Physics Theses and Dissertations

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https://hdl.handle.net/1794/2048

This collection contains some of the theses and dissertations produced by students in the University of Oregon Physics Graduate Program. Paper copies of these and other dissertations and theses are available through the UO Libraries.

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Browsing Physics Theses and Dissertations by Author "Allcock, David"

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    Easy on the Ions: Photon Scattering Errors from Far-Detuned Raman Beams in Trapped-Ion Qubits
    (University of Oregon, 2024-01-09) Moore, Isam; Allcock, David
    The viability of quantum computers depends on the development of scalable platforms with low error rates. Our "Oregon Ions" group has studied one such scalable architecture proposal including the limitations placed on logic gate fidelity by photon scattering. We studied spontaneous Raman scattering-induced errors in stimulated Raman laser beam-driven logic gates in metastable- and ground-manifold-encoded qubits. For certain parameter regimes, we found that previous, simplified models of the process significantly overestimated the gate error rate due to spontaneous photon scattering. We developed an improved model, which shows that there is no fundamental lower limit on gate error due to spontaneous photon scattering for electronic ground state qubits in commonly-used trapped-ion species when the Raman laser beams are red detuned from the main optical transition. Additionally, spontaneous photon scattering errors are studied for qubits encoded in a metastable D5/2 manifold, showing that gate errors below 10^-4 are achievable for all commonly used trapped ions. Furthermore, we extended this theory from hyperfine to Zeeman qubits and we measured scattering rates from far-detuned Raman beams in a metastable D5/2 Zeeman qubits in 40Ca+, obtaining results that matched theoretical expectations. Finally, we present progress towards implementing a two-qubit Mølmer-Sørensen gate with these Raman beams in trapped 40Ca+ ions.
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    The Sound of Ions: Using Trapped Atomic Ion Motion for Quantum Computation and Sensing
    (University of Oregon, 2024-08-07) Metzner, Jeremy; Allcock, David
    Encoding qubits in the electronic states of atoms has enabled the ability toperform computations, sense the environment, and gain a deeper understanding of other physical systems through quantum simulation. In the trapped ion platform, each of these applications is made possible, or enhanced by coupling the qubit to the motion of the trapped ions. The motion can be used to do more than just mediate interactions with qubits and is itself a resource for computation, sensing and simulation. The work presented here focuses on methods for manipulation and entanglement of trapped ion motional states in a spin-independent way while retaining the spin to enable measurement of the quantum state of the motion. We have shown the ability to use a set of spin-independent operations including displacement, beam splitter, squeezing and two-mode squeezing, to sense the phase of the oscillator states with precision exceeding the standard quantum limit (SQL) by up to 5.9 dB and approaching the ultimate Cram´er-Rao bound. With qubits still generally required for utilizing the motional states for quantum information experiments, qubit measurement makes it difficult to preserve any motional state during state detection. We have developed the technique of encoding both states in a metastable manifold which could enable methods to preserve particular motional states of longer-chains during state detection. We present preliminary results demonstrating this preservation of motional states using a mixed atomic-species trap at Lincoln Lab. The metastable encoding also provides the unique ability to engineer and explore non-Hermitian qubit Hamiltonians, where we have shown the ability to break the quantum speed limit.