# Detecting Noisy Channels by Channel Discrimination : Local versus Entangled Resources

## TL;DR

This paper demonstrates that local resources are sufficient to optimally discriminate between ideal unitary gates and noisy channels in quantum systems, aiding in noise detection and characterization without requiring entanglement.

## Contribution

It introduces a method for detecting and estimating noise in quantum gates using channel discrimination with local resources, avoiding the need for entanglement.

## Key findings

- Local resources suffice for optimal discrimination
- The scheme can estimate noise fraction in quantum gates
- Entanglement is not necessary for effective noise detection

## Abstract

Dynamics of many-qubit systems, that may correspond to computational processing with quantum systems, can be efficiently and generally approximated by a sequence of two- and single-qubit gates. In practical applications, however, a quantum gate prepared as a unitary transformation may appear as a noisy channel and consequently may inhibit quantum advantages. In this work, we apply the scheme of channel discrimination to detect if a quantum gate that is actually realized is unitary or noisy. We show that a two-qubit unitary transformation and its noisy counterpart can be optimally discriminated by local resources, without the necessity of creating entanglement repeatedly. It is also shown that the scheme can be applied to estimation of the fraction of noise existing in quantum gates.