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Archiv 2010

     
19.01.2010 13:30
Quantum Information Processing with Ions
Prof. Dr. Ferdinand Schmidt-Kaler
Universität Ulm






Superpositions of quantum logic states |0> und |1> are stored and manipulated in the electronic excitation of ions for a future quantum computer [1]. So far, we know how to deal with a single, two [2,3], and up to eight qubits. For a realization of a scalable quantum device we employ linear segmented micro-structured Paul-traps [4], see figure below. I report on recent progress towards quantum gate operations and experimental studies of non-equilibrium thermodynamics [5].

As alternative to Paul traps, ions for quantum devices may be confined in the matrix of a solid state crystal. While quantum gate operations have been demonstrated for two of such qubits [6], no scalable solid state devices have been fabricated. We have proposed a method which uses a linear Paul trap a deterministic source of sympathetically cooled doping ions [7]. Recently, we have proven experimentally deterministic extraction and focussing of cold ions [8].

[1] J. I. Cirac und P. Zoller, Phys. Rev. Lett. 74, 4091(1995).
[2] F. Schmidt-Kaler et al., Nature 422, 408 (2003).
[3] D. Leibfried et al., Nature 422, 412 (2003).
[4] S. Schulz, et al., New Journal of Physics 10, 045007(2008) and U. Poschinger et al, J. Phys. B: At. Mol. Opt. Phys. 42 154013.
[5] G. Huber, F. Schmidt-Kaler, S. Deffner, E. Lutz, Phys. Rev. Lett 101, 070403 (2008).
[6] P. Neumann et al., Science 320, 1326 (2008).
[7] J. Meijer, et. al. , Appl. Phys. A 83, 321 (2006).
[8] W. Schnitzler et al, arXiv:0912.1258 and W. Schnitzler et al, PRL 102, 070501 (2009).
 

26.01.2010 13:30
Quantum Entanglement of Orbital Angular Momentum
Prof. Dr. Han Woerdman
Leiden University






The phase of a light beam can be twisted as a corkscrew around its axis of propagation. Such fields have drawn much attention, in particular since it was realized in 1992 that a twisted light beam carries Orbital Angular Momentum (OAM), namely lħ per photon; here the integer l is the azimuthal mode index of the beam. The concept of OAM has spread into many branches of optics, ranging from optical trapping to quantum information. In optical trapping OAM enables mechanical rotation due to transfer of OAM from light to matter, where the material object can vary from a Bose-Einstein condensate to a living cell. In quantum information OAM allows a high-dimensional alphabet associated with a single photon instead of the usual two-dimensional polarization qubit. Classically speaking, this OAM multiplexing may increase the capacity of a communication channel.

In the talk I will introduce and compare some of the many methods to produce OAM light beams. This serves as a starting point for the main part of the talk which deals with high-dimensional OAM entanglement of two photons. Particularly interesting is the case that the azimuthal index l of the photon state is non-integer; here the half-integer state plays a special role. Such a state corresponds to a high-dimensional superposition of integer OAM states; it can be easily produced in the lab. Quantifying the dimensionality of bipartite entanglement of these non-integer OAM states requires considerable care; for this purpose we introduce the Shannon dimension, in addition to the better known Schmidt dimension. So far we have demonstrated a Shannon dimension up to 6, and a further increase by an order of magnitude seems possible.  

27.01.2010 16:00
State of the technology and applications of delay line detectors for time resolved imaging of X-rays, ions and electrons.
Sonderseminar, 16:00 Uhr in B 0.22
Dr. Andreas Oelsner
Fa. Surface Concept






05.02.2010 11:00
Control of electron and nuclear spins in semiconductor quantum dots
Sonderseminar, 11:00 Uhr
Prof. Lieven M.K. Vandersypen
Delft University of Technology






Recent advances in nanotechnology and quantum engineering have made the quantum world accessible in solid-state systems at the single particle level. Individual electrons can be trapped in semiconductor quantum dots, and it is now possible to initialize, coherently manipulate and read out the spin state of one such electron, and to couple it coherently to a spin in a neighboring dot. We are even making progress in controlling the otherwise random bath of nuclear spins in the host material, which is the dominant source of decoherence for the electron spin. Ongoing work is directed at using entangled spins as a new resource for quantum information processing. 

09.02.2010 13:30
Test of Quantum Electrodynamics in Strong Coulomb and Intense Photon Fields
Sonderseminar
Prof. Dr. Thomas Stöhlker
GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt






 

17.02.2010 13:30
THE LASER-BEC ANALOGY
Sonderseminar
Prof. Dr. Marlan O. Scully
Texas A&M University and Princeton University






  The study of fluctuations of a Bose-Einstein condensate (BEC) is a subtle problem with many pitfalls and surprises. For example, a simple analytical treatment of fluctuations near the critical temperature has only recently been achieved. In particular, we find that a master equation approach, having much in common with the quantum theory of the laser, yields an accurate and physically transparent picture of BEC fluctuations.

18.03.2010 11:00
Nanoplasmonics: SPASER and Nanolasers
Sonderseminar, 11:00 Uhr
Prof. Dr. Mark I. Stockman
Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30302, USA, Max Planck Institute for Quantum Optics, Garching, Germany (Sabbatical Affiliation)






Nanoplasmonics deals with collective electron dynamics on surfaces of metal nanostructures, which arises as a result of excitations called surface plasmons. The surface plasmons localize optical energy in nanoscopic regions creating highly enhanced, ultrafast local optical fields. We will review numerous existing applications of nanoplasmonics in science, technology, and biomedicine. From the latest developments and original work in nanoplasmonics, we will concentrate on SPASER (Surface Plasmon Amplification by Stimulated Emission of Radiation) as a generator of optical fields on the nanoscale and ultrafast nanoamplifier. Both recent theoretical and experimental developments of SPASER and nanolasers will be discussed.
26.03.2010 11:00
Introduction of the Technical Institute of Physics and Chemistry, CAS
Sonderseminar, 14:15 Uhr
Prof. Zhensheng Zhao
Vice Director of Technical Institute of Physics and Chemistry, Chinese Academy of Sciences






 

20.04.2010 13:30
Quasi-phase-matching of high harmonic generation
abgesagt!!!
Prof. Dr. Simon Hooker
University of Oxford






 

27.04.2010 13:30
The science and technology of Quantum Cascade Lasers
Prof. Dr. Federico Capasso
Harvard University, Cambridge, Massachusetts






Quantum Cascade Lasers (QCLs) are revolutionary light sources due to their radical conceptual departure from solid-state lasers and in particular conventional semiconductor lasers and the fact that they are the first lasers in which the wavelength can be designed to cover almost the entire infrared spectrum from a few micron to hundreds of micron wavelength, with the additional advantage of unprecedented tuning range. As such they are having a major influence on spectroscopy, trace gas analysis and chemical sensing impacting a wide range of applications, which has led to full scale commercial effort by ~ 17 companies. From a physical point of view QCLs have an intrinsic line width smaller than the Schawlow-Townes limit usually applied to all lasers. They are uniquely suited for studying coherent effects due to the large Rabi frequency which, along with spatial hole burning become a key factor in dictating the dynamics of the laser. Recently we have in fact observed for the first time unambiguously the elusive Risken-Nummedal-Haken-Graham instability predicted 40 years ago for ring lasers.
QCLs, because they are based on ultrafast tunneling and phonon-limited optical transitions, belong to the class of lasers which have an extremely fast gain recovery, in the range of a few ps. This has major implication for modelocking forbidding conventional mechanisms. We have recently circumvented these difficulties by achieving ps modelocking by external gain modulation of cavity sections. The talk will conclude with the applications of plasmonics to wave-front engineering of QCLs which has enabled the realization of highly collimated sources, multi-beam lasers and laser with controlled near field for sub-wavelength imaging and controlled polarization  

04.05.2010 13:30
Squeezed atomic clock below the standard quantum limit
Prof. Dr. Vladan Vuletic
MIT, Massachusetts Institute of Technology, Cambridge, MA






The performance of the best atomic clocks and other precision atom interferometers is limited by the quantum noise in the final readout measurement, a situation referred to as the standard quantum limit. This limit arises from the projection postulate when applied to an ensemble of independent particles, i.e. it arises from single-particle quantum mechanics. I will discuss how quantum mechanically correlated (entangled) states of the many-body system can be used to overcome the standard quantum limit, and how to generate such states in an ensemble of distant atoms using light. We demonstrate a clock operated with a phase-squeezed input state that achieves a given precision almost three times faster than a clock operating at the standard quantum limit. 

11.05.2010 13:30
Quantum optics with single molecules
Prof. Dr. Vahid Sandoghdar
ETH – Eidgenössische Technische Hochschule Zürich






In this talk I present an overview of our recent work on the interaction of light and single organic molecules. This will include an experimental and theoretical discussion on the coherent interaction of laser light with organic molecules both in the near and far field [1, 2, 3]. I will show that a single molecule can attenuate, transmit, or amplify a focused laser beam. Furthermore, the efficient coupling between the molecule and the light beam can shift the phase of the latter [4]. In addition to the above-mentioned cavity-free interaction of photons and molecules, we report on a new scanning microcavity for the modification of the radiative properties of single molecules [5, 6]. Finally, I will present new results on the interference of indistinguishable photons from two remote molecules [7] and on the spectroscopy and microscopy of nano-objects with single photons [8].

[1]   I. Gerhardt, G. Wrigge, P. Bushev, G. Zumofen, M. Agio, R. Pfab, V. Sandoghdar, Phys. Rev. Lett. 98, 033601 (2007).
[2]  G. Wrigge, I. Gerhardt, J. Hwang, G. Zumofen, V. Sandoghdar, Nature Phys. 4, 60 (2008).
[3]   J. Hwang, M. Pototschnig, R. Lettow, G. Zumofen, A. Renn. S. Götzinger, V. Sandoghdar, Nature 460, 76 (2009).
[4]  M. Pototschnig, Y. Chassagneux, J. Hwang, A. Renn, S. Götzinger, V. Sandoghdar, in preparation.
[5]  R. Lettow, Y. Rezus, A. Renn, G. Zumofen, E. Ikonen, S. Götzinger, V. Sandoghdar Phys. Rev. Lett. (April 2010).
[6]  C. Toninelli, K. Early, J. Bremi, A. Renn, S. Götzinger, V. Sandoghdar, Opt. Express 18, 6577 (2010).
[7]  C. Toninelli, Y. Delley, T. Stöferle, A. Renn, S. Götzinger, V. Sandoghdar, submitted.
[8]  M. Celebrano, R. Lettow, P. Kukura, M. Agio, A. Renn, S. Götzinger, V. Sandoghdar ArXiV (http://arxiv.org/abs/0911.3028v1) (2009).
 

12.05.2010 11:30
Quantum spin-liquid emerging in correlated fermions on graphene-like lattices
Sonderseminar, 11:30
Prof. Dr. Alejandro Muramatso
Institut für Theoretische Physik III, Universität Stuttgart






Free fermions on graphene-like structures, characterized by two dimensional honeycomb lattices, are known to posses a dispersion relation that corresponds to massless relativistic fermions at low energies. It was proposed that Coulomb interactions can destroy the semimetal of massless Dirac fermions via a direct quantum phase transition to a Mott insulator, or that exotic phases such as gapless spin liquids, charge density wave, quantum spin Hall states, or superconductivity emerge at or near a density of one fermion per site. Here we show, by means of large-scale quantum Monte Carlo simulations of correlated fermions on a honeycomb lattice, that a gapped spin liquid emerges between the state described by massless Dirac fermions and an antiferromagnetically ordered Mott insulator. This unexpected quantum-disordered state is found to be a short-range resonating valence-bond liquid, akin to the one proposed for high-temperature superconductors. Therefore, the possibility of unconventional superconductivity through doping arises in our system. We foresee the experimental realization of this model system using ultra-cold atoms, or group IV elements arranged in honeycomb lattices.

18.05.2010 13:30
Advanced quantum light state generation and manipulation by addition and subtraction of single photons
Prof. Dr. Marco Bellini
LENS, Universität Florenz






I will illustrate some of the recent activities carried out in our laboratory to investigate and control the quantum nature of light. The experimental implementation of some of the most basic quantum operations, like single-photon addition and subtraction, has allowed us to generate and manipulate light at the most accurate levels. This, together with advanced techniques for the complete characterization of the generated light states, has allowed us to probe fundamental rules of quantum physics (like commutation relations) and develop novel tools (like noiseless linear amplification) for future quantum technologies. 

25.05.2010 13:30
Ultrafast dynamics of correlated electron systems
Prof. Dr. Martin Wolf
FU Berlin / Fritz Haber Institut






Time- and angle-resolved photoelectron spectroscopy (trARPES) provides direct access to the dynamics of the electronic band structure of photoexcited materials. In particular both single particle excitations and collective modes (e.g. phonons) can be analyzed via the temporal evo-lution of the spectral function. This interplay between electronic and phonon degrees of freedom is of particular importance for the understanding of highly correlated materials (e.g. superconductors, charge density wave compounds or Mott insulators). In this talk I discuss several applications of femtosecond trARPES to optically excite and probe the dynamics of correlated electron systems, namely the insulator-to-metal transition in TaS2 and TbTe3 as well as high Tc superconductors.  

01.06.2010 13:30
50 Years of Laser spectroscopy: Developments and modern Applications
Prof. Dr. Wolfgang Demtröder
Universität Kaiserslautern






After some historical remarks and a brief description of early laser work, the progress of laser spectroscopy is demonstrated by several examples: The advantages of lasers in spectroscopy with respect to high detection sensitivity, spectral and spatial resolution open the way for some interesting applications in biology, medicine and astronomy. This is illustrated by some selected examples: Single molecule detection and its application to visualizing the path of bacteria into living cells, spatial resolution beyond the Abbe diffraction limit, Doppler-free spectroscopy of large molecules, diagnostics of ear drum diseases and the realization of adaptive optics and optical interferometry in astronomy and its relevance for new discoveries are outlined. 

08.06.2010 13:30
Quantum optics with superconducting circuits: controlling photons, Qubits and their interactions
Prof. Dr. Andreas Wallraff
ETH – Eidgenössische Technische Hochschule Zürich






Using modern micro and nano-fabrication techniques combined with superconducting materials we realize quantum electronic circuits. We create, store, and manipulate individual microwave photons on a chip. The strong interaction of photons with superconducting quantum two-level systems allows us to probe fundamental quantum effects of light and also to develop components for applications in quantum information technology. In particular, I will discuss experiments in which we demonstrate first and second-order correlation function measurements of a microwave frequency single photon source. The source is integrated on the same chip with a 50/50 beam splitter. Linear amplifiers and quadrature amplitude detectors are used for correlation measurements [1], since no efficient single photon counters exist at microwave frequencies to date. Our data clearly displays single photon coherence in first-order [2] and photon antibunching in second-order correlation function measurements of the propagating fields.

[1] M. P. da Silva, D. Bozyigit, A. Wallraff, and A. Blais arXiv:1004.3987 (2010)
[2] D. Bozyigit, C. Lang, L. Steffen, J. M. Fink, M. Baur, R. Bianchetti, P. J. Leek, S. Filipp, M. P. da Silva, A. Blais, and A. Wallraff arXiv:1002.3738 (2010)    

15.06.2010 13:30
Ultrahigh intensity plasma optics: How to generate attosecond pulses with a mirror
Prof. Dr. Fabien Quere
IRAMIS-SPAM CEA Saclay






"Ultrafast lasers are now capable of reaching extremely high intensities, such that any target exposed to the field is turned into plasma. At these intensities, laser-plasma interaction leads to highly non-linear optical processes, which are not only of fundamental interest but can also be exploited to produce new coherent light sources.

We will focus on the process of specular reflection of intense light on plasma mir¬rors, which results in the generation of high-order harmonics, associated in the time domain to attosecond pulses. The mechanisms leading this generation will be analyzed, up to the intensity regime where the motion of electrons becomes relativistic and the Doppler effect plays a dominant role. The experimental evi¬dence obtained so far for these processes will be presented, and the latest devel¬opments, future challenges and applications will be discussed."  

22.06.2010 13:30
Atomic-level view of strongly-driven phase transitions
Double feature
Dr. Ralph Ernstorfer
TU München and Max-Planck-Institut für Quantenoptik






Femtosecond electron diffraction has the potential for providing an atomic-level view of structural changes as they occur, essentially watching atoms move in real time. This technique combines temporal resolution on the femtosecond time scale with real-space structural information on the atomic scale. We applied this technique to study the dynamics of order-to-disorder phase transitions under strongly-driven conditions for metal, semimetal and semiconductor films. The effect of intense excitation on the inter-atomic potential in a solid and its implication on the nature of a subsequent phase transition are strongly material dependent. In the case of semiconductors and semimetals, strong electronic excitation gives rise to an electronically-driven, non-thermal disordering mechanism [1, 2]. In contrast, an increase in lattice stability with increasing electronic excitation has been predicted in the case of gold [3]. For gold excited into the regime of warm dense matter, we find that the disordering of the lattice is slower compared to the energy transfer from the electronic to the vibrational degrees of freedom indicative of an electronically induced lattice hardening [4].

[1] M. Harb et al., Phys. Rev. Lett. 100, 155504 (2008).
[2] G. Sciaini et al., Nature 458, 56 (2009).
[3] V. Recoules et al., Phys. Rev. Lett. 96, 055503 (2006).
[4] R. Ernstorfer et al., Science 323, 1033 (2009).
 

22.06.2010 13:30
Photon-by-photon feedback control of a single-atom trajectory
Double feature
Alexander Kubanek
Max-Planck-Institut für Quantenoptik






Feedback is a general, well developed technique, which provides an important tool to control classical systems in a wide variety of fields. Novel features arise when transferring the idea of feedback into the quantum domain, e.g. to engineer non-trivial quantum states. An interesting question is whether one can influence quantum trajectories by measurement and feedback without violating Heisenberg uncertainty relations. A prerequisite for this is to measure and react in real time with a minimum measurement rate and, hence, disturbance.
By combining the arsenal of cavity QED techniques with blue-light trapping we have now achieved a longstanding goal, namely the real-time feedback control on the motion of a single atom. The feedback acts on a time scale that is 70 times faster than the typical time for the evolution of the centre of mass of the atom. Individual probe photons carrying information about the atomic position activate a dipole laser that steers the atom towards or away from the cavity centre. Depending on the specific implementation, the trapping time is increased by a factor of more than four and the localisation of the atom improved owing to feedback cooling. Such a feedback technique teaches us that one can control an apriori unpredictable atomic trajectory, and thus it marks a step towards the exploration of quantum trajectories.

A. Kubanek, M. Koch, C. Sames, A. Ourjoumtsev, P.W.H. Pinkse, K. Murr, G. Rempe
Photon-by-photon feedback control of a single-atom trajectory
Nature, Volume 462, Issue 7275, pp. 898-901 (2009)

29.06.2010 13:30
Nonlinear Schrödinger Equations: How can mathematicians be really useful for physicists? Modeling and Simulation of BECs
Prof. Dr. Norbert J. Mauser
Universität Wien






We sketch the work of the Applied PDE group at WPI dealing with modeling, analysis and numerics of NLS like Gross-Pitaevskii equations.
We present 3D simulations of the dynamics of BECs (done in interaction with the Atomchip group at TU Wien) and work out the interplay "physics " → "mathematical modeling / numerical technique" required for each phase of the experiment, like "switch off trap" → "switch from homogeneous Dirichlet boundary conditions to absorbing boundary conditions", or "expansion phase" → "rescaling of the domain", or "free flight" →"switch to linear Schrödinger equation"...
We discuss the role that mathematicians could / should play in such collaborations and how to train them, in the context of the "Bologna architecture" and European projects.  

05.07.2010 11:00
Time-resolved photo-electron spectroscopy of atoms and surfaces”
Sonderseminar 11:00 Uhr
Prof. Uwe Thumm
Kansas State University, Manhattan, USA






Photoemission of localized and delocalized electrons from a (possibly adsorbatecovered)metal surface by an XUV pulse of length τXUV into the field of a delayed IR laser pulse with carrier period TIR allows for the time-resolved observation of surface and adsorbate electronic processes. For τXUV << TIR, the energy of emitted photoelectrons (PEs) oscillates with period TIR as a function of the XUVIR pulse delay, which allows for the identification of small (tens of attoseconds, 1 as=10-18 s) temporal shifts between PEs that are emitted from different initial states [1]. In contrast, if τXUV >> TIR, the PE spectrum is characterized by a satellite structure of sideband peaks located at integer multiples of the IR photon energy from the main photoemission peak [2]. Both, streaked and sideband spectra depend on the electronic structure of the substrate. I will discuss this dependence in comparison with recent experiments.
The second part of this talk will focus on specific contributions to temporal shifts in PE spectra. This discussion will be limited to the more transparent case of photoemission from atomic hydrogen: By solving the time-dependent Schrödinger equation (TDSE), one can identify a temporal shift in the streaked photoemission spectra that is due to the combined action of Coulomb and laser forces on the PE and reaches in excess of 50 as at small PE kinetic energies. Close examination of this shift promises to enable i) the experimental scrutiny of such Coulomb-laser coupling effects and ii) tests of theoretical approximations to the exact Coulomb-Volkov final state of the PE. Within an eikonal approximation, I will explain a simple analytical expression for this coupling effect and assess its accuracy by comparison with TDSE numerical results [3].
[1] C.-H. Zhang and U.T.: Phys. Rev. Lett. 102, 123601 (2009); [2] Phys. Rev. A. 80, 032902 (2009); [3] submitted for publication. 

06.07.2010 13:30
Quantum engineering at nanokelvin temperatures: Quantum phase transitions, strong correlations, and novel many-body systems
Prof. Dr. Hanns-Christoph Nägerl
Universität Innsbruck






I will review recent experiments with atomic and molecular quantum gases in the regime of quantum degeneracy, Bose-Einstein condensation, and strong correlations. Ultracold atomic and molecular gases are versatile tunable laboratory systems for the study of complex many-body quantum phenomena as essentially all parameters such as geometry and strength of confinement and the strength of interactions can be controlled with near-perfect isolation from external perturbations. For atoms 1D geometry, I will discuss the strongly-interacting limits of so-called Tonks-Girardeau and super-Tonks-Girardeau phases [1]. We observe the pinning quantum phase transition in the presence of an arbitrarily weak lattice potential [2]. I will outline our efforts to achieve quantum degeneracy of molecules in optical lattice potentials [3] with the aim to generate dipolar quantum gas phases.

[1] Realization of an excited, strongly correlated quantum Gas Phase, E. Haller et al., Science 325, 1224 (2009).
[2] Observation of the pinning quantum phase transition for a Luttinger liquid of strongly interacting bosons, E. Haller et al.,, Nature in print (2010)
[3] An ultracold high-density sample of rovibronic ground-state molecules in an optical lattice, J.G. Danzl et al., Nature Physics 6, 265 (2010).  

13.07.2010 13:30
Bose-Einstein condensates as surface probes: van der Waals forces in the intermediate regime.
Prof. Dr. Claus Zimmermann
Universität Tübingen






Van der Waals forces near a glass surface are combined with an evanescent wave. This forms a trap for cold atoms at distances from the surface well below 1m. The setup allows for a new method to directly measure the spatial dependence of the van der Waals potential in the regime around 200 nm from the surface. The experiment is a first step towards quantum optics near surfaces where dispersive forces may be used to develop a new generation of micro chip based atom optics.  

20.07.2010 13:30
Quantum frequency combs: generation and use
Prof. Dr. Claude Fabre
Laboratoire Kastler Brossel, Paris






Frequency combs, made of many longitudinal modes, are good examples of highly multimode quantum objects, that can be of interest in massively parallel quantum information processing and quantum metrology. We have shown theoretically that frequency combs generated by Synchronously Pumped Parametric Oscillators (SPOPO) exhibit nonclassical features such as multimode squeezing and multipartite entanglement, that can be tailored at will by adjusting the shape of the pump pulses. I will report on the first achievements of our SPOPO experiment and show hw these "quantum frequency combs" can be used in the future to improve time measurements beyond the shot noise limit.

27.09.2010 13:30
Rydberg blockade mediated quantum computing with neutral atoms
Montag
Prof. Dr. Mark Saffman
University of Wisconsin






Neutral atoms have long been attractive candidates for quantum information processing due to the stability and excellent coherence properties of hyperfine ground states. Implementing a strong and controllable long-range interaction has, however, been an open challenge. This challenge was recently met with the demonstration by several groups of quantum logic gates and entangling operations using the Rydberg blockade mechanism.

I will discuss recent developments in this area and present experimental results showing high fidelity gate operations and deterministic entanglement of a pair of neutral atoms. The long range nature of the Rydberg interaction is attractive for scalable quantum information processing using arrays of trapped atoms. Ideas for realizing a medium scale quantum processor, and progress towards that goal will be discussed.   

28.09.2010 13:30

Prof. Dr. Gordon Drake
University of Windsor, Ontario






 The isotope shift method is now well established as an effective method, and in many cases the only available method, to determine the nuclear charge radius of short-lived nuclear species such as the exotic ‘halo’ nuclei. The method depends on high-precision laser resonance measurements of atomic transition frequencies. Three broad series of measurements are now available for light nuclei, extending all the way from 3He to the halo nuclei 6He and 8He [1], 6Li to the halo nucleus 11Li [2], and 7Be to the single-neutron halo nucleus 11Be [3]. The results are particularly significant because they provide an accurate model-independent determination of the nuclear charge radii rc, even in the case of halo nuclei where the abundance is too low to be studied by the conventional electron scattering techniques. Accuracies at the level of ±100 kHz are required for both theory and experiment.
The principle of the method will be discussed in terms of the atomic structure calculations that are required to extract the nuclear charge radius from the isotope shift. The principal theoretical challenges are (a) to obtain sufficient accuracy in the lowest order nonrelativistic and relativistic contributions to the isotope shift, and (b) to calculate the mass dependence of the higher-order QED contributions, such as the Lamb shift [4, 5]. The current status of theory will be reviewed, and compared with experiment. In view of the recently announced discrepancy in the proton radius, a comparison between muonic and electronic helium becomes particularly relevant and interesting.

[1] R. Sanchez et al. Phys. Rev. Lett. 96 (2006) 033002.
[2] P. Mueller et al., Phys. Rev. Lett. 99 (2007) 252501.
[3] M. Zakova et al., J. Phys. G 37, 055107 (2010).
[4] Z.-C. Yan, W. Nörtershäuser, and G.W.F. Drake, Phys. Rev. Lett. 100, 243002 (2008).
[5] M. Puchalski and K. Pachucki, Phys. Rev. A 78, 052511 (2008).

12.10.2010 13:30
Towards quantum magnetism with ultracold atoms
Prof. Dr. Wolfgang Ketterle
Massachusetts Institute of Technology






 Over the last 20 years, science with ultracold atoms has focused on motion: slowing down motion, population of a single motional state (Bose-Einstein condensation, atom lasers), superfluid motion of bosons and fermion pairs. In my talk, I will address the next challenge when motion is frozen out: Spin ordering. A two-component boson or fermion mixture can form magnetic phases such as ferromagnetic, anti¬ferromagnetic ordering and a spin liquid. The challenge is to reach the low tempera¬ture and entropy required to observe these phenomena. I will describe our current efforts and progress towards this goal. This includes the study of fermions with strong repulsive interactions where we obtained evidence for a phase transition to itinerant ferromagnetism, and a new adiabatic gradient demagnetization cooling scheme which has enabled us to realize spin temperatures of less than 50 picokelvin in optical lattices. These are the lowest temperatures ever measured in any physical system.

13.10.2010 10:00
Acquiescent Light
Mittwoch, 10:00 Uhr
Prof. Majid Ebrahim-Zadeh
ICFO-Institute of Photonic Sciences, Barcelona, Spain






Since its first demonstration (Maiman 1960), the laser has become an indispensible tool that has transformed science and technology and impacted many aspects of our daily lives. Yet, after half a century, vast regions of the optical spectrum still remain inaccessible to conventional lasers.

The potential of nonlinear optical phenomena as an alternative means for the generation of coherent light was recognized soon after the invention of the laser (Bloembergen, 1962). However, the promise of nonlinear optics remained unfulfilled for almost another 30 years, until the advent of novel nonlinear materials, advances in laser sources, and innovative design concepts prompted renewed interest this area. Today, nonlinear frequency conversion sources can surmount spectral barriers unattainable with alternative techniques, paving the way for new application areas. In particular, optical parametric oscillators (OPOs) have been established as uniquely versatile sources of coherent light with unmatched spectral and temporal flexibility, overcoming the long-standing limitations of lasers. This talk will provide an overview of the latest advances in OPO technology for the generation of coherent radiation from the ultraviolet to the mid-infrared and THz, and from the continuous-wave to ultrafast femtosecond time-scales. Some novel and emerging applications of OPOs will also be highlighted.

26.10.2010 13:30
Quantum technology taken to its (speed) limit
Prof. Dr. Tommaso Calarco
Universität Ulm






 

02.11.2010 13:30
Invisibility cloaking and perfect imaging
Prof. Dr. Ulf Leonhardt
University of St. Andrews, Scotland






 

05.11.2010 14:00
Benchmarking attosecond science with atomic hydrogen
Sonderseminar 14:00 Uhr
Prof. Dave Kielpinski
Australian Attosecond Science Facility Griffith University, Brisbane, Australia






09.11.2010 13:30
Quantum Opto-Eletronics in 1DNanowires
Prof. Dr. Leo Kouwenhoven
Delft University of Technology






15.11.2010 13:30
Ultrafast x-ray processes at high intensity
Montag
Prof. Dr. Robin Santra
CFEL Hamburg






After a brief introduction to x-ray-induced processes and x-ray free-electron lasers, the principles of x-ray multiphoton ionization will be discussed. Results from some of the first experiments carried out at the world's first x-ray free-electron laser, the Linac Coherent Light Source at SLAC National Accelerator Laboratory, will be presented and compared with theory. It will be shown that the x-rays from the LCLS are so intense that (a) an atom can be completely stripped of all its electrons; (b) inner-shell ionization can be as fast as the Auger decay of an inner-shell hole, thus leading to the efficient formation of double-core-hole states; and (c) the characteristics of the Auger decay process itself can be modified. 

23.11.2010 13:30
Attosecond physics with attosecond pulse trains
Prof. Dr. Anne L’Huillier
Lund University






The generation of attosecond pulse trains through high-order harmonic generation in gases and their characterization will be reviewed.

Applications of these pulses to studies of two- photon and one-photon ionization of atoms will be presented.  

29.11.2010 15:00
A Moving Magnetic Trap Decelerator: a New Source for Cold Atoms and Molecules
Sonderseminar, 15:00 Uhr
Dr. Ed Narevicius
Weizmann Institute of Science, Rehovot, Israel






 We present a new source of cold paramagnetic atoms and molecules. The paramagnetic particles are cooled during the adiabatic expansion and become entrained in an intense, cold but fast supersonic beam. We efficiently decelerate the paramagnetic particles by trapping them in a co-moving decelerating magnetic trap. Since the particles remain trapped in three dimensions during the deceleration process our method is capable of achieving higher densities limited only by the initial density of a supersonic beam. We present our first results on deceleration in a moving magnetic trap by bringing metastable Neon atoms to near rest.

30.11.2010 13:30
From Ultracold Fermi Gases to Neutron Stars
Prof. Dr. Christophe Salomon
Laboratoire Kastler Brossel, Paris






In the recent years ultracold atomic gases have been used to probe some fundamental questions in Many-body Physics. Thanks to the high degree of control of cold atoms using laser fields and magnetic fields, new insights on key problems from condensed matter systems has been gained. In this talk, we will provide one such example through the measurement of the equation of state of strongly interacting Fermi gases [1,2]. The tunability of the interaction between atoms enables one to connect the regime of superfluidity of weakly bound Cooper pairs described by BCS theory to the regime of strongly bound molecular pairs forming a Bose-Einstein condensate. The phase diagram of the dilute Fermi gas has been established experimentally and comparison with advanced many-body theories has revealed several surprises. Our equation of state can be directly used to describe the outer shell of neutron stars despite of 24 orders of magnitude difference in matter density and 14 orders of magnitude in temperature.

[1] S. Nascimbène, N. Navon, K. J. Jiang, F. Chevy, and C. Salomon, Exploring the thermodynamics of a universal Fermi gas, arXiv:0911.0747, Nature, 463, 1057 (2010)
[2] N. Navon, S. Nascimbène, F. Chevy, and C. Salomon, The Equation of State of a Low Temperature Fermi Gas with Tunable Interaction, Science 328, 729 (2010)

30.11.2010 13:30
Maxwell's demon, the second law, and the minimum energy cost for measurement and erasure of information
Sonderseminar, 10:00 Uhr
Prof. Masahito Ueda
Department of Physics, University of Tokyo






The second law of thermodynamics presupposes a clear-cut distinction between the controllable and uncontrollable degrees of freedom by means of macroscopic operations. The cutting-edge technologies in quantum information and nano-science seem to force us to abandon such a notion in favor of the distinction between the accessible and inaccessible degrees of freedom. In this talk, I will discuss the implications of this paradigm shift by focusing on how the second law of thermodynamics can be generalized in the presence of a feedback control [1]. I will also discuss the minimum work required for measurement and erasure of information [2]. The Jarzynski equality has to be generalized in the presence of feedback control [3], as confirmed experimentally using polystyrene beads [4].

References
[1] T. Sagawa and M. Ueda, Phys. Rev. Lett. 100, 080403 (2008).
[2] T. Sagawa and M. Ueda, Phys. Rev. Lett. 102, 250602 (2009).
[3] T. Sagawa and M. Ueda, Phys. Rev. Lett. 104, 090602 (2010).
[4] S. Toyabe, T. Sagawa, M. Ueda, E. Muneyuki, and M. Sano, to appear in Nature Physics, arXiv:1009.5287 (2010).
 

07.12.2010 13:30
Advanced quantum control of single diamond defect centers and their environment
verschoben auf 08.12.2010
Prof. Dr. Ronald Hanson
Delft University of Technology






Quantum control of light and matter is an outstanding challenge in modern science. Diamond-based materials have recently emerged as a unique platform for quantum science and engineering [1]. Spins of single Nitrogen-Vacancy (N-V) color centers in diamond can be imaged, initialized and read out optically, and show quantum coherence even at room temperature. Full control over the spin state and the optical transition may enable exciting applications such as long-distance quantum teleportation and quantum information processing. Moreover, the tunable interactions of the NV center with its environment also make this system an excellent test bed for fundamental studies on decoherence, spin-bath interactions, and light-matter interactions in engineered nanostructures.

In this talk I will present our latest results on schemes to protect single-spin coherence from the surrounding spin bath [2] as well as quantum control of the spin bath itself. Also, I will discuss our progress towards entanglement of distant NV center spins via photon interference [3].

[1] Ronald Hanson and David D. Awschalom, Nature 453, 1043 (2008).
[2] G. de Lange et al., Science 330, 60 (2010).
[3] L. Robledo et al., Phys. Rev. Lett. 105, 177403 (2010); T. van der Sar et al., arXiv:1008.4097 (2010).  

14.12.2010 13:30
Photons, dust and honeybees
Prof. Dr. Diederik Wiersma
LENS Florence