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arXiv:1007.0397 · Physical Review A

Deterministic entanglement of two neutral atoms via Rydberg blockade

X. L. Zhang, L. Isenhower, Alexander Gill, Thad G Walker, Mark E. Saffman

Published Sep 29, 2010• 175 citations
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Abstract

We demonstrate the deterministic entanglement of two individually addressed neutral atoms using a Rydberg blockade mediated controlled-not gate. Parity oscillation measurements reveal a Bell state fidelity of $F=0.58\ifmmode\pm\else\textpm\fi{}0.04$, which is above the entanglement threshold of $F=0.5$, without any correction for atom loss, and $F=0.71\ifmmode\pm\else\textpm\fi{}0.05$ after correcting for background collisional losses. The fidelity results are shown to be in good agreement with a detailed error model.

DOI
10.1103/physreva.82.030306

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We demonstrate the deterministic entanglement of two individually addressed neutral atoms using a Rydberg blockade mediated controlled-not gate. Parity oscillation measurements reveal a Bell state fidelity of F=0.58\ifmmode±\else\textpm\fi0.04F=0.58\ifmmode\pm\else\textpm\fi{}0.04F=0.58\ifmmode±\else\textpm\fi0.04, which is above the entanglement threshold of F=0.5F=0.5F=0.5, without any correction for atom loss, and F=0.71\ifmmode±\else\textpm\fi0.05F=0.71\ifmmode\pm\else\textpm\fi{}0.05F=0.71\ifmmode±\else\textpm\fi0.05 after correcting for background collisional losses. The fidelity results are shown to be in good agreement with a detailed error model.
We present experimental results on two-qubit Rydberg-blockade quantum gates and entanglement in a two-dimensional qubit array. Without postselection against atom loss we achieve a Bell state fidelity of $0.73\ifmmode\pm\else\textpm\fi{}0.05$. The experiments are performed in an array of single Cs atom qubits with a site to site spacing of $3.8\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$. Using the standard protocol for a Rydberg-blockade CZ{C}_{Z}CZ​ gate together with single qubit operations we create Bell states and measure their fidelity using parity oscillations. We analyze the role of ac Stark shifts that occur when using two-photon Rydberg excitation and show how to tune experimental conditions for optimal gate fidelity.
We present the first demonstration of a CNOT gate between two individually addressed neutral atoms. Our implementation of the CNOT uses Rydberg blockade interactions between neutral atoms held in optical traps separated by >8 microm. Using two different gate protocols we measure CNOT fidelities of F=0.73 and 0.72 based on truth table probabilities. The gate was used to generate Bell states with fidelity F=0.48+/-0.06. After correcting for atom loss we obtain an a posteriori entanglement fidelity of F=0.58.
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One can implement fast two-qubit entangling gates by exploiting the Rydberg blockade. Although various theoretical schemes have been proposed, experimenters have not yet been able to demonstrate two-atom gates of high fidelity due to experimental constraints. We propose a novel scheme, which only uses a single Rydberg pulse illuminating both atoms, for the construction of neutral-atom controlled-phase gates. In contrast to the existing schemes, our approach is simpler to implement and requires neither individual addressing of atoms nor adiabatic procedures. With parameters estimated based on actual experimental scenarios, a gate fidelity higher than 0.99 is achievable.
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