Speaker
Aurel Bulgac
Description
The fascinating dynamics of superfluids, often referred to
as quantum coherence revealed at macroscopic scale, has
challenged both experimentalists and theorists for more than
a century now, starting with electron superconductivity
discovered in 1911 by Heike Kamerlingh Onnes. The
phenomenological two-fluid model of Tizsa and its final
formulation due to Landau, is ultimately a classical
approach in which Planck’s constant never appears and it is
unable to describe the generation and dynamics of the
quantized vortices, which are the hallmark characteristics
of superfluidity. Various quantum mechanical
phenomenological models have been developed over the years
by London, Onsager, Feynman, Ginzburg and Landau, Abrikosov,
and many others, but truly microscopic approaches are very
scarce. The Gross-Pitaevskii equation was for many years the
only example, but it is applicable only to a weakly
interacting Bose gas at zero temperature and it has been
used to describe the large variety of experiments in cold
atomic Bose gases. In the case of fermionic superfluids only
a time-dependent mean filed approach existed for a long
time, which is known to be quite inaccurate. With the
emergence of the Density Functional Theory and its
time-dependent extension it became relatively recently
possible to have a truly microscopic approach of their
dynamics, which proves to be extremely relabel in predicting
and describing various experimental results in cold atomic
fermionic gases, nuclei and which can be used as well to
make predictions about the nature and dynamics of vortices
in the neutron star crust. I will describe the
time-dependent superfluid local density approximation, which
is an adiabatic extension of the density functional theory
to superfluid Fermi systems and their real-time dynamics.
This new theoretical framework has been used to
describe/predict a range of phenomena in cold atomic gases
and nuclear collective motion: excitation of the Higgs modes
in strongly interacting Fermi superfluids, generation of
quantized vortices, crossing and reconnection of vortices,
excitation of the superflow at velocities above the critical
velocity, excitation of quantum shock waves, domain walls
and vortex rings in superfluid atomic clouds, and excitation
of collective states in nuclei. This approach is the natural
framework to describe in a time-dependent framework various
low energy nuclear reactions and in particular large
amplitude collective motion and nuclear fission and the
numerical implementation of this formalism requires the
largest supercomputers available to science today.
