T. M. Herbst

Quantum teleportation over 143 kilometres using active feed-forward

The quantum internet is predicted to be the next-generation information processing platform, promising secure communication and an exponential speed-up in distributed computation. The distribution of single qubits over large distances via quantum teleportation is a key ingredient for realizing such a global platform. By using quantum teleportation, unknown quantum states can be transferred over arbitrary distances to a party whose location is unknown. Since the first experimental demonstrations of quantum teleportation of independent external qubits, an internal qubit and squeezed states, researchers have progressively extended the communication distance. Usually this occurs without active feed-forward of the classical Bell-state measurement result, which is an essential ingredient in future applications such as communication between quantum computers. The benchmark for a global quantum internet is quantum teleportation of independent qubits over a free-space link whose attenuation corresponds to the path between a satellite and a ground station. Here we report such an experiment, using active feed-forward in real time. The experiment uses two free-space optical links, quantum and classical, over 143 kilometres between the two Canary Islands of La Palma and Tenerife. To achieve this, we combine advanced techniques involving a frequency-uncorrelated polarization-entangled photon pair source, ultra-low-noise single-photon detectors and entanglement-assisted clock synchronization. The average teleported state fidelity is well beyond the classical limit of two-thirds. Furthermore, we confirm the quality of the quantum teleportation procedure without feed-forward by complete quantum process tomography. Our experiment verifies the maturity and applicability of such technologies in real-world scenarios, in particular for future satellite-based quantum teleportation.Xiao-song Ma, 2 Thomas Herbst, Thomas Scheidl, Daqing Wang, Sebastian Kropatschek, William Naylor, Alexandra Mech, 1 Bernhard Wittmann, 1 Johannes Kofler, 1 Elena Anisimova, 6 Vadim Makarov, 6 Thomas Jennewein, Rupert Ursin, and Anton Zeilinger 2, 3 Institute for Quantum Optics and Quantum Information (IQOQI), Austrian Academy of Sciences, Boltzmanngasse 3, A-1090 Vienna, Austria Vienna Center for Quantum Science and Technology, Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria Faculty of Physics, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria Max Planck Institute of Quantum Optics, Hans-Kopfermann-Str. 1, 85748 Garching/Munich, Germany Institute for Quantum Computing and Department of Physics and Astronomy, University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1, Canada Department of Electronics and Telecommunications, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway (Dated: May 1, 2014)

Darwin - A Mission to Detect and Search for Life on Extrasolar Planets

The discovery of extrasolar planets is one of the greatest achievements of modern astronomy. The detection of planets that vary widely in mass demonstrates that extrasolar planets of low mass exist. In this paper, we describe a mission, called Darwin, whose primary goal is the search for, and characterization of, terrestrial extrasolar planets and the search for life. Accomplishing the mission objectives will require collaborative science across disciplines, including astrophysics, planetary sciences, chemistry, and microbiology. Darwin is designed to detect rocky planets similar to Earth and perform spectroscopic analysis at mid-infrared wavelengths (6-20 mum), where an advantageous contrast ratio between star and planet occurs. The baseline mission is projected to last 5 years and consists of approximately 200 individual target stars. Among these, 25-50 planetary systems can be studied spectroscopically, which will include the search for gases such as CO(2), H(2)O, CH(4), and O(3). Many of the key technologies required for the construction of Darwin have already been demonstrated, and the remainder are estimated to be mature in the near future. Darwin is a mission that will ignite intense interest in both the research community and the wider public.

The Infrared Companions of T Tauri Stars

The infrared companions (IRCs) associated with several normal low-mass pre-main-sequence (T Tauri) stars pose an interesting problem for theories of binary star formation. The IRCs have very low infrared color temperatures and large infrared excesses, which have led observers to suggest that they may be less evolved objects such as protostars. This paper presents an attempt to understand the IRCs as a class by examining a broad range of observations and applying simple arguments and models. We propose that the IRCs may represent relatively normal young low-mass stars experiencing episodes of enhanced circumstellar extinction, possibly due to rapid accretion of disk material perturbed by their gravitational influence at aphelion or perihelion.

Direct measurement of the size and shape of the present-day stellar wind of eta Carinae

We present new high angular resolution observations at near-IR wavelengths of the core of the Luminous Blue Variable Carinae, using NAOS-CONICA at the VLT and VINCI at the VLT Interferometer (VLTI). The latter observations provide spatial information on a scale of 5 milli-arcsec or 11 AU at the distance of Carinae. The present-day stellar wind of Carinae is resolved on a scale of several stellar radii. Assuming spherical symmetry, we find a mass loss rate of 1:610 3 M/yr and a wind clumping factor of 0.26. The VLTI data taken at a baseline of 24 m show that the object is elongated with a de- projected axis ratio of approximately 1.5; the major axis is aligned with that of the large bi-polar nebula that was ejected in the 19th century. The most likely explanation for this observation is a counter-intuitive model in which stellar rotation near the critical velocity causes enhanced mass loss along the rotation axis. This results from the large temperature dierence between pole and equator in rapidly rotating stars. Carinae must rotate in excess of 90 percent of its critical velocity to account for the observed shape. The large outburst may have been shaped in a similar way. Our observations provide strong support for the existence of a theoretically predicted rotational instability, known as the limit.

A spatially resolved photodissociation region in the planetary nebula NGC 7027

High spatial resolution, narrow band, infrared line images and CO (1—0) mm interferometer data are presented for NGC 7027. These data trace emission from the central H II region (Brɑ), the intermediate photodissociation region [H_2 1—0S(1) and 3.3 µm dust feature], and the molecular circumstellar envelope [CO (1—0)]. The H II region lies in a cavity in the CO envelope, and consists of a smooth elliptical shell. A striking change of morphology is seen in the H_2 emission and the dust feature. The H_2 1—0 S(l) emission is composed of two components: (1) an incomplete elliptical ring of knots which bounds the ionized gas; (2) a remarkable thin shell which loops around the H II region with fourfold symmetry. The dust emission is similar to that from the ionized gas, but is displaced further from the center, and extends at low surface brightness into four “ears” which fill in the bays delineated by the outermost loops of H_2 emission. No 3.3 µm emission is detectable beyond the outer H_2 shell. The outer loops of H_2 emission and the 3.3 µm emission occupy the region between the edge of the H II region and the inner edge of the molecular gas. It is natural to ascribe the morphology of NGC 7027 to a photodissociation region which separates the ionized and molecular gas. If this is correct then the exterior H_2 loops are due to molecular gas heated by the far-UV emission escaping from the H II region, and delineate a photodissociation front. The H_2 and CO kinematics rule out shock excitation of the H_2 emission and favor UV excitation.

LUCIFER : a multi-mode NIR instrument for the LBT

LUCIFER (LBT NIR-Spectroscopic Utility with Camera and Integral-Field Unit for Extragalactic Research) is a NIR spectrograph and imager for the Large Binocular Telescope (LBT) on Mt. Graham, Arizona. It is built by a consortium of five German institutes and will be one of the first light instruments for the LBT. Later, a second copy for the second mirror of the telescope will follow. Both instruments will be mounted at the bent Gregorian foci of the two individual telescope mirrors. The final design of the instrument is presently in progress. LUCIFER will work at cryogenic temperature in the wavelength range from 0.9 μm to 2.5 μm. It is equipped with three exchangeable cameras for imaging and spectroscopy: two of them are optimized for seeing-limited conditions, the third camera for the diffraction-limited case with the LBT adaptive secondary mirror working. The spectral resolution will allow for OH suppression. Up to 33 exchangeable masks will be available for longslit and multi-object spectroscopy (MOS) over the full field of view (FOV). The detector will be a Rockwell HAWAII-2 HgCdTe-array.

LUMINOSITY-VARIATION INDEPENDENT LOCATION OF THE CIRCUM-NUCLEAR, HOT DUST IN NGC 4151

After recent sensitivity upgrades at the Keck Interferometer (KI), systematic interferometric 2 μm studies of the innermost dust in nearby Seyfert nuclei are within observational reach. Here, we present the analysis of new interferometric data of NGC4151, discussed in context of the results from recent dust reverberation, spectro-photometric, and interferometric campaigns. The complete data set gives a complex picture, in particular the measured visibilities from now three different nights appear to be rather insensitive to the variation of the nuclear luminosity. KI data alone indicate two scenarios: the K-band emission is either dominated to ∼ 90% by size scales smaller than 30 mpc, which falls short of any dust reverberation measurement in NGC4151 and of theoretical models of circum-nuclear dust distributions. Or contrary, and more likely, the K-band continuum emission is dominated by hot dust (≳1300 K) at linear scales of about 50 mpc. The linear size estimate varies by a few tens of percent depending on the exact morphology observed. Our interferometric, deprojected centro-nuclear dust radius estimate of 55 ± 5mpc is roughly consistent with the earlier published expectations from circum-nuclear, dusty radiative transfer models, and spectro-photometric modeling. However, our data do not support the notion that the dust emission size scale follows the nuclear variability of NGC4151 as an R dust L 0.5nuc scaling relation. Instead variable nuclear activity, lagging, and variable dust response to illumination changes need to be combined to explain the observations.

Geophysical and Atmospheric Evolution of Habitable Planets

The evolution of Earth-like habitable planets is a complex process that depends on the geodynamical and geophysical environments. In particular, it is necessary that plate tectonics remain active over billions of years. These geophysically active environments are strongly coupled to a planets host star parameters, such as mass, luminosity and activity, orbit location of the habitable zone, and the planets initial water inventory. Depending on the host stars radiation and particle flux evolution, the composition in the thermosphere, and the availability of an active magnetic dynamo, the atmospheres of Earth-like planets within their habitable zones are differently affected due to thermal and nonthermal escape processes. For some planets, strong atmospheric escape could even effect the stability of the atmosphere.

First VLTI/MIDI observations of a Be star: Alpha Arae

We present the first VLTI/MIDI observations of the Be star alpha Ara (HD 158 427), showing a nearly unresolved circumstellar disk in the N band. The interferometric measurements made use of the UT1 and UT3 telescopes. The projected baselines were 102 and 74 meters with position angles of 7 ° and 55°, respectively. These measurements put an upper limit on the envelope size in the N band under the uniform disk approximation of φmax= 4±1.5 mas, corresponding to 14 R*, assuming R*=4.8 Rȯ and the Hipparcos distance of 74 pc. On the other hand the disk density must be large enough to produce the observed strong Balmer line emission. In order to estimate the possible circumstellar and stellar parameters we have used the SIMECA code developed by Stee et al. (1995, A&A, 300, 219) and Stee & Bittar (2001, A&A, 367, 532). Optical spectra taken with the echelle instrument Heros and the ESO-50 cm telescope, as well as infrared ones from the 1.6m Brazilian telescope were used together with the MIDI spectra and visibilities. These observations place complementary constraints on the density and geometry of the alpha Ara circumstellar disk. We discuss the potential truncation of the disk by a companion and we present spectroscopic indications of a periodic perturbation of some Balmer lines.

Warm Dust around Blue Hypergiants: Mid-Infrared Imaging of the Luminous Blue Variable HD 168625

We present the first high spatial resolution images of thermal emission from the nebula surrounding the Galactic luminous blue variable (LBV) HD 168625. Four images, centered at 4.7, 10.1, 11.6, and 19.9 μm, have been obtained at UKIRT with MAX, the new mid-IR camera of the Max-Planck-Institut fur Astronomie. A Brγ image taken at UKIRT with IRCAM3 is also presented. On the basis of the available spectrophotometric data and of our photometry of the central star, we revise the distance currently assumed for this source from 2.2 to 1.2 kpc. The dust emission, which is optically thin and therefore sensitive to the mass distribution, clearly indicates the bipolar structure of the nebula. The majority of the infrared (IR) flux comes from a geometrically thin layer of dust tracing the outer edges of the nebular lobes. An inner shell or ring along the equatorial plane is also detected. From the mid-IR spectral energy distribution we constrain the composition and temperature of the grains. Through a simple geometrical model we estimate the dust density and total mass in the shell. Considering the structure of the nebula from an evolutionary point of view, we investigate the formation mechanism (novalike ejection or interacting stellar winds) and the recent past of the LBV precursor. We find that the interaction of the present wind with a slower dusty wind ( 2 × 10−5 M☉ yr-1, v 10 km s-1) ejected by the stellar precursor in a previous phase is by far the most viable formation mechanism for the nebula around HD 168625. Finally, the general occurrence of a redward evolution for the LBV precursors is discussed.