1,659 research outputs found
Absolute frequency measurements of 85Rb nF7/2 Rydberg states using purely optical detection
A three-step laser excitation scheme is used to make absolute frequency
measurements of highly excited nF7/2 Rydberg states in 85Rb for principal
quantum numbers n=33-100. This work demonstrates the first absolute frequency
measurements of rubidium Rydberg levels using a purely optical detection
scheme. The Rydberg states are excited in a heated Rb vapour cell and Doppler
free signals are detected via purely optical means. All of the frequency
measurements are made using a wavemeter which is calibrated against a GPS
disciplined self-referenced optical frequency comb. We find that the measured
levels have a very high frequency stability, and are especially robust to
electric fields. The apparatus has allowed measurements of the states to an
accuracy of 8.0MHz. The new measurements are analysed by extracting the
modified Rydberg-Ritz series parameters.Comment: 12 pages, 5 figures, submitted to New. J. Phy
Nonlinear interaction between two heralded single photons
Harnessing nonlinearities strong enough to allow two single photons to
interact with one another is not only a fascinating challenge but is central to
numerous advanced applications in quantum information science. Currently, all
known approaches are extremely challenging although a few have led to
experimental realisations with attenuated classical laser light. This has
included cross-phase modulation with weak classical light in atomic ensembles
and optical fibres, converting incident laser light into a non-classical stream
of photon or Rydberg blockades as well as all-optical switches with attenuated
classical light in various atomic systems. Here we report the observation of a
nonlinear parametric interaction between two true single photons. Single
photons are initially generated by heralding one photon from each of two
independent spontaneous parametric downconversion sources. The two heralded
single photons are subsequently combined in a nonlinear waveguide where they
are converted into a single photon with a higher energy. Our approach
highlights the potential for quantum nonlinear optics with integrated devices,
and as the photons are at telecom wavelengths, it is well adapted to
applications in quantum communication.Comment: 4 pages, 4 figure
A new Manifestation of Atomic Parity Violation in Cesium: a Chiral Optical Gain induced by linearly polarized 6S-7S Excitation
We have detected, by using stimulated emission, an Atomic Parity Violation
(APV) in the form of a chiral optical gain of a cesium vapor on the 7S -
6P transition,consecutive to linearly polarized 6S-7S excitation. We
demonstrate the validity of this detection method of APV, by presenting a 9%
accurate measurement of expected sign and magnitude. We underline several
advantages of this entirely new approach in which the cylindrical symmetry of
the set-up can be fully exploited. Future measurements at the percent level
will provide an important cross-check of an existing more precise result
obtained by a different method.Comment: 4 pages, 2 figure
Role of the (Mn)superoxide dismutase of Enterococcus faecalis in the in vitro interaction with microglia
Enterococcus faecalis is a significant human pathogen worldwide and is responsible for severenosocomial and community-acquired infections. Although enterococcal meningitis is rare,mortality is considerable, reaching 21 %. Nevertheless, the pathogenetic mechanisms of thisinfection remain poorly understood, even though the ability of E. faecalis to avoid or survivephagocytic attack in vivo may be very important during the infection process. We previouslyshowed that the manganese-cofactored superoxide dismutase (MnSOD) SodA of E. faecalis wasimplicated in oxidative stress responses and, interestingly, in the survival within mouse peritonealmacrophages using an in vivo\u2013in vitro infection model. In the present study, we investigated therole of MnSOD in the interaction of E. faecalis with microglia, the brain-resident macrophages. Byusing an in vitro infection model, murine microglial cells were challenged in parallel with the wildtypestrain JH2-2 and its isogenic sodA deletion mutant. While both strains were phagocytosedby microglia efficiently and to a similar extent, the DsodA mutant was found to be significantlymore susceptible to microglial killing than JH2-2, as assessed by the antimicrobial protectionassay. In addition, a significantly higher percentage of acidic DsodA-containing phagosomes wasfound and these also underwent enhanced maturation as determined by the expression ofendolysosomal markers. In conclusion, these results show that the MnSOD of E. faecaliscontributes to survival of the bacterium in microglial cells by influencing their antimicrobial activity,and this could even be important for intracellular killing in neutrophils and thus for E. faecalispathogenesis
Engineering integrated pure narrow-band photon sources
Engineering and controlling well defined states of light for quantum
information applications is of increasing importance as the complexity of
quantum systems grows. For example, in quantum networks high multi-photon
interference visibility requires properly devised single mode sources. In this
paper we propose a spontaneous parametric down conversion source based on an
integrated cavity-waveguide, where single narrow-band, possibly distinct,
spectral modes for the idler and the signal fields can be generated. This mode
selection takes advantage of the clustering effect, due to the intrinsic
dispersion of the nonlinear material. In combination with a CW laser and fast
detection, our approach provides a means to engineer a source that can
efficiently generate pure photons, without filtering, that is compatible with
long distance quantum communication. Furthermore, it is extremely flexible and
could easily be adapted to a wide variety of wavelengths and applications.Comment: 13 pages, 7 figure
Growth Interruption Effect on the Fabrication of GaAs Concentric Multiple Rings by Droplet Epitaxy
We present the molecular beam epitaxy fabrication and optical properties of complex GaAs nanostructures by droplet epitaxy: concentric triple quantum rings. A significant difference was found between the volumes of the original droplets and the final GaAs structures. By means of atomic force microscopy and photoluminescence spectroscopy, we found that a thin GaAs quantum well-like layer is developed all over the substrate during the growth interruption times, caused by the migration of Ga in a low As background
Clinical guidelines and indications for bronchoalveolar lavage (BAL): pulmonary malignancies.
Ballistic Electron Emission Microscopy on CoSi/Si(111) interfaces: band structure induced atomic-scale resolution and role of localized surface states
Applying a Keldysh Green`s function method it is shown that hot electrons
injected from a STM-tip into a CoSi/Si(111) system form a highly focused
beam due to the silicide band structure. This explains the atomic resolution
obtained in recent Ballistic Electron Emission Microscopy (BEEM) experiments.
Localized surface states in the -reconstruction are found to be
responsible for the also reported anticorrugation of the BEEM current. These
results clearly demonstrate the importance of bulk and surface band structure
effects for a detailed understanding of BEEM data.Comment: 5 pages, RevTex, 4 postscript figures,
http://www.icmm.csic.es/Pandres/pedro.ht
Interaction of Independent Single Photons based on Integrated Nonlinear Optics
Photons are ideal carriers of quantum information, as they can be easily
created and can travel long distances without being affected by decoherence.
For this reason, they are well suited for quantum communication. However, the
interaction between single photons is negligible under most circumstances.
Realising such an interaction is not only fundamentally fascinating but holds
great potential for emerging technologies. It has recently been shown that even
weak optical nonlinearities between single photons can be used to perform
important quantum communication tasks more efficiently than methods based on
linear optics, which have fundamental limitations. Nonlinear optical effects at
single photon levels in atomic media have been studied and demonstrated but
these are neither flexible nor compatible with quantum communication as they
impose restrictions on photons' wavelengths and bandwidths. Here we use a high
efficiency nonlinear waveguide to observe the sum-frequency generation between
a single photon and a single-photon level coherent state from two independent
sources. The use of an integrated, room-temperature device and telecom
wavelengths makes this approach to photon-photon interaction well adapted to
long distance quantum communication, moving quantum nonlinear optics one step
further towards complex quantum networks and future applications such as device
independent quantum key distribution
Self-Assembled Local Artificial Substrates of GaAs on Si Substrate
We propose a self-assembling procedure for the fabrication of GaAs islands by Droplet Epitaxy on silicon substrate. Controlling substrate temperature and amount of supplied gallium is possible to tune the base size of the islands from 70 up to 250 nm and the density from 107 to 109 cm−2. The islands show a standard deviation of base size distribution below 10% and their shape evolves changing the aspect ratio from 0.3 to 0.5 as size increases. Due to their characteristics, these islands are suitable to be used as local artificial substrates for the integration of III–V quantum nanostructures directly on silicon substrate
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