Faster State Preparation across Quantum Phase Transition Assisted by Reinforcement Learning

TL;DR

This paper demonstrates a reinforcement learning-based method to accelerate quantum state preparation across a phase transition, achieving high fidelity and improved sensitivity in Bose-Einstein condensates more efficiently than traditional adiabatic methods.

Contribution

It introduces a deep reinforcement learning approach to optimize quantum state preparation, surpassing adiabatic protocols in speed and robustness, especially in the presence of loss.

Findings

Achieved ≥99% fidelity in a fraction of adiabatic time.

Improved interferometric sensitivity with faster protocols.

Successfully implemented in Bose-Einstein condensates with enhanced number squeezing.

Abstract

An energy gap develops near quantum critical point of quantum phase transition in a finite many-body (MB) system, facilitating the ground state transformation by adiabatic parameter change. In real application scenarios, however, the efficacy for such a protocol is compromised by the need to balance finite system life time with adiabaticity, as exemplified in a recent experiment that prepares three-mode balanced Dicke state near deterministically [PNAS {\bf 115}, 6381 (2018)]. Instead of tracking the instantaneous ground state as unanimously required for most adiabatic crossing, this work reports a faster sweeping policy taking advantage of excited level dynamics. It is obtained based on deep reinforcement learning (DRL) from a multi-step training scheme we develop. In the absence of loss, a fidelity $\ge 99\%$ between prepared and the target Dicke state is achieved over a small fraction of the adiabatically required time. When loss is included, training is carried out according to an operational benchmark, the interferometric sensitivity of the prepared state instead of fidelity, leading to better sensitivity in about half of the previously reported time. Implemented in a Bose-Einstein condensate of $\sim 10^4$ $^{87}$Rb atoms, the balanced three-mode Dicke state exhibiting an improved number squeezing of $13.02\pm0.20$ dB is observed within 766 ms, highlighting the potential of DRL for quantum dynamics control and quantum state preparation in interacting MB systems.