Experimental demonstration of Gaussian protocols for one-sided device-independent quantum key distribution

TL;DR

This paper experimentally demonstrates Gaussian protocols for one-sided device-independent quantum key distribution, revealing protocols that tolerate significant loss and linking EPR steering inequalities to secret key rates, thus enhancing quantum cryptography security.

Contribution

The paper identifies all CV QKD protocols that can be 1sDI, including a protocol using only coherent states, and experimentally demonstrates their feasibility with high loss tolerance.

Findings

Achieved 7.5 km optical fiber loss in entanglement-based protocol

Achieved 3.5 km optical fiber loss in coherent-state protocol

Established a direct link between EPR steering inequality and secret key rate

Abstract

Nonlocal correlations, a longstanding foundational topic in quantum information, have recently found application as a resource for cryptographic tasks where not all devices are trusted, for example in settings with a highly secure central hub, such as a bank or government department, and less secure satellite stations which are inherently more vulnerable to hardware "hacking" attacks. The asymmetric phenomena of Einstein-Podolsky-Rosen steering plays a key role in one-sided device-independent quantum key distribution (1sDI-QKD) protocols. In the context of continuous-variable (CV) QKD schemes utilizing Gaussian states and measurements, we identify all protocols that can be 1sDI and their maximum loss tolerance. Surprisingly, this includes a protocol that uses only coherent states. We also establish a direct link between the relevant EPR steering inequality and the secret key rate, further strengthening the relationship between these asymmetric notions of nonlocality and device independence. We experimentally implement both entanglement-based and coherent-state protocols, and measure the correlations necessary for 1sDI key distribution up to an applied loss equivalent to 7.5 km and 3.5 km of optical fiber transmission respectively. We also engage in detailed modelling to understand the limits of our current experiment and the potential for further improvements. The new protocols we uncover apply the cheap and efficient hardware of CVQKD systems in a significantly more secure setting.