Quantum Computing with Neutral Atoms in an Optical Lattice

 

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Ivan H. Deutsch¹, Gavin K. Brennen¹ and Poul S. Jessen²

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

We present a proposal for quantum information processing with neutral atoms trapped in optical lattices as qubits. Initialization and coherent control of single qubits can be achieved with standard laser cooling and spectroscopic techniques. We consider entangling two-qubit logic gates based on optically induced dipole-dipole interactions, calculating a figure-of-merit for various protocols. Massive parallelism intrinsic to the lattice geometry makes this an intriguing system for scalable, fault-tolerant quantum computation.
 

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Mesoscopic Quantum Coherence in an Optical Lattice

 

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D. L. Haycock¹, P.M. Alsing², I. H. Deutsch², J. Grondalskik² and P. S. Jessenk¹

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

We observe the quantum coherent dynamics of atomic spinor wave packets in the double-well potentials of a far-off resonance optical lattice. With appropriate initial conditions the system Rabi oscillates between the left and right localized states of the ground doublet, and at certain times the wave packet corresponds to a coherent superposition of these mesoscopically distinct quantum states. The atom/optical double-well potential is a flexible and powerful system for further study of quantum coherence, quantum control and the quantum/classical transition.
 

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Entangling Dipole-Dipole Interactions and Quantum Logic in Optical Lattices

 

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Gavin K. Brennen and Ivan H. Deutsch Center for Advanced Studies, Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico 87131 Poul S. Jessen Optical Sciences Center, University of Arizona, Tucson, Arizona 85721
 

We study a means of creating multiparticle entanglement of neutral atoms using pairwise controlled dipole-dipole interactions. For tightly trapped atoms the dipolar interaction energy can be much larger than the photon scattering rate and substantial coherent evolution of the two-atom state can be achieved before decoherence occurs. Excitation of the dipoles can be made conditional on the atomic states, allowing for deterministic generation of entanglement. We derive selection rules and a figure of merit for the dipole-dipole interaction matrix elements, for alkali atoms with hyperfine structure and trapped in localized center of mass states. Different protocols are presented for implementing two-qubit quantum logic gates such as the controlled-phase and swap gates. We analyze the error probability of our gate designs, finite due to decoherence from cooperative spontaneous emission and coherent couplings outside the logical basis. Outlines for extending our model to include the full molecular interactions potentials are discussed.
 

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Quantum Transport in Magneto-Optical Double-Potential Wells

 

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I. H. Deutsch, P. M. Alsing, J. Grondalski, S. Ghose, D. L. Haycock, and Poul S. Jessen
 

We review the quantum transport of ultra-cold alkali atoms trapped in a one dimensional optical lattice of double-potential wells, engineered through a combination of ac-Stark shifts and Zeeman interactions. The system is modeled numerically through analysis of the band-structure and integration of the time dependent Schrdinger equation. By these means we simulate coherent control of the atomic wavepackets. We present results from ongoing experiments on laser cooled Cesium, including the demonstration of quantum state preparation and coherent tunneling. Entanglement between the internal and motional degrees of freedom allows us to access the tunneling dynamics by Stern-Gerlach measurements of the ground state magnetic populations. Schemes to extend this into a full reconstruction of the density matrix for the ground state angular momentum are presented. We further consider the classical dynamics of our system, which displays deterministic chaos. This has important implications for the distinction between classical and quantum mechanical transport.
 

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