Periodic Reporting for period 2 - RESPITE (RECONFIGURABLE SUPERCONDUTING AND PHOTONIC TECHNOLOGIES OF THE FUTURE)
Reporting period: 2024-03-01 to 2025-08-31
Neuromorphic computing, inspired by the brain's structure and function, is an emerging field with applications in machine learning, remote sensing, automotive, biomedicine, and defense. Despite recent successes surpassing supercomputers in certain tasks, emulating human brain performance in vision and recognition remains challenging due to hardware limitations. Metal-oxide-semiconductor (CMOS) technology and multi-level memristors struggle with scaling, causing optical losses and high power consumption. The RESPITE project aims to advance neuromorphic computing by combining superconducting nanowire single-photon detectors (SNSPDs) for low-loss, single-photon-level vision, and superconducting Joule switches (SJSs) and cryogenic phase-change materials (PCMs) for artificial neural networks (ANNs). Leveraging superconducting elements, the project targets unprecedented sensitivity and minimal energy dissipation. RESPITE develops a thermoelectric simulation platform, single-photon imagers, low-dissipation neurons, programmable synaptic weights, and a simulation framework for ANNs. Proof-of-concept devices will scale into technology demonstrators showcasing RESPITE's capabilities.
(i) Benchmarking and Modeling RESPITE’s ANNs: A hardware-specific simulation platform has been developed to benchmark and model RESPITE's ANNs. Using this model, efforts are made to optimize the hardware overheads and mimic hardware-specific constraints.
(ii) SJSs for Fast and Low-Dissipation Switching, Logics, and Memory: Superconducting nanowires are explored for low-dissipation computing elements. A new design using thermal unilateral coupling has been developed. The resulting cryogenic components show fast switching and logic operations with minimal energy dissipation. Multi-input devices form unique reconfigurable logic devices.
(iii) SJSs for Controlling SNSPDs Recovery Time: SJSs are incorporated in the readout circuit of SNSPDs and used as a tunable cryogenic resistor to control the recovery time of the detector and demonstrate faster detection rates.
(iv) Thermoelectric-SPICE Simulation Platform: A Python-based simulation package has been developed to understand the complex dynamics of superconducting components, focusing on electric-thermal coupling and phenomena like current backflow. This tool integrates thermoelectrical models with SPICE for circuit simulation, enabling successful validation tests and ongoing adaptations to incorporate various superconducting elements efficiently. It is openly available on GitHub.
(v) SNSPD-based Imager: An imager based on SNSPD square arrays developed to mimic a retina for vision tasks in RESPITE. This includes optimized signal routing and biasing of pixels, targeting an operation wavelength of 1550 nm. Prototypes of 6x6 and 12x12 SNSPD arrays have been developed and tested with encouraging results. Optimization efforts are underway, as are preparation steps for further scaling up the array size with adequate readout and software.
(vi) Superconducting Amplifiers: A new design uses superconducting nanowires for cryogenic amplification.
(vii) Novel Cryo-PCMs: A promising cryo-PCMs material candidate was identified. An optimized process to produce thin films was developed, and static film characterization efforts are ongoing. Production of memory cells and dynamic characterization is underway.
(viii) SiC Integrated-Photonics for PCM Optical Programming: Novel SiC-based resonators are being developed for optical programming of PCM cells using waveguide-based techniques is being evaluated
(ix) Correcting Mode-Mixing Errors in Optical Communication With Reservoir Computing: A simulation framework was developed for turbulence-induced wavefront distortion compensation for orbital angular momentum multiplexed free-space optical communication and for mode mixing in multimode fibers.
(ii) SJSs for Fast and Low-Dissipation Switching, Logics, and Memory: Superconducting nanowires are explored for low-dissipation computing elements. A new design using thermal unilateral coupling has been developed. The resulting cryogenic components show fast switching and logic operations with minimal energy dissipation. Multi-input devices form unique reconfigurable logic devices.
(iii) SJSs for Controlling SNSPDs Recovery Time: SJSs are incorporated in the readout circuit of SNSPDs and used as a tunable cryogenic resistor to control the recovery time of the detector and demonstrate faster detection rates.
(iv) Thermoelectric-SPICE Simulation Platform: A Python-based simulation package has been developed to understand the complex dynamics of superconducting components, focusing on electric-thermal coupling and phenomena like current backflow. This tool integrates thermoelectrical models with SPICE for circuit simulation, enabling successful validation tests and ongoing adaptations to incorporate various superconducting elements efficiently. It is openly available on GitHub.
(v) SNSPD-based Imager: An imager based on SNSPD square arrays developed to mimic a retina for vision tasks in RESPITE. This includes optimized signal routing and biasing of pixels, targeting an operation wavelength of 1550 nm. Prototypes of 6x6 and 12x12 SNSPD arrays have been developed and tested with encouraging results. Optimization efforts are underway, as are preparation steps for further scaling up the array size with adequate readout and software.
(vi) Superconducting Amplifiers: A new design uses superconducting nanowires for cryogenic amplification.
(vii) Novel Cryo-PCMs: A promising cryo-PCMs material candidate was identified. An optimized process to produce thin films was developed, and static film characterization efforts are ongoing. Production of memory cells and dynamic characterization is underway.
(viii) SiC Integrated-Photonics for PCM Optical Programming: Novel SiC-based resonators are being developed for optical programming of PCM cells using waveguide-based techniques is being evaluated
(ix) Correcting Mode-Mixing Errors in Optical Communication With Reservoir Computing: A simulation framework was developed for turbulence-induced wavefront distortion compensation for orbital angular momentum multiplexed free-space optical communication and for mode mixing in multimode fibers.
1. Cryo-phase-change memory – phase-change memory technology is a mature technology, particularly for binary memory applications, that has led to commercial products. Its use for in-memory and neuromorphic computing, i.e. to act as weights/synapses is well developed in a laboratory setting. However, extending its operation to cryogenic temperatures as planned in the present project is completely novel, and the development of cryogenic a new phase-change memory material and devices is identified as a potentially exploitable outcome of the project. So far, the theoretical considerations are promising and the fabrication of the new phase change material is underway. Furthermore, following an extensive literature review, we have found no indication of competing work. That said, the exploitation potential as well as the impact of this development highly depends on the actual performance of phase change memory devices based on the new material platform. Once measurements indicate promising cryo-phase changes in memory properties, we believe that there would be ample room for filing patent(s) and for subsequent exploitation.
2. Innovative superconducting nanostructures with integrated joule heaters were implemented and tested. The performance outmatches state-of-the-art devices to the best of our knowledge achieving 2 ns switching speed and ~500 attojoule switching power. In addition, and for the first time, we have used our new superconducting joule switches (SJS) to create full binary logic gates such as NOT, AND, OR, NAND, and NOR with power consumptions in the femto-joule regiemes. This latter achievement, paves the way for implementation of arbitrary SJS logics with unprecedented performance and, unlike competing technologies such as RSFQ (rapid single flux quantum), straightforward scalability. The improved switches were found to be not patentable, but we were able to find a new design allowing for reconfigurable logic, and a patent application was submitted to protect the IP.
3. Single-photon imagers based on 2D arrays of SNSPDs – Fast and efficient detection in the VIS-NIR range was demonstrated for fiber-coupled SNSPDs. We aim to extend SNSPD-based detection to large arrays and free-space coupling for quantum applications, imaging and free-space communications. There are already reports on 2D arrays of SNSPDs in the literature. SQ plans to maintain the details of the imager under development as a trade secret and use the internal infrastructure of the company to market them within an existing customer base one they reach a satisfactory level of maturity.
2. Innovative superconducting nanostructures with integrated joule heaters were implemented and tested. The performance outmatches state-of-the-art devices to the best of our knowledge achieving 2 ns switching speed and ~500 attojoule switching power. In addition, and for the first time, we have used our new superconducting joule switches (SJS) to create full binary logic gates such as NOT, AND, OR, NAND, and NOR with power consumptions in the femto-joule regiemes. This latter achievement, paves the way for implementation of arbitrary SJS logics with unprecedented performance and, unlike competing technologies such as RSFQ (rapid single flux quantum), straightforward scalability. The improved switches were found to be not patentable, but we were able to find a new design allowing for reconfigurable logic, and a patent application was submitted to protect the IP.
3. Single-photon imagers based on 2D arrays of SNSPDs – Fast and efficient detection in the VIS-NIR range was demonstrated for fiber-coupled SNSPDs. We aim to extend SNSPD-based detection to large arrays and free-space coupling for quantum applications, imaging and free-space communications. There are already reports on 2D arrays of SNSPDs in the literature. SQ plans to maintain the details of the imager under development as a trade secret and use the internal infrastructure of the company to market them within an existing customer base one they reach a satisfactory level of maturity.