All lectures will be held in Jefferson 250 (17 Oxford Street, Cambridge, MA)
and streamed live through zoom (please see the link below)
Monday, November 13, 4:30pm
Colloquium Tea will be served in Jefferson 450 at 3:30pm
“Scale invariance, a hidden symmetry explored with quantum gases”
Scale invariance, a concept initially introduced in high-energy physics, has gained numerous applications in the physics of quantum fluid. It is applicable to strongly interacting Fermi gases, two-dimensional Bose gases, as well as few-body systems that exhibit the “Efimov effect.” In the presentation, I will illustrate how scale and conformal invariance emerge in cold atomic gases. I will use various examples ranging from thermodynamics to soliton physics to specific structures with periodic time evolution called “breathers”.
Tuesday, November 14, 4:30pm
“Surprises in soliton physics with quantum gas mixtures”
Solitons are nonlinear wave packets that maintain their shape during free propagation. In quantum gases, bright and dark solitons are observed for attractive and repulsive interactions, exhibiting relatively simple behavior. However, mixtures of gases result in a much more complex physics, with the emergence of dark-bright and magnetic solitons. Here, we examine some non-intuitive phenomena in this context, including the following experimental observation: a magnetic soliton exposed to a constant force undergoes periodic motion, similar to the Bloch oscillation of an electron in a perfect crystal, despite lacking an underlying periodic potential in this setup.
Wednesday, November 15, 4:30pm
“Is a zero-temperature Bose-Einstein condensate fully superfluid?”
At zero temperature, a Galilean-invariant Bose fluid is anticipated to be completely superfluid. When translational (and thus Galilean) invariance is broken, A.J. Leggett demonstrated in the 1970s that the superfluid fraction must be strictly less than one. Here, we examine both theoretically and experimentally how the presence of an external 1D periodic potential quenches the superfluid fraction of a dilute Bose-Einstein condensate and compare it to Leggett’s bound. We show that the anisotropy of sound velocity provides a reliable determination of the superfluid fraction and explore the potential application of these principles to other quantum fluids.
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Jean Dalibard is a professor at the Collège de France and leads a research team at the Laboratoire Kastler Brossel in Paris. His research in atomic physics and quantum optics covers both experimental and theoretical aspects. In the 1980s, together with Claude Cohen-Tannoudji, he studied the mechanisms at play in laser cooling of atoms, in particular the “Sisyphus effect”. The modelling of these phenomena led him – along with other authors – to propose the method of “quantum trajectories”. Since the discovery of gaseous Bose-Einstein condensates in 1995, he has been interested in many aspects of this quantum matter, as well as the links that exist between these fluids and other condensed matter systems. He was elected a foreign member of the National Academy of Sciences in 2021.
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The lectures are sponsored by the Morris Loeb Lectureship Fund.
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Zoom webinar
2023 Loeb Lectures – Jean Dalibard
Nov 13, 2023 04:30 PM
Nov 14, 2023 04:30 PM
Nov 15, 2023 04:30 PM
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Jolanta M. Davis, Academic Program Specialist, Physics Chair’s Office
(pronounced Yo-lan-ta)
Harvard University | Department of Physics | 17 Oxford St., Jefferson 352 | Cambridge, MA 02138
Tel.: 617-495-2866 | Fax: 617-495-0416 | https://www.physics.harvard.edu/