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arXiv:quant-ph/0206096 · Physical Review A

Quantum computing in optical microtraps based on the motional states of neutral atoms

K. Eckert, J. Mompart, X. X. Yi, John Schliemann, Dagmar Bruß, G. Birkl, Maciej Lewenstein

Published Oct 23, 2002• 60 citations

Abstract

We investigate quantum computation with neutral atoms in optical microtraps where the qubit is implemented in the motional states of the atoms, i.e., in the two lowest vibrational states of each trap. The quantum gate operation is performed by adiabatically approaching two traps and allowing tunneling and cold collisions to take place. We demonstrate the capability of this scheme to realize a square root of swap gate, and address the problem of double occupation and excitation to other unwanted states. We expand the two-particle wave function in an orthonormal basis and analyze quantum correlations throughout the whole gate process. Fidelity of the gate operation is evaluated as a function of the degree of adiabaticity in moving the traps. Simulations are based on rubidium atoms in state-of-the-art optical microtraps with quantum gate realizations in the few tens of milliseconds duration range.

DOI: 10.1103/physreva.66.042317

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We propose a way to make arrays of optical frequency dipole-force microtraps for cold atoms above a dielectric substrate. Traps are nodes in the evanescent wave fields above an optical waveguide resulting from interference of different waveguide modes. The traps have features sought in developing neutral atom based architectures for quantum computing: $\ensuremath{\sim}1\phantom{\rule{0.3em}{0ex}}\mathrm{mW}$ of laser power yields very tight traps

150\phantom{\rule{0.3em}{0ex}}\mathrm{nm}

above a waveguide with trap vibrational frequencies $\ensuremath{\sim}1\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$ and vibrational ground state sizes $\ensuremath{\sim}10\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. The arrays are scalable and allow addressing of individual sites for quantum logic operations.

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Single atoms in dipole microtraps or optical tweezers have recently become a promising platform for quantum computing and simulation. Here we report a detailed theoretical analysis of the physics underlying an implementation of a Rydberg two-qubit gate in such a system -- a cornerstone protocol in quantum computing with single atoms. We focus on a blockade-type entangling gate and consider various decoherence processes limiting its performance in a real system. We provide numerical estimates for the limits on fidelity of the maximally entangled states and predict the full process matrix corresponding to the noisy two-qubit gate. Our methods and results may find implementation in numerical models for simulation and optimization of neutral atom based quantum processors.