"Coherence and Superfluidity: The Two Sides of the Same Coin, really?" (MCQST Colloquium) (Prof. Jean Dalibard)
- Datum: 18.11.2025
- Uhrzeit: 14:00
- Vortragende(r): Prof. Jean Dalibard
- Collège de France, Paris, France
- Ort: Max Planck Institute of Quantum Optics, Hans-Kopferman-Straße 1, 85748 Garching
- Raum: Herbert Walther Lecture Hall
- Gastgeber: MCQST
In 1925, Einstein predicted that an ideal gas would undergo a phase transition once its density crosses a threshold, with particles condensing into a single quantum state and establishing macroscopic coherence. The subsequent discovery of superfluidity in helium appeared to confirm this prediction, but are coherence and superfluidity truly equivalent?
Experiments with ultracold atoms reveal that superfluidity can exist without long-range coherence, as in low-dimensional fluids, while a fully coherent fluid may exhibit only partial superfluidity—a phenomenon anticipated in the 1970s by Leggett. Today, the question of determining the superfluid fraction of a Bose–Einstein condensate has gained renewed importance with the realization of supersolids in dipolar atomic gases. In this presentation, I will discuss recent experiments that address this fundamental issue in spatially modulated quantum systems.
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