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SUMMARY:Quantum modulation: first-principle derivations of the equations o
 f generalised hydrodynamics in the Lieb-Liniger quantum gas. - Benjamin Do
 yon (King's College London)
DTSTART:20221020T093000Z
DTEND:20221020T100000Z
UID:TALK182576@talks.cam.ac.uk
DESCRIPTION:Hydrodynamics is a powerful framework for large-wavelength phe
 nomena in many-body systems. At its basis is the assumption that one can r
 educe the dynamics to that of long-lived\, effective degrees of freedom ob
 tained from the available conservation laws. This fundamental idea\, appli
 ed traditionally on systems with few conservation laws\, can be extended t
 o integrable systems\, which admit an extensive number. The ensuing ``gene
 ralised hydrodynamics&rdquo\; (GHD) is a universal theory for the large-sc
 ale dynamics in integrable classical and quantum chains\, gases and fields
 . In particular\, the GHD equations are equivalent to the kinetic equation
 s found\, much earlier\, in soliton gases. Until now\, in quantum interact
 ing systems the only derivation available is based on the assumption of lo
 cal generalised thermalisation\, with exact expressions of average current
 s playing a crucial role. By contrast\, in soliton gases\, the kinetic equ
 ations can be derived from an application of Whitham modulation theory. Ar
 e there first-principle derivations\, or a ``quantum modulation theory"\, 
 from which the GHD equations can be obtained without the assumption of loc
 al generalised thermalisation? I will propose such derivations\, in partic
 ular using what can be seen as a simple version of quantum modulation\, in
  a paradigmatic model of quantum integrability\, the Lieb-Liniger gas.
LOCATION:Seminar Room 1\, Newton Institute
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