The Physics of Superconducting Microwave Resonators

The Physics of Superconducting Microwave Resonators

Thesis by

Jiansong Gao

In Partial Fulfillment of the Requirements for the Degree of

Doctor of Philosophy

California Institute of Technology Pasadena, California 2008

(Defended May 28, 2008)

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c 2008 Jiansong Gao All Rights Reserved

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This thesis is dedicated to my dearest wife, Yingyan, who has been a constant source of inspiration and support through all stages of my life since high school, and to our lovely boy, Logan, who came

to our family just before the thesis was finished.

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Acknowledgments

First, I would like to thank my advisor Professor Jonas Zmuidzinas for giving me the opportunity to work on this great project of MKID. I came to Caltech in 2002 and originally planned to work in the field of optics. Failing to join any optics group on campus, I luckily ran across Jonas in a talk on MKID he gave to the students in applied physics major. These detectors made of resonators immediately attracted my interest. I still remember the interview that took place at Jonas' office. Desperate to join a research group, I was advertising how good I was in both theory and experiment. At some point I mentioned that I had taken a mathematical course on stochastic process, which had caught Jonas' attention. He immediately gave me a quiz, asking me to state the Weiner-Kinchin theorem. Fortunately, I was able to give the correct answer promptly. He was very satisfied and said, "Let me show you the lab."

That was how I joined the MKID group and also where my journey of noise study started. It turns out that in the past five years, there wasn't a single day in which I wasn't dealing with the noise spectrum, stochastic process or the Weiner-Kinchin theorem. And of course, I enjoyed it very much. Noise in superconducting microwave resonators is a problem that has never been studied before. It is challenging but equally fascinating. Jonas has given me enough freedom in tackling the problem, as well as critical advice in times I could not find my way out. Every discussion with him boosted my knowledge, deepened my understanding and led to small or big progress in my research.

I also enjoy and benefit a lot from the collaboration with a group of great people. The cryostat and the measurement setup are all taken care of by Dr. Ben Mazin. This has saved me a huge amount of time on the hardware which I'm not good at. Also, as the first student on MKID project, his thesis is the starting point of my work and in some sense I am harvesting the fruits of his previous hard work. Thanks to the fact that an international student has no easy access to JPL. So I don't have to worry about the fabrication at all ? Dr. Rick LeDuc at the microdevice lab in JPL will always turn my drawings into the best made devices. Some other devices are supplied by Miguel Daal, my collaborator and also my best friend from UC Berkeley. His devices appear to be more noisy than Rick's devices, which may be a bad thing for a detector but not bad for me, who study noise on purpose, at all. It turns out his devices has led to some of the most important progress. We also spent a lot of afternoons in front of Red Door Cafe, talking about ideas that were too crazy

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or too stupid to be discussed with professors. Dr. Peter Day from JPL supervised me in the year when Jonas was ill. He has given me a lot of guidance both on theory and experiment, as well as on paper writing. Anastasios Vayonakis taught me a lot of things, from how to use a wire bonder to how to repair a car. Asking him about microwave engineering and cryogenic instrumentation has always been an shortcut for me to solve practical problems in these areas. I would like to give special thanks to Prof. John Martinis form UC Santa Babara, who is very enthusiastic on the noise problem I am working on. Some of my work was inspired by his paper and the discussions with him. Professor Sunil Golowala and Bernald Sadoulet, graduate students Megan Eckart, Shwetank Kumar, James Schlaerth, Omid Noroozian and David Moore have all given me many help and support to this thesis work.

I would also like to thank my parents, my sister and members in my extended family for their remote love and support.

Funding for this project has been provided by NASA, JPL DRDF, and the generous contributions of Alex Lidow, Caltech Trustee.

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