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.
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.
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.
In this paper, a high-rate Gaussian-modulated coherent-state (GMCS) continuous-variable quantum key distribution (CV-QKD) scheme with a local local oscillator is experimentally demonstrated. The transmission of quantum signal and pilot tone in optical fiber adopts frequency and polarization multiplexing technology. By optimizing frequency bandwidth, modulation variance and intensity of the pilot tone, the CVQKD system is demonstrated at different metropolitan distance, and the secure key rate of 13.53Mbps, 8.24Mbps, 5.39Mbps 3.66Mbps and 2.55Mbps over transmission distance of 5km, 10km, 15km, 20km and 25km are obtained, respectively.
We experimentally demonstrated a sub-Mbps key rate Gaussian-modulated coherent-state (GMCS) continuous-variable quantum key distribution (CV-QKD) over a 100-km transmission distance. To efficiently control the excess noise, the quantum signal and the pilot tone are co-transmitted in the fiber channel based on wideband frequency and polarization multiplexing methods. Furthermore, a high-accuracy data-assisted time domain equalization algorithm is carefully designed to compensate the phase noise and polarization variation in low signal-to-noise ratio. The asymptotic secure key rate (SKR) of the demonstrated CV-QKD is experimentally calculated to be 7.55 Mbps, 1.87 Mbps, and 0.51 Mbps over a transmission distance of 50 km, 75 km, and 100 km, respectively. The experimentally demonstrated that the CV-QKD system significantly improves the transmission distance and SKR compared to the state-of-art GMCS CV-QKD experimental results, and shows the potential for long-distance and high-speed secure quantum key distribution.
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.
In the domain of continuous variable quantum key distribution (CV-QKD), a significant challenge arises in achieving precise frequency synchronization, an issue commonly termed as frequency locking. This involves matching the optical frequencies of both the quantum signal laser and the local oscillator laser for accurate symbol demodulation during the exchange of quantum keys. As such, implementations today still grapple with maintaining precise synchronization between sender and receiver frequencies, occasionally hindering the efficiency and reliability of the information exchange. Addressing this challenge, we present and empirically validate a novel approach to CV-QKD by incorporating a pilot tone-assisted frequency locking algorithm to enhance stability when using a locally generated local oscillator (LLO) at the receiver. The proposed design leverages software-based optimization techniques, thereby eliminating the need for high-speed electronic stabilization devices and achieving efficient performance at typical repetition rates. Specifically, the introduction of the pilot tone algorithm allows us to effectively mitigate phase fluctuations and preserve the integrity of the quantum signals during transmission without resorting to time-multiplexed reference pulses or fast-locking electronics in the lasers. Our results suggest the potential for achieving secure key rates of up to 1 Mb/s over a 50 km single-mode fiber when using these techniques, offering promising insights into the feasibility of high-rate, low-complexity CV-QKD implementations under realistic conditions.