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Advanced Fiber Laser Conference (AFL)

Entangled photon pair source with efficient modal phase matching on AlGaAs platform: a solution to fully connected quantum internet

Bin Niu, Xiaodong Zheng, Xu Jing, Cheng Qian, Yufu Li, Yuechan Kong, Tangsheng Chen, Liangliang Lu

Published Mar 18, 2024• 0 citations
Publisher

Abstract

One of the key challenges for realizing large-scale quantum communication in installed fiber networks is to establish communication links between multiple users in a scalable and robust way. Quantum networks based on DWDM quantum correlation utilizing broadband entangled photon pair source could be the solution. Among many integrated photon source techniques, AlGaAs Bragg reflection waveguid (BRW), with its extremely high material χ(2) and negligible birefringence, can produce high brightness, wide bandwidth, post selection free polarization entangled photon pairs. In a scenario of entangled photon and classical light co-fiber transmitting, noise from the classical light could degrade the entanglement. In this paper. we designed and fabricated a Bragg reflection waveguide (BRW) AlGaAs/GaAs chip with high modal overlap to directly generate broadband polarization entanglement, and employed for demonstrate a fully connected three-user noisy network by multiplexing 3 pairings of DWMD channels, each pairing established a quantum communication link between any possible two users. Several causes of noise from chip fluorescence to co-fiber classical light, and their impacts on bit error rate (BER) were analyzed.

DOI
10.1117/12.3023787

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One of the key challenges for realizing large-scale quantum communication in installed fiber networks is to establish communication links between multiple users in a scalable and robust way. Quantum networks based on DWDM quantum correlation utilizing broadband entangled photon pair source could be the solution. Among many integrated photon source techniques, AlGaAs Bragg reflection waveguid (BRW), with its extremely high material χ(2) and negligible birefringence, can produce high brightness, wide bandwidth, post selection free polarization entangled photon pairs. In a scenario of entangled photon and classical light co-fiber transmitting, noise from the classical light could degrade the entanglement. In this paper. we designed and fabricated a Bragg reflection waveguide (BRW) AlGaAs/GaAs chip with high modal overlap to directly generate broadband polarization entanglement, and employed for demonstrate a fully connected three-user noisy network by multiplexing 3 pairings of DWMD channels, each pairing established a quantum communication link between any possible two users. Several causes of noise from chip fluorescence to co-fiber classical light, and their impacts on bit error rate (BER) were analyzed.
We demonstrate efficient photon pair generation for quantum communication using an all-semiconductor approach. In an AlGaAs Bragg-reflection waveguide we employ spontaneous parametric down-conversion to produce photon pairs at telecommunication wavelengths. The various phase-matching solutions present in our device can be used to create timebin or polarization entanglement. This approach can to lead to a fully integrated photon pair source with the pump laser, active and passive optical devices all on a single semiconductor chip.
Building communication links among multiple users in a scalable and robust way is a key objective in achieving large-scale quantum networks. In realistic scenario, noise from the coexisting classical light is inevitable and can ultimately disrupt the entanglement. The previous significant fully connected multiuser entanglement distribution experiments are conducted using dark fiber links and there is no explicit relation between the entanglement degradations induced by classical noise and its error rate. Here we fabricate a semiconductor chip with a high figure-of-merit modal overlap to directly generate broadband polarization entanglement. Our monolithic source maintains polarization entanglement fidelity above 96% for 42 nm bandwidth with a brightness of 1.2 × 107 Hz mW-1. We perform a continuously working quantum entanglement distribution among three users coexisting with classical light. Under finite-key analysis, we establish secure keys and enable images encryption as well as quantum secret sharing between users. Our work paves the way for practical multiparty quantum communication with integrated photonic architecture compatible with real-world fiber optical communication network.
Entangled photons are fundamental resources for quantum communication, computing, and networking. Among them, polarization-entangled photon pairs play an important role due to their straightforward state manipulation and direct use in quantum key distribution, teleportation, and network protocols. However, realizing compact, efficient, and scalable polarization-entangled sources that meet the requirements of practical deployment remains a major challenge. Here, we present a simple yet high-performance on-chip polarization-entangled photon-pair source on thin-film lithium niobate (TFLN). Our device employs dual quasi-phase matching (D-QPM) that sequentially supports type-0 and type-I spontaneous parametric down-conversion in a single nanophotonic waveguide, eliminating the need for interferometers, polarization rotators, or other complex circuits. The source directly produces high-fidelity Bell states with broad bandwidth, high brightness, and low noise. Using this integrated platform, we realize wavelength-multiplexed entanglement distribution in a four-user quantum network deployed over metropolitan fiber links up to 50 km. These results establish a robust and scalable pathway toward practical quantum communication systems and multi-user quantum mesh networks based on integrated photonics.
AlGaAs Bragg reflection waveguides are promising systems for the generation of single and entangled photons through the process of spontaneous parametric down-conversion (SPDC) [1]. We use a type II SPDC process where the downconverted photons are orthogonally polarized. The produced photons are inherently polarization-entangled eliminating the need for any additional entanglement setup. The material AlGaAs is our preferred choice as a nonlinear medium because it features a high nonlinear coefficient allowing for room temperature operation and has the advantage of being a non-birefringent material. Further, the material platform allows for the direct integration of a pump laser into the same chip.
In view of real world applications of quantum information technologies, the combination of miniature quantum resources with existing fibre networks is a crucial issue. Among such resources, on-chip entangled photon sources play a central role for applications spanning quantum communications, computing and metrology. Here, we use a semiconductor source of entangled photons operating at room temperature in conjunction with standard telecom components to demonstrate multi-user quantum key distribution, a core protocol for securing communications in quantum networks. The source consists of an AlGaAs chip emitting polarization entangled photon pairs over a large bandwidth in the main telecom band around 1550 nm without the use of any off-chip compensation or interferometric scheme; the photon pairs are directly launched into a dense wavelength division multiplexer (DWDM) and secret keys are distributed between several pairs of users communicating through different channels. We achieve a visibility measured after the DWDM of 87% and show long-distance key distribution using a 50-km standard telecom fibre link between two network users. These results illustrate a promising route to practical, resource-efficient implementations adapted to quantum network infrastructures.
Correlated photon-pair sources are key components for quantum computing, networking, and sensing applications. Integrated photonics has enabled chip-scale sources using nonlinear processes, producing high-rate entanglement with sub-100 microwatt power at telecom wavelengths. Many quantum systems operate in the visible or near-infrared ranges, necessitating broadband visible-telecom entangled-pair sources for connecting remote systems via entanglement swapping and teleportation. This study evaluates broadband entanglement generation through spontaneous four-wave mixing in various nonlinear integrated photonic materials, including silicon nitride, lithium niobate, aluminum gallium arsenide, indium gallium phosphide, and gallium nitride. We demonstrate how geometric dispersion engineering facilitates phase-matching for each platform and reveals unexpected results, such as robust designs to fabrication variations and a Type-1 cross-polarized phase-matching condition for III-V materials that expands the operational bandwidth. With experimentally attainable parameters, integrated photonic microresonators with optimized designs can achieve pair generation rates greater than ~1 THz/mW2^22.