# Time-bin encoded quantum key distribution over 120 km with a telecom quantum dot source

## TL;DR

Researchers demonstrated a quantum key distribution system using time-bin encoding and a quantum dot source, achieving secure communication over 120 km of fiber.

## Contribution

First experimental validation of time-bin encoded QKD using a telecom-band quantum dot single-photon source.

## Key findings

- Secure key distribution was achieved over a 120 km fiber link using time-bin encoding.
- The system maintained stability for 6 hours of continuous operation.
- This setup achieved the highest secure key rate among time-bin QKDs using single-photon sources.

## Abstract

Quantum key distribution (QKD) with deterministic single photon sources has been demonstrated over intercity fiber and free-space channels. The previous implementations relied mainly on polarization encoding schemes, which are susceptible to birefringence, polarization-mode dispersion and polarization-dependent loss in practical fiber networks. In contrast, time-bin encoding offers inherent robustness and has been widely adopted in mature QKD systems using weak coherent laser pulses. However, its feasibility in conjunction with a deterministic single-photon source has not yet been experimentally demonstrated. In this work, we construct a time-bin encoded QKD system employing a high-brightness quantum dot (QD) single-photon source operating at telecom wavelength. Our proof-of-concept experiment successfully demonstrates the possibility of secure key distribution over fiber link of 120 km, while maintaining extraordinary long-term stability over 6 h of continuous operation, that is highest secure key rate among the time-bin QKDs based on single-photon sources. This work provides the first experimental validation of integrating a QD single-photon source with time-bin encoding in a telecom-band QKD system. This development signifies a substantial advancement in the establishment of a robust and scalable QKD network based on solid-state single-photon technology.

Time-bin–encoded quantum key distribution using actively encoded single photons from a telecom-band quantum dot, achieving transmission over 120 km