Generating entangled graph states of qubits requires high entanglement rates, with efficient detection of multiple indistinguishable photons from separate qubits. Integrating defect-based qubits into photonic devices results in an enhanced photon collection efficiency, however, typically at the cost of a reduced defect emission energy homogeneity. Here, we demonstrate that the reduction in defect homogeneity in an integrated device can be partially offset by electric field tuning. Using photonic device-coupled implanted nitrogen vacancy (NV) centers in a GaP-on-diamond platform, we demonstrate large field-dependent tuning ranges and partial stabilization of defect emission energies. These results address some of the challenges of chip-scale entanglement generation. 19 NV centers within ∼ 15 nm of the diamond surface, created via implantation and annealing, couple evanescently with the GaP layer. As a result of the static dipole moment of the defect's excited state, there is variation in emission energy both between different defects, due to variation in the local environment caused by implantation and processing damage, and in the emission energy of a single defect over time due to electric field fluctuations. However, this dipole moment also enables electric field control of the defect's emission energy. 6,15,20,21 We provide this control through the addition of Ti/Au electrodes to this GaP-on-diamond photonics platform.In the photonic devices used in these experiments, 22Measurements were performed between 12-14 K in a closed-cycle He cryostat. A 532 nm laser was used for optical excitation, focused onto the sample with a 0.7 NA microscope objective. Photoluminescence (PL) was collected from the grating coupler using the same objective, coupled into a grating spectrometer, and detected by a CCD camera (Figure 1(a)).The input and collection optical paths were separated by a 562 nm dichoric beamsplitter.Bias voltages were applied using a computer-controlled piezocontroller in the range of 0-100 V.We first demonstrate electric-field tuning of a waveguide-coupled NV center. Exciting We also electrically control the emission energy of a resonator-coupled NV center. We first tune the cavity mode of a waveguide-coupled disk resonator onto NV ZPL resonance via Xe gas deposition, while collecting the PL emission from the waveguide grating coupler.The Xe gas deposition results in a redshift of the resonator cavity mode. Figure 2 (b, left) shows the resulting Xe gas tuning curve for one disk resonator. Xe gas flow is halted from t ∼ 15 minutes to t ∼ 45 minutes to perform two voltage experiments and then resumed.NV centers that couple with the cavity mode are bright when in resonance with the cavity mode and not visible otherwise.19 There are several NV centers that couple to the cavity mode for this particular disk resonator. With the cavity mode tuned to resonance with two NV centers, we apply a square wave bias voltage (Figure 2(b)), and we see the two ZPL emission lines moving in response to the applied ...

We present chip--scale transmission measurements for three key components of a GaP--on--diamond integrated photonics platform: waveguide--coupled disk resonators, directional couplers, and grating couplers. We also present proof--of--principle measurements demonstrating nitrogen--vacancy (NV) center emission coupled into selected devices. The demonstrated device performance, uniformity and yield place the platform in a strong position to realize measurement--based quantum information protocols utilizing the NV center in diamond.

Solid-state defect qubit systems with spin-photon interfaces show great promise for quantum information and metrology applications. Photon collection efficiency, however, presents a major challenge for defect qubits in high refractive index host materials. Inverse-design optimization of photonic devices enables unprecedented flexibility in tailoring critical parameters of a spin-photon interface including spectral response, photon polarization, and collection mode. Further, the design process can incorporate additional constraints, such as fabrication tolerance and material processing limitations. Here, we design and demonstrate a compact hybrid gallium phosphide on diamond inverse-design planar dielectric structure coupled to single near-surface nitrogen-vacancy centers formed by implantation and annealing. We observe up to a 14-fold broadband enhancement in photon extraction efficiency, in close agreement with simulations. We expect that such inverse-designed devices will enable realization of scalable arrays of single-photon emitters, rapid characterization of new quantum emitters, efficient sensing, and heralded entanglement schemes.

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Knowledge of the nitrogen-vacancy center formation kinetics in diamond is critical to engineering sensors and quantum information devices based on this defect. Here we utilize the longitudinal tracking of single NV centers to elucidate NV defect kinetics during high-temperature annealing from 800-1100 • C in high-purity chemical-vapor-deposition diamond. We observe three phenomena which can coexist: NV formation, NV quenching, and NV orientation changes. Of relevance to NV-based applications, a 6 to 24-fold enhancement in the NV density, in the absence of sample irradiation, is observed by annealing at 980 • C, and NV orientation changes are observed at 1050 • C. With respect to the fundamental understanding of defect kinetics in ultra-pure diamond, our results indicate a significant vacancy source can be activated for NV creation between 950-980 • C and suggests that native hydrogen from NVHy complexes plays a dominant role in NV quenching, in agreement with recent ab initio calculations. Finally, the direct observation of orientation changes allows us to estimate an NV diffusion barrier of 5.1 eV. arXiv:1907.07793v1 [cond-mat.mtrl-sci]

We demonstrate quasi-phase matched, triply-resonant sum frequency conversion in 10.6-µm-diameter integrated gallium phosphide ring resonators. A small-signal, waveguide-to-waveguide power conversion efficiency of 8 ± 1.1%/mW; is measured for conversion from telecom (1536 nm) and near infrared (1117 nm) to visible (647 nm) wavelengths with an absolute power conversion efficiency of 6.3 ± 0.6%; measured at saturation pump power. For the complementary difference frequency generation process, a single photon conversion efficiency of 7.2%/mW from visible to telecom is projected for resonators with optimized coupling. Efficient conversion from visible to telecom will facilitate long-distance transmission of spin-entangled photons from solid-state emitters such as the diamond NV center, allowing long-distance entanglement for quantum networks.

We demonstrate post-fabrication target-wavelength trimming with a gallium phosphide on a silicon nitride integrated photonic platform using controlled electron-beam exposure of hydrogen silsesquioxane cladding. A linear relationship between the electron-beam exposure dose and resonant wavelength red-shift enables deterministic, individual trimming of multiple devices on the same chip to within 30 pm of a single target wavelength. Second harmonic generation from telecom to near infrared at a target wavelength is shown in multiple devices with quality factors on the order of 104. Post-fabrication tuning is an essential tool for targeted wavelength applications including quantum frequency conversion.

Optically addressable solid-state defects are emerging as some of the most promising qubit platforms for quantum networks. Maximizing photon-defect interaction by nanophotonic cavity coupling is key to network efficiency. We demonstrate fabrication of gallium phosphide 1-D photonic crystal waveguide cavities on a silicon oxide carrier and subsequent integration with implanted silicon-vacancy (SiV) centers in diamond using a stamptransfer technique. The stamping process avoids diamond etching and allows fine-tuning of the cavities prior to integration. After transfer to diamond, we measure cavity quality factors (Q) of up to 8900 and perform resonant excitation of single SiV centers coupled to these cavities. For a cavity with a Q of 4100, we observe a 3-fold lifetime reduction on-resonance, corresponding to a maximum potential cooperativity of C = 2. These results indicate promise for high photon-defect interaction in a platform which avoids fabrication of the quantum defect host crystal.