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SUMMARY:Superfluid states of matter: from superfluid helium to polariton c
 ondensates - Dr Natalia Berloff (DPMMS)
DTSTART:20111121T083000Z
DTEND:20111121T093000Z
UID:TALK34737@talks.cam.ac.uk
CONTACT:Mary Fortune
DESCRIPTION:When in 1937 liquid helium was first observed to flow with neg
 ligible viscosity through a narrow gap\, it was clear that\, at low temper
 atures\, helium was different from ordinary fluids. The attemps to underst
 and this phenomenon (called superfluidity by Pyotr Kapitza) led to the dev
 elopment of a two-fluid theory by Lev Landau. In this theory the fluid is 
 modelled as an interacting mixture of  superfluid and normal fluid compone
 nts. In more recent times\, an aspect of superfluidity that has been empha
 sized as most central is that the superfluid velocity is associated with t
 he gradient of the phase of the macroscopic classical complex-valued matte
 r field. Such a description impies that the system possesses a Bose–Eins
 tein condensate (a form of matter that emerges when particles collapse int
 o the same lowest-energy state) — with the matter field being the conden
 sate wavefunction — and\, therefore\, can be described by a nonlinear eq
 uation for classical waves\, known as the nonlinear Schrodinger equation. 
 This description has the ingredients necessary to produce many of the aspe
 cts of superfluidity\, such as frictionless flow below the Landau critical
  velocity\, two-fluid hydrodynamics\, quantized vortices\, and  metastable
  persistent flow in a doughnut-shaped geometry. These features of superflu
 idity have been experimentally observed not only in liquid helium\, but al
 so in ultracold gases and very recently in condensates of semiconductor mi
 crocavity polaritons — entities comprising both matter and light. How th
 e condensate model can be modified and applied to study the dynamics of th
 ese various superfluid systems is the subject of my talk.
LOCATION:Winstanley Lecture Theatre\, Trinity College
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