High-fidelity, near-field microwave gates in a cryogenic surface trap

Thesis

We present a novel dynamical decoupling strategy for near field microwave gradient driven, Mølmer-Sørensen style, two-ion quantum logic gates, which suppresses errors from both fluctuations in the qubit frequency and imperfection in the decoupling drive itself. Using a microwave-integrated surface-trap which is operated cryogenically at 25 K and a magnetically insensitive 43-Ca+ qubit at 288 G, we demonstrate a 331 us two-ion quantum logic gates, with 4.9(11)e-3 logic error probability. This is below the 1% error threshold required for quantum error correction and represents a ~10x gate time reduction when compared to previously demonstrated near field gradient driven microwave gates below the 1% error probability threshold. Additionally, two faster gates were demonstrated without the use of dynamical decoupling. Respectively, these two gates had gate operation durations of 216.8 us & 153.8 us and measured gate error probabilities of 8.5(20)e-3 & 9.8(21)e-3. Further, we develop a method for rapid calculation of ion transport operations. We successfully demonstrate ion transport as well as crystal splitting and merging operations within two different ion traps using the waveforms calculated by this ion transport toolbox.

Authors: Weber, MA

• DOI: 10.5287/ora-zrqaje77n
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: laser free gates; microwave gates; two-qubit gates; quantum computing; calcium 43; ion transport; surface trap; dynamical decoupling; trapped ions
• Subjects: Quantum computing; Physics; Atomic physics; Trapped ions