From ultracold to ultrafast, two instances of analogue simulation using cold atoms

Frédéric Chevy (Ecole Normale Supérieure)
Event Date and Time: 
Mon, 2016-04-18 14:00 - 15:00
Hennings 318
Local Contact: 
Kirk Madison
Intended Audience: 

Over the past few years, ultracold atoms have emerged as priviledged platfoms for the experimental exploration of quantum many-body physics. To demonstrate the versatility of ultracold atomic techniques, I will discuss during my talk two experiments performed recently at ENS addressing widely different physical situations. In the first part, I will show how the possibility of tuning interatomic interactions have paved the road to the observation of the first double Bose-Fermi superfluids. In liquid 3H/4He mixtures where a similar system has been looked for over the past forty years, the critical temperature is strongly reduced by repulsive inter-isotope interactions. Using Feshbach resonances, we were able to stabilize the mixture and cool it to the superfluid regime. By putting the two clouds into relative motion, we have also explored the properties of superfluid counterflows and we have unveiled a novel mechanism for the breakdown of superfluidity that extends Landau's celebrated argument. The second part of my talk will be devoted to the study of Weyl fermions. These massless particles were first thought to describe neutrinos, until the discovery of their oscillations, and have recently been observed in TaAs compunds. Their interest stems form their peculiar topological properties associated with their spin orbit coupling.

I will show that after a phase-space rotation, their dynamics is equivalent to that of magnetically confined atoms and I will present a study of the dynamics of Weyl particles in a harmonic trap. Contrary to massive atoms, the oscillation frequency of massless particles is energy dependent, a peculiar feature leading to a blurring of the center-of-mass motion of the cloud and to a quasi-thermalization of the system driven by the non-linearities of the single-particle hamiltonian.

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