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Início
Agenda
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- 20 de junho de 2018
16h30
Sala
18 (Cristalografia) -
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Marios
Tsatsos
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IFSC
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Elaborating
correlated states and quantum fluctuations: principles and
applications of many-body theories in Bose-Einstein condensates
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Bose-Einstein condensation, theoretically known to
appear at ultralow temperatures since the 1920s, was achieved in
the laboratory only less than 25 years ago, in dilute bosonic
gases at temperatures close to absolute zero. The wide range of
applications and controlabillity of the system parameters has
made them unprecedented tools for exploring novel quantum phases
and behavior. The most common theoretical method employed to
tackle these complex systems, typically consisting of tens of
thousands of interacting particles is the celebrated mean-field
Gross-Pitaevskii model. Even though it has been proven
successful in describing various types of nonlinear excitations
it does not take into consideration fragmentation and
correlations that can develop in time. Consider for instance the
process of the quantum measurement: what result would a
measurement yield for a coherent gas (ie Bose-Einstein
condensed)? As long as no quantum correlations are there, an
N-body measurent immediately reduces to N single-body
measurement. In real situations however the processes are more
complicated and, depending on the experimental settings,
correlations might well affect the final observed state of the
gas. In such situations mean fields fail to give reliable
predictions. To go beyond that, I will briefly present a
systematic theory, the MultiConfigurational Time-Dependet
Hartree for Bosons (MCTDHB) [1] that has been developed in order
to solve the many-body Schroedinger equation beyond the
mean-field approach and can be in principle exact, and the
latest numerical implementation (solver) that is freely
distributed in the web [2]. I will then discuss some particular
applications in Bose gase that are violently perturbed and out
of equilibrium, such as turbulent and granulated gases. Joint
theoretical and experimental work from Sao Carlos and also Rice,
Texas corroborate our views. Last, promising applications from
light-coupled BECs in optical cavities (such as Bloch
oscillations and gravimeters) will be discussed.
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[1] Alexej I. Streltsov, Ofir E. Alon, and Lorenz
S. Cederbaum, Role of Excited States in the Splitting of a
Trapped Interacting Bose-Einstein Condensate by a Time-Dependent
Barrier, Phys. Rev. Lett. 99, 030402 (2007); Ofir E. Alon,
Alexej I. Streltsov, and Lorenz S. Cederbaum,
Multiconfigurational time-dependent Hartree method for bosons:
Many-body dynamics of bosonic systems, Phys. Rev. A 77, 033613
(2008).
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[2] A.U.J. Lode, M.C. Tsatsos and E. Fasshauer, The
Multiconfigurational Time-Dependent Hartree for
Indistinguishable particles software (2016),
http://ultracold.org.
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