************************************ * QUANTUM OPTICS AND ATOM OPTICS * * IN AUSTRALASIA * * * * * * * * MONTHLY NEWSLETTER * * VOL X, NO 3 * * * CONTENTS: * March 2002 * * * 0. EDITORIAL NOTE * ISSN 1325-6467 * Edited by: 1. ABSTRACTS * * Alexei Gilchrist 2. VACANCIES * \ | / * Physics, University of Queensland, 3. BUY/SELL * \__|__/ * QLD 4072, Australia. 4. MISC NEWS * | * email: alexei@physics.uq.edu.au 5. CONFERENCES * | * phone: +61 7 3365 2422 * | * fax: +61 7 3365 1242 Available on WWW at: * * http://www.physics.uq.edu.au/qonews =============================================================================== 0. EDITORIAL NOTE =============================================================================== Sorry for the late mail out this month. Alexei =============================================================================== 1. ABSTRACTS =============================================================================== Entanglement in a simple quantum phase transition Tobias J. Osborne and Michael A. Nielsen quant-ph/0202162 What entanglement is present in naturally occurring physical systems at thermal equilibrium? Most such systems are intractable and it is desirable to study simple but realistic systems which can be solved. An example of such a system is the 1D infinite-lattice anisotropic XY model. This model is exactly solvable using the Jordan-Wigner transform, and it is possible to calculate the two-site reduced density matrix for all pairs of sites. Using the two-site density matrix, the entanglement of formation between any two sites is calculated for all parameter values and temperatures. We also study the entanglement in the transverse Ising model, a special case of the XY model, which exhibits a quantum phase transition. It is found that the next-nearest neighbour entanglement (though not the nearest-neighbour entanglement) is a maximum at the critical point. Furthermore, we show that the critical point in the transverse Ising model corresponds to a transition in the behaviour of the entanglement between a single site and the remainder of the lattice. ------------------------------------------------------------------------------- Gauge P-representations for quantum dynamical problems: removal of boundary terms P. Deuar and P. D. Drummond quant-ph/0203025 P-representation techniques, which have been very successful in quantum optics and in other fields, are also useful for general bosonic quantum dynamical many-body calculations like BEC. We introduce a new representation called the gauge P-representation which greatly widens the range of tractable problems. Our treatment results in an infinite set of possible time-evolution equations, depending on arbitrary gauge functions that can be optimized for a given quantum system. In some cases, previous methods can give erroneous results, due to the usual assumption of vanishing boundary conditions being invalid for those particular systems. Solutions are given to this boundary-term problem for all the cases where it is known to occur: two-photon absorption and the single-mode laser. We also provide some brief guidelines on how to apply the stochastic gauge method to other systems in general, quantify the freedom of choice in the resulting equations, and make a comparison to related recent developments. ------------------------------------------------------------------------------- Non-Markovian Stochastic Schrodinger equations: generalization to real-valued noise using quantum measurement theory Jay Gambetta and H.M. Wiseman quant-ph/0202117 Do stochastic Schrodinger equations, also known as unravelings, have a physical interpretation? In the Markovian limit, where the system {\em on average} obeys a master equation, the answer is yes. Markovian stochastic Schrodinger equations generate quantum trajectories for the system state conditioned on continuously monitoring the bath. For a given master equation, there are many different unravelings, corresponding to different sorts of measurement on the bath. In this paper we address the non-Markovian case, and in particular the sort of stochastic Schrodinger equation introduced by Strunz, Di\' osi, and Gisin [Phys. Rev. Lett. {\bf 82}, 1801 (1999)]. Using a quantum measurement theory approach, we rederive their unraveling which involves complex-valued Gaussian noise. We also derive an unraveling involving real-valued Gaussian noise. We show that in the Markovian limit, these two unravelings correspond to heterodyne and homodyne detection respectively. Although we use quantum measurement theory to define these unravelings, we conclude that the stochastic evolution of the system state is not a true quantum trajectory, as the identity of the state through time is a fiction. ------------------------------------------------------------------------------- Capture and release of a conditional state of a cavity QED system by quantum feedback W.P. Smith, J.E. Reiner, L.A. Orozco, S. Kuhr and H.M. Wiseman quant-ph/0202063 Detection of a single photon escaping an optical cavity QED system prepares a non-classical state of the electromagnetic field. The evolution of the state can be modified by changing the drive of the cavity. For the appropriate feedback, the conditional state can be captured (stabilized) and then released. This is observed by a conditional intensity measurement that shows suppression of vacuum Rabi oscillations for the length of the feedback pulse and their subsequent return. ------------------------------------------------------------------------------- Spin squeezing via quantum feedback L. K. Thomsen, S. Mancini and H. M. Wiseman quant-ph/0202028 We propose a quantum feedback scheme for producing deterministically reproducible spin squeezing. The results of a continuous nondemolition atom number measurement are fed-back to control the quantum state of the sample. For large samples and strong cavity coupling, the squeezing parameter minimum scales inversely with atom number, approaching the Heisenberg limit. Furthermore, ceasing the measurement and feedback when this minimum has been reached will leave the sample in the maximally squeezed spin state. ------------------------------------------------------------------------------- Atom laser coherence and its control via feedback L. K. Thomsen and H. M. Wiseman quant-ph/0202027 We present a quantum mechanical treatment of the coherence properties of a single-mode atom laser. Specifically, we focus on the quantum phase noise of the atomic field as expressed by the first order coherence function, for which we derive analytical expressions in various regimes. The decay of this function is characterized by the coherence time, or its reciprocal, the linewidth. A crucial contributor to the linewidth is the collisional interaction of the atoms. We find four distinct regimes for the linewidth with increasing interaction strength. These range from the standard laser linewidth, through quadratic and linear regimes, to another constant regime due to quantum revivals of the coherence function. The laser output is only coherent (Bose degenerate) up to the linear regime. However, we show that application of a QND measurement and feedback scheme will increase, by many orders of magnitude, the range of interaction strengths for which it remains coherent. ------------------------------------------------------------------------------- Bayesian feedback versus Markovian feedback in a two-level atom H. M. Wiseman, Stefano Mancini and Jin Wang quant-ph/0201145 We compare two different approaches to the control of the dynamics of a continuously monitored open quantum system. The first is Markovian feedback as introduced in quantum optics by Wiseman and Milburn [Phys. Rev. Lett. {\bf 70}, 548 (1993)]. The second is feedback based on an estimate of the system state, developed recently by Doherty {\em et al.} [Phys. Rev. A {\bf 62}, 012105 (2000)]. Here we choose to call it, for brevity, {\em Bayesian feedback}. For systems with nonlinear dynamics, we expect these two methods of feedback control to give markedly different results. The simplest possible nonlinear system is a driven and damped two-level atom, so we choose this as our model system. The monitoring is taken to be homodyne detection of the atomic fluorescence, and the control is by modulating the driving. The aim of the feedback in both cases is to stabilize the internal state of the atom as close as possible to an arbitrarily chosen pure state, in the presence of inefficient detection and other forms of decoherence. Our results (obtain without recourse to stochastic simulations) prove that Bayesian feedback is never inferior, and is usually superior, to Markovian feedback. However it would be far more difficult to implement than Markovian feedback and it loses its superiority when obvious simplifying approximations are made. It is thus not clear which form of feedback would be better in the face of inevitable experimental imperfections. =============================================================================== 2. VACANCIES =============================================================================== Postdoctoral Research Fellowship in Theoretical Quantum Physics Centre for Quantum Dynamics Griffith University, AUSTRALIA Level: Research Fellow Grade 1 Term: Two Years, Full Time. Closing Date: 19 April 2002. Applications are invited for a Research Fellow Grade 1 in Theoretical Quantum Physics. The Fellow will work as part of the Centre for Quantum Dynamics. The position is funded by the project "Novel Aspects and Applications of Quantum Measurement Theory", which includes retrodiction, non-Markovian measurements, and the emergence of classical behaviour. Applicants must hold a Ph.D. in quantum optics, quantum measurement theory, or a related area involving open quantum systems. The fellow will also have the freedom to pursue independent research, and to gain teaching experience if so desired. This is a two year fixed term, full time position available from July 2002. Application process: see http://www.gu.edu.au/jobs/ (search for "physics") Queries about the research project: 1. Dr. H.M. Wiseman (H.Wiseman@gu.edu.au) 2. Prof. D.T. Pegg (D.Pegg@sct.gu.edu.au) =============================================================================== 5. CONFERENCES / WORKSHOPS =============================================================================== CLEO/QELS 2002: Conference on Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference 19 - 24 May 2002 Early registration: April 19, 2002 Long Beach, CA, USA http://www.osa.org/CLEO/ The Conference on Lasers and Electro-Optics (CLEO) is the key forum for the optical device technology development and systems engineering that are the foundation of the ongoing revolution in a wide range of applications. From optical fiber communications to medicine, these applications exploit the latest advances in lasers and electro-optics. Moreoever, the meeting will serve to stimulate the use of more mature technologies in new fields. From the latest research and development to the newest technology, components and systems, CLEO sets the pace for the industry and provides the definitive marketplace for laser and electro-optical equipment. The Quantum Electronics and Laser Science Conference (QELS) is the largest North American conference concerning research in lasers, nonlinear optics, and the fundamental laser spectroscopy of atoms and condensed matter. ------------------------------------------------------------------- 9th Central-European Workshop on Quantum Optics 3 - 6 May 2002 registration deadline: 25th March 2002. submission of abstracts by 4th March 2002 Szeged, Hungary http://www.u-szeged.hu/cewqo The workshop will be a forum of all aspects of quantum optics, including also matter waves, quantum informatics, and fundamentals of quantum mechanics. ------------------------------------------------------------------- NATO Advanced Study Institute on Quantum Information and Communication Technologies 3 - 14 June, 2002 Deadline for registration and payment: February 15, 2002 Ankara, Turkey http://www.fen.bilkent.edu.tr/~quantum The main objective of the meeting is to provide training and offer orientation to young scientists in the field of: * Quantum information technologies * Quantum communication systems, entanglement, encoding, cryptography * Generation and detection of non-classical light * Quantum measurements * Matter wave optics, Bose-Einstein condensation * Propagation of photons in fibers, heterostructures, photonic crystals, and mesoscopic systems ------------------------------------------------------------------- IQEC/LAT 2002: International Quantum Electronics Conference and International Conference on Lasers, Applications and Technologies 22-28 June 2002 Abstract and summary deadline 15 January 2002 Moscow, Russia http://www.ilc.msu.su/iqec2002/ The International Quantum Electronics Conference (IQEC) is the largest international conference featuring the fundamentals of quantum electronics, basic research in lasers, nonlinear and quantum optics, quantum information, and fundamental laser spectroscopy of atoms and condensed matter. IQEC 2002 is organized by the Russian Academy of Sciences and M. V. Lomonosov Moscow State University under the aegis of the International Council on Quantum Electronics (ICQE). The Conference on Lasers, Applications, and Technologies (LAT) provides a forum for an update and review of a wide range of laser technologies and applications including laser device development, processing of advanced materials, optical information technologies, biomedicine and ecology applications. The meeting serves to stimulate the use of more mature optical technologies in different fields. LAT 2002 is organized by the Russian Academy of Sciences, Ministry of Industry, Science and Technology of the Russian Federation, and SPIE/Russia. ------------------------------------------------------------------- 2002 Australian Institute Of Physics Congress 8 - 11 July, 2002 Sydney, Australia http://www.aip.org.au/Congress2002/ ------------------------------------------------------------------- International Conference on Quantum Information 13th-18th July 2002 Deadline for abstract of contributed papers: March 15, 2002 Registration: May 31, 2002 Oviedo, Spain http://www.uniovi.es/Congresos/2001/QI/Welcome.html The main topics of the Conference will include * Quantum Information * Recent Theoretical and Experimental Progress in Quantum Information Processing * Quantum Computation * Conceptual Issues on the Foundations of Quantum Theory ------------------------------------------------------------------- QCM&C'02: Sixth International Conference on Quantum Communication, Measurement and Computing July 22-26, 2002 Deadline for papers: March 15, 2002 Pre-conference registration deadline is 5 July 2002 Massachusetts Institute of Technology http://rleweb.mit.edu/QCMC/ The previous meetings in this series, drew together researchers from many countries and covered topics in quantum information theory, theoretical and experimental aspects of quantum computing, quantum communication systems, cryptography, new quantum effects and their experimental realizations, generation detection and applications of nonclassical light, quantum noise, stochastic processes and filtering, and quantum measurement theory. These same topics will be covered at QCM&C'02. ------------------------------------------------------------------- ICAP 2002: Eighteenth International Conference on Atomic Physics July 28 to August 2, 2002 Early Registration: April 1 Abstracts for posters: May 19 Cambridge, Massachusetts, USA http://cua.mit.edu/icap2002/ The meeting will feature invited talks and posters on the latest developments in Atomic Physics. Topics include atomic tests of fundamental theories, laser spectroscopy, laser cooling and trapping, Bose-Einstein condensation, quantum optics and coherence, atom optics, precision measurements, atomic clocks, atoms in intense laser fields, quantum control, quantum information, atomic structure and atomic collisions. ------------------------------------------------------------------- ISQCI 2002: International School on Quantum Computation and Information 2 - 7 September 2002 The application deadline is the 26th of April 2002 The number of participants to the School is limited to about 60. Lisbon, Portugal http://www.qubit.org/school2002/index.htm The objective of this school is to offer a pedagogic and fairly comprehensive introduction to the emerging field of Quantum Computation and Information, covering both the theoretical and the experimental sides. The school is aimed at those who are considering to start working in this field or at least would like to learn more about it. We therefore welcome applications not only from students, but also from researchers in other areas of physics, as well as mathematicians, computer scientists and engineering scientists. ------------------------------------------------------------------- DICE2002 Decoherence, Information, Complexity and Entropy September 2-6, 2002 Piombino (Tuscany) To stimulate interdisciplinary discussion on fundamental interactions, cosmology, quantum theory, quantum information processing, nonlinear dynamics, and complex systems: http://omnis.if.ufrj.br/~thomas/DICEhp.html ------------------------------------------------------------------- EuroConference on Quantum Atom Optics: From Quantum Science to Technology 21 - 26 September 2002 Applications by 15 May 2002 San Feliu de Guixols, Spain http://www.esf.org/esf_euresco_list.php?language=0&year=2002 Quantum Optics has proven to be a uniquely dynamic field in physics capable of taking up new ideas and developments. At the centre of Quantum Optics is the study of quantum phenomena and quantum processes, which are now becoming increasingly relevant for emerging technologies. The 2002 Quantum Optics conference will have its emphasis on the coherent manipulation of quantum systems and on the quantum physics of coherent matter, with high level contributions from leading research groups. Sessions will be devoted to topical subjects such as quantum atom optics, atom lasers, molecules and interactions, and quantum information processing. A key session will be on technologies emerging from Quantum Optics.