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Coherent Optical Spectroscopy of a Single Semi- Conductor Quantum Dot

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Coherent Optical Spectroscopy of a Single Semi- Conductor Quantum Dot COHERENT OPTICAL SPECTROSCOPY OF A SINGLE SEMI- CONDUCTOR QUANTUM DOT by Xiaodong Xu A dissertation submitted in partial ful¯llment of the requirements for the degree of Doctor of Philosophy (Physics) in The University of Michigan 2008 Doctoral Commitee: Professor Duncan G. Steel, Chair Professor Roberto D. Merlin Professor Theodore B. Norris Professor Georg A. Raithel Associate Professor Luming Duan Xiaodong Xu °c 2008 All Rights Reserved ACKNOWLEDGEMENTS 6 years ago when I joined the group, Elaine gave me a lab tour. I saw Jun and Yanwen sitting in the dark and taking data. At that time there was a big chiller in the time domain lab and making huge noise. Frankly, I was a bit scared since I had never been in a real lab before graduate school. I was wondering whether I could do well in such a lab as an experimental physicist. Now it is 6 years later and I am so happy to say that I made it. During the entire graduate school, there are so many people I would like to thank. The ¯rst and the most important person I would like to thank is my advisor Professor Duncan Steel. I am so lucky to have Duncan as my advisor. He is such a smart scientist with great personality. His working ethics and conscientious attitudes inspired me a lot in research. He always tries to create the best education and research support for me. One of the greatest things is that he tried to develop my weakness, exploit my strength, and carefully shape me to be a good physicist. Duncan is also an advisor with a great sense of humor and it is so much fun to work with him. I would like to thank Professor Paul Berman. His lectures of quantum optics is the class I enjoyed most in my graduate school, which opened the door for me to the wonderful world of quantum optics. He is always there when you need help. He is so knowledgeable that whenever I walk into his o±ce with a question, he always have an answer for me. I would to thank my committee members: Professor Luming Duan, Roberto Mer- line, Ted Noriss and Georg Raithel. Although Luming is a theorist, he is so smart and understand all the experimental details that sometimes it makes me feel like he is ii an experimentalist. Ted is such a great lecturer that I learned a lot of optical knowl- edge from his classes on classical optics and ultrafast optical science. Roberto's o±ce is next door to Duncan's. I feel like every time when I was meeting with Duncan, Roberto was there. I enjoyed all the discussions with him both on science and on the \problems" in China. For the work in this thesis, I gave my special thanks to my collaborators: Dr. Dan Gammon's research group in NRL and Prof Lu Sham's research group in University of California at San Diego. Allan provides the best quantum dot samples in the world, which makes all the work in this thesis possible. Morgan gave me a lot of help when I started to work on the bias controlled quantum dot samples. Lu is that type of physicist who stands on top of the mountain and always gives you the best help. I would also like to thank Wang's creative thoughts on the nuclear spin control work presented in Chapter 7. Clive gave me a lot help on the theoretical calculations of the optical pumping experiment, which is presented in Chapter 5. There were also a lot of fun discussions with Matt, Danny, Michael, Sophia and Renbao, Semion in the conferences. One of the wonderful things about working in Duncan's lab is that I always work with a group of talented people. It is impossible to ¯nish my thesis work without the help of my labmates: Liz, Ealine, Gurudev, Jun, Yanwen, Qiong, Erik, Katherine, Bo, Vasudev, John and Chris, and the visiting scholars: Alberto and Geng. My ¯rst mentor was Ealine. She share with me her own experience and also assigned me a few small projects, which helped me a lot to get a good start in the lab. During that time, I learned the calculations for the bi-exciton system and started the ¯rst experience in the experiment. Later on, I worked with Yanwen, a very smart labmate with a lot of patience. She is a also a good friend and gave me a lot of suggestions both on science and life. I used to call her my intelligence o±cer No.1. After that I worked with Gurudev on the charged quantum dots system. I learned a lot from him about time domain experimental techniques, the four-level calculations, and the coherent control experiment. Those are really fun experience. Starting from my third year I worked with Jun. He is such a smart guy with great working attitude. He taught me how iii to use the instruments in the CW lab, which laid a foundation for my thesis work. Eirk is a great labmate to have and it is so much fun to have him around. I enjoyed all the discussions with him on science, sports, and some \spread" o®enses on peach blossoms. He is also a \xiong di" and my intelligence o±cer No.2. I was so lucky to have Bo as my lackey since he is a super talented guy. We worked together on many experiments. He is so patient and did wonderful jobs on proof reading all my papers. Katherine also helped me a lot on proof reading some of the papers and all the thesis chapters. I also thank John and Vasudev for proof reading part of my thesis. Beyond science, I won't forget all the fun experience I had with this wonderful group of guys, such as pot lucks, football parties, Friday lunches and the great Virginia white water rafting. I would also thank the past graduate students in the lab: Gang, Tod and Anthony. Especially Anthony gave me a lot of suggestions when I started to work on the self-assmebled quantum dots system. I would also like to thank all my friends. The life in Ann Arbor would not have been as much fun as it was without those guys. BBQs, playing cards, sports and PC games with those guys gave me extra dimension of happiness. Finally, I would like to thank my family. Although I cannot see them often, they always support me and encourage me whenever I talked to them. Once my mom told me that my uncle was wondering whether I was held in the graduate school because of bad grades since I did not graduate after the ¯fth year. She said it was ok to tell them the truth, they would always support me. The best thing in the graduate school is that I got married with Ying. It is impossible for me to ¯nish my PhD without her support. Although she was also a PhD student, she did all the house work and took care of me very well. She also kept checking my research progress with questions like \Did you get a good QD state today?". I was joking to her that she actually ¯nished two PhDs. But certainly, to be married with her is the best and smartest thing I have ever done in my life. iv TABLE OF CONTENTS ACKNOWLEDGEMENTS .......................... ii LIST OF FIGURES ............................... viii LIST OF APPENDICES ............................ ix CHAPTER 1. Introduction to Quantum Dots .................... 1 1.1 Quantum Dot Light Emitting Diodes (LED) . 2 1.2 Quantum Dot Solar Cell . 5 1.3 Quantum Dot Quantum Computing . 6 1.4 Thesis chapter outlines . 9 2. Samples, Experimental Techniques and Theoretical Background 13 2.1 Schottky Diode Sample Structure . 14 2.2 Experimental setup and detection techniques . 15 2.3 Physical models and the polarization selection rules for the QD system . 18 2.3.1 Magnetic Field Applied in the Faraday Geometry . 19 2.3.2 Magnetic Field Applied in the Voigt Geometry . 20 2.4 The heavy and light hole mixing e®ect . 21 2.4.1 Zero Magnetic Field . 22 2.4.2 Hole Mixing E®ect in The Presence of an External Magnetic Field . 22 2.4.3 Chapter 2 Summary . 24 3. Coherent Optical Spectroscopy of a Single Neutral Exciton .. 27 3.1 The Optical Characterization of a Neutral Quantum Dot . 27 3.2 A neutral QD driven by a strong optical ¯eld . 30 3.2.1 Optical bloch equations for a QD driven by a strong optical ¯eld . 31 3.2.2 The Demonstration Autler-Townes Splitting . 33 3.2.3 The demonstration of the optical Mollow absorption spectrum 36 v 3.3 Chapter 3 Summary . 38 4. The Optical Mollow Absorption Spectrum of a Single Nega- tively Charged Quantum dot ..................... 41 4.1 The Physical Model of a Trion State at Zero Magnetic Field . 42 4.2 Theory for the Trion Mollow . 43 4.3 Trion Mollow Spectrum with a Strong Resonant Pumping . 45 4.4 Trion Mollow Spectrum with a Detuned Pump . 47 4.5 Chapter 4 Summary . 49 5. Fast Electron Spin State Preparation in a Single Negatively Charged Quantum dot ......................... 52 5.1 Polarization Dependent Study of a Singly Charged Quantum Dot at Zero Magnetic Field . 53 5.2 Nonlinear Fano Interference E®ect . 55 5.3 Fast Spin State Initialization . 60 5.3.1 Theoretical Calculations of Fast Spin State Initialization . 60 5.3.2 Experimental Results . 64 5.4 Nonlinear Di®erential Transmission Measurement of the Optical Pumping E®ect .
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