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Optics Letters

High-visibility energy-time entanglement system enabled by a low-loss silicon-integrated platform

Yue Qin, Hongnan Xu, Gaolei Hu, Hon Ki Tsang

Published Apr 26, 2024• 7 citations
Publisher

Abstract

Energy-time (E-T) entanglement is widely employed in long-distance quantum entanglement distribution due to its strong robustness against transmission fluctuations. In this Letter, we report what we believe to be the first silicon monolithically integrated E-T entanglement system, which integrates the photon sources, wavelength demultiplexers, and Franson interferometers on a single chip. Also, by utilizing low-loss multimode waveguides in Franson interferometers, we measured an on-chip quantum interference visibility of 99.66% (±0.47%), to our knowledge one of the highest values for integrated E-T entanglement systems reported to date. The quantum interference after 1- and 5-km fiber propagation shows visibilities of 96.72% (±0.78%) and 97.46% (±1.23%), respectively. These results demonstrate the potential of using silicon monolithic integration for advance E-T entanglement-based quantum communication networks.

DOI
10.1364/ol.525037

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Abstract Quantum entanglement transceivers (QETs) are essential enablers for scalable photonic quantum networks, supporting applications such as secure communication, distributed quantum sensing, and quantum computing. However, conventional QET implementations rely on bulk optics, consume high power, and suffer fidelity degradation over long‐distance fiber links. Here, a silicon photonic integrated QET is proposed and demonstrated to distribute multi‐channel quantum entanglement over standard single‐mode fibers across a span from 0 to 160 km, without requiring dispersion compensation modules and extra off‐chip spectral filters. This advancement is achieved through monolithic integration of interferometers, wavelength multiplexers, notch filters, and a tunable‐linewidth micro‐resonator photon source, which collectively minimize aggregate loss and optimize photon correlation time. The implemented system supports both time‐bin and energy‐time entanglement across three channels, exhibiting maximum Bell‐state fidelities of 95.55%, 97.63%, and 95.08%, and energy‐time interference visibilities of 99.17%, 99.40%, and 98.50%. Long‐haul transmission experiments demonstrate a 91% time‐bin entanglement fidelity over 80 km and a 95% energy‐time interference raw visibility over 160 km. Furthermore, a 24‐h stability test reveals an average visibility of 87.5%, even in the presence of polarization fluctuations. This work presents a scalable and cost‐effective QET solution for large‐scale photonic quantum networks, advancing the development of integrated quantum communication infrastructures.
An integrated source of time-energy entangled photons is demonstrated through resonantly enhanced spontaneous four-wave mixing in a silicon micro-ring resonator. A Franson type set-up is employed to show the quantum interference between photon pairs with a visibility exceeding 90% and a violation of the Bell's inequality by more than 10 standard deviations. The high spectral brightness and the extremely small footprint of our source make it suitable for the development of quantum information protocols integrated on chip.
Abstract The fruitful association of quantum and integrated photonics holds the promise to produce, manipulate, and detect quantum states of light using compact and scalable systems. Integrating all the building blocks necessary to produce high-quality photonic entanglement in the telecom-wavelength range out of a single chip remains a major challenge, mainly due to the limited performance of on-chip light rejection filters. We report a stand-alone, telecom-compliant device that integrates, on a single substrate, a nonlinear photon-pair generator and a passive pump-rejection filter. Using standard channel-grid fiber demultiplexers, we demonstrate the first entanglement qualification of such an integrated circuit, showing the highest raw quantum interference visibility for time-energy entangled photons over two telecom-wavelength bands. Genuinely pure, maximally entangled states can therefore be generated thanks to the high-level of noise suppression obtained with the pump filter. These results will certainly further promote the development of more advanced and scalable photonic-integrated quantum systems compliant with telecommunication standards.
Abstract The dense quantum entanglement distribution is the basis for practical quantum communication, quantum networks and distributed quantum computation. To make entanglement distribution processes stable enough for practical and large-scale applications, it is necessary to perform them with the integrated pattern. Here, we first integrate a dense wavelength-division demultiplexing system and unbalanced Mach-Zehnder interferometers on one large-scale photonic chip and demonstrate the multi-channel wavelength multiplexing entanglement distribution among distributed photonic chips. Specifically, we use one chip as a sender to produce high-performance and wideband quantum photon pairs, which are then sent to two receiver chips through 1-km standard optical fibers. The receiver chip includes a dense wavelength-division demultiplexing system and unbalanced Mach-Zehnder interferometers and realizes multi-wavelength-channel energy-time entanglement generation and analysis. High quantum interference visibilities prove the effectiveness of the multi-chip system. Our work paves the way for practical entanglement-based quantum key distribution and quantum networks.