We propose a new strategy to integrate superconducting nanowire single-photon detectors in etchless photonic circuits based on bound-states-in-the-continuum. We demonstrate the feasibility of this approach at cryogenic temperatures and report integrated detector with saturated efficiency.
Advancements in integrated photonics have enabled the miniaturization and scaling of complex photonic circuits, providing stability and reliability beyond the capabilities of conventional bulk setups. A central component of quantum photonic circuits is the single-photon detector, responsible for quantum state measurement. Due to the stringent performance requirements of quantum applications, superconducting nanowire single-photon detectors (SNSPDs) have emerged as the preferred detection technology, offering superior efficiency, low noise, and high timing resolution. While tabletop SNSPDs are now mature, commercially available and contributed to significant progress in quantum computing and communication, their integration into photonic circuits is still in its infancy. Integrated SNSPDs have shown the potential to not only match but surpass tabletop detectors in several performance metrics. Nevertheless, demonstrations have largely focused on individual integrated detectors, with limited investigation into more complex integrated circuits and advanced functionalities. In this thesis, we present a novel integration platform based on photonic bound states in the continuum (BICs) to address a critical limitation of conventional SNSPD designs, where nanowires placed directly atop the waveguide core are constrained by the core geometry. The etchless nature of our BIC waveguides provides a flat surface that decouples the design of the electronic readout circuitry below from the optical circuit layer above, enabling innovative integrated-nanowire geometries and facilitating large-scale integration of SNSPDs with CMOS-compatible circuits. We established a complete fabrication and characterization workflow for integrating NbTiN-based superconducting nanowires with BIC waveguides. Our integrated detectors achieved state-of-the-art performance, including detection efficiencies exceeding 70%, intrinsic jitter below 70 ps, and ultrafast recovery times (~1.7 ns). These results pave the way toward GHz-rate quantum state measurements, essential for scalable quantum photonic processors. Leveraging the design flexibility of BIC waveguides, we introduce the concept of inline detection with SNSPDs which exploits their unique ability to precisely engineer absorption through nanowire length control. By cascading multiple partially absorbing SNSPDs, it is possible to significantly reduce the number of required optical components and miniaturize complex quantum measurement setups within an extremely compact footprint. Traditional integration geometries prevent such implementations due to significant scattering losses at nanowire terminations, which limit the feasibility of cascaded designs. On the other hand, the design flexibility provided by our BIC platform makes it ideal for development of inline detection schemes. As a proof-of-concept, we use inline detection to miniaturize two fundamental quantum optics tools: an integrated Hanbury Brown and Twiss (HBT) interferometer and a photon-number-resolving (PNR) detector. We replicated the functionalities of these setups using only two nanowires integrated along a single waveguide. These devices show extremely compact footprint, highlighting the scalability potential of our approach. We validated these devices through characterization of a single-photon source and the discrimination of collinear photon pairs. The experimental results aligned well with previous literature and theoretical predictions, confirming the reliability of our integration method. Overall, this work presents a novel approach to quantum measurements within integrated quantum photonic circuits. Inline detection represents a step forward in quantum integrated photonics, moving from individual device demonstrations toward functional quantum circuits. By introducing our BIC-based integration platform, we simplify detector design and fabrication, lowering barriers to the development of inline detection circuits and opening new opportunities in multiphoton quantum state measurements, single-photon spectroscopy, and multiphoton subtraction.
Photonic integrated circuits hold great potential for realizing quantum technology. Efficient single-photon detectors are an essential constituent of any such quantum photonic implementation. In this regard waveguide-integrated superconducting nanowire single-photon detectors are an ideal match for achieving advanced photon counting capabilities in photonic integrated circuits. However, currently considered material systems do not readily satisfy the demands of next generation nanophotonic quantum technology platforms with integrated single-photon detectors, in terms of refractive-index contrast, band gap, optical nonlinearity, thermo-optic stability and fast single-photon counting with high signal-to-noise ratio. Here we show that such comprehensive functionality can be realized by integrating niobium titanium nitride superconducting nanowire single-photon detectors with tantalum pentoxide waveguides. We demonstrate state-of-the-art detector performance in this novel material system, including devices showing 75% on-chip detection efficiency at tens of dark counts per second, detector decay times below 1 ns and sub-30 ps timing accuracy for telecommunication wavelengths photons at 1550 nm. Notably, we realize saturation of the internal detection efficiency over a previously unattained bias current range for waveguide-integrated niobium titanium nitride superconducting nanowire single-photon detectors. Our work enables the full set of high-performance single-photon detection capabilities on the emerging tantalum pentoxide-on-insulator platform for future applications in integrated quantum photonics.
We present an overview of recent results for new generation of infrared and optical superconducting nanowire single-photon detectors (SNSPDs) that has already demonstrated a performance that makes them devices-of-choice for many applications. SNSPDs provide high efficiency for detecting individual photons while keeping dark counts and timing jitter minimal. Besides superior detection performance over a broad optical bandwidth, SNSPDs are also compatible with an integrated optical platform as a crucial requirement for applications in emerging quantum photonic technologies. By embedding SNSPDs in nanophotonic circuits we realize waveguide integrated single photon detectors which unite all desirable detector properties in a single device.
We report the realization of inline quantum measurements with waveguide-integrated superconducting nanowire single-photon detectors (SNSPDs). To suppress parasitic scattering at detector terminations, while ensuring compatibility with standard photonic substrates and cryogenic operation, we developed a photonic bound states in the continuum (BIC) platform based on etchless polymer waveguides. We show BIC-coupled inline detectors with on-chip efficiency exceeding 80%, recovery time of less than 2 ns, and intrinsic jitter of less than 70 ps. As a proof of principle, we implement Hanbury Brown and Twiss interferometry and photon number resolution with two collinear detectors within a footprint of 60⋅6μm2. The concept of inline quantum measurements could be further developed to support more complex circuit functionalities, such as higher-order correlation measurements, quantum state tomography, and multi-photon subtraction, within a compact architecture.
We report the realization of inline quantum measurements with waveguide-integrated superconducting nanowire single-photon detectors (SNSPDs). To suppress parasitic scattering at detector terminations, while ensuring compatibility with standard photonic substrates and cryogenic operation, we developed a photonic bound state in the continuum (BIC) platform based on etchless polymer waveguides. We show BIC-coupled inline detectors with on-chip efficiency exceeding 80%, recovery time of less than 2 ns, and intrinsic jitter of less than 70 ps. As a proof of principle, we implement Hanbury Brown and Twiss interferometry and photon-number resolution with two collinear detectors within a footprint of 60 × 6 µm 2 . The concept of inline quantum measurements could be further developed to support more complex circuit functionalities, such as higher-order correlation measurements, quantum state tomography, and multi-photon subtraction, within a compact architecture.