Considering the hurdles of experiments with more than one atomic species, the temptation arises of rephrasing Arthur L. Schawlow: "Double-species Bose-Einstein condensates are condensates with one species too many". We think otherwise. Quantum mixtures allow the investigation of a wealth of genuinely quantum phenomena: mixed phases of superfluids and Mott insulators, impurities and polarons, chemistry at zero-temperature.

Laser cooling based on dark states, i.e. states decoupled from light, has proven to be effective to increase the phasespace density of cold trapped atoms. Dark-states cooling requires open atomic transitions, in contrast to the ordinary laser cooling used for example in magneto-optical traps (MOTs), which operate on closed atomic transitions. For alkali atoms, dark-states cooling is therefore commonly operated on the D1 transition nS1/2 → nP1/2. We show that, for 87Rb, thanks to the large hyperfine structure separations the use of this transition is not strictly necessary and that “quasi-dark state” cooling is efficient also on the D2 line, 5S1/2 → 5P1/2. We report temperatures as low as (4.0 ± 0.3) μK and an increase of almost an order of magnitude in the phase space density with respect to ordinary laser sub-Doppler cooling.

S. Rosi, et al.
Λ -enhanced grey molasses on the D2 transition of Rubidium-87 atoms
Sci. Rep. 8, 1301 (2018)

We achieved a 87Rb condensate of 4⨯105 atoms in the F=2, mF=2 state. We use a hybrid trap consisting of a single focused laser beam at 1064nm (dimple) in the horizontal direction and a quadrupole magnetic field. The dimple is vertically shifted with respect to the quadrupole center to avoid Majorana spin-flips. A first evaporation ramp with a microwave driving the (2,2) to (1,1) transition, is followed by an optical evaporation.

In an array of one-dimensional traps, we create impurities of K atoms immersed in reservoir of Rb atoms. The impurities are first localized by an external species-selective potential and then suddenly freed: their subsequent dynamics exhibits "breathing" oscillations, due to a weaker confining potential. We find that the amplitude of these oscillations is reduced when increasing the strength of the impurity-reservoir interaction, irrespective of its sign. We interpret our data with a polaric mass shift model derived following Feynman variational approach.

J. Catani et al.
Quantum dynamics of impurities in a one-dimensional Bose gas
Phys. Rev. A 85, 023623 (2012)

K/Rb people

Alessia Burchianti
Research fellow
Chiara D'Errico
Permanent researcher
Chiara Fort
Permanent researcher
Massimo Inguscio
Permanent researcher
Francesco Minardi
Permanent researcher
Former members:
Giovanni Barontini
Jacopo Catani
Stefano Conclave
Luigi De Sarlo
Giacomo Lamporesi
Paolo Maioli
Sara Rosi
Devang S. Naik
Gregor Thalhammer

K/Rb contacts

For further information, request of material, job opportunities, please contact:

Francesco Minardi
(minardi@lens.unifi.it)

K/Rb funding

PRIN2010-2011
EU FP7 EQuaM
  Progetto Premiale 2013 ABnanotech