Events at Physics
Events on Tuesday, September 21st, 2021
- Network in Neutrinos, Nuclear Astrophysics, and Symmetries (N3AS) Seminar
- Transport in Neutron Star Mergers
- Time: 2:00 pm
- Speaker: Alexander Haber, Washington University in St. Louis
- Abstract: Transport processes in hot and dense matter are an important way to improve our understanding of fundamental interactions and might be accessible via gravitational wave observations. In this talk I will especially focus on modified and direct Urca processes in nuclear matter under conditions that we expect in binary neutron star mergers. Nuclear Urca processes have shown to be a potential significant source of bulk viscosity under merger conditions. I will explain how a correct relativistic treatment can alter the rates and the true beta equilibrium significantly.
- Host: Baha Balantekin
- Thesis Defense
- Correlated Charge Noise and Relaxation Errors in Superconducting Qubits
- Time: 2:00 pm
- Place: Zoom:
- Speaker: Chris Wilen, Physics PhD Graduate Student
- Abstract: A crucial requirement to the surface code is that errors cannot be correlated. Here, we characterize a superconducting multiqubit circuit and find that charge fluctuations are highly correlated on a length scale over 600~μm; moreover, discrete charge jumps are accompanied by a strong transient suppression of qubit energy relaxation time across the millimeter-scale chip. The resulting correlated errors are explained in terms of the charging event and phonon-mediated quasiparticle poisoning associated with absorption of gamma rays and cosmic-ray muons in the qubit substrate. Robust quantum error correction will require the development of mitigation strategies to protect multiqubit arrays from correlated errors due to particle impacts.
- Host: Robert McDermott, faculty advisor
- Theory Seminar (High Energy/Cosmology)
- Computation of Gravitational Particle Production Using Adiabatic Invariants
- Time: 4:00 pm
- Place: Chamberlin 5280
- Speaker: Edward Basso, University of Wisconsin-Madison
- Abstract: Analytic and numerical techniques are presented for computing gravitational production of scalar particles in the limit that the inflaton mass is much larger than the Hubble expansion rate at the end of inflation. These techniques rely upon adiabatic invariants and time modeling of a typical inflaton field which has slow and fast time variation components. A faster computation time for numerical integration is achieved via subtraction of slowly varying components that are ultimately exponentially suppressed. The fast oscillatory remnant results in production of scalar particles with a mass larger than the inflationary Hubble expansion rate through a mechanism analogous to perturbative particle scattering. An improved effective Boltzmann collision equation description of this particle production mechanism is developed. This model allows computation of the spectrum using only adiabatic invariants, avoiding the need to explicitly solve the inflaton equations of motion. Note: This is a hybrid event. A zoom link will be distributed via the seminar mailing list. To join, email the organizer.
- Host: Lars Aalsma