On Ping-Pong protocol and its variant

TL;DR

This paper analyzes the Ping-Pong quantum communication protocol, deriving a trade-off inequality that limits Eve's ability to distinguish messages without detection, applicable to various initial states and protocol variants.

Contribution

It introduces a universal trade-off inequality for the Ping-Pong protocol and its variant, applicable to arbitrary initial states and different communication setups.

Findings

Eve cannot distinguish messages without detection, regardless of initial states.

The derived inequality applies to both the original and a modified protocol.

The results provide fundamental limits on eavesdropping in quantum communication.

Abstract

We discuss the Ping-Pong protocol which was proposed by Bostroem and Felbinger. We derive a simple trade-off inequality between distinguishability of messages for Eve and detectability of Eve for legitimate users. Our inequality holds for arbitrary initial states. That is, even if Eve prepares an initial state, she cannot distinguish messages without being detected. We show that the same inequality holds also on another protocol in which Alice and Bob use one-way quantum communication channel twice.