Nazionale per la Fisica della Materia, Universita La Sapienza, Roma, Italy

for their outstanding contribution on `Beam-coherence-polarization matrix' published in the JEOS Part A, Pure and Applied Optics 1998

Delivered at Berlin, May 1999