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Experiment

Bose-Einstein Condensation

Trento, Italy

Experiments with ultracold atoms

Experiment

Principal investigators:

Gabriele Ferrari (1st rx), Giacomo Lamporesi (3rd lx), Alessandro Zenesini (2nd lx).

PostDoc

Arturo Farolfi (2nd lx).

PhD students:

Louise Wolswijk (3rd rx) and Riccardo Cominotti (1st lx).

 

Main research field:

Recent PhD theses:

WORK WITH US: Students are welcome to join us and work in the lab on any of the ongoing research activities
 

TWO-COMPONENT CONDENSATES

Quantum simulation of quark confinement

Experiment

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. We aim to observe such phenomenon using a sodium two-component BEC in collaboration with TIFPA-INFN under the project FISh.


 

Quantum Torque

Experiment

What happens if in the same system cohexist a region with oscillating population between two states and a region where the population is trapped in one state? This leads to the formation of magnetic domain walls, that get broken from the quantum spin torque, by means of the formation of a shock wave and of a strongly flcutuating regime.

References:
Quantum-torque-induced breaking of magnetic domain walls in ultracold gases
Arturo Farolfi, Alessandro Zenesini, Dimitris Trypogeorgos, Carmelo Mordini, Albert Gallemí, Arko Roy, Alessio Recati, Giacomo Lamporesi, and Gabriele Ferrari, arxiv.org:2011.04271, Manipulation of an elongated internal Josephson junction of bosonic atoms
A. Farolfi, A. Zenesini, D. Trypogeorgos, A. Recati, G. Lamporesi, and G. Ferrari, arxiv:2101.12643


 

Magnetic Solitons

Experiment

The ground state of a two-component miscible mixture sees the two fluids occupying the same volume with equal spatial distribution. Such a system can be excited with modulations of the total density or of the relative density. The latter are also called magnetic excitations. We produce long-living magnetic solitons in a balanced superfluid mixture of sodium and study their dynamics and collisions.

References:
Observation of magnetic solitons in two-component Bose-Einstein condensates
A. Farolfi, D. Trypogeorgos, C. Mordini, G. Lamporesi, G. Ferrari, arxiv.org:1912.10513, Phys. Rev. Lett. 125, 030401 (2020)


 

Static and dynamical properties of a miscible two-component BEC

Experiment

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. Thanks to these nice features we are able to observe spin-dipole oscillations in the linear regime with a frequency about 5 times smaller than the trap frequency. We also measure the strong static polarizability, with an enhancement of a factor 20 in the equilibrium relative displacement of the centers of mass. These strong effects on the spin-dipole frequency and on the spin-dipole polarizability are confirmed by the theoretical predictions for a mixture near the miscible/immiscible transition. In the presence of a large thermal component the spin polarizability is even increased. At finite temperature we investigate the nontrivial dynamics of the four fluids composing the mixture and observe different behaviors for different collisional regimes. In particular, in the collisional regime the thermal components quickly damp their relative motion while the two BECs continue oscillating with negligible damping, a clear signature of spin superfluidity.

References:
Spin-Dipole Oscillation and Polarizability of a Binary Bose-Einstein Condensate near the Miscible-Immiscible Phase Transition
T. Bienaimé, E. Fava, G. Colzi, C. Mordini, S. Serafini, C. Qu, S. Stringari, G. Lamporesi and G. Ferrari, arXiv:1607.04574, Phys. Rev. A 94, 063652 (2016)
Observation of Spin Superfluidity in a Bose Gas Mixture
E. Fava, T. Bienaimé, C. Mordini, G. Colzi, C. Qu, S. Stringari, G. Lamporesi and G. Ferrari, arXiv:1708.03923, Phys. Rev. Lett. 120, 170401 (2018)


 

Magnetic shield

Experiment

Long-time coherent coupling in a spin mixture can be achieved only in a very stable and well-controlled magnetic field environment. We realized a 4-layer magnetic shield that is both able to attenuate external fields by more than 5 orders of magnitude and also compatible with the presence of internal coils, that are needed to generate a known stable field on the atoms.

Reference:
Design and characterisation of a compact magnetic shield for ultracold atomic gas experiments
A. Farolfi, D. Trypogeorgos, G. Colzi, E. Fava, G. Lamporesi and G. Ferrari, arXiv:1907.06457
Rev. Scient. Instr.90, 115114 (2019)


 

 

EQUATION OF STATE

Canonical EoS of a Bose gas

Experiment

We use precise measurements of the density distribution of trapped atomic samples to explore the Equation of State of the uniform, weakly interacting 3D Bose gas. We developed a novel, high-dynamic range imaging method capable of imaging the atomic sample in situ with high precision both in the condensed part and in the thermal wings, whose density differ by almost two orders of magnitude. This allowed us to obtain the canonical EoS in a wide range across the transition point. We observed the dramatic deviations from the ideal Bose gas behavior caused by interactions, and provided a first observation of the non-monotonic behavior of the chemical potential with temperature, which is a consequence of the superfluid nature of the system.

Reference:
Measurement of the Canonical Equation of State of a Weakly Interacting 3D Bose Gas
C. Mordini, D. Trypogeorgos, A. Farolfi, L. Wolswijk, S. Stringari, G. Lamporesi and G. Ferrari, arXiv:2003.13627, Phys. Rev. Lett. 125, 150404 (2020)
Single-shot reconstruction of the density profile of a dense atomic gas
C. Mordini, D. Trypogeorgos, L. Wolswijk, G. Lamporesi and G. Ferrari, Opt. Expr. 28, 29408 (2020) arXiv:2005.05674,


 

 

VORTEX PHYSICS IN SUPERFLUIDS

Vortex-vortex interaction mechanisms

Experiment

Axially 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 Bose-Einstein 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)


 

Vortex dynamics in cigar-shaped BECs

Experiment

Single 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 real-time 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 Bose-Einstein 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)
Observation of a Spinning Top in a Bose-Einstein Condensate
R.N. Bisset, S. Serafini, E. Iseni, M. Barbiero, T. Bienaimé, G. Lamporesi, G. Ferrari and F. Dalfovo, arXiv:1705.09102, Phys. Rev. A 96, 053605 (2017) (see also Synopsis in Physics)


 

Solitonic vortices

Experiment

The 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:
Observation of Solitonic Vortices in Bose-Einstein Condensates
S. Donadello, S. Serafini, M. Tylutki, L.P. Pitaevskii, F. Dalfovo, G. Lamporesi and G. Ferrari, arXiv:1404.4237, Phys. Rev. Lett. 113, 065302 (2014) (see also Physics Viewpoint)
Solitonic Vortices in Bose-Einstein Condensates
M. Tylutki, S. Donadello, S. Serafini, L.P. Pitaevskii, F. Dalfovo, G. Lamporesi and G. Ferrari, arXiv:1410.5475, Eur. Phys. J. Special Topics 224, 473-475 (2015)
Optical visibility and core structure of vortex filaments in a bosonic superfluid
F. Dalfovo, R.N. Bisset, C. Mordini, G. Lamporesi, G. Ferrari, arXiv:1804.03017, J. Exp. Theor. Phys. 127, 804 (2018)


 

Spontaneous generation of defects

Experiment

Quantum 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 Kibble-Zurek mechanism by directly observing the creation of phase defects in the order parameter of a Bose-Einstein condensate for temperature quenched BECs of sodium atoms.

References:
Spontaneous creation of Kibble-Zurek solitons in a Bose-Einstein condensate
G. Lamporesi, S. Donadello, S. Serafini, F. Dalfovo and G. Ferrari, arXiv:1306.4523, Nat. Phys. 9, 656 (2013)
Creation and counting of defects in a temperature-quenched Bose-Einstein condensate
S. Donadello, S. Serafini, T. Bienaimé, F. Dalfovo, G. Lamporesi, and G. Ferrari, arXiv:1605.02982, Phys. Rev. A 94, 023628 (2016)
Dynamical equilibration across a quenched phase transition in a trapped quantum gas
I.-K. Liu, S. Donadello, G. Lamporesi, G. Ferrari, S.-C. Gou, F. Dalfovo, N.P. Proukakis, arXiv:1712.08074, Commun. Phys. 1, 24 (2018)


 


 

COOLING TECHNIQUES

BEC in a hybrid trap

We produce large 23Na Bose-Einstein condensates in a hybrid trap characterized by a weak magnetic field quadrupole and a tightly focused infrared beam. The use of small magnetic field gradients makes the trap compatible with the state-of-the-art magnetic shields. By taking advantage of the deep cooling and high efficiency of gray molasses to improve the initial trap loading conditions, we produce condensates composed of as much as 7 million atoms in less than 30s.

Reference:
Production of large Bose-Einstein condensates in a magnetic-shield-compatible hybrid trap
G. Colzi, E. Fava, M. Barbiero, C. Mordini, G. Lamporesi, G. Ferrari, arxiv:1803.08814, Phys. Rev. A 97, 053625 (2018)


Gray Molasses cooling

We implemented a gray molasses cooling technique on a sodium precooled sample by using blue-detuned light on the D1 transition. Starting from a gas of 3x109 atoms at 350 microK our gray molasses stage allows to obtain a more degenerate sample containing 2x109 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:
Sub-Doppler cooling of sodium atoms in gray molasses
G. Colzi, G. Durastante, E. Fava, S. Serafini, G. Lamporesi and G. Ferrari, arxiv:1512.07053, Phys. Rev. A 93, 023421 (2016)


Compact atomic source

We realized a novel, multi-species, compact cold atomic source. Permanent magnets are used to create a 2D quadrupole magnetic field for a 2D-MOT. 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 2D-MOT axis towards a 3D-MOT cleaner chamber. This geometry also avoids hot atoms from the source to directly reach the 3D-MOT.
A new source of cold atomic strontium is currently being developed in our lab in collaboration with INRIM (Turin) for the realization of an optical clock to be used as a frequency and time reference.

Reference:
Compact high-flux source of cold sodium atoms
G. Lamporesi, S. Donadello, S. Serafini and G. Ferrari, arXiv:1301.6566, Rev. Sci. Instrum. 84, 063102 (2013)
A Sideband-Enhanced Cold Atomic Source For Optical Clocks
M. Barbiero, M.G. Tarallo, D. Calonico, F. Levi, G. Lamporesi and G. Ferrari, arXiv:1909.05810, Phys. Rev. Applied 13, 014013 (2020)


FUNDING

- Provincia Autonoma di Trento
- Q@TN
- TIFPA-INFN (FISh Project)
- EU (QUIC Project)
- QUANTera (NAQUAS Project)