Long-lived Bell states in an array of optical clock qubits

TL;DR

This paper demonstrates the creation of long-lived Bell states in an array of optical clock qubits using Rydberg interactions, achieving high fidelity and coherence times suitable for quantum metrology applications.

Contribution

It introduces a method to generate and maintain high-fidelity Bell states in optical clock qubits with coherence times over four seconds, advancing quantum metrology capabilities.

Findings

Bell states with 92.8% fidelity were generated.

Bell state coherence lifetime measured at 4.2 seconds.

The approach enables potential for many-qubit gates and quantum simulations.

Abstract

The generation of long-lived entanglement on an optical clock transition is a key requirement to unlocking the promise of quantum metrology. Arrays of neutral atoms constitute a capable quantum platform for accessing such physics, where Rydberg-based interactions may generate entanglement between individually controlled and resolved atoms. To this end, we leverage the programmable state preparation afforded by optical tweezers along with the efficient strong confinement of a 3d optical lattice to prepare an ensemble of strontium atom pairs in their motional ground state. We engineer global single-qubit gates on the optical clock transition and two-qubit entangling gates via adiabatic Rydberg dressing, enabling the generation of Bell states, $|\psi\rangle = \frac{1}{\sqrt{2}}\left(|gg\rangle + i|ee\rangle \right)$, with a fidelity of $\mathcal{F}= 92.8(2.0)$%. For use in quantum metrology, it is furthermore critical that the resulting entanglement be long lived; we find that the coherence of the Bell state has a lifetime of $\tau_{bc} = 4.2(6)$ s via parity correlations and simultaneous comparisons between entangled and unentangled ensembles. Such Bell states can be useful for enhancing metrological stability and bandwidth. Further rearrangement of hundreds of atoms into arbitrary configurations using optical tweezers will enable implementation of many-qubit gates and cluster state generation, as well as explorations of the transverse field Ising model and Hubbard models with entangled or finite-range-interacting tunnellers.