Frequency multiplexed entanglement for continuous-variable quantum key distribution

TL;DR

This paper demonstrates that frequency multiplexing of entangled continuous-variable states, combined with data processing techniques, can significantly increase the secret key rate in quantum key distribution over optical fibers.

Contribution

It introduces a method to use frequency multiplexing with crosstalk mitigation in continuous-variable QKD, achieving nearly 15 times higher secret key rates.

Findings

Experimental demonstration of frequency-multiplexed entangled source with 8 modes.

Analysis predicts almost 15-fold increase in secret key rate.

Method effectively mitigates crosstalk in multiplexed quantum channels.

Abstract

Quantum key distribution with continuous variables already uses advantageous high-speed single-mode homodyne detection with low electronic noise at room temperature. Together with continuous-variable information encoding to nonclassical states, the distance for secure key transmission through lossy channels can approach 300 km in current optical fibers. Such protocols tolerate higher channel noise and also limited data processing efficiency compared to coherent-state protocols. The secret key rate can be further increased by increasing the system clock rates, and, further, by a suitable frequency-mode-multiplexing of optical transmission channels. However, the multiplexed modes couple together in the source or any other part of the protocol. Therefore, multiplexed communication will experience crosstalk and the gain can be minuscule. Advantageously, homodyne detectors allow solving this crosstalk problem by proper data processing. It is a potential advantage over protocols with single-photon detectors, which do not enable similar data processing techniques. We demonstrate the positive outcome of this methodology on the experimentally characterized frequency-multiplexed entangled source of femtosecond optical pulses with natural crosstalk between eight entangled pairs of modes. As the main result, we predict almost 15-fold higher secret key rate. This experimental test and analysis of frequency-multiplexed entanglement source opens the way for the field implementation of high-capacity quantum key distribution with continuous variables.