KEYWORDS: Quantum key distribution, Lawrencium, Relays, Vacuum, Sensors, Information security, Lithium, Single photon detectors, Signal processing, Signal attenuation
Quantum Key Distribution (QKD) allows authenticated users to share secure keys, which has the advantage of information-theoretical security based on the fundamental laws of quantum physics. The breakthrough of long-distance QKD technology is the key to the large-scale application of quantum communication. The Twin-Field QKD (TF-QKD) protocol is an effective solution to overcome the linear secret key capacity bound, which is called the Pirandola-Laurenza-Ottaviani-Banchi (PLOB) bound. Among all TF-QKD protocols, the Sending or Not Sending (SNS) TF-QKD protocol has received extensive attention due to its advantage of tolerating large misalignment. In this paper, we analyze the influence of light intensity fluctuation on the secure key rate and transmission distance for the three-intensity decoy SNS-TF-QKD protocol considering the finite-key effect. Based on our proposed optimized key rate formula, we conducted a simulation analysis and found that a light intensity fluctuation within 2% has little effect on the farthest transmission distance of the three-intensity decoy SNS-TF-QKD. Even if the light intensity fluctuates up to 10%, the secure key rate can still break the PLOB bound.
In recent years, underwater wireless optical communication (UWOC) has attracted more and more attention owing to its high bandwidth and high speed. The blue-green band is a transmission window due to its relatively low loss in the underwater channel. However, UWOC is still limited to about 300 meters subjecting to the large channel loss and the mediocre sensitivity of the avalanche photo-diode (APD). In this paper, we propose and experimentally realize an underwater optical communication scheme based on single-photon detection and non-return-to-zero on-off keying (NRZ-OOK) modulation. The key rate of 200 kbps was achieved with a bit error rate (BER) of 1×10−4 below the forward error correction (FEC) limit of 3.8×10−3 with 7% overhead when the power of the light source is 0.02 mW and total channel loss is 67 dB. The relatively good result shows that a system adopting an NRZ-OOK modulation scheme and single-photon detection is promising for high bandwidth and long-distance underwater optical communication.
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