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

January 30 (2015), 2pm SSL150

Andrew King (D-Wave)
Looking and not looking at analog control error in quantum annealing processors

D-Wave quantum annealing processors are subject to transient and systematic analog control errors that at current levels are well understood and can be reduced through technological advances.  In the meantime, we seek a meaningful study of these processors that takes this into account.  We therefore seek input classes and performance metrics whose sensitivity to control error is minimal (i.e. not looking at error).  In this talk I will present our error model and discuss how it affects performance on various input classes (i.e. looking at error).  This motivates the study of time to epsilon, measuring performance via approximate solution whose excitation from the ground state scales based on our error model.  I will then discuss methods for reducing error sensitivity in input classes, which might give us a better look at the dynamics of the platform.

February 4 (2015), 2pm SSC 319
Victor Martin-Mayor (Universidad Complutense Madrid)
Quantum versus Thermal annealing, the role of Temperature Chaos

The "D-Wave Two" machine presumably exploits quantum annealing effects to solve optimization problems. One of the preferred benchmarks is the search of ground-states for spin-glasses, one of the most computationally demanding problems in Physics. In fact, the "Janus" computer has been specifically built for spin-glasses simulations.  Janus has allowed to extend the time scale of classical simulations by a factor of 1000.  Whether D-wave's quantum annealing achieves a real speed-up as compared to the classical (thermal) annealing or not is a matter of investigation.  Difficulties are twofold. On the one hand, the number of q-bits (476), although a World record, is still small. On the other hand, the 476 q-bits are disposed in a particular topology (the chimera lattice), where hard-to-solve instances are extremely rare for a small system.  However, our work with Janus has taught us about a relevant physical effect: temperature chaos. Given a large enough number of q-bits, rough free-energy landscapes should be the rule, rather than the exception.  Therefore, the meaningful question is: how well quantum-annealing performs in those instances displaying temperature-chaos?  For a small number of q-bits, temperature-chaos is rare but fortunately not nonexistent. In the talk, we explain how our previous experience with Janus is allowing us to find chaotic instances for a small chimera lattice. The performance of both thermal annealing and quantum-annealing (D-wave) will be assessed over this set of samples.

February 6 (2015), 2pm UPC
Ansgar Siemer (BIOC)
Solid-State NMR on Toxic and Functional Amyloid Fibrils

Solid-state NMR is a powerful tool to extract atomic resolution information from systems that are difficult to study otherwise. An important class of such systems is amyloid fibrils. Although amyloids were originally described as a key symptom and possible cause of several neurodegenerative diseases, they can also serve functional roles including structural support and cell signaling.
As an example of a functional amyloid, I will present solid-state NMR investigations on Orb2 a member of the CPEB protein family important for long-term memory. We were able confirm the location of the static amyloid core and characterize its secondary structure content. The amyloid core of these functional amyloids is formed by a glutamine rich domain similar to certain proteins responsible for neurodegenerative disease. We are therefore contrasting our results on Orb2 with solid-state NMR data of polyglutamine containing toxic amyloids to see what structurally distinguishes benign from toxic amyloids.

February 13 (2015), 2pm SSL150
Gil Rafael (Caltech)
The Hilbert-glass transition: new universality of many- body dynamical quantum criticality

We study a new class of unconventional critical phenomena that is characterized by singularities only in dynamical quantities and has no thermodynamic signatures. I will develop a real-space renormalization group method for excited state (RSRG-X) that allows us to analyze such transitions, and will focus on the 1D disordered transverse field Ising
model with generic interactions. While thermodynamic phase transitions are generally forbidden in this model, using RSRG-X we find a finite-temperature dynamical transition between two localized phases. The transition is characterized by non-analyticities in the low frequency heat conductivity and in the long-time (dynamic) spin correlation function. The latter is a consequence of an up-down spin symmetry that results in the appearance of an Edwards-Anderson-like order parameter in one of the localized phases.

February 20 (2015), 2pm SSL150

Paul Brumer (Toronto)
Coherence, Decoherence and Incoherence in Natural Light Harvesting Systems

Establishing coherence, and resisting decoherence, are significant requirements in  wide variety of quantum based processes. As a consequence, the experimental photon echo observations of unusually long lived coherences in complex light harvesting  systems generated great enthusiasm for the idea that quantum coherence could persist in complex molecular systems at ambient temperatures. However, there are a number of issues, including the nature of the exciting light, which challenge the significance of such experimental results for natural light-induced dynamics.
We will review these results, and describe new developments in this area, such as the importance of various decoherence time scales and molecular properties for reaching mixed states, and the role of Fano resonances in generating long coherence time scales in the molecular response to natural incoherent light. Examples will be chosen from model systems, such as a generic v-level system, Rydberg atoms interacting with the cosmic microwave background, and PC645 irradiated by sunlight. The significance of these results for sustained quantum coherences in large molecular systems under natural incoherent excitation will be emphasized.

March 6 (2015), 2pm HSC
Tobias Ulmer (BIOC)
Mechanism of Integrin Transmembrane Signaling

When a blood vessel is injured, either by wounding or more chronically by atherosclerosis, the heterodimeric adhesion receptor integrin aIIbb3 is activated to crosslink blood platelets. This aggregation event can lead to occlusive thrombus formation, culminating in heart attack or stroke, the leading causes of death in the Western world. Receiving activating stimuli at the cytosolic integrin b tail leads to the dissociation of the complex formed between the integrin a and b transmembrane (TM) domains. This event causes a structural rearrangement of the large, non-covalently associated ab ectodomains that increases their ligand affinity. To understand the mechanism of integrin receptor activation, we elucidate the structural events that lead to ab TM dissociation and the structural and thermodynamic coupling between ecto- and TM domains.

March 27 (2015), 2pm SSL150
Ilya Krivorotov (UC Irvine)
Spin-orbitronics in metallic nanostructures

Manipulation of the spin of electron by an electric rather than magnetic field is at the core of spintronics. Spin orbit interaction (SOI) is a natural way of coupling the spin to an electric field. In this talk, I will review recent discoveries of surprisingly strong magneto-electric effects in metals, including SOI-induced pure spin currents and electric field control of magnetic anisotropy. I will show how these effects can be employed for generation and control of collective spin excitations in magnetic nanostructures. Applications of these effects in non-volatile computer memory and nanoscale microwave sources will be discussed.

April 3, 2pm UPC
Robert Farley (PHBI)
Molecular Dynamics Simulations of Selective Ion Permeation in Biological Ion Channels

April 10 (2015), 2pm SSL150
Yaroslav Tserkovnyak (UCLA)

April 17 (2015), 2pm SSL150
Guanghou Wang (Nanjing University)
Clustering effect on topological transport of Cu-doped Bi2Te3 crystals

April 24 (2015), 2pm SSL150
Mehrtash Babadi (Caltech)

May 1, 2pm HSC
Robert Chow (PHBI)

Perspectives on Molecular Mechanisms of Exocytosis

June 5, 2pm UPC
Radha Kalluri (OTOL)
From Mechanics to Ion Channels: Biophysics of Sensory Encoding in the Ear

August 7, 2pm UPC
Moh El-Naggar (PHYS)

September 4, 2pm HSC
James Boedicker (PHYS)
Predicting and Controlling the Activity of Microbial Ecosystems

October 2, 2pm UPC
Emily Liman (BIOL)

November 6, 2pm HSC
Stephan Haas (PHYS)
Jarzynski’s Equality, Ion Selectivity & Conduction

December 4, 2pm UPC
Ralf Langen (BIOC)

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