Two-dimensional distributed-phase-reference protocol for quantum key distribution

Abstract

Quantum key distribution (QKD) and quantum communication enable the secure exchange of information between remote parties. Currently, the distributed-phase-reference (DPR) protocols, which are based on weak coherent pulses, are among the most practical solutions for long-range QKD. During the last 10 years, long-distance fiber-based DPR systems have been successfully demonstrated, although fundamental obstacles such as intrinsic channel losses limit their performance. Here, we introduce the first two-dimensional DPR-QKD protocol in which information is encoded in the time and phase of weak coherent pulses. The ability of extracting two bits of information per detection event, enables a higher secret key rate in specific realistic network scenarios. Moreover, despite the use of more dimensions, the proposed protocol remains simple, practical, and fully integrable.

High-dimensional quantum key distribution based on multicore fiber using silicon photonic integrated circuits

“…Recently, tremendous efforts have been put into developing novel protocols to increase the information efficiency. [6][7][8][9][10] Highdimensional QKD (HD-QKD) based on qudit encoding (unit of information in a N dimension space) is an efficient technique to achieve high information efficiency for QKD systems. [11][12][13][14][15][16][17][18] Furthermore, HD-QKD protocols exhibit higher resilience to noise, allowing for lower signal-to-noise ratio (SNR) of the received signal, 10 which in turn may be translated into longer transmission distances.…”

Experimental demonstration of the DPTS QKD protocol over a 170 km fiber link

“…Furthermore, several quantum networks have already been implemented [12,13,14,15]. During the last decades, the efforts of the scientific community were focused on enhancing quantum communication performance in terms of key rate, transmission distance and security aspects [16,17,8,18,19,20,21,22,23,24]. Here, we present a practical implementation of the differential phase-time shifting (DPTS) protocol over 170 km of single mode fiber, proving a higher secure key rate compared with other protocols of the DPR family, such * bdali@fotonik.dtu.dk, † dabac@fotonik.dtu.dk as the coherent one-way (COW) and the differential phase shifting (DPS) [8,10,11].…”

“…However, as opposed to the other DPR protocols, the DPTS exploits more than one degree of freedom at once, namely the position in time and the phase difference among consecutive pulses. This allows the DPTS to improve the secret key rate in an intra-city network scenario (in terms of reachable distances and channel loss), while at the same time being more robust against channel noise as shown in Figure 1a) [8]. In the DPTS protocol the information is encoded in four possible symbols in the alphabet {0, 1, 2, 3}, which are: |0 = |±α |vac |±α |vac , |1 = |±α |vac |∓α |vac , |2 = |vac |±α |vac |±α , |3 = |vac |±α |vac |∓α .…”

“…Hence, Alice and Bob share a sifted key and the following steps in the protocol are given by the classical error correction and privacy amplification. The equations for the final achievable secret key rate, under the assumption of beam splitting attacks, are reported in the supplementary materials [3,8]. Figure 1a) shows a comparison of the achievable secret key rate using DPTS, DPS and COW from the DPR family and the secret key generated with the standard BB84 protocol with decoy state method.…”

“…To prepare the train of time-encoded WCPs, Alice carves with an intensity modulator a continuous wave laser at 1550 nm. The obtained signal has an average block length of N = 6 pulse/block (in a block there are only symbols with the same time encoding [8]). The optical signal is then sent through a phase modulator, which imprints the required phase difference among consecutive WCPs.…”