Photon-mediated coupling between distant matter qubits may enable secure communication over long distances, the implementation of distributed quantum computing schemes, and the exploration of new regimes of many-body quantum dynamics. Solid-state quantum emitters coupled to nanophotonic devices represent a promising approach towards these goals, as they combine strong light-matter interaction and high photon collection efficiencies. However, nanostructured environments introduce mismatch and diffusion in optical transition frequencies of emitters, making reliable photon-mediated entanglement generation infeasible. Here we address this long-standing challenge by employing silicon-vacancy color centers embedded in electromechanically deflectable nanophotonic waveguides. This electromechanical strain control enables control and stabilization of optical resonance between two silicon-vacancy centers on the hour timescale. Using this platform, we observe the signature of an entangled, superradiant state arising from quantum interference between two spatially separated emitters in a waveguide. This demonstration and the developed platform constitute a crucial step towards a scalable quantum network with solid-state quantum emitters.

We demonstrate generation of frequency tunable single-photon emission based on cavity-enhanced Raman emission from a single silicon-vacancy center in diamond. The demonstrated frequency tuning range (100 GHz) significantly exceeds the spectral inhomogeneity of the emitters. © 2019 The Author(s)

We realize an elementary quantum network node consisting of a silicon-vacancy (SiV) color center inside a diamond nanocavity coupled to a nearby nuclear spin with 100 ms long coherence times. Specifically, we describe experimental techniques and discuss effects of strain, magnetic field, microwave driving, and spin bath on the properties of this 2-qubit register. We then employ these techniques to generate Bell-states between the SiV spin and an incident photon as well as between the SiV spin and a nearby nuclear spin. We also discuss control techniques and parameter regimes for utilizing the SiV-nanocavity system as an integrated quantum network node.

Photon-mediated interactions between quantum systems are essential for realizing quantum networks and scalable quantum information processing. We demonstrate such interactions between pairs of silicon-vacancy (SiV) color centers strongly coupled to a diamond nanophotonic cavity. When the optical transitions of the two color centers are tuned into resonance, the coupling to the common cavity mode results in a coherent interaction between them, leading to spectrally-resolved superradiant and subradiant states. We use the electronic spin degrees of freedom of the SiV centers to control these optically-mediated interactions. Our experiments pave the way for implementation of cavity-mediated quantum gates between spin qubits and for realization of scalable quantum network nodes.

Quantum emitters in semiconductors, such as quantum dots and color centers, have been used to demonstrate nonclassical light sources with high purity, indistinguishability, and efficiency. Further improvements can be achieved by employing photonics optimization techniques.

We investigate the properties of optomechanical crystals (OMCs) fabricated in single-crystal diamond in a cryogenic environment (T ~ 5K). We demonstrate high mechanical Q-factors (> 100,000) from localized OMC mechanical modes at 5 & 8 GHz, a 30x improvement from room temperature.

Polymers are a highly versatile class of materials for micro and nanofabrication. They have been studied for applications in photonics as they can be readily processed, integrated, and doped with a wide range of materials, and can be flexible and stretchable, providing numerous opportunities such as wearable devices and structures with tunable photonic response. Roll-to-roll nanoimprint lithography (R2RNIL) is a method to produce all-polymer devices, which provides the opportunity to target applications where low cost and high throughput are needed most. Here, finite difference time domain simulations are performed to determine the requirements for R2RNIL in order to produce functional photonic integrated circuits. A wide range of nanophotonic devices are fabricated, including waveguides, photonic crystals, diffraction gratings, and ring resonators. Loaded quality factors as high as 57500 are measured in ring resonators at the telecom wavelength range, enabling on-chip high resolution sensors and spectrometers.

We control the electronic structure of the silicon-vacancy (SiV) color-center in diamond by changing its static strain environment with a nano-electro-mechanical system. This allows deterministic and local tuning of SiV optical and spin transition frequencies over a wide range, an essential step towards multi-qubit networks. In the process, we infer the strain Hamiltonian of the SiV revealing large strain susceptibilities of order 1 PHz/strain for the electronic orbital states. We identify regimes where the spin-orbit interaction results in a large strain suseptibility of order 100 THz/strain for spin transitions, and propose an experiment where the SiV spin is strongly coupled to a nanomechanical resonator.

We present a platform for the generation and high-efficiency collection of indistinguishable photons from spatially separated silicon-vacancy (SiV) color centers by use of waveguide-coupled nanoelectromechanical systems (NEMS).

We demonstrate strong enhancement of spontaneous emission of a single silicon-vacancy (SiV−) center in diamond embedded in a monolithic optical cavity, with 10-fold lifetime reduction and 42-fold enhancement in emission intensity under resonant condition.

We demonstrate cavity-enhanced Raman emission from a single atomic defect in a solid. Our platform is a single silicon-vacancy center in diamond coupled with a monolithic diamond photonic crystal cavity. The cavity enables an unprecedented frequency tuning range of the Raman emission (100 GHz) that significantly exceeds the spectral inhomogeneity of silicon-vacancy centers in diamond nanostructures. We also show that the cavity selectively suppresses the phonon-induced spontaneous emission that degrades the efficiency of Raman photon generation. Our results pave the way towards photon-mediated many-body interactions between solid-state quantum emitters in a nanophotonic platform.

Quantum emitters are an integral component for a broad range of quantum technologies, including quantum communication, quantum repeaters, and linear optical quantum computation. Solid-state color centers are promising candidates for scalable quantum optics due to their long coherence time and small inhomogeneous broadening. However, once excited, color centers often decay through phonon-assisted processes, limiting the efficiency of single-photon generation and photon-mediated entanglement generation. Herein, we demonstrate strong enhancement of spontaneous emission rate of a single silicon-vacancy center in diamond embedded within a monolithic optical cavity, reaching a regime in which the excited-state lifetime is dominated by spontaneous emission into the cavity mode. We observe 10-fold lifetime reduction and 42-fold enhancement in emission intensity when the cavity is tuned into resonance with the optical transition of a single silicon-vacancy center, corresponding to 90% of the excited-state energy decay occurring through spontaneous emission into the cavity mode. We also demonstrate the largest coupling strength (g/2π = 4.9 ± 0.3 GHz) and cooperativity (C = 1.4) to date for color-center-based cavity quantum electrodynamics systems, bringing the system closer to the strong coupling regime.

Spin coherence time, T-2*, of the silicon vacancy color center in diamond is limited by thermal phonons existing in the lattice. We show how this process can be engineered by applying static strain using a micro-electro-mechanical system (MEMS) fabricated on diamond. By suppressing the relevant thermal process, we demonstrate the improvement of spin T-2*.

Diamond nanophotonics is a rapidly evolving platform in which non-classical light—emitted by defect centers in diamond— can be generated, manipulated, and detected in a single monolithic device (e.g., for quantum information processing applications).1–3 Indeed, novel diamond fabrication techniques make it possible to engineer unique nanostructures in which diamond’s extraordinary material properties (e.g., high refractive index, wide band gap, and large optical transmission window) can be exploited.4, 5 The relatively large Kerr non-linearity6 of diamond also makes it an attractive platform for on-chip nonlinear optics at visible and IR wavelengths.7 This nonlinearity could be used for frequency conversion of photons generated by color centers in diamond (i.e., from their typical visible wavelengths to telecom wavelengths).8 In turn, this would enable transmission of quantum information and distribution of quantum entanglement9, 10 over long distances. Such integrated diamond–quantum photonics platforms would benefit from the use (and realization) of high-performance single-photon detectors that have broadband photon sensitivity and are integrated on the same diamond chip. Superconducting nanowire single-photon detectors (SNSPDs) are a class of cutting-edge photon detectors that outperform other technologies in terms of detection efficiency, dark counts, timing jitter, and maximum count rates.11–13 SNSPDs typically consist of narrow nanowires that are patterned into an ultrathin (4–8nm) superconducting film.14 The nanowires are biased close to the critical current of the superconductor material so that Figure 1. Confocal scan of freestanding diamond waveguides, where bright spots indicate locations of implanted single nitrogen vacancy centers.

We demonstrate a quantum nanophotonics platform based on germanium-vacancy (GeV) color centers in fiber-coupled diamond nanophotonic waveguides. We show that GeV optical transitions have a high quantum efficiency and are nearly lifetime broadened in such nanophotonic structures. These properties yield an efficient interface between waveguide photons and a single GeV center without the use of a cavity or slow-light waveguide. As a result, a single GeV center reduces waveguide transmission by 18±1% on resonance in a single pass. We use a nanophotonic interferometer to perform homodyne detection of GeV resonance fluorescence. By probing the photon statistics of the output field, we demonstrate that the GeV-waveguide system is nonlinear at the single-photon level.

Color centers in diamond provide a promising platform for quantum optics in the solid state, with coherent optical transitions and long-lived electron and nuclear spins. Building upon recent demonstrations of nanophotonic waveguides and optical cavities in single-crystal diamond, we now demonstrate on-chip diamond nanophotonics with a high efficiency fiber-optical interface, achieving > 90% power coupling at visible wavelengths. We use this approach to demonstrate a bright source of narrowband single photons, based on a silicon-vacancy color center embedded within a waveguide-coupled diamond photonic crystal cavity. Our fiber-coupled diamond quantum nanophotonic interface results in a high flux of coherent single photons into a single mode fiber, enabling new possibilities for realizing quantum networks that interface multiple emitters, both on-chip and separated by long distances.

Efficient interfaces between photons and quantum emitters form the basis for quantum networks and enable nonlinear optical devices operating at the single-photon level. We demonstrate an integrated platform for scalable quantum nanophotonics based on silicon-vacancy (SiV) color centers coupled to nanoscale diamond devices. By placing SiV centers inside diamond photonic crystal cavities, we realize a quantum-optical switch controlled by a single color center. We control the switch using SiV metastable orbital states and verify optical switching at the single-photon level by using photon correlation measurements. We use Raman transitions to realize a single-photon source with a tunable frequency and bandwidth in a diamond waveguide. Finally, we create entanglement between two SiV centers by detecting indistinguishable Raman photons emitted into a single waveguide. Entanglement is verified using a novel superradiant feature observed in photon correlation measurements, paving the way for the realization of quantum networks.

Freestanding nanostructures play an important role in optical and mechanical devices for classical and quantum applications. Here, we use reactive ion beam angled etching to fabricate optical resonators in bulk polycrystalline and single crystal diamond. Reported quality factors are approximately 30 000 and 286 000, respectively. The devices show uniformity across 25 mm samples, a significant improvement over comparable techniques yielding freestanding nanostructures.