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DTSTART:20221106T060000
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DTSTART;TZID=America/Toronto:20230809T140000
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URL:https://uwaterloo.ca/institute-for-quantum-computing/events/brendan-bra
 mman-phd-thesis-defence
LOCATION:QNC - Quantum Nano Centre 200 University Avenue West QNC 1201 Wate
 rloo ON N2L 3G1 Canada
SUMMARY:Brendan Bramman PhD Thesis Defence
CLASS:PUBLIC
DESCRIPTION:ABLATION LOADING AND QUDIT MEASUREMENTS WITH BARIUM IONS\n\nBar
 ium is one of the best ions for performing quantum information in a\ntrapp
 ed-ion system. Its long-lived metastable D5/2 state allows for\nsome inter
 esting quantum operations\, including the current best state\npreparation 
 and measurement fidelity in qubits. This metastable state\nalso opens up t
 he possibility of implementing higher dimensional\nqudits instead of qubit
 s. However\, installing a barium metal source in\na vacuum chamber has sho
 wn to be somewhat of a challenge. Here\, we\npresent a loading technique w
 hich uses a barium chloride source\ninstead\, making it much easier to ins
 tall. Laser ablation with a\nhigh-energy pulsed laser is used to generate 
 neutral atoms\, and a\ntwo-step photoionization technique is used to selec
 tively load\ndifferent isotopes of barium in our ion trap. The process of 
 laser\nablation and the plume of atoms it generates are characterized\,\ni
 nforming us on how to best load ions. Loading is achieved\, and\nselectivi
 ty of our method is demonstrated\, giving us a reliable way to\nload ba138
  and ba137 ions. The quadrupole transition into the\nmetastable D5/2 state
  is investigated\, with all of the individual\ntransitions successfully fo
 und and characterized for ba138 and ba137.\nCoherent operations are perfor
 med on these transitions\, allowing us to\nuse them to define a 13-level q
 udit\, on which we perform a state\npreparation and measurement experiment
 . The main error source in\noperations using this transition is identified
  to be magnetic field\nnoise\, and so we present attempts at mitigating th
 is noise. An ac-line\nnoise compensation method is used\, which marginally
  improved the\ncoherence time of the quadrupole transitions\, and an addit
 ional method\nof using permanent magnets is proposed for future work. Thes
 e efforts\nwill help to make trapping barium more reliable\, making it an 
 even\nmore attractive option for trapped ion systems. The state preparatio
 n\nand measurement results using the quadrupole transition to the\nlong-li
 ved metastable D52 state establish barium as an interesting\nplatform for 
 performing high-dimensional qudit quantum computing.
DTSTAMP:20260420T001141Z
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