Large-scale control of nitrogen-vacancy quantum bit arrays in diamond

Abstract

During the last ten years, basic quantum operations on a single electronic spin in the nitrogen-vacancy centre (NV) in diamond have been a rich field of study. These defects have become promising candidates as robust, long-lived qubits. However, in order to realize quantum computers with the help of these qubits one has to find a way to create and control a system of many qubits. One promising way will be introduced in this thesis. Using a wire grid, which is directly produced on the diamond sample, in combination with a STIRAP-inspired (stimulated Raman adiabatic passage) transition gives access to manipulate a specific NV within a large number of other NVs. The reason is that STIRAP requires two photons in order to perform the transfer, which is utilized with the wire grid. By sending one microwave pulse through a horizontal wire and the second pulse through a vertical wire, the condition for STIRAP is only fulfilled at the junction of both. Furthermore, introducing a detuning of these pulses is not only necessary to truly perform a STIRAP-inspired (two-tone) transition but also reduces the effects of the microwave signals at other crossings. The first part of this thesis describes the basic physics of the NV and discusses STIRAP. After explaining the experimental setup the implementation of the two-tone pulses is demonstrated. The second part is dedicated to the usage of the wire grid. First, the performance of the wire grid is anticipated by using a single wire with a single NV, as single wire measurements are easier to control and better understood. The dependence on the microwave power of the two-tone efficiency is obtained and a comparison to the dependence on the distance is made. Additionally, the time-behaviour of the two-tone transfer is observed depending on the detuning of the two-tone pulses. After getting a good estimate of the performance of the wire grid the grid itself is implemented in the experimental setup. Measurements confirm the expected performance and the possibility to address a single site without affecting any other sites. Finally, a way to cancel out any unintended effects at neighbouring crossings is demonstrated in order to show that the wire grid can be built smaller while maintaining high performance qubit control.