Long-distance continuous-variable quantum key distribution by controlling excess noise

Abstract

Quantum cryptography founded on the laws of physics could revolutionize the way in which communication information is protected. Significant progresses in long-distance quantum key distribution based on discrete variables have led to the secure quantum communication in real-world conditions being available. However, the alternative approach implemented with continuous variables has not yet reached the secure distance beyond 100 km. Here, we overcome the previous range limitation by controlling system excess noise and report such a long distance continuous-variable quantum key distribution experiment. Our result paves the road to the large-scale secure quantum communication with continuous variables and serves as a stepping stone in the quest for quantum network.

High-speed free-space optical continuous-variable quantum key distribution enabled by three-dimensional multiplexing

“…This kind of schemes offer the high SKR brought by phase noise mitigation, but potentially open a security loophole for Eve, as discussed in [12]. In addition, cooled avalanched photodiodes (APDs) are also usually applied in current CV-QKD systems [13]. A high SKR is enabled by the electrical noise suppression in these systems, but with the price of limited bandwidth and high cost.…”

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

“…In recent decades, numerous experiments on both DVQKD [9,10] and CVQKD [11,12] have been carried out. In the CVQKD field, generally, the experiments were demonstrated based on the one-way Gaussian-modulated coherent-states (GMCS) scheme.…”

“…In the one-way experiments, quantum signals obtained from the coherent state were transmitted with a strong local oscillator (LO) over a noisy and lossy optical-fiber channel [13], and the quantum signals were transmitted only once. A recent demonstration of one-way GMCS CVQKD has been achieved over 150 km of optical fiber by controlling excess noise [12]. 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.…”

On the problem of non-zero word error rates for fixed-rate error correction codes in continuous variable quantum key distribution

“…Originally limited to short distances [8], the operation range of CVQKD protocols was considerably extended by employing the reverse reconciliation protocol that exploits one-way communication, including forward error correction codes in the error reconciliation post processing step [9]. Low density party check (LDPC) and multi-edge LDPC (ME-LDPC) codes are examples of high-efficiency forward error correction codes that have been employed in CVQKD systems [10][11][12][13][14][15]. The ME-LDPC codes in particular exhibit good error correction performances at low signal-to-noise (SNR) ratios, making them suitable for CVQKD applications.…”

“…The WER is the rate at which the decoder fails to decode the correct codewords. Since the adoption of forward error correction codes in CVQKD systems, the model of the secret key rate has been subsequently modified to include the efficiency and WER of the code [10,15] b…”