Collège de France

Chaire Atomes et rayonnement

 

 

 

New trends in quantum fluid physics: Mixtures and spinor gases

Friday April 15 2022, 14h00 - 18h00

Amphithéâtre Halbwachs, 11 place Marcelin Berthelot, Paris 5ème


Free entrance, no preregistration needed

 
14h00 - 14h25 : Bruno Laburthe-Tolra (Laboratoire de Physique des Lasers, CNRS, Université Sorbonne Paris Nord)
Large spin atoms in optical lattices
 
14h35 - 15h00 : Lauriane Chomaz (Université de Heidelberg)
Quantum-stabilised many-body states in dipolar Bose gases
 
15h10 - 15h35 : Goulven Quemener (Laboratoire Aimé Cotton, CNRS, Université Paris-Saclay)
Ultracold dipolar molecules: Control with fields and applications
 
15h45-16h15 : Coffee break
  
16h15 - 16h40 : Jérôme Beugnon (Laboratoire Kastler Brossel, CNRS, Collège de France, PSL, Sorbonne Université)
Realization of a Townes soliton in a planar Bose-Bose mixture
 
16h50 - 17h15 : Thomas Bourdel (Laboratoire Charles Fabry , Univ. Paris-Saclay, CNRS, Institut d’optique )
Interaction control in two-component Bose-Einstein condensates
 
17h25 - 17h50 : Alessandro Zenesini (INO-CNR, BEC Center, Università di Trento)
Magnetic interfaces, Faraday Waves and other Rabi-coupled stories
    

Each talk will be followed by a 10 minute discussion session


Bruno Laburthe-Tolra
Laboratoire de Physique des Lasers, CNRS, Université Sorbonne Paris Nord

Large spin atoms in optical lattices



Our experimental projects at the Laser Physics Institute (North Paris University) aim at characterizing entanglement for many-body systems made of large spin atoms. For this, we developed two experimental set-ups : one with large-spin strontium fermionic atoms, with spin-independent contact interactions; one with large-spin chromium bosonic atoms, with spin-dependent long-range dipole-dipole interactions.

I will first briefly describe our first measurements of the spin distribution of the SU(N) Fermi gas made of strontium atoms. For this, we used a spin-orbit coupling scheme, where a retroreflected laser beam selectively diffracts two spin components in opposite directions. Spin sensitivity is provided by sweeping through a magnetic-field sensitive transition while dark states ensure that spontaneous emission remains low.

On the chromium machine, we investigated the spin dynamics and quantum thermalization of a macroscopic ensemble of S = 3 spins initially prepared in a pure coherent spin state. The experiment uses a unit-filled array of 10 thousand chromium atoms in a three dimensional optical lattice. Atoms interact at long distance under the effect of magnetic dipole-dipole interactions, realizing the spin-3 XXZ Heisenberg model with long-range couplings. We investigated the build-up of quantum correlations in this many-body system. For this, we measured collective properties such as the total population in the seven different Zeeman states, or the collective spin length. We also found that the measurement of magnetization fluctuations provides direct quantitative estimates for two-body correlations.



Lauriane Chomaz
Physikalisches Institut, Universität Heidelberg

Quantum-stabilised many-body states in dipolar Bose gases


Among the atoms in the periodic table, some display a large magnetic dipole moment in their electronic ground state. This feature comes from a large total (spin and orbital) angular momentum of the electrons. The achievement of quantum degeneracy in gases of atoms possessing such a large magnetic moment has opened up new research directions in which long-range anisotropic dipole-dipole interactions are competing with the conventional short-range contact interactions. For the most magnetic atoms – such as erbium and dysprosium - a fine control of this interaction competition has yielded the discovery of novel many-body quantum states, which are stabilized from the mere effect of quantum fluctuations. These states include liquid-like droplets, droplet crystals, and supersolids, a paradoxical phase of matter which simultaneously exhibits solid and superfluid orders. In my talk, I will review the investigations that we have carried out in my former group in Innsbruck on such exotic states in cigar-shaped three-dimensional quantum Bose gases of erbium and dysprosium. I will also shortly discuss the future research directions that I want to develop in my research group in Heidelberg focusing on  quantum  gases of  magnetic atoms in lower dimensions.


Goulven Quéméner
Laboratoire Aimé Cotton, CNRS, Université Paris-Saclay, Orsay, France

Ultracold dipolar molecules: Control with fields and applications

 

Ultracold dipolar molecules are excellent candidates for engineering quantum applications and controlled chemistry [1]. Therefore a lot of effort is devoted nowadays to produce ground state ultracold molecules in high densities as well as to understand their properties and ways of control [2]. The tools of control available in experiments are for example electric, magnetic and electromagnetic fields. In this talk, I will present recent theoretical and experimental results using these tools of control for different applications such as the formation of long-lived dipolar gases [3], ultracold chemistry [4] and prospects for new states of matter [5]. I will especially focus on the electric field shielding of molecules against destructive collisions [3].

 

[1] L. Carr, D. DeMille, R. V. Krems, J. Ye, New J. Phys. 11, 055049 (2009); J. L. Bohn, A.-M. Rey, J.Ye, Science 357, 1002 (2017)

[2] G. Quéméner, P. Julienne, Chem. Rev. 112, 4949 (2012)

[3] K. Matsuda, L. De Marco, J.-R. Li, W. G. Tobias, G. Valtolina, G. Quéméner, J. Ye, Science 370, 1324 (2020); J.-R. Li, W. G. Tobias, K. Matsuda, C. Miller, G. Valtolina, L. De Marco, R. R. W. Wang, L. Lassablière, G. Quéméner, J. L. Bohn, J. Ye, Nat. Phys. 17, 1144 (2021)

[4] M.-G. Hu, Y. Liu, M. A. Nichols, L. Zhu, G. Quéméner, O. Dulieu, K.-K. Ni, Nat. Chem. 13, 435 (2021); G. Quéméner, M.-G. Hu, Y. Liu, M. A. Nichols, L. Zhu, K.-K. Ni, Phys. Rev. A 104, 052817 (2021); Y. Liu, M.-G. Hu, M. A. Nichols, D. Yang, D. Xie, H. Guo, K.-K. Ni, Nature 593, 379 (2021)

[5] M. Schmidt, L. Lassablière, G. Quéméner, T. Langen, arXiv:2111.06187 (accepted to Phys. Rev. Research (2022))


Jérôme Beugnon
Laboratoire Kastler Brossel, CNRS, Collège de France, PSL, Sorbonne Université

Realization of a Townes soliton in a planar Bose-Bose mixture

 


We will discuss our recent realization of a Townes soliton in a two-component rubidium Bose gas. This soliton is a solution of the two-dimensional nonlinear Schrödinger equation with particular properties. It appears, for a given interaction strength, at a specific atom number and is scale invariant. While its realization with a  single-component gas requires attractive interactions between the atoms, we use here a mixture of two immiscible components with repulsive interactions. In this case, the behavior of a minority component in the bath constituted by the majority component is equivalent to the the single-component attractive case. We use optical imprinting of spin textures on a planar gas to create this soliton and observe its original characteristics.


Thomas Bourdel
Laboratoire Charles Fabry , Univ. Paris-Saclay, CNRS, Institut d’optique

Interaction control in two-component Bose-Einstein condensates

 


Mixtures of Bose-Einstein condensates offer situations where the usually dominant mean-field energy can be reduced such that higher-order terms may play a dominant role in the equation of state. In this context, the case of two component coupled Bose-Einstein condensates will be specifically addressed. First, large attractive effective three-body interactions can be engineered with striking consequences [1]. Second, the beyond-mean field energy is precisely measured and is shown to be modified as compared to the uncoupled case [2]. 

 

[1] A. Hammond, L. Lavoine, T. Bourdel, Tunable 3-body interactions in coherently driven two-component Bose-Einstein condensate, Phys. Rev. Lett. 128, 083401 (2022).

 

[2] L. Lavoine, A. Hammond, A. Recati, D.S. Petrov, T. Bourdel, Beyond-mean-field effects in Rabi-coupled two-component Bose-Einstein condensate, Phys. Rev. Lett. 127, 203402 (2021).


Alessandro Zenesini
INO-CNR, BEC Center, Dipartimento di Fisica, Università di Trento, 
Via Sommarive 14 I-38123 Povo, Italy

Magnetic interfaces, Faraday Waves and other Rabi-coupled stories



Ultracold atoms are one of the most powerful tools to simulate your beloved or hated Hamiltonian. Thanks to the extremely precise and wide tunable properties, they can be used to investigate phenomena spanning from solid state to cosmology, from nuclear physics to chemistry.

One example of a very rich ultracold gas simulator is the mixture of two different hyperfine states of sodium coupled by a coherent microwave field. Due to the interplay between the many body interactions and the coherent coupling, different scenarios can be engineered.

In my talk I will present the two last investigations performed in our lab.

First the simulation of magnetic interfaces. Thanks to non-uniform profile of our cloud, we can simulate the interface between a ferro and a paramagnet and observe its “self-destruction” into magnetic shock-wave.

Secondly the creation of massive spin excitations. While in an uncoupled system, density and spin excitations have linear dispersion relations with associated sound velocities (typical of massless systems), the introduction of a coupling leads to massive spin excitations which are a powerful tool to simulate analog gravity and other high energy phenomena.

I will conclude with some highlights on our future directions.