[Enlarge image]Schematic of the photon-pair source. A pump laser enters the microresonator, then photon pairs are generated from the pump laser through a nonlinear effect.
Quantum science and technology offer a new paradigm for generating, transmitting and processing information. Photons are important carriers of quantum information due to their unrivaled coherence and immunity to ambient perturbation. The use of photons has led to significant developments, such as the demonstration of quantum computational advantage1 and the establishment of metropolitan quantum-communication networks.2 However, since these advances in photonic quantum computation and communications use optical circuits based on free-space and fiber optics, their scalability and robustness are heavily limited.
Integrated photonics enables the synthesis, processing and detection of optical signals using photonic integrated circuits (PICs). Over the past few decades, its successful transition from laboratory research to foundry development has established integrated photonics as a standard technology deployed in high-data-rate telecommunications and data centers. Recently, silicon nitride (Si3N4) integrated photonics has gained prominence,3, 4 primarily driven by the low optical loss offered by Si3N4, which is beyond the reach of silicon and III–V semiconductors. Combined with modest Kerr nonlinearity, tight optical confinement and dispersion engineering, Si3N4 has become the leading candidate for on-chip photonic quantum information processing.
In recent work, we employed a standard CMOS foundry process to fabricate ultralow-loss Si3N4waveguides, building bright, narrow-band photon-pair sources ,5 which are essential building blocks for long-distance quantum communication with quantum repeaters and efficient photon–atom interfaces. We achieved a record on-chip generated photon linewidth of 25.9 MHz. Additionally, in our demonstrations, the photon-pair source exhibited a brightness exceeding 1×109 Hz/mW2/GHz, setting a new record for integrated silicon photonics. This advance also facilitates the creation of a heralded single-photon source, characterized by a heralded second-order correlation g(2)(0)=0.0037(5), as well as an energy–time entanglement source with a raw visibility of 0.973(9).
We believe our work marks a critical step toward using integrated photonics to generate photon pairs whose linewidth can match atomic transitions commonly used for quantum repeaters. It paves the way to constructing efficient photon–atom interfaces in a robust, compact and low-cost manner. We anticipate that our photon-pair sources can naturally mediate a variety of integrated quantum devices. These PIC-based quantum chips can be manufactured at high volume and throughput using established CMOS foundries. Furthermore, we believe that leveraging heterogeneous integration of photon-pair sources and an ultralow-loss linear network with a superconducting nanowire single-photon detector could enable chip-scale quantum communication and internet.
Researchers
Ruiyang Chen, International Quantum Academy, China, and Southern University of Science and Technology, China
Yi-Han Luo and Jinbao Long, International Quantum Academy, China
Baoqi Shi, International Quantum Academy, China, and University of Science and Technology of China
Chen Shen, International Quantum Academy, China, and Qaleido Photonics, China
Junqiu Liu, International Quantum Academy, China, and Hefei National Laboratory, China
References
1. H.-S. Zhong et al. Science 370, 1460 (2020).
2. Y.-A. Chen et al. Nature 589, 214 (2021).
3. J. Liu et al. Nat. Commun. 12, 2236 (2021).
4. Z. Ye et al. Photonics Res. 11, 558 (2023).
5. R. Chen et al. Phys. Rev. Lett. 133, 083803 (2024).