Quantum-gas microscopes - A new tool for cold-atom quantum simulators

This "Perspectives" paper gives a brief overview of the recent developments with quantum-gas microscopes and how they can be used to build the next generation of cold-atom quantum simulators.Comment: "Perspectives" paper for Special Issue "Cold Atom Physics" of Natl. Sci. Rev; published online April 19, 201

A controlled quantum system of individual neutral atoms

This thesis presents novel techniques to realize controllable quantum systems of neutral atoms. Besides the preparation of the exact number of atoms, we manipulate all physical degrees of freedom of the trapped particles. The first part (Chapters 2, 3) reports on a deterministic source of single atoms, which overcomes the limitations imposed by statistical arrival in conventional sources. Single cold cesium atoms prepared in a magneto-optical trap are transferred into a standing wave optical dipole trap, made of two counter-propagating red-detuned Nd:YAG laser beams. Mutual detuning of the laser beam frequencies moves the standing wave pattern, allowing us to accelerate and stop an atom at preselected points along the standing wave. This "optical conveyor belt" can transport one atom over a maximum distance of 10~mm. The second part (Chapters 4, 5) reports on the investigation of the coherence times of the Cs hyperfine ground states using microwave transitions. Using Ramsey spectroscopy techniques we measured coherence times of up to 100 ms. The limiting dephasing effects are experimentally identified and are of technical rather than fundamental nature. We present an analytical model of the reversible and irreversible dephasing mechanisms. Finally, we prove that controlled transport by the optical conveyor belt over macroscopic distances preserves the atomic coherence with slight reduction of coherence time.Gegenstand dieser Arbeit ist die Realisierung von kontrollierten Quantensystemen aus einzelnen neutralen Atomen. Neben der exakten Kontrolle der Anzahl der Atome können wir alle physikalischen Freiheitsgrade der gespeicherten Atome gezielt manipulieren. Der erste Teil (Kapitel 2, 3) berichtet über eine neuartige deterministische Quelle kalter Atome, die die Limitierung statistisch verteilter Ankunftszeiten bei konventionellen Atomquellen überwindet. Einzelne kalte Cäsiumatome werden von einer magneto-optischen Falle in eine optische Stehwellen-Dipolfalle, die von zwei entgegengerichteten Nd:YAG Laserstrahlen erzeugt wird, transferiert. Durch eine relative Verstimmung der beiden Laserfrequenzen kann die Stehwellenstruktur bewegt werden und auf diese Weise die Atome entlang der Strahlachse transportieren. Dieses "optische Förderband" ermöglicht den Transport eines einzelnen Atoms über eine Entfernung von 10 mm. Im zweiten Teil (Kapitel 4, 5) werden die Kohärenzzeiten der Hyperfein-Grundzustände der gespeicherten Cäsiumatome untersucht. Mit Hilfe der Ramsey-Spektroskopie wurden Kohärenzzeiten von mehr als 100 ms gemessen. Die limitierenden Dephasierungseffekte konnten experimentell identifiziert werden und sind rein technischer Natur. Ein analytisches Modell beschreibt die reversiblen und irreversiblen Dephasierungseffekte. Schließlich wird gezeigt, dass ein Transport der Atome mit dem optischen Förderband die Kohärenzen erhält, wobei die Kohärenzzeit nur leicht reduziert wird

A cavity-QED scheme for Heisenberg-limited interferometry

We propose a Ramsey interferometry experiment using an entangled state of N atoms to reach the Heisenberg limit for the estimation of an atomic phase shift if the atom number parity is perfectly determined. In a more realistic situation, due to statistical fluctuations of the atom source and the finite detection efficiency, the parity is unknown. We then achieve about half the Heisenberg limit. The scheme involves an ensemble of circular Rydberg atoms which dispersively interact successively with two initially empty microwave cavities. The scheme does not require very high-Q cavities. An experimental realization with about ten entangled Rydberg atoms is achievable with state of art apparatuses.Comment: 13 pages, 7 figure

Des atomes ultrafroids sous le microscope

Des atomes ultrafroids peuvent être piégés dans un réseau périodique obtenu à l’aide de faisceaux laser. De même que les électrons dans un solide, les atomes dans un tel « réseau optique » peuvent se comporter comme un métal supraconducteur ou au contraire comme un isolant. Les physiciens savent désormais observer ces phénomènes au microscope, atome par atome, avec une résolution comparable au pas du réseau. Ils peuvent aussi manipuler sélectivement les atomes d’un site donné, en changeant leur état quantique. Ces progrès ouvrent des perspectives enthousiasmantes pour le traitement quantique de l’information

Single atoms in a standing-wave dipole trap

We trap a single cesium atom in a standing-wave optical dipole trap. Special experimental procedures, designed to work with single atoms, are used to measure the oscillation frequency and the atomic energy distribution in the dipole trap. These methods rely on unambiguously detecting presence or loss of the atom using its resonance fluorescence in the magneto-optical trap.Comment: 8 pages, 7 figures, submitted to Phys. Rev.

An optical conveyor belt for single neutral atoms

Using optical dipole forces we have realized controlled transport of a single or any desired small number of neutral atoms over a distance of a centimeter with sub-micrometer precision. A standing wave dipole trap is loaded with a prescribed number of cesium atoms from a magneto-optical trap. Mutual detuning of the counter-propagating laser beams moves the interference pattern, allowing us to accelerate and stop the atoms at preselected points along the standing wave. The transportation efficiency is close to 100%. This optical "single-atom conveyor belt" represents a versatile tool for future experiments requiring deterministic delivery of a prescribed number of atoms on demand.Comment: 8 pages, 8 figures, submitted to Applied Physics

Coherent light scattering from a two-dimensional Mott insulator

We experimentally demonstrate coherent light scattering from an atomic Mott insulator in a two-dimensional lattice. The far-field diffraction pattern of small clouds of a few hundred atoms was imaged while simultaneously laser cooling the atoms with the probe beams. We describe the position of the diffraction peaks and the scaling of the peak parameters by a simple analytic model. In contrast to Bragg scattering, scattering from a single plane yields diffraction peaks for any incidence angle. We demonstrate the feasibility of detecting spin correlations via light scattering by artificially creating a one-dimensional antiferromagnetic order as a density wave and observing the appearance of additional diffraction peaks.Comment: 4 pages, 4 figure

Zooming in on ultracold matter : two superresolution microscopy methods can image the atomic density of ultracold quantum gases with nanometer resolution

Ultracold atoms are an exceptionally versatile platform to test novel physical concepts. They have greatly advanced our understanding of the physics of many-body systems and allowed precision measurements of fundamental constants. They are also a promising architecture for quantum computation and quantum simulation. A key to the practicality of ultra-cold atoms is the ability to image them with high spatial resolution. Available microscopy schemes have reached sufficient resolution to detect individual atoms trapped in optical lattices with submicron spacings, but their spatial resolution is typically limited to about half the wavelength of the imaging light. Now, two independent teams—one led by Cheng Chin from the University of Chicago, Illinois, and the other led by Steve Rolston and Trey Porto from the University of Maryland, College Park —have reported subwavelength-resolution imaging techniques for ultracold atoms. The methods, capable of resolving objects up to 50 times smaller than the optical wavelength, have allowed the teams to map the shape of atomic density distributions on nanometer scales. Nanoscale maps of atomic density will be important observables for probing many-body effects in cold atomic and molecular systems

Ultrahigh finesse Fabry-Perot superconducting resonator

We have built a microwave Fabry-Perot resonator made of diamond-machined copper mirrors coated with superconducting niobium. Its damping time (Tc = 130 ms at 51 GHz and 0.8 K) corresponds to a finesse of 4.6 x 109, the highest ever reached for a Fabry-Perot in any frequency range. This result opens novel perspectives for quantum information, decoherence and non-locality studies