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The nonclassical entangled states of two or more particles gave rise to a whole new class of fundamental experiments and applications based on the nonlocality of quantum mechanics. Recent examples can be found in the fields of quantum computing and quantum cryptography1.

We demonstrate the use of electrically contacted vapor cells to switch the transmission of a probe laser. The excitation scheme makes use of electromagnetically induced transparency involving a Rydberg state. The cell fabrication technique involves thin-film-based electric feedthroughs, which are well suited for scaling this concept to many addressable pixels like in flat panel displays.

We review experimental and theoretical tools to excite, study and understand strongly interacting Rydberg gases. The focus lies on the excitation of dense ultracold atomic samples close to, or within quantum degeneracy, to high lying Rydberg states. The major part is dedicated to highly excited S-states of Rubidium, which feature an isotropic van-der-Waals potential. Nevertheless, the setup and the methods presented are also applicable to other atomic species used in the field of laser cooling and atom trapping., Comment: 23 pages, 22 figures, tutorial

We have demonstrated the loss of transverse spatial coherence of an atomic wave function after a single spontaneous emission. ${\mathrm{He}}^{*}$ atoms were both diffracted and excited by a standing light wave with a variable period. After the interaction, the excited atoms decay by a single spontaneously emitted photon. By changing the period of the standing light wave, we have mapped the loss of spatial coherence as a function of the transverse coordinate. By detecting the emitted photon one could "erase" the position information available and recover the transverse coherence in a correlation experiment, or realize a Heisenberg microscope.

Since the first experiments on Bose-Einstein condensates, researchers have tried to use them to make atom lasers. But although pulsed lasers have been demonstrated, continuous atom laser operation has been elusive. In his Perspective, [Pfau][1] highlights the report by [ Chikkatur et al .][2], who have overcome the problem with a conceptually simple but technically challenging apparatus. The challenge now is to develop "high power" atom lasers. [1]: http://www.sciencemag.org/cgi/content/full/296/5576/2155 [2]: http://www.sciencemag.org/cgi/content/short/296/5576/2193

In this contribution we presented experimental results for a new type of beamsplitter and an investigation of the reflecting properties of an evanescent light field. The beamsplitter relies on the diffraction of atomic matter waves from a phase grating with triangular phase modulation produced by a combination of a light field and a magnetic field. We observed a momentum splitting of 42 ħk. In addition, we reported on the reflection of atoms from evanescent waves produced by total internal reflection of a laser beam. We demonstrated that the maximum reflection angle could be increased by enhancing the evanescent wave by a planar waveguide and surface plasmons. Furthermore, we examined the number of spontaneous emission processes in the reflection and concluded that for proper choice of parameters only few atoms will undergo spontaneous emission. A next step could be to investigate the coherence of these elements by combining them in a Mach-Zehnder type interferometer.

The key elements for atom interferometers are atomic beam splitters and recombiners. An atomic beam splitter separates a single atomic wave function into a superposition state corresponding to two center of mass wavepackets that propagate in different spatial directions and a recombiner reunites the atomic beams. We report here on the investigation of 1) an atomic beam splitter with large separation angle based on the optical Stern Gerlach effect, 2) an atomic mirror based on the reflection of atoms by different types of evanescent waves (a simple evanescent wave and a surface plasmon wave), 3) an atomic beam splitter realized by the partial spatial reflection of an atom by an evanescent wave and 4) diffraction of atoms by a standing evanescent wave.

In this letter we present a theoretical study of the coherent diffraction of three-level atoms from a light field with a polarization gradient (counterpropagating crossed linearly polarized beams) and a static magnetic field applied parallel to the laser propagation direction. We show that for a particular ratio of the laser field intensity and the magnetic-field strength, there occurs a resonance between the Larmor precession of the magnetic alignment and the Rabi oscillations. On resonance the atomic wave function is diffracted by an approximately triangular optical potential which leads to a very efficient coherent splitting of the atomic beam. The proposed configuration is particularly interesting in relation to atom interferometry, when efficient coherent beam splitters for atoms are required.

We report on the transverse laser cooling of a magnetically guided beam of ultra cold chromium atoms. Radial compression by a tapering of the guide is employed to adiabatically heat the beam. Inside the tapered section heat is extracted from the atom beam by a two-dimensional optical molasses perpendicular to it, resulting in a significant increase of atomic phase space density. A magnetic offset field is applied to prevent optical pumping to untrapped states. Our results demonstrate that by a suitable choice of the magnetic offset field, the cooling beam intensity and detuning, atom losses and longitudinal heating can be avoided. Final temperatures below 65 microkelvin have been achieved, corresponding to an increase of phase space density in the guided beam by more than a factor of 30., Comment: 9 pages, 4 figures

The capture of a moving atom by a non-dissipative trap, such as an optical dipole trap, requires the removal of the excessive kinetic energy of the atom. In this article we develop a mechanism to harvest ultra cold atoms from a guided atom beam into an optical dipole trap by removing their directed kinetic energy. We propose a continuous loading scheme where this is accomplished via deceleration by a magnetic potential barrier followed by optical pumping to the energetically lowest Zeeman sublevel. We theoretically investigate the application of this scheme to the transfer of ultra cold chromium atoms from a magnetically guided atom beam into a deep optical dipole trap. We discuss the realization of a suitable magnetic field configuration. Based on numerical simulations of the loading process we analyze the feasibility and efficiency of our loading scheme., 10 pages, 5 figures

We report the observation of a very high flux of ultra-cold bosonic chromium atoms in a magnetic guide. The beam is created by operating a magneto-optical trap/moving optical molasses within the magnetic field of the guide. A relative detuning between two pairs of the cooling lasers cools the atoms into a frame moving along the axes of the guide. When the atoms are cooled into a moving frame with a velocity of 6 m s−1 we observe a maximum of the flux of 6 × 109 atoms s−1. For these parameters the transversal temperature of the atoms after a 25 fold increase of the confining magnetic potential is about 1.2 mK. The longitudinal temperature is 400 µK.

We experimentally investigate the collapse dynamics of dipolar Bose- Einstein condensates of chromium atoms in different harmonic trap geometries, from prolate to oblate. The evolutions of the condensates in the unstable regime are compared to three-dimensional simulations of the Gross-Pitaevskii equation including three-body losses. In order to probe the phase coherence of collapsed condensates, we induce the collapse in several condensates simultaneously and let them interfere.

At low enough temperatures and at microscopic length scales the laws of quantum mechanics become apparent. The underlying superposition principle leads to interference phenomena for one degree of freedom and to the concept of entanglement for two and more. Entangled degrees of freedom are often correlated beyond their classically allowed correlation. These quantum correlations also appear in very large systems and are caused by strong interactions between the constituents. Strongly correlated forms of quantum matter became ubiquitous in condensed matter physics, with the discovery of heavy fermion materials, cuprates and other unconventional superconductors. Here the main players are electrons embedded in solid matter. But they also can be found in interacting quantum gases, where the main players are atoms. In the latter case the required temperatures for quantum correlations to appear are much lower. But in turn the length scales are larger and they can be embedded in well controlled potentials. A fascinating possibility offered by present day technologies is to tailor matter in order to induce the emergence of new phenomena by controlling quantum correlations. One of the routes leading to spectacular advances is the configuration of nanomaterials like quantum dots or quantum wires on the basis of semiconducting substrates that allow, e.g., to manipulate the Kondo effect or Luttinger liquids affecting transport properties through such nanostructures. Another quite different route with at the moment unlimited potential is offered by quantum optics and atomic physics, when implemented to bring quantum gases into the strongly interacting regime. This can be achieved by optical lattices leading to Mott-insulators, or to two dimensional systems displaying Kosterlitz–Thouless behavior in bosonic gases, or by Feshbach resonances, leading to fermionic systems with unconventional superfluid states like the Fulde–Ferrel–Larkin–Ovchinnikov (FFLO) one. In spite of the very different experimental realizations leading to the two routes mentioned above, they share a common goal, namely achieving a deep understanding of quantum correlations that will ultimately allow to control them and possibly realize new forms of matter. They also share the flexibility that allows to increase the complexity in quantum correlations by joining in a controlled manner well understood building units and/or by regulating their coupling to the environment. It is under the common goal of understanding and controlling quantum correlations that we see the topics presented in this focus issue of New Journal of Physics, where both lines of development, that is on solid-state substrates or with quantum gases, give a timely view of the advances towards the above mentioned common goal. Focus on Quantum Correlations in Tailored Matter Contents Temperature changes when adiabatically ramping up an optical lattice Lode Pollet, Corinna Kollath, Kris Van Houcke and Matthias Troyer Numerical study of two-body correlation in a 1D lattice with perfect blockade B Sun and F Robicheaux Kinetic Monte Carlo modeling of dipole blockade in Rydberg excitation experiment Amodsen Chotia, Matthieu Viteau, Thibault Vogt, Daniel Comparat and Pierre Pillet Motion of Rydberg atoms induced by resonant dipole–dipole interactions C Ates, A Eisfeld and J M Rost Quantum coherence due to Bose–Einstein condensation of parametrically driven magnons S O Demokritov, V E Demidov, O Dzyapko, G A Melkov and A N Slavin Chaotic dynamics in spinor Bose–Einstein condensates J Kronjager, K Sengstock and K Bongs Damped Bloch oscillations of Bose–Einstein condensates in disordered potential gradients S Drenkelforth, G Kleine Buning, J Will, T Schulte, N Murray, W Ertmer, L Santos and J J Arlt Rabi oscillations between ground and Rydberg states and van der Waals blockade in a mesoscopic frozen Rydberg gas M Reetz-Lamour, J Deiglmayr, T Amthor and M Weidemuller Excitations in two-component Bose gases A Kleine, C Kollath, I P McCulloch, T Giamarchi and U Schollwock Exploring the growth of correlations in a quasi one-dimensional trapped Bose gas M Eckart, R Walser and W P Schleich How to fix a broken symmetry: quantum dynamics of symmetry restoration in a ferromagnetic Bose–Einstein condensate Bogdan Damski and Wojciech H Zurek Landau levels of cold atoms in non-Abelian gauge fields A Jacob, P Ohberg, G Juzeliunas and L Santos Atomic four-wave mixing via condensate collisions A Perrin, C M Savage, D Boiron, V Krachmalnicoff, C I Westbrook and K V Kheruntsyan Semifluxons in superconductivity and cold atomic gases R Walser, E Goldobin, O Crasser, D Koelle, R Kleiner and W P Schleich Disorder-induced trapping versus Anderson localization in Bose–Einstein condensates expanding in disordered potentials L Sanchez-Palencia, D Clement, P Lugan, P Bouyer and A Aspect Critical tunneling currents in the regime of bilayer excitons L Tiemann, W Dietsche, M Hauser and K von Klitzing Quantum phases of trapped ions in an optical lattice R Schmied, T Roscilde, V Murg, D Porras and J I Cirac Generation and detection of a spin entanglement in nonequilibrium quantum dots Stefan Legel, Jurgen Konig and Gerd Schon Slow light in inhomogeneous and transverse fields Leon Karpa and Martin Weitz FFLO state in 1-, 2- and 3-dimensional optical lattices combined with a non-uniform background potential T K Koponen, T Paananen, J-P Martikainen, M R Bakhtiari and P Torma Geometry-dependent interplay of long- and short-range interactions in ultracold fermionic gases: models for condensed matter and astrophysics B Deb, G Kurizki and I E Mazets Fermionic renormalization group methods for transport through inhomogeneous Luttinger liquids V Meden, S Andergassen, T Enss, H Schoeller and K Schonhammer Luttinger hydrodynamics of confined one-dimensional Bose gases with dipolar interactions R Citro, S De Palo, E Orignac, P Pedri and M-L Chiofalo Towards deterministically controlled InGaAs/GaAs lateral quantum dot molecules L Wang, A Rastelli, S Kiravittaya, P Atkinson, F Ding, C C Bof Bufon, C Hermannstadter, M Witzany, G J Beirne, P Michler and O G Schmidt Effective parameters for weakly coupled Bose–Einstein condensates S Giovanazzi, J Esteve and M K Oberthaler Current statistics of correlated charge tunnelling through an impurity in a 1D wire Alexander Herzog and Ulrich Weiss Sideband cooling and coherent dynamics in a microchip multi-segmented ion trap Stephan A Schulz, Ulrich Poschinger, Frank Ziesel and Ferdinand Schmidt-Kaler The trapped two-dimensional Bose gas: from Bose–Einstein condensation to Berezinskii–Kosterlitz–Thouless physics Z Hadzibabic, P Kruger, M Cheneau, S P Rath and J Dalibard Dynamical protection of quantum computation from decoherence in laser-driven cold-ion and cold-atom systems Goren Gordon and Gershon Kurizki Spin-flip and spin-conserving optical transitions of the nitrogen-vacancy centre in diamond Ph Tamarat, N B Manson, J P Harrison, R L McMurtrie, A Nizovtsev, C Santori, R G Beausoleil, P Neumann, T Gaebel, F Jelezko, P Hemmer and J Wrachtrup Superconductivity in the attractive Hubbard model: functional renormalization group analysis R Gersch, C Honerkamp and W Metzner Quantum stability of Mott-insulator states of ultracold atoms in optical resonators Jonas Larson, Sonia Fernandez-Vidal, Giovanna Morigi and Maciej Lewenstein

We report on the experimental realization of an ultrahigh vacuum (UHV) indium sealing between a conflat knife edge and an optical window. The sealing requires a very low clamping force and thus allows for the use of very thin and fragile windows.

One of the most counterintuitive consequences of quantum mechanics is that particles can behave like waves. This wavelike nature is seen not only for elementary particles, such as electrons as they orbit the nucleus, but also for free particle beams, as shown by many experiments in electron, neutron and atom optics. Interference effects provide unambiguous proof of wave-like behaviour and in the last five years such effects have been widely used for beams of neutral atomic particles. Researchers are now starting to exploit the wave nature of these beams further by using many tricks already established for optics.

We have studied a general technique for laser cooling a cloud of polarized trapped atoms down to the Doppler temperature. A one-dimensional optical molasses created with polarized light cools the axial motional degree of freedom of the atoms in the trap. Cooling of the radial degrees of freedom can be modeled by reabsorption of scattered photons in the optically dense cloud. We present experimental results for a cloud of chromium atoms in a magnetic trap. A simple model based on rate equations shows quantitative agreement with the experimental results. This scheme allows us to readily prepare a dense cloud of atoms in a magnetic trap with good starting conditions for evaporative cooling.

We have produced an elementary, continuously operating integrated circuit for atoms. The circuit, which is realized by purely optical means, combines an atom source, a switchable channel guide, and a local atom detector within the geometry of a planar atomic waveguide at submicrometer distance from a metallic surface.

We describe two experiments that use neutral atomic beam techniques to write nanostructures. In the chromium experiment, we have used neutral chromium atoms to write one- and two-dimensional periodic nanometer-scale structures in a direct way. The periodic structure is given to the atomic beam by a laser light mask. In a second experiment, we have used a self-assembling monolayer as a resist for metastable helium atoms in a proximity printing experiment.

We show that coherence times of ~ 100 ns are achievable with coherent Rydberg atom spectroscopy in micrometre-sized thermal vapour cells making them robust and promising candidates for scalable quantum devices like single-photon sources.

Fakulta ¨tfur Physik, Universita¨t Konstanz, 78434 Konstanz, Germany~Received 10 June 1996; revised manuscript received 18 December 1996!We report on an experimental observation of correlated atom-photon pairs produced in an atom-opticalexperiment. The pairs are generated from an excited atom that spontaneously emit a single photon. Clearevidence for the pair identification as well as correlation measurements in the atomic motion are reported.@S1050-2947~97!50604-4#PACS number~s!: 42.50.Ct, 32.80.2t, 03.65.Bz, 42.50.Vk

A quantum network which consists of several components should ideally work on a single physical platform. Neutral alkali atoms have the potential to be very well suited for this purpose due to their electronic structure which involves long lived nuclear spins and very sensitive highly excited Rydberg states. In this paper we describe a fabrication method based on quartz glass to structure arbitrary shapes of microscopic vapor cells. We show that the usual spectroscopic properties known from macroscopic vapor cells are almost unaffected by the strong confinement., Comment: 3 pages, 3 figures

We experimentally demonstrate a nanoplasmonic analog of electromagnetically induced transparency utilizing a stacked optical metamaterial. Specifically, we achieve a very narrow transparency window with high modulation depth due to nearly complete suppression of radiative losses.

We study theoretically and experimentally the behaviour of a strongly confined dipolar Bose-Einstein condensate, in the regime of quantum-mechanical stabilization by beyond-mean-field effects. Theoretically, we demonstrate that self-organized striped ground states are predicted in the framework of the extended Gross-Pitaevskii theory. Experimentally, by tilting the magnetic dipoles we show that self-organized striped states can be generated, likely in their metastable state. Matter-wave interference experiments with multiple stripes show that there is no long-range off-diagonal order (global phase coherence). We outline a parameter range where global phase coherence could be established, thus paving the way towards the observation of supersolid states in this system., Comment: 9 pages, 7 figures

Pattern formation is a ubiquitous phenomenon observed in nonlinear and out-of-equilibrium systems. In equilibrium, quantum ferrofluids formed from ultracold atoms were recently shown to spontaneously develop coherent density patterns, manifesting a supersolid. We theoretically investigate the phase diagram of such quantum ferrofluids in oblate trap geometries and find an even wider range of exotic states of matter. Two-dimensional supersolid crystals formed from individual ferrofluid quantum droplets dominate the phase diagram at low densities. For higher densities we find honeycomb and labyrinthine states, as well as a pumpkin phase. We discuss scaling relations which allow us to find these phases for a wide variety of trap geometries, interaction strengths, and atom numbers. Our study illuminates the origin of the various possible patterns of quantum ferrofluids and shows that their occurrence is generic of strongly dipolar interacting systems stabilized by beyond mean-field effects., Comment: 16 pages, 5+2 figures