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Optics Letters

Optical injection locking based local oscillator regeneration for continuous variable quantum key distribution

Zikang Su, Dajian Cai, Hao Jiang, Jintao Wang, Dawei Wang, Xiaojie Guo, Zhaohui Li

Published Jan 31, 2022• 11 citations
Publisher

Abstract

We develop an optical injection locking (OIL) based local oscillator (LO) regeneration for continuous variable quantum key distribution (CVQKD) by sending a weak polarization multiplexed pilot carrier from the transmitter. The OIL at the receiver has superior performance in terms of minimum input power and noise level at offset frequencies to the erbium-doped fiber amplifier (EDFA)-based scheme. The weak pilot carrier is recovered both in power and phase via the OIL while incurring little excess noise to the CVQKD system. The phase-locked LO enables heterodyne detection of a Gaussian modulated quantum signal with a simple data-aided phase recovery without pilot tone. The obtained parameters are compatible with a raw key rate of 0.83 Mbit/s in the asymptotic regime over a 22-km fiber transmission. The technique is expected to be used in more phase-sensitive quantum optical applications.

DOI
10.1364/ol.451670

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We develop an optical injection locking (OIL) based local oscillator (LO) regeneration for continuous variable quantum key distribution (CVQKD) by sending a weak polarization multiplexed pilot carrier from the transmitter. The OIL at the receiver has superior performance in terms of minimum input power and noise level at offset frequencies to the erbium-doped fiber amplifier (EDFA)-based scheme. The weak pilot carrier is recovered both in power and phase via the OIL while incurring little excess noise to the CVQKD system. The phase-locked LO enables heterodyne detection of a Gaussian modulated quantum signal with a simple data-aided phase recovery without pilot tone. The obtained parameters are compatible with a raw key rate of 0.83 Mbit/s in the asymptotic regime over a 22-km fiber transmission. The technique is expected to be used in more phase-sensitive quantum optical applications.
We experimentally demonstrate a 25 MHz repetition rate pilot-tone-assisted Gaussian-modulated continuous-variable quantum key distribution (CVQKD) with a local local oscillator (LLO) by employing the frequency-multiplexing and polarization-multiplexing techniques. In the proposed LLO-CVQKD system, the strong pilot tone and weak quantum signal can be separated in different frequency and polarization domain for avoiding the crosstalk between them and guaranteeing different detection requirements of low-noise for quantum signal and high-saturation limitation for pilot tone. Moreover, the dominant phase noise over 25 km optical fiber channel can be compensated in real time for supporting high secure key rate of 1.61 Mbps in the asymptotic regime.
A high-speed Gaussian-modulated continuous-variable quantum key distribution (CVQKD) with a local local oscillator (LLO) is experimentally demonstrated based on pilot-tone-assisted phase compensation. In the proposed scheme, the frequency-multiplexing and polarization-multiplexing techniques are used for the separate transmission and heterodyne detection between quantum signal and pilot tone, guaranteeing no crosstalk from strong pilot tone to weak quantum signal and different detection requirements of low-noise for quantum signal and high-saturation limitation for pilot tone. Moreover, compared with the conventional CVQKD based on homodyne detection, the proposed LLO-CVQKD scheme can measure X and P quadrature simultaneously using heterodyne detection without need of extra random basis selection. Besides, the phase noise, which contains the fast-drift phase noise due to the relative phase of two independent lasers and the slow-drift phase noise introduced by quantum channel disturbance, has been compensated experimentally in real time, so that a low level of excess noise with a 25 km optical fiber channel (with 5 dB loss) is obtained for the achievable secure key rate of 7.04 Mbps in the asymptotic regime and 1.85 Mbps under the finite-size block of 107.
This paper proposes a scheme for simultaneous classical communication and continuous variable quantum key distribution with a true local oscillator. In this scheme, the emitter’s laser, after binary phase-shift keying (BPSK) modulation, is multiplexed in polarization with the quantum signal and sent to the receiver. After BPSK demodulation and correction, this signal is used for local oscillator regeneration by an optical injection phase-locked loop method. Comparing the effective noise sources in this scheme with typical local local oscillator schemes revealed that continuous variable quantum key distribution (CV-QKD) with a true local oscillator based on the optical injection phase-locked loop encounters lower levels of noise in comparison to the pre-existing genuine local oscillator CV-QKDs.
In this paper, a frequency-shifted-assisted continuous variable quantum key distribution with local local oscillator (LLOCVQKD) scheme is proposed based on Gaussian modulated coherent state. In the proposed scheme, the quantum signal and pilot tone can be completely isolated in frequency domain by frequency-shifting quantum optical carrier, so that the crosstalk from strong pilot tone to weak quantum signal can be effectively eliminated compared with our former pilottone scheme based on CS-DSB modulation. Moreover, an improved phase noise compensation scheme based on pilottone- assisted phase calibration and adaptive phase rotation is proposed for eliminating the dominate phase noise without the help of any training sequences, which promotes the blocks of the quantum key. Besides, a low level of excess noise is experimentally obtained for supporting the secure key rate of 7.15 Mbps over secure transmission distance of 25 km, verifying the simple and high-rate LLO-CVQKD.
We propose a pilot-multiplexed continuous-variable quantum key distribution (CVQKD) scheme based on a local local oscillator (LLO). Our scheme utilizes time-multiplexing and polarization-multiplexing techniques to dramatically isolate the quantum signal from the pilot, employs two heterodyne detectors to separately detect the signal and the pilot, and adopts a phase compensation method to almost eliminate the multifrequency phase jitter. In order to analyze the performance of our scheme, a general LLO noise model is constructed. Besides the phase noise and the modulation noise, the photon-leakage noise from the reference path and the quantization noise due to the analog-to-digital converter (ADC) are also considered, which are first analyzed in the LLO regime. Under such general noise model, our scheme has a higher key rate and longer secure distance compared with the preexisting LLO schemes. Moreover, we also conduct an experiment to verify our pilot-multiplexed scheme. Results show that it maintains a low level of the phase noise and is expected to obtain a 554-Kbps secure key rate within a 15-km distance under the finite-size effect.
We develop and experimentally demonstrate a phase-sensitive continuous variable quantum key distribution system with improved secure key rate. This is achieved using multimode coherent states with phase-conjugated subcarrier modulation and phase-sensitive detection. The local oscillator for phase-sensitive detection is regenerated from a polarization-multiplexed carrier wave via optical injection locking. The proposed scheme has a higher classical information capacity at a given number of received photons and exhibits a higher secure key rate when applying the security analysis of the GG02 protocol. Experimental results confirm the higher secret key rate and better excess noise tolerance of the new scheme compared to the typical implementation of GG02.