CLXXIII International School of Physics “Enrico Fermi”
Nano optics and atomics:transport of light and matter waves
Varenna, Como Lake, Italy / 23rd June - 3rd July 2009
Abstracts of Participants’ Contributions
Towards low-dimensional and strongly correlatedultracold bosons on atom chip
J. Armijo, C. L. Garrido Alzar, I. Bouchoule
Laboratoire Charles Fabry de l’Institut d’Optique, Palaiseau, France
We use current-carying wires deposited on a microfabricated chip to mag-netically confine and manipulate cold 87Rb clouds. We have recently assembleda new chip that we are now operating.
Our projects take advantage of the strong confinements that can “easily” beachieved with atom chips because the atoms are manipulated at some 10-100µm only from the field sources. In such potentials, at low enough energy, themotion of the atoms can be frozen in one or two directions of space so that theeffective dimensionality is reduced, which has dramatic effects on the coherenceproperties and phase diagram of the gas.
As a first step we plan to continue studying weakly interacting 1D gases inthe typical elongated traps that are created above a wire. We wish to improvethe understanding of the tansition from the decoherent to the quasi-condensateregime1.
Our second project relies on the technique of rapid current modulation2
that allows to smooth out the wire potential’s roughness so that the atoms canbe brought very close to the chip, in highly confining traps. In this way we cancreate a single bosonic gas in the Tonks-Girardeau regime3, where the atomsbehave as inpenetrable bosons.
In the third project, we plan to produce a 2D trap using adiabatic dressedpotentials4. We aim at studying the Kosterlitz-Thouless transition which isthe superfluid transition that happens in 2D, due to the (un)binding of vortexpairs5.
The poster describes our apparatus, including the new chip and our recentstudy of its thermal properties6, as well as the different research projects.
1J. Esteve et al., Phys. Rev. Lett. 96, 130403 (2006).2J. B. Trebbia et al., Phys. Rev. Lett. 98, 263201 (2007).3T. Kinoshita et al., Science 305, 1125 (2004).4Y. Colombe et al, Europhys. Lett. 67, 593 (2004).5Z. Hadzibabic et al., Nature 441, 1118 (2004).6J. Armijo et al., in preparation.
Levy Glasses: Levy Walk in quenched environment
P. Barthelemy1, J. Bertolotti1, S. Lepri2, D. S. Wiersma1
1LENS European Laboratory for Nonlinear Spectroscopy, Firenze, Italy2Istituto dei Sistemi Complessi, CNR, Firenze, Italy
Levy Walks have shown to describe very diverse phenomena in nature, rang-ing from transport of pollutants1 to statistics of human travels2. Due to theheavy tail of their step length distribution, their transport properties are dom-inated by the occurrence of rare, very large steps. These walk hence inducesuperdiffusion. Recently, we have reported the fabrication of a new opticalmaterial3, that we called Levy Glass, where multiple elastic scattering in aninhomogeneous system gives rise to a Levy-like transport for light. The su-perdiffusive behaviour of light transport is here due to fluctuations of localscattering properties. In this contribution, we present an analysis of the influ-ence of this quenched nature of disorder on the parameters of the superdiffusionin two-dimensional Levy Glasses.
1Y. Zhang, M. M. Meerschaert, B. Baeumer, Phys. Rev. E 78, 036705 (2008).2L. D. Brockmann, L. Hufnagel, and T. Geisel, Nature 439, 462465 (2006).3P. Barthelemy, J. Bertolotti, and D. S. Wiersma, Nature 453, 495 (2008).
Coherent manipulation of holes in dipole trap arrays
A. Benseny1, S. Fernandez-Vidal1, J. Baguda1,R. Corbalan1, L. Roso2, J. Mompart1
1Departament de Fısica, Universitat Autonoma de Barcelona, Bellaterra, Spain2Departamento de Fısica Aplicada, Universidad de Salamanca, Salamanca, Spain
Quantum gases trapped in optical potentials1,2 have attracted considerableattention since they fulfill all the basic requirements for quantum informationprocessing (QIP). In fact, neutral atoms in dipole trap arrays with short-rangeor state selective long-range interactions do not present intrinsic limitations intheir scalability. Thus, quantum registers with single site addressing of abouta hundred qubits in 2D optical microtrap arrays1 and cluster entangled statesof thousands of atoms in 3D optical lattices2 have been reported.
Here, we investigate single occupancy dipole trap arrays loaded with a gas ofeither fermions or bosons presenting some isolated defects consisting in emptysites, i.e., holes (see figure). We will extend the three-level atom optics tech-niques3 to the coherent manipulation of the external degrees of freedom of theseholes. By integrating the corresponding Schrodinger equation, we investigatethe adiabatic transport of holes between the two extreme traps of a triple-well(see figure) to prepare defect-free trap domains, design of single atom tran-sistors, and even for QIP with the hole itself being the quantum bit carrier.Introducing hole creation and annihilation operators in the Hubbard formalismwe extend the previous results to a single hole in an arbitrarily large trap array.
Figure: a) Isolated defects, i.e., holes, in a single atom occupancy dipole trap, to beremoved from the computation area. b) From left to right, top to bottom: snapshotsfor different times of the spatial joint probability distribution for two non-interactingfermions in a 1D triple-well potential demonstrating the hole transport from the left
to the right trap. α−1 is the harmonic oscillation length of the traps.
1R. Dumke et al., Phys. Rev. Lett. 89, 097903 (2002).2O. Mandel et al., Nature 425, 937-940 (2003).3K. Eckert et al., Phys. Rev. A 70, 023606 (2004); Optics Comm. 264, 264-270 (2006).
Decoherence in driven solid state qubit
M. Berritta, A. D’Arrigo, E. Paladino, G. Falci
Dipartimento di Metodologie Fisiche e Chimiche (DMFCI)Universita di Catania. Viale A. Doria 6, 95125 Catania (Italy)
MATIS - Istituto Nazionale per la Fisica della Materia, Catania (Italy)
Mesoscopic solid state devices for quantum computation offer advantage inflexibility of the design and manipulation. One of the most relevant problemfor quantum computation and quantum information processing is decoherence.Solid state device are subject to many noise sources that cause decoherence:electromagnetic fluctuation, quasiparticles and bistable fluctuators that are rep-resentative model of charge impurities. The accurate characterization beyondphenomenology of the physics of the noise sources is a priori inefficient becausewe need a huge number of parameters for a microscopic characterization. Tostudy the decoherence on solid state device is necessary characterize noise relat-ing to phenomenology that noise induce on the device. This procedure allowsus to recognize a subset of properties which are enough to describe the effectson the dynamics of the system, extending the idea of Caldeira-Leggett model1.We identify three classes of noise2:1)Quantum noise that is fast noise and produce transition between quantumlevel;2)Adiabatic noise that is principal source of dephasing and doesn’t producetransitions;3)Strong coupled noise that modify the engineered of energy spectrum of thequbits.The calculation of the effects of interplay of these classes of noise3 providesresults in excellent agreement with experiment.Our attempt is to extend this classification to study the effect of decoherenceon dynamics of Rabi oscillation. At the lower order, calculated damping timefor Rabi oscillations at resonance, is greater than the damping time of coher-ent oscillation, this is in agreement with experiment that measure a number ofRabi oscillation greater than the number of coherent oscillation (Ramsey) 4.
1A. Caldeira and A. J. Leggett, Influence of dissipation on quantum tunneling in macro-scopic systems, Phys. Rev. Lett. 46, 211 (1981).
2G. Falci and R. Fazio, Quantum computation with Josephson qubits, Proceeding ofinternational school of Physics “Enrico Fermi”, Course CLXII, on “Quantum Computer,Algorithms and Chaos”, edited by G. Casati, D. L. Shepelyansky and P. Zoller (directors ofthe course) and G. Benenti, IOS Bologna (2005).
3G. Falci, A. D’Arrigo, A. Mastellone, E. Paladino, Phys. Rev. Lett. 94, 167002 (2005).4D. Vion, A. Aassime, A. Cottet, P. Joyez, H. Pothier, C. Urbina, D. Esteve, M. H. De-
voret, Science 296, 886 (2002).
Towards Anderson Localization of Light with Cold Atoms
T. Bienaime, R. Kaiser
Institut Non-Lineaire de Nice, Valbonne, France
This poster presents the experiment we are currently building at INLNwhich aims at studying Anderson localization1 of light waves using cold atomsas random media. The localization threshold is supposed to be k · l ∼ 1, wherek is the wave vector of light and l the mean free path of photons.
The first part of the project is to compress the atomic cloud to reach thelocalization threshold - it corresponds to a compression by 10 in each spatialdimension (in a M.O.T., k ·l ∼ 1000). We propose to use a blue-detuned opticaldipole trap which consists of a single, rapidly rotating laser beam2. First, theMOT is surrounded by the dipole trap. Then the MOT is turned off and theradius of the trap R(t) is reduced to compress the atoms (see figure below).
Figure: Our idea to compress the atoms down to the localization threshold.
1P. W. Anderson, Phys. Rev. 109, 1492 (1958).2N. Friedman, L. Khaykovich, R. Ozeri and N. Davidson, Phys. Rev. A. 61, 031403
(1999).
Emission Properties of Nanostructured PolymerNanofibers
A. Camposeo1, S. Pagliara1,2, F. Di Benedetto1, E. Mele1, L. Persano1,R. Cingolani1, D. Pisignano1,2
1National Nanotechnology Laboratory of CNR-INFM, c/o Distretto Tecnologico,Universita del Salento, via Arnesano I-73100, Lecce, Italy
2Scuola Superiore ISUFI, Universita del Salento, via Arnesano I-73100, Lecce, Italy
Polymer nanofibers are attracting an increasing interest as novel quasi 1-dimensional (1D) nanostructures, exhibiting peculiar, smart properties usefulfor many applications1. These quasi 1D systems exhibit also unique opticaland electronic properties, influencing the charge conduction and the propaga-tion of light through the nanofibers. In this work we report on the realizationof polymer nanofibers, emitting in the visible (VIS) and near infrared (NIR)spectral range2 by electrospinning, a technique based on the uniaxial stretch-ing of a polymer solution by electric fields. Fibers are made by light-emittingconjugated polymers and by polymethylmethacrilate (PMMA) doped with or-ganic dyes. The fibers are characterized by average diameters of few hundredsof nanometers, depending on the process parameters (applied voltage, solutionfeeding rate, needle-collector distance). The light-emitting nanofibers exhibitphotoluminescence tunable in the spectral range 440-920 nm depending on theexploited polymer or dye, and self-waveguiding of the emitted light with typicalloss coefficients in the range 102-103 cm−1.
Furthermore, the nanofibers can be nanostructured by room temperaturenanoimprint lithography (RT-NIL)3. The nanofibers structured with wavelen-gth-scale 1D gratings show an increase of the forward emission due to the Braggscattering of the waveguided mode, evidenced by angle-resolved photolumines-cence spectroscopy. We have investigated also the cavity effects occurring inemitting fibers with micrometer scale length and sub-micron diameter, findingevidence of equally-spaced modes, typical of a Fabry-Perot cavity4.
1D. Li and Y. Xia, Adv. Mater. 16, 1151 (2004).2A. Camposeo, F. Di Benedetto, R. Cingolani, D. Pisignano, Appl. Phys. Lett. 94,
043109 (2009).3F. Di Benedetto, A. Camposeo, S. Pagliara, E. Mele, L. Persano, R. Stabile, R. Cingolani,
D. Pisignano, Nature Nanotechnology 3, 614-619 (2008).4A. Camposeo, F. Di Benedetto, R. Stabile, A. A. R. Neves, R. Cingolani, D. Pisignano,
Small 5, 562 (2009).
Dynamics of colloidal particles in a binary liquid close tothe critical point
L. Chantada, R. Cerbino1, F. Scheffold
Soft matter and photonics group, University of Fribourg, Switzerland
The so-called critical Casimir effect appears when two surfaces are placedclose in binary liquids near the critical demixing point of the bulk mixture.This effect is a classical analogue of the quantum effect which is responsible forthe attraction between two close conduction surfaces in vacuum2. The originof this force are the boundary conditions set by two close metallic surfaces,which limit the oscillation frequencies of the otherwise random fluctuations inthe electromagnetic field, giving rise to a net attractive force. Equivalently, theconcentration fluctuations which occur close to the demixing critical point to-gether with the inevitable preference for the surfaces for one of the two speciesresult in a net force. When both surfaces preferentially absorb the same ma-terial of the binary mixture, an attractive force between the surfaces appears,while the surfaces repulse each other when they prefer different materials3.
Our aim is to measure the dynamics of spherical particles in a mixture oflutidine and water close to its critical point. By approaching the critical pointthe presence of Casimir forces modify the particle-particle potential changingthe particles dynamics otherwise governed by Brownian motion. To make thismeasurements we have built a heterodyne near field light scattering set-up,which belongs to a new kind of low angle light scattering devices introducedby M. Giglio in 20004. In contrast with traditional small angle light scatteringdevices (SALS) which collect the light in the far field yielding one-to-one iden-tification between the scattering angle and the pixel position, near field devicescollect the light close to the sample in such a way that every pixel of the sensordetects light scattered by the sample at every possible angles5. The scatteringintensity distribution is obtained by proper statistical analysis of the recordedspeckle images. This technique implies some advantages with respect to thetraditional SALS: the obtained intensity distribution is self-reference, meaningthat the absolute scattering cross section can be obtained without performingany measurements in the reference sample; the scattered signal is amplified bythe transmitted beam yielding higher sensitivity; and the stray light can berigorously subtracted without the need of any black measurements.
1Present address: Complex fluids and Molecular biophysics lab, Biochemistry and Medicalbiotechnologies, University of Milan, Italy.
2H. B. G. Casimir, Koninklijke Nederlandse Akad. Wetenschappen B51, 793-795 (1948).3C. Hertlein, L. Helden, A. Gambassi, S. Dietrich, C. Bechinger, Nature 451, 172 (2008).4M. Giglio, M. Carpineti, A. Vailati, Phys. Rev. Lett. 85, 1416 (2000).5F. Ferri, D. Magatti, D. Pescini, M. Potenza, M. Giglio, Phys. Rev. E 70, 041405 (2004).
Control of collective resonance fluorescence using thecavity standing wave
N. Ciobanu and N. A. Enaki
Laboratory of Quantum Optics and Kinetic Processes,Institute of Applied Physics of the Academy of Sciences of Moldova,
Chisinau MD-2028, Moldova
In this paper we discuss the cooperative spontaneous emission from an en-semble of Λ type three-level atoms dressed by standing wave that is in resonancewith electromagnetic field. Taking into account the cavity parameters and in-tensity of external field, the manipulation with the spontaneous emission rateis investigated. The spatial interference effect of fluorescent field as function ofthe distance between the radiators and relative position of atoms in the stand-ing wave is analyzed. In the undistinguished situation, the kinetic equationsthat describe the cooperative effect between two atoms and the second photoncorrelation function are studied.
From cavity laser with cold atoms to random laser
V. Eremeev, S. E. Skipetrov
Laboratoire de Physique et Modelisation des Milieux Condenses, Universite JosephFourier and CNRS, 25 rue des Martyrs, 38042 Grenoble, France
We present a theoretical model to explain the gain and the lasing processeswith cold atoms confined in the cavity and compare some of the results with theexperimental data1. Based on some ideas of this model we propose to developfurther an adequate theory for random lasers.
We have studied the Mollow gain mechanism for laser with cold atoms incavity by considering the dressed-state formalism for two-level atoms. Tak-ing into account the method2, we derived semi-classical kinetic equations forquantum-mechanical expectation values of operators which describe the cou-pled system of atoms and modes of the electromagnetic field. By solving theseequations we are able to analyze in details the light and atoms properties. Westudied dynamics of the lasing and found some different regimes of the laserevolution for which the power spectra are ploted. Also we investigated the laserthreshold by our model and found good concordance with other approaches.
The next step in our investigation is the development of an approach forthe process of random lasing by using the similarities with the physics of cav-ity lasing, i.e. to develop and solve the master equation for the system oftwo-level atoms with pumping but without the cavity by taking into accountmulti-scattering processes between the atoms, and gain mechanism respectively.Concerning this problem we present the general methodology and some priorresults since the study is still in progress.
1W. Guerin, F. Michaud, R. Kaiser, Phys. Rev. Lett. 101, 093002 (2008).2J. Zakrzewski, M. Lewenstein, Phys. Rev. A 45, 2057 (1992).
Bragg spectroscopy of strongly interacting bosons inoptical lattices
N. Fabbri, D. Clement, L. Fallani, C. Fort, M. Inguscio
LENS European Laboratory for Nonlinear Spectroscopy, Firenze, Italyand CNR-INFM Istituto Nazionale di Fisica della Materia
Inelastic light scattering is an experimental technique largely used in con-densed-matter physics, providing important information about the dynamics ofthe excitations of a system. We are interested in many-body quantum systemsof ultracold atoms with strong correlations between the particles. They areamong the most intriguing physical systems, since no simple picture capturestheir behaviour.
In this work we study one-dimensional (1d) ultracold gases in optical lat-tices: they allows us to create strongly correlated quantum phases in a highlycontrollable way. We induce the cross-over between a strongly correlated super-fluid and an inhomogeneous Mott insulator phase by the presence of an opticallattice in the direction of the 1d gases. Using light scattering (Bragg spec-troscopy)1 we probe the excitations of the system in a linear response regimeunaccessible to previous works. Low-energy excitations of the system exhibitsignificant modification when the system is driven into the insulating phase bytuning the amplitude of the lattice2. The presence of the optical lattice alsoinduces an energy band structure in the system: combining Bragg spectroscopywith a band-mapping technique we probe the dispersion relation in such higherenergy bands.
Figure: Schematic view of the Bragg spectroscopy on a gas in an optical lattice.
1M. Kozuma et al., Phys. Rev. Lett. 82, 871 (1999); J. Stenger et al., Phys. Rev. Lett.82, 4569 (1999); R. Ozeri et al. Rev. Mod. Phys. 77, 187 (2005).
2D. Clement, N. Fabbri, L. Fallani, C. Fort and M. Inguscio, Phys. Rev. Lett. 102,155301 (2009).
Plasmonic Resonances in Nanostructured Gold/PolymerSurfaces obtained by Colloidal Lithography
S. Giudicatti1, A. Valsesia1,2, F. Marabelli1, P. Colpo2, F. Rossi2
1Dipartimento di Fisica ‘A.Volta’, Universita degli Studi di Pavia, Pavia, Italy2European Commission, Joint Research Centre, Institute for Health and Consumer
Protection, Ispra (Varese), Italy
In recent years, a large number of studies on the interaction of electro-magnetic waves with nanostructured metallic surfaces has been reported inliterature. Most of them deals with propagating Surface Plasmon Polaritonsor, alternatively, localized charge resonances. However, real samples often com-bine both kinds of properties.
We investigated gold/polymer 2D plasmonic crystals obtained by a newdeposition procedure based on colloidal lithography. They consist of a hexag-onal lattice of plasma polymerized Poly Acrylic Acid pillars embedded in anoptically thick gold film on a glass substrate. The optical characterization wascarried out by angle-resolved reflection and transmission measurements withTE- and TM-polarized light incident from both the air and the glass side. Theoptical response can be interpreted as the result of the interplay between Sur-face Plasmon Polaritons propagating at gold/glass and gold/air interfaces andSurface Plasmon Resonances localized at the acrylic acid pillars. Measuredspectra were compared with the results of simple theoretical models.
The strong interplay between plasmonic modes on both sample sides andthe simple fabrication technique provide an interesting playground to studyinteraction effects and a promising configuration for biosensing applications.
Figure: Reflectance measured by TM polarized light from the substrate.(a) Reflectance spectra for different incidence angles. (b) Intensity of second
derivative of reflectance spectra. Gray scale is dark for lower intensities and whitefor higher intensities. Calculated energy dispersions of surface plasmon polaritons(solid lines) and Wood’s anomalies (dashed lines) at the air and glass sides (upper
and lower groups, respectively) are superimposed on experimental data.
Ultra Short-Wavelength Solid State Laser
M. M. S. Gualini1, M. A. Baig2, S. Iqbal3, M. Farooq4
1Dept. of Electronics Engineering, Politecnico di Torino, Turin, Italy2Dept. of Physics, Quaid-i-Azam University, Islamabad, Pakistan
3Dept. of Electronics Engineering, International I University, Islamabad, Pakistan4Dept. of Applied Physics, Federal Urdu University of Arts Sciences & Tech,
Islamabad, Pakistan
In a novel analysis of lasing conditions, enhanced per unit gain (G ap-proximately close to 1) in plastically deformed crystals excited at anomaloustransmission conditions is shown possible, while the semi-empirical results forthis are also confirmed by the rigorous complex field analysis. The results arecompared with those obtained by applying the conditions of Lasing-Without-Inversion (LWI) to the proposed scheme, with detailed simulation of suggestedconditions.
Deformation induces splitting of states and generates emissions dependingon Rabi frequencies when suitably excited by a probe beam; and in criticaldeformation conditions this enables constructive coherent interference of themultiple diffracted waves propagating in the crystal, thus enabling laser emis-sion at ultra short wavelengths.
A possible practical implementation of the scheme can be realized utilizingthe cold-trapped lattices deformed by optical tweezers and dressed to produceLWI. Laser performances are modeled accordingly.
Transport of Bose-Einstein condensates throughtwo-dimensional billiard geometries
T. Hartmann, M. Hartung, P. Schlagheck
Institute for Theoretical Physics, University of Regensburg, D-93040 Regensburg,Germany
The tremendous progress in the experimental techniques for Bose-Einsteincondensates during the last decade lead to the realization of almost arbi-trarily shaped confinement and waveguide geometries for interacting matterwaves1,2,3. This opens new experimental possibilities for probing the trans-port of Bose-Einstein condensates through various mesoscopic structures.
We numerically investigate the quasi-stationary propagation of a condensatethrough two-dimensional cavities within the mean-field approximation of thecondensate. Our calculations rely on a nonlinear Green function method thatis based on the Gross-Pitaevskii equation. This is in principle a generalisationof the approach used in Ref.4 to two dimensions.
Here we study resonant transport through nearly closed cavities, where thepresence of the nonlinearity results in strong nontrivial distortions of the reso-nance peaks. We observe complex transmission spectra with complicated hys-teresis behavior. The dynamical stability of the stationary solutions obtainedwith the Green function method is investigated quantitatively. Complementaryresults are obtained with time propagation methods.
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1W. Guerin et al., Phys. Rev. Lett. 97, 200402 (2006).2V. Milner et al. Phys. Rev. Lett. 86, 1514 (2001).3N. Friedman et al. Phys. Rev. Lett. 86, 1518 (2001).4T. Paul et al., Phys. Rev. Lett. 94, 020404 (2005); Phys. Rev. A 76, 063605 (2007).
Elastic Waves in a Strongly Scattering Porous Mesoglass
W. K. Hildebrand, J. H. Page, L. A. E. B. Cobus, J. Beck1, R. Holmes2,J. Bobowski3
Ultrasonics Research Laboratory, University of Manitoba, Winnipeg, Canada
Given the recent success in observing transverse localization in a randomthree-dimensional elastic network, the characteristics of acoustic wave transportin such systems are of considerable interest4. In our experiments, we measurethe density of states and diffusion coefficient of a highly porous mesoglass,made by sintering polydisperse glass beads to form a disordered solid witha wide distribution of pore sizes. This material is observed to have fractalbehaviour over a range of length scales (spanning approximately one decade),and very strong scattering is observed in the corresponding frequency regime,with values of kl approaching one. In this intermediate frequency regime, boththe density of states and the diffusion coefficient exhibit unusual behaviour,which is compared with numerical simulations of network models of disorderedglassy systems.
Figure: Image of the mesoglass sample obtained by x-ray tomography.
1Present address: CancerCare Manitoba, Winnipeg, Canada.2Present address: Department of Chemical Engineering and Materials Science, Univer-
sity of Minnesota, Minneapolis, USA.3Present address: Department of Physics, University of British Columbia, Vancouver,
Canada.4H. Hu et al., Nature Physics 4, 945 (2008).
Resonant energy transport in aggregates of ultracoldRydberg-Atoms
C. S. Hofmann, G. Gunter, H. Schempp, N. Muller, O. Mulken1, A. Blumen1,A. Eisfeld2, T. Amthor, M. Weidemuller
Physics Department, University of Heidelberg, Heidelberg, Germany1Physics Department, University of Freiburg, Freiburg, Germany
2Max Planck Institute for the Physics of Complex Systems, Dresden, Germany
Due to the long-range character of the interaction between highly excitedatoms, the dynamics of an ultracold gas of Rydberg atoms is entirely deter-mined by van-der-Waals and dipole–dipole interactions. One outstanding prop-erty is the tunability of strength and character of the interactions by meansof static electric fields. This allows to explore the transition from weakly cou-pled two-body systems to strongly interacting many-body systems. Importanteffects include the crossover from the van-der-Waals blockade to the dipoleblockade, the latter being realized by electrically tuning the system to a socalled Forster resonance.
Making use of such Forster resonances, Rydberg atoms can be seen as a pro-totype system to investigate resonant energy transfer processes. Such processesfor instance play an important role in many biological systems like in photo-synthetic units of purple bacteria, where light is absorbed by light harvestingcomplexes and then transported to reaction centers. We present a Monte Carlomodel describing the many-body character of this radiationless energy transferin an unstructured atom cloud and compare it with density-dependent mea-surements1. The model is based on simulations of small subensembles involvingup to ten atoms interacting via coherent pair processes. Good agreement be-tween the experimental data and the predictions of our model is found. Thisallows us to deduce that the system has to be described in terms of many-bodydynamics, and that the energy transfer preserves coherence on microsecondtimescales.
Furthermore we present theoretical studies investigating survival probabil-ities in coherent exciton transfer2. We discuss excitation migration propertieson a chain of Rydberg atoms with exciton traps on both ends. The excitonsurvival probability is analyzed in the continuous-time quantum walk frame-work as well as in the classical limits of random walk techniques. Moreover theinfluence of spatial disorder within the Rydberg atom chain is investigated andmechanisms which dephase the energy transport are discussed. Finally possibleexperimental implementations of the described systems will be presented whichexploit the unique features of ultra cold structured Rydberg gases.
1S. Westermann et al., Eur. Phys. J. D 40, 37 (2006).2O. Mulken et al., Phys. Rev. Lett. 99, 090601 (2007).
Towards Exploring Ultracold HeteronuclearKRb Systems
S. Hoinka, A. Rakonjac, C. R. McKenzie, A. C. Wilson
Jack Dodd Centre for Quantum Science & Technology, Department of Physics,University of Otago, Dunedin, New Zealand
Heteronuclear mixtures of ultracold atomic gases exhibit a wide range ofnovel properties and thus are promising candidates for fascinating future exper-iments in the field of ultracold quantum gases. Currently we are constructinga new apparatus for creating ultracold samples of 40K and 87Rb. We use amechanical transfer scheme to transport atoms from a dual-species magneto-optical trap to an ultra-high vacuum science cell, where the mixture is evapo-ratively and sympathetically cooled in a magnetic trap and transferred into anoptical dipole trap for further cooling to degeneracy. To tune interactions be-tween the two species for subsequent experiments, we utilise magnetic Feshbachresonances. Our research focuses on heteronuclear collisions1 and ultimatelyfermionic polar molecules in the rovibrational ground state trapped in a 3Doptical lattice2. We report on the design and progress of the apparatus so farand describe our experimental objectives for the near future.
1N. R. Thomas et al., Phys. Rev. Lett. 93, 173201 (2004).2T. Kohler et al., Rev. Mod. Phys. 78, 1311 (2006).
Routes towards using a spatial light modulator to imposeadditional potentials onto a condensate
M. Holynski1, M. Baumert1, N. Meyer1,2, A. C. Rudge1, J. Kronjager1 andK. Bongs1
1MUARC, School of Physics and Astronomy, University of Birmingham, Edgbaston,Birmingham B15 2TT, UK
2Institut fur Laser-Physik, Universitat Hamburg, Luruper Chaussee 149, 22761Hamburg, Germany
Placing a Bose-Einstein condensate into an optical potential provides aquantum simulator. In such a system it is possible to study quantum phenom-ena familiar from solid-state physics with an unprecedented degree of control.A spatial light modulator (SLM) can be used to image chosen pixelated poten-tials onto an optically held condensate. This produces a potential constructedof a distribution of blurred, overlapping, pixels in which the condensate sits.
A particularly interesting application of such a distribution is the produc-tion of harmonic potentials. These could be used to negate the harmonic con-finement that occurs in an optical potential due to the gaussian profile of abeam. The result would be a potential landscape more representative of con-densed matter systems. The use of an SLM also allows the introduction of achosen, reproducible disorder potential. This would provide a novel tool forstudy of phenomena such as weak localisation and mesoscopic physics such asmagnetic fingerprints.
This study was conducted to determine the advantages of using a SLMpossessing greyscale pixels compared to one capable of only binary values. Inorder to study the capabilities of the two pixel types, potentials for each casehave been modelled numerically with pixels being represented as gaussian inshape. When representing a smooth harmonic potential with a binary SLMthe pixel resolution must be reduced to achieve results comparable to thosepossible with greyscale pixels. For the application of disorder the two pixeltypes can be used to produce near equivalent potentials.
Figure: A disordered potential with a harmonic bias built up from binary pixels,illustrative of what can be achieved with a binary SLM
Ramsey interference in one-dimensional systems:dynamics of full distribution function of fringe contrast
T. Kitagawa1, S. Pielawa1, A. Imambekov2, E. Demler1
1Harvard University, United States2Rice University, United States
Noise was suggested and probed to reveal correlations in equilibrium, many-body state1,2. In this work, we suggest that noise study is also effective toexplore the physics of non-equilibrium, strongly correlated system.
In particular, we consider two-component Bose gas in 1D3. We obtained theanalytic form of full (spin) distribution function (FDF) as a function of time,where the system evolves under Ramsey-like sequence. Analogous to quasi-distribution function used for spin system4, distribution function allows us tovisualize and characterize the dynamics of highly entangled quantum state.We observe a clear signature of quantum fluctuation in FDF, and FDF is asmoking- gun for Bosonic Luttinger liquid in ultracold atom.
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Figure: Time evolution of full spindistribution function in one
dimensional system
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dimensional system
1E. Altman et al., Phys. Rev. A 70, 013603 (2004).2S. Hofferberth et al., Nature Physics 4, 489 (2008).3A. Widera et al., Phys. Rev. Lett. 100, 140401 (2008).4Kitagawa et al., PRA 46, 7
Compact diode-pumped Yb3+:KY(WO4)2 planarwaveguide laser
S. V. Kurilchik1, N. V. Kuleshov1, A. A. Lagatsky2, S. A. Guretsky3
1Institute for Optical Materials and Technologies, BNTU, Minsk, Belarus2School of Physics and Astronomy, University of St. Andrews, St. Andrews, UK3The Scientific and Practical Materials Research Center, NASB, Minsk, Belarus
Nowadays the progress of optoelectronic devices towards practicality andintegration directly depends on their compactness and efficiency. High-power,waveguide-based microchip laser devices designed for integrated optical circuitsare perspective to apply in communications, data processing, biomedical analy-sis, imaging and environmental diagnostics. Waveguide laser configuration en-sures highly efficient and low threshold operation combined with simple mono-lithic laser structure that can be incorporated into practical integrated devices.As efficient gain media for lasing at 1 µm the potassium double tungstates,notably KY(WO4)2 (KYW) and KGd(WO4)2, doped with trivalent ytterbium(Yb3+), have been identified1,2.
In our research high-quality single-crystalline layers of Yb(3at.%):KYWwith a thickness of 14 µm with low propagation losses were grown by liquid-phase epitaxy technique. A schematic of the laser set-up is shown in Figurewhere the pump source was a 980 nm fiber-coupled single-mode laser diodethat produced up to 480 mW of output power. A thin fused silica substrate,coated for high transmission at 980 nm and high reflection at 1020-1100 nm,was held in place to the surface of the crystal by the surface tension. An out-put coupler was similarly located at the other facet of the crystal to create amicrochip monolithic plane-plane cavity. To achieve Q-switching the output-coupling mirror was replaced by a semiconductor saturable absorber mirror.
In cw planar waveguide mode a maximum output power of 148 mW wasproduced at 1040 nm using the 5% output coupler, and the corresponding slopeefficiency made up 62%. The lasing threshold was measured to be as low as40mW of absorbed pump power. Propagation losses of the Yb:KYW LPE layerwere found to be 0.06 dBcm−1. In Q-switched mode pulses of around 170 ns,with energies up to 44 nJ and 722 kHz repetition rate were obtained.
1A. A. Lagatsky, N. V. Kuleshov, V. P. Mikhailov, Opt. Comm. 165, 71 (1999).2A. Brenier, J. Lumin. 92, 199 (2001).
Localization and nonlinearity in disordered andincommensurate photonic lattices
Y. Lahini1, R. Pugatch1, R. Morandotti2, D. N. Christodoulides3
N. Davidson1, Y. Silberberg1
1The Weizmann Institute of Science, Rehovot, Israel2Institut National de la Recherche Scientifique, Varennes, Quebec, Canada
3CREOL/College of Optics, University of Central Florida, Orlando, Florida, USA
We present an experimental study of the transverse localization1,2 of lightin nonlinear a-periodic lattices. We describe the observation of exponential(Anderson) localization of expanding wavepackets and localized eigenmodes indisordered lattices, and an experimental study of the effect of weak nonlinearityon Anderson localization in one dimension3. The effect of nonlinearity is foundto be highly dependent on the exact initial condition. We also present pre-liminary results for intensity correlation measurements that reveal underlyinglinear and nonlinear effects.
In a different set of experiments4 we report the observation of the signatureof a localization transition for light in one-dimensional quasi-periodic photoniclattices5, by directly measuring the expansion rates of initially narrow wavepackets propagating in the lattice. Below the transition all the modes of thesystem are extended and therefore an initially narrow wave-packet eventuallyspreads across the entire lattice. Above the critical point, all modes are local-ized and expansion is suppressed. In addition, we measure the effect of focusingnonlinear interaction on the propagation and find it increases the width of thelocalized wave-packets.
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Figure: Measurements of a localization transition in incommensurate photoniclattices. (a,b) Below the predicted transition point an initially narrow wave-packetexpands as it propagates. (c) above the transition expansion is fully suppressed. (d)
Experiments (dots) are found to be in good agreement with theory (black line).
1H. De Raedt et al., Phys. Rev. Lett. 62, 47 (1989).2T. Schwartz et al., Nature 446, 53 (2007).3Y. Lahini et al., Phys. Rev. Lett. 100, 013906 (2008).4Y. Lahini, R. Pugatch et al., in print.5S. Aubry and G. Andre, Ann. Israel. Phys. Soc. 3, 133 (1980).
Effects of interaction on the localization of ultracoldatoms in a 1D quasi-periodic potential
M. Larcher1, M. Modugno2, F. Dalfovo1
1CNR-INFM BEC Center and Physics Department, University of Trento, I-38050Povo, Trento, Italy
2LENS and Physics Department, University of Florence and CNR-INFM, Via NelloCarrara 1, I-50019 Sesto Fiorentino, Italy
We study the time evolution of an atomic wave-packet in a 1D quasi-periodicpotential by numerically solving a discrete non-linear Schrodinger equation.The results are compared with those obtained for non-interacting particles. Inparticular we consider the problem of the interplay between Anderson localiza-tion1 and interaction. For the shape of the initial wave-packet we use both awavefunction completely localized in a single lattice site and a broader wave-function having Gaussian envelope. In both cases, there are evidences of adestruction of the localization by the interaction between atoms. We discussalso the connection between our results and current experiments with ultracoldatoms in bichromatic lattices.
1P. W. Anderson, Phys. Rev. 109, 1492 (1958).
Coherent control of light propagation in opticalwaveguides
R. Menchon1, A. Llobera2, J. Mompart1, V. Ahufinger1,3
1Grup d’Optica, Dept. de Fısica, Universitat Autonoma de Barcelona, E-08193Bellaterra, Spain
2Departament de Micro i Nanosistemes, Institut de Microelectronica de Barcelona -Centre Nacional de Microelectronica, E-08193 Bellaterra, Spain
3ICREA Institucio Catalana de Recerca i Estudis Avancats, Barcelona, Spain
Stimulated Raman Adiabatic Passage (STIRAP)1 is a robust techniquethat is routinely used in three-level atomic systems in interaction with twolaser pulses to transfer the atomic population between two of the three levels.The high efficiency of this coherent technique has motivated its application toother research fields such as atomic transport in optical microtraps2 or lightpropagation in coupled waveguides3.
In the present work, we focus our investigations on the development oftechniques to coherently control and manipulate the propagation of light ina system of coupled rib total internal reflection (TIR) waveguides, followingthe lines of a recent work by S. Longhi et al.3 The system consists of threewaveguides coupled through evanescent field. By an appropriate variation ofthe distance among the waveguides, it is possible to transfer a beam of lightbetween the outermost waveguides without almost any excitement of the centralguide, ressembing the STIRAP technique among internal atomic levels.
In addition, we have studied a double STIRAP process, which consists inchaining two STIRAP processes in a system of three coupled waveguides. Inthis case, light will be transmitted to the outermost waveguide and will comeback to the initial one without almost any excitement of the central waveguidewhich implies an effective reduction of the speed of light propagating throughthe structure, in a close analogy to the well known electromagnetic inducedtransparency4 technique.
1K. Bergmann, H. Theuer, B. W. Shore, Rev. Mod. Phys. 70, 1003 (1998).2K. Eckert, M. Lewenstein, R. Corbalan, G. Birkl, W. Ertmer and J. Mompart, Phys.
Rev. A 70, 023606 (2004); K. Eckert, J. Mompart, R. Corbalan, M. Lewenstein, and G. Birkl,Opt. Comm. 264, 264 (2006).
3S. Longhi et al., Phys. Rev. B 76, 201101 (2007).4S. E. Harris, Phys. Today 50(7), 36 (1997); J. P. Marangos, J. Mod. Opt. 45, 471
(1998); L. V. Hau, S. E. Harris, Z. Dutton, C. H. Behroozi, Nature 397, 594 (1999).
Towards a Random Laser with Cold Atoms
N. Mercadier, W. Guerin, R. Kaiser
Institut Non Lineaire de Nice, CNRS and Universite de Nice Sophia-Antipolis,1361, route des Lucioles, 06560 Valbonne, France
A standard laser is built upon two basic ingredients: an amplifying mediumand an optical cavity ensuring that photons go through the gain medium manytimes. Lasing can however be achieved without cavity using a disordered gainmedia where scattering provides the required optical feedback1. Such randomlasers have been observed in several condensed matter systems2, but manyfeatures remain to be investigated, for which a better characterized samplecould be highly valuable. A cloud of cold atoms could provide a promisingalternative to achieve random lasing, allowing for a detailed understandingof the involved microscopic phenomena. Several gain mechanisms have beenidentified and studied, that can be good candidates to reach that goal, includingMollow and Raman gain, but also parametric processes such as non degenerateFour-Wave Mixing (FWM). Combining gain with scattering is however notobvious, as pumping drastically reduces the scattering rate, but both theoriticalinvestigations for Mollow gain and experimental ones for Raman processes havelead to a threshold condition that seems experimentally achievable3,4. I willreport here our work on the estimation of the threshold condition with thesedifferent gain mechanisms and discuss forthcoming work towards the realizationof a random laser with cold atoms.
Figure: Critical optical thickness b0 to obtain random lasing in an atom cloud withMollow gain, as a function of the pump beams detuning (∆) and intensity (Ω).
1V. S. Letokhov, Sov. Phys. JETP 26, 835 (1968).2D. S. Wiersma, Nature Phys. 4, 359 (2008).3L. S. Froufe-Perez, W. Guerin, R. Carminati and R. Kaiser, PRL 102, 173903 (2009).4W. Guerin, N. Mercadier, D. Brivio and R. Kaiser, Opt. Express 17, 13 (2009).
Towards a Bose-Fermi mixture experiment in a 2Doptical lattice
N. Meyer1,2, M. Baumert1, M. Holynski1, A. Rudge1, J. Kronjager1,K. Sengstock2, K. Bongs1
1MUARC, School of Physics and Astronomy, University of Birmingham, Edgbaston,Birmingham B15 2TT, UK
2Institut fur Laser-Physik, Universitat Hamburg, Luruper Chaussee 149,22761 Hamburg, Germany
An ultra stable laser system for a Bose-Fermi mixture experiment relyingon the developments in context of droptower experiments at ZARM/Bremen ispresented. Due to its temperature and mechanical stability an unprecedentedlongterm term stability for laboratory experiments (and drop experiments1)is expected. This particular laser system stands out due to high modularityand possible versatile applications. Latest developments of laser modules madeout of glass ceramic even improve the temperature stability for possible use infuture space missions. In addition a short proposal of a magnetic transportabout macroscopic scales is presented which is to be used at a new Bose-Fermi mixture vacuum chamber with single site resolution investigating opticaldisorder effects with and without interactions and particle-induced disorder2.Further calculations of optical 2D lattices and appropriate Wannier functionsare presented.
Figure: Optical mounts and parts of the master module
1see poster of S. Seidel.2see poster of M. Holynski.
Interference fringes from multiple scattering media:Taking apart the Enhanced Backscattering cone
B. P. J. Bret, F. P. Ferreira, E. J. Nunes-Pereira, M. S. Belsley
Centro de Fısica, Universidade do Minho,Campus de Gualtar, 4710-057 Braga, Portugal
We present results from a novel experiment aimed at understanding moreprofoundly the interference effects in multiple scattering, and in particular thoserelated to the enhanced backscattering (EBS). EBS arises from constructive in-terference of reciprocal paths. After ensemble averaging, and in the regime ofweak scattering where the mean free path is much larger than the wavelengthof the light, interference of light only contributes to a very narrow cone in theexact backscattering direction of a plane wave impinging on a diffusive sample.The EBS cone can be described as an integral, over a size distribution set bythe mean free path, of interference fringes with various periods which all sumup in phase at the exact backscattering direction. By illuminating the multiplescattering medium with two focused beams separated by a distance D, insteadof a single plane wave as above, reciprocal paths between the two illuminatedspots create interference fringes. This interference effect is present in all space,whereas its average over all distances D recovers the EBS cone, which has avery narrow extent. A combination of the 2-spots illumination with a schemewhich detects only light coming from the 2 directly illuminated areas theo-retically allows the observation of fringes with contrast up to 50%. Varyingthe optical dephasing between the two incident beams permits us to distin-guish with accuracy the EBS fringes and spurious ’mirror-like’ fringes, sincethey shift in opposite directions (see Figure). Careful data analysis recoversboth contributions, EBS and specular reflection fringes and show without anydoubt how one can observe interference fringes from light propagating througha multiple scattering medium.
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Figure: Interference fringes as a function of optical dephasing between the twoincident beams. On the left plot, reflected from a mirror, the specular reflectionfringes shift to the left. On the right plot, reflected from a diffusive sample, the
fringes shift to the right, as a signature of the reciprocal paths giving rise to the EBS.
A Truncated Levy Flight for Light
E. J. Nunes-Pereira1, J. M. G. Martinho2, M. N. Berberan-Santos2
1Centro de Fısica, Universidade do MinhoCampus de Gualtar, 4710-057 Braga, Portugal
2Centro de Quımica-Fısica MolecularInstituto Superior Tecnico, 1049-001 Lisboa, Portugal
A Truncated Levy Flight (TLF) is a stochastic process exhibiting a tran-sition from a superdiffusive (supralinear mean square displacement with time;short time/distances) to a standard Brownian diffusive behavior (linear; time/distances higher than some cut-off). We present an analytical model for a TLFfor light, corresponding to the case of partially coherent redistribution of reso-nance radiation for a thermal vapor. This case is motivated from the radiationtransport problem in an astrophysical context but is also similar to the particletransport in heterogeneous media in some geochemical formations.
Figure: A Truncated Levy Flight for thermal atomic vapor under partial frequencyredistribution conditions: jump size probability density function. The full
superdiffusive Levy Flight for Doppler and Lorentz for a single line under completeredistribution has a non-truncated power law. A simple exponential truncated Levy
Flight is included for comparison. See Refs.1,2 for full details.
1M. N. Berberan-Santos, E. J. Nunes-Pereira, J. M. G. Martinho, Photonic superdiffusivemotion in resonance radiation trapping, J. Chem. Phys. 125, 174308 (2006).
2A. R. Alves-Pereira, E. J. Nunes-Pereira, J. M. G. Martinho, M. N. Berberan-Santos,Photonic superdiffusive motion in resonance line radiation trapping: partial frequency redis-tribution effects, J. Chem. Phys. 126, 154505 (2007).
Spatial Quantum Correlations in a Multiple ScatteringMedium
J. R. Ott, N. A. Mortensen, P. Lodahl
DTU Fotonik, Department of Photonics Engineering, Kgs. Lyngby, Denmark
The transport of quantized light through a multiple scattering non-absorbingmedium is investigated. The multiple scattering medium is modeled as havingan input and an output surface. The input and output surfaces each has an un-specified number of input/output modes. This investigation shows that, afteraveraging over all realizations of disorder, a single mode input will experiencenon-classical correlation phenomena when transmitted through the scatteringmedium. The correlations are shown to occur even for negligible inverse ofthe mesoscopic conductance 1/g = L/N`, with L the medium thickness, Nthe number of conducting modes and ` the transport mean free part. Thesequantum correlations were theoretically predicted by Lodahl et al.1 and wererecently experimentally verified by Smolka et al.2 We currently extend thework of Lodahl et al.1 to also include the impact of multiple input modes.
Figure: Sketch of a random scattering event from a single mode input.
1P. Lodahl, A. P. Mosk, and A. Lagendijk, Phys. Rev. Lett. 95, 173901 (2005).2S. Smolka, A. Huck, U. L. Andersen, A. Lagendijk, and P. Lodahl, Phys. Rev. Lett.
102, 193901 (2009).
Transport of ultracold Bose gases in presence of disorder
T. Paul1, M. Albert2, N. Pavloff2, P. Leboeuf2, T. Ernst3, P. Schlagheck4
1Institut fur theoretische Physik, Universitat Heidelberg2LPTMS, Universite Paris Sud, Orsay3 CTCP Massey University Auckland
4 Institut fur theoretische Physik, Universitat Heidelberg
We study the coherent flow of interacting Bose-condensed atoms in presenceof a disordered potential. The Mean-Field description of the condensate pre-dicts that a variation of the condensate velocity with respect to the disorderedpotential induces different regimes of quantum transport, such as a superfluidmotion as well as a regime where signatures of Anderson localization are found.In particularly we investigate the breakdown and the critical velocity of thesuperfluid motion and present an analytical approach that relates the criticalvelocity beyond which the superflow breaks down with the statistical propertiesof the disorder potential. As an extension of the pure mean field-description weestimate the amount of quantum excitation and depletion during the transportprocess in the framework of the Hartree-Fock-Bogoliubov approach.
Observation of two-photon speckle
W. H. Peeters, J. J. D. Moerman, M. P. van Exter
Leiden Institute of Physics, P.O. Box 9504, 2300 RA Leiden, The Netherlands
We report the observation of fourth-order speckle patterns in the far fieldof a scattering random medium. The scattering medium is illuminated with aspatially entangled two-photon state. After scattering, quantum interferencebetween scattered components of the two-photon state results in a specklepattern in spatial photon correlations. These spatial correlations are detectedas simultaneous photon arrivals in two independently-moving detectors.
An exponential distribution of the two-photon intensity is observed. Thisdistribution proves that the incident two-photon state is pure and that thespatial correlations have a quantum nature rather than a classical one. Ourexperiments also demonstrate that two-photon speckle from an entangled two-photon state contain more information about the scattering medium than (clas-sical) second-order speckle. They for instance allow one to distinguish a surfacescatterer from a volume scatterer.
Figure: Measured variations of the intensity and two-photon coincidences in thefar-field of a diffuser, recorded by scanning the position of detector 1. The single
photon count rate (a) shows that (classical) intensity speckle are absent. Theincident light is thus spatially incoherent at the one-photon level. The coincidencecount rate (b) is measured with the second detector kept at a fixed position. The
pattern is a fully-developed speckle pattern, which demonstrates that there is spatialcoherence at the two-photon level.
Nonuniversal Dynamic Conductance Fluctuations
Abe Pena1, A. A. Chabanov1, N. Cherroret2, S. E. Skipetrov2
1University of Texas at San Antonio, San Antonio, TX, USA2Laboratoire de Physique et Modlisation des Milieux Condenss, Grenoble, France
A prominent feature of wave transport in mesoscopic systems is the uni-versal conductance fluctuations (UCF)1. The origin of UCF can be traced tocorrelations of transmission channels of a random sample2. However, all stud-ies of UCF yet conducted have only concerned the steady-state conductance.In this work we study fluctuations of the time-dependent conductance of adisordered system by means of diagrammatic theory and microwave pulsedtransmission measurements3. We show that the universality of conductancefluctuations is lost in the dynamic experiment: the fluctuations depend on thelength of sample and mean free path. The variance of normalized transmit-tance is observed to increase as a third power of delay time from an excitingpulse. A comparative analysis of the underlying mesoscopic correlations allowsus to identify a new characteristic time scale in the evolution of fluctuations oftransport properties.
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Figure: Scaling properties of var[T (t)/〈T 〉] ∝ τpτ3, τp = tp/tD and tD being thediffusion time, for three values of the pulse duration, tp. The inset shows the same
plot on a log-log scale.
1R. A. Webb, S. Washburn, C. P. Umbach, and R. B. Laibowitz, Phys. Rev. Lett. 54,2696 (1985).
2S. Feng, C. Kane, P. A. Lee, and A. D. Stone, Phys. Rev. Lett. 61, 834 (1988).3N. Cherroret, A. Pena, A. A. Chabanov, and S. E. Skipetrov, arXiv:0901.3668.
Resonant Scattering of light by high-Q photonic crystalsnanocavities
S. L. Portalupi1, M. Galli1, M. Belotti1, L. C. Andreani1, L. O’Faolain2,T. F. Krauss2
1Dipartimento di Fisica “A.Volta” and CNISM, Universita di Pavia, Pavia, Italy2School of Physics and Astronomy, University of St.Andrews, United Kingdom
In this work we show that wavelength-resolved laser light scattering can bevery efficiently used as a high-resolution technique for a precise characteriza-tion of passive PhC nanocavities with very high Q factors. By measuring thecrossed-polarized light scattering1 from silicon-based L3 type PhC nanocavi-ties, we observe sharp Fano-like resonances corresponding to the excitation oflocalized cavity modes, as shown in Fig. 1b. Results are interpreted accord-ing to the Fano model of quantum interference between two coupled scatteringchannels. This yield to a precise estimation of resonance energy and Q factor.Q factors as high as 1.1×105 can be directly measured for a L3 cavity in whichthe nearby holes shift (∆x/a) takes the value 0.192.
Measuring several samples with different lattice disorder, indicated by thedisorder parameter σ (defined as the root mean square deviation of hole radii),ranging from nominal 0 nm up to 10 nm3 we see that the Q factors decreasesin function of the disorder following4 1/Q ∝ σ2 (Fig. 1c). We also see that,increasing the lattice disorder, there is a breaking of the mode symmetry, indi-cated by the increase of the scattering signal for different sample orientation.
Figure: a) SEM image of L3 nanocavity; b) Typical Fano-like spectrum observed inour experiment; c) Scaling of inverse Q factor as a function of disorder parameter σ
1M. W. McCutcheon et al., Phys. Lett. 87, 221110 (2005).2M. Galli et al., Appl. Phys. Lett. 94, 071101 (2009).3L. O’Faolain et al., Electron. Lett. 42, 1454 (2006).4D. Gerace and L. C. Andreani, Photon. Nanostructure 3, 120 (2005).
Universal Spectra of Coherent Atoms in a RecurrentRandom Walk
R. Pugatch1, O. Firstenberg2, M. Shuker2, Nir Davidson1
1Department of Physics of Complex Systems, Weizmann Institute of Science,Rehovot 76100, Israel
2Department of Physics, Technion-Israel Institute of Technology, Haifa 32000, Israel
We report an experiment that directly measures the Laplace transform ofthe recurrence probability in one dimension using electromagnetically inducedtransparency (EIT) of coherent atoms diffusing in a vapor cell filled with buffergas. We find a regime where the limiting form of the complex EIT spectrumis universal and only depends on the effective dimensionality in which the ran-dom recurrence takes place. In an effective one-dimensional diffusion setting,the measured spectrum exhibits power-law dependence over two decades inthe frequency domain with a critical exponent of 0.56 close to the expectedvalue 0.5. We discuss our current effort to observe “imaginary time Anderson-localization” and its connection to anomalous diffusion in the presence of traps.
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Figure: Measured signal vs the two-photon detuning ∆ and the power-law fit. Inset(a): zoom-in of the measured signal over the range ±300 Hz. Inset (b): an
illustration of the one-dimensional beam experiment. Returning atoms contribute tothe total intensity irrespective of the location of their reentry point thus effectively
reducing the dimensionality to one.
Non-interacting electrons in a nanoshell
K. Putteneers, F. Brosens
Theory of Quantum and Complex Systems, Antwerpen, Belgium
Nanoshells are nanosize particles which consist of a core and one or morealternating dielectric and metallic layers. The kind of particles investigated inmy PhD are concentric spherical nanoshells with a dielectric core (e.g. SiO2;40-100 nm) and a metallic shell (e.g. gold, silver; 5-20 nm). The workingmechanism of the particles is called ‘Localized Surface Plasmon Resonance’.It can appear at a dielectric-metallic boundary when light of the appropriatewave length is shone on a nanoshell. This property makes the nanoshells usefulfor biosensing, SERS, ‘plasmonics’ (plasmon-electronics), ...
The goal of my PhD is to investigate the influence of the electron-phononinteraction on the properties of such nanoshells. Up to now the first step toreach that goal has been achieved: calculating the ground state properties offree (conduction) electrons in a nanoshell. This we have done by solving theSchrodinger equation with corresponding boundary conditions. For the nu-merical calculations we have also applied the method of the transfer matrix1
to increase the speed of the planned self-consistent potential calculations forwhich the ground state properties form the basis. The results of the introduc-tory calculations with the nanoshell considered as an infinite and as a finitepotential well are shown in the figure.
Figure: Left panel: one-electron energy levels En,l as a function of the angularquantum number l for different values of the radial quantum number n. Right panel:
Fermi energy EF and mean energy per particle Etot/N as a function of the ratiobetween the radii.
1W. Magnus, W. Schoenmaker, Journal of Applied Physics 88, 5833-5842 (2000).
Light scattering of ultracold atoms in an optical lattice
S. Rist1,2, C. Menotti3, G. Morigi1
1Departament de Fısica, Universitat Autonoma de Barcelona, 08193 Bellaterra,Spain
2Abteilung Quantenphysik, Universitat Ulm, D-89069 Ulm, Germany3CNR-INFM BEC, and Dipartimento di Fisica, Universita di Trento, I-38050 Povo,
Italy
We investigate theoretically light scattering of photons by ultracold atomsin an optical lattice in the linear regime. A full quantum theory for the atom-photon interactions is developed as a function of the atomic state in the latticealong the Mott-insulator – superfluid phase transition, and the photonic scat-tering cross section is evaluated as a function of the energy and of the directionof emission1. We compare our results with previous works2,3 and show that,when performing Bragg spectroscopy with light scattering, the photon recoilgives rise to an additional atomic site to site hopping, which can interfere withordinary tunneling of matter waves and can significantly affect the photonicscattering cross section.
Figure: Inelastic scattered light intensity for atoms in a Mott Insulator as a functionof frequency and scattering angle.
1S. Rist, C. Menotti and G. Morigi, arXiv:0904.0915.2I. B. Mekhov, C. Maschler and H. Ritsch, Phys. Rev. A 76, 053618 (2007).3A. M. Rey, P. B. Blakie, G. Pupillo, C. J. Williams, and C. W. Clark, Phys. Rev. A 72,
023407 (2005).
All-optical runaway evaporation to Bose-Einsteincondensation
M. Robert-de-Saint-Vincent1, J.-P. Brantut1, J.-F. Clement1, R. A. Nyman,C. J. Borde2, A. Aspect1, T. Bourdel1, P. Bouyer1
1Laboratoire Charles Fabry de l’Institut d’Optique, CNRS, Univ. Paris-Sud,Palaiseau, France
2LNE-SYRTE, Observatoire de Paris, France
We demonstrate runaway evaporative cooling directly with a tightly-con-fining optical-dipole trap and achieve fast production of condensates of 1.5 105
87Rb atoms. Our scheme uses a specific crossed trap configuration where thetwo beams have different waists and intersect off centered. It is characterizedby independent control of the trap confinement and depth, allowing forced all-optical evaporation in the runaway regime. Our configuration is particularlywell suited to the case of 87Rb atoms in a 1565 nm optical trap, where anefficient loading combining light-shift induced optical pumping with extremelyfar detuned optical molasses is possible. However, our scheme is general andwill allow all-optical evaporative cooling at constant stiffness for every optically-trappable atomic or even molecular species1.
The ability to produce condensates with a cycling time of the order ofone second opens the way to use Bose-Einstein condensates for high precisionmeasurement applications. In this direction, we present a multiple path atom-interferometer that intrinsically levitates a Bose-Einstein condensate againstgravity. It uses multiple order diffraction by a 1D standing wave, and can beused to measure external forces such as gravity.
Figure: a,b) Absorption images after 10 diffraction pulses. On top of the imagesstands the suspended cloud, while we observe below the losses of each pulse. c) Ratioof the suspended atom number to the total atom number, as a function of the pulse
period.
1J.-F. Clement, J.-P. Brantut, M. Robert-de-Saint-Vincent, R. A. Nyman, A. Aspect,T. Bourdel, and P. Bouyer, arXiv:0903.2745 [physics.atom-ph].
Particle dynamics in non-conservativewhirllight force fields
S. Albaladejo1, I. Zapata2, M. I. Marques1, M. Laroche3, J. M. Parrondo4,F. Scheffold5, F. Sols2, J. J. Saenz1
1Moving Light and Electrons (Mole) Group, Univ. Autonoma de Madrid, Spain.2Dpto. Fısica de Materiales, Universidad Complutense de Madrid, Spain.
3Institut d’Optique, CNRS, Universite Paris-Sud, France.4Dpto. Fısica Atomica y Molecular, Universidad Complutense de Madrid, Spain.
5Department of Physics, University of Fribourg, Switzerland
Light forces on small (Rayleigh) particles are usually described as the sumof two terms: the dipolar or gradient force and the scattering or radiationpressure force. The scattering force is traditionally considered proportional tothe Poynting vector, which gives the direction and magnitude of the momentumflow. However, as we will show, when the light field has a non-uniform spatialdistribution of spin angular momentum, an additional scattering force arises asa reaction of the particle against the rotation of the spin. This non-conservativeforce term is proportional to the curl of the spin angular momentum of the lightfield1. We will illustrate the relevance of the spin force in the particular simplecase of a 2D field geometry arising in the intersection region of two standingwaves2
We will also discuss the peculiar particle dynamics in the non-conservativeforce field of an optical vortex lattice3. Radiation pressure in the whirllight field(arising in the intersection region of two crossed optical standing waves2) playsan active role spinning the particles out of the whirls sites leading to a giantacceleration of free diffusion. Interestingly, we show that a simple combinationof null-average conservative and nonconservative steady forces can rectify theflow of damped particles. We propose a “deterministic ratchet” stemmingfrom purely stationary forces4 that represents a novel concept in dynamicswith considerable potential for fundamental and practical implications.
1S. Albaladejo, M. Laroche, M. Marques, J. J. Saenz, PRL 102, 113602 (2009).2A. Hemmerich, T. W. Hansch, Phys. Rev. Lett. 68, 1492 (1992).3S. Albaladejo, M. I. Marques, F. Scheffold, J. J. Saenz, to be published (2009).4I. Zapata, S. Albaladejo, J. M. Parrondo, J. J. Saenz, F. Sols, arXiv:0905.3796 (2009).
Monte-Carlo Simulations of a Bose Gas in a FluctuatingPotential
M. S. Samoylova1, D. A. Ivanov1,2, T. Yu. Ivanova1,2
1Physical Faculty, Saint-Petersburg State University, Petrodvoretz, Russia2Laser Research Institute, Saint-Petersburg State University, Petrodvoretz, Russia
Experimental facilities used for cooling and trapping of atoms have rapidlydeveloped in the last few years allowing for production of Bose-Einstein con-densates (BEC) of atoms and molecules. One of the promising routes is usingmicro traps or the so called atom chips1. These devices can find potentialapplication in many fields such as, for example, surface investigation, atomicinterferometry, and quantum computing. In most of these applications oneneeds to operate with coherent matter waves. It is, however, evident that allatomic traps, due to technical reasons, have fluctuating trapping potential.This, for instance, is one of the causes of trap loss1. The loss of atoms ormolecules is not the only problem due to trap imperfections. It is also possiblethat the noise leads to loss of coherence in the atomic or molecular ensemblewhile keeping the average number of particles unperturbed. The investigationof such a fluctuation-induced de-coherence is the subject of this contribution.
In a toy model we consider a 1D gas of trapped bosonic atoms interactingvia delta-potential. This system can easily be experimentally realized in microtraps. In addition it is assumed that the minimum of the trapping potentialrandomly moves. In the reference frame of the potential this is equivalent tofluctuation of the center of mass of the cloud. Taking into account quantumcharacter of these fluctuations the equation of motion for the many-particleoperator ρ in the potential reference frame takes the Lindblad form2 ∂ρ
∂t =−i[H, ρ]− θ[X, [X, ρ]]. Here H is the Hamiltonian of the trapped gas, X playsthe role of the center-of-mass position operator. The parameter θ describesthe strength of the potential fluctuations. In second quantization, the modelHamiltonian is H =
∫[ h2
2m∇ψ+(x)∇ψ(x)+V (x)ψ+(x)ψ(x)+U2 ψ+(x)2ψ(x)2]dx.
Here ψ(x) is the field operator, m is the mass, U > 0 is the coupling constantfor the interparticle interaction, and V (x) is an external potential.
To numerically solve the equation of motion we choose the method similarto the Monte-Carlo approach of Ref.3 First the problem is reformulated interms of the Fokker-Planck type equation for the stochastic gauge represen-tation function. Then the corresponding stochastic differential equations arenumerically solved. To simulate the evolution of the interacting gas we find theinitial conditions by solving for the dynamics in imaginary time.
1J. Fortagh and C. Zimmermann, Rev. Mod. Phys. 79, 235 (2007).2G. Lindblad, Commun. Math. Phys. 48, 119 (1976).3P. D. Drummond, P. Deuar, K. V. Kheruntsyan, Phys. Rev. Lett. 92, 040405 (2004).
Bose-Einstein Condensation in Microgravity
S. T. Seidel, H. Ahlers, E. M. Rasel for the QUANTUS Collaboration
Institut of Quantum Optics, Leibniz University Hannover, Germany
The successful demonstration of Bose-Einstein-Condensation in micrograv-ity in 2007 opens the way to realize an atom interferometer operated in theunique environment of weightlessness. Within the QUANTUS project (Quan-tum systems under microgravity) an atom interferometer based on Rubidium87 will be implemented in the drop tower at ZARM, Bremen. The apparatusproduces a BEC of 104 atoms at a temperature of a few nK. In this regime it ispossible to operate an interferometer with a coherent evolution on a timescaleup to 1 second. The atom interferometer is designed as a Mach-Zehnder-schemebased on Bragg-scattering as a coherent beam splitter mechanism.
The produced BEC has a chemical potential of almost 10−31 J and a healinglength on the order of 7 µm. These properties make it an ideal source for thestudy of transport phenomena in disordered potentials.
The QUANTUS project is a collaboration of the U Hamburg, U Ulm, HUBerlin, MPQ Munich, ZARM at U Bremen, and the LU Hanover. It is sup-ported by the German Space Agency DLR with funds provided by the FederalMinistry of Economics and Technology (BMWi) under grant number DLR 50WM 0346.
XRF and XPS investigations of carbon nanowalls
M. Straticiuc, I. Burducea, C. Ionescu
Horia Hulubei National Institute of Physics and Nuclear Engineering - IFIN HHBucharest, Magurele, Ilfov, Romania
Two-dimensional carbon nanowalls (CNWs) were prepared by radiofre-quency plasma-enhanced chemical-vapor deposition (PECVD plasma) at lowpressure, combined with magnetron sputtering. In this paper it has been in-vestigated the presence of impurities in carbon nanowalls structures, due tothe deposition technique. Quantitative measurements in order to determineimpurities concentration or even impurities distribution in our samples are im-perative. Atomic Force Microscopy (AFM) was used to observe their topology.
X-Ray Fluorescence (XRF) and X-ray Photoelectron Spectroscopy (XPS)observations of three different catalyzer samples were made. The results showthe presence of Mo impurities, due to the nozzle used to focus the RF plasmajet. XRF method didn’t allow observation of the Mo spectral lines because theanticathode of the X ray tube is made of the same element. XPS quantitativemeasurements were also performed, although they are affected by errors up to10% because surfaces of the samples haven’t been cleaned. Further experimentswith accelerated ion beam are planned for a better understanding of how theseimpurities influence their properties.
Quantum phase estimation in the presence of phase noisein qubit systems
B. Teklu, S. Olivares, M. G. A. Paris
Dipartimento di Fisica, Universita di Milano, I-20133 Milano, Italy
We address quantum estimation protocols designed to estimate physicalparameters of qubit gates in the presence of phase noise. We derive analyticalformulae for the precision of phase estimation obtainable with qubit probeand show the optimality of equatorial qubit probes. We explicitly evaluatequantum Fisher information and show that ultimate quantum limit to precisionmay be achieved by an observable measurable with current technology. Anexperimental setup for the implementation of the suggested measurement isdiscussed in some details.
Composite Metal-Dielectric Films as Near-FieldSuperlenses
M. D. Thoreson, V. P. Drachev, A. V. Kildishev, Z. Liu, V. M. Shalaev
Purdue University, West Lafayette, Indiana, USA
We have fabricated and studied composite metal-dielectric samples for useas tunable superlenses. Basing our work on the now well-known silver slab su-perlens designs1,2 and the analytical work of Cai and coauthors3, we designeddilute-metal superlenses using silver and silicon dioxide deposited with stan-dard physical vapor deposition processes. Our results show that it is possibleto create a delicate mixture of metal and dielectric constituents, but the fullcharacterization of the fabricated samples is challenging. In particular, theeffective medium theory4 (EMT) technique appears to be insufficent to com-pletely describe the electromagnetic interactions within the composite struc-ture. Finite-difference time domain (FDTD) analyses are under way, and de-riving an acceptable 3D geometry for use in FDTD that properly simulates theactual film structure remains a challenge.
1Z. Liu, N. Fang, T. J. Yen, and X. Zhang, Appl. Phys. Lett. 83, 5184 (2003).2D. O. S. Melville, R. J. Blaikie and C. R. Wolf, Appl. Phys. Lett. 84, 4403 (2004).3W. Cai et al., Phys. Rev. B 72, 193101 (2005).4D. A. G. Bruggeman, Ann. Phys. 24, 636 (1935).
Experiments on Calorimetry of a Bose-EinsteinCondensate
A. Ullah, S. Ruddell, M. D. Hoogerland
Department of Physics, University of Auckland, New Zealand
A Bose-Einstein Condensate (BEC), trapped in a harmonic trap, can becharacterised by the total atom number (N), the internal energy (U) and thetrap frequency (ω). The internal energy has been difficult to measure experi-mentally with any accuracy. However, when a discernible condensate fraction ispresent, the temperature can be measured using time-of-flight. Recently, waysto impart a precisely defined amount of energy on a BEC has been proposedby Blakie et al.1 We are presenting a series of precision calorimetry measure-ments, finding the internal energy of a Bose-Einstein Condensate as a functionof temperature, based on their proposal.
1P. B. Blakie, E. Toth and M. J. Davis, J. Phys. B: At. Mol. Opt. Phys. 40, 3273 (2007).
Supertransmission and light concentration at nanoscale
F. J. Valdivia-Valero, M. Nieto-Vesperinas
Instituto de Ciencia de Materiales de Madrid (CSIC), Madrid, Spain
This work deals with a combination of two subjects in nanophotonics: one isthe phenomenon of anomalous transmission, or supertransmission1,2, througha subwavelength slit; the other pertains to light concentration inside dielec-tric particles by excitation of morphology-dependent resonances (MDR)3,4,5
as either whispering gallery modes (WGM) or localised plasmons (LP).In this study we address particles of nanometric size and show computer
simulation results in the near field range. In order to observe supertransmis-sion by a nanoslit in a metallic slab, we consider p-polarised light. Both thewavelength and the aperture width are adjusted so that the supertransmittedwave also excites the MDRs of nanoparticles in front of the aperture.
Results show enhancements of transmission much larger than from the slitalone, and concentration of both WGM and LP in the particles for these con-figurations. This suggests that the excitation of these resonances produce giant“extraction” of light through apertures, and it is associated to large intensityconcentrations of both WGMs and LPs. Therefore such nanoparticles act as aswitch for light. Several configurations of particle sets are considered.
Figure: Light extraction at λ = 919 nm at a metallic slab nanoslit by means of aWGE31-resonating dielectric nanocylinder.
1F. J. Garcıa-Vidal, L. Martın-Moreno, Phys. Rev. B 66, 155412 (2002).2N. Garcıa, M. Nieto-Vesperinas, J. Opt. A: Pure Appl. Opt. 9, 490-495 (1958).3K. Vahala, Nature 424, 840 (2003).4B. R. Johnson, J. Opt. Soc. Am. A Vol. 10, N. 2 (February 1993).5B. R. Johnson, J. Opt. Soc. Am. A Vol. 11, N. 7 (July 1994).
Left-handed behavior and two-dimensional necklacestates in periodic and disordered sets of dielectric rods
K. Vynck1,2, D. Felbacq1, E. Centeno1, D. Cassagne1, D. S. Wiersma2
1Groupe d’Etude des Semiconducteurs, Montpellier, France2European Laboratory for Non-linear Spectroscopy (LENS), Firenze, Italy
The optical properties of collections of scatterers have been a long-standingtopic and yet are still at the heart of current researches in many areas, includ-ing telecommunications, natural sciences and solar energy. Numbers of originalconcepts and applications are attributed to metamaterials, which, owing to theresonances of their microscopic elements, can exhibit very unusual macroscopicoptical properties. All-dielectric metamaterials have recently received increas-ing attention due to their potential to overcome the scaling and losses issuesexperienced by metallic metamaterials at optical frequencies. In particular,experiments by Peng et al.1 have suggested that collections of dielectric rodscould exhibit a left-handed behavior, i.e. imitate a medium with simultaneouslynegative permittivity and permeability, irrespectively of structural periodicity.These results have however not yet been confirmed theoretically.
In the first part of this work, we give a rigorous theoretical explanationto the origin of the effective permittivity and permeability in periodic arraysof dielectric rods2 by deriving explicit expressions of the electric and mag-netic dipole polarizabilities of isolated rods in the long-wavelength limit. Theappearance of photonic band gaps and left-handed dispersion curves is thenjustified in terms of interacting dipoles. We show that these effects can bereproduced at different frequencies by tuning the rod resonances and illustrateour claim by the numerical demonstration of a true left-handed behavior atoptical frequencies.
In the second part of this work, we study the effect of structural disorderon the optical features of rod arrays, still on the basis of coupled dipoles. Weexplain why photonic band gaps are relatively insentitive to positional disorderand thus, are sustained up to a certain degree of disorder, and find that thepropagation of light in the left-handed range relies on the creation of chains ofresonances, which we identify as two-dimensional microscopic necklace states3.
1L. Peng et al., Phys. Rev. Lett. 98, 157403 (2007).2K. Vynck et al., Phys. Rev. Lett. 102, 133901 (2009).3J. Bertolotti et al., Phys. Rev. Lett. 94, 113903 (2005).
Fabrication and characterization of photonic structureson nanofibers
C. Wuttke1, A. Sehrbrock2, S. Irsen2, A. Rauschenbeutel1
1Division QUANTUM, Institute for Physics, Johannes Gutenberg-Universitaet,Mainz, Germany
2Research Center caesar, Laboratory for Electron Microscopy and Analytics, Bonn,Germany
We present experimental results on the fabrication and characterization ofphotonic structures on nanofibers. They are realized from standard opticalfibers which are flame heated while simultaneously pulling to produce a waistwith a diameter of 500 nm. The photonic structure is then carved out of theultrathin part of the fiber using focused ion beam milling (FIB). An exampleof such a structure can be seen in the figure below. The optical propertiesare spectrally characterized by transmission and reflection measurements. Ourcurrent focus lies on the improvement of the periodicity and the reflectivityof the photonic structures and their use for realizing ultra-low mode-volumeoptical microresonators.
Financial support by the Volkswagen Foundation and the ESF is gratefullyacknowledged.
Figure: Photonic structure carved out by focused ion beam milling in a nanofiber
