9We demonstrate high resolution scanning fluorescence resonance energy transfer 10 microscopy between a single nitrogen-vacancy center as donor and graphene as acceptor. 11Images with few nanometer resolution of single and multilayer graphene structures were 12attained. An energy transfer efficiency of 30% at distances of 10nm between a single 13 defect and graphene was measured.

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Control of molecular spins and their readout with a solid-state qubit are described as a unit cell in a quantum spin network.

Controlled enhancement of NV center fluorescence in nanodiamonds via control over the formation process and surface parameters.

Magnetic sensing and imaging instruments are important tools in biological and material sciences. There is an increasing demand for attaining higher sensitivity and spatial resolution, with implementations using a single qubit offering potential improvements in both directions. In this article we describe a scanning magnetometer based on the nitrogen-vacancy center in diamond as the sensor. By means of a quantum-assisted readout scheme together with advances in photon collection efficiency, our device exhibits an enhancement in signal to noise ratio of close to an order of magnitude compared to the standard fluorescence readout of the nitrogenvacancy center. This is demonstrated by comparing non-assisted and assisted methods in a T 1 relaxation time measurement.

Coupled micro-and nanomechanical oscillators are of fundamental and technical interest for emerging quantum technologies. Upon interfacing with long-lived solid-state spins, the coherent manipulation of the quantum hybrid system becomes possible even at ambient conditions. While, the ability of these systems to act as a quantum bus inducing long-range spin-spin interactions has been known, the possibility to coherently couple electron/nuclear spins to the common modes of multiple oscillators and map their mechanical motion to spin-polarization has not been experimentally demonstrated. We here report experiments on interfacing spins to the common modes of a coupled cantilever system, and show their correlation by translating ultra-low forces induced by radiation from one oscillator to a distant spin. Further, we analyze the coherent spin-spin coupling induced by the common modes and estimate the entanglement generation among distant spins.

We demonstrate that a recently introduced family of direct-emitting green laser diodes is a simple yet efficient light source for excitation of NV centers in diamond. Thanks to their fast (sub-ns) response time, these sources are suitable for a broad variety of measurements, including pulsed optically detected magnetic resonance (ODMR) and fluorescence lifetime imaging. This feature, together with a drastically simplified design, is a significant advantage over the traditional excitation system comprising an Nd: YAG laser switched by an acousto-optic modulator. We introduce a simple design for such a compact laser system and experimentally verify that it enables simultaneous lifetime and ODMR measurements on NV centers. In particular, we find that the NV(-) charge state remains stable in spite of the short excitation wavelength of the new source.

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