Self-Referenced Continuous-Variable Quantum Key Distribution Protocol

Abstract

We introduce a new continuous-variable quantum key distribution (CV-QKD) protocol, self-referenced CV-QKD, that eliminates the need for transmission of a high-power local oscillator between the communicating parties. In this protocol, each signal pulse is accompanied by a reference pulse (or a pair of twin reference pulses), used to align Alice's and Bob's measurement bases. The method of phase estimation and compensation based on the reference pulse measurement can be viewed as a quantum analog of intradyne detection used in classical coherent communication, which extracts the phase information from the modulated signal. We present a proof-of-principle, fiber-based experimental demonstration of the protocol and quantify the expected secret key rates by expressing them in terms of experimental parameters. Our analysis of the secret key rate fully takes into account the inherent uncertainty associated with the quantum nature of the reference pulse(s) and quantifies the limit at which the theoretical key rate approaches that of the respective conventional protocol that requires local oscillator transmission. The self-referenced protocol greatly simplifies the hardware required for CV-QKD, especially for potential integrated photonics implementations of transmitters and receivers, with minimum sacrifice of performance. As such, it provides a pathway towards scalable integrated CV-QKD transceivers, a vital step towards large-scale QKD networks.

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

“…We use Eq. (16) and Eq. (17) to perform numerical evaluation ofT sat andξ sat , in order to study the impact of the saturation attack.…”

“…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.…”

Semi-quantum Key Distribution Protocol Based on Bell States

“…Fortunately Bennett-Brassard (BB84) [1] pointed out how to use the properties of quantum mechanics for the purpose of the cryptography, independently rediscovered by Ekert (E91) using entanglement states [2] a few years later, which was the beginning of quantum key distribution (QKD), and had been proven to be unconditionally secure [3] when both parties are quantum. So far, there are many quantum key distribution (QKD) schemes have already been put forward [4,5,6,7,8,9].…”