Quantum technology employs physical systems which are best described using the language of quantum mechanics for useful and sometimes novel applications. The immense promise of quantum technology to impact the fields of computing, communication, and metrology is rivaled by the immense challenge of controlling a system's quantum degrees of freedom. This fine-grained control is made possible by recent advances in high speed electronics and precise nanofabrication and provides access to exploration of new technical frontiers. This thesis presents experiments in which nanostructures in diamonds are the foundation for advancements in quantum technology. We advance two separate platforms -- a building block of a quantum communication network based on silicon-vacancy centers (SiVs) in nanophotonic cavities and a novel platform for nanoscale nuclear magnetic resonance spectroscopy (NMR) based on nitrogen-vacancy centers (NVs) in sealed nanowells. Both platforms employ coherent control of optically-accessible quantum spins, made possible through nanoscale fabrication of the materials platform and advanced electronic measurement and control systems. To advance the SiV platform, we develop a new nanophotonic cavity design framework through which we design novel asymmetric cavities tailored for coherent single photon generation. We also explore the capabilities and practical limitations of the nanophotonic device as a cavity quantum electrodynamics (CQED) system especially with regard to ultra-small mode volume cavities. Along the way, we develop software and simulation infrastructure which are also reported here. The second platform is a newly developed system for performing NMR with NVs on nanoconfined liquids. This system is operated at room temperature, and it takes advantage of the NV's nanoscale magnetic sensing capabilities. We perform a series of foundational experiments with this new platform which ultimately culminate in demonstrating proton NMR of nanoconfined water. Together, these advances demonstrate the potential of diamond nanofabrication by advancing the field of quantum information processing with defect centers in solid-state systems and more broadly, making contributions to nanophotonics, quantum communication, and nanoscale metrology.
Quantum technology employs physical systems which are best described using the language of quantum mechanics for useful and sometimes novel applications. The immense promise of quantum technology to impact the fields of computing, communication, and metrology is rivaled by the immense challenge of controlling a system's quantum degrees of freedom. This fine-grained control is made possible by recent advances in high speed electronics and precise nanofabrication and provides access to exploration of new technical frontiers. This thesis presents experiments in which nanostructures in diamonds are the foundation for advancements in quantum technology. We advance two separate platforms -- a building block of a quantum communication network based on silicon-vacancy centers (SiVs) in nanophotonic cavities and a novel platform for nanoscale nuclear magnetic resonance spectroscopy (NMR) based on nitrogen-vacancy centers (NVs) in sealed nanowells. Both platforms employ coherent control of optically-accessible quantum spins, made possible through nanoscale fabrication of the materials platform and advanced electronic measurement and control systems. To advance the SiV platform, we develop a new nanophotonic cavity design framework through which we design novel asymmetric cavities tailored for coherent single photon generation. We also explore the capabilities and practical limitations of the nanophotonic device as a cavity quantum electrodynamics (CQED) system especially with regard to ultra-small mode volume cavities. Along the way, we develop software and simulation infrastructure which are also reported here. The second platform is a newly developed system for performing NMR with NVs on nanoconfined liquids. This system is operated at room temperature, and it takes advantage of the NV's nanoscale magnetic sensing capabilities. We perform a series of foundational experiments with this new platform which ultimately culminate in demonstrating proton NMR of nanoconfined water. Together, these advances demonstrate the potential of diamond nanofabrication by advancing the field of quantum information processing with defect centers in solid-state systems and more broadly, making contributions to nanophotonics, quantum communication, and nanoscale metrology.
The construction of a quantum internet, an interconnected network which can distribute and store quantum states, is an essential step towards the development of next generation quantum technologies, including unconditionally secure communication, enhanced metrology, and distributed quantum computing. Development of these networks require functional nodes consisting of stationary registers with the capability of high-fidelity quantum information processing and storage, which efficiently interface with photonic qubits. This thesis outlines one emerging platform for building a quantum network node using the silicon-vacancy color center in diamond (SiV). Although previous work has established the SiV as a superior optical emitter capable of strong light-matter coupling, its feasibility as a quantum memory has remained elusive, primarily due to coupling to thermal phonons. This suggests two branching research directions: one where this coupling is investigated and characterized as a nanoscale sensor, and one where this coupling is supressed in order to realize the SiV as a quantum information processor. This thesis begins by highlighting the extreme phonon sensitivity as a metrological tool, where an ensemble of SiVs are used as an all-optical thermometer, capable of \SI{70}{\milli\kelvin} precision at room temperature. When incorporated into nanodiamonds, the sensing properties deviate by less than 1% between nanodiamonds, enabling calibration-free thermometry for sensing and control of complex nanoscale systems. For quantum information tasks, coherent control of the SiV electronic spin qubit is enabled by suppressing phonon-induced dephasing by five orders of magnitude at temperatures below \SI{500}{\milli\kelvin}. By aligning the magnetic field along the silicon-vacancy symmetry axis, optical transitions are highly spin-conserving, allowing for single-shot readout of the qubit with high fidelity. This coherent control is used to demonstrate a spin coherence time T2> \SI{13}{\milli\second} and spin relaxation time T1> \SI{1}{\second} at \SI{100}{\milli\kelvin}. Finally, SiV quantum memories are packaged into a fully integrated quantum network node by incorporating SiV qubits into nanophotonic cavities. The efficient SiV-cavity coupling (with cooperativity C>30) provides a nearly-deterministic interface between photons and the spin qubit, which enables heralded single-photon storage. Coherent coupling to nearby \cnuc\ nuclear spins (with nearly second-long coherence times) enables multi-qubit registers and paves the way towards large-scale quantum networks.
Efficient interfaces between optical photons and quantum bits are fundamental building blocks for quantum networks and large-scale quantum computers. We demonstrate an integrated platform for scalable quantum optics based on color centers coupled to diamond nanodevices. First, we incorporate nitrogen-vacancy (NV) centers in diamond into hybrid nanophotonic crystal cavities. Despite our progress towards coupling the NV to cavity photons, we find that the NV-cavity interface is limited by the imperfections of the color center's properties and its local environment. We approach this challenge first by characterizing and modifying the diamond surface to reduce the environmental noise affecting the NV optical transition. Subsequently, we develop a new approach that makes use of a quantum emitter with intrinsic protection from this noise: the silicon-vacancy (SiV) center in diamond. We demonstrate that SiV centers introduced through ion implantation feature highly coherent optical transitions, even inside nanostructures. By placing SiV centers inside all-diamond photonic crystal cavities, we achieve strong SiV-photon coupling with a cooperativity of greater than 20. Using this platform, we realize a quantum-optical switch controlled by the spin degree of freedom of a single SiV. By measuring intensity correlations of indistinguishable Raman photons emitted into a single waveguide, we observe a quantum interference effect resulting from the superradiant emission of two probabilistically entangled SiV centers. Finally, we demonstrate controllable photon-mediated interactions between the spin degrees of freedom of two cavity-coupled SiV centers. When the optical transitions of the two SiV centers are tuned into resonance, the coupling of each SiV to the common cavity mode results in a coherent interaction between the two SiVs, leading to the observation of super- and sub-radiant two-SiV states.
Point defects in diamond, particularly nitrogen-vacancy (NV) centers, have emerged as powerful tools for a broad range of quantum technologies. These defects are promising candidates for quantum information science, serving as deterministic single-photon sources and solid-state quantum memories. They have also been employed as nanoscale quantum sensors to detect various physical quantities, including magnetic fields, electric fields, and temperature, owing to their long spin coherence time at room temperature. Development of these diamond-based quantum technologies has been rapidly boosted by a recent quantum leap in nanofabrication technologies for high-quality single-crystal diamond. Incorporating these color centers into diamond nanostructures with mature integrated photonics provides a promising route to build scalable and practical systems for quantum applications. This review discusses recent progress and challenges in the hybrid integration of diamond color centers on cutting-edge photonic platforms. Nitrogen-vacancy centers in diamond have emerged as powerful tools for a broad range of quantum technologies. This review discusses recent progress and challenges in the hybrid integration of diamond color centers on cutting-edge photonic platforms.
Quantum networks hold the potential to enable quantum-secured communication, distributed quantum computing, and non-local quantum sensing. To realize these applications, a versatile quantum network infrastructure must support entanglement between network nodes capable of storing, processing, and distributing quantum information, alongside high-fidelity photonic qubits that efficiently interface with these nodes. The silicon-vacancy (SiV) center in diamond, coupled to nanophotonic cavities, has recently emerged as a promising platform to meet these requirements. This system provides access to an electron spin as an optically active communication qubit and a 29Si nuclear spin as a memory qubit, capable of storing quantum information for extended periods. We first demonstrate that the SiV center's electron spin can efficiently generate single photons with complex spatiotemporal waveforms, facilitated by a novel asymmetric nanophotonic cavity design. We then establish a two-node quantum network between two SiV centers housed in separate laboratories and connected via optical fiber. To do so, we use photonic qubits to mediate entanglement between two spatially separated electron spins, as well as between two spatially separated nuclear spins. Finally, using bidirectional quantum frequency conversion, we convert the photonic qubits to telecommunication frequencies, enabling entanglement generation between the two nuclear spins via a 35 km fiber deployed in the Boston metropolitan area. These advancements mark progress toward large-scale, deployable quantum networks using SiV centers coupled to nanophotonic cavities.
Nitrogen-vacancy (NV) centers in diamond have recently emerged as a unique platform for fundamental studies in quantum information and nanoscience. The special properties of these impurity centers allow robust, room-temperature operation of solid-state qubits and have enabled several remarkable demonstrations in quantum information processing and precision nanoscale sensing. This article reviews the recent advances in magnetic and optical manipulation of the NV center’s quantum spin and their importance for prospective applications. We discuss how quantum control of individual centers can be harnessed for the protection of NV-center spin coherence, for multiqubit quantum operations in the presence of decoherence, and for high-fidelity initialization and readout. We also discuss the progress in resonant optical control, which has led to interfaces between spin and photonic qubits and may lead to spin networks based on diamond photonics. Many of these recently developed diamond-based technologies constitute critical components for the future leap toward practical multiqubit devices.
Developing technologies for distributing entanglement over long distances, and employing this technology to create quantum communication networks, has been a standing goal of the quantum optics community for almost two decades. Such networks could be used for secure communication enabled by quantum key distribution (QKD), enhancement of quantum sensors, and even the creation of networked quantum computers. We present a platform, based on the negatively charged Silicon Vacancy (SiV) in diamond, capable of correcting for the photon loss that currently limits the size of such networks. Furthermore, we lay the groundwork for its use for scalable implementation of the full quantum repeater protocol, the missing ingredient for the deployment of large quantum networks. First, we demonstrate improved diamond nanofabrication techniques that enable the creation of an integrated, cooperativity 100 spin-photon interface. We further discuss the techniques used to integrate this platform with microwave coplanar waveguides (CPWs) that enable coherent control of the SiV spin state. Next, we demonstrate the integration of diamond nanophotonic technology with nanomechanical strain control, enabling the reduction of variations between, and fluctuations of, diamond color center optical and spin properties. These techniques are used to enable quantum interference between two initially distinguishable quantum emitters. To further demonstrate the utility of this platform, we employ coherent spin control and our platform's high cooperativity spin-photon interface to create an integrated quantum network node capable of high fidelity, coherent photon storage and the formation of multiqubit quantum registers. We discuss the engineering and physics principles relevant to the implementation of such a system, and provide a framework for future improvements to the underlying technology. Finally, we employ the developed techniques to perform Bell state measurements between asynchronously arriving photons. By utilizing this technique we demonstrate enhancement of the quantum communication rate between two parties, thus implementing the key functionality of a single quantum repeater node. This demonstration, combined with the other technical advances presented here, positions the diamond photonics-SiV platform as a leading candidate for the implementation quantum networking technology and provides a path towards large scale deployment of such systems.