Hot-spot relaxation time current dependence in niobium nitride waveguide-integrated superconducting nanowire single-photon detectors

Considerations for Neuromorphic Supercomputing in Semiconducting and Superconducting Optoelectronic Hardware

Any large-scale spiking neuromorphic system striving for complexity at the level of the human brain and beyond will need to be co-optimized for communication and computation. Such reasoning leads to the proposal for optoelectronic neuromorphic platforms that leverage the complementary properties of optics and electronics. Starting from the conjecture that future large-scale neuromorphic systems will utilize integrated photonics and fiber optics for communication in conjunction with analog electronics for computation, we consider two possible paths toward achieving this vision. The first is a semiconductor platform based on analog CMOS circuits and waveguide-integrated photodiodes. The second is a superconducting approach that utilizes Josephson junctions and waveguide-integrated superconducting single-photon detectors. We discuss available devices, assess scaling potential, and provide a list of key metrics and demonstrations for each platform. Both platforms hold potential, but their development will diverge in important respects. Semiconductor systems benefit from a robust fabrication ecosystem and can build on extensive progress made in purely electronic neuromorphic computing but will require III-V light source integration with electronics at an unprecedented scale, further advances in ultra-low capacitance photodiodes, and success from emerging memory technologies. Superconducting systems place near theoretically minimum burdens on light sources (a tremendous boon to one of the most speculative aspects of either platform) and provide new opportunities for integrated, high-endurance synaptic memory. However, superconducting optoelectronic systems will also contend with interfacing low-voltage electronic circuits to semiconductor light sources, the serial biasing of superconducting devices on an unprecedented scale, a less mature fabrication ecosystem, and cryogenic infrastructure.

Photon energy-dependent timing jitter and spectrum resolution research based on time-resolved SNSPDs

Superconducting nanowire-based single-photon detectors (SNSPDs) are promising devices, especially with unrivalled timing jitter ability. However, the intrinsic physical mechanism and the ultimate limit of the timing jitter are still unknown. Here, we investigated the timing jitter of the SNSPD response to different excitation wavelengths from visible to near-infrared (NIR) as a function of the relative bias currents and the substrate temperature. We established a physical model based on a 1D electrothermal model to describe the hotspot evolution and thermal diffusion process after a single photon irradiated the nanowire. The simulations are in good agreement with the experimental results and reveal the other influencing factors and potential ways to further improve the timing jitter of SNSPDs. Finally, we introduce a new time-resolved approach, where by collecting the instrument response function (IRF) of SNSPDs, the wavelength of the incident photons can be easily discriminated with a resolution below 80 nm.

Hotspot relaxation time of NbN superconducting nanowire single-photon detectors on various substrates

Hotspot relaxation time (τ_th) is one of the essential parameter which defines the maximum count rate of superconducting nanowire single-photon detectors (SNSPDs). We studied the τ_th for NbN-based SNSPDs on various substrates using the two-photon detection method based on the pump-probe spectroscopy technique. We observed that τ_th strongly increased with increasing bias current in the two-photon detection regime. In addition, the minimum hotspot relaxation time (τ_th)_min was not significantly affected by the bath temperature; this is different from the previous observations reported for WSi SNSPDs. In addition, a strong dependency of (τ_th)_min on the substrate was found. The minimum (τ_th)_min was 11.6 ps for SNSPDs made of 5.5-nm-thick NbN on MgO (100), whereas the maximum (τ_th)_min was 34.5 ps for SNSPDs made of 7.5-nm-thick NbN on Si (100). We presented a direct correlation between the values of τ_th and degrees of disorder of NbN films grown on different substrates.