Interference of short optical pulses from independent gain-switched laser diodes for quantum secure communications

TL;DR

This paper demonstrates high-visibility interference between independent gain-switched laser diodes at 1GHz, supporting their use in advanced quantum communication schemes like measurement-device-independent QKD.

Contribution

It provides the first experimental verification of high-visibility interference from independent GS lasers suitable for high-speed quantum communication.

Findings

Achieved high-visibility interference at 1GHz between independent GS lasers.

Characterized laser frequency chirp and jitter to relate to interference quality.

Validated results with parameter-free analysis and numerical simulations.

Abstract

Since the introduction of the decoy-state technique, phase-randomised weak coherent light pulses have been the key to increase the practicality of quantum-based communications. Their ultra-fast generation was accomplished via compact gain-switched (GS) lasers, leading to high key rates in quantum key distribution (QKD). Recently, the question arose of whether the same laser could be employed to achieve high-speed measurement-device-independent-QKD, a scheme that promises long-haul quantum communications immune to all detector attacks. For that, a challenging highvisibility interference between independent picosecond optical pulses is required. Here, we answer the above question in the affirmative by demonstrating high-visibility interference from two independent GS lasers triggered at 1GHz. The result is obtained through a careful characterization of the laser frequency chirp and time jitter. By relating these quantities to the interference visibility, we obtain a parameter-free verification of the experimental data and a numerical simulation of the achievable key rates. These findings are beneficial to other applications making use of GS lasers, including random number generation and standard QKD.