Quantum cryptography with an ideal local relay

TL;DR

This paper investigates the theoretical and experimental limits of continuous-variable measurement-device-independent quantum key distribution with an ideal local relay, demonstrating potential for secure communication over 170 km.

Contribution

It provides an analysis of optimal CV MDI QKD performance with a lossless local relay and confirms findings through experimental simulation.

Findings

Potential to distribute 10^-4 secret bits per use at 170 km

Ideal relay setup enhances QKD performance

Experimental simulation supports theoretical predictions

Abstract

We consider two remote parties connected to a relay by two quantum channels. To generate a secret key, they transmit coherent states to the relay, where the states are subject to a continuous-variable (CV) Bell detection. We study the ideal case where Alice's channel is lossless, i.e., the relay is locally situated in her lab and the Bell detection is performed with unit efficiency. This configuration allows us to explore the optimal performances achievable by CV measurement-device-independent (MDI) quantum key distribution (QKD). This corresponds to the limit of a trusted local relay, where the detection loss can be re-scaled. Our theoretical analysis is confirmed by an experimental simulation where 10^-4 secret bits per use can potentially be distributed at 170km assuming ideal reconciliation.