Cryogenic, near-field quantum logic chips with passive field nulling on 43Ca+

Thesis

This work describes the design and implementation of a new apparatus to achieve quantum information processing in trapped ions using microwave methods. The apparatus involves many design improvements over a previous quantum processing experiment which achieved the highest single-qubit gate fidelity, longest coherence time, and highest microwave based two-qubit fidelity. The goal of this new experiment is a two-qubit gate speed and a fidelity improvement of a factor of 10, making microwave based gates much more feasible as quantum processors. To this end, a novel clock qubit within ⁴³Ca⁺ is chosen, and the ion height is nearly halved. An anticipated heating rate increase is counteracted by the use of cryogenics. A novel ion chip design is implemented via wafer-scale fabrication and subsequently attached using a novel eutectic bonding technique. The implementation required many design and fabrication problems to be solved; these are described. The vacuum system reaches < 10⁻¹¹ mbar even at room temperature, lowering experimental difficulty and allowing for performance comparisons at a wide temperature range. A new experiment control system, ARTIQ, and corresponding Sinara hardware is used for control. Experimental results achieved so far include a study of contributing factors to the ion loading rate, and a comparison between the designed and measured microwave fields. All results achieved to date are compatible with the main speed and fidelity goal, which should be achieved in the near future.

Authors: Wolf, J

• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Microwave gates; physics; Quantum computing; Lasers; Ion trap fabrication; Quantum Information; Cryogenic; Ultra high vacuum; Ion trapping
• Subjects: Quantum computing; Lasers; Atomic physics; Quantum physics; Physics; Cryogenics