Meissner qubit: architecture, characterization and vortex-probing applications

Ku, Jaseung

Permalink

https://hdl.handle.net/2142/90582 Copy

Description

Title

Meissner qubit: architecture, characterization and vortex-probing applications

Author(s)

Ku, Jaseung

Issue Date

2016-04-20

Director of Research (if dissertation) or Advisor (if thesis)

Bezryadin, Alexey

Doctoral Committee Chair(s)

Eckstein, James

Committee Member(s)

• Thaler, Jon
• Clark, Bryan

Department of Study

Physics

Discipline

Physics

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Quantum computing
• Superconducting qubit
• Transmon
• Abrikosov vortex

Abstract

Quantum computing has drawn enormous attention in physics community in both scientific and technological perspectives. Among several promising architectures for quantum computer are superconducting qubits based on Josephson junctions. Over the last few decades, there has been a dramatic improvement on the coherence time by a few orders of magnitude from a few nanoseconds to about a hundred microsecond. Such improvements were possible due to the elimination or suppression of various decoherence sources. Thus, it is critical to investigate the origin of such decoherence to extend our understanding and practically improve the coherence time. For example, Abrikosov vortices knowingly could be one of the decoherence source, and yet the quantitative research on the interaction of a superconducting qubit with such vortices has been lacking. We present a new type of transmon split-junction qubit which can be tuned by Meissner screening currents in the adjacent superconducting film electrodes. The qubits were measured using a 3D microwave cavity in the dispersive regime at the base temperature 45 mK. The measurement protocols were based on the circuit quantum electrodynamics (cQED) architecture and so-called high-power measurement. The achieved period of oscillation with magnetic field was much smaller than in usual SQUID-based transmon qubits, thus a strong effective field amplification has been realized. The best measured relaxation time was of the order of 50 μs and the dephasing time about 40 μs. This Meissner qubit allows an efficient coupling to superconducting vortices, which were induced by external applied magnetic field. We intend to present a quantitative analysis of the radiation-free energy relaxation in the qubits coupled to the Abrikosov vortices. The estimated relaxation rate combined with vortex counting process provided a good agreement with the experimental results. Also, the observation of coherent quantum oscillations provides strong evidence that vortices can exist in coherent quantum superposition of different position states. According to our suggested model, the wave function collapse is defined by Caldeira-Leggett dissipation associated with viscous motion of the vortex cores.

Graduation Semester

2016-05

Type of Resource

text

Permalink

http://hdl.handle.net/2142/90582

Copyright and License Information

Copyright 2016 Jaseung Ku

Owning Collections