Pitaevskii Center on Bose-Einstein Condensation

Collective excitations are a distint fingerprint of any many-body system. In our sodium mixture we are able to control their behaviour, converting them from massless to massive by adding a coherent coupling between the two involved states. We reveal their dispersion relation by generating density and spin Faraday patterns on demand.

References:
Observation of Massless and Massive Collective Excitations with Faraday Patterns in a Two-Component Superfluid
Cominotti, Riccardo; Berti, Anna; Farolfi, Arturo; Zenesini, Alessandro; Lamporesi, Giacomo; Carusotto, Iacopo; Recati, Alessio; Ferrari, G.
arxiv.2112.09880.
Phys. Rev. Lett. 128, 210401 (2022).

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 interface, 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 interface in ultracold gases
Arturo Farolfi, Alessandro Zenesini, Dimitris Trypogeorgos, Carmelo Mordini, Albert Gallemí, Arko Roy, Alessio Recati, Giacomo Lamporesi, and Gabriele Ferrari, Nat. Phys. 17 (12) 1359 (2021), arxiv.org:2011.04271,
Manipulation of an elongated internal Josephson junction of bosonic atoms
A. Farolfi, A. Zenesini, R. Cominotti, D. Trypogeorgos, A. Recati, G. Lamporesi, and G. Ferrari, Phys. Rev. A 104 023326 (2021) arxiv:2101.12643

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)

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)

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. We developed a protocols that allow to measure and compensate the magnetic field down to few microG.

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)
Progress toward a zero-magnetic-field environment for ultracold-atom experiments
C. Rogora, R. Cominotti, C. Baroni, D. Andreoni, G. Lamporesi, A. Zenesini, G. Ferrari, arXiv:2404.19565
PhysRevA 110 013319 (2024)

The goal of this project is to engineer interactions between ultracold atoms in table top experiments to emulate and study typical phenomena of field theory and strongly correlated matter. Most relevant example is the decay of metastable field, commonly known as False Vacuum Decay. The power of this approach is twofold: first, the esquisite control of experimental parameters allows a fine tuning of coupling constants and a dedicated focus on significant system observables; secondly, the typical tools of atomic Physics and the accessible length and energy scales allow a direct access to particle detection and numerous atomic properties, as dynamics, correlation function and excitation spectra.

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,

Studying out-of-equilibrium dynamics or quench dynamics in cold-atom systems has become a paradigm for studying phase transitions. In this paper, we experimentally study the relaxation dynamics of a trapped ultracold Bose gas cooled across the BEC threshold. We find, among other things, a delay in the onset of condensate formation depending on the collision rate of the gas and a universal condensate growth depending only on the cooling rate.

Reference:
Measurement of the order parameter and its spatial fluctuations across Bose-Einstein condensation
Wolswijk, Louise; Mordini, Carmelo; Farolfi, Arturo; Trypogeorgos, Dimitrios; Dalfovo, Franco; Zenesini, Alessandro; Ferrari, Gabriele; Lamporesi, Giacomo
Physical Review A 105 033316 (2022) arxiv.2201.08569.
 

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)

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)

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)

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)