

Wed 22 May

Erik Mau

SystemReservoir Entanglement and Entropy Production

Each thermodynamical system
can be ascribed an entropy that measures the amount of ignorance about the
system state. In quantum mechanics, the von Neumann entropy is completely
described by the density matrix of the system.
The talk presents an exact quantummechanical expression for the entropy
of a system in contact to a reservoir, containing entropy production and
flow to the reservoir. Since the total entropy stays constant in this
setup, one can infer a negative entropy hidden in the correlations
(entanglement) between system and reservoir that is exactly as large as
the produced entropy.
The expression for the entropy production is compared to an alternative
result from the theory of open quantum systems. In a simple fewlevel
system, the advantage of the derived expression becomes obvious, as it
remains a positive quantity, while the alternative version suggests a
negative entropy production.
M. Esposito, K. Lindenberg, and Ch. Van den Broeck,
"Entropy production as correlation between system and reservoir",
New J. Phys. 12, 013013 (2010).

Wed 05 Jun

Thea M. Schneider

Topology of Black Hole binarysingle interactions

In 1916 Einstein predicted with his theory of general relativity that
accelerating masses emit gravitational radiation. These disturbances in the
curvature of spacetime that propagate like waves at the speed of light are
called gravitational waves (GWs). One hundred years later in 2016 the phenomenon
was directly observed for the first time by the LIGO experiment. It is of big
interest to connect the observed GW events to their astrophysical origin, like
binarysingle systems of three black holes. The presentation gives a short
introduction to PostNewtonian Mechanics. The concept of topology of black hole
binarysingle interactions refers to a graphical representation of the
distribution of interaction outcomes as a function of the orbital initial
conditions.
Johan Samsing, Teva Ilan,
"Topology of black hole binarysingle interactions",
Mon. N. Roy. Astron. Soc. 476(2),154860 (2018).

Wed 12 Jun

Anja Seegebrecht

Crossover from anomalous to normal diffusion: truncated powerlaw noise
correlations and applications to dynamics in lipid bilayers

Diffusion, the stochastic motion of a particle, is usually described by the mean
squared displacement (MSD). It scales linear with time for normal (Brownian)
diffusion. In many systems this is violated and the MSD scales like time with an
exponent. Then one speaks of anomalous diffusion. Subdiffusion is "slower" than
Brownian motion and describes for example particles in crowded environments like
the cytoplasm or lipidbilayer of biological cells. Due to active motion,
diffusion can be faster and is called superdiffusion. At long times both kinds
of anomalous diffusion show a crossover to normal behavior if the system is
finite. This can be modelled with different exponents for different time scales.
To portray the crossover region correctly, truncation, socalled tempering, can
be applied and one thus gets a complete description.
Literature:
D. MolinaGarcia et al.
"Crossover from anomalous to normal diffusion: truncated powerlaw noise correlations and applications to dynamics in lipid bilayers",
New J. Phys. 20(10), 103027 (2018).

Wed 19 Jun

Hon Tim Zam

Lie groups in physics

Symmetries of a physical system allow us to classify its properties, such
as the conserved quantities in classical mechanics or the quantum
mechanical states of the system. Lie groups and their associated Lie
algebras are the mathematical language for the symmetries of physical
systems.
The presentation provides a brief introduction to Lie groups, with an
example of the groups SO(3) (for rotations in threedimensional space),
SU(2) and
SO(3,1) (for Lorentz transformation in Minkowski space). We
illustrate the concepts of generators and structure constants of the
corresponding Lie algebras, and show the strong relationship to linear
transformations in physics. These groups share common mathematical
structures and can be regarded as subgroups of the General Linear group
each having an invariance condition.
Literature:
Y. S. Kim,
"Lorentz group in polarization optics",
J. Opt. B: Quantum Semiclass. Opt. 2, R15 (2000).

Wed 26 Jun

Olga Gritsai

Nonlinear Newtonian gravity

Newtonian gravitational theory is linear. General relativity
is strongly nonlinear and rather complex. Here an intermediate
"Nonlinear Newtonian gravity" is discussed, which works without
curvature. We describe a field whose sources are mass and charge,
and compare with the general relativity results. As an example,
we consider a charged black hole bombarded by charged particles.
We determine the position of a turnaround point and critical
charge/mass ratio for the nonrelativistic and relativistic cases.
This is an important result to predict the stability of charged
black holes.
Literature: Michael R. R. Good,
"On a nonlinear Newtonian gravity and charging a black hole",
Am. J. Phys. 86(6), 45359 (2018).

Wed 03 Jul

Christian Michaelis

Spectral Content of a single Brownian Trajectory

When analyzing a timedependent process, one often uses the
power spectral density (PSD) which is calculated with a
Fourier transform in the limit of infinite observation time
and taking an ensemble average. Many experiments do not have the
possibility to create sufficiently large datasets for ensemble
averages and also the observation time is always finite. So
it is interesting to ask what information one can extract
from just a single trajectory with finite observation time
and what are the limits.
The talk will introduce the PSD in the framework of Brownian motion
and will discuss what information can be extracted from single
trajectories.
Literature:
Diego Krapf, Enzo Marinari, Ralf Metzler, Gleb Oshanin, Xinran Xu
and Alessio Squarcini,
"Power spectral density of a single Brownian trajectory:
what one can and cannot learn from it",
New J. Phys. 20, 023029 (2018).

Wed 03 Jul

Jannik Kühn

Dispute about the "correct" entropy

Negative absolute temperatures, a popular example being the population
inversion in laser physics, are a well established concept in theoretical
physics. Nevertheless, in 2013, Dunkel and Hilbert claimed that negative
temperatures are only due to the often used, but in their opinion "wrong"
definition of entropy, introduced by Boltzmann. Instead the Gibbs (or
rather) Hertz entropy is proposed, that is supposed to solve the problem
with absolute negative temperatures. We discuss this paper, the advantages
and disadvantages of both entropies, and the plausibility of negative
temperatures with the help of a comment on this paper.
Literature:
J. Dunkel, S. Hilbert,
"Consistent thermostatistics forbids negative absolute temperatures",
Nature Phys. 10, 67 (2013);
U. Schneider, S. Mandt, et al.
"Comment on 'Consistent thermostatistics forbids negative
absolute temperatures'", arXiv:1407.4127 (2014)



