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Seminars
Contact :
Hèléne Berthoumieux
Tel : +33 (0) 1 40 79 xx xx
Paddy Royall
Tel : +33 (0) 1 40 79 xx xx
Gulliver seminars take place on Mondays at 11:30 AM in the F304 room, and typically last one hour including questions. The seminars are in English, and the scientific topics are mainly those studied in the laboratory.
Gulliver Seminar : Michel Fruchart (Gulliver, ESPCI)
Non-reciprocal phase transitions
Out of equilibrium, a lack of reciprocity is the rule rather than the exception. Non-reciprocity occurs, for instance, in active matter, non-equilibrium systems, networks of neurons, social groups with conformist and contrarian members, directional interface growth phenomena and metamaterials. Although wave propagation in non-reciprocal media has recently been closely studied, less is known about the consequences of non-reciprocity on the collective behaviour of many-body systems. Here we show that non-reciprocity leads to time-dependent phases in which spontaneously broken continuous symmetries are dynamically restored. We illustrate this mechanism with simple robotic demonstrations. The resulting phase transitions are controlled by spectral singularities called exceptional points. We describe the emergence of these phases using insights from bifurcation theory and non-Hermitian quantum mechanics. Our approach captures non-reciprocal generalizations of three archetypal classes of self-organization out of equilibrium : synchronization, flocking and pattern formation. Collective phenomena in these systems range from active time-(quasi)crystals to exceptional-point-enforced pattern formation and hysteresis. Our work lays the foundation for a general theory of critical phenomena in systems whose dynamics is not governed by an optimization principle.
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The audience is often heterogeneous - because of the wide range of scientific topics covered in the lab - so planning a talk for a broader audience would be preferred. The seminar is in English, and speakers are thus invited to prepare their slides in English.
The seminar starts at 11:30 AM. The speaker is asked to arrive in the lab at least 15 minutes in advance to set up their computer. The talks last typically 45 minutes, and are followed by a discussion time.