# Experimental demonstration of the DPTS QKD protocol over a 170 km fiber link

## TL;DR

This paper demonstrates the DPTS quantum key distribution protocol over 170 km fiber, showing improved secret key rates compared to other protocols and compatibility with classical signals, advancing practical quantum communication.

## Contribution

First experimental demonstration of the DPTS QKD protocol over 170 km fiber, with performance comparison to COW and DPS protocols and classical signal coexistence.

## Key findings

- DPTS achieves higher secret key rate up to 100 km.
- Successful coexistence of quantum and classical signals in the same fiber.
- Demonstrated feasibility of long-distance QKD with enhanced protocols.

## Abstract

Quantum key distribution (QKD) is a promising technology aiming at solving the security problem arising from the advent of quantum computers. While the main theoretical aspects are well developed today, limited performances, in terms of achievable link distance and secret key rate, are preventing the deployment of this technology on a large scale. More recent QKD protocols, which use multiple degrees of freedom for the encoding of the quantum states, allow an enhancement of the system performances. Here, we present the experimental demonstration of the differential phase-time shifting protocol (DPTS) up to 170 km of fiber link. We compare its performance with the well-known coherent one-way (COW) and the differential phase shifting (DPS) protocols, demonstrating a higher secret key rate up to 100 km. Moreover, we propagate a classical signal in the same fiber, proving the compatibility of quantum and classical light.