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arXiv:2401.04327 · Optica Quantum

Implementation of space-division multiplexed entanglement-based quantum cryptography over multicore fiber

Evelyn A. Ortega, Jorge Fuenzalida, Krishna Dovzhik, R. F. Shiozaki, Juan Carlos Alvarado-Zacarias, Rodrigo Amezcua‐Correa, Martin Bohmann, Sören Wengerowsky, Rupert Ursin

Published Jul 3, 2024• 6 citations
arXivHTMLPDF

Abstract

Quantum key distribution has shown promising advances in information transmission security. In particular, quantum communication schemes based on entanglement have enormous potential to enhance the security and efficiency of information transmission. Therefore, today’s efforts address overcoming issues related to high data transmission and long-distance implementations to enable real-world quantum communication applications. Here, we experimentally demonstrate a multiplexing technique to enhance the secret key rate by exploiting the momentum correlation of photon pairs generated by spontaneous parametric downconversion. We distributed polarization-entangled photon pairs into opposite cores within a 19-core multicore fiber. We estimated the secret key rates in a configuration with 6 and 12 cores from the entanglement visibility after transmission through a 411-m-long multicore fiber. Our results can lead to the transmission of more information per photon and the establishment of novel quantum networks with one common communication channel, which opens the possibility of deploying new quantum channels over longer distances.

DOI
10.1364/opticaq.527903

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The development and wide application of quantum technologies highly depend on the capacity of the communication channels distributing entanglement. Space-division multiplexing (SDM) enhanced channel capacities in classical telecommunication and bears the potential to transfer the idea to quantum communication using current infrastructure. Here, we demonstrate an SDM of polarization-entangled photons over a 411m long 19-core multicore fiber distributing polarization-entangled photon pairs through up to 12 channels simultaneously. The quality of the multiplexed transfer is evidenced by high polarization visibility and CHSH Bell inequality violation for each pair of opposite cores. Our distribution scheme shows high stability over 24 hours without any active polarization stabilization and can be effortlessly adapted to a higher number of channels. This technique increases the quantum-channel capacity and allows the reliable implementation of quantum networks of multiple users based on a single entangled-photon pair source.
The development and wide application of quantum technologies highly depend on the capacity of the communication channels distributing entanglement.Space-division multiplexing (SDM) enhances data channel transmission capacity in classical telecommunication and bears the potential to transfer the idea to quantum communication using current infrastructure.Here, we demonstrate a SDM of polarizationentangled photons over a 411 m long 19-core multicore fiber distributing polarization-entangled photon pairs through up to 12 channels simultaneously.The quality of the multiplexed transfer is evidenced by high polarization visibility and Clauser-Horne-Shimony-Holt (CHSH) Bell inequality violation for each pair of opposite cores.Our distribution scheme shows high stability over 24 h without any active polarization stabilization and can be effortlessly adapted to a higher number of channels.This technique increases the quantum-channel capacity and allows the reliable implementation of quantum networks of multiple users based on a single entangled photon pair source.
Multiplexing is a strategy to augment the transmission capacity of a communication system. It consists of combining multiple signals over the same data channel and it has been very successful in classical communications. However, the use of enhanced channels has only reached limited practicality in quantum communications (QC) as it requires the manipulation of quantum systems of higher dimensions. Considerable effort is being made towards QC using high-dimensional quantum systems encoded into the transverse momentum of single photons, but so far no approach has been proven to be fully compatible with the existing telecommunication fibers. Here we overcome such a challenge and demonstrate a secure high-dimensional decoy-state quantum key distribution session over a 300-m-long multicore optical fiber. The high-dimensional quantum states are defined in terms of the transverse core modes available for the photon transmission over the fiber, and theoretical analyses show that positive secret key rates can be achieved through metropolitan distances.
Abstract Entanglement distribution is at the heart of most quantum communication protocols. Inevitable loss of photons along quantum channels is a major obstacle for distributing entangled photons over long distances, as the no-cloning theorem forbids the information to simply be amplified along the way as is done in classical communication. It is therefore desirable for every successfully transmitted photon pair to carry as much entanglement as possible. Spontaneous parametric down-conversion (SPDC) creates photons entangled in multiple high-dimensional degrees of freedom simultaneously, often referred to as hyper-entanglement. In this work, we use a multicore fiber (MCF) to show that energy-time and polarization degrees of freedom can simultaneously be transmitted in multiple fiber cores, even maintaining path entanglement across the cores. We verify a fidelity to the ideal Bell state of at least 95% in all degrees of freedom. Furthermore, because the entangled photons are created with a center wavelength of 1560 nm, our approach can readily be integrated into modern telecommunication infrastructure, thus paving the way for high-rate quantum key distribution and many other entanglement-based quantum communication protocols.
Quantum key distribution (QKD) guarantees unconditional security and has thus been intensely studied both from a theoretical and an experimental point of view [1]. However, limitations due to transmission loss and noise are still detrimental for these systems performance in terms of reachable distance and key rates, having so far confined QKD implementations to the use of dedicated channels and hence reduced a successful integration with the classical network, with few exceptions [2–6]. In this work we demonstrate a step forward in the co-existence of QKD with classical bright signals, exploiting a 7.9-km long 37-core heterogeneous multicore fiber (MCF) [7], and a space division multiplexing (SDM) technique to achieve a total of 87 Mbit/s secret key generation rate (SKR) in the finite key scenario with a simultaneous co-propagating classical signal of 10 Gbit/s.
Abstract In state-of-the-art quantum key distribution systems, the main limiting factor in increasing the key generation rate is the timing resolution in detecting photons. Here, we present and experimentally demonstrate a strategy to overcome this limitation, also for high-loss and long-distance implementations. We exploit the intrinsic wavelength correlations of entangled photons using wavelength multiplexing to generate a quantum secure key from polarization entanglement. The presented approach can be integrated into both fiber- and satellite-based quantum-communication schemes, without any changes to most types of entanglement sources. This technique features a huge scaling potential allowing to increase the secure key rate by several orders of magnitude as compared to non-multiplexed schemes.