Feasibility of continuous-variable quantum key distribution with noisy coherent states

Abstract

We address security of the quantum key distribution scheme based on the noisy modulation of coherent states and investigate how it is robust against noise in the modulation regardless of the particular technical implementation. As the trusted preparation noise is shown to be security breaking even for purely lossy channels, we reveal the essential difference between two types of trusted noise, namely sender-side preparation noise and receiver-side detection noise, the latter being security preserving. We consider the method of sender-side state purification to compensate the preparation noise and show its applicability in the realistic conditions of channel loss, untrusted channel excess noise, and trusted detection noise. We show that purification makes the scheme robust to the preparation noise (i.e., even the arbitrary noisy coherent states can in principle be used for the purpose of quantum key distribution). We also take into account the effect of realistic reconciliation and show that the purification method is still efficient in this case up to a limited value of preparation noise.

Continuous Variable Quantum Key Distribution with a Noisy Laser

“…CV QKD using a noisy laser was first suggested in [16,17] using reverse reconciliation, however, it was realized that the preparation noise dramatically reduced the secure key rate, eventually making it impossible to obtain a secure key. To regain security purification of the state was proposed by attenuating the modulated noisy state at Alice's private trusted station.…”

Entanglement-based continuous-variable quantum key distribution with multimode states and detectors

“…In the multimode case the detectors must be calibrated apart of the protocol using a known and controllable multimode source (studied with a multimode measurement [25][26][27][28][29][30]) that allows obtaining the parameters of the LOC of the given multimode detector. However, the multimode influence in the case of the trusted homodyne detection becomes equivalent to the trusted preparation noise [18,19] and trusted detection noise [17] for a single-mode protocol. This may still lead to security break, when auxiliary modes are not occupied.…”

“…The semiclassical nature of light still surprisingly allows transmission of secure key rate for the large distances [16]. Advantageously, the noise on the trusted sides is tolerable, allowing CV QKD with the noisy homodyne detection [17] and even with the thermal states [18][19][20][21]. Recently, the entanglement-based CV QKD with homodyne detection overcoming limits of the coherent state CV QKD [22] has been experimentally verified [23].…”

Gaussian one-way thermal quantum cryptography with finite-size effects

“…Schemes based on Gaussian modulations of coherent states have been investigated in great detail [13][14][15][16][17][18][19], and we have now also experimental implementations over long distances [20][21][22]. Besides one-way protocols, it has been proposed to exploit two-way communication [23][24][25], quantum illumination [26], floodlight QKD [27][28][29][30], and measurement-device-independence (MDI) [31,32], the latter very promising to establish end-to-end communications [33,34].…”