Speaker
Description
With solely visible and near-infrared wavelength fine-structure transitions, and isotopes with diverse nuclear spins, Barium makes an ideal candidate for developing novel quantum computing architectures. I will present our designs for a versatile and open-access quantum computer which leverages these favorable features of Barium. The visible and near-infrared wavelengths allows for the use of fibre and integrated optic technologies which increases the mechanical stability of the optical systems required to prepare laser light for interfacing with a chain of trapped Barium ions. The Raman beams for manipulating the hyperfine states are at a wavelength of 532 nm and I will present a design based on femtosecond laser direct-written waveguides and fibre-based AOMs for preparing a set of 16 individually controlled Raman beams at the ion positions. The chains of isotopically pure $^{133}$Ba$^+$ ions will be loaded using laser ablation, and I will present preliminary loading statistics from laser ablating barium chloride towards our final goal of isotope selective loading of Barium ions. The quantum computer will be enabled by an advanced control system based on a set of tightly coupled FPGA boards. The control system will parse remote commands by a user and translate them into trapped ion experimental sequences, while maintaining the stability and calibration of the system. This will allow for members of the research community to access an advanced ion trap set up, decreasing barriers to testing of new theoretical protocols.
The spin-3/2 nucleus of $^{137}$Ba$^+$ provides an ideal testbed for exploring higher dimensional quantum logic in trapped ions. Typically, hyperfine states of the S$_{1/2}$ manifold are used to encode qubit states, and efforts are taken to prevent population of the other states. We propose using these additional hyperfine states to store qudits. Using the known error sources from qubit manipulations in trapped ions, we have quantified the realistic, expected fidelities for universal qudit quantum computation with trapped Barium ions [1]. I will outline modified protocols for state preparation, single-qudit gates, two-qudit gates, and measurements. For qutrits we calculate that expected fidelities are all above the 99.25% fault tolerance threshold. Five level qudits have >99% fidelities, with the exception of two-qudit gate fidelities being reduced by undesired couplings to other hyperfine states. We expect these reduced two-qudit gate fidelities could be improved using a different encoding or entangling scheme and are not a fundamental limitation.
[1] Low, Pei Jiang, et al. "Practical trapped-ion protocols for universal qudit-based quantum computing." arXiv preprint arXiv:1907.08569 (2019).
