Old Dog, New Trick: High Fidelity, Background-free State Detection of an Ytterbium Ion Qubit
Abstract
The highly popular ytterbium-171(I) (^171 Yb ^+) ion is commonly employed in quantum information research as a qubit whose excellent coherence time and fast, simple state preparation has allowed cutting edge work in quantum computation and simulation. Despite these large benefits, the demonstrated measurement fidelity of this ion has lagged the state preparation and gate fidelity achieved to date. In this thesis we investigate and realize methods of increasing the measurement fidelity of ^171 Yb ^+ in a scaleable way for large quantum systems. Using methods of coherent control, we implement a pulsed state detection scheme using a mode-locked laser to perform background-free spectroscopy of the bright state of the qubit. The small hyperfine splitting of the ion necessitates the use of multiple (two) pulses to manipulate time dynamics of the ion to excite a single transition. A Mach-Zender interferometer is constructed to control these pulse separations both coarsely ( 237 ps) and on a fine sub-femtosecond scale. These pulses cause destructive/constructive interference of the electron wavepacket of a single ion levitated in vacuum and are engineered to state-selectively excite the qubit. This allows measurement of the qubit whose transition frequency is much smaller than the bandwidth of the interrogation laser. During this spectroscopy, mechanical forces from the mode-locked laser frequency comb can drive the ion into large coherent states of motion. This motion has been dubbed phonon lasing. We investigate the phonon lasing affect and how the ion interacts with multiple comb teeth. The large amount of teeth leads to a protection mechanism from runaway energy gain by near-by blue detuned teeth, allowing ions to be trapped and cooled by the mode-locked laser, regardless of its detuning. We further explore these discrete amplitude coherent states by injecting energy into the ions motion and exciting higher-order oscillations.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 2020
- Accession Number
- AD1222002
Entities
People
- Anthony M. Ransford
Organizations
- University of California, Los Angeles