524 research outputs found
A high-fidelity photon gun: intensity-squeezed light from a single molecule
A two-level atom cannot emit more than one photon at a time. As early as the
1980s, this quantum feature was identified as a gateway to "single-photon
sources", where a regular excitation sequence would create a stream of light
particles with photon number fluctuations below the shot noise. Such an
intensity squeezed beam of light would be desirable for a range of applications
such as quantum imaging, sensing, enhanced precision measurements and
information processing. However, experimental realizations of these sources
have been hindered by large losses caused by low photon collection efficiencies
and photophysical shortcomings. By using a planar metallo-dielectric antenna
applied to an organic molecule, we demonstrate the most regular stream of
single photons reported to date. Measured intensity fluctuations reveal 2.2 dB
squeezing limited by our detection efficiency, equivalent to 6.2 dB intensity
squeezing right after the antenna.Comment: 9 pages, 3 figure
High-resolution spectroscopy of single Pr ions on the H-D transition
Rare earth ions in crystals exhibit narrow spectral features and
hyperfine-split ground states with exceptionally long coherence times. These
features make them ideal platforms for quantum information processing in the
solid state. Recently, we reported on the first high-resolution spectroscopy of
single Pr ions in yttrium orthosilicate (YSO) nanocrystals. While in
that work we examined the less explored H-P transition at a
wavelength of 488 nm, here we extend our investigations to the
H-D transition at 606 nm. In addition, we present measurements
of the second-order autocorrelation function, fluorescence lifetime, and
emission spectra of single ions as well as their polarization dependencies on
both transitions; these data were not within the reach of the first experiments
reported earlier. Furthermore, we show that by a proper choice of the
crystallite, one can obtain narrower spectral lines and, thus, resolve the
hyperfine levels of the excited state. We expect our results to make single-ion
spectroscopy accessible to a larger scientific community.Comment: 5 pages, 5 figure
Few-photon coherent nonlinear optics with a single molecule
The pioneering experiments of linear spectroscopy were performed using flames
in the 1800s, but nonlinear optical measurements had to wait until lasers
became available in the twentieth century. Because the nonlinear cross section
of materials is very small, usually macroscopic bulk samples and pulsed lasers
are used. Numerous efforts have explored coherent nonlinear signal generation
from individual nanoparticles or small atomic ensembles with millions of atoms.
Experiments on a single semiconductor quantum dot have also been reported,
albeit with a very small yield. Here, we report on coherent nonlinear
spectroscopy of a single molecule under continuous-wave single-pass
illumination, where efficient photon-molecule coupling in a tight focus allows
switching of a laser beam by less than a handful of pump photons nearly
resonant with the sharp molecular transition. Aside from their fundamental
importance, our results emphasize the potential of organic molecules for
applications such as quantum information processing, which require strong
nonlinearities.Comment: 6 pages, 5 figure
Coherent Interaction of Light and Single Molecules in a Dielectric Nanoguide
We present a new scheme for performing optical spectroscopy on single
molecules. A glass capillary with a diameter of 600 nm filled with an organic
crystal tightly guides the excitation light and provides a maximum spontaneous
emission coupling factor () of 18% for the dye molecules doped in the
organic crystal. Combination of extinction, fluorescence excitation and
resonance fluorescence spectroscopy with microscopy provides high-resolution
spatio-spectral access to a very large number of single molecules in a linear
geometry. We discuss strategies for exploring a range of quantum optical
phenomena, including coherent cooperative interactions in a mesoscopic ensemble
of molecules mediated by a single mode of propagating photons.Comment: 5 pages, 5 figure
Integration and calibration of a conceptual rainfall-runoff model in the framework of a decision support system for river basin management
International audienceWater balance models provide significant input to integrated models that are used to simulate river basin processes. However, one of the primary problems involves the coupling and simultaneous calibration of rainfall-runoff and groundwater models. This problem manifests itself through circular arguments - the hydrologic model is modified to calculate highly discretized groundwater recharge rates as input to the groundwater model which provides modeled base flow for the flood-routing module of the rainfall-runoff model. A possibility to overcome this problem using a modified version of the HBV Model is presented in this paper. Regionalisation and optimization methods lead to objective and efficient calibration despite large numbers of parameters. The representation of model parameters by transfer functions of catchment characteristics enables consistent parameter estimation. By establishing such relationships, models are calibrated for the parameters of the transfer functions instead of the model parameters themselves. Simulated annealing, using weighted Nash-Sutcliffe-coefficients of variable temporal aggregation, assists in efficient parameterisations. The simulations are compared to observed discharge and groundwater recharge modeled by the State Institute for Environmental Protection Baden-WĂĽrttemberg using the model TRAIN-GWN
Detection, spectroscopy and state preparation of a single praseodymium ion in a crystal
Solid-state emitters with atom-like optical and magnetic transitions are
highly desirable for efficient and scalable quantum state engineering and
information processing. Quantum dots, color centers and impurities embedded in
inorganic hosts have attracted a great deal of attention in this context, but
influences from the matrix continue to pose challenges on the degree of
attainable coherence in each system. We report on a new solid-state platform
based on the optical detection of single praseodymium ions via 4f intrashell
transitions, which are well shielded from their surroundings. By combining
cryogenic high-resolution laser spectroscopy with fluorescence microscopy, we
were able to spectrally select and spatially resolve individual ions. In
addition to elaborating on the essential experimental steps for achieving this
long-sought goal, we demonstrate state preparation and read out of the three
ground-state hyperfine levels, which are known to have lifetimes of the order
of hundred seconds
Molecules as Sources for Indistinguishable Single Photons
We report on the triggered generation of indistinguishable 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 indispensible for the
realization of various quantum information processing schemes proposed. The
solid-state approach presented here prepares the way towards the integration of
multiple bright sources of single photons on a single chip.Comment: Accepted for publication in J. Mod. Opt. This is the original
submitted versio
A scanning microcavity for in-situ control of single-molecule emission
We report on the fabrication and characterization of a scannable Fabry-Perot
microcavity, consisting of a curved micromirror at the end of an optical fiber
and a planar distributed Bragg reflector. Furthermore, we demonstrate the
coupling of single organic molecules embedded in a thin film to well-defined
resonator modes. We discuss the choice of cavity parameters that will allow
sufficiently high Purcell factors for enhancing the zero-phonon transition
between the vibrational ground levels of the electronic excited and ground
states.Comment: 8 page
Hydrological modelling for meso-scale catchments using globally available data
International audienceThis study focuses on modelling water balances for catchments with limited data availability. The objective was to use globally available data for water balance modelling of meso-scale catchments. The study is carried out in two catchments; one having enough data for the performance check of the model and the other with very few data for model validation. Globally available meteorological and geographical data is used for the basic model inputs. Dissaggregation of the global data, both spatially and temporally, was conducted to distribute the available data across the watershed and to attain higher resolution input data for the model. In addition, a glacier module was developed for the regions covered by glaciers. The HBV-IWS model developed at the Institute of Hydraulic Engineering at the University of Stuttgart is applied. The outcomes of the modelling provide noteworthy results for both catchments that can be used in water resources planning and management issues. Moreover, the research presents the potential for modelling water balances using predominantly globally available data and proposes appropriate disaggregation methods for global data usage
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