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Expanding the 171Yb+ toolbox: the 2F7/2 state as resource for quantum information science


The $^{171}$Yb$^+$ ion has seen wide scale adoption as a trapped ion qubit across the globe for use in quantum information experiments. It has emerged as a mature and highly efficient platform for large scale quantum simulation and as the workhorse for pushing trapped ion quantum computation into the realm where the so called ``quantum advantage" may be realized.

In this thesis we investigate and develop methods of performing state preparation and measurement of the $^{171}$Yb$^+$ ground state qubit that takes advantage of the often overlooked long lived $^2$F$^o_{7/2}$ state. By performing narrow-band optical pumping of qubit population to the $^2$F$^o_{7/2}$ state, we show that high fidelity state preparation and measurement in $^{171}$Yb$^+$ is possible without the need to enhance photon detection efficiency. We achieve a state preparation and measurement fidelity of $\mathcal{F} = 0.99984^{+4}_{-4}$, the best to date demonstrated in any qubit platform we are aware of, limited by our single qubit gates. We use multiple microwave pulses to show that a state preparation and measurement fidelity of $0.99993^{+2}_{-3}$ is achievable with better single qubit gates.

We then utilize the optically separated qubit populations to perform high fidelity background free state detection of the ground state qubit with mode locked lasers, achieving a state preparation and measurement fidelity of $\mathcal{F} = 0.9993^{+3}_{-6}$ in the presence of large amounts of background scatter. This method increased the signal to background ratio by a factor of 150, and provides a pathway to faithful qubit readout in environments where rejection of excitation laser scatter is difficult.

We begin development of a new trapped ion quantum information paradigm, utilizing additional qubits hosted in metastable electronic states to improve the flexibility of quantum information processors. The metastable qubit we develop in $^{171}$Yb$^+$ is a zero-field clock state qubit in the $^2$F$^o_{7/2}$ state. We identify the qubit transition frequency and develop a method for heralding state preparation of both computational basis states. The ability to herald state preparation allows us to demonstrate high fidelity state preparation and measurement of the metastable qubit, achieving a fidelity of $\mathcal{F} = 0.9995^{+2}_{-3}$. In this proposed architecture, dissipative operations in the ground state manifold can be implemented in the presence of metastable qubit for sympathetic cooling, and we quantify the effects these lasers may have on the metastable qubit.

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