Experimental single-photon quantum key distribution surpassing the fundamental coherent-state rate limit

TL;DR

This paper demonstrates a high-rate quantum key distribution (QKD) surpassing the fundamental rate limit of coherent light by using a high-efficiency single-photon source, advancing quantum internet technology.

Contribution

It introduces a bright, on-demand semiconductor quantum-dot single-photon source that exceeds the coherent light rate limit, enabling superior QKD performance.

Findings

Achieved a secret key rate of 0.00108 bits per pulse over a free-space urban channel.

Surpassed the coherent light rate limit by approximately 2.87 dB.

Demonstrated the practical advantage of nanotechnology-based single-photon sources for QKD.

Abstract

Single-photon sources are essential for quantum networks, enabling applications ranging from quantum key distribution (QKD) to the burgeoning quantum internet. Despite the remarkable advancements, the current reliance of QKD on attenuated coherent (laser) light sources has imposed a fundamental limit on the secret key rate (SKR). This constraint is primarily attributable to the scarcity of single-photon components within coherent light, confined by an inherent upper bound of 1/e. Here, we report high-rate QKD using a high-efficiency single-photon source, enabling an SKR transcending the fundamental rate limit of coherent light. We developed an on-demand, bright semiconductor quantum-dot single-photon source with an efficiency of 0.71(2), exceeding the inherent bound of coherent light by approximately 2.87 dB. Implementing narrow-bandwidth filtering and random polarization modulation, we conducted a field QKD trial over a 14.6(1.1)-dB-loss free-space urban channel, achieving an SKR of 0.00108 bits per pulse. This surpasses the practical limit of coherent-light-based QKD by 2.53 dB. Our findings conclusively demonstrate the superior performance of nanotechnology-based single-photon sources over coherent light for QKD applications, marking a pivotal stride towards the realization of a global quantum internet.