# One-shot quantum state exchange

## TL;DR

This paper investigates a one-shot quantum state exchange protocol, establishing entanglement bounds, conditions for zero entanglement cost, and revealing counter-intuitive phenomena that differ from standard SWAP operations.

## Contribution

It introduces the first analysis of one-shot quantum state exchange, deriving entanglement bounds and uncovering novel phenomena in entanglement management.

## Key findings

- Lower bounds on entanglement needed for one-shot exchange
- Conditions for zero entanglement cost in the protocol
- Discovery of counter-intuitive phenomena in entanglement handling

## Abstract

The quantum state exchange is a quantum communication task in which two users exchange their respective quantum information in the asymptotic setting. In this work, we consider a one-shot version of the quantum state exchange task, in which the users hold a single copy of the initial state, and they exchange their parts of the initial state by means of entanglement-assisted local operations and classical communication. We first derive lower bounds on the least amount of entanglement required for carrying out this task, and provide conditions on the initial state such that the protocol succeeds with zero entanglement cost. Based on these results, we reveal two counter-intuitive phenomena in this task, which make it different from a conventional SWAP operation. One tells how the users deal with their symmetric information in order to reduce the entanglement cost. The other shows that it is possible for the users to gain extra shared entanglement after this task.