Nanostructuring of a bulk material is used to change its mechanical, optical, and electronic properties and to enable many new applications. We present a scalable fabrication technique that enables the creation of densely packed diamond nanopillars for quantum technology applications. The process yields tunable feature sizes without the employment of lithographic techniques. High-aspect-ratio pillars are created through oxygen-plasma etching of diamond with a dewetted palladium film as an etch mask. We demonstrate an iterative renewal of the palladium etch mask, by which the initial mask thickness is not the limiting factor for the etch depth. Following the process, 300-400 million densely packed 100 nm wide and 1 μm tall diamond pillars were created on a 3 × 3 mm2 diamond sample. The fabrication technique is tailored specifically to enable applications and research involving quantum coherent defect center spins in diamond, such as nitrogen-vacancy (NV) centers, which are widely used in quantum science and engineering. To demonstrate the compatibility of our technique with quantum sensing, NV centers are created in the nanopillar sidewalls and are used to sense 1H nuclei in liquid wetting the nanostructured surface. This nanostructuring process is an important element for enabling the wide-scale implementation of NV-driven magnetic resonance imaging or NV-driven NMR.

We investigate nuclear spin hyperpolarization from nitrogen vacancy centers in isotopically enriched diamonds with $^{13}$C concentrations up to 100%. $^{13}$C enrichment leads to hyperfine structure of the nitrogen vacancy electron spin resonance spectrum and as a result the spectrum of dynamic nuclear polarization. We show that strongly-coupled $^{13}$C spins in the first shell surrounding a nitrogen vacancy center generate resolved hyperfine splittings, but do not act as an intermediary in the transfer of hyperpolarization of bulk nuclear spins. High levels of $^{13}$C enrichment are desirable to increase the efficiency of hyperpolarizaiton for magnetic resonance signal enhancement, imaging contrast agents, and as a platform for quantum sensing and many-body physics.

Synthetic single-crystal diamond has recently emerged as a promising platform for Raman lasers at exotic wavelengths due to its giant Raman shift, large transparency window and excellent thermal properties yielding a greatly enhanced figure-of-merit compared to conventional materials. To date, diamond Raman lasers have been realized using bulk plates placed inside macroscopic cavities, requiring careful alignment and resulting in high threshold powers (~W-kW). Here we demonstrate an on-chip Raman laser based on fully-integrated, high quality-factor, diamond racetrack micro-resonators embedded in silica. Pumping at telecom wavelengths, we show Stokes output discretely tunable over a ~100nm bandwidth around 2-{\mu}m with output powers >250 {\mu}W, extending the functionality of diamond Raman lasers to an interesting wavelength range at the edge of the mid-infrared spectrum. Continuous-wave operation with only ~85 mW pump threshold power in the feeding waveguide is demonstrated along with continuous, mode-hop-free tuning over ~7.5 GHz in a compact, integrated-optics platform.

Parametric (that is, without transfer of energy or momentum between light and its propagating medium) frequency conversion via optical nonlinearities in an on-chip platform is of great interest for developing compact, robust, low-power, broadband, coherent light sources. Such laser-like light sources, based on optical gain from parametric amplification rather than stimulated emission, have applications in spectroscopy, metrology, sensing, and all-optical information processing.1, 2 So far, nonlinear nanophotonic systems have been realized in traditional materials used in the semiconductor industry, including silica (SiO2), silicon (Si), silicon nitride (Si3N4), and group III–V compounds. However, these traditional materials suffer from linear and nonlinear loss mechanisms, especially at shorter wavelengths of light (e.g., the visible spectrum). In comparison, diamond has an extremely wide transparency window (spanning IR to UV wavelengths), a relatively large refractive index, and various color-centers acting as quantum emitters, which make it a promising material for photonic applications.3, 4 In addition, the superior thermal properties of diamond enable it to handle large optical powers in a robust, temperature-insensitive manner. Despite these features, optical nonlinearities in diamond (apart from Raman scattering—a nonparametric process—in bulk samples) have not been explored much until now. We have realized nonlinear photonics in diamond for the first time by demonstrating optical parametric oscillation (OPO) via four-wave mixing (FWM) in single-crystal diamond (SCD) micro-ring resonators that are integrated into waveguides and offer a high quality (Q) factor.5 FWM is a third-order nonlinear parametric process whereby two pump photons at frequency P are converted to two different photons at C and (denoted by signal and idler), such that energy is conserved (2 P D C C /. OPO is achieved Figure 1. Integrated single-crystal diamond (SCD) ring resonators for nonlinear optics. (a) Scanning electron micrograph of an array of buswaveguide-coupled SCD ring resonators on a silica/silicon (SiO2/Si) chip. Inset shows magnified view of the ring-bus-waveguide coupling section. The devices are later capped with a layer of deposited SiO2. (b) Normalized transmission spectrum of a ring resonator reveals high quality (Q)-factor modes. A loaded Q-factor of QL 1 106 is inferred from a Lorentzian fit for the mode at 1545.1nm. a.u.: Arbitrary units.

We report the observation of stable optical transitions in nitrogen-vacancy (NV) centers created by ion implantation. Using a combination of high temperature annealing and subsequent surface treatment, we reproducibly create NV centers with zero-phonon lines (ZPL) exhibiting spectral diffusion that is close to the lifetime-limited optical line width. The residual spectral diffusion is further reduced by using resonant optical pumping to maintain the NV- charge state. This approach allows for placement of NV centers with excellent optical coherence in a well-defined device layer, which is a crucial step in the development of diamond-based devices for quantum optics, nanophotonics, and quantum information science.

We describe top-down nanofabrication approaches to photonic devices in single-crystal diamond and analyze their performance by optical characterization. The devices presented include nanowires, angle-etched nanobeams, plasmonic resonators and integrated planar resonators, which have been used to engineer the collection efficiency and spontaneous emission rate for nitrogen–vacancy (NV) centers.

n optical parametric oscillator in the telecom wavelength range is realized in a diamond system consisting of a ring resonator coupled to a diamond waveguide. Threshold powers as low as 20 mW are measured and up to 20 new wavelengths are generated from a single-frequency pump laser.

Electron and nuclear spins associated with point defects in insulators are promising systems for solid-state quantum technology1,2,3. The electron spin is usually used for readout and addressing, and nuclear spins are used as exquisite quantum bits4,5 and memory systems3,6. With these systems, single-shot readout of single nuclear spins5,7 as well as entanglement4,8,9, aided by the electron spin, have been shown. Although the electron spin in this example is essential for readout, it usually limits the nuclear spin coherence10, leading to a quest for defects with spin-free ground states9,11. Here, we isolate a hitherto unidentified defect in diamond and use it at room temperature to demonstrate optical spin polarization and readout with exceptionally high contrast (up to 45%), coherent manipulation of an individual excited triplet state spin, and coherent nuclear spin manipulation using the triplet electron spin as a metastable ancilla. We demonstrate nuclear magnetic resonance and Rabi oscillations of the uncoupled nuclear spin in the spin-free electronic ground state. Our study demonstrates that nuclei coupled to single metastable electron spins are useful quantum systems with long memory times, in spite of electronic relaxation processes. An unidentified defect in diamond is used to demonstrate optical spin polarization and readout with high contrast.

Efficient, on-chip optical nonlinear processes are of great interest for the development of compact, robust, low-power consuming systems for applications in spectroscopy, metrology, sensing and classical and quantum optical information processing. Diamond holds promise for these applications, owing to its exceptional properties. However, although significant progress has been made in the development of an integrated diamond photonics platform, optical nonlinearities in diamond have not been explored much apart from Raman processes in bulk samples. Here, we demonstrate optical parametric oscillations (OPO) via four wave mixing (FWM) in single crystal diamond (SCD) optical networks on-chip consisting of waveguide-coupled microring resonators. Threshold powers as low as 20mW are enabled by ultra-high quality factor (1*10^6) diamond ring resonators operating at telecom wavelengths, and up to 20 new wavelengths are generated from a single-frequency pump laser. We also report the inferred nonlinear refractive index due to the third-order nonlinearity in diamond at telecom wavelengths.

We demonstrate optical parametric oscillation via four-wave mixing in waveguide-integrated, single crystal diamond micro-ring resonators. Threshold powers as low as 20 mW are enabled by high quality factor (~1 million) resonators operating at telecom wavelengths.

The realization of an integrated diamond photonic platform, based on a thin single crystal diamond film on top of a silicon dioxide/silicon substrate, is reported. Using this approach, we demonstrate high-quality factor single crystal diamond race-track resonators, operating at near-infrared wavelengths (1550 nm). The devices are integrated with low-loss diamond waveguides terminated with polymer pads (spot size converters) to facilitate in- (out-) coupling of light from (to) an optical fiber. Optical characterization of these resonators reveal quality factors as high as ~250,000 and overall insertion losses as low as 1 dB/facet. Scattering induced mode splitting as well as signatures of nonlinear effects such as optical bistability are observed at an input pump power of ~100 mW in the waveguides.

The realization of efficient optical interfaces for solid-state atom-like systems is an important problem in quantum science with potential applications in quantum communications and quantum information processing. We describe and demonstrate a technique for coupling single nitrogen vacancy (NV) centers to suspended diamond photonic crystal cavities with quality factors up to 6000. Specifically, we present an enhancement of the NV center's zero-phonon line fluorescence by a factor of ~ 7 in low-temperature measurements.

We demonstrate an approach, based on plasmonic apertures and gratings, to enhance the radiative decay rate of single NV centers in diamond, while simultaneously improving their collection efficiency. Our structures are based on metallic resonators formed by surrounding sub-wavelength diamond nanoposts with a silver film, which can enhance the spontaneous emission rate of an embedded NV center. However, the collection efficiency of emitted photons remains low due to losses to surface plasmons and reflections at the diamond-air interface. In this work, we mitigate photon losses into these channels by incorporating grating structures into the plasmonic cavity system.

A variety of nanoscale photonic, mechanical, electronic, and optoelectronic devices require scalable thin film fabrication. Typically, the device layer is defined by thin film deposition on a substrate of a different material, and optical or electrical isolation is provided by the material properties of the substrate or by removal of the substrate. For a number of materials this planar approach is not feasible, and new fabrication techniques are required to realize complex nanoscale devices. Here, we report a three-dimensional fabrication technique based on anisotropic plasma etching at an oblique angle to the sample surface. As a proof of concept, this angled-etching methodology is used to fabricate free-standing nanoscale components in bulk single-crystal diamond, including nanobeam mechanical resonators, optical waveguides, and photonic crystal and microdisk cavities. Potential applications of the fabricated prototypes range from classical and quantum photonic devices to nanomechanical-based sensors and actuators.

Diamond nanophotonics have evolved tremendously from the study of color centers in bulk single crystals and nanocrystals to their characterization in nanostructured environments. This development was facilitated by the ability to generate monolithic, sophisticated nanodevices in high quality single crystal diamond. Here, we present some recent contributions to the field of diamond nanophotonics: increase in single photon collection from nitrogen vacancy (NV) centers embedded in diamond nanowires, broadband spontaneous emission enhancement of single NV centers in plasmonic resonators, and coupling of single NV centers to planar resonators on-chip.

We demonstrate integrated on-chip ring resonators on a single crystal diamond on insulator substrate with wide band operation around 1550nm with quality factors as large as 15000 for TE and TM modes.