Significant changes to projected dipoles for two-level systems using alternating bias

Two-level systems (TLSs), which originate in amorphous materials, are energy states that couple electrically to qubits and resonators while also coupling to mechanical modes in a material. This coupling results in energy loss for both qubits and resonators. To understand the fundamental properties of TLSs, we probed them with an LC oscillator with a tri-layer capacitor. A high density of TLSs resides in the capacitor dielectric of amorphous oxide (a-Al₂O₃), and the small volume of the capacitor strongly couples resonant TLSs to the resonator mode. We can adjust the energy of TLSs by slowly varying an applied bias that is galvanically connected to our capacitor pads while operating the resonator in the single photon regime. Tuning the TLS energy adjusts their frequency in and out of resonance with the resonator, allowing us to observe avoided crossings and extract their projected dipole moments. We then apply an alternating bias that mimics alternating bias assisted annealing but at cryogenic temperatures. Results show a significant change in the dipole moment of coupled TLSs. After temperature sweeps to 10 K, we observe a shift of dipole moments back to pre-biasing magnitudes. Interestingly, intrinsic loss tangents show no change before or after biasing at cryogenic temperatures, indicating that intrinsic loss is likely not related to strongly coupled TLSs. [LLNL-PRES-2000696]