COUPLING NITROGEN VACANCY CENTERS IN DIAMOND TO A NANOMECHANICAL OSCILLATOR
Oo, Thein Htay
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Oo, Thein Htay
Exotic aspects of quantum mechanics, such as quantum entanglement, can be exploited to solve computational problems that are impractical to solve with conventional computers. With the realization of robust solid-state qubits, such as Nitrogen Vacancy (NV) centers in diamond, an outstanding challenge is to develop experimental approaches that can control the interactions between individual qubits. This dissertation develops a diamond-based experimental system that exploits acoustic waves or mechanical vibrations to mediate interactions between spin qubits. This spin-mechanical system features three essential elements: robust qubits, high quality-factor diamond nanomechanical resonator, and strong spin- mechanical coupling, thus enabling a new and promising platform for pursuing solid- state quantum computer. For the spin-mechanical system, NV centers are created near the surface of a bulk diamond through nitrogen ion implantation followed by stepwise high temperature annealing. We successfully suppress environmental fluctuations and achieve NV centers with stable and spectrally narrow (< 50 MHz) fluorescence at low temperature, which is crucial for the spin-mechanical system. Diamond nanomechanical resonators with a fundamental frequency near 1 GHz have been successfully fabricated with a diamond-on-insulator approach. The resonators are suspended from a silicon substrate and are supported with long and thin tethers, decoupling the mechanical modes from the surrounding environment. Diamond nanofabrication is still in its infancy. Numerous fabrication problems occurring during etching, mask transfer, and wafer bonding have been painstakingly resolved. Strong spin-mechanical coupling is demonstrated via the strain coupling of the NV excited-states. The spin-mechanical coupling takes place through a 𝚲-type three- level system, where two ground-spin-states couple to an excited-state through a phonon-assisted as well as a direct dipole optical transition. Both coherent population trapping and optically-driven spin transitions have been realized. The coherent population trapping demonstrates the coupling between an acoustic wave and an electron spin coherence through a dark state, thus avoiding the short lifetime of the excited state. The optically-driven spin transitions can enable the quantum control of both spin and mechanical degrees of freedom. This dissertation includes previously published co-authored material.