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arXiv:2004.09964 · Physical Review Letters

Efficient Generation of High-Dimensional Entanglement through Multipath Down-Conversion

Xiao‐Min Hu, Wen-Bo Xing, Bi‐Heng Liu, Yun‐Feng Huang, Chuan‐Feng Li, Guang‐Can Guo, Paul Erker, Marcus Huber

Published Aug 28, 2020• 103 citations
arXivHTMLPDF

Abstract

High-dimensional entanglement promises to greatly enhance the performance of quantum communication and enable quantum advantages unreachable by qubit entanglement. One of the great challenges, however, is the reliable production, distribution, and local certification of high-dimensional sources of entanglement. In this Letter, we present an optical setup capable of producing quantum states with an exceptionally high level of scalability, control, and quality that, together with novel certification techniques, achieve the highest amount of entanglement recorded so far. We showcase entanglement in 32-spatial dimensions with record fidelity to the maximally entangled state (F=0.933±0.001) and introduce measurement efficient schemes to certify entanglement of formation (E_{oF}=3.728±0.006). Combined with the existing multicore fiber technology, our results will lay a solid foundation for the construction of high-dimensional quantum networks.

DOI
10.1103/physrevlett.125.090503

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High-dimensional entanglement promises to greatly enhance the performance of quantum communication and enable quantum advantages unreachable by qubit entanglement. One of the great challenges, however, is the reliable production, distribution, and local certification of high-dimensional sources of entanglement. In this Letter, we present an optical setup capable of producing quantum states with an exceptionally high level of scalability, control, and quality that, together with novel certification techniques, achieve the highest amount of entanglement recorded so far. We showcase entanglement in 32-spatial dimensions with record fidelity to the maximally entangled state (F=0.933±0.001) and introduce measurement efficient schemes to certify entanglement of formation (E_{oF}=3.728±0.006). Combined with the existing multicore fiber technology, our results will lay a solid foundation for the construction of high-dimensional quantum networks.
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High-dimensional entanglement provides unique ways of transcending the limitations of current approaches in quantum information processing, quantum communications based on qubits. The generation of time-frequency qudit states offer significantly increased quantum capacities while keeping the number of photons constant, but pose significant challenges regarding the possible measurements for certification of entanglement. Here, we develop a new scheme and experimentally demonstrate the certification of 24-dimensional entanglement and a 9-dimensional quantum steering. We then subject our photon-pairs to dispersion conditions equivalent to the transmission through 600-km of fiber and still certify 21-dimensional entanglement. Furthermore, we use a steering inequality to prove 7-dimensional entanglement in a semi-device independent manner, proving that large chromatic dispersion is not an obstacle in distributing and certifying high-dimensional entanglement and quantum steering. Our approach, leveraging intrinsic large-alphabet nature of telecom-band photons, enables scalable, commercially viable, and field-deployable entangled and steerable quantum sources, providing a pathway towards fully scalable quantum information processer and high-dimensional quantum communication networks.
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Abstract High-dimensional entanglement is a valuable resource for quantum information processing and quantum communication. All-fiber implementations are particularly attractive for fiber-based quantum networks, as they offer compactness, intrinsic stability, and direct compatibility with existing fiber infrastructure. Here we demonstrate an all-fiber source of high-dimensional time-bin entangled photon pairs based on spontaneous parametric down-conversion (SPDC) in a single double-pass PPLN waveguide. By precisely matching the delay of an asymmetric Faraday-Michelson interfer-ometer to the pump-pulse spacing, we obtain a two-photon interference visibility of 99.23% ± 0.31%. We obtain a lower bound on the entanglement of formation (EoF) and certify at least 4 × 4-dimensional entanglement by applying semidefinite-programming-based certification to sparse measurement data. We further demonstrate that optimizing the encoding dimension enables more efficient utilization of entanglement resources across different source brightness levels, highlighting a distinct advantage of high-dimensional sources over two-dimensional entangled sources. Our work offers a compact and stable all-fiber route to high-dimensional entanglement for fiber-based quantum communication.
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Many quantum communication protocols rely on the distribution of entanglement between the different participating parties. One example is quantum key distribution (QKD), an application that has matured to commercial use in recent years. However, difficulties remain, especially with noise resilience and channel capacity in long-distance communication. One way to overcome these problems is to use high-dimensional entanglement, which has been shown to be more robust to noise and enables higher secret-key rates. It is therefore important to have access to certifiable high-dimensional entanglement sources to confidently implement these advanced QKD protocols. Here we develop a method for certifying high-dimensional time-bin entanglement in fiber-loop systems. In these systems, entanglement creation and detection can utilize the same physical components, and the number of time bins, and thus the entanglement dimension, can be adapted without making physical changes to the setup. Our certification method builds on previous proposals for the certification of angular-momentum entanglement in photon pairs. In particular, measurements in only two experimentally accessible bases are sufficient to obtain a lower bound on the entanglement dimension for both two- and multiphoton quantum states. Numerical simulations show that the method is robust against typical experimental noise effects and works well even with limited measurement statistics, thus establishing time-bin encoded photons as a promising platform for high-dimensional quantum-communication protocols.