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Single-qubit gates based on targeted phase shifts in a 3D neutral atom array

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Science  24 Jun 2016:
Vol. 352, Issue 6293, pp. 1562-1565
DOI: 10.1126/science.aaf2581

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How to single out the right atoms

For a quantum computer to be useful, its qubits have to be able to change their state in response to external stimuli. But when a large number of qubits are packed in a three-dimensional (3D) structure to optimize the use of space, altering one qubit can unintentionally change the state of others. Wang et al. devised a clever way to perform high-fidelity quantum gates only on intended qubits in a 3D array of Cs atoms. Although the operation initially changed the state of some of the other atoms, additional manipulation recovered their original state. The technique may be applicable to other quantum computing implementations.

Science, this issue p. 1562

Abstract

Although the quality of individual quantum bits (qubits) and quantum gates has been steadily improving, the number of qubits in a single system has increased quite slowly. Here, we demonstrate arbitrary single-qubit gates based on targeted phase shifts, an approach that can be applied to atom, ion, or other atom-like systems. These gates are highly insensitive to addressing beam imperfections and have little cross-talk, allowing for a dramatic scaling up of qubit number. We have performed gates in series on 48 individually targeted sites in a 40% full 5 by 5 by 5 three-dimensional array created by an optical lattice. Using randomized benchmarking, we demonstrate an average gate fidelity of 0.9962(16), with an average cross-talk fidelity of 0.9979(2) (numbers in parentheses indicate the one standard deviation uncertainty in the final digits).

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