Mixed state discrimination using optimal control

TL;DR

This paper develops and experimentally demonstrates an optimal local measurement strategy for discriminating two nonorthogonal quantum states with multiple copies, outperforming other schemes especially under noise conditions.

Contribution

It introduces a globally optimal local measurement strategy derived via optimal control theory for state discrimination under noise, with experimental validation.

Findings

Optimal control-based measurement outperforms other local schemes under noise.

Repeating single-copy optimal measurement can be better than noise-affected optimal schemes.

Experimental results confirm the superiority of the derived optimal strategy.

Abstract

We present theory and experiment for the task of discriminating two nonorthogonal states, given multiple copies. We implement several local measurement schemes, on both pure states and states mixed by depolarizing noise. We find that schemes which are optimal (or have optimal scaling) without noise perform worse with noise than simply repeating the optimal single-copy measurement. Applying optimal control theory, we derive the globally optimal local measurement strategy, which outperforms all other local schemes, and experimentally implement it for various levels of noise.