Circuit-QED characterization of a topological Josephson junction

The search for topological superconductivity in topological insulator (TI) nanowires have attracted a lot of interest due to potential applications in the field of topologically protected quantum computation [1-3]. One route to emulate unconventional superconductivity is to build a topological Josephson junction from a TI nanowire (Bi₂Se₃) connected to two conventional superconducting electrodes (Al). Such topological Josephson junctions are expected to host Majorana zero-energy modes (bound states) when they are phase-biased at pi. The bound state spectrum of a junction hosting several transport modes consists of topological trivial Andreev bound states and topologically protected Majorana bound states. The phase dependence of those bound states has been studied experimentally using a circuit-QED-like setup, where the topological junction is embedded in a superconducting resonator. Here the frequency response of the coupled resonator/junction system to an externally applied magnetic field (phase bias) at various temperatures is used to deduce information about the phase dependence of the bound state spectrum of the junction. I detail, the contributions to the junction dissipation (which is directly reflected in the inverse quality factor of the coupled resonator/junction system) originating from zero-energy bound states and topological trivial Andreev bound states are rather distinct, which is mainly reflected in their phase bias dependence around and their evolution in temperature.