Micro Cavity-based Spectroscopy of individual Nano Particles (M. Mader) / PEPS and local (gauge) symmetries (Dr. E. Zohar)
- Double Feature!
- Datum: 29.11.2016
- Uhrzeit: 14:30 - 15:30
- Vortragende(r): Mathias Mader, Doctoral Candidate, Laser Spectroscopy Division / Dr. Erez Zohar, Postdoc, Theory Division
- Raum: Herbert Walther Lecture Hall
- Gastgeber: MPQ
"Micro Cavity-based Spectroscopy of individual Nano Particles" (M.
Mader)
Optical characterisation and imaging of individual nano systems
beyond fluorescence bears the potential to provide a wealth of
information. However it is very challenging to observe signals for
extinction and dispersion of a single nano particle. At the same time,
it is desirable to get information on the single particle level as nano
systems can vary in size and shape. We present two complementary
approaches for ultra-sensitive detection and characterisation of
individual nano systems, both based on signal enhancement in a
high-finesse optical cavity.Using a cavity made of a micro-machined and
high reflectively coated mirror on the end-facet of an optical fiber and
a plane mirror, that can be transversally scanned with respect to the
fiber, the cavity mode can be used as a scanning probe to precisely
measure the extinction of nano objects placed on the plane mirror.
Furthermore, exploiting higher order resonances of the resonator,
frequency shifts due to the object can be retrieved. Combining both
measurements allows a full reconstruction of the complex polarizability
tensor of the object.In an alternative approach, we integrate a fully
fiber-based microcavity into a microfluidic cell to allow for
ultra-sensitive spectroscopy of individual nano systems in an aqueous
environment under well-controlled conditions. In addition to dispersive
detection of the nano object by detecting a shift in the resonance
frequency, absorption measurements are possible by observing the
transmitted light. At the same time, the cavity mode can be used as an
optical tweezer to trap particles. This opens the possibility to store a
particle without binding to a surface and to investigate e.g. reaction
dynamics on a single particle level.
"PEPS and local (gauge)
symmetries" (Dr. E. Zohar)
Tensor
networks, and in particular Projected Entangled Pair States (PEPS), are a powerful tool for the study of quantum many
body physics, thanks to both their built-in ability of classifying and studying
symmetries, and the efficient numerical calculations they allow. In the works I
will present, we introduced a way to extend the set of symmetric PEPS in order to include local
gauge invariance and investigate lattice gauge theories with fermionic matter.
I will review the basic ingredients of PEPS and the
way of handling global symmetries with them, and show how to gauge them and
make the symmetry local. As examples, I will
present our construction of fermionic PEPS, based
on Gaussian schemes, invariant under both global and local
U(1) or SU(2) gauge transformations. The obtained states describe a truncated
U(1) or SU(2) lattice gauge theory in 2+1 dimensions, involving both the gauge
field and fermionic matter; I will present the methods which enabled us to
study these states, and the results in which some well-known physical phases
were identified (e.g. confinement of static charges and screening of dynamical
ones).