Physics and Astronomy Calendar

Week of Monday, April 29th 2019

Monday, April 29th 2019
12:15 pm:
Speaker: Patrick Kelly, UMN

Tuesday, April 30th 2019
Speaker: TBD
Subject: TBD
Faculty Host: Vuk Mandic

Wednesday, May 1st 2019
1:25 pm:
Speaker: Jack Harris, Yale University
Subject: A pedagogical introduction to the emergence of topology in non-Hermitian dynamics

A collection of coupled linear oscillators is widely regarded as a trivial physical system. Nevertheless, in recent years it has become evident that weak loss (or gain) in these systems can result in a variety of qualitative surprises - even in the purely linear regime. Effects that have attracted considerable attention include: PT symmetry breaking, exceptional points, non reciprocity, and topological control. I will describe a simple framework that unites these "non-Hermitian" effects and explains why topology emerges generically in damped coupled linear oscillators. I will discuss the application of these concepts in classical systems and in quantum systems. Lastly, I will describe an optomechanical experiment that offers a natural way to realize generic non-Hermiticity.

Faculty Host: Paul Crowell

Thursday, May 2nd 2019
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: TBD
12:10 pm:
Speaker: Tom Jones and Jamie Cheshire
3:35 pm:
Speaker: Jack Harris (Yale University)
Subject: Quantum optomechanics with superfluid helium
Note change of room for this week only. Refreshments in atrium after the Colloquium.

To observe quantum effects in the motion of macroscopic objects typically requires high-precision readout, low temperature, and low optical and mechanical loss. Superfluid helium offers many advantages in these regards. I will describe two optomechanics experiments based on superfluid helium. In the first, the superfluid fills a Fabry-Perot optical cavity. The cavity is used to monitor the quantum fluctuations of the superfluid's acoustic modes. This system is amenable to single photon/phonon detection schemes, and so may provide a route to more exotic quantum effects in massive objects. The second experiment uses magnetic levitation to suspend a mm-scale drop of superfluid in vacuum. I will describe preliminary measurements of the drop's formation, trapping, and evaporative cooling, and of the drop's mechanical resonances and optical resonances.

Faculty Host: Paul Crowell
4:00 pm:
A.O.C. Nier Lecture in B50 Tate
Speaker: Kenneth A. Farley, W.M. Keck Foundation Professor of Geochemistry
Subject:  The geologic record of asteroid collisions and comet showers from cosmic dust 3He in marine sediments

Friday, May 3rd 2019
11:00 am:
Nuclear Physics Seminar in Physics Tate 301-20
Speaker: Samuel Giuliani, NSCL/FRIB Laboratory, Michigan State University
Subject: r process, kilonova and nucleosynthesis of superheavy elements: The role of fission

The rapid neutron capture process (r process) is responsible for the production of half of the elements heavier than iron that we observe in the Universe. The quest to identify its actual astrophysical site is still ongoing, but there are strong indications, including the recent observation of the GW170817 electromagnetic counterpart, that make neutron star mergers (NSM) a likely candidate. Reliable estimates of nucleosynthesis yields on NSM require an accurate description of the relevant nuclear physics inputs including nuclear masses, neutron capture rates, β- and α-decay rates and, for fissioning nuclei, fission rates and fission fragments distributions. Several of these quantities can be computed from a consistent theoretical framework using the energy density functional (EDF) approach.
In this talk I will revise how uncertainties in the nuclear physics properties of neutron-rich nuclei impact nucleosynthesis calculations, with a focus in the fission properties of (super)heavy nuclei. I will present a new set of fission rates obtained from microscopic nuclear many-body calculations, which are used as a nuclear input in r-process nucleosynthesis calculations in NSM. The possible formation of superheavy elements during the r-process nucleosynthesis as well as the impact on kilonova light curve, a quasithermal transient powered by freshly synthesized r-process nuclei, will be discussed. Finally, I will introduce recent developments in the estimation of fission yields and the possible extension to r-process nuclei.

12:20 pm:
Speaker: Saumitran Kastirurangan
Subject: Effect of disorder on boundary modes in nodal topological materials
12:30 pm:
Speaker: Sergei Dubovsky (NYU)
2:30 pm:
There will be no colloquium this week
4:00 pm:
Speaker: Nina Bielinski
Subject: Investigation of Superconducting Fluctuations via Torque Magnetometry in LSCO
Faculty Host: Paul Crowell

The weekly calendar is also available via subscription to the physics-announce mailing list, and by RSS feed.