Quantum technologies

2012

• N. Spethmann, F. Kindermann, S. John, C. Weber, D. Meschede and A. Widera
  Dynamics of single neutral impurity atoms immersed in an ultracold gas, Phys. Rev. Lett. 109, 235301 (2012)arXivBibTeX
  ABSTRACT »

  We report on controlled doping of an ultracold Rb gas with single neutral Cs impurity atoms. Elastic two-body collisions lead to a rapid thermalization of the impurity inside the Rb gas, representing the first realization of an ultracold gas doped with a precisely known number of impurity atoms interacting via s-wave collisions. Inelastic interactions are restricted to a single three-body recombination channel in a highly controlled and pure setting, which allows to determine the Rb-Rb-Cs three-body loss rate with unprecedented precision. Our results pave the way for a coherently interacting hybrid system of individually controllable impurities in a quantum many-body system.

• N. Spethmann, F. Kindermann, S. John, C. Weber, D. Meschede and A. Widera
  Inserting single Cs atoms into an ultracold Rb gas, Appl. Phys. B 106, 513 (2012)arXivBibTeX
  ABSTRACT »

  We report on the controlled insertion of individual Cs atoms into an ultracold Rb gas at ≈400 nK. This requires one to combine the techniques necessary for cooling, trapping and manipulating single laser cooled atoms around the Doppler temperature with an experiment to produce ultracold degenerate quantum gases. In our approach, both systems are prepared in separated traps and then combined. Our results pave the way for coherent interaction between a quantum gas and a single or few neutral atoms of another species.

2010

• C. Weber, S. John, N. Spethmann, D. Meschede and A. Widera
  Single Cs Atoms as Collisional Probes in a large Rb Magneto-Optical Trap, Phys. Rev. A 82, 042722 (2010)arXivBibTeX
  ABSTRACT »

  We study cold interspecies collisions of cesium and rubidium in a strongly imbalanced system with single and few Cs atoms. Observation of the single-atom fluorescence dynamics yields insight into light-induced loss mechanisms, while both subsystems can remain in steady state. This significantly simplifies the analysis of the dynamics, as Cs-Cs collisions are effectively absent and the majority component remains unaffected, allowing us to extract a precise value of the Rb-Cs collision parameter. Extending our results to ground-state collisions would allow to use single neutral atoms as coherent probes for larger quantum systems.

2007

• M. Haas, V. Leung, D. Frese, D. Haubrich, S. John, C. Weber, A. Rauschenbeutel and D. Meschede
  Species-selective microwave cooling of a mixture of rubidium and caesium atoms, New J. Phys. 9, 147 (2007)BibTeX
  ABSTRACT »

  We have sympathetically cooled a small sample of 133Cs atoms with 87Rb to below 1 μK. Evaporative cooling was realized with microwave radiation driving the Rb ground-state hyperfine transition. By analysing the sympathetic cooling dynamics, we derive a lower limit of the modulus of the Rb–Cs interspecies triplet s-wave scattering length of 200 a_0. For temperatures below 5 μK we observe strong non-exponential losses of the Cs sample in the presence of the Rb sample.