Improvements of readout signal integrity in mid-infrared superconducting nanowire single-photon detectors
Sahil J. Patel, Marco Colangelo, Andrew D. Beyer, Gregor G. Taylor, Jason P. Allmaras, Bruce Bumble, Emma E. Wollman, Matthew D. Shaw, Karl K. Berggren, Boris A. Korzh
Superconducting nanowire single-photon detectors (SNSPDs) in the mid-infrared (MIR) have the potential to open up numerous opportunities in fields such as exoplanet searches, direct dark matter detection, physical chemistry, and remote sensing. One challenge in pushing SNSPD sensitivity to the MIR is a decrease in the signal-to-noise ratio (SNR) of the readout signal, as the critical currents become increasingly smaller. We overcome this trade-off with a device architecture that employs impedance matching tapers and superconducting nanowire avalanche photodetectors to demonstrate increased SNR while maintaining saturated internal detection efficiency at 7.4 μm and approaching saturation at 10.6 μm. This work provides a platform for pushing SNSPD sensitivity to longer wavelengths while enabling the scalability to large arrays.
Superconducting nanowire single-photon detectors (SNSPDs) in the mid-infrared (MIR) have the potential to open up numerous opportunities in fields such as exoplanet searches, direct dark matter detection, physical chemistry, and remote sensing. One challenge in pushing SNSPD sensitivity to the MIR is a decrease in the signal-to-noise ratio (SNR) of the readout signal, as the critical currents become increasingly smaller. We overcome this trade-off with a device architecture that employs impedance matching tapers and superconducting nanowire avalanche photodetectors to demonstrate increased SNR while maintaining saturated internal detection efficiency at 7.4 μm and approaching saturation at 10.6 μm. This work provides a platform for pushing SNSPD sensitivity to longer wavelengths while enabling the scalability to large arrays.
Superconducting Nanowire Single-Photon Detectors (SNSPDs) are the premier single-photon counting technology in the near-infrared regime. Operating via a photon-induced phase transition from the superconducting to the normal state, SNSPDs act as highly sensitive digital detectors that now play a critical role in quantum communication, deep-space optical communications, and direct dark matter detection. As the demand for these detectors scales, there is a pressing need to extend their performance capabilities toward longer wavelengths, larger active areas, and higher operating temperatures. However, advancing these metrics requires navigating complex physical trade-offs inherent to the detection mechanism. This thesis explores the material optimizations, novel detector architectures, and fundamental device physics required to push SNSPD technology beyond its current limits. The first thrust of this work focuses on extending SNSPD sensitivity into the mid-infrared (MIR) and far-infrared regimes. By developing a low-Tc (sub-1 K) WSi film engineered to reduce the characteristic detection energy, the threshold for long-wavelength detection is significantly lowered. Coupled with a novel detector architecture utilizing impedance-matching tapers and superconducting nanowire avalanche photon detectors (SNAPs), sensitivity is initially demonstrated at wavelengths up to 29um using a blackbody thermal source. Expanding beyond this limit, the implementation of quantum cascade lasers enables the demonstration of single-photon counting at wavelengths up to 88um, marking a major improvement over the current state of the art. To address the practical MIR detection challenges of low signal-to-noise ratio and restricted fill factors, this work also demonstrates a 1 mm x 1mm array of superconducting microwire single-photon detectors (SMSPDs) sensitive out to 3.7um, establishing a pathway for future antenna-coupled detectors. The second thrust investigates the development of micrometer-scale wires to simultaneously increase active area and operating temperature. Moving to microwire geometries raises fundamental questions regarding intrinsic detection mechanisms. Using a scanning lens setup, this work demonstrates the first direct observation of transverse coordinate effects in microwires, where the precise location of photon incidence across the wire width significantly alters the detector's slew rate and timing performance. To counteract this, new rectification schemes are introduced to produce a more uniform detection landscape. Specifically, the integration of a superconducting rail alongside the main detector is shown to successfully mitigate the transverse coordinate effect, improve timing performance, and increase the viable operating temperature of the detector. The third thrust explores the use of unconventional superconductors, namely MgB2 to achieve an appreciably higher-temperature single-photon detection pathway. This section details the distinct challenges associated with the growth and fabrication of detectors using air-sensitive materials and evaluates their long-term viability for the SNSPD platform. Ultimately, this thesis highlights the critical material and architectural parameters required to advance the field of single-photon detection. By elucidating the metrics and mechanisms that govern ideal detector performance, this work aims to broaden the understanding and future application of SNSPDs across diverse scientific disciplines. All the data presented here is my own unless otherwise mentioned.
The ability to detect single photons in the mid-infrared spectral range (beyond 2 μm wavelength, photon energy below 0.62 eV) is the key to unlocking a range of emerging scientific applications, from remote sensing LIDAR, molecular spectroscopy, and powerful new approaches to dark matter detection. Conventional detector types, such as semiconductor single-photon avalanche diodes, lose sensitivity at such low photon energy. Superconducting materials, with a much lower characteristic energy gap, hold particular promise. In this Perspective, we focus on recent advances in superconducting nanowire single-photon detectors, which have recently extended single-photon sensitivity up to 29 μm (0.043 eV). We discuss the potential for future advances and strategies to overcome challenges to technological development.
Mid-infrared (MIR) single-photon detection is emerging as an important technology for various applications. Superconducting nanowire single photon detectors (SNSPDs) fabricated with superconducting films with energy gaps of a few meV are natural broadband single-photon detectors. Recently, extending SNSPDs’ operation wavelengths into the MIR region is highly attractive. γ-Nb4N3 has a reduced N content and lower energy gap than the commonly used δ-NbN, making SNSPDs based on γ-Nb4N3 film more sensitive to low energy photons. We report on a Nb4N3-SNSPD based on 62-nm wide nanowire, with an optical absorption enhancement design and an optimized device package for efficient ZBLAN fiber coupling and dark count filtering. The developed device has a unity intrinsic detection efficiency (IDE) in the 1.5–4 µm wavelength region, and the device detection efficiency at 2.95 µm was measured to be 32.5%, with an uncertainty of 12.7%. Furthermore, we reduced the device geometry, and measured 3–10 µm photon response of a device based on 5-nm film and 42-nm nanowire, with an IDE of 95%, 81%, 40%, and 6% for 4.8, 6, 8, and 10 µm, respectively.
Superconducting nanowire single-photon detectors (SNSPDs) are among the most sensitive single-photon detectors available and have the potential to transform fields ranging from infrared astrophysics to molecular spectroscopy. However, extending their performance into the mid-infrared spectral region - crucial for applications such as exoplanet transit spectroscopy and vibrational fingerprinting of molecules - has remained a major challenge, primarily due to material limitations and scalability constraints. Here, we report on the development of SNSPDs based on tungsten germanide, a novel material system that combines high mid-infrared sensitivity with compatibility for large-scale fabrication. Our detectors exhibit saturated internal detection efficiency at wavelengths up to 29 μm, while using 2.7x thicker films (8 nm vs 3 nm) and up to 4.5x wider nanowires (360 nm vs 80 nm) compared to mid-infrared-optimized SNSPDs fabricated from tungsten silicide. This advance will enable scalable, high-performance single-photon detection in a spectral region that was previously inaccessible, opening new frontiers in remote sensing, thermal imaging, environmental monitoring, molecular physics, and astronomy.
Extending single-photon detection capabilities into the mid- infrared is expected to have far-reaching implications for long-wavelength quantum optics, quantum and free-space communication, astronomy, environmental monitoring, and fundamental molecular sciences. We showcase the development of short-wave infrared (2.2-2.3 µm) and mid- wave infrared (3.0 µm) superconducting nanowire single-photon detectors (SNSPDs). In both wavelength ranges, we venture beyond state-of-the-art and achieve the best-reported system detection efficiencies and specific detectivity. We discuss the challenges in cryogenics, optics, and SNSPD design and use our mid-infrared single-photon detection to characterize emerging materials platforms and quantum emitters in a previously unattainable manner.