Towards large scale quantum information processing with trapped ions
Prof. Dr. Winfried Hensinger (University of Sussex)

To this point, entanglement operations on ion qubits have predominantly been performed using lasers. When scaling to larger qubit numbers however this becomes problematic due to the challenging engineering that might be required. The use of microwaves combined with a static magnetic field gradient overcomes this problem. Microwave entanglement gates operate on magnetic-field sensitive states which leave them vulnerable to decoherence due to fluctuating magnetic fields. By dressing the ions with microwaves we can protect against this source of noise. We have developed a new powerful method of dressed state manipulation which gives us the ability to perform the arbitrary Bloch sphere rotations which are required for quantum computing while only requiring few rf fields for gate operations.
Using multiple in-vacuum permanent rare earth magnets we have realized a large static magnetic field gradient at the position of a trapped ion (24 T/m). Using this setup we demonstrated the individually addressing of closely spaced ions by tuning the microwave frequency. We have also demonstrated motional sidebands transitions using the coupling between the ion’s internal states and its motion induced by the magnetic field gradient. Such transitions are the key requirement for realizing entanglement gates. We also demonstrated motional sideband transitions in the dressed state qubit basis and I will present our progress towards realizing entanglement gates with microwaves.
We have developed several microfabricated traps for quantum information processing. I report the successful operation of the first two-dimensional ion trap lattice integrated on a microchip. I will also report our progress in the operation of a centrally segmented microfabricated ring trap featuring 90 electrodes capable of storing 1000 ions. This electrode arrangement provides periodic boundary conditions and therefore homogeneous ion-ion spacings which opens up the possibility to study quantum systems such as the homogenous Kibble-Zureck mechanism.
Ion trapping in a cryogenic environment has a multitude of application. We have successfully constructed a cryogenic ion trap experiment and I will discuss the experiment including the design of a high-Q superconducting integrated resonator microwave ion chip.