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Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2021)

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.

    Cover page: Expanding the 171Yb+ toolbox: the 2F7/2 state as resource for quantum information science
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2020)
    Short pulses from mode-locked lasers can produce background-free atomic fluorescence by allowing temporal separation of the prompt incidental scatter from the subsequent atomic emission. We use this to improve our quantum state detection of optical-frequency and electron-shelved trapped ion qubits by more than two orders of magnitude. For direct detection of qubits defined on atomic hyperfine structure, however, the large bandwidth of short pulses is greater than the hyperfine splitting, and repeated excitation is not qubit state selective. Here, we show that the state resolution needed for projective quantum measurement of hyperfine qubits can be recovered by applying techniques from coherent control to the orbiting valence electron of the queried ion. We demonstrate electron wavepacket interference to allow readout of the original qubit state using broadband pulses, even in the presence of large amounts of background laser scatter.
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2018)
      We demonstrate the use of a frequency-doubled optical frequency comb to load, cool, and crystallize trapped atomic ions as an alternative to ultraviolet (UV) or even deep UV continuous-wave lasers. We find that the Doppler shift from the atom's oscillation in the trap, driven by the blue-detuned comb teeth, introduces additional cooling and amplification which gives rise to steady-state phonon lasing of the ion's harmonic motion in the trap. The phonon laser's gain saturation keeps the optical frequency comb from continually adding energy without bound. This protection allows us to demonstrate loading and crystallization of hot ions directly with the comb, eliminating the need for a continuous-wave cooling laser, a technique that is extendable to the deep UV.
        Cover page: Phonon Lasing from Optical Frequency Comb Illumination of Trapped Ions
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2020)
        Hyperfine structure (HFS) of atomic energy levels arises due to interactions of atomic electrons with a hierarchy of nuclear multipole moments, including magnetic dipole, electric quadrupole and higher rank moments. Recently, a determination of the magnetic octupole moment of the $^{173}\mathrm{Yb}$ nucleus was reported from HFS measurements in neutral ${}^{173}\mathrm{Yb}$ [PRA 87, 012512 (2013)], and is four orders of magnitude larger than the nuclear theory prediction. Considering this substantial discrepancy between the spectroscopically extracted value and nuclear theory, here we propose to use an alternative system to resolve this tension, a singly charged ion of the same $^{173}\mathrm{Yb}$ isotope. Utilizing the substantial suite of tools developed around $\mathrm{Yb}^+$ for quantum information applications, we propose to extract nuclear octupole and hexadecapole moments from measuring hyperfine splittings in the extremely long lived first excited state ($4f^{13}(^2\!F^{o})6s^2$, $J=7/2$) of $^{173}\mathrm{Yb}^+$. We present results of atomic structure calculations in support of the proposed measurements.
          Cover page: Hyperfine structure of Yb+173: Toward resolving the Yb173 nuclear-octupole-moment puzzle
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