A Laser Frequency Comb System for Absolute Calibration of the VTT Echelle Spectrograph

A wavelength calibration system based on a laser frequency comb (LFC) was developed in a co-operation between the Kiepenheuer-Institut f\"ur Sonnenphysik, Freiburg, Germany and the Max-Planck-Institut f\"ur Quantenoptik, Garching, Germany for permanent installation at the German Vacuum Tower Telescope (VTT) on Tenerife, Canary Islands. The system was installed successfully in October 2011. By simultaneously recording the spectra from the Sun and the LFC, for each exposure a calibration curve can be derived from the known frequencies of the comb modes that is suitable for absolute calibration at the meters per second level. We briefly summarize some topics in solar physics that benefit from absolute spectroscopy and point out the advantages of LFC compared to traditional calibration techniques. We also sketch the basic setup of the VTT calibration system and its integration with the existing echelle spectrograph.Comment: 9 pages, 2 figures; Solar Physics 277 (2012

Searching for Exoplanets Using a Microresonator Astrocomb

Detection of weak radial velocity shifts of host stars induced by orbiting planets is an important technique for discovering and characterizing planets beyond our solar system. Optical frequency combs enable calibration of stellar radial velocity shifts at levels required for detection of Earth analogs. A new chip-based device, the Kerr soliton microcomb, has properties ideal for ubiquitous application outside the lab and even in future space-borne instruments. Moreover, microcomb spectra are ideally suited for astronomical spectrograph calibration and eliminate filtering steps required by conventional mode-locked-laser frequency combs. Here, for the calibration of astronomical spectrographs, we demonstrate an atomic/molecular line-referenced, near-infrared soliton microcomb. Efforts to search for the known exoplanet HD 187123b were conducted at the Keck-II telescope as a first in-the-field demonstration of microcombs

Restricting quark matter models by gravitational wave observation

We consider the possibilities for obtaining information about the equation of state for quark matter by using future direct observational data on gravitational waves. We study the nonradial oscillations of both fluid and spacetime modes of pure quark stars. If we observe the $f$ and the lowest $w_{\rm II}$ modes from quark stars, by using the simultaneously obtained radiation radius we can constrain the bag constant $B$ with reasonable accuracy, independently of the $s$ quark mass.Comment: To appear in Phys. Rev.

The Magnificent Seven: Magnetic fields and surface temperature distributions

Presently seven nearby radio-quiet isolated neutron stars discovered in ROSAT data and characterized by thermal X-ray spectra are known. They exhibit very similar properties and despite intensive searches their number remained constant since 2001 which led to their name ``The Magnificent Seven''. Five of the stars exhibit pulsations in their X-ray flux with periods in the range of 3.4 s to 11.4 s. XMM-Newton observations revealed broad absorption lines in the X-ray spectra which are interpreted as cyclotron resonance absorption lines by protons or heavy ions and / or atomic transitions shifted to X-ray energies by strong magnetic fields of the order of 10^13 G. New XMM-Newton observations indicate more complex X-ray spectra with multiple absorption lines. Pulse-phase spectroscopy of the best studied pulsars RX J0720.4-3125 and RBS 1223 reveals variations in derived emission temperature and absorption line depth with pulse phase. Moreover, RX J0720.4-3125 shows long-term spectral changes which are interpreted as due to free precession of the neutron star. Modeling of the pulse profiles of RX J0720.4-3125 and RBS 1223 provides information about the surface temperature distribution of the neutron stars indicating hot polar caps which have different temperatures, different sizes and are probably not located in antipodal positions.Comment: 10 pages, 8 figures, to appear in Astrophysics and Space Science, in the proceedings of "Isolated Neutron Stars: from the Interior to the Surface", edited by D. Page, R. Turolla and S. Zan

Photonic quantum technologies

The first quantum technology, which harnesses uniquely quantum mechanical effects for its core operation, has arrived in the form of commercially available quantum key distribution systems that achieve enhanced security by encoding information in photons such that information gained by an eavesdropper can be detected. Anticipated future quantum technologies include large-scale secure networks, enhanced measurement and lithography, and quantum information processors, promising exponentially greater computation power for particular tasks. Photonics is destined for a central role in such technologies owing to the need for high-speed transmission and the outstanding low-noise properties of photons. These technologies may use single photons or quantum states of bright laser beams, or both, and will undoubtably apply and drive state-of-the-art developments in photonics

Cavity electromagnetically induced transparency and all-optical switching using ion Coulomb crystals

The control of one light field by another, ultimately at the single photon level, is a challenging task which has numerous interesting applications within nonlinear optics and quantum information science. Due to the extremely weak direct interactions between optical photons in vacuum, this type of control can in practice only be achieved through highly nonlinear interactions within a medium. Electromagnetic induced transparency (EIT) constitutes one such means to obtain the extremely strong nonlinear coupling needed to facilitate interactions between two faint light fields. Here, we demonstrate for the first time EIT as well as all-optical EIT-based light switching using ion Coulomb crystals situated in an optical cavity. Unprecedented narrow cavity EIT feature widths down to a few kHz and a change from essentially full transmission to full absorption of the probe field within a window of only ~100 kHz are achieved. By applying a weak switching field, we furthermore demonstrate nearly perfect switching of the transmission of the probe field. These results represent important milestones for future realizations of quantum information processing devices, such as high-efficiency quantum memories, single-photon transistors and single-photon gates

Appraising the intention of other people: Ecological validity and procedures for investigating effects of lighting for pedestrians

One of the aims of outdoor lighting public spaces such as pathways and subsidiary roads is to help pedestrians to evaluate the intentions of other people. This paper discusses how a pedestrians’ appraisal of another persons’ intentions in artificially lit outdoor environments can be studied. We review the visual cues that might be used, and the experimental design with which effects of changes in lighting could be investigated to best resemble the pedestrian experience in artificially lit urban environments. Proposals are made to establish appropriate operationalisation of the identified visual cues, choice of methods and measurements representing critical situations. It is concluded that the intentions of other people should be evaluated using facial emotion recognition; eye tracking data suggest a tendency to make these observations at an interpersonal distance of 15 m and for a duration of 500 ms. Photographs are considered suitable for evaluating the effect of changes in light level and spectral power distribution. To support investigation of changes in spatial distribution further investigation is needed with 3D targets. Further data are also required to examine the influence of glare

Atomic spectroscopy on a chip

Abstract: We demonstrate the ability to generate extremely large rubidium densities in uncoated hollow-core photonic band-gap fibers using lightinduced atomic desorption. Once the fiber is exposed to Rb vapor for 1-2 weeks, and this atomic source is removed, the fiber yields large desorbable densities for an extended period of time. We show that optical depths greater than e -1200 can be created within seconds. Our observed Rb densities are several orders of magnitude larger than any previously reported to be generated optically, and allow for the demonstration of a relatively easy-touse fiber-based vapor cell capable of producing large optical depths without the need for thermal tuning. H. Schmidt and A. Imamoğlu, "Giant Kerr nonlinearities obtained by electromagnetically-induced transparency," Opt. Lett. 21, 1936Lett. 21, -1938Lett. 21, (199

Symmetry of the Neutron and Proton Superfluidity Effects in Cooling Neutron Stars

We investigate the combined effect of neutron and proton superfluidities on the cooling of neutron stars whose cores consist of nucleons and electrons. We consider singlet-state pairing of protons and triplet-state pairing of neutrons in the cores of neutron stars. The critical superfluid temperatures T_c are assumed to depend on the density of matter. We study two types of neutron pairing with different components of the total angular momentum of Cooper pairs along the quantization axis (|m_J| =0 or 2). Our calculations are compared with observations of thermal emission from isolated neutron stars. We show that the observations can be interpreted by using two classes of superfluidity models: (1) strong proton superfluidity with a maximum critical temperature in the stellar core T_c^{max} > 4 \times 10^9 K and weak neutron superfluidity of any type (T_c^{max} < 2 \times 10^8 K); (2) strong neutron superfluidity (pairing with |m_J|=0) and weak proton superfluidity. The two types of models reflect an approximate symmetry with respect to an interchange of the critical temperatures of neutron and proton pairing.Comment: 20 pages, 8 figure

Recognition of human faces by dogs (Canis familiaris) requires visibility of head contour

Researchers have suggested that dogs are able to recognise human faces, but conclusive evidence has yet to be found. Experiment 1 of this study investigated whether dogs can recognise humans using visual information from the face/head region, and whether this also occurs in conditions of suboptimal visibility of the face. Dogs were presented with their owner's and a stranger's heads, protruding through openings of an apparatus in opposite parts of the experimental setting. Presentations occurred in conditions of either optimal or suboptimal visibility; the latter featured non-frontal orientation, uneven illumination and invisibility of outer contours of the heads. Instances where dogs approached their owners with a higher frequency than predicted by chance were considered evidence of recognition. This occurred only in the optimal condition. With a similar paradigm, Experiment 2 investigated which of the alterations in visibility that characterised the suboptimal condition accounted for dogs' inability to recognise owners. Dogs approached their owners more frequently than predicted by chance if outer head contours were visible, but not if heads were either frontally oriented or evenly illuminated. Moreover, male dogs were slightly better at recognition than females. These findings represent the first clear demonstration that dogs can recognise human faces and that outer face elements are crucial for such a task, complementing previous research on human face processing in dogs. Parallels with face recognition abilities observed in other animal species, as well as with human infants, point to the relevance of these results from a comparative standpoint