Trapping of a nanodiamond/microdiamond containing Nitrogen-Vacancy centers in the vacuum is an ideal platform to develop a hybrid mechanical system. In such a system, the coupling between the Nitrogen-Vacancy centers and the mechanical motion of a trapped diamond provides pathways for generating a quantum superposition state of the mechanical motion with long coherence time. In this work, I demonstrate our preliminary data in the detection of Nitrogen-Vacancy spin signals from trapped diamonds using optical and magneto-gravitational trapping technologies. I compared the advantages and drawbacks of both techniques and improvements need to be made. I also explored the charge dynamics of Nitrogen-Vacancy centers in diamonds under near-IR laser illumination and first demonstrate low energy (0.95 to 1.18 eV or 1050 to 1300 nm) Multi-photon Photoluminescence Excitation (PLE) spectrum of NV centers in a sub-millimeter diamond crystal.
Trapping of a nanodiamond/microdiamond containing Nitrogen-Vacancy centers in the vacuum is an ideal platform to develop a hybrid mechanical system. In such a system, the coupling between the Nitrogen-Vacancy centers and the mechanical motion of a trapped diamond provides pathways for generating a quantum superposition state of the mechanical motion with long coherence time. In this work, I demonstrate our preliminary data in the detection of Nitrogen-Vacancy spin signals from trapped diamonds using optical and magneto-gravitational trapping technologies. I compared the advantages and drawbacks of both techniques and improvements need to be made. I also explored the charge dynamics of Nitrogen-Vacancy centers in diamonds under near-IR laser illumination and first demonstrate low energy (0.95 to 1.18 eV or 1050 to 1300 nm) Multi-photon Photoluminescence Excitation (PLE) spectrum of NV centers in a sub-millimeter diamond crystal.
Hybrid quantum devices, in which disparate quantum elements are combined in order to achieve enhanced functionality, have received much attention in recent years due to their exciting potential to address key problems in quantum information processing, communication, and control. Specifically, significant progress has been made in the field of hybrid mechanical devices, in which a qubit is coupled to a mechanical oscillator. Strong coupling in such devices has been demonstrated with superconducting qubits, and coupling defect qubits to mechanical elements via crystal strain has enabled novel methods of qubit measurement and control. In this paper we demonstrate the fabrication of diamond optomechanical crystals with embedded nitrogen-vacancy (NV) centers, a preliminary step toward reaching the quantum regime with defect qubit hybrid mechanical devices. We measure optical and mechanical resonances of diamond optomechanical crystals as well as the spin coherence of single embedded NV centers. We find that the spin has long coherence times T2∗=1.5μs and T2=72μs despite its proximity to nanofabricated surfaces. Finally, we discuss potential improvements of these devices and prospects for future experiments in the quantum regime.
Abstract Hybrid quantum devices, in which disparate quantum elements are combined in order to achieve enhanced functionality, have received much attention in recent years due to their exciting potential to address key problems in quantum information processing, communication, and control. Specifically, significant progress has been made in the field of hybrid mechanical devices, in which a qubit is coupled to a mechanical oscillator. High cooperativity in such devices has been demonstrated with superconducting qubits, and coupling defect qubits to mechanical elements via crystal strain has enabled novel methods of qubit measurement and control. In this paper we demonstrate the fabrication of diamond optomechanical crystals (OMCs) with embedded nitrogen-vacancy (NV) centers, a preliminary step toward reaching the quantum regime with defect qubit hybrid mechanical devices. We measure optical and mechanical resonances of diamond OMCs as well as the spin coherence of single embedded NV centers. We find that the spin has long coherence times T 2 * = 1.5 μ s and T 2 = 72 μ s despite its proximity to nanofabricated surfaces. Finally, we discuss potential improvements of these devices and prospects for future experiments in the quantum regime.
Defect centers in diamond are regarded as a promising candidate for future solid state quantum technology. In particular the nitrogen vacancy (NV) center attracts researchers attention, as it promises to emit indistinguishable single photons and provides a triplet ground state with ultra long spin coherence times. In particular NV centers in nano diamonds are attractive, since they can be integrated into quantum photonic hybrid devices with nano manipulation techniques. We report on first demonstrations of the integration of NV-centers into photonic hybrid devices, and point out future applications. Beside the striking demonstrations of the integrability, nanodiamonds have several drawbacks. In particular the spectral diffusion of the zero-phonon line is addressed.
This thesis describes a series of experiments on the control of the optical properties of the nitrogen-vacancy (NV) center in diamond, and on control of the electron and nuclear spin states associated with the NV center. The NV center is a fluorescing atomic defect center in diamond, consisting of a substitutional nitrogen atom adjacent to a vacancy in the diamond carbon lattice. The electron spin of the NV center can be initialized and read out optically, and coherently manipulated with high fidelity even at room temperature. This unique combination of properties has attracted much attention to the NV center in recent years for application in quantum information technologies. The experiments in this work focus on exploiting the intrinsic hybrid nature of the NV center. The NV center forms a hybrid spin register, as its electron spin is always coupled to the nuclear spin of its own nitrogen nucleus, and can furthermore be coupled to additional nuclear carbon-13 spins in the diamond. In addition, the electronic spin state can be mapped onto the state of a photon, in principle allowing long range transmission of quantum information and measurement-based entanglement of distant NV center registers. The long-term goal is to achieve a large scale quantum network where the different constituents each perform the task they are most well suited for: the stable nuclear spins store the quantum information, photons transfer quantum information over long distances, and the fast electron spin interfaces between spin and photon states. For measurement-based entanglement of distant NV centers it is of primary importance to maximize the emission and detection of coherent photons emitted by the NV center. Spontaneous emission can be controlled and enhanced by coupling an emitter to a photonic cavity. Chapters 3, 4, and 5 of this thesis describe experiments aimed at maximizing the coherent photon emission rate of an NV center by coupling the NV center to a photonic crystal cavity. One of the main challenges is to position a single NV center into the nanometer-sized cavity mode. Chapter 3 describes the development of a nanopositioning technique, which allows diamond nanocrystals ~50 nm in size containing single NV centers to be placed at arbitrary locations on a chip, with nanometer precision. By using a sharp etched tungsten tip, individual nanocrystals can be picked up, moved and placed under real-time imaging with an electron microscope. We explicitly demonstrate that the unique optical and spin properties of the NV center are conserved by the nanopositioning process. In chapter 4, we apply the nanopositioning technique to couple single NV centers contained in a diamond nanocrystals to gallium phosphide photonic crystal cavities. These cavities resonate in the visible with high quality factors, and are designed to have the lowest energy mode coincide with the zero-phonon line of the NV center. Efficient coupling is evidenced by a strong enhancement of NV center emission at the cavity wavelength. The high quality factor of a photonic crystal cavity is a result of careful design and fabrication. The introduction of a nanocrystal may therefore be expected to have a detrimental effect on the optical properties of a cavity. In chapter 5 we investigate the effect of a nanocrystal on the optical properties of photonic crystal cavities. Our simulations and measurements show that the effect of a nanocrystal is in fact only minor, a promising result for future work on cavity-QED systems in the solid state and with diamond defect centers in particular. Understanding and mitigating decoherence is a key challenge for quantum science and technology. The main source of decoherence for solid-state spin systems is the uncontrolled spin bath environment. Chapter 6 describes experiments that exploit quantum control of the NV center and recently developed dynamical decoupling techniques to study the properties of the surrounding bath of spins belonging to single substitutional nitrogen atoms. The coherence properties of a single NV center are affected by changes in the state of the bath spins, allowing a single NV center to be used as a probe to detect bath spin resonances and study the quantum dynamics of the spin bath. We use quantum control of the spin bath to extend the dephasing time of the NV center, important for the application of the NV center in DC magnetometry. In chapter 7 we describe the development and implementation of decoherence protected quantum gates for the hybrid spin register formed by the NV center electron spin that is coupled to the nuclear spin of its own nitrogen atom. Electron and nuclear spins evolve and decohere at vastly different rates, making it challenging to use such a hybrid system as a fully functional quantum register. We create a universal set of two-qubit quantum gates by integrating dynamical decoupling techniques into the gate operation. We demonstrate the power of our gate design by implementing for the first time Grover's quantum search algorithm on a solid-state spin register.
A fully functional quantum computer must contain at least two important components: a quantum memory for storing and manipulating quantum information and a quantum data bus to securely transfer information between quantum memories. Typically, a quantum memory is composed of a matter system, such as an atom or an electron spin, due to their prolonged quantum coherence. Alternatively, a quantum data bus is typically composed of some propagating degree of freedom, such as a photon, which can retain quantum information over long distances. Therefore, a quantum computer will likely be a hybrid quantum device, consisting of two or more disparate quantum systems. However, there must be a reliable and controllable quantum interface between the memory and bus in order to faithfully interconvert quantum information. The current engineering challenge for quantum computers is scaling the device to large numbers of controllable quantum systems, which will ultimately depend on the choice of the quantum elements and interfaces utilized in the device. In this thesis, we present and characterize a hybrid quantum device comprised of single nitrogen-vacancy (NV) centers embedded in a high quality factor diamond mechanical oscillator. The electron spin of the NV center is a leading candidate for the realization of a quantum memory due to its exceptional quantum coherence times. On the other hand, mechanical oscillators are highly sensitive to a wide variety of external forces, and have the potential to serve as a long-range quantum bus between quantum systems of disparate energy scales. These two elements are interfaced through crystal strain generated by vibrations of the mechanical oscillator. Importantly, a strain interface allows for a scalable architecture, and furthermore, opens the door to integration into a larger quantum network through coupling to an optical interface.There are a few important engineering challenges associated with this device. First, there have been no previous demonstrations of a strain-mediated spin-mechanical interface and hence the system is largely uncharacterized. Second, fabricating high quality diamond mechanical oscillators is difficult due to the robust and chemically inert nature of diamond. Finally, engineering highly coherent NV centers with a coherent optical interface in nanostructured diamond remains an outstanding challenge. In this thesis, we theoretically and experimentally address each of these challenges, and show that with future improvements, this device is suitable for future quantum-enabled applications. First, we theoretically and experimentally demonstrate a dynamic, strain-mediated coupling between the spin and orbital degrees of freedom of the NV center and the driven mechanical motion of a single-crystal diamond cantilever. We employ Ramsey interferometry to demonstrate coherent, mechanical driving of the NV spin evolution. Using this interferometry technique, we present the first demonstration of nanoscale strain imaging, and quantitatively characterize the previously unknown spin-strain coupling constants. Next, we use the driven motion of the cantilever to perform deterministic control of the frequency and polarization dependence of the optical transitions of the NV center. Importantly, this experiment constitutes the first demonstration of on-chip control of both the frequency and polarization state of a single photon produced by a quantum emitter. In the final experiment, we use mechanical driving to engineer a series of spin ``clock" states and demonstrate a significant increase in the spin coherence time of the NV center. We conclude this thesis with a theoretical discussion of prospective applications for this device, including generation of non-classical mechanical states and spin-spin entanglement, as well as an evaluation of the current limitations of our devices, including a possible avenues for improvement to reach the regime of strong spin-phonon coupling.
Solid-state technologies for quantum mechanical application require delicate materials that can operate stably with a long coherence time. Nitrogen vacancy (NV) centers in diamond is one of the most promising candidates for quantum physics, with applications such as single photon emitters, quantum computation, and magnetic sensor.\n\nTo fully exploit the capability of defect centers in diamond for opto-electronics and quantum engineering, a number of improvements are needed. Among these are optimization of the NV centers yield in bulk diamond, nanodiamond (ND) size reduction, photocurrent study of the defect band-trap electronic structure in diamonds, and optimization of high-speed NV qubit control. For NV centers yield optimization, both the experimental magnetic sensitivity optimization as well as theoretical simulation of NV concentration are implemented. For NDs size characterization, we analyzed the size and photon autocorrelation function of NV in NDs after air oxidation treatment using a combined atomic force microscopy/confocal system. To study defect band-trap electronic structure in diamond, excitation and quenching as well as the recovery of the quenched photocurrent was investigated to better understand photocurrent dynamics in diamond. For qubit high-speed control optimization, a microwave pulse based on a nonlinear numeric solution of the Schrodinger equation is used to rotate the NV spin faster than the ordinary Rabi flip rate. Together these approaches promise to significantly speed up the development of diamond for quantum engineering applications.