Defect-induced color centers in solids are promising candidates for applications in quantum information science. Quantum sensing applications and quantum-logic operations can utilize quantum entanglements mediated by coherent coupling between color centers. Therefore, a critical step is to enable deterministic coherent coupling of individual optically addressable color centers. This work reports our effort of probing coupling between SiV color centers by using optical two-dimensional coherent spectroscopy (2DCS), a technique that provides an extremely sensitive and background-free detection of coupling. Arrays of SiV color centers were fabricated by implanting Si ions into a diamond substrate with a focused ion beam. Optical 2DCS measurements on these color center arrays revealed coherent coupling between single color centers.
Defect-induced color centers in solids are promising candidates for applications in quantum information science. Quantum sensing applications and quantum-logic operations can utilize quantum entanglements mediated by coherent coupling between color centers. Therefore, a critical step is to enable deterministic coherent coupling of individual optically addressable color centers. This work reports our effort of probing coupling between SiV color centers by using optical two-dimensional coherent spectroscopy (2DCS), a technique that provides an extremely sensitive and background-free detection of coupling. Arrays of SiV color centers were fabricated by implanting Si ions into a diamond substrate with a focused ion beam. Optical 2DCS measurements on these color center arrays revealed coherent coupling between single color centers.
Realization of physical systems for quantum information processing fundamentally rests on the ability to generate entanglement among many quantum bits. To this end, solid state quantum systems are often considered a scalable approach due to the relative ease of generating of a large number of individual qubits. However, realizing strong coherent interactions that dominate decoherence processes in the solid state environment is a formidable challenge that has continued to motivate the investigation of new physical systems to store quantum information and new mechanisms to achieve controllable interactions. This thesis takes steps in these directions with diamond color centers, which can store optically accessible quantum information in their electronic spin. We study color center spins as acoustic two level systems, and consider whether their interaction with single phonons in diamond can be engineered to be coherent. Through spectroscopy of color centers in diamond nanomechanical devices and follow-up theoretical work, we identify the negatively charged silicon vacancy (SiV) color center as a promising candidate for phonon-mediated quantum information processing. In the process, an electromechanical device platform capable of tuning the strain environment of color centers is developed. It is used to mitigate thermal decoherence of the SiV spin and demonstrate photon-mediated quantum interference between two SiV centers on a diamond chip, highlighting the utility of nanomechanical devices for photonic quantum networks. Finally, we present high quality factor, wavelength scale acoustic resonators in diamond using phononic crystals towards a coherent interface between SiV centers and single phonons.
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.
Control over the charge states of color centers in solids is necessary to fully utilize them in quantum technologies. However, the microscopic charge dynamics of deep defects in wide-band-gap semiconductors are complex, and much remains unknown. We utilize a single-shot charge-state readout of an individual nitrogen-vacancy (NV) center to probe the charge dynamics of the surrounding defects in diamond. We show that the NV center charge state can be converted through the capture of holes produced by optical illumination of defects many micrometers away. With this method, we study the optical charge conversion of silicon-vacancy (SiV) centers and provide evidence that the dark state of the SiV center under optical illumination is SiV 2– . These measurements illustrate that charge carrier generation, transport, and capture are important considerations in the design and implementation of quantum devices with color centers and provide a novel way to probe and control charge dynamics in diamond.
Summary form only given. Deterministic coupling of a single emitter to a photonic crystal cavity is an important step towards the realization of integrated solid-state devices for quantum photonics. As single emitters, color centers in diamond, e.g. the Nitrogen-Vacancy (NV) center or the Silicon-Vacancy (SiV) center have attracted significant interest due to their extraordinary properties like long spin-coherence times or narrowband and bright single photon emission, respectively. For the realization of recent proposals like cavity-enhanced spin measurements or cavity-enhanced single photon sources, it is necessary to couple single color centers to a cavity with small mode volume and high quality factor. Photonic crystal cavities directly fabricated within a monocrystalline diamond membrane are well suited for this task, as they offer tiny mode volumes for efficient emitter-cavity coupling as well as scalable architectures for integrated photonic devices.In order to achieve controlled coupling of a color center to a photonic crystal cavity, several challenges have to be tackled, e.g. exact emitter positioning and alignment of its dipole moment with the cavity electric field as well as the ability for cavity tuning. For deterministic emitter-cavity positioning, two different routes can be pursued: In the first approach, a single emitter is localized within the diamond, its dipole orientation is determined and the cavity is subsequently structured around it. In the second approach, the cavity is fabricated first and a single color center is created within the cavity, e.g. via ion implantion or creation of vacancies. Here we present strategies to realize both methods for deterministic emitter-cavity coupling. For the first approach, we use a monocrystalline diamond film containing single SiV centers. Figure 1a) shows a fluorescence scan of a single SiV center with position markers next to it. The position markers are subsequently used to structure a photonic crystal cavity around the color center using focused ion beam milling [1]. Figures 1b) and c) show SEMimages before and after the cavity fabrication. The photonic crystal lattice constant a ≈ 283nm is chosen such that the cavity modes are red shifted with respect to the SiV emission lines. Using an oxidation tuning method, the cavity modes are tuned into resonance with the zero-phonon line at 740nm of a single SiV center (see Fig. 1d)). On resonance, we measure an intensity enhancement by a factor of 3.8 compared to the off-resonant case.
Silicon-vacancy (SiV) color centers in diamond offer novel possibilities to probe light-matter interaction in nano-quantum optics and provide a scalable quantum system suitable for single-photon emission. However, their effective count-rate is still limited by non-radiative decay channels, radiation at wide angles and total internal reflection at the diamond interface. Recently optical antennas have been utilized in order to modify light-matter interaction at the nanoscale. Acting as resonators, they are able to increase the spontaneous emission rate of quantum emitters by several orders of magnitude in a broad spectral range. Because coupling a quantum emitter to a nano-antenna requires close proximity between the two systems, we implant Si ions on very thin diamond membranes that provide the required dimension for near-field interaction in a controlled manner and investigate the optical properties of SiV color centers in such diamond membranes. We consider gold nano-cones as nano-antennas, fabricated by focused electron beam induced deposition (EBID), followed by sputtering and focused ion beam (FIB) milling. The finite-difference time-domain (FDTD) calculations show that gold nano-cones can provide more than four orders of magnitude enhancement in the Purcell factor with an antenna efficiency (AE) of 80%.
Arrays of identical and individually addressable qubits lay the foundation for the creation of scalable quantum hardware such as quantum processors and repeaters. Silicon vacancy centers in diamond (SiV) offer excellent physical properties such as low inhomogeneous broadening, fast photon emission, and a large Debye-Waller factor, while the possibility for all-optical ultrafast manipulation and techniques to extend the spin coherence times make them very promising candidates for qubits. Here, we have developed arrays of nanopillars containing single SiV centers with high yield, and we demonstrate ultrafast all-optical complete coherent control of the state of a single SiV center. The high quality of the chemical vapor deposition (CVD) grown SiV centers provides excellent spectral stability, which allows us to coherently manipulate and quasi-resonantly read out the state of individual SiV centers on picosecond timescales using ultrafast optical pulses. This work opens new opportunities towards the creation of a scalable on-chip diamond platform for quantum information processing and scalable nanophotonics applications.