Demonstration of Free-space Reference Frame Independent Quantum Key Distribution

TL;DR

This paper demonstrates the practical implementation of reference frame independent quantum key distribution over free space, addressing device calibration issues and paving the way for mobile QKD applications.

Contribution

It experimentally shows free-space RFI QKD with uncalibrated devices and finite data, advancing mobile quantum communication technology.

Findings

Successful free-space RFI QKD demonstration

Extended security analysis for uncalibrated devices

Progress towards handheld QKD device deployment

Abstract

Quantum key distribution (QKD) is moving from research laboratories towards applications. As computing becomes more mobile, cashless as well as cardless payment solutions are introduced, and a need arises for incorporating QKD in a mobile device. Handheld devices present a particular challenge as the orientation and the phase of a qubit will depend on device motion. This problem is addressed by the reference frame independent (RFI) QKD scheme. The scheme tolerates an unknown phase between logical states that varies slowly compared to the rate of particle repetition. Here we experimentally demonstrate the feasibility of RFI QKD over a free-space link in a prepare and measure scheme using polarisation encoding. We extend the security analysis of the RFI QKD scheme to be able to deal with uncalibrated devices and a finite number of measurements. Together these advances are an important step towards mass production of handheld QKD devices.