Monday February 9, 2009

POSTER SESSION 1

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Photon-number-resolving detection using a detector array for use in quantum optics

I. Afek, A. Natan, O. Ambar and Y. Silberberg

Many experiments in quantum optics require knowledge of the exact number of photons in a

pulse of light. Such experiments include the proposal for linear optics quantum computation and various suggestions for obtaining the Heisenberg Limit with multi-photon entangled states. A number of approaches have been taken to construct detectors with photon number resolution, these include cryogenic devices such as the VLPC [1] a superconducting bolometer [2] and time multiplexing [3]. Here we present an experimental study of the use of a Multiple Pixel Photon Counter (MPPC) (Hamamatsu) for photon number resolved single photon measurements. We show that the MPPC is an attractive candidate for use in quantum optics.

The MPPC consists of an array of Avalanche Photo Diode (APD) pixels operating in Geiger mode. Each APD pixel outputs a pulse signal when it detects a photon. The signal output of the MPPC is the total sum of the outputs from all APD pixels. To evaluate the MPPC we used a pulsed laser (Tsunami, Spectra-Physics) λ = 810 nm with a rep rate of 1 MHz reduced from 80 MHz using a pulse picker (Pulse Select, APE).

The MPPC has very good photon number resolution up to N=10 as can be seen in Fig 1. In addition it can be operated at the relatively high rep rate of ~1MHz. The MPPC does not require any type of cooling or additional optical auxiliary setup, making it much simpler and cheaper than the other available photon number resolving solutions. We obtained a dark count rate of ~0.003 photons per pulse using gated detection. In addition, the MPPC pixels exhibit a small degree of cross-talk which may be easily compensated for by using a method which we have developed, see Fig 2.

The main limitation of the MPPC is that its peak detection efficiency is currently at 400 nm

with an efficiency of only ~10 % at 800 nm. We expect that the MPPC will be shortly available with peak efficiency at 800 nm making it an invaluable tool for quantum optics in the near future. [1] J. Kim, S. Takeuchi, Y. Yamamoto and H.H. Hogue 1999, Appl. Phys. Lett.,74 902 [2] B. Cabrera et. al. 1998, Appl. Phys. Lett.,73 735 [3] D. Achilles et. al. 2004, J. Mod. Opt. ,51 1499

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Fig 1: Pulse height histogram measured with MPPC for average photon number nav = 2.3.

Fig 2: Measured photon number distribution (bars) and best fit for coherent state (squares)

for nav = 1.65. Left pane: raw data. Right pane: data corrected for cross-talk.

Photon Localization and Dicke Superradiance in Atomic Gases§

E. Akkermans1,2, A. Gero1, and R. Kaiser3

1Department of Physics, Technion—Israel Institute of Technology, Haifa 32000, Israel 2Department of Applied Physics and Physics, Yale University, USA

3Institut Non Line´aire de Nice, UMR 6618 CNRS, France We study photon emission rates from an atomic gas while taking into account cooperative effects, such

as superradiance and subradiance, between the scatterers. To this purpose we consider N identical

atoms, placed at random positions in an external radiation field. The photon escape rates from the

atomic gas are derived by diagonalizing an N×N Euclidean random matrix U for a broad range of

sample size and disorder strength. For a three-dimensional geometry Uij = sin(xij) / xij , while for a one-

dimensional gas Uij = cos(xij), where xij is the dimensionless random distance between any two atoms.

A scaling function, which measures the relative number of states having vanishing escape rates, is

introduced. We find out that for a large sample of three-dimensional gas the photons undergo a

crossover from delocalization towards localization rather than a disorder-driven phase transition as for

Anderson localization. By using a stochastic Markov model, we show that photon localization is

primarily determined by cooperative effects and not by disorder, and a disorder-induced phase

transition is unlikely to take place. For one dimensional geometry, due to the periodic nature of the

coupling matrix, the single atom limit is never reached and the photons are always localized.

This crossover from delocalization towards localization also provides an interesting link to the recently

studied "small world networks" which exhibit a crossover, rather than a phase transition, between

regular (ordered) lattices and random networks.

§E. Akkermans, A. Gero, and R. Kaiser, Phys. Rev. Lett. 101, 103602 (2008)

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Incoherent Surface-Solitons in Effectively- Instantaneous Nonlinear Media Barak Alfassi, Carmel Rotschild, and Mordechai Segev

Physics Department and Solid State Institute, Technion, Haifa 32000, Israel eorddba@tx.technion.ac.il

Surface waves, propagating at the interface between two media with different optical properties, are intriguing phenomena. Optical surface wave were studied both in the linear domain [ 1, 2, 3], and in the nonlinear domain, [ 4, 5, 6]. However, until recently, it was believed that incoherent spatial solitons can exist only in a non-instantaneous nonlinearity whose the response time τ is much slower than the fluctuation time tc of the incoherent field (τ >>tc). However, nonlocal nonlinearities can overcome this obstacle, as was recently proposed and demonstrated [ 7 8].

Here, we present the first experimental and theoretical study of incoherent surface-solitons in instantaneous nonlocal nonlinear media: self-trapped incoherent beams propagating between linear and a nonlocal effectively-instantaneous nonlinear medium. As a model system for a long-range nonlocal nonlinear medium, we use the thermal nonlinearity of lead glass [ 8]. Figure 1 shows a sketch of a sample of width 2d with all the relevant boundary conditions [ 6]. We first neglect the interference terms and find the modes forming an incoherent solitons in non-instantaneous nonlinearities (Fig. 2a,b). The linear diffraction of such beam is depicted in (Fig 2c). Then, we use those modes (Fig.2a) as the initial condition to simulate surface soliton in our instantaneous nonlinearity. Under these conditions, one can think of an incoherent beam as an ensemble average over a sequences of different realizations r =1,2… , each of a duration ct . Fig. 2d shows the simulated propagation of three random realizations. Although each realization has a different initial intensity distribution and is propagating at a different trajectory, all of them are self trapped near the interface. The ensemble average over 200 realizations is depicted in Fig. 2e-f, the time-averaged beam is self-trapped, forming a incoherent surf-soliton that showing no evidence of broadening or statistical nonlinear diffraction, as is the case for incoherent bulk soliton [ 7, 8]. Experimentally, we pass an 80µm FWHM 488nm coherent laser beam through a diffuser and then launch it into a lead-glass sample of dimensions 2x2x80 mm3. The experimental results, depicted in Fig 3, show (a) an incoherent (ensemble-averaged) surface soliton, (b) an incoherent input beam attracts to the surface, (c) linear diffraction of such beam, and (d) a single realization of the multimode surface waves.

To conclude, we presented the first experiments & theory of surface-solitons in instantaneous nonlocal nonlinearities. 1. W. L. Barnes, A. Dereux, and T.W. Ebbesen, Nature 424, 824 (2003) 2. P. Yeh, A. Yariv, and A.Y. Cho, Appl. Phys. Lett. 32, 104 (1978). 3. D. Artigas, and L. Torner, Phys. Rev. Lett. 94, 013901 (2005). 4. G. S. Garcia Quirino et al., Phys. Rev. A 51, 1571 (1995); M. Cronin-Golomb, Opt. Lett. 20, 2075 (1995). 5. S. Suntsov, et al., Phys. Rev. Lett. 96, 063901 (2006). 6. B. Alfassi, et al., Phys. Rev. Lett. 98, 213901 (2007); A. Barak, et al., Opt. Lett. 32, 2450 (2007). 7. O. Cohen, H. Buljan, T. Schwartz, J. W. Fleischer, and M. Segev, Phys. Rev. E, 73, 015601 (2006). 8. C. Rotschild, T. Schwartz, O. Cohen, and M. Segev, Nature Photonics 2, 371 - 376 (2008).

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Fig. 2.

Fig. 1.

Fig. 3.

Diode-pumped alkali vapor lasers: the next generation of high power lasers?

B. D. Barmashenko and S. Rosenwaks

Department of Physics, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel Diode-pumped alkali lasers (DPALs) convert un-phased low beam quality radiation from diode laser arrays into coherent, high quality ~ 800 nm wavelength radiation of alkali (Cs, Rb) atoms. The diode laser in-band pumping of the higher fine-structure level 2P3/2, via the D2 (2S1/2 → 2P3/2) transition, is followed by rapid relaxation of 2P3/2 to the 2P1/2 fine-structure level and lasing on the D1 (2P1/2 → 2S1/2) transition. DPALs developed during the last several years have attracted increasing attention because of their potential to achieve high power with a high quality beam.

For currently developed low power (< 100 W) DPALs there is no need to replenish the gas mixture. However, at higher, e.g., ~ 100 kW powers, the heat release due to relaxation between the fine-structure levels of the alkali atoms reaches several kW and there is a need to flow or at least transport the gas in a closed system to decrease the temperature.

We are currently developing a model of a gas flow DPAL with the flow direction either transverse (perpendicular) or parallel to the optical axis of the resonator. The gain g and the available lasing power Pav in such systems are strongly non-uniform in the transverse direction due to the following reasons: Firstly, in the currently used systems the pumping beam is focused into the alkali-vapor cell so that the diameter of the pumping beam waist (< 100 μm) is smaller than both the mirror aperture and the laser beam waist. As a result the pumping rate and population inversion strongly change in the transverse direction. Secondly, in transverse flow DPALs the temperature increases in the flow direction. Due to the quasi-equilibrium between the fine-structure levels of the alkali atoms the temperature strongly affects the population of the upper laser level 2P1/2. This effect is especially important in Cs where the spin-orbit splitting EΔ is 800 K, the initial temperature T = 450-500 K and in a static cell it might be a few hundreds K higher. As a result, even if the cell is pumped by many diodes and the pumping is spatially uniform, both g and Pav strongly change in the transverse direction and depend on the flow velocity.

For the simplest case of the spatially uniform pumping we derived the following expression for the small signal gain on the lasing D1 transition

Athbb

bthstim n

IITkETkETkE

IIg)/)](/exp(3[1)/exp(

1)/exp()1/(

Δ++−Δ−Δ

−= σ , (1)

where stimσ is the stimulated emission cross section, I the intensity of the pumping beam,

1)/exp()/exp(2

−ΔΔ+

≡TkE

TkEhIb

b

absth τσ

ν , the threshold pumping intensity and nA the density of the alkali atoms.

It is seen that for small EΔ , due to the factor 1)/exp( −Δ TkE B , g strongly decreases and Ith strongly increases with increasing T. Hence it is indeed very important to avoid the excessive heating of the system, i.e., to flow the alkali vapor.

We calculated the small signal gain and temperature spatial distributions for transverse flow DPALs and their dependence on the power and diameter of the pumping beam and the flow velocity, and found the optimal beam and flow parameters corresponding to the maximum gain and minimum temperature gradients. The optimal system geometry and pumping parameters for high power operation are predicted.

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Nonlinear optics in structured functionalized waveguide array

Nadia Belabas*1, Juan Ariel Levenson1, Christophe Minot2,1 and Jean-Marie Moison1 1 Laboratory of Photonics and Nanostructures -UPR20 CNRS, Route de Nozay, Marcoussis, F-91460, France

2Institut Telecom / Telecom ParisTech, 46 rue Barrault, 75634 Paris Cedex 13, France *Corresponding author: nadia.belabas@lpn.cnrs.fr

Manipulation of light propagation in the guided regime has been pursued for a long time [1] to combine the best of two worlds (the control of propagation of the guided regime with the flexibility of free-space design).

Fig 1 Coupling in homogeneous arrays (grey frame, left) enables diffraction engineering and soliton creation and steering in the non linear regime. Structuring the coupling constant (green frame, right) opens a whole world of signal processing functions. We show how patterning the coupling constant between neighboring waveguides leads to a complete set of signal processing functions such as redirecting, guiding, focusing, and routing (Fig 1 right) in contrast with demonstration of stimulating effects in the literature [2] involving mostly propagation in homogeneous and infinite arrays (Fig 1 left). We detail how discrete photonics in such a functionalized space are similar but not identical to their continuous counterparts. Building blocks for discrete photonics device are thus simulated and open new routes to develop alloptical signal processing in the linear and non-linear regime. Finally we exemplify the benefit of patterning the coupling constant on the paradigmatic problem of commuting and modulating light flow via a controlling beam (Fig 2). 1) The pump power threshold associated to usual schemes [3,4] involving homogeneous waveguide arrays can be significantly lowered when divergence of the pump is suppressed using a channel of higher coupling constant between two semi-infinite barrier of lower coupling constant [5]. 2) One conceptual step further, tuning the resonances of a double barrier structure is demonstrated to yield a threshold-less device whose transmission curve can be, in addition, inverted by tuning the incidence angle on the device (Fig 2).

Fig 2 Combining a structured functionalized space with non linear optics in coupled waveguide arrays. The red arrow represents the pump field. Orange curve and corresponding input field arrow of the device sketched in the gray frame: homogeneous array approach in the literature. Blue curves and arrow in the corresponding sketch: structuring the coupling constant to suppress the divergence of the pump. Green curves and arrows in the corresponding sketch: accessing the levels of discrete Fabry-Perot for a controllable threshold-less modulator.

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1. A. L. Jones J. Opt. Soc. Am. 55, 261 (1965). S. M. Jensen, IEEE J. Quantum Electron. QE-18, 1580 (1982). A. B. Aceves and M. Santagiustina Phys. Rev. E 56, 1113 (1997). I. Garanovich, A. Sukhorukov, and Y. Kivshar Opt. Express 13, 5704-5710 (2005) 2. D. N. Christodoulides, F. Lederer and Y. Silberberg, Nature 424, 817-823 (2003). J. Fleischer, G. Bartal, O. Cohen, T. Schwartz, O. Manela, B. Freedman, M. Segev, H. Buljan, and N. Efremidis, Opt. Express 13, 1780-1796 (2005) 3. D. N. Christodoulides and E. D. Eugenieva Phys. Rev. Lett. 87, 233901 (2001). 4. J. M. Moison and C. Minot, French Patent n° 07 54872 (2007). Nadia Belabas, Sophie Bouchoule, Isabelle Sagnes, Juan Ariel Levenson, Christophe Minot and Jean-Marie Moison submitted (2008) 5. J. M. Moison and C. Minot, French Patent n° 08 05307 (2008). J. M. Moison, N. Belabas, C. Minot, and J. A. Levenson to be submitted (2008)

Strong Field Coherent Control Using 2D Spatio-Temporal Mapping

B. D. Bruner, H. Suchowski, and Y. Silberberg Dept. of Physics of Complex Systems, Weizmann Institute of Science, Rehovot, 76100 Israel e-mail: Barry.Bruner@weizmann.ac.il

Strong field multiphoton excitation in a three level resonant system was controlled by a 2D spatio-temporal scheme, in which quadratic phase and a second, arbitrary phase parameter are scanned using a pulse shaper. The parameter space is mapped onto a two-dimensional landscape, as described in detail in our earlier work [1]. In the present experiment, a 100 fs ultrashort laser pulse laser centred at 780 nm covered both the 5S1/2 5P3/2 (780 nm) and the 5P3/2 5D1/2 (776 nm) resonant transitions in Rb85. A π-step phase was scanned across the spectral envelope using a programmable liquid crystal Spatial Light Modulator (SLM), aligned in a standard 4-f configuration.

Fig. 1. (left) 2D spatio-temporal maps of Rb85. The excited state fluorescence (from the 5D1/2 level) is plotted in a 2D grid as a function of π-step position (vertical axis) and the quadratic spectral phase (GDD) of the excitation pulse (horizontal axis). The peak intensities at zero GDD are (a) 130, (b) 60, (c) 24, (d) 10 GW/cm

2

. (right) Population transfer in a dressed three level system using chirped pulses. Several key features emerge in the weak-to-strong field mappings. The maximum enhancement does not occur at zero GDD, but rather for combinations of specific π-step and GDD values (also seen from dressed state picture in Ref. [2]). For strong fields, the adiabatic population transfer occurs for at negative GDD via a process that is analogous to the counterintuitive pathway in STIRAP. The resonant transition frequencies are strongly dependent on the fluence. As the fluence is increased, the resonant enhancement features broaden and shift from their intensity independent values and acquire a pronounced curvature for small GDD. These spatio-temporal mappings should be an effective method for strong field coherent control in a variety of multilevel systems. [1] H. Suchowski, A. Natan, B. D. Bruner, Y. Silberberg, J. Phys. B. 41 (7), 074008/1-9 (2008). 2] M. Wollenhaupt, A. Praekelt, C. Sarpe-Tudoran, D. Liese, T. Baumert, Appl. Phys. B 82 (2), 183-188 (2006

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Strong Field Atomic Population Transfer Stephen D. Clow1, Carlos Trallero-Herrero2, Thomas Bergeman1, and Thomas Weinacht1

1Department of Physics, Stony Brook University, Stony Brook, NY, 11794, USA 2National Research Council of Canada, 100 Sussex Drive, Ottawa, Canada

There is significant interest in controlling atomic and molecular dynamics using shaped ultrafast laser pulses, an important aspect of which is selectively populating a particular target state with high efficiency. To achieve this beyond the limits of single-photon excitation, one has to consider multiple interfering pathways and dynamic Stark shifts (DSS), which make resonance conditions time-dependent and substantially modify the phase advance of the bare states during the atom/molecule-field interaction1. In this work, we demonstrate strong-field atomic population transfer in a three-level system via three-photon absorption from a single shaped ultrafast laser pulse. The optimal pulse shape for efficient population transfer is discovered using closed-loop learning control (Fig. 1) and interpreted via pulse shape parameter scans and numerical integration of the Schrodinger equation (Fig. 2). In Fig. 2b the solid, dashed, dashed-dot, and red curves represent the pulse envelope, ground, intermediate, and excited states, respectively. We show a population inversion can be achieved and measured using a combination of spontaneous and stimulated emission2. Our interpretation of the pulse shape dependence illustrates the advantages of sequential population transfer over adiabatic rapid passage with multiphoton coupling between levels3. We are currently applying strong-field control over single atom dynamics to the collective emission from ensembles of atoms (i.e. superfluorescence ). 1. C. Trallero-Herrero, et.al. Phys. Rev. A 74, 051403 (2006) 2. C. Trallero-Herrero, et.al. J. Phys. B: At. Mol. Opt. Phys. 41, 074014 (2008) 3. S. Clow, et.al. Phys. Rev. Lett. 100, 233603 (2008)

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Figure 2: (a) Calculated Wigner distribution for the experimentally

determined chirp rate. (b) Corresponding electronic dynamics and pulse envelope.

Figure 1: Wigner distribution of an experimentally retrieved optimal pulse.

(a)

(b)

Towards high fidelity single ion-qubit gates

Yoni Dallal, Nitzan Akerman, Yinnon Glickman, Shlomi Kotler, Ana Weksler and Roee Ozeri

Weizmann Institute of Science, Rehovot 76100, Israel

Fault tolerant quantum error-correction schemes requires the implementation of high fidelity quantum

gates. The fidelity of a quantum gate is defined as ˆ| |F ψ ρ ψ=< > where |ψ > is the ideal final state

and ρ̂ is the density operator of the real final (mixed) state. We designed and built a system that will

implement high fidelity stimulated Raman gates on single trapped 88Sr+ ion-qubits. Our qubit levels

are the two Zeeman states of the 1 25S electronic ground level, separated by 2.8MHz G . Raman

transitions are induced by an External Cavity Diode Laser, where the Laser diode used is a violet LD

of 405nm, off-resonance with the transitions to the 1 25P and 3 25P levels at 422 and 408 nm

respectively. The two, co-propagating, Raman beams are the two polarization components of the

405nm light where one polarization component phase modulated at the qubit Level separation by an

EOM. The Rabi frequency is directly monitored by mixing down the beat-note of the two Raman

beams and actively stabilized using feedback control. A Field Programmable Gate Array card is used

to implement the control electronics with the advantage of flexibility and better integration with the

experiment. Classical noises were suppressed such that the expected error ( 1 Fε = − ) is expected to be

quantum limited due to spontaneous scattering of photons and smaller than 410− .

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Magnetic Interactions of Cold Atoms with Anisotropic Conductors

T. David1, Y. Japha1, V. Dikovsky1, R. Salem1, C. Henkel2 and R. Folman1 1Atom Chip Group, Ben Gurion University, Israel: www.bgu.ac.il/atomchip

2Universität Potsdam, Germany An atom chip is an apparatus where isolated cold atoms are trapped microns above the chip surface, creating a solid state device with long coherence times. One of the limitations on the lifetime and coherence of atoms trapped above the surface is the interaction of the atoms with current fluctuations in the wire, which is usually not ideal and held in room temperature. This work is focused on extending these coherence times so that the atom chip may offer new experimental opportunity to investigate the foundations of quantum mechanics (e.g. interferometry and decoherence) as well as serve as a base for quantum technology including clocks, sensors and quantum information processing and communications. We analyze atom-surface magnetic interactions on atom chips where the magnetic trapping potentials are produced by current-carrying wires made of electrically anisotropic materials. We present a theory for time-dependent fluctuations of the magnetic potential, arising from thermal noise originating from the surface. It is shown that using materials with a large electrical anisotropy results in a considerable reduction of heating and decoherence rates of ultra-cold atoms trapped near the surface, of up to several orders of magnitude, also at room temperature. We also show that spatial fluctuations of the currents in the wire, which cause static perturbations in the magnetic potential along the wire, may be significantly reduced by replacing conventional wires with wires made of electrically anisotropic materials. This improvement may allow use of these wires to generate smooth potentials for guiding and trapping ultracold atoms very close to the surface. Materials, fabrication, and experimental issues are discussed, and specific candidate materials are suggested.

Figure. Lines: spin decoherence rate as a function of electrical anisotropy r = σxx/σyy, for layered and quasi-1D conducting materials. For these lines, the good conductivity along the wire was assumed to be identical to that of Au. For layered materials having the badly conducting axis along the wire thickness (dashed red) the dependence on the anisotropy is negligible.

References: T. David et al., Euro. Phys. Jour. D48, 321, (2008). This paper was chosen by the editors of EPJ as a “Highlight Paper”, and Tal David, the author, has just been chosen for a Graduate Student Award by the U.S. Materials Research Society.

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Generation of Airy Beams with Quadratic Nonlinear Photonic Crystals

Tal Ellenbogen, Noa Voloch, Ayelet Ganany-Padowicz, Ady Arie Dept. of Physical Electronics, Faculty of Engineering, University of Tel-Aviv, Tel-Aviv 69978

e-mail address: ellenbog@post.tau.ac.il Last year Siviloglou et al [1] reported the first experimental observation of a new class of optical beams with non-diffracting wave packets that accelerate in free space. Up until now, these beams were generated by linear reflection from a spatial light modulator. We demonstrate a new method for generating Airy beams by a three-wave mixing process in a quadratic nonlinear photonic crystal. The nonlinear generation enables to obtain Airy beams at new wavelengths, and opens new possibilities for switching and manipulating these beams. To generate the Airy beam we designed a quadratic nonlinear photonic structure with the following poling function of the quadratic coefficient: χ(2)(x,y)=sign{cos[2π(fxx+fcy3)]}, where fx is the spatial frequency of the modulation in the beam’s propagation direction and fc controls the strength of the cubic modulation in the transverse direction. The structure is illustrated in Fig. 1 (a). We manufactured the proposed structure in a 0.5mm thick z-cut stoichiometric lithium tantalite crystal and designed it to generate an Airy beam at the second harmonic of a single mode Gaussian Nd:YLF pump laser. We performed an optical Fourier transform to the output of the nonlinear photonic crystal, using a lens of 100 mm focal length, and recorded the propagation dynamics of the Fourier transformed pump and second harmonic waves. Figure 1 (b) shows a profile photograph of the green second harmonic Airy beam and Fig. 1 (c) and (d) shows the propagation dynamics of the output pump wave and the output second harmonic wave respectively. The output pump wave has a Gaussian beam propagation dynamics with slight intensity modulations which might be caused by small linear variations in the crystal due to the poling process. The output second harmonic beam shows the propagation dynamics of a truncated Airy beam, i.e., nearly non-diffracting and “freely accelerating” to one side. In addition to generating Airy beams at new wavelengths as shown here, the nonlinear interaction enables new exciting possibilities, e.g., to all-optically control the acceleration rate and the acceleration direction of the Airy beam.

ω 2ωFar field

χ(2)ω 2ω

Far field

χ(2)

FH p

rofil

e [m

m]

Propagation direction [mm]0 100 200 300 400

-3-2-10123

SH

pro

file

[mm

]

Propagation direction [mm]0 100 200 300 400

-3-2-10123

(a) (b)

(c) (d)

Fig. 1. (a) Illustration of the nonlinear structure. (b) Photograph of green Airy beam at the second harmonic. Propagation dynamics of (c) output fundamental wave and (d) output second harmonic wave. [1] G. A. Siviloglou, J. Broky, A. Dogariu, and D. N. Christodoulides, Phys. Rev. Lett. 99, 213901 (2007).

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Monolithic vertical cavity laser with a saturable absorber : towards an integrated cavity

soliton laser T. Elsass, S. Barbay, K. Gauthron, G. Beaudoin, I. Sagnes and R. Kuszelewicz

Laboratoire de Photonique et de Nanostructures, CNRS-UPR20, Rte de Nozay, 91460 Marcoussis, France.

email : tiffany.elsass @lpn.cnrs.fr Summary Cavity solitons in semiconductor systems have been first demonstrated in optical amplifiers, and recently in a laser with external grating feedback. We propose an original design of a monolithic and integrated vertical cavity laser with saturable absorber and discuss experimental results showing the formation and control of bistable laser spots. Cavity solitons (CSs) are self-localized spots appearing in the transverse plane of a nonlinear cavity. Their existence is now well established, in particular in semiconductor systems [1,2] where most of the potential applications reside. They have also been recently found in a laser system [3] consisting in a vertical cavity surface emitting laser (VCSEL) with an external feedback grating and two mutually-coupled VCSELs [4] in presence of saturable absorption. One of the main advantages of a CS laser relies on the fact that it is a source and not an amplifier, thus making it easier to cascade several CS devices for optical information processing, while being generally simpler to operate. Indeed there is no need anymore for a coherent injection making it much more attractive and cost effective. We have designed and fabricated a monolithic, optically pumped VCSEL structure with intracavity gain and saturable absorber sections [5].We show experimental results obtained in different samples with different gain-to-saturable absorber lifetime ratios. Several regimes are identified close to threshold. One of them is a stationnary regime with the appearance of bright spots (Fig.1 left). These spots appear sub-critically (Fig.1 center) and can be excited and erased repetitively with externally addressed local excitation pulses as short as 60ps, at a maximum repetition rate of 80MHz. These pulses act principally as a kink on the carrier density distribution. Another regime corresponds to self-pulsing (Fig.1 right). We shall discuss the observed temporal dynamics in relation with the spatial response.

Fig. 1: Left : Average near-field intensity image of the system in the bistable regime. Center : Bistable output vs pump characteristics. Right : Pulsing regime of period 9ns. We ackowledge support from the European project IST-STREP FunFACS. References [1] S. Barland et al., Nature 445, 699 (2002). [2] S. Barbay et al., Optics Letters 31, 1504 (2006). [3] Y. Tanguy et al., Physical Review Letters 100, 013907 (2008). [4] P. Genevet et al., Physical Review Letters, 101, 123905 (2008). [5] S. Barbay et al., report on the FunFACS IST-FET-STREP Project #4868

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High accuracy space-time positioning

beyond the standard quantum noise limit

C. Fabre, N. Treps, G. De Valcarcel, G. Patera, O. Pinel, B. Chalopin, B. Lamine

Laboratoire Kastler Brossel Université Pierre et Marie Curie-Paris6, ENS, CNRS 4 Place Jussieu, CC74, 75252 Paris cedex 05, France

fabre@spectro.jussieu.fr Accurate space-time positioning is an important issue of physics, both from a fundamental perspective and for its numerous practical applications. Considering successively the spatial and temporal positioning methods using optical methods, we demonstrate that there is a basic quantum limit to their accuracy, independent of the measurement protocol, when one uses shot noise limited light. We will then show how to reach this standard quantum noise limit. Finally we will show that his limit can be circumvented using a specifically designed quantum-entangled non-classical light beam, resulting from the superposition of a coherent state and a vacuum squeezed state in two different spatial or temporal modes. An OPO synchronously pumped by a mode-locked laser (the OPO cavity length is equal to the spatial distance between successive pulses) turns out to be a very efficient device to produce squeezed states when the pump intensity is slightly less than the oscillation threshold. Squeezing is effective not in a single frequency mode, as usual, but instead in a whole set of "super-modes", which are well defined linear combinations of signal modes of different frequencies, i.e. of trains of pulses of well defined shapes. Such modes are precisely the ones needed to improve time positioning measurements. We will also report on the progress of the experiment that we are currently developing to produce such squeezed and/or entangled frequency combs.

We finally describe a scheme that allows us to beat the standard quantum limit in clock synchronisation and ranging measurements, which could be used in space experiments where losses are small and high precision needed. It is based on the use of a homodyne technique with squeezed frequency combs and local oscillator pulses in appropriately shaped super-modes, and turns out to be less sensitive to phase noise than other proposed techniques based on few-photon entangled states. N. Treps, N. Grosse, C. Fabre, H. Bachor, P.K. Lam, “The "Quantum Laser Pointer"", Science 301, 940 (2003) V. Delaubert, N. Treps, C. Fabre, H. Bachor, P. Réfrégier, “Quantum limits in image processing” Europhys. Letters 81 44001 (2008) B. Lamine, C. Fabre, N. Treps, “Quantum improvement of time transfer between remote clocks” Phys. Rev. Letters 101 123601(2008)

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Ultrafast electron dynamics at the DNA-Au interface studied by time-resolved two-photon

photoemission and femtosecond pulse shaping

B. Golana , Z. Fradkina , T. Markusa , D. Oronb , and R. Naamana*

a) Dept. of Chemical Physics

b) Dept. of Complex Matter Physics

The Weizmann Institute of Science, Rehovot 76100, Israel

The dynamics of electronic excitations at molecule-metal interfaces is crucial for understanding

interfacial charge transfer at molecular electronic based devices. In addition, the electronic properties

of oxidized DNA bases and their interaction with low energy electrons are important for understanding

radiation related DNA damage.

Using an experimental set up that combines photoelectron imaging, two-photon photoemission

(2PPE), and spectral phase and polarization pulse shaping we investigated the dynamics of electron

transfer through self assembled single strand DNA monolayers containing oxidized bases on gold

films.

By imaging of the photoelectrons angular distribution, it was found that the organic DNA monolayer

filters the electron emission angles, permitting mainly emission normal to the surface. In addition,

chirped-pulse 2PPE validates that upon adsorption of DNA a two photon absorption process which

involves high energy intermediate states is preferred. The electronic dispersion of these states was

investigated using angle-resolved 2PPE, and a difference has been observed between the electron

localization in the DNA-induced surface states and states on bare Au.

By applying time-resolved 2PPE measurements, we obtained the population dynamics in transiently

populated electronic states in the DNA-induced surface.

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Inelastic collisions near Feshbach resonances in ultra-cold 7Li

Noam Gross, Zav Shotan and Lev Khaykovich Department of Physics, Bar-Ilan University, Ramat Gan, 59200 Israel

Recently we reported on a successful achievement of 7Li Bose-Einstein condensate (BEC) by means of forced evaporation in a crossed-beam optical trap [1]. The method requires the use of Feshabch resonances in order to tune elastic collision rate. However, the inelastic processes such as dipole relaxation and three-body recombination show dramatic enhancement in the vicinity of Feshabch resonances and may limit atom densities and trap lifetime [2]. Indeed we obtained only a few hundreds of atoms in the BEC and its lifetime was extremely short. We inveatigate two- and three-body losses in the vicinity of two Feshbach resonances on the |F=1,mF=0> state. Fig. 1 shows the remaining atoms after preliminary evaporation that was performed at different magnetic fields for two durations (1.4 s and 6 s). Two minima indicate the location of Feshabch resonances. For short evaporation time maximum of remaining atoms is achieved between the resonances while for long evaporation time it appears before the first resonance. Thus, inelastic processes are very strong in-between the resonances despite the presence of a zero crossing point where scattering length vanishes. In the region of strong inelastic losses short lifetimes and quick drop in density are obtained (Fig. 2). Fig. 2a shows the atom density after 100 ms (empty squares) and 10 s (filled circles) of waiting time at a given magnetic field. By measuring lifetime of atoms in the trap (Fig 2b) we extract two- and three-body loss coefficients. At a magnetic field of 870 Gauss (empty circles) two-body loss coefficient is measured to be β = 1.16*10-13 cm3/sec, an order of magnitude higher than at 824 Gauss (filled triangles) where it already returns to its zero field value of β = 1*10-14 cm3/sec. The upper limit for three-body loss at 870 Gauss is K=9.5*10-26 cm6/sec. The investigation of the inelastic losses allows us to find an optimal magnetic field for evaporation and increase the number of atoms in the BEC by a factor of 10. [1] N. Gross and L. Khaykovich, Phys. Rev A 77, 023604 (2008). [2] S. Inouye et.al., Nature 392, 151 (1998); J. Stenger et.al. Phys. Rev. Lett. 82, 2422 (1999) ; J.L. Roberts, et.al., Phys. Rev. Lett. 85, 728 (2000).

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Spatiotemporal Pulse-Train Solitons Hassid C. Gurgov and Oren Cohen

Solid state institute and physics department, Technion – Israel Institute of Technology, Haifa, Israel gurgov@tx.technion.ac.il

We propose spatiotemporal solitons that consist of trains of short pulses. The pulses are collectively trapped in the

transversal directions by a slow nonlinearity and each pulse is selftrapped temporally by a fast nonlinearity. A spatiotemporal optical soliton is a self-localized entity that maintains its shape in the longitudinal (temporal) direction as well as in its transversal direction(s) through a robust balance between diffraction, group velocity dispersion and nonlinearity.1,2 However, spatialtemporal pulses in Kerr media are unstable. Several possibilities to allow the existence of spatiotemporal solitons were considered, yet, the only successful experiment in this field was the creation of (1+1+1)D spatiotemporal solitons through the process of phase-mismatched second harmonic generation in quadratic nonlinear media.3 The experimental demonstration of selflocalized entity in three dimensions is still considered a ‘grand challenge’ in nonlinear optics [1]. We propose a new kind of spatiotemporal solitons: pulse-train solitons. This soliton consists of short pulses that are collectively trapped in the spatial (transversal) domain by a slow selffocusing nonlinearity (e.g. thermal) whose nonlinear response time is much larger than the time between adjacent pulses, T, and each pulse is self-trapped in the temporal domain by an instantaneous (e.g. Kerr) nonlinearity (Fig. 1a). We solved theoretically and demonstrate numerically (1+1+1)D pulse-train solitons in a medium with both the optical Kerr nonlinearity and a slowly-responding and highly-nonlocal self-focusing nonlinearity. Figure 1b show the intensity of a single pulse in the train where x and t are the dimensionless transverse direction and time, respectively. The pulse is much more confined in x than in t because the slow nonlinearity is much stronger that the Kerr nonlinearity. The slow nonlinearity, which is transparent to the fact that the beam consists of pulses, leads to the formation of a spatial soliton. Each pulse is injected into a waveguide that was induced in the medium by former pulses in the train and can self-tapped temporally by the Kerr nonlinearity, similarly to temporal solitons in fibers. We verified the stability of this pulse-train soliton by simulating the propagation with 5% initial noise in amplitude and phase (Fig. 2b).

Figure 1: (a) schematic of pulse-train solitons. (b,c) Numerical example of (1+1+1)D pulse-train soliton in medium with both Kerr nonlinearity and with slow and highly nonlocal self-fucusing nonlinearity. (b) Intensity of a pulse in a pulse-train solitons © Peak intensity as a function of the propagation distance. The pulse train soliton consist of pulses shown in plot (a). The dispersion length (the distance in which the width of the pulse is broaden by a factor of 2) is z=103. The pulse propagates over 100 dispersion lengths with only small variations in its shape. The periodic variations in the peak intensity result from beating between multiple modes of the induced waveguide. Higher order modes are slightly populated because the initial beam includes 5% noise in the amplitude and phase. References [1] F.Wise, P. Trapani, “Spatiotemporal optical solitons,” OPN 13, 28-32 (2002) [2] Y. Silberberg, “Collapse of optical pulses,” Opt. Lett. 15, 1282 (1990). [3] R. Chiao, E. Garmire, C.Townes, “Self-trapping of optical beams,” Phys. Rev. Lett. 13, 479 – 482 (1964)

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Generation of intense keV attosecond pulses

W. Helml¹, G. Marcus¹, Y. Deng¹, V. S. Yakovlev², K. Schmid¹, X. Gu¹, R. Kienberger¹,³, F. Krausz¹,²

¹ Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, D-85748 Garching, Germany

² Department für Physik, LMU München, Am Coulombwall 1, D-85748 Garching, Germany ³ Physik Department, Technische Universität München, James Franck Str., 85748 Garching, Germany

We investigate the possibility of increasing the harmonic yield in the keV-region by using a freely adjustable multi-gas-jet array to modulate the target density for quasi-phasematching during the harmonic build-up process [1]. To push attosecond-pulse generation towards higher photon energies compared to HHG driven by the conventionally used Ti:Sa lasers [2], we developed a 2.1 µm few-cycle OPCPA system [3] to extend the energetic cut-off (Ecutoff ~ λ2

driv). Coherent growth of soft x-ray radiation during HHG is primarily restricted by the increasing ionization of the gas, which gives rise to dephasing between the fundamental laser and the generated harmonic field. A fundamental limit of the build-up process is reached when this phase-mismatch equals π, at which point there evolves destructive interference between different contributions to the harmonic wave. It has recently been demonstrated [4] that already the use of two gas nozzles can increase the effective coherence length by a factor of four (Figure 1.a).

Our approach of quasi-phase-matching in the multi-jet gas target has two main advantages (Figure 1.b). On the one hand each source can be optimized individually for the best high harmonic yield and also positioned independently of the others, such that the density modulation can be adjusted to the changing field of the driving laser as it propagates through the gas, on the other hand it is possible, by setting up the multi-jet-system to enhance the contribution from a specific electron trajectory, to efficiently control the spectral and temporal structure of the generated harmonic field. This would lead to the generation of extremely short single attosecond pulses with tunable photon energy. References [1] V. Tosa, V. S. Yakovlev, F. Krausz, New J. of Phys. 10, 025016 (2008) [2] A. L. Cavalieri, E. Goulielmakis, B. Horvath, W. Helml, M. Schultze, M. Fieß, V. Pervak, L. Veisz, V. S. Yakovlev, M. Uiberacker, A. Apolonski, F. Krausz, R. Kienberger, New J. Phys. 9 , 242 (2007) [3] X. Gu, G. Marcus, Y. Deng, T. Metzger, C. Teisset, N. Ishii, T. Fuji, A. Baltuska, H. Ishizuki, T. Taira, T. Kobayashi, R. Kienberger, F. Krausz, Generation of carrier-envelope phase-stable two-cycle 740-μJ pulses at 2.1 μm carrier wavelength, accepted by Opt.Express [4] J. Seres, V. S. Yakovlev, E. Seres, Ch. Streli, P. Wobrauschek, Ch. Spielmann, F. Krausz, Nature Physics 3, 878 (2007)

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Figure 1.a Figure 1.b Fig. 1.a Harmonic intensity depending on atomic densities

for 1, 2 or 3 subsequent nozzles.

Fig. 1.b Build-up of harmonic intensity

in multi-jet-systems designed for

enhancement of 2 different electron

trajectories

Indication of a very large proton diffusion in ice Ih

by Dan Huppert, Itay Presiado and Anna Uritski

Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel Aviv University, Tel Aviv 69978, Israel

The physics of ice has been studied1 for a long time, posing many questions that still puzzle us today. We studied the proton diffusion in ice by a chemical reaction of several molecules in their excited-state with a proton added to the ice as a small concentrations of the strong mineral acid HCl. We used a time-resolved emission technique to monitor the excess by excess protons reaction in both liquid water and in ice. The electrical conductivity measurements of Eigen2 in the early sixties of the 20th

century resulted in a surprisingly large mobility value for the proton in ice. The results of the present study and of our previous one3,4 indicate that the proton mobility in ice is indeed larger than in water, at least on a nanometric distance scale. Already in 1983 Nagle advocated the existence of proton wires in ice and in enzymatic systems in which the proton transport is carried out via a concerted mechanism (Grotthuss mechanism) on a limited length scale. Under certain assumptions and approximations, we deduced the proton diffusion constant in bulk ice from the experimental data fit by using the irreversible diffusion-assisted recombination model based on the Debye-Smoluchowski equation. We found that the proton diffusion in ice Ih at 240 - 263 K is about 10 times larger than in liquid water at 295 K. Ice conductance has been extensively studied for more than four decades. Our findings are in accord with the electrical measurements of Eigen and deMaeyer, but contradict conductivity measurements of ice from 1968 to this day. We explained the large difference between the results of the present study and the conductivity measurements by the proton diffusion length in the two types of measurements. In our measurements, we monitored a small diffusion sphere of about 50 nm around the excited photoacid molecules, whereas in the conductance measurements the distances between electrodes were in the range of 1 mm. 1 Petrenko, V. F.; Whitworth, R. W. The Physics of Ice; Oxford University, Press: 1999. 2 (a) Eigen, M. Proton Transfer, Angew. Chem., Int. Ed. 1964, 3,1. 3 Uritski, A.; Presiado I.; Huppert, D. J. Phys. Chem. C 2008, 112, 11991. 4 Uritski, A.; Presiado, I.; Huppert, D. J. Phys. Chem. C accepted for publication

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Phase rigidity and incoherent operation of guided matter-wave Sagnac interferometers

Yonathan Japha, Ofir Arzouan, Yshai Avishai and Ron Folman Physics Department, Ben Gurion University, Israel

www.bgu.ac.il/atomchip Sagnac interferometry is based on the effect of rotation or acceleration on the phase difference between counter-propagating waves in a closed loop. The effect of these rotations on matter waves of massive particles is many orders of magnitude larger than on light waves, which are usually used in navigation systems. We present a theory of the transmission of Sagnac interferometers based on guided matter waves. An interferometer of this type consists of one or more input and output channels connected by beam splitters and waveguides serving as the interferometer arms. In analogy to mesoscopic solid-state electron interferometers, we find phase rigidity in configurations with only one input and one output port. Phase rigidity, namely the fact that the transmission depends mainly on the Sagnac phase shift and not on arm-length differences, is due to time-reversal symmetry. It allows incoherent operation which is robust to arm-length differences. This sensitivity makes possible the operation of highly sensitive interferometers with high-flux atom sources, which are available for laser-cooled atoms. High-finesse configurations offer very high rotation sensitivity even for miniature loops on an atom chip.

aout

ain

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α

i

i’

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α’

o

o’

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ain a

out

a+

b+

a−

b−

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α

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ain

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(b) Figure: Geometries of guided matter-wave Sagnac interferometers: (a) Mach-Zehnder. Horizontal lines represent 50-50% beamsplitters. Open squares indicate controllable reflectivity. When fully reflecting, the interferometer displays phase rigidity. (b) High-finesse 2-port loop. Closed squares are fully reflecting mirrors. Vertical lines are low-transmission beam-splitters. (c) 4-port loop. No phase rigidity. (d) High-finesse single-junction loop. For this loop it is shown that high sensitivity is possible even with multimode operation.

Reference: Y. Japha, O. Arzouan, Y. Avishai and R. Folman, Phys. Rev. Lett. 99, 060402 (2007).

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Long-Range Order in Electronic Transport through Disordered Metal Films

Y. Japha1, O. Entin-Wohlman1, T. David1, R. Salem1, R. Folman1, S. Aigner2, L. Della Pietra2 and J. Schmiedmayer2

1Atom Chip Group, Ben Gurion University, Israel: www.bgu.ac.il/atomchip 2Heidelberg University, Austria

Ultracold-atom magnetic-field microscopy permits probing of electron transport patterns in planar structures with unprecedented sensitivity and resolution. In polycrystalline metal (gold) films we observe long-range correlations, forming organized patterns oriented at ±45◦ relative to the mean current flow, even at room temperature and at length scales orders of magnitude larger than the diffusion length or the grain size. The tendency to form patterns at these angles is a direct consequence of universal scattering properties at defects. The observed amplitude of the current-direction fluctuations scales inversely to that expected from the relative-thickness variations, the grain size and the defect concentration, all determined independently by standard methods. A careful comparison of the different measurements with our theoretical models, assuming bulk and surface long-range disorder in the wire structure, offers new insight into the structure and the nature of electron transport in polycrystalline metal films. The theoretical model also provides predictions regarding the dependence of current fluctuations on the geometry of the wires. The results indicate that ultracold atom magnetometry provides new insight into the interplay between disorder and transport.

x (μm)

Figure 1. Atomic density fluctuations, 3.5μm above a thin gold film, due to current-directional deviations in the wire. The simulation (b) regenerates patterns similar to those measured (a). Figure 2. Microscopic and macroscopic models for the 45◦ effect. A-B: a microscopic conductivity-changing defect repels or attracts the current lines, thus generating a field of vertical current component oriented at 45◦. C: current scattering by a step-like defect. Maximum transverse current is generated by steps oriented by 45◦.

References: S. Aigner et al., Science 319, 1226 (2008)

Y. Yapha et al., Phys. Rev. B77, 201407(R) (2008)

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Shaped Femtosecond Pulses for Standoff Detection of Chemical Traces O. Katz 1, A. Natan 1 , S. Rosenwaks 2 , Y. Silberberg 1

1 Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot, 76100 Israel 2 Department of Physics, Ben Gurion University of the Negev, Beer Sheva 84105, Israel.

E-mail: yaron.silberberg@weizmann.ac.il, Remotely detecting and identifying traces of hazardous materials at standoff distances is one of the recent concerns at the focus of current research activities. The vibrational spectrum of molecules provides an excellent fingerprint for chemical species identification, and can be harnessed for this task. We have experimentally utilized one of our group's femtosecond coherent-control techniques1 for remote detection and identification of minute amounts of solids and liquids at a standoff (>10m) distance. In this Coherent Anti-Stokes Raman Scattering (CARS) technique, a single ultrashort pulse supplies both the broadband pump and Stokes photons, and a narrow-band portion of the same pulse is phase-shifted to serve as the probe beam using a pulse shaper (Fig. 1c). Furthermore, we exploited the strong nonresonant four-wave mixing background for amplification of the weak backscattered resonant CARS signal through a homodyne detection scheme. We have succeeded in rapidly resolving the vibrational spectrum of trace amounts of contaminants such as explosives and nitrate samples, from the weak backscattered photons under ambient light conditions 2. This highly sensitive single-beam spectroscopic technique has a potential for hazardous materials standoff detection applications.

Fig. 1: (a) Resolved femtosecond CARS vibrational spectra of two trace samples obtained at a standoff distance of 12m (<1000μg crystallized KNO3 particle, and RDX explosive particles with a total mass of <4mg); Each spectrum was resolved from a single measurement with an integration time of <3 seconds. The known vibrational lines of the samples are plotted in gray bars. (b) Image of the KNO3 contaminant sample, placed 12m from the measuring apparatus. (c) The experimental setup. The laser source is an amplified femtosecond Ti:Sapphire laser (0.5mJ, 30fs, 1KHz repetition rate). The pulses are phase-shaped in a pulse shaper using an electronically controlled liquid-crystal spatial light modulator. The beam is focused on a distant sample through a telescope, and the backscattered radiation is collected to a spectrometer with a 7.5" diameter lens. 1 D. Oron, N. Dudovich, and Y. Silberberg, Phys. Rev. Lett. 89 (2002) 273001. 2 O. Katz, A. Natan, S. Rosenwaks, Y. Silberberg , Appl. Phys. Lett. 92, 171116 (2008).

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Optical Generation and Control of Plasma Lens System

Y.Katzir, M.Levin, S.Eisenman, A.Zigler

Racah Institute of Physics, Hebrew University, Jerusalem, 91904 Israel

Abstract: We present a novel approach for focusing and collimating a NIR femtosecond laser

pulse, by use of a plasma lens system. The plasma lens was created at the entrance of a polyethylene

capillary by another nanosecond laser which was used to ablate the capillary entrance in a

configuration which focuses the femtosecond laser pulse and allows it to pass through the capillary at

higher transmittance. This configuration offers versatility in the plasma lens f-number for extremely

tight focusing of high power lasers with no damage threshold restrictions of regular optical

components.

Experimental setup:

Results:

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Experimental setup

The igniting laser (pink) was

focused approximately 3cm from

the capillary entrance and was

used to ablate the capillary

entrance, which generated a

plasma plume in a configuration

that created a plasma lens.

According to measurements of

plasma density, the guided pulse

(red) was focused 1cm before the

capillary entrance, and its

transmittance was measured at

the capillary exit.

Results:

Guided laser train pulses

intensity as a function of

time. The instance of

igniting laser hitting the

capillary (20mJ) is marked

by the dotted line at t=0.

An increase by a factor of

three in guided laser

transmittance was detected

after 45ns.

PHOTOISOMERIZATION VERSUS PHOTODISSOCIATION; QUANTUM DYNAMICAL SIMULATIONS ON A CHIRAL OLEFIN

Daniel Kinzel,1 Sherin Alfalah,2 Jesús González-Vázquez, 1 Leticia González1

1Institut für Physikalische Chemie, Friedrich-Schiller Universität Jena, Helmholtzweg 4, Jena, Germany

2Faculty of Pharmacy, Al-Quds University, Jerusalem, Palestine E-mail: Daniel.Kinzel@uni-jena.de

The (4-methylcyclohexylidene) fluoromethane (4MCF) system is a chiral molecule whose R/S enantiomers are obtained upon photoisomerization around the olefinic double bond [1,2], see Scheme 1. Recently, it has been suggested that 4MCF might serve as a substrate for a laser-induced molecular rotor [3]. As it is well-known in olefins, 4MCF presents several conical intersections (CI) between the lowest singlet excited state and the electronically ground state [4]. Moreover, besides the “typical” twisted, pyramidalized, and H-migration CIs found in ethylenic systems, here a CI for HF dissociation has been located [5]. This CI is expected to be populated in gas phase, competing then with the R/S photoisomerization pathway. In this contribution, the competition of R/S photoisomerization against HF dissociation is investigated. For that purpose, two-dimensional potential energy surfaces (PES) have been calculated for both the ground and lowest excited states along the isomerization and dissociation degrees of freedom using multiconfigurational CASSCF methods. Additionally, nonadiabatic couplings and permanent-, as well as, transition- dipole moments are also obtained at the same level of theory. The PESs show two degeneracy points with a strong coupling out of the Franck-Condon region, which correspond to the CIs between the ground and first excited states.

Based on this PESs and ab initio couplings, quantum dynamical simulations in the diabatic representation have been performed in order to evaluate whether this chiral rotor is destroyed upon excitation. S R

Scheme 1. The R and S enantiomers of 4MCF

[1] D. Kröner, M. F. Shibl and L. González, Chem. Phys. Lett. 372, 242 (2003). [2] D. Kröner and L. González, Chem. Phys. 298, 55 (2004). [3] Y. Fujimuro, L. González, D. Kröner, J. Manz, I. Mehdaoui and B. Schmidt, Chem. Phys. Lett. 386, 248 (2004). [4] M. Schreiber, M. Barbatti, S. Zilberg, H. Lischka and L. González, J. Phys. Chem. A 111, 238 (2007). [5] S. Zilberg, S. Cogan, Y. Haas, O. Deeb and L. González, Chem. Phys. Lett. 443, 43 (2007). Acknowledgements: We are grateful for the support by the DFG, project Nr. GO 1059/5-2.

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FH

H3C

HF

H3C

Wave focusing by plano-concave lenses based on 2D photonic quasicrystal and 2D photonic crystal super-lattice

Y. Neve-Oz1, Y. Saado1 , T. Pollok2, M. Golosovsky1, S. Burger2 and D. Davidov1

1The Racah Institute of Physics, the Hebrew University of Jerusalem, Israel

2Zuse Institute Berlin, Germany

We report on microwave focusing by a plano-concave lens based on planar array of dielectric rods arranged in a crystalline or quasicrystalline (QC) configuration.

We designed a 2D photonic crystal superlattice from the dielectric rods of two different diameters. This device was designed for the operation in the microwave range. The composite unit cell of the superlattice results in a narrow transmission subband inside the photonic stop-band. Due to Brillouin zone folding in the superlattice, this transmission band is characterized by a negative refractive index. This was verified experimentally by constructing a plano-concave lens that focused the microwave radiation into a subwavelength spot.

Another way to achieve focusing by the plano-concave lens was to use aperiodic, quasicrystalline arrangement of the dielectric rods. We studied microwave propagation in such arrays using JCM-Wave software that is based on a time-harmonic, adaptive, higher-order finite-element method. We found that in specially designed dielectric rod arrays based on Penrose tilings with 5- and 10-fold symmetry, there is light localization, resulting from multiple scattering. This results in a very small refractive index (fast light). We showed by numeric simulations that a plano-concave lens built from such material exhibits focusing (Figure 1). Figure 1. A plano-concave quasicrystalline lens. The phase distribution shows almost constant phase inside the lens and a uniform phase front on the concave face. The intensity distribution shows focusing.

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Rotational dephasing and depopulation rates measured via non-adiabatic alignment

Nina Owschimikow1, Jochen Maurer1*, Falk Königsmann1, Burkhard Schmidt2,

and Nikolaus Schwentner1

1 Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany 2 Institut für Mathematik, Freie Universität Berlin, Arnimallee 6, 14195 Berlin, Germany

Ambient conditions, i.e. temperatures of order of 100 K and pressures of order of 1 atm, are standard for studies of physical and chemical properties of molecules in the gas phase. Under these conditions, bimolecular collisions, and therefore decoherence and dissipation, typically occur on a picosecond time scale. The dynamics in experiments on non-adiabatic alignment covers exactly this time range. We show that laser induced alignment of diatomic molecules can be used to quantitatively study relaxation processes of both phase and population.

Figure 1. Figure 2.

We use a Ti:Sa amplified fiber laser with a pulse length of 160 fs focused to an intensity of 1013 W/cm2 to induce alignment in a sample of N2 at pressures of 100 to 900 mbar and temperatures between 80 and 300 K. The excitation is followed by recurrent transient bursts of molecular alignment reflecting the phase coherence (Fig. 1), which are monitored in a homodyne detected optical Kerr effect experiment. Random bimolecular collisions result in a loss of phase coherence and thus an exponential decay of intensity of the revivals. The collision rate is connected with thermal equilibration via the collision number Zr, which describes the number of collisions necessary to re-establish equilibrium between translational and rotational degrees of freedom. A mean free path analysis of the experimental decay rates, after weighting with Zr, yields rotational relaxation cross sections that are in excellent agreement with values from the literature (Fig. 2, black: our results; grey: literature data from Ref. 1). Additionally, at high intensities, a non-equilibrium population of M quantum numbers is created upon excitation and is reflected in a weak structureless offset in the detected signal. By decomposing the theoretically calculated signal into a coherence part and a population part according to Ref. 2 and fitting to our data, we show that the slower thermalization of population compared to phase relaxation is contained in a change of revival shape over time (inset Fig.1), and thus both times can be extracted directly from an alignment experiment. [1] F. J. Aoiz et. al., J. Phys. Chem. A 103, 823 (1999), and references therein [2] S. Ramakrishna and T. Seideman, Phys. Rev. Lett. 95, 113001 (2006)

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A Novel Atom Trap Based on Carbon Nanotubes

Plamen G. Petrov, Saeed Younis, Roberto Macaluso, Shimi Machluf*, Tal David, Benyamin Hadad, Yoni Japha, Mark Keil, Ernesto Joselevich, and Ron Folman

Department of Physics, Atom Chip Group, Ben Gurion University, Be’er Sheva, Israel

* machlufs@bgu.ac.il The recent realization of micron-scale magnetic potentials through standard microelectronic fabrication techniques has led to the development of miniature atom traps near surfaces, in what are widely known as atomchips. Bringing atoms ever closer to the source of the magnetic potentials enables tighter traps and opens new avenues for quantum manipulation (e.g., control of tunneling barriers on the order of 1μm, the atomic deBroglie wavelength). The motivation to use carbon nanotube (CNT)-based devices ranges from improving atom optics technology to fundamental studies of CNTs. Atom-surface interactions due to the Casimir-Polder force become important at sub-micron distances; the resulting trap losses caused by tunneling to the surface can be controlled for CNT-based traps since the amount of matter near the atoms can be very small. CNT-based traps are also expected to exhibit ballistic electron transport, thereby reducing electron scattering and improving the smoothness of the magnetic potential. Thermally induced electromagnetic noise will be improved, reducing trap loss and decoherence. Relative to normal conductors, CNTs offer sharp absorption peaks and hence may serve as useful electrodes near high-finesse resonators since they will not absorb resonator photons. They may also serve as mechanical oscillators, leading to atom-oscillator coupled systems in which the laser-cooled atom can cool the CNT oscillatory motion. Finally, once the trap is realized, atoms may serve as extremely sensitive probes of electron transport and other aspects of CNT science. We present a feasibility study for loading cold atomic clouds into magnetic traps created by CNTs grown directly onto dielectric surfaces (submitted to Phys. Rev. A). We show that atoms may be captured for experimentally sustainable nanotube currents, generating trapped clouds whose densities and lifetimes are sufficient to enable detection by simple imaging methods.

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general view of the BGU atomchip

schematic view of the carbon nanotube trap

simulated isopotential surface for ultracold atoms hovering ~1 μm above the carbon nanotube

BEC transition for 87Rb at BGU

The Minimal Temperature of Quantum Refrigerators

Tova Feldmann, Yair Rezek and Ronnie Kosloff

Institute of Chemistry the Hebrew University, Jerusalem 91904, Israel

A first principle reciprocating quantum refrigerator is investigated with the purpose of determining the limitations of cooling to absolute zero. We find that if the energy spectrum of the working medium possesses an uncontrollable gap, then there is a minimum achievable temperature above zero. The reason is that such a gap, combined with a negligible amount of noise, prevents adiabatic following during the expansion stage which is the necessary condition for reaching Tc =0. For the case where the gap can be forced to close, the scaling of the optimal cooling power of a reciprocating quantum refrigerator is sought as a function of the cold bath temperature as Tc approaches zero. In this case the working medium consists of a gas of noninteracting particles in a harmonic potential. Two closed-form solutions of the refrigeration cycle are analyzed, and compared to a numerical optimization scheme, focusing on cooling toward zero temperature. The optimal cycle is characterized by a linear relation between the heat extracted from the cold bath, the energy level spacing of the working medium and the temperature. The scaling of the optimal cooling rate is found to be proportional to

Tc^{3/2} giving a dynamical interpretation to the third law of thermodynamics.

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How to produce “high-N00N” atom states via RF pulses on a (1μm)2 flux qubit

D. Rohrlich, Y. Japha and R. Folman

Atom Chip Group, Ben Gurion University, Israel: www.bgu.ac.il/atomchip “High-N00N” states are maximally entangled states of a high number N of identical two-level systems: if 0N represents all of the N systems in one of the states and N0 represents all of them in the other,

then ( ) 2/00 NN + is a high-N00N state. High-N00N states can beat the shot noise limit N/1≥Δφ for the detection of the quantum phase φ of the systems and can, in principle, saturate [1] the “Heisenberg limit” N/1≥Δφ . We propose to use a “flux qubit” – a mesoscopic superconducting ring – for efficient preparation of high-N00N states of two-level atoms. For example, the flux qubit shown in the micrograph was fabricated by a group at Delft University of Technology [2]. It is roughly (1 μm)2 in area and couples to a SQUID. Rabi oscillations generated by the flux qubit appear on the schematic diagram. This flux qubit supports superposed fluxes B1, B2 that differ by half a flux quantum, B2–B1= hc/2e, with coherence lasting from 0.5 μs to 4 μs at 25 mK. We show how to transfer the superposition from such a superposed magnetic field to the two-level atoms. First, we toggle the atoms selectively using an RF (radio frequency) pulse that addresses only the B2 term: Since B2–B1 = (hc/2e )/(1 μm)2 = (2 x 10–7 cm2 G )/(1 μm)2 = 20 G, the frequency splitting ν = (B2–B1)(μB/h) for the RF pulse is (20 G)(1.4x106 Hz/G) ≈ 30 MHz, and there is no problem addressing only the B2 term. Next, a π/2-pulse on the superconducting ring, followed by a measurement of the magnetic field, reduces the atoms to a high-N00N state. A (1 μm)3 box in the superconducting ring could contain 100 atoms, assuming a BEC cloud with a density of 1014 atoms/cm3. Thus, our challenge is to produce high-N00N states with N=100.

[1] J. J. Bollinger, W. M. Itano, D. J. Wineland and D. J. Heinzen, Phys. Rev. A54, R4649 (1996). [2] I. Chiorescu et al., Science 299, 1869 (2003).

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( ) ( ) . 002

1 02

12121 BNBNBBN ⊗+⊗→+⊗

High-Quality Micro-Resonator for Trapping and Detecting a Single Atom on a Chip Michael Rosenblit1, Yonathan Japha1, Peter Horak2 and Ron Folman1

1Atom Chip Group, Ben Gurion University, Israel: www.bgu.ac.il/atomchip. 2Optoelectronics Research Centre, University of Southampton, U.K. We describe the use of whispering gallery modes (WGM) of a microdisk resonator for the optical detection of single rubidium and cesium atoms near the surface of a substrate. Light is coupled in two high-Q whispering-gallery modes of the disk which can provide attractive and/or repulsive potentials, respectively, via their evanescent fields. The sum potential, including van der Waals/Casimir-Polder surface forces, may be tuned to exhibit a minimum at distances on the order of 100 nm from the disk surface. We discuss the possibility of simultaneously optically trapping and detecting atoms, when the back-action of an atom held in this trap on the light fields is sufficiently strong to provide a measurable effect. The goal is to enable state preparation, manipulation and probing of single atoms, molecules, or clusters using the spectral properties of a monolithically fabricated high-quality micro-resonator. Expected applications, for example, will be quantum state preparation and manipulation as well as detection e.g. for matter-wave interferometry, and for quantum information processing. We have shown that a single atom can be detected near the surface of a microdisk resonator with and without trapping, such that it can be detected with negligible heating. The atom is detected via a blue-detuned WGM of the resonator, while trapping at a fixed position is achieved by a second, red-detuned WGM. The two light fields create a trapping potential at a distance of 100-150 nm from the disk surface. At this distance, the atom-surface attractive interaction (van der Waals force) is much weaker than the light force, while the optical potential is sufficiently strong to create a deep trap for the atom. The atom is then confined in the radial direction and in the z direction (perpendicular to the chip surface). For trapping in the tangential direction, we suggest that the red-light WGM be coupled to the microdisk from both sides, such that a red-detuned standing wave is formed along the disk perimeter and the atom may be trapped in any of the maxima of the red detuned light.

Figure. Scheme of the detection and trapping system: An optical waveguide (1) is coupled to the microdisk (2). Adiabatic tapers (3) couple light into and out of the waveguide. An atom (4) initially trapped by a magnetic field generated by a wire (5) is then loaded into the bichromatic optical trap created by the light coupled into the disk. The atom causes a detectable phase shift of the light at the output port.

References: M. Rosenblit et al., Phys. Rev. A73, 063804 (2006). Rosenblit et al., J. Nanophotonics 1, 011670 (2007). U.S. Patent approved; patent number due January 2009.

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Multiphoton Femtosecond Control of Resonance-Mediated Generation of Short-Wavelength Coherent Broadband Radiation

Leonid Rybak, Lev Chuntonov, Andrey Gandman, Naser Shakour and Zohar Amitay Schulich Faculty of Chemistry, Technion, Haifa, Israel (rleo@tx.technion.ac.il)

We introduce a new scheme for generating short-wavelength coherent broadband radiation with well-controlled spectral characteristics. It is based on shaping long-wavelength femtosecond pulse to coherently control atomic resonance-mediated (2+1) three-photon excitation to a broad far-from-resonance continuum (see Fig. 1). Here, the spectrum (central frequency and bandwidth) of deep-ultraviolet (UV) coherent broadband radiation generated in Na vapor is experimentally controlled by tuning the linear chirp that we apply to the driving phase-shaped near-infrared femtosecond pulse. Figure 2 presents the complete set of the experimentally generated chirp-controlled UV spectra as a function of the applied NIR chirp. The results are presented as a color-coded map, with each UV spectrum normalized independently by its maximal intensity. This is a first step in implementing the full scheme for producing shaped femtosecond pulses at wavelengths down-to the vacuum-ultraviolet (VUV) range, which currently is inaccessible by the present pulse shaping techniques. Inspired by past demonstrations of narrowband coherent VUV generation via resonance-mediated threephoton atomic excitation, the extension to the VUV range can be achieved by a proper change of the excited atomic species and the driving pulse wavelength. Such shaped pulses will make many VUV-absorbing molecular species newly available for coherent control.

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Fig. 2: The experimentally generated chirp-controlled UV spectra as a function of the applied NIR chirp.

Fig. 1: The excitation scheme of Na for the generation of deep-ultraviolet (UV) coherent broadband radiation by shaped NIR femtosecond pulse via resonance-mediated (2+1) three-photon

i i

Engineered Fragmentation: Generating a 1D Magnetic Lattice Ran Salem, Yenon Ben-Hayim, Julien Chabé, Ramon Szmuk, Mark Keil, Yonathan Japha and Ron Folman Atom Chip Group, Ben Gurion University, Israel www.bgu.ac.il/atomchip In this work, we use the atom chip to investigate the tunneling and interference of matter waves (ultracold atoms) which are released from a chain of magnetic traps in one dimension (1D). Atoms are extremely sensitive to directional deviations of the current in the wire. We propose to exploit this sensitivity by engineering a novel 1D magnetic lattice. We have already fabricated a gold wire with a periodic sinusoidal center shift on the chip. (See Fig. 1.) Next, we will load an atomic Bose-Einstein condensate into the periodic 1D waveguide potential generated a few microns from the wire by the current in the chip wire. By controlling the height of the waveguide potential from the chip wire we will be able to generate many-body atomic states of either separate condensates in many traps or a coherently correlated Bose gas extending over many traps. By releasing the potential and observing the interference pattern of the atoms we may be able to characterize their ground state properties and dynamics. Figure 1: An SEM image of the periodically perturbed gold wire fabricated on the chip (left) and an isopotential plot of the trapping potential at 1.5µK.

Figure 2: Simulation of the atomic density creating an interference pattern 10 msec after release from a coherent state in a chain of 4 traps. The details of the interference pattern in a real measurement will permit characterization of the initial atomic state and dynamics.

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Qubit Coherent Control with Squeezed Light Fields

Ephraim Shahmoon1, Shimon Levit1 and Roee Ozeri2

1Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot, 76100, Israel 2Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot, 76100, Israel

(ephraim.shahmoon@weizmann.ac.il)

Quantum control fields that operate on a qubit in a single quantum gate may become entangled with the qubit and thus contribute to the gate error [1,2]. For coherent state control fields the error was shown to be exactly the one due to atomic radiative decay in free space with a classical and deterministic control field [3]. Here, we study the use of squeezed light for qubit coherent control and compare it with coherent light control field. We calculate the entanglement between a short pulse of resonant squeezed light and a two-level atom in free space during the π pulse operation and the resulting operation error. We find that for squeezed light, the interplay of three phases - the squeezing phase, the phase of the light field and the atomic superposition, determines the error and the entanglement magnitude. In fact, in comparison with coherent control using coherent light state, the error and the entanglement can be either enhanced or suppressed depending on the above phase relations [see Fig. 1]. These results are explained intuitively by using the Bloch sphere picture and quantitatively by quantum interference effects in the evolution of the atom-pulse quantum state. For quantum information processing purposes the relevant error is that averaged over all possible initial states. To this end, the use of squeezed light would not reduce the average error compared with the coherent light case by a practicably useful amount. In fact, in most cases the average error increases as a result of the enhancement of atom-pulse entanglement by squeezing. We discuss the possibility of measuring the increased gate error as a signature of this entanglement.

FIG. 1: The atom-pulse entanglement vs squeezing. In this specific calculation, the atom coupling to the rest of the free space field modes is neglected. Results are shown for four atomic initial states and for the squeezing phases φ=0,π/2 (|g› and |e› denote the atom's ground and excited states repectively). Compared with the coherent light case (r=0), one obtains a squeezing phase dependent suppression and enhancement of the entanglement as squeezing gets larger. The error probability follows similar trends.

[1] S. J. van Enk and H. J. Kimble, Quantum Inf. Comput. 2, 1 (2002) [2] A. Silberfarb and I. H. Deutsch, Phys. Rev. A 69, 042308 (2004) [3] W. M. Itano, Phys. Rev. A 68, 046301 (2003)

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