Heralded telecom single photons from a visible–telecom pair source on a hybrid PPKTP–PIC platform
Vijay Soorya Shunmuga Sundaram, Evan Manfreda-Schulz, Todd Hawthorne, Tony Roberts, Thomas Palone, Venkatesh Deenadayalan, Mario Ciminelli, Philip R. Battle, Gerald Leake, Daniel J. Coleman, Michael L. Fanto, A. Nick Vamivakas, Gregory A. Howland, Stefan F. Preble
We present a heralded photon-pair source using periodically poled potassium titanyl phosphate (PPKTP) waveguides coupled with photonic integrated circuits (PICs). The PPKTP generates correlated visible–telecom photon pairs, processed by the dual-band silicon and silicon nitride PIC. Heralding at visible wavelengths removes the need for large superconducting nanowire single-photon detectors (SNSPDs). Silicon Mach–Zehnder interferometers (MZIs) on the PIC modulate the telecom single photons and also serve as pump-rejection filters. We demonstrate an insertion loss of 2.37 ± 1.03 dB (4.46 ± 1.32 dB) at the visible (telecom) wavelength between the PPKTP waveguides and PIC edge couplers, and an on-chip pump suppression of 92.5 ± 2.5 dB. This platform will enable remote quantum nodes to securely communicate over telecom fiber-optic networks.
We present a heralded photon-pair source using periodically poled potassium titanyl phosphate (PPKTP) waveguides coupled with photonic integrated circuits (PICs). The PPKTP generates correlated visible–telecom photon pairs, processed by the dual-band silicon and silicon nitride PIC. Heralding at visible wavelengths removes the need for large superconducting nanowire single-photon detectors (SNSPDs). Silicon Mach–Zehnder interferometers (MZIs) on the PIC modulate the telecom single photons and also serve as pump-rejection filters. We demonstrate an insertion loss of 2.37 ± 1.03 dB (4.46 ± 1.32 dB) at the visible (telecom) wavelength between the PPKTP waveguides and PIC edge couplers, and an on-chip pump suppression of 92.5 ± 2.5 dB. This platform will enable remote quantum nodes to securely communicate over telecom fiber-optic networks.
We propose silicon nitride (Si3N4) nanowaveguide-based CMOS-compatible integrated sources of spectrally pure visible-telecom photon pairs. Our designs are intrinsically devoid of spectral correlations, eradicating the need for narrow-band filtering that reduces the source brightness. Further, the signal photons lie in the visible--near-infrared (vis-NIR) band, which can provide increased heralding efficiency of the idler photon in the telecom band using high-efficiency single-photon detectors. For example, a rectangular-cross-section silica-clad Si3N4 nanowaveguide with dimensions $680\text{~nm}\ifmmode\times\else\texttimes\fi{}840\text{~nm}$ and length 7 cm provides a heralded single-photon purity of approximately $91\mathrm{%}$ for a pump wavelength of 956.8 nm and a pump bandwidth of 1200 GHz, with the signal and idler lying in the visible and telecom bands at approximately 701 nm and approximately 1505 nm, respectively, demonstrating a peak spectral brightness of approximately $1.2\ifmmode\times\else\texttimes\fi{}{10}^{4}$ photon pairs/s/nm/mW2 for a linear propagation loss of 0.5 dB/cm. The effect of propagation losses on the purity is also studied for such source designs. We also propose some designs capable of generating high-purity photon pairs to address various specific vis-NIR quantum memory transitions with telecom-band interfacing for long-distance hybrid quantum networks. Such compact on-chip sources could have potential applications in various quantum technologies, such as sensing, simulation, computing, communication, and networking.
Quantum networking enables the distribution of quantum information across distant nodes, unlocking capabilities such as secure communication, distributed quantum computing, enhanced metrology, and tests of fundamental physics. Photons serve as the natural carriers of quantum information over long distances due to their low loss in optical fibers and robustness to environmental decoherence. However, the practical realization of quantum networks remains limited by the lack of photon sources that are simultaneously compatible with diverse quantum systems, stable over long timescales, and suitable for deployment in real-world fiber infrastructure. This dissertation addresses these challenges through the co-development of photon-pair sources and a field-deployed quantum networking testbed. We present two complementary chip-scale sources of correlated photon pairs tailored for distinct bottlenecks in quantum networking. The first is a hybrid visible–telecom photon-pair source designed to address a fundamental spectral mismatch between quantum nodes and communication channels. While most quantum memories and processors operate at visible to near- nfrared wavelengths, optical fibers exhibit minimal loss in the telecommunications band. By integrating periodically poled nonlinear waveguides with photonic integrated circuits, we demonstrate a platform capable of directly generating visible–telecom photon pairs, enabling efficient interfacing between heterogeneous quantum systems and existing fiber networks. The second source is a fully packaged, broadband telecom photon-pair source based on silicon waveguide spirals, designed for stable, long-duration operation. This stability enables extended measurements necessary to overcome channel losses and environmental drifts in deployed fiber networks. These sources are evaluated within RoQNET (Rochester Quantum Network), a ∼20 km fiber link between the Rochester Institute of Technology and the University of Rochester. Using this platform, we demonstrate the transmission and on-chip modulation of heralded telecom single photons, verify their nonclassical statistics, and characterize long-term channel behavior. Additionally, we explore programmable time-bin entanglement distribution using spectral waveshapers, providing a flexible approach to quantum communication. Together, this work establishes a co-designed source–network framework for scalable, heterogeneous quantum networking.
We report on the generation of an indistinguishable heralded single-photon state, using highly nondegenerate spontaneous parametric downconversion (SPDC). Spectrally factorable photon pairs can be generated by incorporating a broadband pump pulse and a group-velocity matching (GVM) condition in a periodically-poled potassium titanyl phosphate (PPKTP) crystal. The heralding photon is in the near IR, close to the peak detection efficiency of off-the-shelf Si single-photon detectors; meanwhile, the heralded photon is in the telecom L-band where fiber losses are at a minimum. We observe spectral factorability of the SPDC source and consequently high purity (90%) of the produced heralded single photons by several different techniques. Because this source can also realize a high heralding efficiency (> 90%), it would be suitable for time-multiplexing techniques, enabling a pseudo-deterministic single-photon source, a critical resource for optical quantum information and communication technology.
Photon pair sources are fundamental building blocks for quantum entanglement and quantum communication. Recent studies in silicon photonics have documented promising characteristics for photon pair sources within the telecommunications band, including sub-milliwatt optical pump power, high spectral brightness, and high photon purity. However, most quantum systems suitable for local operation (e.g., storage/computation) support optical transitions in the visible or short nearinfrared bands. In comparison to telecommunications wavelengths, the significantly higher optical attenuation in silica at such wavelengths limits the length scale over which optical-fiber-based quantum communication between such local nodes can take place. One approach to connect such systems over fiber is through a photon pair source that can bridge the visible and telecom bands, but an appropriate source, which should produce narrow-band photon pairs with a high signal-to-noise ratio, has not yet been developed in an integrated platform. Here, we demonstrate a nanophotonic visible-telecom photon pair source for the first time, using high quality factor silicon nitride resonators to generate narrow-band photon pairs with unprecedented purity and brightness, with coincidence-toaccidental ratio (CAR) up to 3,780 ± 140 and detected photon-pair flux up to (18,400 ± 1,000) pairs/s. We further demonstrate visible-telecom time-energy entanglement and its distribution over a 20 km fiber, far exceeding the fiber length over which purely visible wavelength quantum light sources can be transmitted. Finally, we show how dispersion engineering of the microresonators enables the connections of different species of trapped atoms/ions, defect centers, and quantum dots to the telecommunications bands for future quantum communication systems.