Abstract
Continuous-variable quantum key distribution (CV-QKD) protocols based on coherent detection have been studied extensively in both theory and experiment. In all the existing implementations of CV-QKD, both the quantum signal and the local oscillator (LO) are generated from the same laser and propagate through the insecure quantum channel. This arrangement may open security loopholes and limit the potential applications of CV-QKD. In this paper, we propose and demonstrate a pilot-aided feedforward data recovery scheme that enables reliable coherent detection using a “locally” generated LO. Using two independent commercial laser sources and a spool of 25-km optical fiber, we construct a coherent communication system. The variance of the phase noise introduced by the proposed scheme is measured to be 0.04 (), which is small enough to enable secure key distribution. This technology also opens the door for other quantum communication protocols, such as the recently proposed measurement-device-independent CV-QKD, where independent light sources are employed by different users.
4 More- Received 2 March 2015
DOI:https://doi.org/10.1103/PhysRevX.5.041009
This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Popular Summary
Quantum mechanics can be used to create secret key distribution techniques that enable uncrackable cryptographic protocols. The majority of previous quantum key distribution (QKD) implementations have been costly because they typically required dedicated optical fibers for the key generation. Continuous-variable QKD protocols are less expensive because they use coherent communication techniques in which the quantum signal can easily coexist with classical signal channels thanks to the selectivity of the local oscillator employed in coherent detection. However, this approach also introduces a new barrier to QKD implementation: The need to transmit a phase reference for coherent detection. Here, we propose an intradyne continuous-variable QKD scheme and demonstrate that it is possible to perform low-noise coherent detection using a local oscillator generated from an independent laser source located at the receiver’s side.
In most setups, the local oscillator propagates insecurely; it is preferable to generate the local oscillator locally (i.e., at the receiver’s end). We experimentally demonstrate this procedure using commercially available lasers and a 25-km optical fiber as a quantum channel. We test sending a pattern of 1s and 0s, and we generate 25,000 signal pulses and 25,000 reference pulses. We introduce a postprocessing step in continuous-variable QKD. Although the quantum signal is measured in an arbitrarily rotated basis because of the phase drift between the signal laser and the local oscillator, the receiver can determine the phase drift by measuring a weak reference pulse from the signal laser. Using this phase drift, information carried by the quantum signal can be reliably recovered with noise well below the threshold for secure key distribution. Our solution not only simplifies the implementation of continuous-variable QKD but also greatly enhances its security by closing potential security loopholes associated with an untrusted local oscillator.
We expect that our scheme will be widely adopted in continuous-variable QKD. Our results may open the door to widespread adoption of quantum encryption.