Limits on atomic qubit control from laser noise

TL;DR

This paper investigates how the spectral structure of laser noise impacts atomic qubit control fidelity and introduces a new metric to optimize laser stabilization for quantum control below the spontaneous emission limit.

Contribution

It presents a novel spectral noise metric and stabilization requirements that surpass previous linewidth narrowing approaches for atomic qubit control.

Findings

Spectral noise structure significantly affects control fidelity.

New stabilization bandwidth requirements are identified.

The $hi$-separation line metric aids in laser source optimization.

Abstract

Technical noise present in laser systems can limit their ability to perform high fidelity quantum control of atomic qubits. The ultimate fidelity floor for atomic qubits driven with laser radiation is due to spontaneous emission from excited energy levels. The goal is to suppress the technical noise from the laser source to below the spontaneous emission floor such that it is no longer a limiting factor. It has been shown that the spectral structure of control noise can have a large influence on achievable control fidelities, while prior studies of laser noise contributions have been restricted to noise magnitudes. Here, we study the unique spectral structure of laser noise and introduce a new metric that determines when a stabilised laser source has been optimised for quantum control of atomic qubits. We find requirements on stabilisation bandwidths that can be orders of magnitude higher than those required to simply narrow the linewidth of a laser. We introduce a new metric, the $\chi$-separation line, that provides a tool for the study and engineering of laser sources for quantum control of atomic qubits below the spontaneous emission floor.