SPIN-PHOTON INTERFACE USING CHARGE TUNABLE QUANTUM DOTS
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The unconditional security of quantum networks and unparalleled acceleration of quantum algorithms enabled by “quantum computers” has motivated significant research across scientific communities. Among these different architectures to achieve such quantum information processing paradigms, a promising and straightforward proposal is the use of photons as flying qubits to transfer quantum information as well as local quantum memories to store and process quantum information. Toward this goal, it is very important to develop a type of quantum memory that can efficiently interface with photons while possessing good qubit properties, including a long coherence time and good scalability. To date, researchers have developed promising solid state quantum memory platforms, such as defects in diamond and other group IV compounds, rare earth ions hosted in various materials and self-assembled quantum dots. While each platform has its strengths and challenges, this thesis will focus on charge tunable InAs quantum dots grown inside a GaAs matrix that is doped into a PN junction. Though not long after the first demonstration of optically active self-assembled quantum dots, researchers have already developed the idea to sandwich them inside a PN junction to tune their charge status. The spin manipulation in the strong coupling regime has been mostly using these dots without PN junction doping, which has resulted in limited dot-cavity cooperativity and spin lifetime due to electron tunneling.
In this thesis, I will first show the design, fabrication and characterization of several common photonic cavities, with their performance compared. Second I will show strong coupling between a negatively charged quantum dot and photonic crystal cavity, where the resonant cavity reflectivity is strongly dependent on the spin state. Third I will show that the electron spin lifetime (T1) can be significantly shortened by an off-resonant laser that reaches the device surface. While the exact reason for this undesired effect is not clear yet, we did observe the thickness of the electron tunnel barrier of the quantum dot wafer can result in distinct spin properties. I will present electron spin T1 characterization across several different quantum dot samples with different electron tunneling barrier thickness. Lastly, I will present coherent control of electron spin using picosecond laser pulse and sidebands of modulated continuous wave laser with limited spin rotation fidelity due to the off-resonant laser induced deterioration of the spin properties.