Date: 3 December 2008
Time: 4pm - 5pm
Venue: NUS University Hall Auditorium, Lee Kong Chian Wing, Level 2
Speaker: Philippe Grangier, Institut d’Optique, Palaiseau
Media: Video

Abstract:
We describe recent experiments [1, 2, 3] manipulating the quantum state of femtosecond light pulses, in order to generate photon number states (Fock states with n= 1 or 2 photons), quantum superpositions of coherent states (Schrödinger's cats and kittens [1, 2]), and non- gaussian entangled states [3]. We will also discuss possible applications of these new states for quantum communications.



References
[1] A. Ourjoumtsev et al., "Generating optical Schrödinger kittens for quantum information processing", Science 312: 83-86 (2006 )
[2] A. Ourjoumtsev et al., "Generation of optical "Schrödinger cats' from photon number states Nature 448: 784-786 (2007)
[3] A. Ourjoumtsev et al. "Increasing entanglement between Gaussian states by coherent photon subtraction", PRL 98:030502 (2007)

Date: 2 December 2008
Time: 5:30pm - 6:30pm
Venue: NUS University Hall Auditorium, Lee Kong Chian Wing, Level 2
Speaker: Jun Ye, JILA, National Institute of Standards and Technology and University of Colorado
Media: Video

Abstract:
Quantum state engineering of ultracold matter and precise control of optical fields have allowed accurate measurement of light-matter interactions for applications ranging from precision tests of fundamental physics to quantum information science. State-of-the-art lasers now maintain optical phase coherence over one second. Optical frequency combs distribute this optical phase coherence across the entire visible and infrared parts of the electromagnetic spectrum, leading to direct visualization and measurement of light ripples. A new generation of light-based atomic clocks has been developed, with ultracold Sr atoms confined in a carefully engineered optical lattice offering unprecedented coherence times for light-matter interactions. The uncertainty of this new clock has reached 1 × 10^-16, a factor of 4 below the current best Cs primary standard. These developments represent a remarkable convergence of ultracold science, laser technology, and ultrafast science. Further improvements are still tantalizing, with quantum measurement and precision metrology combining forces to explore the next frontier.

Date: 2 December 2008
Time: 4pm - 5pm
Venue: NUS University Hall Auditorium, Lee Kong Chian Wing, Level 2
Speaker: Alain Aspect, Institut d’Optique, Palaiseau
Media: Video   PDF

Abstract:
In 1935, with co-authors Podolsky and Rosen, Einstein discovered an amazing quantum situation, where particles in a pair are so strongly correlated that Schrödinger called them “entangled”. By analyzing that situation, Einstein concluded that the quantum formalism was incomplete. Niels Bohr immediately opposed that conclusion, and the debate lasted until the death of these two giants of physics, in the 1950’s.

In 1964, John Bell produced his famous inequalities which would allow experimentalists to settle the debate, and to show that the revolutionary concept of entanglement is indeed a reality.

Based on that concept, a new field of research has emerged, quantum information, where one uses entanglement between qubits to develop conceptually new methods for processing and transmitting information. Large scale practical implementation of such concepts might revolutionize our society, as did the laser, the transistor and integrated circuits, some of the most striking fruits of the first quantum revolution, which began with the 20th century.

Date: 2 October 2008
Time: 4pm - 5pm
Venue: Physics Conference Room S13, Level M
Speaker: Kazimierz Rzążewski
Abstract:
While all experiments with ultra cold atomic gases are performed at finite, nonzero temperatures most theory papers are assuming a temperature of zero Kelvin. We have developed a simple approximation which is applicable to a gas at nonzero temperature. It treats the atomic field as a c-number rather than as an operator. We call this “the classical field approximation”.

In my lecture I will explain the classical field approximation. I will compare this approximation and the exact quantum solution for a simple case of the ideal Bose gas. In the last part I will apply the method to multiply charged vortices, where some recent experiments are available.

Recommended Pre-reading Materials:
M. Brewczyk, M. Gajda, and K. Rzążewski, Classical fields approximation for bosons at nonzero temperature, Journ. of Physics B 40, R1-R37 (2007)

Date: 28 August 2008
Time: 4pm - 5pm
Venue: Physics Conference Room S13, Level M
Speaker: Dieter Jaksch
Abstract:
I will investigate the properties of atoms which are trapped in an optical lattice and immersed into a Bose-Einstein condensate (BEC). I will show that interspecies interactions lead to dephasing of the lattice atoms and, via BEC phonons, mediate an attractive interaction between them. This may cause lattice atoms to aggregate into a cluster. I will also study the impact of the BEC on transport properties and find a crossover from coherent behaviour described by an extended Hubbard model to diffusive hopping. Furthermore I will show that weak attractive interspecies interactions may give rise to instabilities. I will discuss the relation of this atomic lattice immersion to condensed matter systems and how it may be used for direct quantum simulations. Finally, I will extend these considerations to moving and rotating Bose-Einstein condensates and show how magnetic phenomena can be simulated in lattice immersions.

Date: 17 July 2008
Time: 4pm - 5pm
Venue: Physics Conference Room S13, Level M
Speaker: Rosario Fazio
Abstract:
Recent proposals of realizing condensed phases in cavity-QED like systems opened a number of new exciting possibilities in the physics of strongly interacting photonic systems. Arrays of coupled QED cavities have been shown to have superfluid, insulating and glassy phases. They can be used for transferring quantum information and for simulating interacting spin systems. Coupled cavities can be realized in a wide range of physical systems, from nanocavities in photonic crystals to Cooper pair boxes in superconducting resonators.

After a brief introduction to the field, I will review the main features of the phase diagram and of the signatures of the various phases. I will discuss how, in principle, it might be possible to distinguish between the different phases by measuring photons fluctuations. I will finally discuss dynamical instabilities in these arrays when control parameters are varied in time.

Date: 29 May 2008
Time: 4pm - 5pm
Venue: Physics Conference Room S13, Level M
Speaker: Howard Carmichael
Abstract:
An introduction to the treatment of open quantum systems as stochastic scattering processes (quantum trajectories) will be presented, together with some applications to illustrate the ideas. The final application will address the question: is optical coherence in fact a fiction [Moelmer, PRA 55, 3195 (1997)] or rather more fact than fiction [Noh and Carmichael, PRL 100, 120405 (2008)]?

Date: 17 April 2008
Time: 4pm - 5pm
Venue: S16 - LT31
Speaker: Scott Parkins
Media: Video   PDF

Abstract:
Over the past two decades, strong interactions of light and matter at the single-atom and single-photon level have enabled a wide set of scientific advances in quantum optics and quantum information science.

Single, ultra-cold atoms can now be made to interact strongly and controllably with single-photon light fields confined within microscopic optical resonators (cavity quantum electrodynamics, or cavity QED). Moreover, new resonator configurations, such as lithographically-fabricated monolithic microresonators, hold great promise for the implementation of quantum networks and quantum logic with atoms and photons. In this colloquium I describe some elementary cavity QED systems and potential applications of these systems in quantum information processing. This includes recent theoretical and experimental results for cavity QED with toroidal microresonators.

Date: 27 March 2008
Time: 4pm - 5pm
Venue: S16 - LT31
Speaker: Hans Briegel
Abstract:
Quantum computers offer a promising new way of information processing, in which the distinguishing features of quantum mechanics can fruitfully be exploited. Next to the standard quantum circuit model, various other models for quantum computation exist. Although these models have been shown to be formally equivalent, their underlying elementary concepts, as well the requirements for their practical realization, differ significantly. Exciting perspectives are offered by the new paradigm of measurement-based quantum computation, where the processing of quantum information takes place by rounds of simple measurements on a system of spins prepared in a highly entangled state. In this talk I will discuss a number of recent developments in measurement-based quantum computation on both fundamental and practical issues, e.g. regarding the power of quantum computation and its relation to entanglement, as well as steps toward its experimental realization. Furthermore, I will highlight the various ways in which this field is connected to other branches in physics and mathematics.

Date: 28 February 2008
Time: 4pm - 5pm
Venue: S16 - LT31
Speaker: Nobuyuki Imoto
Abstract:
Quantum information processing is one of the most promising research areas for its possibility of bringing a revolutionary change in the information society. To realize it, however, there are several fundamental issues to be examined, namely, how to protect the quantum information from environmental noise, how to realize one-way computation using the cluster states, and how to guarantee the security of quantum cryptography under realistic noise and imperfection of the devices. In this talk I will introduce the basics of these issues and will describe the possible solutions mainly with photons including activity in my research group in Osaka University.

Date: 10 January 2008
Time: 4pm - 5pm
Venue: CQT Seminar Room, S15-03-15
Speaker: Nicolas Gisin
Abstract: