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arXiv:2211.16472 · Optics Express

Device-independent quantum key distribution with realistic single-photon source implementations

Eva M. González-Ruiz, Javier Rivera-Dean, Marina F. B. Cenni, Anders Søndberg Sørensen, Antonio Acín, Enky Oudot

Published Jan 23, 2024• 17 citations
arXivHTMLPDF

Abstract

Device-independent quantum key distribution (DIQKD) aims at generating secret keys between distant parties without the parties trusting their devices. We investigate a proposal for performing fully photonic DIQKD, based on single photon sources and heralding measurements at a central station placed between the two parties. We derive conditions to attain non-zero secret-key rates in terms of the photon efficiency, indistinguishability and the second order autocorrelation function of the single-photon sources. Exploiting new results on the security bound of such protocols allows us to reduce the requirements on the physical parameters of the setup. Our analysis shows that in the considered schemes, key rates of several hundreds of secret bits per second are within reach at distances of several tens of kilometers.

DOI
10.1364/oe.497935

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Device-independent quantum key distribution (DIQKD) aims at generating secret keys between distant parties without the parties trusting their devices. We investigate a proposal for performing fully photonic DIQKD, based on single photon sources and heralding measurements at a central station placed between the two parties. We derive conditions to attain non-zero secret-key rates in terms of the photon efficiency, indistinguishability and the second order autocorrelation function of the single-photon sources. Exploiting new results on the security bound of such protocols allows us to reduce the requirements on the physical parameters of the setup. Our analysis shows that in the considered schemes, key rates of several hundreds of secret bits per second are within reach at distances of several tens of kilometers.
Device-independent quantum key distribution protocols allow two honest users to establish a secret key with minimal levels of trust on the provider, as security is proven without any assumption on the inner working of the devices used for the distribution. Unfortunately, the implementation of these protocols is challenging, as it requires the observation of a large Bell-inequality violation between the two distant users. Here, we introduce novel photonic protocols for device-independent quantum key distribution exploiting single-photon sources and heralding-type architectures . The heralding process is designed so that transmission losses become irrelevant for security. We then show how the use of single-photon sources for entanglement distribution in these architectures, instead of standard entangled-pair generation schemes, provides significant improvements on the attainable key rates and distances over previous proposals. Given the current progress in single-photon sources, our work opens up a promising avenue for device-independent quantum key distribution implementations.
Device-independent quantum key distribution (DIQKD) exploits the violation of a Bell inequality to extract secure keys even if users' devices are untrusted. Currently, all DIQKD protocols suffer from the secret key capacity bound, i.e., the secret key rate scales linearly with the transmittance of two users. Here we propose a heralded DIQKD scheme based on entangled coherent states to improve entangling rates whereby long-distance entanglement is created by single-photon-type interference. The secret key rate of our scheme can significantly outperform the traditional two-photon-type Bell-state measurement scheme and, importantly, surpass the above capacity bound. Our protocol therefore is an important step towards a realization of DIQKD and can be a promising candidate scheme for entanglement swapping in the future quantum internet.
Abstract Device-independent quantum key distribution (DIQKD) enables the generation of secret keys over an untrusted channel using uncharacterized and potentially untrusted devices 1–9 . The proper and secure functioning of the devices can be certified by a statistical test using a Bell inequality 10–12 . This test originates from the foundations of quantum physics and also ensures robustness against implementation loopholes 13 , thereby leaving only the integrity of the users’ locations to be guaranteed by other means. The realization of DIQKD, however, is extremely challenging—mainly because it is difficult to establish high-quality entangled states between two remote locations with high detection efficiency. Here we present an experimental system that enables for DIQKD between two distant users. The experiment is based on the generation and analysis of event-ready entanglement between two independently trapped single rubidium atoms located in buildings 400 metre apart 14 . By achieving an entanglement fidelity of F ≥0.892(23) {\mathcal F} \,\ge 0.892(23)F≥0.892(23) ℱ ≥ 0.892 ( 23 ) and implementing a DIQKD protocol with random key basis 15 , we observe a significant violation of a Bell inequality of S = 2.578(75)—above the classical limit of 2—and a quantum bit error rate of only 0.078(9). For the protocol, this results in a secret key rate of 0.07 bits per entanglement generation event in the asymptotic limit, and thus demonstrates the system’s capability to generate secret keys. Our results of secure key exchange with potentially untrusted devices pave the way to the ultimate form of quantum secure communications in future quantum networks.
Quantum Key Distribution (QKD) protocols enable two distant parties to communicate with information-theoretically proven secrecy. However, these protocols are generally vulnerable to potential mismatches between the physical modeling and the implementation of their quantum operations, thereby opening opportunities for side channel attacks. Device-Independent (DI) QKD addresses this problem by reducing the degree of device modeling to a black-box setting. The stronger security obtained in this way comes at the cost of a reduced noise tolerance, rendering experimental demonstrations more challenging: so far, only one experiment based on trapped ions was able to successfully generate a secret key. Photonic platforms have however long been preferred for QKD thanks to their suitability to optical fiber transmission, high repetition rates, readily available hardware, and potential for circuit integration. In this work, we assess the feasibility of DIQKD on a photonic circuit recently identified by machine learning techniques. For this, we introduce an efficient converging hierarchy of semi-definite programs (SDP) to bound the conditional von Neumann entropy and develop a finite-statistics analysis that takes into account full outcome statistics. Our analysis shows that the proposed optical circuit is sufficiently resistant to noise to make an experimental realization realistic.
Device-independent quantum key distribution (DIQKD) is a key distribution scheme whose security is based on the laws of quantum physics but does not require any assumptions about the devices used in the protocol. The security of the existing entanglement-based DIQKD protocol relies on the Bell test. Here, we propose an efficient device-independent quantum key distribution (EDIQKD) protocol in which one participant prepares states and transmits them to another participant through a quantum channel to measure. In this prepare-and-measure protocol, the transmission process between participants is characterized according to the process tomography for security, ruling out any mimicry using the classical initial, transmission, and final state. Comparing the minimal number of bits of the raw key to guarantee security against collective attacks, the efficiency of the EDIQKD protocol is two orders of magnitude more than that of the DIQKD protocol for the reliable key of which quantum bit error rate is allowed up to 6.5\%. This advantage will enable participants to substantially conserve the entangled pair's demanded resources and the measurement. According to the highest detection efficiency in the recent most advanced photonic experiment, our protocol can be realized with a non-zero key rate and remains more efficient than usual DIQKD. Our protocol and its security analysis may offer helpful insight into identifying the typical prepare-and-measure quantum information tasks with the device-independent scenario.