Stroboskop für Quantenphysiker
Archiv 2009
| 13.01.2009 13:30
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Spin squeezing and phase coherence in Bose-Einstein condensates
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Dr. Alice Sinatra Laboratoire Kastler Brossel, Paris |
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Abstract. Interactions between atoms in a condensate provide an intrinsic nonlinearity for the atomic field that can be used to prepare the system in correlated states such as spin squeezed states or Schrödinger cats. The main interest of such states is that the quantum correlations between atoms could be used to improve the accuracy of precision measurements, in atomic clocks or interferometers. In the first part of my talk I will discuss some possible methods to create spin squeezing in condensates in connection with recent and present experiments. In the second part of the talk I will address the fundamental problem of the phase coherence time of a Bose-Einstein condensate at finite temperature.
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| 23.01.2009 13:30
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Single atom detection and photon echo quantum memory
Sonderseminar |
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Dr. Ben Buchler Australian National University, Canberra, ARC Centre |
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Abstract. The ACQAO groups at ANU have two atom related experiments that I will describe: 1) building detectors for atom laser measurement and 2) a photon echo quantum memory. 1) Atom lasers are often proposed as a source for precision metrology experiments. There are also suggestions for atom laser squeezing and other quantum phenomena. Before any of this is possible, we require a high quantum efficiency technique for atom detection. Many groups have used optical cavities for detecting atoms, but the motivation has generally been cavity QED work. We have carried out some modelling aimed at finding the best possible parameters for atom detection using cavities of moderate finesse (~10 000). We have shown that quantum efficiencies of ~99% are quite feasible with realistic parameters for detection cavity and atom laser profile. We have started construction of our detectors based on this design work.Refs: Hétet et al. Multimodal Properties and Dynamics of Gradient Echo Quantum Memory. Phys. Rev. Lett. vol.101, 203601 (2008) Hétet et al. Photon echoes generated by reversing magnetic field gradients in a rubidium vapor. Optics Letters vol. 33 (20) pp. 2323 (2008) Hétet et al. Delay of squeezing and entanglement using electromagnetically induced transparency in a vapour cell. Opt Express vol. 16 (10) pp. 7369 (2008) Poldy et al. Single-atom detection with optical cavities. Phys. Rev. A vol. 78 (1) pp. 013640 (2008)
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| 03.02.2009 13:30
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Structure and Reactivity of Metal Oxide Clusters in the Gas Phase
Fällt aus! |
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Prof. Joachim Sauer Humboldt-Universität zu Berlin, Institut für Chemie |
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Abstract: Understanding the structure and reactivity of solid supported transition metal oxide catalysts is facilitated by investigating less complex model systems such as gas phase clusters, deposited clusters, crystal surfaces and thin films. For gas phase clusters, density functional theory (DFT) and other quantum chemical methods in concert with experiments are used to answer questions such as: What is the structure of gas phase cluster ions and how do they differ from supported species and bulk materials? How can IR spectroscopy and photoelectron spectroscopy in combination with DFT calculations be used to identify global minimum structures among many possible isomers? Can gas phase clusters model the reactivity of solid catalysts and to which extent? The oxides considered include aluminium oxides and vanadium oxides.
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| 09.03.2009 13:30
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A hybrid approach towards “single photon-photonics”
Sonderseminar |
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Prof. O. Benson Nano-Optik, Humboldt-Universität, Berlin |
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Abstract: Single photon sources have been realized in many different systems [1]. Important results with the potential to make true devices have been achieved with semiconductor based sources. After a brief overview of several applications of different sources in quantum information processing, such as multiplexed quantum cryptography [2] and demonstration of all-optical quantum computing [3], I will introduce an approach using nanoassembly of single emitters and resonant photonic as well as plasmonic structures. In contrast to first experiments where single quantum dots were positioned within e.g. photonic crystal cavities [4] we exploit scanning probes (AFM) to establish a nano-manipulation technique. With this technique we are able to position single quantum emitters at will and to assemble structures of increasing complexity. Ideal emitters for our approach are single defect centers in diamond nano-crystals. We report results concerning the optimization of SiN photonic crystal structures with bandgaps in the visisble [5], on-demand coupling of single defect centers to spherical microresonators [6], and plasmonic enhancement of single photon emission at room temperature [7]. [1] Focus issue of New Journal of Physics 6 (2004) [2] T. Aichele, G. Reinaudi, O. Benson, Phys. Rev. B 70, 235329 (2004) [3] M. Scholz, T. Aichele, S. Ramelow, and O. Benson, Phys. Rev. Lett. 96, 180501 (2006) [4] A. Badolato, K. Hennessy, M. Atatüre, J. Dreiser, P.M. Petroff, A. Imamoglu, Science, 308, 1158 (2005) [5] M. Barth, J. Kouba, J. Stingl, B. Löchel, and O. Benson, Opt. Express 15, 17231 (2007) [6] S. Schietinger, T. Schröder, O. Benson, Nano Lett. 8, 3911 (2008) [7] S. Schietinger, M. Barth, T. Aichele, O. Benson, submitted
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| 10.03.2009 13:30
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Quantum Imaging: Enhanced Image Formation Using Quantum States of Light
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Prof. Robert W. Boyd The Institute of Optics, University of Rochester, USA |
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Abstract: Image formation making use of quantum states of light allow dramatic new possibilities in the field of image science. In this contribution, we review some of the conceptual possibilities afforded by quantum imaging and describe some recent work that displays some of these features. In addition, we present some new experimental results on the role of coherence and indistinguishability in determining the properties of two-photon interference.
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| 16.03.2009 16:15
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Evidence for a violation of Bell's inequality in a localization based EPR experiment
Sonderseminar |
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Prof. Uwe Becker Fritz-Haber-Institut der Max-Planck-Gesellschaft |
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Abstract: In their famous paper Einstein, Podolsky and Rosen questioned 1935 the completeness of quantum mechanics concerning a local realistic description of our reality. They argued on the basis of superpositions of position and momentum states against the inherent non-locality and loss of information on prior conditions by quantum mechanics. This pioneering proposal was, however, too vague to be implemented in any experimental proof. Following a proposal of Bohm angular momentum related variables such as the polarization of light became the working horse of all experiments proving the EPR predictions. Here we present the first evidence that non-locality and loss of prior quantum state information occurs also for position in ordinary space. This shows that the tunnelling effect and entanglement are inherently correlated
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| 17.03.2009 13:30
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Ultrafast Atomic and Molecular Dynamics with X-Ray High Order Harmonics
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Prof. Stephen R. Leone University of California, Berkeley, and Lawrence Berkeley National Laboratory |
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Abstract: Laser-produced high order harmonics are used to probe chemical dynamics of atoms and molecules on femtosecond and attosecond timescales. Two basic methods are developed, ultrafast transient absorption and photoelectron spectroscopy. The high order harmonics are produced with an 800 nm Ti:sapphire laser focused into a capillary or rare gas jet. Both inner shell core levels and outer shell valence states are investigated. The transient absorption of xenon ions produced by high field ionization of neutral xenon atoms is probed by core level spectroscopy. The alignment of the vacancy created in forming the ion is measured as a function of pump-probe delay by promotion of an inner d electron to the vacancy in the outer shell. This work is extended in a collaboration with the MPQ to probe attosecond time dynamics of a high field ionization process in Kr atoms. Small molecules are excited to repulsive dissociative states and individual harmonics are used to obtain time-resolved photoelectron spectra of the atomic and molecular neutral and ion fragments. By use of velocity map imaging, the angular distributions of outgoing photoelectrons are analyzed for selected excited states of He atoms, providing new information about the relative phases and matrix elements resulting from the photoionization into the outgoing d and s waves. Finally, streak field detection of isolated attosecond inner shell ionization processes is being explored and will be discussed.
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| 20.03.2009 13:30
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Buffer-gas Cooling of Neutral Atoms and Moleculed: Quo Vadis?
Sonderseminar |
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Prof. Dr. John Doyle Harvard University, Department of Physics |
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Abstract: Cooling atoms and simple molecules to temperatures around 1-10 K can be done with cryogenic helium or neon. Starting from this basic idea, and deep magnetic traps up to 4 Tesla deep, we have made several studies. This talk will give an overview of this work, which includes study of cold spin inelastic collisions in sigma doublet and triplet molecules, measurement of vibrational lifetimes using trapped molecules, creation of ultracold atoms without laser cooling, demonstration of a bright beam of cold atoms and molecules, trapping of new atomic species, creation of a compact high optical density source of atoms, and initiation of a new experiment to search for the source of the matter-antimatter asymmetry in the universe. The future of buffer-gas cooled sources and the possible new physics that can be sought with them will also be discussed.
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| 21.04.2009 13:30
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New Horizons of Nanoplasmonics: From Attoseconds to Terahertz
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Prof. Dr. Mark I. Stockman Georgia State University, Atlanta, Department of Physics and Astronomy |
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Abstract: Nanoplasmonics deals with collective electron dynamics on the surface of metal nanostructures, which arises as a result of excitations called surface plasmons. The surface plasmons localize and concentrate optical energy in nanoscopic regions creating highly enhanced local optical fields. They undergo ultrafast dynamics with timescales as short as a few hundred attoseconds. There are numerous existing applications of nanoplasmonics: nanoantennas and waveguides for efficient coupling of light with semiconductor devices including photovoltaic cells and light-emitting diodes, labels for biomedical research, ultrasensitive detectors and sensors of molecules and biological objects for biomedicine and defense, etc. We will focus on the latest developments in nanoplasmonics. Among them is SPASER as a quantum nanoscale generator of optical fields, generation of high harmonics in the EUV range, ultrafast optical modulator with THz bandwidth, generators and modulators of THz radiation, etc.
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| 22.04.2009 10:30
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Nanoplasmonics: Optical Properties of Metal Nanostructures (Short Course)
MAP-Seminar |
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Prof. Dr. Mark I. Stockman Georgia State University, Atlanta, Department of Physics and Astronomy; Max Plank Institute for Quantum Optics, Garching; Ludwig Maximilian University, Munich |
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Abstract: 1. Plasmon Polaritonics: Properties of Surface Plasmon Polaritons in Nanostructured Systems 1.1. Introduction2. Nanoplasmonics of Nanosystems1.2. Surface plasmon polaritons1.1.1. Problem of nanolocalization of energy 2.1. Introduction; Local fields of a sphere3. Ultrafast and Quantum Nanoplasmonics 3.1. Introduction: Problem of nanoscale control of local optical fieldsThis short course is designed for advanced graduated students and PhD’s interested in the modern state of the nanooptics and nanoplasmonics. It includes presentation of the physics and applications of surface plasmons, including the concentration of energy on nanoscale, control of nanooptical phenomena, and ultrafast and nonlinear nanoplasmonics. It contains both review of the existing state of the field, and theory and applications of nanoplasmonic phenomena.
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| 23.04.2009 14:00
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Funding opportunities for post-docs in the 7th Framework programme
EU-Seminar in B 0.22 |
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Dr. Layla Bahmad and Julia Epp With presentations from Dr. Olivier Arcizet, Dr. Eleftherios Goulielmakis and Dr. Peter Hommelhoff, Max Plank Institute for Quantum Optics, Garching |
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Abstract: We will focus in particular on individual funding schemes in the Marie Curie Actions, followed by a short presentation of the ERC Starting Grant.
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| 28.04.2009 13:30
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Laser Cooling by Collisional Redistribution of Radation
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Prof. Dr. Martin Weitz Institut für Angewandte Physik der Universität Bonn |
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Abstract: The general idea that optical radiation may cool matter was put forward by Pringsheim already in 1929. Doppler cooling of dilute atomic gases is an extremely successful application of this concept [1], and more recently anti-Stokes cooling in multilevel systems has been explored, culminating in the optical refrigeration of solids [2]. Collisional redistribution of radiation is a proposed different cooling mechanism that involves atomic two-level systems [3], though experimental investigations in gases with moderate density have so far not reached the cooling regime [4]. Here I report on the experimental demonstration of laser cooling of an atomic gas based on collisional redistribution of radiation, using rubidium atoms subject to 230 bar of argon buffer gas pressure [5]. The frequent collisions in the ultradense gas transiently shift a far red detuned laser beam into resonance, while spontaneous decay occurs close to the unperturbed atomic resonance frequency. During each excitation cycle, a kinetic energy of order of the thermal energy kBT is extracted from the dense atomic sample. In a proof of principle experiment with a thermally non-isolated sample, we experimentally demonstrate relative cooling by 66 K. The cooled gas has a density of more than 10 orders of magnitude above the typical values in Doppler cooling experiments, and the cooling power reaches 87 mW. Future prospects of the demonstrated effect include studies of supercooling beyond the homogeneous nucleation temperature and optical chillers. In my talk, I will also describe experimental efforts directed at a Bose-Einstein condensation of polaritons in the high pressure buffer gas system. References: [1] See, e.g.: C. S. Adams and E. Riis, Progress in Quantum Electronics 21, 1 (1997). [2] See, e.g.: M. Sheik-Bahae and R. I. Epstein, Nature Photonics 12, 693 (2007). [3] P. R. Berman and S. Stenholm, Opt. Commun. 24, 155 (1978). [4] E. Giacobino, M. Tawil, P. R. Berman, O. Redi, and H. H. Stroke, Phys. Rev. A 28, 2555 (1983). [5] U. Vogl and M. Weitz, to be published.
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| 05.05.2009 13:30
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Structure and Reactivity of Metal Oxide Clusters in the Gas Phase
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Prof. Dr. Joachim Sauer Humboldt-Universität zu Berlin, Institut für Chemie |
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Abstract: Understanding the structure and reactivity of solid supported transition metal oxide catalysts is facilitated by investigating less complex model systems such as gas phase clusters, deposited clusters, crystal surfaces and thin films. For gas phase clusters, density functional theory (DFT) and other quantum chemical methods in concert with experiments are used to answer questions such as: What is the structure of gas phase cluster ions and how do they differ from supported species and bulk materials? How can IR spectroscopy and photoelectron spectroscopy in combination with DFT calculations be used to identify global minimum structures among many possible isomers? Can gas phase clusters model the reactivity of solid catalysts and to which extent? The oxides considered include aluminium oxides and vanadium oxides.
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| 08.05.2009 11:30
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Linking quantum phase transition and entanglment via density functional theorey (DFT)
Sonderseminar, Freitag |
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Dr. Lian-Ao Wu Theoretical Physics and History of Science, University of the Basque Country |
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Abstract: Density functional theory (DFT) is shown to provide a novel conceptual and computational framework for entanglement in interacting many-body quantum systems. DFT can, in particular, shed light on the intriguing relationship between quantum phase transitions and entanglement. We use DFT concepts to express entanglement measures in terms of the first or second derivative of the ground state energy. We illustrate the versatility of the DFT approach via a variety of analytically solvable models. As a further application we discuss entanglement and quantum phase transitions in the case of mean field approximations for realistic models of many-body systems.
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| 12.05.2009 13:30
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Laser Photoemission Electron Microscopy
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Prof. Dr. Ulf Kleineberg Ludwig Maximilians Universität München |
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Perspectives for time-resolved surface plasmon dynamics, magnetization dynamics and electron momentum imaging The combination of Photoelectron Emission Microscopy (PEEM) with sample irradiation by ultra-short laser pulses and integrated time-of-flight electron detection allows for studying fast electron dynamics on surfaces confined to lateral nanoscales. The talk highlights ongoing research activities as well as future experiments and applications in the field of localized surface plasmon dynamics, magnetization dynamics and time-resolved band structure imaging.
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| 19.05.2009 13:30
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Trapping States of a Trapped Ion, Revisited
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Prof. Dr. Peter E. Toschek Universität Hamburg, Institut für Laser-Physik |
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The vibration of an ion in a trap has served for the first demonstration of laser cooling and is an essential ingredient of concepts for quantum information processing. The ion motion couples to a driven internal ion resonance such that the system obeys a Jaynes-Cummings (J-C) model that predicts coherently generated “trapping states” of the oscillatory excitation known from micro-maser dynamics. In the past, metastable states of the vibrational excitation of an individual trapped Ba ion had been observed. They were tentatively identified with the trapping states of the J-C model. Recently, a nonlinear extension of this model has been shown to give rise to another type of trapping states that are robust under decoherence. The characteristics of these novel trapping states seem to well represent the observed metastable vibrational states.
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| 26.05.2009 13:30
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Plasmonics
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Prof. Dr. Albert Polman AMOLF, Amsterdam |
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Surface plasmon polaritons propagating on suitably engineered metal nanostructures show unique dispersion behavior that can be used to guide and concentrate light at the true nanoscale. I will review our recent work in this area, demonstrating concentration of 1500 nm light into < 100 nm diameter hot spots in plasmonic nanotapers, confinement of plasmons in nanoscale whispering gallery cavities with extremely small mode volume, and highly dispersive coaxial plasmonic metal-insulator-metal structures that serve as building blocks for a novel metamaterial that has an negative refractive index in the blue. Albert Polman obtained his Ph.D. from the University of Utrecht, the Netherlands, in 1989. He was a post-doctoral researcher at AT&T Bell Laboratories until 1991 and then became group leader at the FOM-Institute for Atomic and Molecular Physics (AMOLF) in Amsterdam, the Netherlands. In 2003 he spent a sabbatical year at CALTECH. Since 2006 he combines running his research group with the directorship of AMOLF. Polman is associated with the University of Utrecht as a professor of nanophotonics. His research interests are energy transfer in photonic nanostructures, plasmonics, microcavities, silicon nanostructures and photovoltaics. Polman specializes in studies at the interface between optical physics and materials science, and has regularly demonstrated transfer of knowledge to applied concepts.
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| 28.05.2009 13:00
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Laser Plasma Accelerators and the Energy Frontier
Sonderseminar, Donnerstag Änderung der Zeit, Start um 13:00 Uhr !! |
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Prof. Luís O. Silva Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Lissabon, Portugal |
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The outstanding developments of ultra high intensity laser technology are opening new opportunities for plasma based accelerators. As systems in the 10 PW range start to be designed and built, it is critical to examine the different acceleration regimes, to assess their relevance to particle acceleration, and to develop the tools to explore these regimes. Besides lasers, two of the enabling technologies are full scale 3D numerical simulations and long plasma sources. I will describe recent advances in numerical simulations that are allowing us to model very long propagation distances (meter scale), with energy gains in excess of 40 GeV for 10 PW lasers, and to explore the different possible acceleration regimes, ranging from the extreme blow-out to moderate blow-out. The opportunities opened by these beams for radiation generation in the plasma will also be discussed. The full realization of these possibilities can only be achieved if long plasma channels are available. I will also present recent work on the formation of low density plasma channels in structured targets, which can scale to channel lengths as long as 10 cm, and, in the future, to 1 meter. Finally, the prospects opened by the combination of these technologies will be presented.
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| 28.05.2009 14:00
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Terahertz photonics in gases
Sonderseminar, Donnerstag, kleiner Hörsaal !! |
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Dr. Nick Karpowicz Rensselaer Polytechnic Institute, Troy, USA |
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The near perfect isolation of ultracold atom systems allows to study their intrinsic many-body quantum dynamics. A common approach is to prepare the system in some state, and observe the ensuing time evolution. In general, such quench dynamics is expected to be complicated and non universal because it may involve all energy scales. However, I will show that under certain conditions dynamical modes with very long and even diverging time scales are expected to emerge in the process. I will give examples from systems currently under experimental investigation: (i) a quench across the superfluid to Mott insulator transition; (ii) Quantum dynamics of spin-chains; (iii) Many-body Rabi oscillations of interacting bosons tunneling between a pair of 1d tubes. Finally I will show that many-body quantum dynamics can be utilized to generate interesting quantum phases as long-lived meta-stable states in a non-equilibrium process.
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| 28.05.2009 15:15
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Correlated quantum dynamics in systems of ultracold atoms
Sonderseminar, Donnerstag |
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Dr. Ehud Altman Weizmann Institute of Science, Israel |
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The near perfect isolation of ultracold atom systems allows to study their intrinsic many-body quantum dynamics. A common approach is to prepare the system in some state, and observe the ensuing time evolution. In general, such quench dynamics is expected to be complicated and non universal because it may involve all energy scales. However, I will show that under certain conditions dynamical modes with very long and even diverging time scales are expected to emerge in the process. I will give examples from systems currently under experimental investigation: (i) a quench across the superfluid to Mott insulator transition; (ii) Quantum dynamics of spin-chains; (iii) Many-body Rabi oscillations of interacting bosons tunneling between a pair of 1d tubes. Finally I will show that many-body quantum dynamics can be utilized to generate interesting quantum phases as long-lived meta-stable states in a non-equilibrium process.
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| 29.05.2009 10:30
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Probing many-body systems of ultracold atoms
Sonderseminar, Freitag |
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Prof. Eugene Demler Professor of Physics, Harvard University, Cambridge |
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I will review several theoretical ideas for probing strongly correlated many-body states of ultracold atoms. I will discuss: 1) extensions of noise correlations to phase sensitive measurements of order parameters in paired states; 2) analysis of thermal and quantum fluctuations in one and two dimensional condensates using density ripples in expanding clouds; 3) spin noise as a probe of antiferromagnetic correlations in optical lattices.
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| 02.06.2009 13:30
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Atomic giants shuffle tiny lights: non-linear optics with Rydberg atoms
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Prof. Dr. Charles Adams Durham University, UK |
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Our work focuses on exploiting the strongly interacting character of Rydberg atoms for non-linear optics [1-3] with the aim of realizing a robust quantum interface to control single pho-tons. We will describe elements of the Rydberg atom-light interaction such as Rydberg dark states [1,3], the Kerr [2] and Faraday effects [4], and potential applications. [1] Mohapatra et al. Phys. Rev. Lett. 98, 113003 (2007). [2] Mohapatra et al. Nature Phys. 4, 890 (2008). [3] Weatherill et al. J. Phys. B 41, 201002 (2008). [4] Siddons et al. arXiv:0811.2316 Nature Photon. (to appear).
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| 04.06.2009 14:00
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QED cascades in the strong laser field
Sonderseminar, Donnerstag, in B 0.22 |
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Dr. A. Fedotov Department of Theoretical Physics, Moscow State Engineering Physics Institute (Technical University) |
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The long QED cascades (i.e., the chains of successive hard photon emission and electron-positron pair production events) caused by a charged particle in a strong laser field will be discussed. Formation of long QED cascades is one of the manifestations of the so-called Quantum Radiation-Dominated Regime of the laser-matter interaction. Two possible scenarios will be considered: (i) the cascades caused by high-energy particles with the now-days or near future available laser intensities, and (ii) the recently predicted `self-induced' cascades caused by even initially slow particles provided that laser intensity is larger than 10^(24) W/cm2. This case will be extremely important for ELI. The appearance of QED cascades should be taken into account in designing experiments with high-intensity lasers as well as incorporated in the computer codes for numerical simulations of laser-matter interaction at high laser intensities. |
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| 09.06.2009 13:30
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Quantum Optics on a Chip
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Prof. Dr. Rudolf Gross Walther Meissner Institut, Bayerische Akademie der Wissenschaften, Garching |
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| 16.06.2009 13:30
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En Route to Quantum Biology: Non Trivial Quantum Effects in Radical Ion Pair Reactions
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Prof. Dr. Iannis K. Kominis University of Crete, Heraklion |
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Non-trivial quantum effects in biology have been sought after for a long time. It was recently discovered that a familiar biological system, namely radical-ion pairs and their reactions, exhibits a number of quantum effects such as quantum coherence, quantum jumps and the quantum Zeno effect. Radical-ion pairs, at the basis of photosynthesis and avian magnetic navigation, are shown to be a paradigm biological system where the full machinery of quantum measurement theory can be fruitfully applied. This opens the way to several vistas in theoretical and experimental quantum biology, from the understanding of the fundamental connections between quantum-dynamic effects and biology, to the design and experimental demonstration of novel quantum-limited biochemical-reaction magnetometers and last but not least to the exploration of quantum information processing at the biological level.
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| 19.06.2009 10:30
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Experimental investigation of the dynamics in a strongly interacting Fermi gas
Sonderseminar, Freitag |
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Mag. Stefan Riedl Universität Innsbruck, Österreich |
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| 23.06.2009 13:30
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Towards Comprehensive Control of Atomic and Molecular Motion
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Prof. Dr. Mark G. Raizen The University of Texas at Austin |
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The method of laser cooling has opened the door to low temperature physics of dilute gases. Despite the great success of this method, it has been limited to a very small set of atoms in the periodic table and no molecules. I will describe in this talk new approaches to trapping and cooling that have been developed in my group. The first step uses pulsed magnetic fields to stop atoms and molecules where they can be magnetically trapped. The next step is an experimental realization of informational cooling as first proposed by Leo Szilard in 1929 in an effort to resolve the paradox of Maxwell's demon. Together, these provide a two-step comprehensive solution to trapping and cooling. I will describe our progress in applying these new methods to trapping and cooling of hydrogen isotopes. In the short term, we are working to trap hydrogen and deuterium, which will serve as a step towards trapping of atomic tritium. This system will be used for precision measurement of beta decay towards determination of the neutrino rest mass. Our methods are also very applicable to trapping and cooling of anti-hydrogen, and a collaboration at an accelerator laboratory is being pursued.
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| 25.06.2009 11:30
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Many-Body Excitations and their Decay in a BEC
Sonderseminar, Donnerstag |
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Dr. Nir Bar-Gill Weizmann Institute of Science, Israel |
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| 30.06.2009 13:30
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Optomechanical correlations between light and mirrors
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Prof. Dr. Antoine Heidmann Laboratoire Kastler Brossel, Université P. et M. Curie, Paris |
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Recent progress in high-finesse optical cavities and mechanical resonators allows one to reach a new regime in which the dynamical properties of an optomechanical system are governed by the radiation pressure exerted by light on mirrors. This optomechanical coupling leads to quantum limits in ultra-sensitive interferometric measurements such as gravitational-wave detectors, but also to very efficient laser-cooling mechanisms. To experimentally study this optomechanical coupling, we monitor in a very high finesse cavity the displacements of moving mirrors, either coated on a cm-size substrate or on a micro-resonator. We have recently observed the optomechanical correlations induced by radiation pressure between a tiny classical intensity noise of a light beam and the resulting mirror displacements. This scheme can be extended down to the quantum level and has applications both in high-sensitivity measurements and in quantum optics.
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| 02.07.2009 13:30
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Quantum dots in photonic crystals: from quantum information processing to optical switching at a single photon level
Sonderseminar, Donnerstag entfällt wegen Krankheit |
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Prof. Dr. Jelena Vuckovic Ginzton Laboratory, Stanford University, Stanford, USA |
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Quantum dots in photonic crystals are interesting both as a testbed for fundamental cavity quantum electrodynamics (QED) experiments, as well as a platform for quantum and classical information processing. Quantum dot-photonic crystal cavity QED has been probed both in photoluminescence and coherently, by resonant light scattering from such a system [1]. In the latter case, both intensity and photon statistics of the reflected beam have been analyzed as a function of wavelength, leading to observation of effects such as photon blockade and photon induced tunneling - for the first time in solid state [2]. The system has also been employed to achieve a controlled phase and amplitude modulation between two modes of light at the single photon level [3] – nonlinearity observed so far only in atomic physics systems. Finally, electrical modulation of a single quantum dot strongly coupled to a cavity has been performed at 150MHz speed, by employing quantum confined Stark effect induced by lateral electric field. These demonstrations lie at the core of a number of proposals for quantum information process¬ing, and could also be employed to build novel devices, such as electro-optical switches controlled at a single photon level. 1. Dirk Englund, Andrei Faraon, Ilya Fushman, Nick Stoltz, Pierre Petroff, and Jelena Vuckovic, "Controlling cavity reflectivity with a single quantum dot," Nature, vol. 450, No. 7171, pp. 857-861, December 2007 2. Andrei Faraon, Ilya Fushman, Dirk Englund, Nick Stoltz, Pierre Petroff, and Jelena Vuckovic, "Coherent generation of nonclassical light on a chip via photon-induced tunneling and blockade," Nature Physics, Vol. 4, pp. 859 - 863 (2008) 3. Ilya Fushman, Dirk Englund, Andrei Faraon, Nick Stoltz, Pierre Petroff, and Jelena Vuckovic, "Controlled phase shift with a single quantum dot," Science, vol. 320, number 5877, pp. 769-772 (2008)
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| 07.07.2009 13:30
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Laser Ignition of Engines
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Prof. Dr. Ernst Wintner Technische Universität Wien |
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With the improvement of modern solid-state lasers new applications become more and more widespread, the initiation and diagnostics of chemical processes [1] being one special class of them. The initiation of a plasma by nanosecond laser pulses or shorter ones allows e.g. to reli-ably and efficiently start combustion processes which is of special importance in case of internal combustion engines. Therefore a worldwide race towards the first realization of laser-ignited engines has been going on within the last years. Advantages may comprise higher efficiency and substantial reduction of pollutant emissions as well extended service intervals. The development of laser ignition comprises manifold basic research like the investigation of the dependence of plasma threshold on various ambient parameters like pressure, temperature, combustible gas mixture, concentration of seed charges etc. On the other hand, the specifications of the laser pulses applied are of crucial importance: wavelength, pulse energy, pulse duration, focal diameter, and potentially the repetition rate of several pulses. Aspects of the incoupling window have to be solved satisfyingly. Recently, we succeeded in realizing a laser spark plug as a demonstrator for engine operation. Additional applications like in rocketry are under preparation. [1] M. Lackner “Lasers in Chemistry - Probing and Influencing Matter”, ISBN-13:978-3-527-31997-8 - Wiley-VCH, Weinheim, 2008; H. Kofler, J. Tauer, E. Wintner, „Laser-induced ignition for combustion engines”.
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| 09.07.2009 13:30
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Photonic quantum measurements
Sonderseminar, Donnerstag |
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Prof. Geoff Pryde Griffith University, Brisbane, Australia |
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| 14.07.2009 13:30
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Trends in application of optical technologies
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Dr. Frank Stietz Senior Vice President Corporate Research and Technology, Carl Zeiss AG, Oberkochen |
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contents:
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| 21.07.2009 13:30
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From Slow Light to FAST CARS
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Prof. Dr. George R. Welch Texas A&M University, College Station, Texas |
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Quantum mechanical coherence effects are responsible for many new and exciting results in quantum optics. Coherence between multiple atomic states has lead to the ability to propagate light through thousands of absorption lengths of an opaque medium, lasing without population inversion, group velocities as low as meters per second, and the ability to store quantum states of light. I will review the physics behind these remarkable effects, including ultra-slow (and ultra-fast) group velocity of light, and then give a survey of many applications of this system. I will show how the coherence effects responsible can be applied to Coherent Anti-Stokes Raman Scattering (CARS) and how it can be applied to the detection of bio-molecules with a wide range of application ranging from detection of Anthrax spores to non-invasive glucose detection.
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| 22.07.2009 13:30
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Quantum Optical Computing, Imaging and Metrology: The Lowdown of High-NOON States
Sonderseminar,Achtung! Verschoben auf Donnerstag 16:00 !!!! |
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Prof. Dr. Jonathan P. Dowling Louisiana State University, Baton Rouge |
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Quantum entanglement has the potential to revolutionize the entire field of interferometric sensing by providing many orders of magnitude improvement in interferometer sensitivity. The quantum-entangled particle interferometer approach is very general and applies to many types of interferometers. In particular, without nonlocal entanglement, a generic classical interferometer has a statistical-sampling shot-noise limited sensitivity that scales like 1/pN, where N is the number of particles passing through the interferometer per unit time. However, if carefully prepared quantum correlations are engineered between the particles, then the interferometer sensitivity improves by a factor of pN to scale like 1/N, which is the limit imposed by the Heisenberg Uncertainty Principle. For optical interferometers operating at milliwatts of optical power, this quantum sensitivity boost corresponds to an eight-order-of-magnitude improvement of signal to noise. I will discuss a number of recent theoretical and experimental developments using so called photonic N00N states to beat the shot-noise limit; work that has benefited from a close connection to linear optical quantum computing. I will also discuss our efforts to develop coherent, stable, matter-wave gyroscopes in Bose-Einstein condensates, which are controlled by orbital angular momentum states of light.
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| 23.07.2009 13:30
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Open Quantum Systems: Cavity QED with Dissipation
Sonderseminar, Donnerstag |
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Prof. Dr. Howard Carmichael University of Auckland, New Zeeland |
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The Jaynes-Cummings model with dissipation has for many years been a fundamental model of optical frequency cavity QED. Little attention has been payed, however, to the unique consequences of the added dissipation: the possible occurrence of dissipative quantum phase transitions when the system is driven far away from thermal equilibrium. Over nearly two decades, experiments in cavity QED have focused on physics seen at the weakest levels of excitation---such things as vacuum Rabi splitting, single-photon sources, and two-photon correlations. While the last of these begins to probe the unique nonlinearity of the Jaynes-Cummings spectrum, the features attracting experimental attention are realized with sources that emit far less than one photon per cavity lifetime. My talk will review this background, and then move on to the new physics that arises when highly excited states of the dissipative Jaynes-Cummings model are accessed. The second part of the talk takes its inspiration from recent advances in circuit QED, where states of a few intracavity quanta are observed. It concludes with recent theoretical results which demonstrate the existence of a dissipative quantum phase transition under conditions of very strong coupling and high excitation.
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| 14.09.2009 15:00
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Formation of Mott-insulating domains and scalable quantum information processing based on ultracold atoms in optical lattices
Sonderseminar, Montag |
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Prof. Cheng Chin James Franck Institute and Physics Department, University of Chicago |
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Abstract. We present a direct measurement of the density profile of a two-dimensional Mott Insulator formed by ultracold atoms in an optical lattice. High resolution absorption imaging is used to probe the “wedding-cake” structure of a trapped gas as it crosses the boundary from a unit-filled Mott insulating phase to the superfluid phase at finite temperature. Detailed analysis of images yields measurements of temperature and local compressibility; for the latter we observe a strong suppression deep in the Mott-insulating phase, which is recovered for the superfluid and normal phases. Furthermore, we measure spatially resolved fluctuations in the local density, showing a suppression of fluctuations in the insulator. Results are consistent with the fluctuation-dissipation theorem for insulator, superfluid and normal gas. Quantum simulation and quantum information processing based on atoms in Mott domains will be discussed.
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| 15.09.2009 10:00
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Dynamics on the nanoscale: spatio-temporal imaging and control of light using plasmonics
Sonderseminar, Dienstag |
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Prof. M. Raschke Department of Chemistry, University of Washington, Seattle |
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Abstract. The spatially resolved optical probing and control of matter on nanometer length scales has remained one of the great challenges of nanoscience. I will discuss new developments enabling optical imaging and spectroscopy with ultrahigh spatial and temporal resolution combining concepts from scanning probe microscopy, plasmonics, optical antennas, and nonlinear and ultrafast laser optics. This enables the study of the ultrafast electronic dephasing of individual plasmonic nanostructures with unprecedented precision - as a laboratory providing insight into the fundamental physics of electrons in metals. The development of new optical antenna concepts allows for controlling light on nanometer length scales and the extension of radio-frequency antenna theory into the optical regime. Furthermore, I will discuss new concepts for the rational design of a true nanoconfined light sources taking advantage of some unique metamaterials properties of propagating plasmons on 3D nanostructures.
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| 13.10.2009 13:30
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Photonic quantum logic in waveguide circuits
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Prof. Dr. Jeremy O’Brien University of Bristol, UK |
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Abstract: Encoding quantum information in single photons is an appealing approach to quantum information processing [1], metrology [2] and measurement [3]. However, the implementation of optical circuits with bulk optics is reaching practical limits. We have developed an integrated waveguide approach to photonic quantum circuits for high performance, miniaturization and scalability [4]. We demonstrate high-fidelity silica-on-silicon integrated optical realizations of key quantum photonic circuits, including two-photon quantum interference and a controlled-NOT logic gate. We have demonstrated controlled manipulation of up to four photons on-chip, including high-fidelity single qubit operations, using a lithographically patterned resistive phase shifter [6]. We have also used this architecture to implement a small-scale compiled version of Shor’s quantum factoring algorithm [7]. Finally we have demonstrated how quantum process discrimination can be implemented with photonic circuits [8]. [1] JL O’Brien, Science 318, 1567 (2007) [2] T Nagata, R Okamoto, JL O’Brien, K Sasaki, S Takeuchi, Science 316, 726 (2007) [3] R Okamoto, JL O’Brien, HF Hofmann, T Nagata, K Sasaki, S Takeuchi, Science 323, 483 (2009) [4] A Politi, MJ Cryan, JG Rarity, S Yu, and JL O’Brien, Science 320, 646 (2008) [6] JCF Matthews, A Politi, A Stefanov, JL O'Brien Nature Photonics 3, 346 (2009) [7] A Politi, JCF Matthews, JL O'Brien Science 325, 1221 (2009) [8] A Laing, T Rudolph, and JL O'Brien, Phys. Rev. Lett. 102, 160502 (2009)
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| 20.10.2009 13:30
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Optical lattice clocks toward 10 to the power of -17 uncertainty
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Prof. Dr. Hidetoshi Katori University of Tokyo |
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Abstract: To date, optical clocks based on singly trapped ions and ultracold neutral atoms trapped in the Stark-shift-free optical lattices are regarded as promising candidates for future atomic clocks. So far “optical lattice clocks” have been evaluated with the uncertainty of 1×10-15 on the basis of Cs atomic clocks. However, the latter performance is not enough to fully evaluate the former stability as well as accuracy. Therefore, frequency comparison between highly-stable and accurate optical lattice clocks is crucial for further evaluation of lattice clocks. One of the essential experimental challenges in the development of “optical lattice clocks” is to find out the better lattice geometries as well as interrogated atom species (including their quantum statistics) that bring out the potential performance of the clock scheme, taking into account the collisional frequency shift, the Black body radiation (BBR) shift, the atomic multipolar and hyperpolarizability effects. In this talk, we discuss optimal lattice geometries in view of the quantum statistics and related spins of interrogated atoms. This leads to two promising configurations for the clock: One-dimensional (1D) lattice loaded with spin-polarized fermions and 3D lattice loaded with bosons. We present frequency comparison of these two optical lattice clocks using fermionic 87Sr and bosonic 88Sr. Such lattice clock comparison will offer an important step to ascertain the clocks’ uncertainty beyond the Cs limit of 1×10-15. As for the BBR and the lattice laser related uncertainties, we discuss prospects for a cryogenic clock, a “blue-detuned” magic wavelength, and a Hg based optical lattice clock.
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| 26.10.2009 15:00
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Interfacing quantum states of ions and photons
Sonderseminar 15:00 |
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Prof. Dr. Wolfgang Lange University of Sussex, Brighton, United Kingdom |
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Abstract: The controlled interaction of ions and photons at the single quantum level is a key element of quantum information processing. Three schemes to achieve this goal are presently implemented at the University of Sussex, using a range of techniques to access different regimes of optical cavity-QED.
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| 29.10.2009 15:15
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Classically simulatable quantum computations
Sonderseminar 15:15 |
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Prof. Richard Jozsa University of Bristol, UK |
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Abstract: Quantum computations that can be classically efficiently simulated offer no direct computational benefits over classical computation, yet their study is of great interest for illuminating possible origins of quantum computational power. We will review some of the best known examples of simulatable computations and describe a simple general formalism for generating such classes. We will show that the efficient simulation of Clifford circuits (Gottesman-Knill theorem) and of matchgate circuits (Valiant's theorem), appear as two special cases. Further examination of the techniques used in the simulations can reveal a more precise characterisation of the computational power of the circuits. Correspondingly we may briefly describe how matchgate circuits can be related to so-called log-space bounded quantum computation.
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| 03.11.2009 13:30
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Measuring the mass of the (anti)proton by laser spectroscopy of antiprotonic helium
Double feature |
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Dr. Masaki Hori Max-Planck-Institut für Quantenoptik, Garching |
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Abstract: Antiprotonic helium is a three-body atom consisting of a helium nucleus, an orbital electron in the 1s ground state, and the antiproton in a metastable Rydberg state. Our MPQ group has carried out precise laser spectroscopy of these atoms at the Antiproton Decelerator facility of CERN, using nanosecond pulsed lasers stabilized to a femtosecond frequency comb. By comparing the measured atomic frequencies with QED calculations, the antiproton-to-electron mass ratio was determined with parts-per-billion relative precision. This constituted a consistency test of the CPT symmetry.
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| 03.11.2009 14:00
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Measurement of the Lamb shift in muonic hydrogen
Double feature |
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Dr. Randolf Pohl Max-Planck-Institut für Quantenoptik, Garching |
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Abstract: Surprisingly, the (rms charge) radius of the proton has so far been only known to about 2 per cent relative accuracy. This ignorance has so far limited the test of bound-state QED using hydrogen spectroscopy. We have recently measured the Lamb shift in muonic hydrogen, where the finite size effect is huge. From this measurement we can determine the rms proton charge radius to 10-3. Our measurement leads also to a 6-fold improvement in the Rydberg constant.
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| 05.11.2009 13:30
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Title: 6Li - 40K, an exploration into HeteroNuclear Fermi-Fermi systems
Sonderseminar |
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Dr. Devang S. Naik Austrian Academy of Sciences, Institut für Quantenoptik |
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Abstract: Recently the study of heteronuclear fermionic mixtures, in particular the 6Li - 40K, has strongly gained interest due to its additional mass imbalance. Experimentally unexplored properties of these mixtures include: superfluidity in mass imbalanced systems, phase seperation, crystalline phases, exotic pairing mechanisms, and long-lived trimer. Incombination with spectroscopic measurements, precision measurements of Feshbach resonances can push the accuracy of intermolecular potentials beyond the limitations of the Born Opppenheimer approximations. We will present results on the first studies on the scattering propertis of these mixtures, the first stable three-component fermi-fermi mixture in mass imbalanced systems, and the creation of heteronuclear molecules that were done in the Institute of Quantum Optics and Quantum Information at the Austrian Academy of Sciences.
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| 10.11.2009 13:30
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Ultracold atoms in artificial gauge fields
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Prof. Dr. Maciej Lewenstein ICFO Barcelona, Spanien |
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Abstract. Recently there is a revival of interest in generating artificial gauge fields in ultracold atoms systems using laser light and studying properties of such systems. I will review recent efforts toward this goal and review possible physical effects that are expected to be observed in the near future. I will discuss standard "magnetic" gauge fields, but will focus on artificial non-Abelian gauge fields and their effects, such as anomalous integer quantum Hall effect, or graphene-like artificial relativistic physics.
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| 17.11.2009 13:30
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Controlling strongly correlated electron systems with light
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Prof. Dr. Andrea Cavalleri DESY Hamburg |
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| 19.11.2009 09:30
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Cr2+ZnSe as Ti:sapphire Laser of the Infrared: What’s the Difference?
Sonderseminar um 9:30 Uhr |
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Prof. Irina Sorokina Department of Physics, NTNU-Norwegian University of Science and Technology, Trondheim, Norway |
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Abstract: The talk reviews principles, history of the development and advances in generation of broadly tunable continuous-wave, pulsed and ultrashort pulsed radiation from Cr2+lasers, with the particular focus on femtosecond Cr2+ZnSe laser. The solid-state oscillator based on Cr2+ZnSe laser is the first and the most advanced member of Cr2+-chalcogenide family of lasers, having the broadest emission bandwidth among all existing lasers. It resembles in many respects its ancestor, Ti:sapphire laser, is yet different, mainly due to the semiconductor nature of its host. The latter opens up exciting opportunities in applications, as well as perspective of development of a yet new class of electrically pumped fiber lasers, the first really broadband fiber lasers in the mid-infrared. The initial steps on this way render this ambitious aim as feasible. |
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| 24.11.2009 13:30
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Applying microsystem-diodelasers for Raman-spectroscopic investigations in the ocean and for spoiled meat
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Prof. Dr. Heinz-Detlef Kronfeldt Technische Universität Berlin |
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| 01.12.2009 13:30
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Nanofibre Photonics and Quantum Optics
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Prof. Dr. Arno Rauschenbeutel Universität Mainz |
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Abstract: Recently, optical nanofibers with diameters smaller than the wavelength of the guided light have attracted considerable interest in the field of quantum optics due to their high potential for efficiently interfacing light and matter. In my talk I will report on two experiments using such nanofiber-optical interfaces. In the first experiment, we perform ultra-sensitive spectroscopic measurements on 3,4,9,10-perylene-tetracarboxylic dianhydride molecules (PTCDA) deposited on the fiber surface at ambient conditions. We use the guided mode of the nanofiber both for excitation of the molecules and for fluorescence collection and we show that surface coverages as small as 1 ‰ of a compact monolayer still give rise to absorption and fluorescence spectra with a good signal to noise ratio. In the second experiment, we trap about 2000 cold neutral cesium atoms close to the surface of an optical nanofiber using the optical dipole force exerted by the evanescent field of the nanofiber guided light. The atoms are probed with a weak resonant field which is sent through the nanofiber and which interfaces with the atoms via the evanescent field. Remarkably, the atomic ensemble almost entirely absorbs this probe field, yielding an optical depth of up to 18. This opens the route towards non-linear optics and quantum communication applications with fiber-coupled atomic ensembles.
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| 02.12.2009 10:00
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General metrology of amplitude and phase noise
Sonderseminar Teil 1/3 10:00 Uhr |
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Prof. Enrico Rubiola Université de Franche Comté and the Department of Time and Frequency of the FEMTO-ST Institute, Besançon, France |
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Prof. Rubiola has worked on various topics of electronics and metrology, navigation systems, time and frequency comparisons, and Cs frequency standards. His main fields of interest are precision electronics form dc to microwaves and phase noise metrology, which include frequency synthesis, high spectral purity oscillators, photonic systems, sophisticated instrumentation, and noise. He has developed a new generation of instruments for AM/PM noise measurement with ultimate sensitivity, based on synchronous detection of the error signal in a sophisticated version of the Wheatstone bridge, and on a variety of signal-processing methods. The course will consist of three lectures Dec 2nd: General metrology of amplitude and phase noise Dec 9th: The origin of frequency instability and noise in oscillators Dec 11th: The cross-spectrum experimental method
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| 02.12.2009 13:30
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Localization of Interacting Bosons in a Lattice: Interplay between Disorder and Commensurability
Sonderseminar |
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Prof. Dr. Boris Svistunov University of Massachussetts, Amherst |
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Abstract: The interplay between disorder and interaction in a lattice bosonic system, at an integer filling, is by no means a mere synergy between Mott and Anderson localization scenarios. We prove a theorem resolving a 20-year-old controversy concerning the topology of the groundstate phase diagram of the system (featuring three phases: superfluid, Mott insulator and Bose glass). Numerically, we reveal an accurate--and rather curious--phase diagram of the 3D disordered Bose Hubbard model. The numeric results are perfectly consistent with our analytic findings.
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| 08.12.2009 13:30
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Ultracold atoms near superconductors and carbon nanotubes
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Prof. Dr. József Fortágh Physikalisches Institut der Universität Tübingen |
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Abstract: Hybrid quantum systems, which combine ultra-cold atoms with solid state devices, have attracted considerable attention in the last few years. Promising applications are in the areas of precision sensing and quantum information processing. I report on our experimental efforts towards the realization of such systems based on ultracold atoms, superconductors and carbon nanotubes. The cold atom/superconductor experiment consists of a rubidium BEC apparatus and a thermally shielded helium flow cryostat at 4.2 K in the same ultrahigh vacuum system. Atom clouds are loaded into a magnetic microtrap formed near a superconducting niobium wire. We observe the impact of the Meissner effect on the trap parameters and measure the spin coherence of atoms near the superconductor. The measured coherence times are the longest yet observed in the vicinity of a highly conducting material and confirm the suppression of Johnson noise in superconductors. The results have implications for the development of coherently coupled cold atom/solid state quantum devices, in which cold atoms serve as long term quantum memory. In a second experiment, we investigate the interaction between ultracold atoms and carbon nanotubes. Free standing single nanotubes, periodic structures, and “carpets” of nanotubes are grown on the surface of an atom chip. We observe the scattering of ultracold atoms on the nanotubes. In addition, we describe a novel atom detector based on field ionization of ground state atoms near carbon nanotubes and subsequent ion counting.
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| 09.12.2009 10:00
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The origin of frequency instability and noise in oscillators
Sonderseminar Teil 2/3 10:00 Uhr |
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Prof. Enrico Rubiola Université de Franche Comté and the Department of Time and Frequency of the FEMTO-ST Institute, Besançon, France |
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Prof. Rubiola has worked on various topics of electronics and metrology, navigation systems, time and frequency comparisons, and Cs frequency standards. His main fields of interest are precision electronics form dc to microwaves and phase noise metrology, which include frequency synthesis, high spectral purity oscillators, photonic systems, sophisticated instrumentation, and noise. He has developed a new generation of instruments for AM/PM noise measurement with ultimate sensitivity, based on synchronous detection of the error signal in a sophisticated version of the Wheatstone bridge, and on a variety of signal-processing methods. The course will consist of three lectures Dec 2nd: General metrology of amplitude and phase noise Dec 9th: The origin of frequency instability and noise in oscillators Dec 11th: The cross-spectrum experimental method
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| 11.12.2009 13:30
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The cross-spectrum experimental method
Sonderseminar Teil 3/3 |
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Prof. Enrico Rubiola Université de Franche Comté and the Department of Time and Frequency of the FEMTO-ST Institute, Besançon, France |
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Prof. Rubiola has worked on various topics of electronics and metrology, navigation systems, time and frequency comparisons, and Cs frequency standards. His main fields of interest are precision electronics form dc to microwaves and phase noise metrology, which include frequency synthesis, high spectral purity oscillators, photonic systems, sophisticated instrumentation, and noise. He has developed a new generation of instruments for AM/PM noise measurement with ultimate sensitivity, based on synchronous detection of the error signal in a sophisticated version of the Wheatstone bridge, and on a variety of signal-processing methods. The course will consist of three lectures Dec 2nd: General metrology of amplitude and phase noise Dec 9th: The origin of frequency instability and noise in oscillators Dec 11th: The cross-spectrum experimental method
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| 15.12.2009 13:30
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Resonant amplification of quantum fluctuations with a spinor gas
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Prof. Dr. Wolfgang Ertmer Leibniz Universität Hannover |
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Abstract: Bose-Einstein condensates of atoms with non-zero spin constitute not only an optimal scenario to investigate fundamental properties of magnetic superfluids, but also an ideal system for the study of macroscopic amplification of quantum and classical fluctuations. This is strikingly manifested in a sample initially prepared in the m = 0 state, where spin-changing collisions triggered by quantum fluctuations may lead to the creation of correlated pairs in m = ± 1. We show that the pair creation efficiency is strongly influenced by the interplay between the external trapping potential and the Zeeman Effect and reflects the confinement-induced magnetic-field dependence of elementary spin excitations of the trapped condensate. Remarkably, pair production in our experiments is characterized by a multi-resonant dependence on the magnetic field. Pair creation at these resonances acts as strong parametric matter-wave amplifier. Depending on the resonance condition, this amplification can be extremely sensitive or insensitive to the presence of seed atoms. We show that pair creation at a resonance which is insensitive to the presence of seed atoms is triggered by quantum fluctuations and thus the system acts as a matter-wave amplifier for the vacuum state.
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| 21.12.2009 14:30
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Trapped ions: A precise toolbox for quantum engineers
Sonderseminar 14:30 |
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Dr. Dietrich Leibfried National Institute of Standards and Technology, Boulder, Colorado 80305, USA |
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Abstract: This talk will give an overview of recent work in quantum engineering with trapped ions and the exciting prospects that steady progress in this field has opened up for future research. Internal states of trapped ions have remarkable quantum coherence that lies at the heart of both the currently most precise atomic clocks and their excellent suitability as the physical keepers of quantum information. The ions' charge offers a strong handle to confine them in deep trapping potentials for very long times and to move them and manipulate their quantum state of motion with great precision. Most importantly, Coulomb coupling between several ions is utilized for high quality quantum logic gates and for producing entangled quantum states of unprecedented complexity. Optical transitions efficiently couple trapped ions to the electromagnetic vacuum that provides an almost perfect entropy sink. This enables precise initialization of internal and motional degrees of freedom without the need for low temperature experiments. The unique combination of features of trapped ions has recently led to advances in several fields, especially in quantum information processing and precision tests of fundamental physics. Perhaps most notably, it has spawned a multitude of novel experimental techniques that could also be leveraged (for example) towards quantum-enabled sensors, quantum simulation, novel spectroscopy methods, cavity QED with ions, coupling atomic physics systems to solid-state systems and the quantum coherence of well isolated mesoscopic systems. All these possibilities have in common that they expand our ability to control the quantum world. If history is any guide, such expanded abilities might well lead to more, possibly unforeseen applications and intriguing insights into some of the most fundamental questions.
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Dr. Alice Sinatra
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