Discriminating qubit amplitude damping channels

TL;DR

This paper investigates methods for distinguishing two-qubit amplitude damping channels, highlighting the limited benefit of entanglement and the advantages of feedback, and develops optimal strategies for different scenarios.

Contribution

It provides new insights into channel discrimination strategies, showing when entanglement helps or is unnecessary, and introduces optimal adaptive measurement techniques.

Findings

Feedback assistance improves discrimination performance.

Entangled inputs are not useful for two-shot discrimination.

Optimal adaptive strategies outperform non-adaptive ones.

Abstract

We address the issue of the discrimination between two-qubit amplitude damping channels by exploring several strategies. For the single-shot, we show that the excited state does not always give the optimal input, and that side entanglement assistance has limited benefit. On the contrary, feedback assistance from the environment is more beneficial. For the two-shot, we prove the in-utility of entangled inputs. Then focusing on individual (local) measurements, we find the optimal adaptive strategy.