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, 1 arXiv:1608.05147v1 [quant-ph]

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...

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.arXiv:1801.09833v2 [quant-ph]

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 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. Such controlled interactions will be crucial in developing cavity-mediated quantum gates between spin qubits and for realizing scalable quantum network nodes.

The controlled creation of defect centre—nanocavity systems is one of the outstanding challenges for efficiently interfacing spin quantum memories with photons for photon-based entanglement operations in a quantum network. Here we demonstrate direct, maskless creation of atom-like single silicon vacancy (SiV) centres in diamond nanostructures via focused ion beam implantation with ∼32 nm lateral precision and <50 nm positioning accuracy relative to a nanocavity. We determine the Si+ ion to SiV centre conversion yield to be ∼2.5% and observe a 10-fold conversion yield increase by additional electron irradiation. Low-temperature spectroscopy reveals inhomogeneously broadened ensemble emission linewidths of ∼51 GHz and close to lifetime-limited single-emitter transition linewidths down to 126±13 MHz corresponding to ∼1.4 times the natural linewidth. This method for the targeted generation of nearly transform-limited quantum emitters should facilitate the development of scalable solid-state quantum information processors.