Experimental Trapped-Ion Quantum Computing with Lasers and Microwaves
There are two important criteria for a physical system to meet before it can be used as a qubit in a quantum computer. It must be possible to perform quantum operations, both upon single qubits and pairs of qubits, and the system must be well isolated from the external environment. Single trapped ions meet both of these criteria, with two energy levels of the outer electron being used for the qubit states. High-quality quantum operations can be achieved by applying laser pulses to the ions, which are kept isolated by using electric and magnetic fields to trap them in a vacuum.
However, to create a useful quantum computer the system needs to be scaled up to a large number of qubits. It is currently quite time-consuming to build and maintain the lasers required for laser-driven operations, so significantly increasing the system size would be challenging. An alternative approach is to use near-field microwaves, which are applied using oscillating currents near the ions. This takes advantage of the ease with which high-quality microwave-frequency currents can be generated.
Whilst this approach is in its infancy, the Ion Trap Quantum Computing group in Oxford has already used it to achieve the best single-qubit operations in the world, and physicists at the National Institute of Standards and Technology in the United States have used it to perform high-quality two-qubit operations. My project is to develop a new trap to improve upon these results.