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arXiv:2111.03211

Fully passive entanglement based quantum key distribution scheme

Liu, Bo, Matej Pivoluska, Johannes Handsteiner, Dominik Rauch, Marcus Huber, Fabian Steinlechner, Rupert Ursin, Thomas Scheidl

Published Nov 5, 2021• 1 citation
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Abstract

In general, generation of entangled photon pairs and also the random choice of measurement basis can be implemented with passive optical devices in entanglement based quantum key distribution (QKD) system. However, auxiliary random numbers are still mandatory for conducting the privacy amplification procedure. In this paper, we propose a fully passive entanglement based QKD scheme in which certified random bits for privacy amplification are extracted from detection events of measurement-basis-mismatched entangled photon pairs. The privacy of these random bits can be certified by estimating the phase error rate in the sifted key. The idea of extracting certified random numbers from measurement-basis-mismatched photons, can be extended to all practical QKD schemes.

DOI
10.48550/arxiv.2111.03211

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In general, generation of entangled photon pairs and also the random choice of measurement basis can be implemented with passive optical devices in entanglement based quantum key distribution (QKD) system. However, auxiliary random numbers are still mandatory for conducting the privacy amplification procedure. In this paper, we propose a fully passive entanglement based QKD scheme in which certified random bits for privacy amplification are extracted from detection events of measurement-basis-mismatched entangled photon pairs. The privacy of these random bits can be certified by estimating the phase error rate in the sifted key. The idea of extracting certified random numbers from measurement-basis-mismatched photons, can be extended to all practical QKD schemes.
To date, only active-decoy-state methods have been adopted in current measurement-device-independent (MDI) quantum key distribution (QKD) protocols, causing security loopholes when modulating multiple light intensities with practical devices. To solve this problem, the passive-decoy-state method will be a good choice. Until today practical passive-decoy-state MDI QKD is still missing. In this paper, based on a recently discussed structure of heralded single-photon sources, we propose a passive-decoy-state MDI QKD protocol. In present work, one does not need to modulate light sources into different intensities, but utilizes the built-in local detection events to passively generate different decoy states. Furthermore, through carrying out an appropriate mathematical method, we are able to give very precise estimations for single-photon-pair contributions. As a result, our protocol can exhibit distinct advantages compared with state-of-the-art MDI QKD schemes even when the finite-key-size effect is taken into account. Therefore, our protocol seems a promising candidate to enhance both the security and performance of MDI QKD in practical implementation.
[[abstract]]An enhanced version of the quantum key distribution (QKD) protocol in quantum cryptography is proposed. We consider that realistic detectors and imperfect devices may introduce noise into the transmission thereby causing a high error rate. The proposed scheme is based on an error rate analysis and a random sampling procedure in statistics to produce a probabilistic bound on the error estimation. Confidence intervals are used to interpret the error estimate with a specified confidence level. Based on the information obtained, Alice and Bob judge what caused the errors and establish confidence levels for the error rate of the remaining untested bits. Hence, they can determine the maximum number of times reconciliation needs to be performed to remove all errors from what remains of a raw key to produce an error-free secret key. As a result, the tedious reconciliation process can be reduced and a neglectful probability of not detecting the existence of remaining errors can be avoided as well. The privacy amplification is then applied: (1) to extract a secret key from a partially secret key, and (2) to enlarge the length of the secret key into the final key. The proposed scheme can work when dealing with errors caused by random noise and eavesdropping.
We investigate a quantum key distribution (QKD) scheme which utilizes a biased basis choice in order to increase the efficiency of the scheme. The optimal bias between the two measurement bases, a more refined error analysis, and finite key size effects are all studied in order to assure the security of the final key generated with the system. We then implement the scheme in a local entangled QKD system that uses polarization entangled photon pairs to securely distribute the key. A 50/50 non-polarizing beamsplitter with different optical attenuators is used to simulate a variable beamsplitter in order to allow us to study the operation of the system for different biases. Over 6 hours of continuous operation with a total bias of 0.9837/0.0163 (Z/X), we were able to generate 0.4567 secure key bits per raw key bit as compared to 0.2550 secure key bits per raw key bit for the unbiased case. This represents an increase in the efficiency of the key generation rate by 79%.
Entanglement is an essential ingredient in many quantum communication protocols. In particular, entanglement can be exploited in quantum key distribution (QKD) to generate two correlated random bit strings whose randomness is guaranteed by the nonlocal property of quantum mechanics. Most of QKD protocols tested to date rely on polarization and/or time-bin encoding. Despite compatibility with existing fiber-optic infrastructure and ease of manipulation with standard components, frequency-bin QKD have not yet been fully explored. Here we report a demonstration of entanglement-based QKD using frequency-bin encoding. We implement the BBM92 protocol using photon pairs generated by two independent, high-finesse, ring resonators on a silicon photonic chip. We perform a passive basis selection scheme and simultaneously record sixteen projective measurements. A key finding is that frequency-bin encoding is sensitive to the random phase noise induced by thermal fluctuations of the environment. To correct for this effect, we developed a real-time adaptive phase rotation of the measurement basis, achieving stable transmission over a 26 km fiber spool with a secure key rate ≥ 4.5 bit/s. Our work introduces a new degree of freedom for the realization of entangled based QKD protocols in telecom networks.
We investigate a quantum key distribution (QKD) scheme that utilizes a biased basis choice in order to increase the efficiency of the scheme. The optimal bias between the two measurement bases, a more refined error analysis and finite key size effects are all studied in order to assure the security of the final key generated with the system. We then implement the scheme in a local entangled QKD system that uses polarization entangled photon pairs to securely distribute the key. A 50/50 non-polarizing beamsplitter (BS) with different optical attenuators is used to simulate a variable BS in order to allow us to study the operation of the system for different biases. Over 6 h of continuous operation with a total bias of 0.9837/0.0163 ( Z / X ), we were able to generate 0.4567 secure key bits per raw key bit as compared to 0.2550 secure key bits per raw key bit for the unbiased case. This represents an increase in the efficiency of the key generation rate by 79%.
A simple protocol which takes advantage of the inherent random times of detections in single photon counting modules is presented for random active basis choices when using entanglement-based protocols for Quantum Key Distribution (QKD). It may also be applicable to the BB84 protocol in certain cases. The scheme presented uses the single photon detectors already present on a QKD setup, working on the same rate as the system is capable of detecting, and is, therefore, not limited by the output rates of quantum random number generators. This protocol only requires small hardware modifications making it an attractive solution. We perform a proof-of-principle experiment employing a spontaneous parametric down-conversion process in a χ(2)\chi^{(2)}χ(2) non-linear crystal to demonstrate the feasibility of our scheme, and show that the generated sequence passes randomness tests.