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CRC Press eBooks

Advancements in quantum key distribution

Mark Joyce, Kanchiraopally Vyaahruthi, S. V. Samyuktaa, Alagusundaram Divyashree, Vishal Sharma

Published Aug 11, 2025• 0 citations
Publisher

Abstract

Quantum key distribution (QKD) leverages quantum mechanics to establish secure communication channels. Recent advancements in differential phase shift QKD (DPS-QKD) have enabled secure key distribution over 200 km with a 42 dB channel loss, facilitated by technologies like superconducting single-photon detectors (SSPDs) and high-performing nanowires. This paper delves into the mathematical modeling of QKD protocols, experimental achievements, and their implications for long-distance secure communication. Theoretical formulations for secure key rates, channel losses, and error probabilities are presented, alongside a review of relevant works that laid the foundation for modern QKD systems.

DOI
10.1201/9781003597414-4

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Quantum key distribution (QKD) leverages quantum mechanics to establish secure communication channels. Recent advancements in differential phase shift QKD (DPS-QKD) have enabled secure key distribution over 200 km with a 42 dB channel loss, facilitated by technologies like superconducting single-photon detectors (SSPDs) and high-performing nanowires. This paper delves into the mathematical modeling of QKD protocols, experimental achievements, and their implications for long-distance secure communication. Theoretical formulations for secure key rates, channel losses, and error probabilities are presented, alongside a review of relevant works that laid the foundation for modern QKD systems.
Quantum key distribution (QKD) has been studied as an ultimate method for secure communications, and it now is emerging as a technology that can be deployed in real fibre networks. Here, we present our QKD experiments based on the differential phase shift QKD (DPS-QKD) protocol. A DPS-QKD system has a simple configuration that is easy to implement with conventional optical communication components, and it is suitable for a high clock rate system. Moreover, although the DPS-QKD system is implemented with an attenuated laser source, it is inherently secure against strong eavesdropping attacks called photon number splitting attacks, which pose a serious threat to conventional QKD systems with attenuated laser sources. We also describe three types of single photon detectors that are suitable for high-speed, long-distance QKD: an upconversion detector, a superconducting single photon detector, and a sinusoidally gated InGaAs avalanche photodiode. We present our record setting QKD experiments that employed those detectors.
The recent advances in superconducting nanowire single-photon detector (SNSPD or SSPD) technology has enabled long distance quantum key distribution (QKD) over an optical fiber. We point out that the performance of SNSPDs play a crucial role in achieving a secure transmission distance of 100 km or longer. We analyze such an impact from a simplified model and use it to interpret results from our differential-phase-shift (DPS) QKD experiment. This allows us to discuss the optimization of the detection time window and the clock frequency given the detector characteristics such as dark count rate, detection efficiency, and timing jitter.
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Quantum cryptography can provide unconditional secure communication between two authorized parties based on the basic principles of quantum mechanics. However, imperfect practical conditions limit its transmission distance and communication speed. Here, we implemented the differential phase shift (DPS) quantum key distribution (QKD) with an up-conversion-assisted hybrid photon detector (HPD) and achieved a 1.3 Mbits per second secure key rate over a 10 km fiber, which is tolerant against photon number splitting (PNS) attack, general collective attacks on individual photons and any other known sequential unambiguous state discrimination (USD) attacks.