Quantentechnologie

2005

• I. Dotsenko, W. Alt, M. Khudaverdyan, S. Kuhr, D. Meschede, Y. Miroshnychenko, D. Schrader and A. Rauschenbeutel
  Submicrometer position control of single trapped neutral atoms, Phys. Rev. Lett. 95, 033002 (2005)arXivBibTeX
  ABSTRACT »

  We optically detect the positions of single neutral cesium atoms stored in a standing wave dipole trap with a sub-wavelength resolution of 143 nm rms. The distance between two simultaneously trapped atoms is measured with an even higher precision of 36 nm rms. We resolve the discreteness of the interatomic distances due to the 532 nm spatial period of the standing wave potential and infer the exact number of trapping potential wells separating the atoms. Finally, combining an initial position detection with a controlled transport, we place single atoms at a predetermined position along the trap axis to within 300 nm rms.

• M. Khudaverdyan, W. Alt, I. Dotsenko, L. Förster, S. Kuhr, D. Meschede, Y. Miroshnychenko, D. Schrader and A. Rauschenbeutel
  Adiabatic Quantum State Manipulation of Single Trapped Atoms, Phys. Rev. A 71, 031404 (2005)arXivBibTeX
  ABSTRACT »

  We use microwave induced adiabatic passages for selective spin flips within a string of optically trapped individual neutral Cs atoms. We position-dependently shift the atomic transition frequency with a magnetic field gradient. To flip the spin of a selected atom, we optically measure its position and sweep the microwave frequency across its respective resonance frequency. We analyze the addressing resolution and the experimental robustness of this scheme. Furthermore, we show that adiabatic spin flips can also be induced with a fixed microwave frequency by deterministically transporting the atoms across the position of resonance.

• S. Kuhr, W. Alt, D. Schrader, I. Dotsenko, Y. Miroshnychenko, A. Rauschenbeutel and D. Meschede
  Analysis of dephasing mechanisms in a standing-wave dipole trap, Phys. Rev. A 72, 023406 (2005)arXivBibTeX
  ABSTRACT »

  We study in detail the mechanisms causing dephasing of hyperfine coherences of cesium atoms confined by a far off-resonant standing wave optical dipole trap [S. Kuhr et al., Phys. Rev. Lett. 91, 213002 (2003)]. Using Ramsey spectroscopy and spin echo techniques, we measure the reversible and irreversible dephasing times of the ground state coherences. We present an analytical model to interpret the experimental data and identify the homogeneous and inhomogeneous dephasing mechanisms. Our scheme to prepare and detect the atomic hyperfine state is applied at the level of a single atom as well as for ensembles of up to 50 atoms.

2004

• I. Dotsenko, W. Alt, S. Kuhr, D. Schrader, M. Müller, Y. Miroshnychenko, V. Gomer, A. Rauschenbeutel and D. Meschede
  Application of electro-optically generated light fields for Raman spectroscopy of trapped Cesium atoms, Appl. Phys. B 78, 711-717 (2004)BibTeX
  ABSTRACT »

  We present an apparatus for generating a multi-frequency laser field to coherently couple the F=3 and F=4 ground state of trapped cesium atoms through Raman transitions. We use a single frequency diode laser and generate sidebands by means of a 9.2 GHz electro-optic modulator. With an interferometer, we separated the sidebands and carrier, sending them to the trapped atoms in opposite directions. The Rabi oscillation of the populations of F=3 and F=4 is monitored. We find that due to destructive quantum interference of two simultaneous Raman transitions the expected Rabi frequency is reduced by a factor that is in quantitative agreement with theoretical expectations. It is demonstrated how this interference can be suppressed experimentally. Besides, we demonstrate the application of the setup for Raman spectroscopy of Zeeman sublevels and of the vibrational states of a small number of trapped atoms.

2003

• S. Kuhr
  A controlled quantum system of individual neutral atoms, (2003), DoktorarbeitBibTeX

• Y. Miroshnychenko, D. Schrader, S. Kuhr, W. Alt, I. Dotsenko, M. Khudaverdyan, A. Rauschenbeutel and D. Meschede
  Continued imaging of the transport of a single neutral atom, Opt. Express 11, 3498-3502 (2003)BibTeX
  ABSTRACT »

  We have continuously imaged the controlled motion of a single atom as well as of a small number of distinguishable atoms with observation times exceeding one minute. The Cesium atoms are confined to potential wells of a standing wave optical dipole trap which allows to transport them over macroscopic distances. The atoms are imaged by an intensified CCD camera, and spatial resolution near the diffraction limit is obtained.

• D. Schrader, S. Kuhr, W. Alt, Y. Miroshnychenko, I. Dotsenko, W. Rosenfeld, M. Khudaverdyan, V. Gomer, A. Rauschenbeutel and D. Meschede
  Controlled transport of single neutral atom qubits, Proceedings of the 16th ICOLS, (2003)BibTeX
  ABSTRACT »

  We have prepared and detected quantum coherences of trapped cesium atoms with long dephasing times. Controlled transport by an “optical conveyor belt” over macroscopic distances preserves the atomic coherence with slight reduction of coherence time. The dominating dephasing effects are experimentally identified and found to be of technical rather than fundamental nature.

• S. Kuhr, W. Alt, D. Schrader, I. Dotsenko, Y. Miroshnychenko, W. Rosenfeld, M. Khudaverdyan, V. Gomer, A. Rauschenbeutel and D. Meschede
  Coherence properties and quantum state transportation in an optical conveyor belt, Phys. Rev. Lett. 91, 213002 (2003)arXivBibTeX
  ABSTRACT »

  We have prepared and detected quantum coherences with long dephasing times at the level of single trapped cesium atoms. Controlled transport by an "optical conveyor belt" over macroscopic distances preserves the atomic coherence with slight reduction of coherence time. 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. Coherent quantum bit operations along with quantum state transport open the route towards a "quantum shift register" of individual neutral atoms.

• W. Alt, D. Schrader, S. Kuhr, M. Müller, V. Gomer and D. Meschede
  Single atoms in a standing-wave dipole trap, Phys. Rev. A 67, 033403 (2003)arXivBibTeX
  ABSTRACT »

  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.

2002

• B. Ueberholz, S. Kuhr, D. Frese, V. Gomer and D. Meschede
  Cold collisions in a high-gradient magneto-optical trap, J. Phys. B: At. Mol. Opt. Phys. 35, 4899 (2002)BibTeX
  ABSTRACT »

  We present a detailed analysis of the cold collision measurements performed in a high-gradient magneto-optical trapwith a few trapped Cs atomsfirst presented in Ueberholz et al (J. Phys. B: At.Mol. Opt. Phys. 33 (2000) L135). The ability to observe individual loss events allows us to identify two-body collisions that lead to the escape of only one of the colliding atoms (up to 10% of all collisional losses). Possible origins of these events are discussed here. We also observed strong modifications of the total loss rate with variations in the repumping laser intensity. This is explained by a simple semiclassical model based on optical suppression of hyperfine-changing collisions between ground-state atoms.

2001

• S. Kuhr, W. Alt, D. Schrader, M. Müller, V. Gomer and D. Meschede
  Deterministic Delivery of a Single Atom, Science 293, 278 (2001)BibTeX
  ABSTRACT »

  We report the realization of a deterministic source of single atoms. A standing-wave dipole trap is loaded with one or any desired number of cold cesium atoms from a magneto-optical trap. By controlling the motion of the standing wave, we adiabatically transport the atom with submicrometer precision over macroscopic distances on the order of a centimeter. The displaced atom is observed directly in the dipole trap by fluorescence detection. The trapping field can also be accelerated to eject a single atom into free flight with well-defined velocities.

• D. Schrader, S. Kuhr, W. Alt, M. Müller, V. Gomer and D. Meschede
  An optical conveyor belt for single neutral atoms, Appl. Phys. B 73, 819 (2001)arXivBibTeX
  ABSTRACT »

  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.

2000

• D. Frese, B. Ueberholz, S. Kuhr, W. Alt, D. Schrader, V. Gomer and D. Meschede
  Single Atoms in an Optical Dipole Trap: Towards a Deterministic Source of Cold Atoms, Phys. Rev. Lett. 85, 3777 (2000)arXivBibTeX
  ABSTRACT »

  We describe a simple experimental technique which allows us to store a small and deterministic number of neutral atoms in an optical dipole trap. The desired atom number is prepared in a magneto-optical trap overlapped with a single focused Nd:YAG laser beam. Dipole trap loading efficiency of 100% and storage times of about one minute have been achieved. We have also prepared atoms in a certain hyperfine state and demonstrated the feasibility of a state-selective detection via resonance fluorescence at the level of a few neutral atoms. A spin relaxation time of the polarized sample of $4.2\pm 0.7$ s has been measured. Possible applications are briefly discussed.

• B. Ueberholz, S. Kuhr, D. Frese, D. Meschede and V. Gomer
  Counting Cold Collisions, J. Phys. B: At. Mol. Opt. Phys. 33, L135 (2000)arXivBibTeX
  ABSTRACT »

  We have experimentally explored a novel possibility to study exoergic cold atomic collisions. Trapping of small countable atom numbers in a shallow magneto-optical trap and monitoring of their temporal dynamics allows us to directly observe isolated two-body atomic collisions and provides detailed information on loss statistics. A substantial fraction of such cold collisional events has been found to result in the loss of one atom only. We have also observed for the first time a strong optical suppression of ground-state hyperfine-changing collisions in the trap by its repump laser field.

1999

• S. Kuhr
  Kalte Stöße mit einzelnen Atomen, (1999), DiplomarbeitBibTeX
  ABSTRACT »

  Im Rahmen dieser Arbeit wurde ein Einblick in die Stoßprozesse zwischen einzelnen Cäsium-Atomen gewonnen. Unsere Ergebnisse unterscheiden sich signifikant von denen anderer Experimente, die an Standard-MOTs mit vielen Atomen durchgeführt wurden. Die Beobachtung nur weniger Atome sowie die geringe Potentialtiefe der MOT haben es ermöglicht, völlig neuartige Effekte zu studieren. Die gemessene Abhängigkeit der Verlustraten wird mit Hilfe eines semiklassischen Modells zufriedenstellend gedeutet. Aus den Meßdaten kann außerdem der experimentell nur schwer zugängliche Verlustkoeffizient für Grundzustandsstöße ermittelt werden. Die Ergebnisse dieses Experiments sind hierbei um eine Größenordnung genauer als bisherige Messungen. Ein hervorzuhebendes Ergebnis ist die gemessene Abnahme der Verlustraten bei zunehmender Leistung des Rückpumplasers. Sorgfältige Berechnungen legen die Interpretation nahe, daß der Rückpumplaser eine Unterdrückung der Grundzustandsstöße durch Optical Shielding bewirkt. Es handelt sich also um einen MOT-intrinsischen Effekt, der in anderen Experimenten bisher nicht erkannt wurde. Eine Besonderheit unserer Messungen ist der Nachweis von Stoßprozessen zwischen zwei Atomen, bei denen nur ein Atom die Falle verläßt. Dies widerspricht der vorher angenommenen Symmetrie des Stoßprozesses und des Fallenpotentials. Zur Erklärung wurden verschiedene Ansätze diskutiert. Am plausibelsten erweist sich eine Interpretation, daß es sich um strahlungsumverteilende Prozesse handelt. Aufgrund der räumlichen Anisotropie des Fallenpotentials ist es dabei möglich, daß ein Atom die Falle verläßt, wogegen das andere wieder eingefangen wird.