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.

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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

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

Colour centres in diamond have emerged as versatile tools for solid-state quantum technologies ranging from quantum information to metrology, where the nitrogen-vacancy centre is the most studied to date. Recently, this toolbox has expanded to include novel colour centres to realize more efficient spin-photon quantum interfaces. Of these, the silicon-vacancy centre stands out with highly desirable photonic properties. The challenge for utilizing this centre is to realize the hitherto elusive optical access to its electronic spin. Here we report spin-tagged resonance fluorescence from the negatively charged silicon-vacancy centre. Our measurements reveal a spin-state purity approaching unity in the excited state, highlighting the potential of the centre as an efficient spin-photon quantum interface.

Deterministic coupling of single solid-state emitters to nanocavities is the key for integrated quantum information devices. We here fabricate a photonic crystal cavity around a preselected single silicon-vacancy color center in diamond and demonstrate modification of the emitters internal population dynamics and radiative quantum efficiency. The controlled, room-temperature cavity coupling gives rise to a resonant Purcell enhancement of the zero-phonon transition by a factor of 19, coming along with a 2.5-fold reduction of the emitter's lifetime.

We studied the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state established due to the proximity effect in superconducting Nb/Cu 41 Ni 59 bilayers. Using a special wedge-type deposition technique, series of 20-35 samples could be fabricated by magnetron sputtering during one run. The layer thickness of only a few nanometers, the composition of the alloy, and the quality of interfaces were controlled by Rutherford backscattering spectrometry, high resolution transmission electron microscopy, and Auger spectroscopy. The magnetic properties of the ferromagnetic alloy layer were characterized with superconducting quantum interference device (SQUID) magnetometry. These studies yield precise information about the thickness, and demonstrate the homogeneity of the alloy composition and magnetic properties along the sample series. The dependencies of the critical temperature on the Nb and Cu 41 Ni 59 layer thickness, T c (d S ) and T c (d F ), were investigated for constant thickness d F of the magnetic alloy layer and d S of the superconducting layer, respectively. All types of non-monotonic behaviors of T c versus d F predicted by the theory could be realized experimentally: from reentrant superconducting behavior with a broad extinction region to a slight suppression of superconductivity with a shallow minimum. Even a double extinction of superconductivity was observed, giving evidence for the multiple reentrant behavior predicted by theory. All critical temperature curves were fitted with suitable sets of parameters. Then, T c (d F ) diagrams of a hypothetical F/S/F spin-switch core structure were calculated using these parameters. Finally, superconducting spin-switch fabrication issues are discussed in detail in view of the achieved results.

We report on the first observation of a pronounced re-entrant superconductivity phenomenon in superconductor/ferromagnetic layered systems. The results were obtained using a superconductor/ferromagnetic-alloy bilayer of Nb/Cu1−xNix. The superconducting transition temperature Tc drops sharply with increasing thickness dCuNi of the ferromagnetic layer, until complete suppression of superconductivity is observed at dCuNi ≈4 nm. Increasing the Cu1−xNix layer thickness further, superconductivity reappears at dCuNi≈13 nm. Our experiments give evidence for the pairing function oscillations associated with a realization of the quasi-one dimensional Fulde-FerrellLarkin-Ovchinnikov (FFLO) like state in the ferromagnetic layer.The coexistence of superconductivity (S) and ferromagnetism (F) in a homogeneous material, described by Fulde-Ferrell and Larkin-Ovchinnikov (FFLO) [1,2], is restricted to an extremely narrow range of parameters [3]. So far no indisputable experimental evidence for the FFLO state exists.In general, superconductivity and ferromagnetism do not coexist, since superconductivity requires the conduction electrons to form Cooper pairs with antiparallel spins, whereas ferromagnetism forces the electrons to align their spins parallel. This antagonism can be overcome if superconducting and ferromagnetic regions are spatially separated, as for example, in artificially layered superconductor/ferromagnet (S/F) nanostructures (see, e.g. [4], for an early review). The two long-range ordered states influence each other via the penetration of electrons through their common interface. Superconductivity in such a proximity system can survive, even if the exchange splitting energy E ex ∼ k B θ Curie in the ferromagnetic layer is orders of magnitude larger than the superconducting order parameter ∆ ∼ k B T c , with T c the superconducting transition temperature. Cooper pairs entering from the superconducting into the ferromagnetic region experience conditions drastically different from those in a non-magnetic metal. This is due to the fact that spin-up and spin-down partners in a Cooper pair occupy different exchange-split spin-subbands of the conduction band in the ferromagnet. Thus, the spin-up and spin-down wave-vectors of electrons in a pair, which have opposite directions, cannot longer be of equal magnitude and the Cooper pair acquires a finite pairing momentum [5]. This results in a pairing function that does not simply decay as in a non-magnetic metal, but in addition oscillates on a characteristic length scale. This length scale is the magnetic coherence length ξ F , which will be specified below.Various unusual phenomena follow from the oscillation of the pairing wave function in ferromagnets (see, e.g. the recent reviews [6,7,8] and references therein). A prominent example is the oscillatory S/F proximity effect. It can be qualitatively described using the analogy with the interference of reflected light in a Fabry-Pérot interferometer at normal incidence. As the conditions change periodically between construc...