Entanglement of neutral-atom qubits with long ground-Rydberg coherence times

TL;DR

This paper demonstrates high-fidelity entanglement of neutral-atom qubits with long coherence times, enabling advanced quantum information processing without the need for adjustable interatomic spacing.

Contribution

It introduces a ground-state entanglement protocol for Cs atoms using Rydberg blockade and Raman transitions, achieving record fidelity and long coherence times without adjustable spacing.

Findings

Bell state fidelity of 0.81(5) achieved

Ground-state coherence times of 10 ms (T2*) and 0.14 s (T2')

Long ground-Rydberg coherence times of 17 μs

Abstract

We report results of a ground-state entanglement protocol for a pair of Cs atoms separated by 6~$\mu$m, combining the Rydberg blockade mechanism with a two-photon Raman transitions to prepare the $\vert\Psi^+\rangle=(\vert 10\rangle+\vert 01\rangle)/\sqrt{2}$ Bell state with a loss-corrected fidelity of 0.81(5), equal to the best demonstrated fidelity for atoms trapped in optical tweezers but without the requirement for dynamically adjustable interatomic spacing. Qubit state coherence is also critical for quantum information applications, and we characterise both ground-state and ground-Rydberg dephasing rates using Ramsey spectroscopy. We demonstrate transverse dephasing times $T_2^*=10(1)$~ms and $T_2'=0.14(1)$~s for the qubit levels and achieve long ground-Rydberg coherence times of $T_2^*=17(2)~\mu$s as required for implementing high-fidelity multi-qubit gate sequences where a control atom remains in the Rydberg state while applying local operations on neighbouring target qubits.