Dissertation Committee Chair: Christopher Lobb
Committee:
Kevin Osborn (Co-chair)
Steven Anlage
Alicia Kollar
John Cumings (Dean’s representative)
Abstract: We report recent achievements toward understanding the nanoscale two-level systems (TLS) within the oxide layers of aluminum. TLSs create a major decoherence source in quantum information processors. We utilize three techniques to understand TLS, i.e., (1) a traditional power dependent loss, which provides the information of collective TLS effects, (2) spectroscopy of individual TLSs by DC-tuning and (3) two-tone spectroscopy of ensemble TLSs by a second saturation tone. We realize the behaviors of TLSs in different structural phases have distinguished features. Utilizing the DC-tuning feature of our sensor, we further extract dipole moments from individual TLSs and provide the moment histograms of two aluminum oxide films. We observe polycrystalline oxide has small average dipole moment and a single-peak histogram suggesting a single TLS origin. On the other hand, amorphous oxide has a wide spread of dipole moment values probably due to the nature of oxygen deficiency content. TLSs in both bulk films show a square root dependency of power indicating the TLSs can be treated as stable in frequency. However, TLSs on the surface fit well with the model assuming that TLS frequencies are under stochastic fluctuations resulting in a weak dependency of power. Moreover, TLSs in polycrystalline phase are relatively stable in the time domain than TLSs in amorphous phase.
Location: PHYS 1201