A central challenge in developing quantum computers and long-range quantum networks lies in the distribution of entanglement across many individually controllable qubits 1 . Colour centres in diamond have emerged as leading solid-state 'artificial atom' qubits 2,3 , enabling on-demand remote entanglement 4 , coherent control of over 10 ancillae qubits with minute-long coherence times 5 , and memory-enhanced quantum communication 6 . A critical next step is to integrate large numbers of artificial atoms with photonic architectures to enable large-scale quantum information processing systems. To date, these efforts have been stymied by qubit inhomogeneities, low device yield, and complex device requirements. Here, we introduce a process for the high-yield heterogeneous integration of 'quantum micro-chiplets' (QMCs) -diamond waveguide arrays containing highly coherent colour centreswith an aluminium nitride (AlN) photonic integrated circuit (PIC). Our process enables the development of a 72-channel defect-free array of germanium-vacancy (GeV) and silicon-vacancy (SiV) colour centres in a PIC. Photoluminescence spectroscopy reveals long-term stable and narrow average optical linewidths of 54 MHz (146 MHz) for GeV (SiV) emitters, close to the lifetime-limited linewidth of 32 MHz (93 MHz). Additionally, inhomogeneities in the individual qubits can be compensated in situ with integrated tuning of the optical frequencies over 100 GHz. The ability to assemble large numbers of nearly indistinguishable artificial atoms into phase-stable PICs provides an architecture toward multiplexed quantum repeaters 7,8 and general-purpose quantum computers [9][10][11] . Main textArtificial atom qubits in diamond combine minute-scale quantum memory times 5 with efficient spin-photon interfaces 2 , making them attractive for processing and distributing quantum information 1,3 . However, the low device yield of functional qubit systems presents a critical barrier to large-scale quantum information processing (QIP). Furthermore, although individual diamond cavity systems coupled to artificial atoms can now achieve excellent performance, the lack of active chip-integrated photonic components and wafer-scale single crystal diamond currently prohibit scaling to large-scale QIP applications [8][9][10][11] . A promising method to alleviate these constraints is heterogeneous integration (HI), which is increasingly used in advanced microelectronics to assemble separately fabricated sub-components into a single, multifunctional chip. HI approaches have also recently been used to integrate PICs with quantum devices, including quantum dot single-photon sources 12,13 , superconducting nanowire single-photon detectors 14 , and nitrogen-vacancy (NV) centre diamond waveguides 15 . However, these demonstrations assembled components one-by-one, which presents a formidable scaling challenge. The diamond 'quantum micro-chiplet (QMC)' introduced here significantly improves HI assembly yield and accuracy to enable a 72-channel defect-free waveguide-coupled art...

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.

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]

Artificial atoms in solids have emerged as leading systems for quantum information processing tasks such as quantum networking [1][2][3][4], sensing [5], and computing [6, 7]. A central goal is to develop platforms for precise and scalable control of individually addressable artificial atoms with efficient optical interfaces. Color centers in silicon [8][9][10][11], such as the recently-isolated carbonrelated 'G-center ' [12, 13], exhibit emission directly into the telecommunications O-band and can leverage the maturity of silicon-on-insulator (SOI) photonics. Here, we demonstrate the generation and individual addressing of G-center artificial atoms in an SOI photonic integrated circuit (PIC) platform. Focusing on the neutral charge state emission at 1278 nm, we observe waveguide-coupled single photon emission with an exceptionally narrow inhomogeneous distribution with standard deviation of 1.1 nm, an excited state lifetime of 8.3 ± 0.7 ns, and no degradation after months of operation. This demonstration opens the path to quantum information processing based on implantable artificial atoms in very large scale integrated (VLSI) photonics.