Controlling the interaction of a single quantum emitter with its environment is a key challenge in quantum optics. Here, we demonstrate deterministic coupling of single nitrogen-vacancy ͑NV͒ centers to high-quality photonic crystal cavities. We preselect single NV centers and position their 50-nm-sized host nanocrystals into the mode maximum of photonic crystal S1 cavities with few-nanometer accuracy. The coupling results in a strong enhancement of NV center emission at the cavity wavelength. © 2011 American Institute of Physics. ͓doi:10.1063/1.3571437͔Spontaneous light emission can be controlled by enhancing or suppressing the vacuum fluctuations of the electromagnetic field at the location of the light source. 1 When placed into highly confined optical fields, such as those created in optical cavities or plasmonic structures, the optical properties of single quantum emitters can change drastically. [2][3][4][5] In particular, photonic crystal ͑PC͒ cavities show high quality factors combined with an extremely small mode volume. 6 It is challenging however to efficiently couple single photon sources to a PC cavity because the emitter has to be positioned in the localized optical mode, which is confined to an extremely small volume with a size of about a wavelength. [7][8][9] Nitrogen-vacancy ͑NV͒ centers in diamond are promising candidates for application as solid state quantum bits. [10][11][12] Long distance entanglement between NV centers enabling quantum repeater protocols may be achieved by two-photon quantum interference, 13,14 but is hindered by the NV centers' weak coherent photon emission rate. Being able to control and reshape the emission spectrum of a single NV center is therefore not only of fundamental interest but could also have potential applications in solid state quantum information processing. 15 Fabrication of high-quality PC cavities in diamond would be a natural way to control the emission properties of embedded NV centers but this is challenging because of the difficulties in growing and etching diamond single-crystal thin films. 16,17 An alternative, hybrid approach is to position a diamond nanocrystal with a single NV center near a PC cavity of a different material. [18][19][20][21] Because of the small size of such a crystal, the NV center can be placed in the highly confined optical mode where coupling can be efficient.Here, we demonstrate the deterministic nanoassembly of coupled single NV center-PC cavity systems by positioning ϳ50 nm sized diamond nanocrystals into gallium phosphide S1 cavities located on a different chip. The S1 cavity offers unique advantages over the well-studied L3 cavity. 19,20 Whereas in the L3 cavity the mode maximum is confined within the dielectric material, the mode maximum of the S1 cavity is localized in the air holes surrounding the cavity, making it accessible for coupling to external emitters. We are able to pick up and place a preselected diamond nanocrystal exactly into the mode maximum of a PC cavity, due to the versatility of our nanopositioning ...

Precise control over the position of a single quantum object is important for many experiments in quantum science and nanotechnology. We report on a technique for high-accuracy positioning of individual diamond nanocrystals. The positioning is done with a home-built nanomanipulator under real-time scanning electron imaging, yielding an accuracy of a few nanometers. This technique is applied to pick up, move, and position a single nitrogen-vacancy ͑NV͒ defect center contained in a diamond nanocrystal. We verify that the unique optical and spin properties of the NV center are conserved by the positioning process. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3120558͔The coupling of a single quantum object to degrees of freedom in its environment is a central theme in quantum science and engineering. Examples are the coupling of a single-photon source to an optical resonator 1,2 or to a plasmonic waveguide, 3 and the coupling of a single spin to surrounding spins. 4,5 Studying and engineering such couplings is not only of fundamental interest, but may also lead to dramatic improvements in fluorescence detection efficiency, 6 ultrasensitive magnetometry, 7-11 and applications in quantum information processing.2,12,13 Controlled and precise positioning of the quantum object under study is essential for many of these experiments.Examples of well-studied single-photon emitters in a solid-state environment are quantum dots, fluorescing dye molecules, and nitrogen-vacancy ͑NV͒ centers in diamond. In particular NV centers, which consist of a substitutional nitrogen atom next to an adjacent vacancy in the diamond lattice, are extremely stable sources of single photons.14,15 In addition, they have the unique property of a paramagnetic spin whose quantum state can be read out optically using fluorescence microscopy 16 and be coherently controlled using magnetic resonance. 17 Crucially, all these properties are retained under ambient conditions. Since NV centers can form in nanocrystals as small as 10 nm, 18 their position can in principle be controlled with an accuracy of a few nanometers.The potential of NV centers for quantum optical experiments is underlined by recent reports demonstrating coupling to confined optical modes of a microsphere 19,20 and a microdisk cavity. 21 In these experiments, however, the positioning accuracy of the diamond nanocrystals was determined by the resolution of the optical setup ͑ϳ500 nm͒, whereas subwavelength resolution is desired.Here, we demonstrate a versatile technique to position a single NV center contained in a diamond nanocrystal to an arbitrary location. We locate and characterize diamond nanocrystals with single NV centers using a scanning confocal microscope. Subsequently, we use a home-built nanomanipulator, consisting of a sharp probe mounted on a piezoelectrically controlled system inside a scanning electron microscope ͑SEM͒, for picking up and positioning the nanocrystal with nanometer precision. This technique is directly applicable to studies of the coupling of a s...

MEMS comb drives made in surface micromachining can suffer from a parasitic out-of-plane motion (levitation) in addition to the intended lateral motion. We have developed a model that accurately describes the capacitance changes of an actuated comb drive that suffers from levitation. We show that the model can be used to very accurately extract the lateral motion as a function of actuation voltage. This enables us to use the comb drive as a position sensor with very high accuracy, which does not suffer from levitation-induced nonlinearities.

A procedure was developed to mount individual semiconductor indium arsenide nanowires onto tungsten support tips to serve as electron field-emission sources. The electron emission properties of the single nanowires were precisely determined by measuring the emission pattern, current-voltage curve, and the energy spectrum of the emitted electron beam. The two investigated nanowires showed stable, Fowler-Nordheim-like emission behavior and a small energy spread. Their morphology was characterized afterward using transmission electron microscopy. The experimentally derived field enhancement factor corresponded to the one calculated using the basic structural information. The observed emission behavior contrasts the often unstable emission and large energy spread found for semiconductor emitters and supports the concept of Fermi-level pinning in indium arsenide nanowires. Indium arsenide nanowires may thus present a new type of semiconductor electron sources.

A compact, two-stage nanomanipulator was designed and built for use inside a scanning electron microscope. It consists of a fine stage employing piezostacks that provide a 15 microm range in three dimensions and a coarse stage based on commercially available stick-slip motors. Besides the fabrication of enhanced probes for scanning probe microscopy and the enhancement of electron field emitters, other novel manipulation processes were developed, such as locating, picking up, and positioning small nanostructures with an accuracy of approximately 10 nm. In combination with in situ I-V experiments, welding, and etching, this results in a multipurpose nanofactory, enabling a new range of experiments.

We report new results from field emission microscopy studies of multiwall carbon nanotubes and from energy spectrum measurements of beams from diamond field emitters. In both systems, we find that resonant tunneling through adsorbed species on the emitter surface is an important and sometimes dominant effect. For diamond emitters our observations include order-of-magnitude emission enhancement without spectral broadening, complex spectral structure, and sensitivity of that structure to the applied electric field. For carbon nanotubes we have observed electron beams from individual adsorbates which are estimated to approach the maximum beam brightness allowed by Pauli exclusion.

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A method is reported to make an electron source consisting of an individual multi-walled carbon nanotube (MWNT) mounted on a tungsten support tip, and cut to length using localized electron beam irradiation in a scanning electron microscope. The apex of the MWNT was transformed into a closed cap with at least one fullerene-like layer via an annealing process involving simultaneous heating and the extraction of an emission current of ∼ 1 mA. The electron emission occurred at localized emission sites. The electron emission showed Fowler-Nordheim behavior, was highly stable with time, and exhibited a low energy spread. The structure of the caps of two MWNTs was studied with transmission electron microscopy before and after the cap closure.