# Two-way communication with a single quantum particle

## TL;DR

This paper demonstrates that quantum systems can enable two-way communication with a single particle in superposition, surpassing classical limits and allowing perfect success in a multi-party game, unlike classical strategies.

## Contribution

It introduces a quantum communication protocol that achieves two-way signaling with a single particle, exceeding classical constraints and providing a new quantum advantage in multi-party scenarios.

## Key findings

- Quantum systems enable two-way signaling with a single particle.
- Classical strategies fail to maintain success probability as parties increase.
- Quantum strategies guarantee success regardless of the number of parties.

## Abstract

In this letter we show that communication when restricted to a single information carrier (i.e. single particle) and finite speed of propagation is fundamentally limited for classical systems. On the other hand, quantum systems can surpass this limitation. We show that communication bounded to the exchange of a single quantum particle (in superposition of different spatial locations) can result in "two-way signaling" which is impossible in classical physics. We quantify the discrepancy between classical and quantum scenarios by the probability of winning a game played by distant players. We generalize our result to an arbitrary number of parties and we show that the probability of success is asymptotically decreasing to zero as the number of parties grows, for all classical strategies. In contrast, quantum strategy allows players to win the game with certainty.