


Projects
 Optimal timedependent lattice models for nonequilibrium dynamics
We have recently found a way to design optimal lattice models based entirely
on the principle of least action. As an example we present the
optimal BoseHubbard model. One of our results is that the commonly
used parameters U and J are actually timedependent and lattice
sitedependent functions. Also the optimal coupling constants for
stationary states can be found using our new concept. We have
thereby provided a tool to end the longlasting search for the
optimal parameters of lattice models.
 Exact quantum dynamics of a bosonic Josephson junction
Few problems in the ultracold atoms literature have been studied
as extensively as the bosonic Josephson Junction problem. The
literature relies heavily on the use of either the GrossPitaevskii
approximation or the BoseHubbard model. We have provided the
first numerically exact results on this subject based on the
timedependent manybody Schrödinger equation. It
turns out that the true physics is quite different from the
predictions of either the GrossPitaevskii equation or the
BoseHubbard model.
 Correlation functions and coherence of trapped
BoseEinstein condensates
In this work we investigate the ground state of the
manybody Schrödinger equation of a BEC in
a double well potential. We provide the correlation
functions and show how the nature of the condensate
changes depending on the barrier height from condensed
to fragmented.
 BoseEinstein
condensate on a ring
Lieb and Liniger's model is a hallmark of mathematical physics.
In this work we solved Lieb and Liniger's equations for finite
numbers of particles and studied the approach to the thermodynamic
limit with increasing particle numbers as well as the approach
to Girardeau's gas of impenetrable bosons. The energies for
repulsive and attractive interaction are listed on the above website.
 Stochastic motion of a driven magnetic nanoparticle
A magnetic nanoparticle in a magnetic field is generally
subject to thermal fluctuations. These fluctuations can flip the
orientation of the magnetization. The mean first passage times of
such flips are computed.
Talks
Software
