SEMINÁRIO DO DEPARTAMENTO DE FÍSICA EXPERIMENTAL - FEP
“TIME CRYSTALS: New physics or simple fiction?”
J.T. Mendonça, IPFN, Instituto Superior Técnico, Universidade de Lisboa
Dia: 31 de março, sexta-feira, às 14h.
Local: Auditório Sul, IFUSP
Abstract:
Time crystals recently attracted the attentions of the world press, when two independent groups in USA announced that they had built such systems in the laboratory. The idea of a time crystal was proposed five years ago by Frank Wilczek, and explores the similarities between space and time. The idea is however controversial, and some theoreticians have denied its existence. The subject of time crystal is revisited in the present talk, from the point of view of temporal optics. In this context, temporal Fresnel formulae for optical transmission across the time crystal, and a temporal Bragg’s law for resonant scattering can be established. From this point of view, time crystals can simply be seen as a particular case of time refraction, and are closely related with the so-called dynamical Casimir effect. The related concept of temporal beam-splitters will also be defined. The controversy associated with time crystals, and recent experimental results in temporal optics will be reviewed. A distinction between internal and external time symmetry breaking will be made. Examples of time crystals probed with photons, as well as with phonons, and possible configurations using ultra-cold atoms and Bose- Einstein condensates will be discussed.
