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The Physics of Superconducting Microwave Resonators


Gao, Jiansong (2008) The Physics of Superconducting Microwave Resonators. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/RAT0-VM75.


Over the past decade, low temperature detectors have brought astronomers revolutionary new observational capabilities and led to many great discoveries. Although a single low temperature detector has very impressive sensitivity, a large detector array would be much more powerful and are highly demanded for the study of more difficult and fundamental problems in astronomy. However, current detector technologies, such as transition edge sensors and superconducting tunnel junction detectors, are difficult to integrate into a large array.

The microwave kinetic inductance detector (MKID)is a promising new detector technology invented at Caltech and JPL which provides both high sensitivity and an easy solution to the detector integration. It senses the change in the surface impedance of a superconductor as incoming photons break Cooper pairs, by using high-Q superconducting microwave resonators capacitively coupled to a common feedline. This architecture allows thousands of detectors to be easily integrated through passive frequency domain multiplexing.

In this thesis, we explore the rich and interesting physics behind these superconducting microwave resonators. The first part of the thesis discusses the surface impedance of a superconductor, the kinetic inductance of a superconducting coplanar waveguide, and the circuit response of a resonator. These topics are related with the responsivity of MKIDs. The second part presents the study of the excess frequency noise that is universally observed in these resonators. The properties of the excess noise, including power, temperature, material, and geometry dependence, have been quantified. The noise source has been identified to be the two-level systems in the dielectric material on the surface of the resonator. A semi-empirical noise model has been developed to explain the power and geometry dependence of the noise, which is useful to predict the noise for a specified resonator geometry. The detailed physical noise mechanism, however, is still not clear.

With the theoretical results of the responsivity and the semi-empirical noise model established in this thesis, a prediction of the detector sensitivity (noise equivalent power) and an optimization of the detector design are now possible.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:background limited detection; conformal mapping
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Applied Physics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Zmuidzinas, Jonas
Group:Astronomy Department
Thesis Committee:
  • Zmuidzinas, Jonas (chair)
  • Eisenstein, James P.
  • Bockrath, Marc William
  • Bellan, Paul Murray
Defense Date:28 May 2008
Non-Caltech Author Email:jiansong.gao (AT)
Record Number:CaltechETD:etd-06092008-235549
Persistent URL:
Gao, Jiansong0000-0001-9972-6220
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2530
Deposited By: Imported from ETD-db
Deposited On:11 Jun 2008
Last Modified:10 Mar 2020 23:27

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