Robust control and optimal Rydberg states for neutral atom two-qubit gates

TL;DR

This paper develops robust two-qubit gates for neutral atom quantum computing using Rydberg states, achieving high fidelity despite experimental control deviations, and identifies optimal Rydberg states to minimize errors.

Contribution

It introduces quantum optimal control techniques to create robust CZ gates resilient to control deviations and accounts for Rydberg state lifetimes, enhancing near-term quantum device performance.

Findings

Achieved Bell state fidelity > 0.999 with robust control pulses.

Identified optimal Rydberg states for minimal infidelity.

Designed gates operable within Rydberg state lifetimes.

Abstract

We investigate the robustness of two-qubit gates to deviations of experimental controls, on a neutral atom platform utilizing Rydberg states. We construct robust CZ gates - employing techniques from quantum optimal control - that retain high Bell state fidelity $F > 0.999$ in the presence of significant deviations of the coupling strength to the Rydberg state. Such deviations can arise from laser intensity noise and atomic motion in an inhomogeneous coupling field. We also discuss methods to mitigate errors due to deviations of the laser detuning. The designed pulses operate on timescales that are short compared to the fundamental decay timescale set by spontaneous emission and blackbody radiation. We account for the finite lifetime of the Rydberg state in both the optimisation and fidelity calculations - this makes the gates conducive to noisy intermediate-scale quantum experiments, meaning that our protocols can reduce infidelity on near-term quantum computing devices. We calculate physical properties associated with infidelity for strontium-88 atoms - including lifetimes, polarisabilities and blockade strengths - and use these calculations to identify optimal Rydberg states for our protocols, which allows for further minimisation of infidelity.