# Channel discrimination power of bipartite quantum states

## TL;DR

This paper introduces a measure of how effectively bipartite quantum states can distinguish quantum channels, linking it to entanglement and quantum discord, with exact calculations for pure states and bounds for mixed states.

## Contribution

It defines a new quantifier for bipartite state usefulness in channel discrimination, connecting it to operator Schmidt decomposition and quantum discord, with exact and bounded results.

## Key findings

- Pure states have exactly computable discrimination power.
- Highly entangled states outperform certain separable states.
- Discrimination power is bounded by quantum discord.

## Abstract

We quantify the usefulness of a bipartite quantum state in the ancilla-assisted channel discrimination of arbitrary quantum channels, formally defining a worst-case-scenario channel discrimination power for bipartite quantum states. We show that such a quantifier is deeply connected with the operator Schmidt decomposition of the state. We compute the channel discrimination power exactly for pure states, and provide upper and lower bounds for general mixed states. We show that highly entangled states can outperform any state that passes the realignment criterion for separability. Furthermore, while also unentangled states can be used in ancilla-assisted channel discrimination, we show that the channel discrimination power of a state is bounded by its quantum discord.