Generating the Local Oscillator “Locally” in Continuous-Variable Quantum Key Distribution Based on Coherent Detection

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 (rad 2 ), 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.

Practical challenges in quantum key distribution

“…43 Further progress continues to be pursued, targeting also higher efficiency, which is currently around 60% for fibre-coupled detectors at telecom wavelengths. 42 Furthermore, as shown in Figure 1c, a practical issue in these systems is that the strong phase reference pulse (or local oscillator) needs to be transmitted together with the signal at high clock rates; recent proposals that avoid this and use instead a local oscillator generated at Bob's site [58][59][60] are promising and will lead to more practical, high performance implementations.…”

Quantum hacking: Saturation attack on practical continuous-variable quantum key distribution

“…While all previous attacks on CV-QKD had focused on local oscillator manipulation and biasing excess noise evaluation, our attack has no influence on the local oscillator, and can thus not be ruled out by generating the local oscillator locally [15,16]. It is therefore important to propose practical solutions against this attack, and we have presented in detail two effective counter-measures based on post-selection, that can be implemented without requiring any modification at the hardware level.…”

“…Hence the LO can be accessed, and thus manipulated by an attacker in practical implementations. It is important to note that the LO can in principle be generated locally at Bob side, as demonstrated in recent proof-of-principle experiments [15,16], where the LO is phase-locked with the quantum signals emitted by Alice. However, phase-locking two distant lasers brings more complexity and noise and all practical CV-QKD full demonstrations have so far been performed with a "public" LO.…”

“…The threat of such attacks can be removed if Alice and Bob "locally" generate LO pulse [15,16] or measure the shot noise in real time instead of relying on an off-line calibration [30]. LO is an important issue for the practical security in CV-QKD, but as we will demonstrate with the introduction of the saturation, it is not the only implementation loophole that should be considered in practical CV-QKD.…”

Performance Improvement of Plug-and-Play Dual-Phase-Modulated Quantum Key Distribution by Using a Noiseless Amplifier

“…However, the ignorance of the nonlocal arrangement of LO will lead to wavelength attacks [14], calibration attacks [15] and LO fluctuation attacks [16], which are all related to the loopholes of LO. Therefore, self-referenced CVQKD without sending an LO is proposed, and it can effectively remove the loopholes introduced by the LO transmission [17]. Nevertheless, in the real-life experiments, it is a hard problem to realize content detection for two separate lasers, since model illustrated in Figure 1, we can depict the scheme as follows.…”