NaK Lab

Congratulations to our new Master in Physics!

Pedro had just presented his master thesis titles "Modulation instability in a binary Bose-Einstein condensate". He will now start a PhD in Physics at the university Sorbonne Paris Nord, in France, at the group of Hélène Perrin. We hope all the best during this new step in Academia.

We realized transfer between different hyperfine states of a sodium BEC connecting the F=1 and F=2 ground-states with the aid of a microwave radiation at ~ 1.76 GHz. This new tool will make it possible to study miscibility effects and the out-of-equilibrium dynamics of a mixture. In the figures we see the two different states (F=1 upper and F=2 lower) which are transferred in a coherent fashion as it can be seen from the Rabi oscillations between the populations in each state shown in the graph below.

The experimental realization of Bose-Einstein condensates of two atomic species is a great challenge due to the difficulties in ensuring a good operation of the system and the experimental sequence for both species. In the specific case of sodium and potassium atoms, the high three-body interspecies loss rate, presented already in the initial steps of the experiment, has been our biggest challenge since it can only be minimized once the atoms are trapped in a purely optical trap.

In december 2021, we achieved an important result: the achievement of a Bose-Einstein condensate of 23Na with 2 x 105 atoms coexisting with a ultracold cloud of about 1 x 104 atoms of 39K at only 80 nK.

Congratulations to the students who achieved this great result!

Two-species atomic condensates present a rich phase diagram in which the transition from the miscible phase, with the two condensates sharing the same space, to the immiscible phase, where the condensates remain phase separated with well-defined domains, can be studied under different experimental conditions, e.g. trapping potential, number of atoms, etc.

In the case of inhomogeneous systems, such as gases trapped by harmonic potentials, characterizing the miscible-immiscible transition requires some care and finding the best experimental parameters in this direction is still a challenge, especially when taking into account all experimental conditions. In a recent work, we carried out a theoretical study of the ground state of a 23Na-39K atomic mixture condensate considering real experimental conditions like those we have in the experiment. Having defined the spatial overlap of the atomic clouds, we find the miscible-immiscible transition point for different ratios of the number of atoms. This study will enable the direct characterization of the miscibility regimes of the 23Na-39K mixture in our experiment.

The Na-K experimental system is composed of three vacuum chambers: two chambers (on the sides of the figure) used only as a source of atoms, in which we perform a two-dimensional magneto-optical trap (MOT) for sodium and potassium atoms independently, and a main chamber (in the center of the figure) in which the previously cooled atoms are trapped again in a three-dimensional MOT and where the entire experimental sequence takes place until obtaining the atomic mixture condensate.

P. C. M. Castilho, E. Pedrozo-Peñafiel, E. M. Gutierrez, P. L. Mazo, G. Roati, K. M. Farias, V. S. Bagnato
A compact experimental machine for studying tunable Bose–Bose superfluid mixtures
Laser Phys. Lett. 16, 035501 (2019). pdf

E. Pedrozo-Peñafiel, F. Vivanco, P. C. M. Castilho, R. R. Paiva, K. M. Farias, V. S. Bagnato
Direct comparison between a two-dimensional magneto-optical trap and a Zeeman slower as sources of cold sodium atoms
Laser Phys. Lett. 13, 065501 (2016). pdf