Entanglement-based quantum key distribution with biased basis choice via free space

TL;DR

This paper demonstrates a free-space entanglement-based quantum key distribution experiment using a biased basis protocol over 15.3 km, achieving a higher key rate than standard methods and showing potential for ground-satellite quantum communication.

Contribution

First experimental implementation of biased basis entanglement-based QKD over free space with finite-key analysis and improved key rate.

Findings

Achieved a 4293-bit secure key after 3 hours of operation.

Final key rate of 0.124 bit per raw bit, 14.8% higher than standard BB84.

Demonstrated feasibility for ground-satellite quantum communication.

Abstract

We report a free-space entanglement-based quantum key distribution experiment, implementing the biased basis protocol between two sites which are 15.3 km apart. Photon pairs from a polarization-entangled source are distributed through two 7.8-km free-space optical links. An optimal bias 20:80 between the X and Z basis is used. A post-processing scheme with finite-key analysis is applied to extract the final secure key. After three-hour continuous operation at night, a 4293-bit secure key is obtained, with a final key rate of 0.124 bit per raw key bit which increases the final key rate by 14.8% comparing to the standard BB84 case. Our results experimentally demonstrate that the efficient BB84 protocol, which increases key generation efficiency by biasing Alice and Bob's basis choices, is potentially useful for the ground-satellite quantum communication.