Quantum and Semiclassical Optics: Journal of the European Optical Society Part B

Beyond their use as numerical tools, quantum trajectories can be ascribed a degree of reality in terms of quantum measurement theory. In fact, they arise naturally from considering continuous observation of a damped quantum system. A particularly useful form of quantum trajectories is as linear (but non-unitary) stochastic Schrödinger equations. In the limit where a strong local oscillator is used in the detection, and where the system is not driven, these quantum trajectories can be solved. This gives an alternative derivation of the probability distributions for completed homodyne and heterodyne detection schemes. It also allows the previously intractable problem of real-time adaptive measurements to be treated. The results for an analytically soluble example of adaptive phase measurements are presented, and future developments discussed.

Institute of Physics Publishing is pleased to announce the merger of two current optics titles, Journal of Optics (formerly Nouvelle Revue d'Optique) and Pure and Applied Optics. The new journal, to be titled Journal of Optics A: Pure and Applied Optics, will cover all aspects, both theoretical and experimental, of modern and classical optics. It is intended that this merger will unite the editorial strengths of each journal, eradicate overlap, and create a strong platform for the development of a world-class optics journal.

In conjunction with this merger, Quantum and Semiclassical Optics is to be relaunched under the new title Journal of Optics B: Quantum and Semiclassical Optics. Journal of Optics, comprising parts A and B, will be an integral part of Institute of Physics Publishing's dedicated optics programme.

A feature of these journals has always been strong European support, and we are delighted to confirm that Journal of Optics will be the official journal of the European Optical Society (EOS). Each title will consist of six bi-monthly issues, published in A4 format, beginning with the first issue of Journal of Optics A in January 1999, and Journal of Optics B in the following month. Subscribers to these journals will receive all the benefits that Institute of Physics Publishing journals offer; full text electronic access including six-year archives, a thirty-year abstract archive and new Hypercite^TM citation linking.

Both titles will begin under new Editorship, and we would like to take this opportunity to thank Professor Boccara, Professor Bertolotti and Professor Mandel for their achievements during their respective terms of office. We hope that both journals will continue in the tradition of excellence that has been established through their efforts.

In association with the changes outlined above, all editorial processing will be transferred to the main Institute of Physics Publishing offices. Our special thanks go to Françoise Chavel and Michèle Bouchareine at the EOS offices in Paris for their hard work and important contribution over recent years.

All new submissions should therefore be sent directly to:

Publishing Editor Journal of Optics Institute of Physics Publishing Dirac House Temple Back Bristol, BS1 6BE United Kingdom

We are also pleased to introduce electronic submission for both titles. Please refer to Notes for Authors for full details.

This is the last issue of the journal to be published under my editorship. It offers a good example of what the journal has become: a balanced mix of quantum optics and semiclassical optics. On the eve of my retirement, it is a pleasure to look back and consider the evolution of the journal. The recent publication of the 1997 impact factors by ISI has confirmed our position as the premier European journal devoted exclusively to optics research. Such a result could only have been achieved through teamwork, and I wish to express my gratitude to all those who contributed to this result: Michèle Bouchareine and Françoise Chavel from the EOS secretariat in Paris, John Haynes, Liz Martin and Tom Spicer from Institute of Physics Publishing in Bristol, and all the members of the Board. But I cannot conclude without a special expression of gratitude to Neal B Abraham whose experience in journal management is probably unsurpassed by anyone in our field, and who always found time to advise me when necessary.

Paul Mandel

Recently, Bishop and co-workers (1996 Phys. Rev. A 54 R4657) applied the coupled-cluster method to study the ground state of the Jaynes - Cummings model without the rotating-wave approximation and reported strong evidence for a second-order quantum phase transition which was believed to be caused by spontaneous breaking of the parity symmetry of the system. In the present work we have re-investigated this conjecture via examining the nature of the exact (numerical) ground state of the system. Our analysis has indicated that the ground state has definite positive parity and there is no spontaneous breaking of the parity symmetry of the system.

We discuss generation and measurement strategies for maximum-likelihood estimation of small phase shifts. We demonstrate that optimal encoding of small phase shifts and optimal measurements of small phase shifts require different states. We also show that states with identical phase resolution may have rather different Pegg-Barnett phase distributions. Hence, the connection between phase distribution and quantum phase resolution is rather weak.

The possibility of storing information in an amplifying optical fibre loop operating in a laser regime is discussed. Numerical simulations show that storage is possible and optimal when data are encoded in one of the polarization eigenstates of the fibre, provided the polarization direction of the light propagating inside the loop is switched between two orthogonal states every round trip.

Circularly polarized laser beams propagating through sodium vapour and tuned to the buffer-gas-broadened atomic transition can optically pump sodium atoms into a non-absorbing ground state. This causes an intensity-dependent refractive index gradient along as well as transverse to the laser beam propagation direction, giving rise to a number of nonlinear spatio-temporal intensity and polarization pattern creating processes. In the case of a single circularly polarized laser beam we have observed self-focusing and defocusing, the transformation of the incident Gaussian beam intensity profiles into ring profiles, a large shift of about 5 GHz of the maximum of the absorption profile when suitable magnetic fields are applied and the deflection of a beam by the inhomogeneous transverse magnetic field of a current-carrying wire. When two beams of opposite circular polarization are superimposed, astonishing effects such as the mutual deflection of both beams (beam bouncing), the mutual extinction of both beams (beam switching), the separation of initially overlapping beams (beam splitting) and the mutual attraction of both beams (beam attraction) can be observed. While most of the effects can be well described for the stationary state by a to atomic transition model, the correct description of the dynamics requires the consideration of all hyperfine states.

The occurrence of polarization instabilities in alkaline vapours and their coupling with spatial degrees of freedom are considered. We discuss experiments in which a laser beam is transmitted through a vapour cell without external feedback or with feedback by a single mirror. In both cases a lateral separation of the light field into domains of orthogonal circular polarization is found. Without feedback, relatively simple structures like rings or two spots are obtained. With feedback, more complicated polarization patterns result from spontaneous symmetry breaking. We emphasize the crucial role of the polarization ellipticity of the input beam. Changing this control parameter we observe a transition from positive to negative hexagons in one of the circular polarization components, while simultaneously the opposite transition occurs in the other one. The transition is mediated by square patterns occurring for linear input polarization. This metamorphosis is governed by symmetry principles and therefore provides an example of the ease of influencing the symmetry properties of systems consisting of multilevel atoms interacting with a vector light field.

Emission from a tensile-strained ridge-waveguide InGaAsP-InP laser, which exhibits a transition between TE and TM polarization when the DC injection current exceeds a certain value, was investigated by time- and polarization-resolved measurements. Under excitation with 100 ps current pulses the laser emits pairs of TE and TM pulses of about 50 ps duration. The longitudinal modes of the emission spectrum exhibit different spectral profiles depending on the mode wavelength, which can be explained in terms of the mode competition and asymmetric gain dispersion. The near-field intensity distribution of the laser excited with a 1.4 ns current pulse shows periodic changes of its lateral width associated with 3 GHz relaxation oscillations alternating between TE and TM polarization.

Weakly vectorial lasers with intracavity wave retardation plates can exhibit a rich variety of unusual dynamic polarization characteristics. For example, the output of an external-cavity semiconductor laser with an intracavity quarter-wave plate shows polarization self-modulations alternating between TE and TM modes at a fundamental frequency corresponding to twice the cavity round-trip time and at odd harmonics of this fundamental frequency. Higher-order harmonics greater than the 30th harmonic at frequencies above 5 GHz have been observed, which is much higher than the relaxation-oscillation frequency of the laser. As the pumping level is increased, the period-doubling route to chaos and hysteresis behaviour associated with higher harmonic bifurcations and multiple stable states has also been observed. These experimental results as well as preliminary numerical simulation results are summarized on the basis of a fairly simple model. Apart from possible applications, these results raise interesting questions about the fundamental polarization and nonlinear dynamic characteristics of such lasers. Some of these general issues are discussed.

We study the polarization of the electric field in Fabry-Perot resonators which contain at least two optically birefringent elements. One of them is a frequency-doubling crystal, the other being either a passive and/or an active crystal. Using the Jones matrix technique, we review the polarization properties of the linear Fabry-Perot cavity and extend these results to V-shaped cavities. For these configurations, we derive the rate of conversion of the fundamental frequencies into the second harmonic and the sum frequencies. These conversion rates are interpreted as intensity-dependent losses for the rate equations of the fundamental modes which are derived.