Quantum computing presents a much different challenge than controlling a classical computer. The main difference lies between the methods of control of quantum bits (qubits) and classical bits. Unlike their classical counterparts, which have discrete states defined by voltages, qubits are defined by some quantum state and are not so easily manipulated. Nitrogen-vacancy (NV) centers are defects that occur in diamond that can be utilized as a two-level system, showing promise for a qubit platform. To use NV centers in this manner, microwave excitation must be applied to control their spin states. An external magnetic field is applied to the NV center to lift state degeneracy, allowing us to define a two-level system. Applying resonant microwave excitation causes oscillatory population transfer between the states defining that two-level system. To apply this excitation, we will construct an antenna that is capable of aligning a microwave field to the NV center. These antennas will be designed to maximize the Rabi frequency at lower input powers. To do so, we maximize microwave field strength and optimize power transmission through antenna geometry and impedance matching. Positioning of the antenna on the sample close to the NV center assures the high field strength excites it. We make use of field simulation software to model and simulate various antenna designs. Select designs are chosen for initial fabrication runs on copper, and are used to verify that simulated results align with physical testing. Once that is verified, we finalize designs for fabrication onto diamond via photolithography. We will physically test the antennas by characterizing them using a vector network analyzer. We expect to be able to fabricate and characterize a broadband gold antenna on a diamond sample that matches simulations, and use it to demonstrate spin manipulation through resonant excitation of an NV center.  

The negatively-charged nitrogen-vacancy (NV) center in diamond, consisting of a substitutional nitrogen atom and an adjacent vacancy defect, can provide an ideal platform for quantum computing. The NV center has many useful properties such as its optical stability and long spin-coherence times. However, due to the high refractive index of diamond, the light-collection efficiency of NV centers is very low. To solve this problem, I registered the positions of the promising NV center candidates in diamond and fabricated solid-immersion-lenses around the pre-selected NV centers. As a next step towards building a diamond quantum processor, here I present the construction of a cryogenic confocal microscope, which consists of a confocal imaging system with 515 nm laser and a 637 nm laser. Through optical pumping by the 515 nm laser and on-resonance driving by the 637 nm laser, this setup will allow for single-shot readout of the NV electronic spin state. This paves the way for our futhure implementation of quantum protocols and small-scale quantum algorithms for both pedagogical and research purposes.

The trapping of individual ions has allowed physicists to control and observe otherwise inaccessible phenomena. Ion traps have enabled the most precise measurements of fundamental physical constants, mass spectrometry for chemical characterization, atomic clocks that would only lose a fraction of a second over the entire age of the universe, and the direct observation of many core concepts in quantum mechanics. Many crucial developments in ion traps occurred here at the University of Washington in the group of Hans Dehmelt, who shared the 1989 Nobel Prize in physics for that work. Today, techniques in ion trapping continue to be developed because trapped ions are one platform for creating qubits in quantum computers. With the growth of quantum information science in academia and industry, there is a need for inexpensive, scalable educational labs to introduce students to concepts in quantum computing. To fill this need, we developed a reproducible lab, which demonstrates key concepts in ion trapping. Our process utilized, first, a comparative approach with reference to literature and, second, iterative improvement on built components. The lab consists of two, independent quadrupole traps: a four-rod trap and a planar five-rail trap. To reduce cost and complexity, we trap charged particles with 25 µm and 50 µm diameter, rather than atomic ions. The particles are trapped in air, at atmospheric pressure. Due to the damping forces provided by this background gas, the trapped particles are easy to control. The result of our project is a lab capable of several experiments, including controlling the number of particles trapped through voltage modulation at a constant frequency, studying the phase transition between one- and two-dimensional Coulomb crystals, exploring micromotion compensation, observing two- and three-particle secular modes, and demonstrating particle shuttling along the trapping axis of the planar trap.