The emerging integrated quantum photonics is pushing forward the establishment of quantum networks. To interconnect individual chip-based quantum sources, high-performance entanglement swapping is indispensable. Here, using low-loss silicon chips with waveguide structure and frequency-offset pumps, high-rate cross-channel entanglement swapping is demonstrated. A record-high swapping rate of 207 counts per hour is obtained, and the measured swapping visibilities between each of two pairs of channels exceed 90%. The proposed cross-channel architecture allows dynamic channel switching by adjusting pump wavelengths, enabling flexible user pairing in quantum networks. This work makes a concrete benchmark for chip-based entanglement swapping and provides a viable solution for real-world quantum communication.
The emerging integrated quantum photonics is pushing forward the establishment of quantum networks. To interconnect individual chip-based quantum sources, high-performance entanglement swapping is indispensable. Here, using low-loss silicon chips with waveguide structure and frequency-offset pumps, high-rate cross-channel entanglement swapping is demonstrated. A record-high swapping rate of 207 counts per hour is obtained, and the measured swapping visibilities between each of two pairs of channels exceed 90%. The proposed cross-channel architecture allows dynamic channel switching by adjusting pump wavelengths, enabling flexible user pairing in quantum networks. This work makes a concrete benchmark for chip-based entanglement swapping and provides a viable solution for real-world quantum communication.
Abstract Integrated photonics represents a technology that could greatly improve quantum communication networks in terms of cost, size, scaling, and robustness. A key benchmark for this is to demonstrate their performance in complex quantum networking protocols, such as entanglement swapping between truly independent photon-pair sources. Here, using two independent, asynchronously-pumped, integrated Si 3 N 4 microring resonator photon-pair sources, operating in the continuous-wave regime with time-resolved detections, we obtained state of the art Hong–Ou–Mandel (93.2 ± 1.6%) and entanglement swapping (91.2 ± 3.4%) visibilities, while maintaining high rates. The time-resolved detection facilitates high spectral purities without the need for spectral filtering. Our results demonstrate the potential of such telecom-band sources for practical, real-world quantum communication.
ABSTRACT Quantum key distribution (QKD) provides an information‐theoretic security framework for building QKD networks (QNs). However, existing QN architectures face critical challenges: trusted‐node‐based designs inherently expose relay nodes to physical compromise, while entanglement‐based approaches suffer from high implementation costs of sources. Here, this work proposes and conceptually validates a fully‐connected chip‐integrated reconfigurable QN based on the mode‐pairing (MP) QKD protocol. By combining hybrid‐integrated external‐cavity laser (ECL) chips with wavelength selective switch (WSS) chips, this architecture enables simultaneous secure key sharing among arbitrary users using only two wavelengths through a wavelength‐path dynamic resource allocation mechanism. Compared to conventional QN architectures, this approach significantly reduces the required port count and wavelength resources while supporting flexible reconfiguration such as on‐demand secure key supplementation and rapid reconstruction of faulty links‐capabilities unattainable in existing schemes. Experimental results demonstrate that the system achieves an average finite‐size secret key rate (SKR) of 5.72 kbps for each user pair under a channel loss of 40 dB. The compact design, cost‐effectiveness, and scalability of this architecture establish a robust foundation for the deployment of practical QNs.
Silicon-on-chip photonic circuits are among some very promising platforms for generating nonclassical photonic quantum state, because of its low loss, small footprint, and compatibility with complementary metal-oxide-semiconductor (CMOS) and telecommunications techniques. Dense wavelength division multiplexing (DWDM) is a leading technique for enhancing the transmission capacity of both classical and quantum communications. To bridge the frequency gap between silicon-chip and other quantum systems, such as quantum memories, a quantum interface is indispensable. Here, we demonstrate a quantum interface for multiplexed energy-time entanglement states, which are generated on a silicon micro-ring cavity that is based on frequency up-conversion. By switching the pump wavelength, energy-time entanglement from any channel can be selected at will after being up-converted. The high visibilities of two-photon interference over three channels after frequency up-conversion clearly prove that the entanglement is fully preserved during the quantum frequency conversion (QFC) process. Our work provides new perspectives regarding channel capacity enhancement in quantum communications and for quantum resources being transferred between two different quantum systems.
Abstract Quantum communication networks enable applications ranging from highly secure communication to clock synchronization and distributed quantum computing. Miniaturized, flexible, and cost-efficient resources will be key elements for ensuring the scalability of such networks as they progress towards large-scale deployed infrastructures. Here, we bring these elements together by combining an on-chip, telecom-wavelength, broadband entangled photon source with industry-grade flexible-grid wavelength division multiplexing techniques, to demonstrate reconfigurable entanglement distribution between up to 8 users in a resource-optimized quantum network topology. As a benchmark application we use quantum key distribution, and show low error and high secret key generation rates across several frequency channels, over both symmetric and asymmetric metropolitan-distance optical fibered links and including finite-size effects. By adapting the bandwidth allocation to specific network constraints, we also illustrate the flexible networking capability of our configuration. Together with the potential of our semiconductor source for distributing secret keys over a 60 nm bandwidth with commercial multiplexing technology, these results offer a promising route to the deployment of scalable quantum network architectures.
Entangled photon pairs are a ubiquitous resource in quantum technologies, used in quantum key distribution and quantum networking as well as fundamental tests of non-locality. For scalable quantum networks, pairs that are indistinguishable in all unentangled degrees of freedom are essential, as they enable high-fidelity entanglement swapping across network nodes. To date the most-studied sources of "swappable" entangled photon pairs have been based on spontaneous parametric down-conversion (SPDC) in non-linear crystals. However, the probabilistic nature and unavoidable trade-off between brightness and unwanted multi-photon emission limits their performance in lossy channels. Here, we demonstrate a high-fidelity source of "swappable" entangled photon pairs using a semiconductor quantum dot (QD) coupled to a tunable microcavity. By actively modulating the QD emission between orthogonal polarisation states, delaying one path in a low-loss Herriott cell, and recombining the two on a balanced beam splitter, we generate entangled photon pairs with a fidelity of 96.1±0.5 %. We identify and mitigate fidelity-limiting factors, achieving a maximum fidelity of 98.1±0.5 % through time-resolved post-selection. The scheme suppresses residual multi-photon events concentrated near the excitation pulse and has only a modest impact on the rate. Furthermore, the photons are mutually indistinguishable, enabling efficient entanglement swapping. Our results establish semiconductor QDs as a viable platform for quantum network-compatible swappable entangled photon pair generation, with feasible entanglement generation rates exceeding 0.5 Gpairs/s.
Abstract Integrated photonics has recently become a leading platform for the realization and processing of optical entangled quantum states in compact, robust, and scalable chip formats with applications in long-distance quantum-secured communication, quantum-accelerated information processing, and non-classical metrology. However, the quantum light sources developed so far have relied on external bulky excitation lasers making them impractical, not reproducible prototype devices, hindering scalability and the transfer out of the lab into real-world applications. Here we demonstrate a fully integrated quantum light source, which overcomes these challenges through the combined integration of a laser cavity, a highly efficient tunable noise suppression filter (> 55 dB) exploiting the Vernier effect, and a nonlinear microring for entangled photon pair generation through spontaneous four-wave mixing. The hybrid quantum source employs an electrically-pumped InP gain section and a Si₃N₄ low-loss microring filter system and demonstrates high-performance parameters, i.e., a pair emission over four resonant modes in the telecom band (bandwidth ∼ 1 THz), and a remarkable pair detection rate of ∼ 620 Hz at a high coincidence-to-accidental ratio of ∼80. The source directly creates high-dimensional frequency-bin entangled quantum states (qubits/qudits), verified by quantum interference measurements with visibilities up to 96% (violating Bell-inequality) and by density matrix reconstruction through state tomography showing fidelities of up to 99%. Our approach, leveraging a hybrid photonic platform, enables commercial-viable, low-cost, compact, light-weight, and field-deployable entangled quantum sources, quintessential for practical, out-of-lab applications, e.g., in quantum processors and quantum satellite communications systems.