Southwest Quantum Information and Technology

Tenth Annual Meeting, February 14-17, 2008
University of New Mexico, Santa Fe, New Mexico

Full Program | Thursday Tutorials | Friday | Saturday | Sunday

SESSION 1: Quantum and Atom Optics
Session Chair: JM Geremia
08:45-09:30	Serge Haroche, Ecole Normale Supérieure (invited)
	Quantum Non-Demolition counting of photons in Cavity QED
	Abstract. Rydberg atoms crossing one by one a high-Q cavity extract information from the field stored in it, without absorbing the photons. The procedure realizes an ideal quantum-non demolition (QND) measurement of light. Initially prepared in a coherent state, the field quickly collapses into a Fock state of well-defined photon number, then undergoes successive jumps towards vacuum due to cavity relaxation. We have checked Planck's law and the predictions of quantum field theory by performing a statistical analysis of thousands of individual quantum trajectories recorded in this way. As the photon number is pinned down to a single value by the QND procedure, the field's phase is blurred. The first stage of this blurring process, induced by a single atom, prepares a photonic Schrödinger cat in the cavity, i.e. a coherent superposition of two field states with different phases. By displacing this cat state in phase space and performing a QND measurement on the translated field, we have reconstructed its Wigner function. It exhibits two classical components and, between them, an interference feature presenting negative parts. which is a signature of the cat state quantum coherence. This interference component vanishes much faster than the decay of the field intensity. This tomographic procedure opens the way to a direct investigation of the decoherence process on cat states containing up to a few tens of photons.
09:30-10:00	Thomas Gerrits, National Institute of Standards and Technology
	Generation of optical Cat States by squeezed photon subtraction
	Abstract. Optical Cat States are superpositions of coherent states with opposite phases. Those states may be useful for optical phase measurements, as an interferometer's sensitivity is enhanced compared to a classical interferometer, when the light in both interferometers contains equal mean number of photons and wavelength. Also, in quantum computing they are a fundamental resource of fault-tolerant algorithms. Cat States are very sensitive to decoherence, and as a result their preparation is challenging and can serve as a demonstration of good quantum control. We will present our recent effort in generating and detecting these Cat States. Using a femtosecond laser and a KNbO3 downconversion source we are able to generate non-Gaussian states, which are similar to a Schroedinger Cat State.
10:30-11:00	Steve Flammia, Perimeter Institute
	Ultracompact Generation of Continuous-Variable Cluster States
	Abstract. We propose an experimental scheme that has the potential for large-scale realization of continuous-variable (CV) cluster states for universal quantum computation. We do this by mapping CV cluster-state graphs onto two-mode squeezing graphs, which can be engineered into a single optical parametric oscillator (OPO). The desired CV cluster state is produced directly from a joint squeezing operation on the vacuum using a multi-frequency pump beam. This method has potential for ultracompact experimental implementation. As an illustration, we detail an experimental proposal for creating a four-mode square CV cluster state with a single OPO. (PRA 76, 010302 (2007) and arXiv:0710.4980)