USC Physics Seminars
Quantum Information –
Condensed Matter – Biophysics
These seminars are scheduled on Fridays at 2:00pm, and the location is SSL 150, unless otherwise noted. Some of the seminars will be held jointly with UCLA and CALTECH.
For more information contact Lorenzo Campos Venuti (condensed matter) or Ben Reichardt (quantum information). Biophysics seminars are held the first Friday of each month and are indicated in blue.
UPC seminar location: Ahmanson Center for Biological Research, ACB 238. UPC location for remote viewing of HSC seminars: To be determined.
HSC seminar location: Herklotz seminar room, Zilkha Neurogenetic Institute HSC. Location for remote viewing of UPC seminars: Herklotz
August 28, 2pm SSL150
Andreia Seguia (Universidade Federal Fluminense Brazil)
Quantum phase transitions in a chain with two- and four-spin interactions in a transverse field
We use entanglement entropy to investigate the ground-state properties of a spin-1/2 Ising chain with two-spin (J2) and four-spin (J4) interactions in a transverse magnetic field (B). We concentrate our study on the unexplored critical region B=1 and obtain the phase diagram of the model in the (J4-J2) plane. The phases found include ferromagnetic (F), antiferromagnetic (AF), as well as more complex phases involving spin configurations with multiple periodicity. The system presents both first- and second-order transitions separated by tricritical points. We find an unusual phase boundary on the semi-infinite segment (J4<1,J2=0) separating the F and AF phases.
September 4, 2pm HSC
James Boedicker (PHYS)
2015 BIOPHYSICS SEMINAR SERIESPredicting and Controlling the Activity of Microbial Ecosystems
September 18, 2pm SSL150
Jie Yuan (RWTH Aachen, Germany)
Triplet pairing driven by Hund's coupling in doped monolayer MoS2
We investigate superconducting pairing driven by electron-electron interactions in a theoretical model for monolayer MoS2 with the temperature-flow functional renormalization group (fRG). At low doping, the dominant instability is toward odd-parity pairing with f-wave Mo-nearest-neighbor structure. We compute the fRG phase diagram versus electron doping below the van Hove filling of the conduction band. In the superconducting regime, the critical temperature grows with doping, comparable to the experiments. Near van Hove filling the system favors a ferromagnetic state. We demonstrate that the triplet pairing is driven by ferromagnetic fluctuations and that the multiorbital nature of the conduction band as well as the Hund’s coupling appear crucial in making the physics of MoS2 different from e.g. doped graphene.
Emily Liman (BIOL)
October 9, 2pm SSL150
Paul Majoram (USC)
October 23, 2pm
Ariane Briegel (Caltech)
October 30, 2pm SSL150
Micah McCauley (Northeastern)
Energy Landscapes Determined from Single Molecule Non-Equilibrium Experiments
HIV-1 nucleocapsid (NC) proteins facilitate the rearrangement of nucleic acid secondary structure, allowing the transactivation response (TAR) RNA hairpin to be transiently destabilized during reverse transcription. Single molecule optical tweezers measurements were used to probe the stability of RNA hairpins as NC was introduced. Unfortunately, these experiments produce forces that drive hairpin unfolding/folding far from equilibrium. To overcome this limitation, the methods of Jarzynski, Crooks, Bennett and Dudko have been developed to deduce equilibrium and transition state energies of a reaction during non-equilibrium experiments. Combining these results with a quantitative mfold-based model, we characterize the equilibrium TAR stability and unfolding barrier for TAR RNA. We find that a subset of preferential protein binding sites is responsible for the observed changes in the unfolding landscape, including an unusual shift in the transition state, and results in the dramatic destabilization of this specific structure that is required for reverse transcription.
November 6, 2pm HSC
Osman Kahraman (USC)
November 13, 2pm SSL150
Michael Peterson (California State University Long Beach)
December 4, 2pm UPC
Ralf Langen (BIOC)
2015 BIOPHYSICS SEMINAR SERIES
December 11, 2pm SSL150
Lea F. Santos (Yeshiva University, New York)
Nonequilibrium dynamics and thermalization of isolated many-body quantum systems
We study the evolution of isolated systems with two-body interactions after an abrupt perturbation. Two aspects are addressed: the conditions for the system to reach thermal equilibrium and the description of the relaxation process. Both depend on the interplay between the initial state and the Hamiltonian after the perturbation, rather than only on the regime of the system. Thermalization may not occur in the chaotic regime if the energy of the initial state is close to the edges of the spectrum and it may take place in integrable systems provided the initial state be sufficiently delocalized in the energy eigenbasis. In the latter case, the dynamics is very fast. The decay may be exponential, Gaussian, and even faster than Gaussian. We show how the limit imposed by the energy-time uncertainty relation can be reached. In contrast, the time evolution slows down significantly when the system undergoes an excited state quantum phase transition or when disorder is added to the Hamiltonian.
USC Caltech UCLA ITP