[show abstract][hide abstract] ABSTRACT: A diamond nano-crystal hosting a single nitrogen vacancy (NV) center is
optically selected with a confocal scanning microscope and positioned
deterministically onto the subwavelength-diameter waist of a tapered optical
fiber (TOF) with the help of an atomic force microscope. Based on this
nano-manipulation technique we experimentally demonstrate the evanescent
coupling of single fluorescence photons emitted by a single NV-center to the
guided mode of the TOF. By comparing photon count rates of the fiber-guided and
the free-space modes and by analyzing the second-order correlation function of
the fluorescence light, we determine a coupling efficiency of $(8.1\pm0.6)%$.
Our results are a promising starting point for future integration of single
photon sources into photonic quantum networks and applications in quantum
[show abstract][hide abstract] ABSTRACT: We demonstrate a quantum key distribution (QKD) testbed for room temperature
single photon sources based on defect centres in diamond. A BB84 protocol over
a short free-space transmission line is implemented. The performance of
nitrogen-vacancy (NV) as well as silicon-vacancy defect (SiV) centres is
evaluated and an extrapolation for next-generation sources with enhanced
efficiency is discussed.
New Journal of Physics 10/2013; 16(2). · 4.06 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this paper we study thermo-optical effects in gallium phosphite photonic crystal cavities in the visible range. By measuring the shift of narrow resonances, we derive the temperature dependency of the local refractive index of gallium phosphide in an attoliter volume over a temperature range between 5 and 300 K at a wavelength of about 605 nm. Additionally, the potential of photonic crystal cavities for thermo-optical switching of visible light is investigated. As an example we demonstrate thermo-optical switching with 13 dB contrast.
[show abstract][hide abstract] ABSTRACT: In this Letter we study the relations among shape, symmetry, and plasmon resonance shift in a single gold nanoparticle during laser melting. A beam of an argon ion laser is focused on a selected particle, while its optical and shape properties can be observed with the help of a combined dark-field/photoluminescence microscope and an atomic force microscope, respectively. Starting from a spherical shape, radiation pressure forms the melting gold particle into an upright standing rod on a glass substrate, showing a characteristic dipole scattering pattern. A red-shift of the photoluminescence signal and the scattering spectrum is observed. The melting process can be controlled allowing the formation of different particle heights and plasmon resonance shifts. In situ tuning of the plasmon resonance of individual particles is possible with this reversible melting process.
[show abstract][hide abstract] ABSTRACT: A fully integrated quantum optical technology requires active quantum systems
incorporated into resonant optical microstructures and inter-connected in three
dimensions via photonic wires. Nitrogen vacancy-centres (NV-centres) in diamond
which are excellent photostable room temperature single-photon emitters are
ideal candidates for that purpose. Extensive research efforts to couple
NV-centres to photonic structures such as optical microresonators,
microcavities, and waveguides have been pursued. Strategies for integration
range from top-down fabrication via etching of diamond membranes to
sophisticated bottom-up assembly of hybrid structures using diamond
nanocrystals where the latter approach allows for deterministic coupling.
Recently, another approach based on the incorporation of nanodiamonds in soft
glass optical fibres via a melting process has been introduced. Here, we
utilize two-photon direct laser writing (DLW) to fabricate fully
three-dimensional (3D) structures from a photoresist mixed with a solution of
nanodiamonds containing NV-centres. For the first time, this approach
facilitates building integrated 3D quantum photonic elements of nearly
[show abstract][hide abstract] ABSTRACT: To fully integrate quantum optical technology, active quantum systems must be combined with resonant microstructures and optical interconnects harvesting and routing photons in three diemsnsions (3D) on one chip. We fabricate such combined structures for the first time by using two-photon laser lithography and a photoresist containing nanodiamonds including nitrogen vacancy-centers. As an example for possible functionality, single-photon generation, collection, and transport is successfully accomplished. The single photons are efficiently collected via resonators and routed in 3D through waveguides, all on one optical chip. Our one-step fabrication scheme is easy to implement, scalable and flexible. Thus, other complex assemblies of 3D quantum optical structures are feasible as well.
[show abstract][hide abstract] ABSTRACT: Precisely timed detection of single photons plays an important role in the field of quantum information processing and fluorescence sensing. The method of time-correlated single photon counting is therefore constantly evolving and the associated instrumentation is being improved with new ideas and technologies. Simultaneous, time tagged readout of multiple detector channels is invaluable in many applications, spanning from fluorescence lifetime imaging in biology to the measurement of quantum optical correlations in basic research. Here we present a new integrated design, providing up to three independent input channels, a very short dead time, very high throughput, and a timing resolution of 25 ps at reasonable cost and small size. Apart from design features and test results of the instrument, we show an application in quantum optics, namely, the measurement of the photon statistics of a heralded single photon source based on cavity-enhanced spontaneous parametric down-conversion.
The Review of scientific instruments 04/2013; 84(4):043102. · 1.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: Their intrinsic properties render single quantum systems as ideal tools for
quantum enhanced sensing and microscopy. As an additional benefit, their size
is typically on an atomic scale which enables sensing with very high spatial
resolution. Here, we report on utilizing a single nitrogen vacancy center in
nanodiamond for performing three-dimensional scanning-probe fluorescence
lifetime imaging microscopy. By measuring changes of the single emitter's
lifetime information on the local density of optical states is acquired at the
nanoscale. This technique to gather information on the local density of optical
states is important for the understanding of fundamental quantum optical
processes as well as for the engineering of novel photonic and plasmonic
[show abstract][hide abstract] ABSTRACT: Further improvement of infrared single photon sources is a major
challenge for future implementations of quantum information and quantum
communication applications. In this paper, we give further insight into
a recently presented, conceptually novel method for the generation of
single photons.1 The method is of particular interest for
spectral domains where stable room temperature single photon sources are
not available. For example, this is the presently the case for the
near-infrared. This wavelength regime is important for data transfer
over long distances where optical losses in fibers are minimal. The
presented method is based on the following idea. The fundamental key
requirement for single photon generation is the generation of a single
excitation in an optically active system. It is not the presence of a
single quantum system. The presented method is applied to realize a
stable, non-blinking, room temperature infrared single photon source by
converting visible single photons from a defect center in diamond to the
near infrared. For the presented implementation, the theoretical
conversion efficiency was estimated to be 26 %. In a first prove of
principle experiment, a conversion efficiency of 0.1 % was achieved.
[show abstract][hide abstract] ABSTRACT: We investigate an efficient method for fine-tuning whispering gallery mode resonances in disk-type silica microresonators to reach an arbitrary frequency within the free spectral range of the system. This method is based on a post-production hydrofluoric acid etching process to precisely resize the radius of such microresonators. We show the effectiveness of this approach by tuning their resonance frequency within 10 GHz of specific hydrogen cyanide reference lines (P16, P18). This technique allows for simple and exact matching of narrow-linewidth lasers or spectroscopic lines with the high-Q resonances of on-chip silica microresonators.
[show abstract][hide abstract] ABSTRACT: The quantum Zeno effect, i.e. the inhibition of coherent quantum dynamics by
projective measurements is one of the most intriguing predictions of quantum
mechanics. Here we experimentally demonstrate the quantum Zeno effect by
inhibiting the microwave driven coherent spin dynamics between two ground state
spin levels of the nitrogen vacancy center in diamond nano-crystals. Our
experiments are supported by a detailed analysis of the population dynamics via
a semi-classical model.
[show abstract][hide abstract] ABSTRACT: A new tuning method for tuning whispering gallery modes (WGMs) in a cryogenic environment is presented. Within a home-made exchange gas cryostat the applicability of pressure tuning in microbubbles at liquid nitrogen (LN) temperature is shown. The general thermal shift and tuning behavior of borosilicate microbubbles is theoretically analyzed and compared to experimental data. We show that stress/strain tuning using compressed gas is widely unaffected by system temperature.
[show abstract][hide abstract] ABSTRACT: Spectral diffusion is the phenomenon of random jumps in the emission wavelength of narrow lines. This phenomenon is a major hurdle for applications of solid state quantum emitters like quantum dots, molecules, or diamond defect centers in an integrated quantum optical technology. Here, we provide further insight into the underlying processes of spectral diffusion of the zero-phonon line of single nitrogen vacancy centers in nano-size diamond by using a novel method based on photon correlation interferometry. The method works although the spectral diffusion rate is several orders of magnitude higher than the photon detection rate and thereby improves the time resolution of previous experiments with nano-size diamond by 6 orders of magnitude. We study the dependency of the spectral diffusion rate on the excitation power, temperature, and excitation wavelength under off-resonant excitation. Our results bring insight into the mechanism of spectral diffusion and suggest a strategy to increase the number of spectrally indistinguishable photons emitted by diamond nanocrystals.
[show abstract][hide abstract] ABSTRACT: We set up a long-term stable filtering system that consists of cascaded monolithic Fabry-Pérot filters to enhance the suppression and free spectral range. An effective free spectral range of hundreds of GHz allows the system to be used as a high resolution monochromator, with a linewidth of 192 MHz. As an important application a single mode is filtered from photon pairs generated by a parametric down-conversion source, and their indistinguishability is proven by measuring the Hong-Ou-Mandel effect with a visibility of 96%. We report that undesired birefringence, which is often encountered with monolithic cavities, can be avoided by stress-free mounting.
[show abstract][hide abstract] ABSTRACT: We present the synthesis and analysis of silica-coated Au/Ag bimetallic nanorods with controlled surface plasmon bands. Depending on the thickness of Ag shell deposited on the Au nanorod surface, there is a blue-shift on the longitudinal surface plasmon band of Au nanorods, which can be expressed by an approximate formula derived from the absorption profile of light in Ag films using finite difference time domain simulations. The subsequent coating of silica shell not only enhances the stability of the Au/Ag bimetallic nanorods but also provides a mesoporous host for optically active species. Minute red-shifts of the longitudinal resonance mode, induced by stepwise increased silica shell volumes, are shown. Application as carrier for fluorescent rhodamine B molecules is demonstrated by photoluminescence analysis. On the single-particle level, dark field microscopy of Au/Ag-silica nanorods was finally employed. This introduces a route towards revealing the relation between structure, shape, and optical (plasmonic) properties of complex composite metal particles as well as fabrication strategies for nanoassemblies of tailored structures in the field of nanoplasmonics.
Colloid and Polymer Science 01/2013; 291(3):585-594. · 2.16 Impact Factor
[show abstract][hide abstract] ABSTRACT: We design an on-chip single mode photon to surface-plasmon coupler. Our coupler consists of a tapered dielectric waveguide and a V-shaped plasmonic part. In contrast to other concepts designated to minimized-loss coupling into long-ranging waveguides, we focus on an easy-to-fabricate structure working in the visible spectral range. The air-cladded design provides full experimental access to the evanescent fields emerging from the plasmonic stripe guide. An adaptive finite element method for full three dimensional simulations is used combined with the Taguchi method for optimization, which makes our procedure extremely time-efficient and executable on standard personal computers.
[show abstract][hide abstract] ABSTRACT: An elementary experiment in optics consists of a light source and a detector. Yet, if the source generates nonclassical correlations such an experiment is capable of unambiguously demonstrating the quantum nature of light. We realized such an experiment with a defect center in diamond and a superconducting detector. Previous experiments relied on more complex setups, such as the Hanbury Brown and Twiss configuration, where a beam splitter directs light to two photodetectors, creating the false impression that the beam splitter is a fundamentally required element. As an additional benefit, our results provide a simplification of the widely used photon-correlation techniques.
Physical Review A 11/2012; 86(5). · 3.04 Impact Factor