My research is focused on solid-state quantum optics. In the past few years I have, for example, investigated methods to collect single photons with near-unity efficiency. Another emphasis is on techniques which can be used to enhance the interaction of a single photon with a single emitter.
Circular Grating Resonators as Small Mode-Volume Microcavities for Switching
Sophie Schoenenberger,
Nikolaj Moll,
Thilo Stoeferle,
Rainer F. Mahrt,
Bert J. Offrein,
Stephan Götzinger,
Vahid Sandoghdar,
Jens Bolten,
Thorsten Wahlbrink, et al.
We demonstrate the suitability of microcavities based on circular grating resonators (CGRs) as fast switches. This type of optical resonator is characterized by a high quality factor and very small mode volume. The waveguide-coupled CGRs are fabricated with silicon-on-insulator technology compatible with standard complementary metal-oxide semiconductor (CMOS) processing. The linear optical properties of the CGRs are investigated by transmission spectroscopy. From 3D finite-difference time-domain simulations of isolated CGRs, we identify the measured resonances. We probe the spatial distribution and the parasitic losses of a resonant optical mode with scanning near-field optical microscopy. We observe fast all-optical switching within a few picoseconds by optically generating free charge carriers within the cavity. (C) 2009 Optical Society of America
A single-molecule optical transistor
J. Hwang,
M. Pototschnig,
R. Lettow,
G. Zumofen,
A. Renn,
Stephan Götzinger,
Vahid Sandoghdar
The transistor is one of the most influential inventions of modern times and is ubiquitous in present-day technologies. In the continuing development of increasingly powerful computers as well as alternative technologies based on the prospects of quantum information processing, switching and amplification functionalities are being sought in ultrasmall objects, such as nanotubes, molecules or atoms(1-9). Among the possible choices of signal carriers, photons are particularly attractive because of their robustness against decoherence, but their control at the nano-metre scale poses a significant challenge as conventional nonlinear materials become ineffective. To remedy this shortcoming, resonances in optical emitters can be exploited, and atomic ensembles have been successfully used to mediate weak light beams(7). However, single-emitter manipulation of photonic signals has remained elusive and has only been studied in high-finesse microcavities(10-13) or waveguides(8,14). Here we demonstrate that a single dye molecule can operate as an optical transistor and coherently attenuate or amplify a tightly focused laser beam, depending on the power of a second 'gating' beam that controls the degree of population inversion. Such a quantum optical transistor has also the potential for manipulating non-classical light fields down to the single-photon level. We discuss some of the hurdles along the road towards practical implementations, and their possible solutions.
Resolution and Enhancement in Nanoantenna-Based Fluorescence Microscopy
Hadi Eghlidi,
Kwang Geol Lee,
Xue-Wen Chen,
Stephan Götzinger,
Vahid Sandoghdar
Single gold nanoparticles can act as nanoantennas for enhancing the fluorescence of emitters in their near fields. Here we present experimental and theoretical studies of scanning antenna-based fluorescence microscopy as a function of the diameter of the gold nanoparticle. We examine the interplay between fluorescence enhancement and spatial resolution and discuss the requirements for deciphering single molecules in a dense sample. Resolutions better than 20 nm and fluorescence enhancement up to 30 times are demonstrated experimentally. By accounting for the tip shaft and the sample interface in finite-difference time-domain calculations, we explain why the measured fluorescence enhancements are higher in the presence of an interface than the values predicted for a homogeneous environment.
Molecules as sources for indistinguishable single photons
Ville Ahtee,
Robert Lettow,
Robert Pfab,
Alois Renn,
Erkki Ikonen,
Stephan Götzinger,
Vahid Sandoghdar
Journal of Modern Optics
56
PII 907848818
161-166
(2009)
| Journal
We report on the triggered generation of identical photons by solid-state single-photon sources in two separate cryogenic laser scanning microscopes. Organic fluorescent molecules were used as emitters and investigated by means of high resolution laser spectroscopy. Continuous-wave photon correlation measurements on individual molecules proved the isolation of single quantum systems. By using frequency selective pulsed excitation of the molecule and efficient spectral filtering of its emission, we produced triggered Fourier-limited single photons. In a further step, local electric fields were applied to match the emission wavelengths of two different molecules via Stark effect. Identical single photons are indispensable for the realization of various quantum information processing schemes proposed. The solid-state approach presented here paves the way to the integration of multiple bright sources of single photons on a single chip.
Spectral dynamics and spatial localization of single molecules in a polymer
A. Walser,
G. Zumofen,
A. Renn,
Stephan Götzinger,
Vahid Sandoghdar
We report on the high-resolution spectroscopy of single dibenzanthanthrene molecules embedded in polymethyl methacrylate (PMMA). We employed three methods for the characterization of spectral line shapes based on fitting a Lorentzian function, determining full widths at half-maxima, and calculation of the second-order spectral cumulant. The three approaches provide comparable histograms of linewidth distributions, displaying slowly decaying tails that are indicative of the Levy stable law. In addition, we introduce an alternative method for the analysis of spectral dynamics, in which ensemble spectra are reconstructed by adding single molecule spectral autocorrelations. Furthermore, we examine the spectral width and distributions of single molecules on the PMMA chain length over three orders of magnitude and find a very small dependence. Lastly, we demonstrate that, despite the strong spectral dynamics, it is possible to collect enough photons from single molecules to localize their positions to better than 10 nm.
Lifetime-limited zero-phonon spectra of single molecules in methyl methacrylate
A. Walser,
A. Renn,
Stephan Götzinger,
Vahid Sandoghdar
Chemical Physics Letters
472
44-47
(2009)
| Journal
We report on high resolution single molecule spectroscopy in frozen methyl methacrylate (MMA). We show that the zero-phonon transitions of single dibenzanthanthrene molecules in this polar matrix can reach their natural linewidth limit at T = 1.4 K. Our X-ray diffraction measurements and direct study of single molecule dipole orientation provide clear evidence for the crystalline nature of MMA at low temperatures. Our results hold promise for the controlled study of the transition between crystalline and amorphous matrices, and have implications on cryogenic single molecule microscopy in biological applications. (C) 2009 Elsevier B. V. All rights reserved.
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