Center for Functional Nanomaterials Seminar

As computational workloads continue to grow, reducing the energy cost of information processing has become a critical challenge. Reversible computing, where logic operations can proceed without energy dissipation, offers a promising path forward. My research focuses on developing ballistic reversible superconducting circuits that use fluxons and antifluxons in long Josephson junctions (LJJs) to represent and process information. These circuits operate without external power, relying solely on the inertia of flux quanta to perform computation near the thermodynamic limit of energy efficiency. In this talk, I will present the design and experimental progress of a ballistic flip-flop (BFF) gate, a fundamental element of Reversible Fluxon Logic (RFL). The BFF employs a two-polarity detector that distinguishes and routes fluxons of opposite polarity, enabling logical state recognition and reversible gate operations. Our experiments demonstrate low-energy fluxon propagation through discrete LJJs with energy dissipation as low as 0.32 zJ per operation, achieved at cryogenic temperatures in a 4K cryogen-free refrigerator. These results represent an important step toward unpowered, ultrafast superconducting logic, demonstrating performance that is faster and more energy-efficient than conventional CMOS technology. I will also briefly discuss related work on high-Tc superconducting digital circuits fabricated using focused helium-ion beam irradiation, as well as my experience with superconducting transmon qubits, flux-qubit–NV center hybrid systems, and Nb resonator arrays for investigating two-level systems. These studies establish a foundation for integrating superconducting digital electronics with quantum hardware, paving the way for energy-efficient qubit control, high-fidelity readout, and scalable quantum–classical interfaces. Reversible logic provides a pathway toward sustainable fast classical computing and offers significant potential for energy-efficient quantum control, readout, and cryogenic signal processing in future quantum technologies.