15_control

Quantum Control and Information Processing in Optical Lattices

 


P. S. Jessen, D.L. Haycock, G. Klose, G. Smith, I.H. Deutsch, and G.K. Brennen
 

Neutral atoms offer a promising platform for single- and many-body quantum control, as required for quantum information processing. This includes excellent isolation from the decohering influence of the environment, and the existence of well developed techniques for atom trapping and coherent manipulation. We present a review of our work to implement quantum control and measurement for ultra-cold atoms in far-off resonance optical lattice traps. In recent experiments we have demonstrated coherent behavior of mesoscopic spinor wavepackets in optical double-well potentials, and carried out quantum state tomography to reconstruct the full density matrix for the atomic spin degrees of freedom. This model system shares a number of important features with proposals to implement quantum logic and quantum computing in optical lattices. We present a theoretical analysis of a protocol for universal quantum logic via single qubit operations and an entangling gate based on electric dipole-dipole interactions. Detailed calculations including the full atomic hyperfine structure suggests that high-fidelity quantum gates are possible under realistic experimental conditions.
 

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14_density

Measuring the Quantum State of a Large Angular Momentum

 


G. Klose, G. Smith, and Poul S. Jessen

Optical Sciences Center, University of Arizona, Tucson, AZ 85721
 

We demonstrate a general method to measure the quantum state of an angular momentum of arbitrary magnitude. The (2F+1) x (2F+1) density matrix is completely determined from a set of Stern-Gerlach measurements with (4F+1) different orientations of the quantization axis. We implement the protocol for laser cooled Cesium atoms in the 6 S1/2 (F=4) hyperfine ground state and apply it to a variety of test states prepared by optical pumping and Larmor precession. A comparison of input and measured states shows typical reconstruction fidelities greater than about 0.95.
 

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