Continuous Weak Measurement and Nonlinear Dynamics in a Cold Spin Ensemble

 

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Greg A. Smith¹, Souma Chaudhury¹, Andrew Silberfarb², Ivan H. Deutsch², and Poul S. Jessen¹
 

1. Optical Sciences Center, University of Arizona, Tucson, AZ 85721
2. Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87131
 

A weak continuous quantum measurement of an atomic spin ensemble can be implemented via Faraday rotation of an off-resonance probe beam, and may be used to create and probe nonclassical spin states and dynamics. We show that the probe light shift leads to nonlinearity in the spin dynamics and limits the useful Faraday measurement window. Removing the nonlinearity allows a non-perturbing measurement on the much longer timescale set by decoherence. The nonlinear spin Hamiltonian is of interest for studies of quantum chaos and real-time quantum state estimation.
 

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Quantum Information Processing with Trapped Neutral Atoms

 

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P. S. Jessen, I. H. Deutsch, and R. Stock
 

Quantum information can be processed using large ensembles of ultracold and trapped neutral atoms, building naturally on the techniques developed for high-precision spectroscopy and metrology. This article reviews some of the most important protocols for universal quantum logic with trapped neutrals, as well as the history and the state-of-the-art of experimental work to implement these in the laboratory. Some general observations are made concerning the different strategies for qubit encoding, transport and interaction, including trade-offs between de-coherence rates and the likelihood of two-qubit gate errors. These trade-offs must be addressed through further refinements of logic protocols and trapping technologies before one can undertake the design of a general-purpose neutral-atom quantum processor.
 

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