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...

Quantum devices for sensing and computing applications require coherent quantum systems, which can be manipulated in fast and robust ways 1 . Such quantum control is typically achieved using external electromagnetic fields, which drive the system's orbital 2 , charge 3 or spin 4,5 degrees of freedom. However, most existing approaches require complex and unwieldy gate structures, and with few exceptions 6,7 are limited to the regime of weak coherent driving. Here, we present a novel approach to coherently drive a single electronic spin using internal strain fields 8-10 in an integrated quantum device. Specifically, we employ time-varying strain in a diamond cantilever to induce long-lasting, coherent oscillations of an embedded nitrogen-vacancy (NV) centre spin. We perform direct spectroscopy of the phonon-dressed states emerging from this drive and observe hallmarks of the sought-after strong-driving regime 6,11 , where the spin rotation frequency exceeds the spin splitting. Furthermore, we employ our continuous strain driving to significantly enhance the NV's spin coherence time 12 . Our room-temperature experiments thereby constitute an important step towards strain-driven, integrated quantum devices and open new perspectives to investigate unexplored regimes of strongly driven multilevel systems 13 and exotic spin dynamics in hybrid spin-oscillator devices 14 .The use of crystal strain for the manipulation of single quantum systems ('spins') in the solid state brings vital advantages compared to established methods relying on electromagnetic fields. Strain fields can be straightforwardly engineered in the solid state and can offer a direct coupling mechanism to embedded spins 8,15 . As they are intrinsic to these systems, strain fields are immune to drifts in the coupling strength. Also, strain does not generate spurious stray fields, which are unavoidable with electric or magnetic driving and can cause unwanted dephasing or heating of the environment. Furthermore, coupling spins to strain offers attractive features of fundamental interest. For instance, strain can be used to shuttle information between distant quantum systems 15 , and has been proposed to generate squeezed spin ensembles 14 or to cool mechanical oscillators to their quantum ground state 16 . These attractive perspectives for strain-coupled hybrid quantum systems motivated recent studies of the influence of strain on nitrogen-vacancy (NV) centre electronic spins 9,10,17 and experiments on strain-induced, coherent driving of large NV spin ensembles 8 . Promoting such experiments to the single-spin regime, however, remains an outstanding challenge, and would constitute a major step towards the implementation of integrated, strain-driven quantum systems.Here, we demonstrate the coherent manipulation of a single electronic spin using time-periodic, intrinsic strain fields generated in a single-crystalline diamond mechanical oscillator. We show that such strain fields allow us to manipulate the spin in the strongdriving regime, where the spin mani...

Single silicon vacancy (SiV) color centers in diamond have recently shown the ability for high brightness, narrow bandwidth, room temperature single photon emission. This work develops a model describing the three level population dynamics of single SiV centers in diamond nanocrystals on iridium surfaces including an intensity dependent de-shelving process. Furthermore, we investigate the brightness and photostability of single centers and find maximum single photon rates of 6.2 Mcps under continuous excitation. We investigate the collection efficiency of the fluorescence and estimate quantum efficiencies of the SiV centers.

We study single silicon vacancy (SiV) centres in chemical vapour deposition (CVD) nanodiamonds on iridium as well as an ensemble of SiV centres in a high-quality, low-stress CVD diamond film by using temperaturedependent luminescence spectroscopy in the temperature range 5-295 K. We investigate in detail the temperature-dependent fine structure of the zero-phonon line (ZPL) of the SiV centres. The ZPL transition is affected by inhomogeneous as well as temperature-dependent homogeneous broadening and blue shifts by about 20 cm −1 upon cooling from room temperature to 5 K. We employ 6