Quantum noise in a transversely-pumped-cavity Bose-Hubbard model

2019. 02. 04. 14:15
Building F, Entrance III, seminar room of Department of Theoretical Physics
Gergely Szirmai (Wigner)

A weakly interacting gas of bosonic atoms moving in the periodic
potential of an optical lattice goes through a phase transition at a
sufficiently low temperature. This phase transition is characterized
by the macroscopic occupation of the single particle ground state and
called as Bose-Einstein condensation. This Bose-Einstein condensate
is, however, sensitive to particle interactions. When the interaction
between particles becomes strong, the Bose-Einstein condensate can
freeze into a Mott insulator.

When the Bose gas is placed inside an optical resonator, atom-light
interaction may create an infinite range interaction between the atoms
and may cause, in certain geometries, another interesting phase
transition: the formation of a charge-density wave. The charge-density
wave combined with Bose-Einstein condensation is called as super solid.

During the talk, we discuss the Bose gas inside an optical resonator,
paying special attention to another very important feature: the
driven-dissipative nature of the cavity. The photons eventually escape
the cavity resulting in a quantum noise for the atomic dynamics.

Somatic Evolution - How Multicellular Organisms Can Live Long

2019. 03. 12. 14:30
Building F, Entrance III, room F3123
Imre Derényi (ELTE)

All the cells of a multicellular organism are the product of cell divisions organized into a single binary tree. Cell divisions are, however, accompanied by replication errors, which result in somatic evolution and can potentially lead to aging, tissue deterioration, and cancer. Using mathematical models we show that a well orchestrated pattern of cell divisions during tissue development and maintenance can dramatically slow down somatic evolution and can ensure a long lifespan for large multicellular organisms.

The angulon quasiparticle

2019. 04. 05. 10:15
Building F, Entrance III, seminar room of Department of Theoretical Physics
Mikhail Lemeshko (IST Vienna)

The angulon quasiparticle: from molecules in superfluids to ultrafast magnetism


Recently we have predicted a new quasiparticle - the angulon - which is formed when a quantum impurity (such as an electron, atom, or molecule) exchanges its orbital angular momentum with a many-particle environment (such as lattice phonons or a Fermi sea) [1,2].

Soon thereafter we obtained strong evidence that angulons are formed in experiments on molecules trapped inside superfluid helium nanodroplets [3]. The angulon theory thereby provided a simple explanation for experimental data accumulated during the last two decades. Moreover, casting the many-particle problem in terms of angulons amounts to a drastic simplification and allows to tackle previously intractable problems related to quantum dynamics [4].
In this presentation we will introduce the angulon concept and discuss novel physical phenomena [1,5,6] arising from the angular momentum exchange in quantum many-particle systems. We will describe the applications of angulons to modern experiments on quantum impurities and on non-equilibrium magnetism [7].
[1] R. Schmidt, M. Lemeshko, Phys. Rev. Lett. 114, 203001 (2015)
[2] R. Schmidt, M. Lemeshko, Phys. Rev. X 6, 011012 (2016)
[3] M. Lemeshko, Phys. Rev. Lett., 118, 095301 (2017); Viewpoint: Physics 10, 20 (2017)
[4] B. Shepperson, A. A. Sondergaard, L. Christiansen, J. Kaczmarczyk, R. E. Zillich, M. Lemeshko, H. Stapelfeldt, Phys. Rev. Lett. 118, 203203 (2017)
[5] E. Yakaboylu, M. Lemeshko, Phys. Rev. Lett. 118, 085302 (2017)
[6] E. Yakaboylu, A. Deuchert, M. Lemeshko, Phys. Rev. Lett. 119, 235301 (2017)
[7] J.H. Mentink, M.I. Katsnelson, M. Lemeshko, Phys. Rev. B 99, 064428 (2019)