Study of atomic two-level defects within a Josephson junction proxy

In superconducting qubits, thermally grown aluminum oxide is generally used as the barrier between two superconducting electrodes to form the S-I-S Josephson junction (JJ). This oxide is amorphous and is known to contain random, atomic-sized two-level systems (TLSs) which are a source of decoherence in superconducting qubits. Here, we present a study of TLSs in parallel plate capacitors mimicking a JJ (Al/AlOx/Al), but where the dielectric layer is 20 nm and therefore block the tunneling supercurrent. In this JJ proxy, the defects near the in AlOx and near the interface ofAl/AlOx can be studies using a new analysis method only demonstrated before with a different dielectric. Using a resonator device with a four-arm bridge capacitor, one can tune the frequency of TLSs by applying a DC electric field, and observe individual TLSs reach degeneracy with the resonator in a demonstration of cavity QED with TLS. The transmission versus applied electric field would give us the TLS dipole moment’s z-component. We will study these resonators in an effort to better understand TLSs within typical JJs.