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Fully passive measurement-device-independent quantum key distribution

Jinjie Li, Wenyuan Wang, and Hoi-Kwong Lo

Phys. Rev. Applied 21, 064056 – Published 25 June 2024

Abstract

A recently proposed fully passive quantum key distribution (QKD) removes all source modulator side channels. In this work, we combine fully passive sources with measurement-device-independent (MDI) QKD to simultaneously remove side channels from source modulators and detectors. We show a numerical simulation of passive MDI QKD, and we obtain an acceptable key rate while achieving much better implementation security, as well as ease of implementation, compared with a recently proposed fully passive twin-field QKD, paving the way towards more secure and practical QKD systems. We prove that a fully passive protocol is compatible with MDI QKD and we propose a novel idea that can improve the sifting efficiency.

Received 6 December 2023
Revised 26 April 2024
Accepted 17 May 2024

DOI:https://doi.org/10.1103/PhysRevApplied.21.064056

Physics Subject Headings (PhySH)

Optical quantum information processing Photonics Quantum communication, protocols & technology Quantum cryptography

Quantum Information, Science & TechnologyAtomic, Molecular & OpticalCondensed Matter, Materials & Applied Physics

Authors & Affiliations

Jinjie Li¹, Wenyuan Wang^1,2,*, and Hoi-Kwong Lo^3,4,5,6,†

¹Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong
²HK Institute of Quantum Science & Technology, University of Hong Kong, Pokfulam Road, Hong Kong
³Dept. of Electrical & Computer Engineering, University of Toronto, Toronto, Ontario M5S 3G4, Canada
⁴Centre for Quantum Information and Quantum Control (CQIQC), University of Toronto, Toronto, Ontario M5S 1A7, Canada
⁵Dept. of Physics, University of Toronto, Toronto, Ontario M5S 1A7, Canada
⁶Quantum Bridge Technologies, Inc., 100 College Street, Toronto ON M5G 1L5, Canada

^*Corresponding author: [email protected]
^†Corresponding author: [email protected]

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Vol. 21, Iss. 6 — June 2024

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Figure 1
Fully passive MDI-QKD setup. Alice and Bob each possess a fully passive source, and Charlie possesses the usual MDI measurement device. The fully passive sources and Charlie’s setup are reproduced from Refs. [12] and [8], respectively. Figure is reproduced with modifications from Fig. 1 in W. Wang et al., Phys. Rev. Lett. 130, 220801 (2023) with permission. Copyright 2023, American Physical Society.
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Figure 2
Alice’s postselection regions and decoy settings shown in $μ_{H}, μ_{V}, ϕ$ space. Three decoys are used. The whole setup is determined by six parameters, ${Δ_{Z}, Δ_{X Y}, Δ_{ϕ}, t_{1}, t_{2}, t_{3}}$ . Bob possesses the same decoy setting. This figure is reproduced from [12]. Figure is reproduced with modifications from Fig. 2 in W. Wang et al., Phys. Rev. Lett. 130, 220801 (2023) with permission. Copyright 2023, American Physical Society.
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Figure 3
Key rate of passive MDI QKD (green) and active MDI QKD (red), along with the key rate of the newly proposed method (dashed blue line; see Sec. 4). There is a misalignment of $1 %$ (Alice and Bob $0.5 %$ each) on the $X$ - $Z$ plane, and three decoy settings are used in both passive and active schemes. In the passive cases, $Δ_{Z}$ is optimized within the range $[0.01, 0.05]$ and $t_{3}$ is optimized within the range $[0.1, 0.99]$ . The other parameters used are fixed: $Δ_{X Y} = 0.2, Δ_{ϕ} = 0.2, t_{1} = 0.02 / u_{max}, t_{2} = 0.04 / u_{max}$ . In the active case, the three intensities $[μ, ν, ω]$ are used; all three intensities are optimized within the range $[0, 1.0]$ . In both cases, we use a channel loss coefficient of $0.2 dB {km}^{- 1}$ and a detector dark count of $10^{- 6}$ . The passive MDI QKD’s key rate is reasonable. It is about 2–3 orders of magnitude lower than the active one. However, it possesses the advantage of the removal of all source modulator side channels. In the “small-ring” method key rate calculation, the three decoy-state intensities used are the same as the passive one. We see an improvement in the key rate by about $6 %$ .
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Figure 4
An additional method that could improve the key rate. The key generation regions, $H$ and $V$ , are subdivided into smaller rings (shaded regions between dark blue lines), and the key rate of each “ring” is calculated and integrated together; see Eq. (17). Panels (a) and (b) show the ring’s corresponding regions in $μ_{H} - μ_{V}$ space for Alice and Bob, respectively. Panels (c) and (d) show the rings on the Bloch spheres for Alice and Bob, respectively. The rings are labeled by the polar angle, $θ$ , and have a thickness of $d θ$ . On Alice’s Bloch sphere, the integration limits of Eq. (17), $0$ and $Δ_{Z}$ , are labeled. Bob’s integration limits are the same.
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Physical Review Applied

Fully passive measurement-device-independent quantum key distribution

Jinjie Li, Wenyuan Wang, and Hoi-Kwong Lo

Phys. Rev. Applied 21, 064056 – Published 25 June 2024

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