# Measurement-device-independent quantum key distribution coexisting with classical communication

## TL;DR

This paper demonstrates that measurement-device-independent quantum key distribution can coexist with multiple high-speed classical communication channels over the same optical fiber, supporting the future integration of quantum and classical networks.

## Contribution

The study provides the first experimental validation of MDI-QKD coexisting with multiple classical channels on the same fiber, showing practical feasibility for quantum and classical network integration.

## Key findings

- MDI-QKD operates simultaneously with five 10 Gbps classical channels over 40 km fiber.
- Projected communication rates exceed 10 THz when shifting to the second telecommunication window.
- Quantum and classical networks can share infrastructure, enabling scalable quantum internet deployment.

## Abstract

The possibility for quantum and classical communication to coexist on the same fibre is important for deployment and widespread adoption of quantum key distribution (QKD) and, more generally, a future quantum internet. While coexistence has been demonstrated for different QKD implementations, a comprehensive investigation for measurement-device independent (MDI) QKD -- a recently proposed QKD protocol that cannot be broken by quantum hacking that targets vulnerabilities of single-photon detectors -- is still missing. Here we experimentally demonstrate that MDI-QKD can operate simultaneously with at least five 10 Gbps bidirectional classical communication channels operating at around 1550 nm wavelength and over 40 km of spooled fibre, and we project communication rates in excess of 10 THz when moving the quantum channel from the third to the second telecommunication window. The similarity of MDI-QKD with quantum repeaters suggests that classical and generalised quantum networks can co-exist on the same fibre infrastructure.