Fast Laser Cooling Using Optimal Quantum Control

TL;DR

This paper introduces a quantum control method using automatic differentiation to optimize laser cooling of trapped ions, surpassing traditional limits and enabling faster cooling while maintaining low phonon occupation.

Contribution

It presents a novel quantum control approach that finds optimal cooling conditions beyond the weak coupling regime, improving cooling speed and efficiency.

Findings

Faster cooling achieved with optimized conditions

Applicable to sideband and EIT cooling schemes

Maintains low phonon occupation during rapid cooling

Abstract

Cooling down a trapped ion into its motional ground state is a central step for trapped ions based quantum information processing. State of the art cooling schemes often work under a set of optimal cooling conditions derived analytically using a perturbative approach, in which the sideband coupling is assumed to be the weakest of all the relevant transitions. As a result the cooling rate is severely limited. Here we propose to use quantum control technique powered with automatic differentiation to speed up the classical cooling schemes. We demonstrate the efficacy of our approach by applying it to find the optimal cooling conditions for classical sideband cooling and electromagnetically induced transparency cooling schemes, which are in general beyond the weak sideband coupling regime. Based on those numerically found optimal cooling conditions, we show that faster cooling can be achieved while at the same time a low average phonon occupation can be retained.