CM Seminar - measuring current-phase relations in exotic Josephson junctions

Abstract: Theorists have proposed various exotic Josephson junctions both for fundamental demonstrations of exotic behaviors and as highly desirable platforms for qubits. The supercurrent, I, versus the phase, ϕ, across the junction is called the current-phase relation (CPR) and reveals fundamental properties of the junction. Using a scanning SQUID, we measure the CPR of individual Josephson junctions. In InAs nanowire Josephson junctions, we find skewed CPRs with small critical currents, indicating few-mode junctions with high transmissions. In gate-tunable junctions, we found that the CPR varied with gate voltage: Near the onset of supercurrent, we observed behavior consistent with resonant tunneling through a single, highly transmitting mode. The gate dependence is consistent with modeled subband structure that includes an effective tunneling barrier due to an abrupt change in the Fermi level at the boundary of the gate-tuned region. These measurements of skewed, tunable, few-mode CPRs are promising both for applications that require anharmonic junctions and for Majorana readout proposals.

Bio: Kathryn A."Kam" Moler is the Vice Provost and Dean of Research, the Marvin Chodorow Professor, and Professor of Applied Physics and of Physics at Stanford University. She conducts research in magnetic imaging, develops tools that measure nanoscale magnetic fields, and studies quantum materials and devices. Among other honors, she received a national Presidential Early Career Award for Scientists and Engineers, held a Packard Fellowship for Science and Engineering, received the William L. McMillan Award “for her fundamental studies of the superconducting pairing state, Josephson vortices, and the role of interlayer coupling in high-temperature superconductors,” and was elected a Fellow of the American Physical Society. To honor her sustained commitment to teaching, the American Association of Physics Teachers awarded her the Richtmyer Award for Outstanding Leadership in Physics Education, and Stanford appointed her as the Sapp Family Fellow in Undergraduate Education. She was previously the Senior Associate Dean of Natural Sciences in the School of Humanities and Sciences and the Director of the Stanford Nano Shared Facilities. She is a member of the NanoFront (TU-Delft/Leiden) Scientific Advisory Board and the Physics Frontier Center—Joint Quantum Institute Advisory Board.