This research presents the integration of ultra low loss (<1dB/cm) silicon nitride waveguides with a superconducting single photon detector with photon number resolving (PNR) capability - the Microwave Kinetic Inductance Detector - introducing a new photonic integrated circuit platform. Our approach is to integrate waveguides and MKIDs on a sapphire substrate, which minimizes the two level system noise for the MKIDs and serves as a bottom cladding for waveguides. Silicon nitride is used as the core of the waveguides and either SiO2 or SiOxNy is used as the top cladding. We present findings on how the fabrications processes -- including the materials used and the method of deposition -- affect the quality of the MKIDs and waveguides. The integrated system would ultimately be used to make photon number resolving detectors for quantum information applications and high resolution spectrometers for astrophysics and metrology applications.
This research presents the integration of ultra low loss (<1dB/cm) silicon nitride waveguides with a superconducting single photon detector with photon number resolving (PNR) capability - the Microwave Kinetic Inductance Detector - introducing a new photonic integrated circuit platform. Our approach is to integrate waveguides and MKIDs on a sapphire substrate, which minimizes the two level system noise for the MKIDs and serves as a bottom cladding for waveguides. Silicon nitride is used as the core of the waveguides and either SiO2 or SiOxNy is used as the top cladding. We present findings on how the fabrications processes -- including the materials used and the method of deposition -- affect the quality of the MKIDs and waveguides. The integrated system would ultimately be used to make photon number resolving detectors for quantum information applications and high resolution spectrometers for astrophysics and metrology applications.
We report on the development of microwave kinetic inductance detectors (MKIDs) using platinum silicide as the sensor material. MKIDs are an emerging superconducting detector technology, capable of measuring the arrival times of single photons to better than two microseconds and their energies to around ten percent. Previously, MKIDs have been fabricated using either sub-stoichiometric titanium nitride or aluminum, but TiN suffers from the spatial inhomogeneities in the superconducting critical temperature and Al has a low kinetic inductance fraction, causing low detector sensitivity. To address these issues, we have instead fabricated the PtSi microresonators with the superconducting critical temperatures of 944 ± 12 mK and high internal quality factors (Qi≳106). These devices show typical quasiparticle lifetimes of τqp≈30–40 μs and spectral resolution, R=λ/Δλ, of 8 at 406.6 nm. We compare PtSi MKIDs to those fabricated with TiN and detail the substantial advantages that PtSi MKIDs have to offer.
Nanophotonic integrated circuits are emerging as a promising platform for quantum photonics. A key building block are waveguide integrated detectors with superior performance. Detectors based on superconductor nanowires (SNSPDs) attached to optical waveguides have been shown to provide high efficiency and good timing performance, as well as broad bandwidth. To move towards applications in high bandwidth quantum communication and processing, ultrafast single-photon detectors with high efficiency are needed. The speed of meander type SNSPDs is limited because the required high absorption efficiency necessitates long nanowires deposited on top of the waveguide. This enhances the kinetic inductance and makes the detectors slow. We overcome this problem by aligning the nanowire perpendicular to the waveguide to realize devices with a length below 1 µm. By integrating the nanowire into a photonic crystal cavity, we recover high absorption efficiency, thus enhancing the detection efficiency by more than an order of magnitude. Our cavity enhanced superconducting nanowire detectors are fully embedded in silicon nanophotonic circuits and efficiently detect single photons at telecom wavelengths. The detectors possess sub-nanosecond decay (~ 120 ps) and recovery times (~ 510 ps), and thus show potential for GHz count rates at low timing jitter (~ 32 ps).
The ability to resolve photon numbers is crucial in quantum information science and technology, driving the development of detectors with intrinsic photon-number resolving (PNR) capabilities. Although transition edge sensors represent the state-of-the-art in PNR performance, superconducting nanowire single-photon detectors (SNSPDs) offer superior efficiency, speed, noise reduction, and timing precision. Directly inferring photon numbers, however, has only recently become feasible due to advances in readout technology. Despite this, photon-number discrimination remains constrained by the nanowire's electrical properties and readout jitter. In this work, we employ waveguide-integrated SNSPDs and time-resolved measurements to explore how the nanowire kinetic inductance and system jitter affect PNR capabilities. By analyzing the latency time of the photon detection, we can resolve changes in the rising edge of the detection pulse. We find that lower jitter as well as increased kinetic inductance enhances the pulse separation for different photon numbers and improves the PNR capability. Enhancing the kinetic inductance from 165 nH to 872 nH improves PNR quality by 12%, 31% and 23% over the first three photon numbers, though at the cost of reducing the detector's count rate from 165 Mcps to 19 Mcps. Our findings highlight the trade-off between PNR resolution and detector speed.
Integration of photon number resolving superconducting nanowire single-photon detectors (PNR-SNSPDs) with nanophotonic waveguides is a key technology that enables a broad range of quantum technologies on chip-scale platforms. However, all on-chip integrated SNSPDs are fabricated above the waveguide layer, which makes the characteristics of the detector’s photoresponsive film material only depend on the waveguide material, thus lowering the waveguide selectivity. Here, we report an on-chip integrated SNSPD based on optimized topology that the nanowire is sandwiched between the waveguide and the substrate. This device maintains the film characteristics with different waveguides and the light transmitted from the upper waveguide to the substrate is absorbed by the film, which not only increases the selectivity of the waveguide, but also improves light absorption of SNSPD. As an example, SiO2 waveguide with the lower optical transmission loss was fabricated in an integrated PNR-SNSPD. We proposed a multi-channel photon response amplitude superposition multiplexing scheme, which realized photon detection by integrating SNSPD on the optical transmission waveguide in the photonic integrated circuit. The solution not only can effectively read the photon responses of multiple SNSPDs through a readout port, but also can distinguish the number of photons and the corresponding response channels through the amplitude of the readout circuit, thereby realizing a photonic integrated circuit with multiple modes. Finally, we prepared a 4-channel integrated PNR-SNSPD, which resolved the number of photons and corresponding photon response positions through 16 different signal amplitudes. This result is compatible of a wide range of waveguide materials, overcoming the limitation of single photon detector integrated on waveguide for quantum photonic integrated circuit.
Abstract A microwave kinetic inductance detector (MKID) is a cutting-edge superconducting detector. It comprises a resonator circuit constructed with a superconducting film on a dielectric substrate. To expand its field of application, it is important to establish a method to suppress the two-level system (TLS) noise that is caused by the electric fluctuations between the two energy states at the surface of the substrate. The electric field density can be decreased by expanding the strip width (S) and gap width from the ground plane (W) in the MKID circuit, allowing the suppression of TLS noise. However, this effect has not yet been confirmed for MKIDs made with niobium films on silicon substrates. In this study, we demonstrate its effectiveness for such MKIDs. We expanded the dimension of the circuit from (S, W) = (3.00 μm, 4.00 μm) to (S, W) = (5.00 μm, 23.7 μm), and achieved an increased suppression of 5.5 dB in TLS noise.
We present our progress in the realization of a waveguide-integrated, near-infrared, 20-channel pseudo photon number resolving architecture realized on the silicon nitride platform. Each channel consists of a space multiplexing network directing to 8 superconducting nanowire single-photon detectors connected in series. Our design focusses on minimizing splitting losses, ensuring robust response across different wavelengths in the near-infrared range and achieving low noise electrical readout. Specifically, we will report on the design of wavelength-independent splitting elements operating in the near-infrared, the realization of low-loss fiber-to-chip coupling and detail the implementation of the cryogenic biasing and readout scheme. Our work constitutes a significant advancement towards practical multi-channel photon number resolving detectors, serving as a promising building block for scalable and high-performance quantum information processing systems.