Istituto Nazionale di Ottica BoseEinstein Condensation Trento, Italy  
Former students PhD thesis:
Simone Serafini (2017) "Dynamics of Vortices and their Interactions in BoseEinstein Condensates".
Simone Donadello (2016) "Observation of the KibbleZurek mechanism in a bosonic gas".
Students are welcome to join us and work in the lab on any of the ongoing research activities
Vortexvortex interaction mechanismsAxially symmetric elongated traps allow transverse vortices to approach with random relative velocity and orientation, differently from what happens in flat traps or in rotating condensates. We observe in real time the vortex filament orientation and position in the condensate and study different interaction mechanisms that occur depending on their approaching velocities and relative orientation. Reference:Vortex Reconnections and Rebounds in Trapped Atomic BoseEinstein Condensates S. Serafini, L. Galantucci, E. Iseni, T. Bienaimé, R.N. Bisset, C.F. Barenghi, F. Dalfovo, G. Lamporesi and G. Ferrari arXiv:1611.01691, Phys. Rev. X 7, 021031 (2017) 
Two orthogonal vortices approach and may bounce without touching (if their relative velocity is small enough) or touch and reconnect changing their tails (for large relative velocities). 
Vortex dynamics in cigarshaped BECsSingle vortices in elongated condensates are mainly oriented along a radial direction and tend to move on elliptical orbits around the center. We track their dynamics by performing a realtime weakly destructive imaging. The measured period verifies the predicted dependence on the local chemical potential. Whenever vortices do not lie on a radial plane but are slightly tilted, they experience a torque that forces them to precess around the long symmetry axis of the trap to conserve the angular momentum along such axis. References:Dynamics and Interaction of Vortex Lines in an Elongated BoseEinstein Condensate S. Serafini, M. Barbiero, M. Debortoli, S. Donadello, F. Larcher, F. Dalfovo, G. Lamporesi and G. Ferrari arXiv:1507.01511, Phys. Rev. Lett. 115, 170402 (2015)


Solitonic vorticesThe geometrical properties of a system have an influence on the nature of defects that can be supported. Besides common solitons in quasi 1D systems and vortices in round pancake like condensates, we observed solitonic vortices in elongated samples. These hybrid defects are vortices aligned along a short axis with a 2pi phase winding, but also show a planar density depletion in the radial plane containing the vortex.
References:

Triaxial absorption imaging of elongated BECs after a long time of flight providing clear signatures of the presence of solitonic vortices with opposite circulation. 
Spontaneous generation of defectsQuantum criticalities are mechanisms driving disparate phenomena ranging from the origin of our universe to the appearance of defects in uniform systems. We use ultracold atoms at the BEC transition to explore the KibbleZurek mechanism by directly observing the creation of phase defects in the order parameter of a BoseEinstein condensate for temperature quenched BECs of sodium atoms.
References:

A condensate of Sodium atoms is formed by quenching the temperature across the BEC phase transition. If the quench is fast, defects appear in the order parameter due to the KibbleZurek mechanism. 
Quantum simultion of quark confinement
A slowly rotating binary BEC might have a vortex in each component that orbits around the trap center.
In presence of a coherent coupling, the two vortices lock at a precise distance given by the intercomponent interaction strength.
The force between such vortices is strongly analogous to the force that confines quarks. If an external force tries to separate the two beyond their equilibrium distance then a new pair of vortices is created.

Dipolar excitations at T=0
A mixture of Na atoms in the mF=1 and mF=1 of the F=1 hyperfine state is a fully miscible mixture and thanks to the intrinsic perfect symmetry it does not show buoyancy when held in a harmonic confinement, differently from any other binary BEC studied in cold atoms. This mixture is close to the miscible/immiscible phase transition.
Reference:

Static polarizability: (left) Measured enhanced displacement of the relative centers of mass as a function of the trap minima separation. (right) Spindipole oscillation observed after time of flight for different trap separations. 
Gray Molasses coolingWe implemented a gray molasses cooling technique on a sodium precooled sample by using bluedetuned light on the D1 transition. Starting from a gas of 3x10^{9} atoms at 350 microK our gray molasses stage allows to obtain a more degenerate sample containing 2x10^{9} atoms at 9 microK. The final PSD is 10^{4}, one order of magnitude higher than the best we obtained with a molasses stage using the D2 transition.
Reference:
SubDoppler cooling of sodium atoms in gray molasses

Compact atomic sourceWe realized a novel, multispecies, compact cold atomic source. Permanent magnets are used to create a 2D quadrupole magnetic field for a 2DMOT. Their residual field in combination with a vertical laser beam form a compact Zeeman slower that enhances the number of trappable atoms. Eventually cooled atoms are pushed along the 2DMOT axis towards a 3DMOT cleaner chamber. This geometry also avoids hot atoms from the source to directly reach the 3DMOT.
Reference:
Compact highflux source of cold sodium atoms

Scheme of the multispecies compact cold atom source. 