Focus on Atom Optics and its Applications

Atom optics employs the modern techniques of quantum optics and laser cooling to enable applications which often outperform current standard technologies. Atomic matter wave interferometers allow for ultra-precise sensors; metrology and clocks are pushed to an extraordinary accuracy of 17 digits using single atoms. Miniaturization and integration are driven forward for both atomic clocks and atom optical circuits. With the miniaturization of information-storage and -processing devices, the scale of single atoms is approached in solid state devices, where the laws of quantum physics lead to novel, advantageous features and functionalities. An upcoming branch of atom optics is the control of single atoms, potentially allowing solid state devices to be built atom by atom; some of which would be applicable in future quantum information processing devices. Selective manipulation of individual atoms also enables trace analysis of extremely rare isotopes. Additionally, sources of neutral atoms with high brightness are being developed and, if combined with photo ionization, even novel focused ion beam sources are within reach. Ultracold chemistry is fertilized by atomic techniques, when reactions of chemical constituents are investigated between ions, atoms, molecules, trapped or aligned in designed fields and cooled to ultra-low temperatures such that the reaction kinetics can be studied in a completely state-resolved manner. Focus on Atom Optics and its Applications Contents Sensitive gravity-gradiometry with atom interferometry: progress towards an improved determination of the gravitational constant F Sorrentino, Y-H Lien, G Rosi, L Cacciapuoti, M Prevedelli and G M Tino A single-atom detector integrated on an atom chip: fabrication, characterization and application D Heine, W Rohringer, D Fischer, M Wilzbach, T Raub, S Loziczky, XiYuan Liu, S Groth, B Hessmo and J Schmiedmayer Interaction of a propagating guided matter wave with a localized potential G L Gattobigio, A Couvert, B Georgeot and D Guéry-Odelin Analysis of the entanglement between two individual atoms using global Raman rotations A Gaëtan, C Evellin, J Wolters, P Grangier, T Wilk and A Browaeys Spin polarization transfer in ground and metastable helium atom collisions D Vrinceanu and H R Sadeghpour A fiber Fabry–Perot cavity with high finesse D Hunger, T Steinmetz, Y Colombe, C Deutsch, T W Hänsch and J Reichel Atomic wave packets in amplitude-modulated vertical optical lattices A Alberti, G Ferrari, V V Ivanov, M L Chiofalo and G M Tino Atom interferometry with trapped Bose–Einstein condensates: impact of atom–atom interactions Julian Grond, Ulrich Hohenester, Igor Mazets and Jörg Schmiedmayer Storage of protonated water clusters in a biplanar multipole rf trap C Greve, M Kröner, S Trippel, P Woias, R Wester and M Weidemüller Single-atom detection on a chip: from realization to application A Stibor, H Bender, S Kühnhold, J Fortágh, C Zimmermann and A Günther Ultracold atoms as a target: absolute scattering cross-section measurements P Würtz, T Gericke, A Vogler and H Ott Entanglement-assisted atomic clock beyond the projection noise limit Anne Louchet-Chauvet, Jürgen Appel, Jelmer J Renema, Daniel Oblak, Niels Kjaergaard and Eugene S Polzik Towards the realization of atom trap trace analysis for 39Ar J Welte, F Ritterbusch, I Steinke, M Henrich, W Aeschbach-Hertig and M K Oberthaler Resonant superfluidity in an optical lattice I Titvinidze, M Snoek and W Hofstetter Interference of interacting matter waves Mattias Gustavsson, Elmar Haller, Manfred J Mark, Johann G Danzl, Russell Hart, Andrew J Daley and Hanns-Christoph Nägerl Magnetic trapping of NH molecules with 20 s lifetimes E Tsikata, W C Campbell, M T Hummon, H-I Lu and J M Doyle Imprinting patterns of neutral atoms in an optical lattice using magnetic resonance techniques Michal Karski, Leonid Förster, Jai-Min Choi, Andreas Steffen, Noomen Belmechri, Wolfgang Alt, Dieter Meschede and Artur Widera Frequency stability of optical lattice clocks Jérôme Lodewyck, Philip G Westergaard, Arnaud Lecallier, Luca Lorini and Pierre Lemonde Ultracold quantum gases in triangular optical lattices C Becker, P Soltan-Panahi, J Kronjäger, S Dörscher, K Bongs and K Sengstock Cold atoms near superconductors: atomic spin coherence beyond the Johnson noise limit B Kasch, H Hattermann, D Cano, T E Judd, S Scheel, C Zimmermann, R Kleiner, D Koelle and J Fortágh Focusing a deterministic single-ion beam Wolfgang Schnitzler, Georg Jacob, Robert Fickler, Ferdinand Schmidt-Kaler and Kilian Singer Tuning the structural and dynamical properties of a dipolar Bose–Einstein condensate: ripples and instability islands M Asad-uz-Zaman and D Blume Double-resonance lineshapes in a cell with wall coating and buffer gas Svenja Knappe and Hugh G Robinson Transport and interaction blockade of cold bosonic atoms in a triple-well potential P Schlagheck, F Malet, J C Cremon and S M Reimann Fabrication of a planar micro Penning trap and numerical investigations of versatile ion positioning protocols M Hellwig, A Bautista-Salvador, K Singer, G Werth and F Schmidt-Kaler Laser cooling of a magnetically guided ultracold atom beam A Aghajani-Talesh, M Falkenau, V V Volchkov, L E Trafford, T Pfau and A Griesmaier Creation efficiency of nitrogen-vacancy centres in diamond S Pezzagna, B Naydenov, F Jelezko, J Wrachtrup and J Meijer Top-down pathways to devices with few and single atoms placed to high precision Jessica A Van Donkelaar, Andrew D Greentree, Andrew D C Alves, Lenneke M Jong, Lloyd C L Hollenberg and David N Jamieson Enhanced electric field sensitivity of rf-dressed Rydberg dark states M G Bason, M Tanasittikosol, A Sargsyan, A K Mohapatra, D Sarkisyan, R M Potvliege and C S Adams


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As early as 1933, Frisch [1] observed the transfer of momentum from light to atoms. However, a new era of atomic physics was introduced by the seminal proposals for laser cooling of atoms in dilute gases and beams made by Hänsch and Schawlow [2] and independently by Wineland and Dehmelt [3]. Since then, laser cooling and, more generally, the manipulation of all motional degrees of freedom such as velocity and position down to the limits dictated by quantum laws, have been enormously successful. About 20 years ago mirrors, beam splitters, lenses, decelerators, accelerators, and deflectors for atoms were realized experimentally for the first time [4]- [7]. Though still very far from being a realistic route for atom optical applications at that time, those experiments already demonstrated that matter waves can be handled in almost the same way as light. After the advent of Bose-Einstein condensates in 1995, atom-lasers became available as laser-like coherent sources of matter waves. Simultaneously, matter wave interferometers of different types were developed with an impressive sensitivity to inertial and gravitational effects, outperforming optical interferometers in several cases.
Today we are witnessing a rapid evolution of this field in various application-oriented directions, including developments in precision sensors, single atom fabrication, quantum emulation of macroscopic quantum phenomena, miniaturization and integration, ultra-precise metrology, trace gas analysis, and single atom controlled molecular optics. This focus issue of New Journal of Physics, which provides a broad view of the state of the art in this field of applied atom optics, emerged from the ATOMICS conference 6 , where a number of recent highlights in interferometry and sensing, lithography and nanostructures, metrology and clocks, quantum information, and ultra-cold chemistry were presented.
Since the early demonstration experiments, atom optics has enabled development of novel types of sensor, based on the interaction of atoms with external fields. One of the bestestablished atom sensing methods relies on atom-light interaction. When enhanced by an optical cavity, ultimately even a single photon and a single atom interact with one another. The novel enabling technology of fibre-optical high-finesse micro-cavities [8] can be adapted as a sensing tool for neutral trapped atoms, Bose-Einstein condensates or single trapped ions, working as well for these as for solid state quantum emitters delivering single photons in quantum communication protocols. Further topics of interest in atomic sensing include surface-atom interactions, inertial effects, gravitational and weak electric or magnetic field detection. For example, Rydberg atoms are highly susceptible to electric fields and the resulting type of sensor may be tuned and optimized by an additionally applied radio frequency field [9]. Alternatively, if ultra-cold atoms are brought close to a superconducting surface they experience the modified noise spectrum of this body. This measurement is one of the very first to join ultralow temperatures of atoms with a nearby cryogenic surface [10,11]. Interference effects in a lattice potential for atoms may be useful as gravity sensors at the micrometer scale [12]. The interference of matter waves is also a very sensitive probe for interactions among atoms [13,14]. Besides interferometric sensors transport measurements, e.g. in multi-well potentials, are also affected by interaction effects [15].
In view of these applications, a continuous high-flux source of degenerate quantum matter is the focus of [16]. If successful, such a device would deliver in a steady-state fashion a coherent atomic matter wave, quite similar to the well-known stimulated light emission from a cw-laser.
In a different direction, quantum manipulation of individual atoms is making impressive progress. Beautiful examples illustrating this point include the counting of atoms one by 3 one [17], trace analysis of very rare isotopes to determine the age of water samples [18], and likewise single atom counting [19] or high-resolution positioning of single atoms. Here one relies on single atoms or ions to place them with high spatial resolution into a solid state crystal. In this way, atom optical experiments constitute an enabling technology for modern solid state physics at the nm-scale [20,21]. One of the applications of such single ion delivery is the deterministic formation of nitrogen vacancy centers in diamonds, as discussed in [22].
In addition to the fabrication side, the modeling of strongly correlated materials and their nonequilibrium quantum dynamics are intriguing directions for research, in particular for ultracold atomic ensembles in optical lattices. However, they represent major theoretical challenges, and new approaches have to be developed to describe the time evolution of such strongly interacting bosonic/fermionic systems that exploit the availability of Feshbach resonances for continuously tunable interactions. A detailed knowledge and understanding of the ultra-cold collision dynamics represents a key ingredient for the design and modeling of the corresponding many-body systems. Inelastic collisions, in particular those involving metastable partners, lead to a quantum gas governed by energy and spin excitation transfer processes [23]. Generalized dynamical mean-field theory is used to detect novel quantum phase transitions, leading to fermionic Mott insulators at half filling [24]. Preparing arbitrary patterns of neutral atoms in optical lattices in a controlled way is a key ingredient for designing new structures and materials, reaching novel quantum dynamics and for quantum information and simulation. Single site precision can be achieved by using microwave radiation in a magnetic field gradient [25]. Dipolar Bose-Einstein condensates are envisaged by exploiting the long-range interactions of, e.g., ultra-cold heteronuclear dimers in electric fields. Already on the mean-field level, dipolar condensates show novel phase diagrams and structured ground states [26]. Aspects of trapping ultra-cold heteronuclear molecules are presented in [27]. The geometry of quantum spins in a lattice governs its properties, as proposed for a frustrated anti-ferromagnet [28]. It is surprising how such atom optics experiments emulate the behavior of solid state Hamiltonians, using very clean and tunable interaction strengths and geometries [29,30]. Hardly possible for a real world solid state system, but realized in the atom optics setting, the dynamics of the Mott-insulator-tosuperfluid phase transition was observed, and future investigations will address Neel ordering and spin liquid phases. Yet another way to position atomic spins in arbitrary lattice shapes is presented in [31], where micro-structured planar Penning trap arrays are employed. Traps for ions and molecular ions are optimized to study chemical reactions at low temperatures under well-controlled conditions [32].
Atomic clocks and frequency standards are within the traditional métier of applied atomic physics, either with single trapped ions [33] or with ensembles of a large number of neutral atoms [34]. These devices show an improvement in performance when entangled atoms are used, as reported in [36]. Lattice clocks employ many neutral atoms, but in order to avoid their collisional frequency shifts and uncertainties they are trapped in appropriate optical lattices [35,37]. The coherent-population-trapping atomic clock is based on the quantum interference of excitations of two clock states into a third level. Here, a compact but still highly accurate frequency standard is envisioned [38]. A magic coating and the buffer gas filling increase nuclear spin T 2 coherence times such that even a low-cost device can serve as either a sensitive magnetometer or an atomic clock.
This collection of papers can only give a first impression of the depth and breadth of modern developments in atomic physics and their interesting applications. However, it reflects