UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

Browse

Filters

20221

Settings

Subject: search.filters.subject.Two-level system

Search Results

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Quantum Circuit Studies with Two-Level Defects of Aluminum Oxide in a Polycrystalline Phase, Amorphous Phase, and at a Metal Surface
    (2022) Hung, Chih-Chiao; Osborn, Kevin D; Lobb, Christopher J; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This thesis reports on recent achievements toward understanding the nanoscale two-level systems (TLS) within aluminum oxide layers. I will discuss novel experimental and theoretical methods using superconducting resonator data to characterize the TLSs, which are deleterious to qubit coherence. This includes (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 find that the behaviors of TLSs in different structural phases have distinguishing features. Utilizing the DC-tuning feature of our sensor, we further extract dipole moments from individual TLSs and provide the moment histograms of the two aluminum oxide film types. We observe polycrystalline oxide has an average dipole moment = 2.6 Debye and a single-peak histogram consistent with a single TLS origin. On the other hand, TLSs in amorphous oxide have a wide spread of dipole moment values probably due to oxygen deficiency. Saturation slopes of TLSs in bulk films (polycrystalline and amorphous phases) show a square root dependence of power indicating an ignorable TLS-TLS interaction. Moreover, TLSs in the polycrystalline phase are more stable in the time domain than TLSs in the amorphous phase. Unlike the previous two bulk TLSs, TLSs at the metal-air interface require an explanation from the model assuming TLS frequencies are under stochastic fluctuations originating from TLS-TLS interaction since we find a weak power dependence. We also demonstrate the first published transmon qubits which are solely made from optical lithography. They have a comparable relaxation time and junction resistance to those made from e-beam lithography.