Atreju Tauschinsky

Spatially resolved excitation of Rydberg atoms and surface effects on an atom chip

We demonstrate spatially resolved, coherent excitation of Rydberg atoms on an atom chip. Electromagnetically induced transparency (EIT) is used to investigate the properties of the Rydberg atoms near the gold-coated chip surface. We measure distance-dependent shifts ({approx}10 MHz) of the Rydberg energy levels caused by a spatially inhomogeneous electric field. The measured field strength and distance dependence is in agreement with a simple model for the electric field produced by a localized patch of Rb adsorbates deposited on the chip surface during experiments. The EIT resonances remain narrow (<4 MHz) and the observed widths are independent of atom-surface distance down to {approx} 20 {mu}m, indicating relatively long lifetime of the Rydberg states. Our results open the way to studies of dipolar physics, collective excitations, quantum metrology, and quantum information processing involving interacting Rydberg excited atoms on atom chips.

Detection of small atom numbers through image processing

We demonstrate improved detection of small trapped atomic ensembles through advanced postprocessing and optimal analysis of absorption images. A fringe-removal algorithm reduces imaging noise to the fundamental photon-shot-noise level and proves beneficial even in the absence of fringes. A maximum-likelihood estimator is then derived for optimal atom-number estimation in well-localized ensembles and is applied to real experimental data to measure the population differences and intrinsic atom shot noise between spatially separated ensembles each comprising between 10 and 2000 atoms. The combined techniques improve our signal-to-noise ratio by a factor of 3, to a minimum resolvable population difference of 17 atoms, close to our ultimate detection limit.

Magnetic-film atom chip with 10 μm period lattices of microtraps for quantum information science with Rydberg atoms

We describe the fabrication and construction of a setup for creating lattices of magnetic microtraps for ultracold atoms on an atom chip. The lattice is defined by lithographic patterning of a permanent magnetic film. Patterned magnetic-film atom chips enable a large variety of trapping geometries over a wide range of length scales. We demonstrate an atom chip with a lattice constant of 10 μm, suitable for experiments in quantum information science employing the interaction between atoms in highly excited Rydberg energy levels. The active trapping region contains lattice regions with square and hexagonal symmetry, with the two regions joined at an interface. A structure of macroscopic wires, cutout of a silver foil, was mounted under the atom chip in order to load ultracold (87)Rb atoms into the microtraps. We demonstrate loading of atoms into the square and hexagonal lattice sections simultaneously and show resolved imaging of individual lattice sites. Magnetic-film lattices on atom chips provide a versatile platform for experiments with ultracold atoms, in particular for quantum information science and quantum simulation.

Observation of Stückelberg oscillations in dipole-dipole interactions

We have observed Stueckelberg oscillations in the dipole-dipole interaction between Rydberg atoms with an externally applied radio-frequency field. The oscillating rf field brings the interaction between cold Rydberg atoms in two separated volumes into resonance. We observe multiphoton transitions when varying the amplitude of the rf field and the static electric field offset. The angular momentum states we use show a quadratic Stark shift, which leads to a fundamentally different behavior than linearly shifting states. Both cases are studied theoretically using the Floquet approach and are compared. The amplitude of the sidebands, related to the interaction strength, is given by the Bessel function in the linearly shifting case and by the generalized Bessel function in the quadratically shifting case. The oscillatory behavior of both functions corresponds to Stueckelberg oscillations, an interference effect described by the semiclassical Landau-Zener-Stueckelberg model. The measurements prove coherent dipole-dipole interaction during at least 0.6 mus.

Measurement of 87Rb Rydberg-state hyperfine splitting in a room-temperature vapor cell

We present direct measurements of the hyperfine splitting of Rydberg states in 87Rb using electromagnetically induced transparency (EIT) spectroscopy in a room-temperature vapor cell. With this method, and in spite of Doppler broadening, linewidths of 3.7 MHz FWHM, i.e., significantly below the intermediate-state natural linewidth, are reached. This allows resolving hyperfine splittings for Rydberg s states with n=20,...,24. With this method we are able to determine Rydberg state hyperfine splittings with an accuracy of approximately 100 kHz. Ultimately, our method allows accuracies of order 5 kHz to be reached. Furthermore, we present a direct measurement of hyperfine-resolved Rydberg-state Stark shifts. These results will be of great value for future experiments relying on excellent knowledge of Rydberg-state energies and polarizabilities.

Zeeman deceleration of electron-impact-excited metastable helium atoms

We present experimental results that demonstrate - for the first time - the Zeeman deceleration of helium atoms in the metastable 2^3S_1state. A more than 40% decrease of the kinetic energy of the beam is achieved for deceleration from 490 m/s to a final velocity of 370 m/s. Metastable atom generation is achieved with an electron-impact-excitation source whose performance is enhanced through an additional discharge-type process which we characterize in detail. Comparison of deceleration data at different electron beam pulse durations confirms that a matching between the initial particle distribution and the phase-space acceptance of the decelerator is crucial for the production of a decelerated packet with a well-defined velocity distribution. The experimental findings are in good agreement with three-dimensional numerical particle trajectory simulations.

Ejection of Coulomb Crystals from a Linear Paul Ion Trap for Ion-Molecule Reaction Studies.

Coulomb crystals are being increasingly employed as a highly localized source of cold ions for the study of ion-molecule chemical reactions. To extend the scope of reactions that can be studied in Coulomb crystals-from simple reactions involving laser-cooled atomic ions, to more complex systems where molecular reactants give rise to multiple product channels-sensitive product detection methodologies are required. The use of a digital ion trap (DIT) and a new damped cosine trap (DCT) are described, which facilitate the ejection of Coulomb-crystallized ions onto an external detector for the recording of time-of-flight (TOF) mass spectra. This enables the examination of reaction dynamics and kinetics between Coulomb-crystallized ions and neutral molecules: ionic products are typically cotrapped, thus ejecting the crystal onto an external detector reveals the masses, identities, and quantities of all ionic species at a selected point in the reaction. Two reaction systems are examined: the reaction of Ca(+) with deuterated isotopologues of water, and the charge exchange between cotrapped Xe(+) with deuterated isotopologues of ammonia. These reactions are examples of two distinct types of experiment, the first involving direct reaction of the laser-cooled ions, and the second involving reaction of sympathetically-cooled heavy ions to form a mixture of light product ions. Extensive simulations are conducted to interpret experimental results and calculate optimal operating parameters, facilitating a comparison between the DIT and DCT approaches. The simulations also demonstrate a correlation between crystal shape and image shape on the detector, suggesting a possible means for determining crystal geometry for nonfluorescing ions.

Sensitive absorption imaging of single atoms in front of a mirror

In this paper we show that the sensitivity of absorption imaging of ultracold atoms can be significantly improved by imaging in a standing-wave configuration. We present simulations of single-atom absorption imaging both for a travelling-wave and a standing-wave imaging setup, based on a scattering approach to calculate the optical density of a single atom. We find that the optical density of a single atom is determined only by the numerical aperture of the imaging system. We determine optimum imaging parameters, taking all relevant sources of noise into account. For reflective imaging we find an improvement of 1.7 in the maximum signal-to-noise ratio can be achieved. This is particularly useful for imaging in the vicinity of an atom chip, where a reflective surface is naturally present.

Electromagnetically induced transparency with Rydberg atoms across the Breit-Rabi regime

We present experimental results on the influence of magnetic fields and laser polarization on electromagnetically induced transparency (EIT) using Rydberg levels of

Microtrap Arrays On Magnetic Film Atom Chips For Quantum Information Science

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