We introduce a process for the fabrication of high quality, spatially isolated nano-diamonds on iridium via microwave plasma assisted CVD-growth. We perform spectroscopy of single silicon-vacancy (SiV)-centres produced during the growth of the nano-diamonds. The colour centres exhibit extraordinary narrow zero-phonon-lines down to 0.7 nm at room temperature. Single photon count rates up to 4.8 Mcps at saturation make these SiV-centres the brightest diamond based single photon sources to date. We measure for the first time the fine structure of a single SiV-centre thus confirming the atomic composition of the investigated colour centres.

We report on single electronic spins coupled to the motion of mechanical resonators by a novel mechanism based on crystal strain. Our device consists of single-crystal diamond cantilevers with embedded nitrogen-vacancy center spins. Using optically detected electron spin resonance, we determine the unknown spin-strain coupling constants and demonstrate that our system resides well within the resolved sideband regime. We realize coupling strengths exceeding 10 MHz under mechanical driving and show that our system has the potential to reach strong coupling. Our novel hybrid system forms a resource for future experiments on spin-based cantilever cooling and coherent spin-oscillator coupling. DOI: 10.1103/PhysRevLett.113.020503 PACS numbers: 03.67.Lx, 42.50.Wk, 76.30.Mi, 85.85.+j Recent years have brought significant advances in the control of nanoscale mechanical oscillators, which culminated in experiments to prepare such oscillators close to their quantum ground state [1,2] or a single-phonon excited state [3]. Generating and studying such states and further extending quantum control of macroscopic mechanical oscillators brings exciting perspectives for high precision sensing, quantum technologies [4], and fundamental studies of the quantum-to-classical crossover [5][6][7]. An attractive route towards these goals is to couple individual quantum two-level systems to mechanical oscillators and thereby enable efficient oscillator cooling [8] or state transfer [9] between a quantum system and oscillator in analogy to established concepts in ion trapping [10]. A prerequisite for most of these schemes [8,10,11] is the resolved sideband regime, where the transition between the two quantum states exhibits well-resolved, frequency-modulated sidebands at the oscillator eigenfrequency. Various hybrid systems are currently being explored in this context and include mechanical oscillators coupled to cold atoms [12], superconducting qubits [3], quantum dots [13,14], or solid-state spin systems [15,16]. None of these systems, however, have reached the resolved sideband regime thus far and novel approaches are needed to further advance quantum control of macroscopic mechanical systems.An important aspect that distinguishes existing hybrid systems is the physical mechanism they exploit to couple quantum system and oscillator. Coupling through electric [13], magnetic [15,16], or strain fields [14], as well as through optical forces [12] has been demonstrated as of now. Strain coupling is based on electronic level shifts [8,17] induced by crystal strain during mechanical motion and is particularly appealing in the context of hybrid systems. On one hand, strain coupling is predicted to result in interesting and unique system dynamics, such as spin squeezing [18] or phonon lasing [19] and can be used for mechanical spin driving [20]. On the other hand, strain coupling brings decisive technological advantages as it is intrinsic to the system. It thereby allows for monolithic and compact devices which are robust against manufacturi...

The burgeoning field of nanophotonics has grown to be a major research area, primarily because of the ability to control and manipulate single quantum systems (emitters)

The development of solid-state photonic quantum technologies is of great interest for fundamental studies of light-matter interactions and quantum information science. Diamond has turned out to be an attractive material for integrated quantum information processing due to the extraordinary properties of its colour centres enabling e.g. bright single photon emission and spin quantum bits. To control emitted photons and to interconnect distant quantum bits, micro-cavities directly fabricated in the diamond material are desired. However, the production of photonic devices in high-quality diamond has been a challenge so far. Here we present a method to fabricate one-and two-dimensional photonic crystal micro-cavities in single-crystal diamond, yielding quality factors up to 700. Using a post-processing etching technique, we tune the cavity modes into resonance with the zero phonon line of an ensemble of silicon-vacancy centres and measure an intensity enhancement by a factor of 2.8. The controlled coupling to small mode volume photonic crystal cavities paves the way to larger scale photonic quantum devices based on single-crystal diamond.A number of seminal experiments have demonstrated the prospects of colour centres in diamond, in particular the negatively charged nitrogen-vacancy centre

The nitrogen-vacancy (NV) center in diamond has an optically addressable, highly coherent spin. However, an NV center even in high quality single-crystalline material is a very poor source of single photons: extraction out of the high-index diamond is inefficient, the emission of coherent photons represents just a few per cent of the total emission, and the decay time is large. In principle, all three problems can be addressed with a resonant microcavity. In practice, it has proved difficult to implement this concept: photonic engineering hinges on nano-fabrication yet it is notoriously difficult to process diamond without degrading the NV centers. We present here a microcavity scheme which uses minimally processed diamond, thereby preserving the high quality of the starting material, and a tunable microcavity platform. We demonstrate a clear change in the lifetime for multiple individual NV centers on tuning both the cavity frequency and anti-node position, a Purcell effect. The overall Purcell factor FP = 2.0 translates to a Purcell factor for the zero phonon line (ZPL) of F ZPL P ∼ 30 and an increase in the ZPL emission probability from ∼ 3 % to ∼ 46 %. By making a step-change in the NV's optical properties in a deterministic way, these results pave the way for much enhanced spin-photon and spin-spin entanglement rates.The nitrogen-vacancy (NV) center in diamond constitutes a workhorse in quantum technology on account of its optically addressable, coherent electron spin [1]. The NV stands out for its long spin coherence times [2], robust single photon emission [3] and the possibility of mapping its spin state to nearby nuclear spins [4]. Advances in spin-photon entanglement [5] and two-photon quantum interference protocols [6,7] pave the way for the implementation of quantum teleportation [8] and long-distance spin-spin entanglement [9]. However, the success rate of these protocols and the scaling up to extended networks are both limited by the very small generation rate of indistinguishable photons from individual NV centers [10].There are at least four factors which limit the generation rate of indistinguishable photons. First, the lifetime of NV centers is relatively long, ∼ 12 ns. Secondly, only a small fraction, ∼ 3 − 4 %, of the NV emission goes into the zero phonon line (ZPL) [11,12]. Only ZPL emission is useful for photon-based entanglement-swapping protocols as the phonon involved in non-ZPL emission dephases very rapidly. Thirdly, the photon extraction efficiency out of the diamond is hindered by the large refractive index of diamond itself. Finally, there are random spectral fluctuations in the exact frequency of the NV emission caused by charge noise in the diamond host [6].Coupling the NV center to a high quality factor, low mode volume optical microcavity offers a potential remedy to the first three factors thereby dramatically im- * Electronic address: daniel.riedel@unibas.ch proving the rate of coherent photon generation. These improvements depend on the weak coupling regime of cavity quantum e...