Study of two-level defects in a thin amorphous material by electrical capacitor bridge

In superconducting qubits, thermally grown aluminum oxide is usually used as a barrier between two superconducting electrodes to form an S-I-S Josephson junction (JJ). This leads to an inevitable source of decoherence in superconducting qubits. Here, we present a study of TLSs in parallel plate capacitors mimicking JJ (Al/AlOx/Al) due to the use of a thin AlOx film. These will be as thin as 10 nm,and therefore within an order of magnitude of the JJ barrier thickness. Using a four-arm bridge capacitor design, we can tune the frequency of TLSs by applying a DC electric field, and observe individual TLSs reach degeneracy with resonator in a demonstration of cavity QED with TLS. The transmission versus applied electric field will also give us the TLS dipole moment’s z-component. We will study these resonators over a range of thicknesses and determine if the TLSs are affected by proximity to the electrodes which is less than the superconducting coherence length.