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Frontiers in Optics

Effect of Pulse-shape Mismatch on the Security of Measurement-device-independent QKD Protocols

Shashank Kumar Ranu, Anil Prabhakar, Prabha Mandayam

Published Jan 1, 2022• 0 citations
Publisher

Abstract

Pulse-width mismatch, primarily caused by channel asymmetry, affects the visibility of Hong-Ou-Mandel (HOM) interference. We show that a channel asymmetry of 176.5 km reduces HOM visibility to 0.37, rendering a polarization-based MDI-QKD protocol completely insecure.
DOI
10.1364/fio.2022.jw4b.29

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Hong-Ou-Mandel (HOM) interference is one of the most important experimental phenomena in quantum optics. It has drawn considerable attention with respect to quantum cryptography and quantum communication because of the advent of the measurement device independent (MDI) quantum key distribution (QKD) protocol. Here, we realize HOM interference, having a visibility of approximately 38.1%, using two independent heralded single-photon sources (HSPSs). The HOM interference between two independent HSPSs is a core technology for realizing the long-distance MDI QKD protocol, the quantum coin-tossing protocol, and other quantum cryptography protocols.
Measurement-device-independent quantum key distribution (MDI QKD) is a promising and practical protocol for remote secret sharing, where the Hong-Ou-Mandel (HOM) type interference in the measurement side provides a simple and economic way to resist malicious attacks on the measurement devices. Because the HOM interference greatly indicates the performance of MDI QKD system, its interferential behavior in practical situations deserve to be studied. In this work, we analyzed HOM visibility with several practical imperfections, such as the deviation of the beam splitting ratio, detection efficiency mismatch of detectors, inconsistent intensities of two incident pulses. In particular, we discussed the afterpulse effect of InGaAs avalanche photodiode detectors with a non-Markovian model, where we take the avalanche history into consideration and provide a new and more accurate perspective for afterpulse analysis. Simulation results indicate that the afterpulse effect in practical situation has a greater impact on the HOM performance than other imperfections. The results exhibit its value in realistic high-speed MDI QKD systems as well as other fiber-based HOM applications.
Measurement-device-independent quantum key distribution (MDI-QKD) protects legitimate users from attacks on measurement devices. The decoy method allows for unconditionally secure quantum key generation using lasers. One of the most important issues in MDI-QKD is that photons from two independent lasers must be indistinguishable. Because Alice and Bob send Charlie laser pulses through separate fiber links, the arrival times of the pulses fluctuate independently. According to the Hong-Ou-Mandel (HOM) interference at Charlie's relay, the time delay between two photons has the greatest effect on distinguishability. However, to date, these effects have not been analyzed. Our study uses simulations to investigate the effects of two-photon temporal distinguishability in terms of the visibility of the HOM-dip of two photons on the final key rate of finite-size MDI-QKD. Furthermore, an acceptable time delay range was estimated based on photons with Gaussian spectral amplitude functions.
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Recently, the Hong–Ou–Mandel (HOM) interference between two independent weak coherent pulses (WCPs) has been paid much attention due to the measurement-device-independent (MDI) quantum key distribution (QKD). Using classical wave theory, articles reported before show that the visibility of this kind of HOM-type interference is ≤ 50%. In this work, we analyze this kind of interference using quantum optics, which reveals more details compared to the wave theory. Analyses confirm the maximum visibility of 50%. And we conclude that the maximum visibility of 50% comes from the two single-photon states in WCPs, without considering the noise. In the experiment, we successfully approach the visibility of 50% by using WCPs splitting from the single pico-second laser source and phase scanning. Since this kind of HOM interference is immune to slow phase fluctuations, both the realized and proposed experiment designs can provide stable ways of high-resolution optical distance detection.