In May 2026, we congratulate Dr. Emma Batson, Dr. Camron Blackburn, and Dr. Matteo Castellani on their succesful thesis defenses!
Emma Batson successfully defended her PhD thesis entitled “Counting Events in Superconducting Magnesium Diboride and Niobium Nitride Thin-Film Strips” on May 6, 2026.
Abstract:
Detection of single infrared photons at wavelengths beyond the silicon bandgap is necessary to enable quantum communication, dark matter search, deep space communication, and deep imaging of biological tissues. Superconducting nanowire single-photon detectors (SNSPDs) could fill this technological need. However, existing SNSPDs require low operating temperatures which limit their utility in environments with constraints on space, power, or operating cost. Moving to material platforms with higher transition temperatures could open up a broader application space, but fabrication challenges and poorly-understood material and device physics have been major obstacles to reproducible and scalable operation of SNSPDs at elevated operating temperatures.
In this thesis, we study novel fabrication techniques for SNSPDs in magnesium diboride (\MgB) and reveal a simple mechanism for unintuitive device behaviors at high fractions of \Tc, demonstrating paths forward to 1) more reliably fabricate \MgB\ devices with operating temperatures from 10-20~K and 2) engineer materials to operate at higher fractions of \Tc.
Towards the first goal, we simulate and perform irradiation of a micron-wide \MgB\ detector with 30-keV helium ions. The device is at first insensitive to photons, but after irradiation it detects 1550-nm light at 1000~cps at 10~K with few-photon sensitivity. Towards the second goal, we incorporate a realistic thermal Langevin term and spatial variations of \Tc\ based on grain distribution measurements into a numerical TDGL solver and simulate dark count rates in devices of different geometries, then compare the results to experimental data. We demonstrate quantitatively that spatial inhomogeneity can explain switching current suppression and that including simple Langevin mechanics in a carefully applied time-dependent Ginzburg-Landau (TDGL) model can explain the unintuitive decrease of switching rate at high temperatures. This model can be used to make quantitative predictions about material engineering for improved device performance, potentially enabling increases in both operating current and temperature with respect to their critical values. Finally, we present results on the usage of different etching strategies for producing nanoscale \MgB\ devices, and show that irradiation of 400-nm-wide \MgB\ constrictions with 125-keV electrons modifies sheet resistance and retrapping current in a way similar to helium ion irradiation.
With these advances, we lay the groundwork to operate SNSPDs at higher temperatures in order to expand their feasibility in different applications.
Abstract:
The world’s artificial intelligence data centers are on track to consume more electricity than many industrialized nations, but the silicon transistors powering them dissipate energy 10,000 times above the physical minimum dictated by thermodynamics. In contrast, the Adiabatic Quantum Flux Parametron (AQFP) is a superconducting digital logic device capable of switching at energies near this fundamental thermodynamic limit, i.e. AQFP dissipates about 10^-21 J per operation at 5 GHz. Even accounting for a ~1000 W/W cryogenic cooling overhead to maintain superconducting operation at 4 K, this represents roughly 100× lower energy dissipation than the ~10^-16 J switching energy of modern CMOS transistors. Yet superconducting digital logic has long struggled to translate device-level efficiency into practical system-level gains, hindered by the absence of dense superconducting memory, complex clocking networks that limit scalability, and, until recently, the continued dominance of Moore’s law CMOS scaling.
This dissertation demonstrates how AQFP circuits can move beyond device-level promise toward system-level viability through contributions at four levels of the hardware abstraction stack. First, I develop and experimentally characterize synchronizer circuits that relax AQFP’s rigid timing requirements, enabling scalable multi-clock domain designs. Second, I design, fabricate, and test a compact AQFP SR-Loop register file for low-level on-chip memory and characterize Long Josephson Junction devices as a candidate technology for future high-capacity cryogenic delay-line memories. Third, I introduce a high-throughput dataflow microarchitecture that exploits AQFP’s clocked pipeline structure to achieve high compute utilization on AI workloads. Fourth, I extend established CMOS accelerator modeling tools to superconducting electronics, enabling the first quantitative full-stack comparison between AQFP and CMOS systems on real-world AI workloads. Taken together, these contributions chart a practical path toward scalable superconducting computing with the potential for orders-of-magnitude improvement in energy performance.
Matteo Castellani successfully defended his PhD thesis entitled “Superconducting Nanowire Electronics for Single-Photon Detector Control and Readout” on May 1, 2026.
Abstract:
Quantum technologies are driving the development of large-scale cryogenic systems for communication, computation, and sensing. Superconducting nanowire single-photon detectors (SNSPDs), with their exceptional sensitivity and timing resolution, are central to many of these platforms, including photonic quantum circuits and classical imaging systems for space exploration and biological analysis. However, scaling SNSPD arrays and any other cryogenic architectures introduces major challenges: managing the complexity and heat load of readout cables connecting devices to room-temperature stages; enabling low-latency edge processing; and distributing power efficiently within the cryostat.
Superconducting electronics, with ultra-low energy consumption and intrinsic cryogenic compatibility, can help address these challenges. In particular, superconducting nanowires, beyond sensing, offer a promising alternative or complement to Josephson junctions, the gold-standard device for superconducting circuits. Owing to their simple fabrication, resilience to magnetic flux noise, and CMOS-compatible impedance, nanowire electronics are attractive for building co-processors monolithically integrated with SNSPDs.
This thesis presents four nanowire-based circuits for integrated signal processing, control, and power handling. A photon counter is developed for pixel-level digitization in SNSPD arrays, and a reconfigurable logic gate is introduced to enable on-chip photon-coincidence detection for quantum photonic feedforward. A comparator is integrated with a photon-number-resolving SNSPD to discriminate single-photon events for heralding operations, and superconducting diodes and bridge rectifiers are demonstrated for cryogenic power distribution. Together, these results highlight the potential of a unified superconducting platform for sensing and electronics to scale quantum and classical architectures.