Engineering Current Phase Relations with Superconducting Quantum Point Contacts for Novel Qubits

Superconducting-semiconducting (S-Sm) josephson junctions conduct current through discrete Andreev Bound States (ABS), which directly correspond to classical conduction channels. In typical planar josephson junctions there are hundreds of ABS with varying transparency, so the study of individual modes has been predominantly confined to nanowires. However, by creating a superconducting quantum point contact, which exhibits both stepwise normal conductance and critical current, we can study individual ABS in a 2DEG based device. By gating down to the few channel regime we ensure that only high transparency conduction channels remain. Using a Superconducting QPC squid loop, the current phase relationship can be modulated and studied in both the relatively lower transparency ungated limit and the high transparency few mode limit. Such in situ control over both junction transparency and the current phase relation opens pathways toward novel qubit designs and applications.