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Spring 2018 Colloquium Series

Date: Thursday, June 7th, 2018
Speaker: Greg Stephens, Vrije University and Okinawa Institute of Science and Technology

Title: Towards a physics of behavior: If Newton watched the worm, not the apple

Abstract: We use the posture dynamics of the nematode C. elegans to explore whether we can be as precise about the laws and principles that govern the emergent scale of entire organisms as we are about the molecules, cells and circuits from which behavior is ultimately derived. We exploit ideas from dynamical systems and statistical physics to reconstruct the worm’s phase space directly from the movement time series. We show that the dynamics lie on a 6D manifold, composed of forward, backward and turning motions. In contrast to global stereotypy, local variability is evident in positive Lyapunov exponents for each behavior. Over the full phase space, positive, chaotic exponents driving variability are balanced by negative, dissipative exponents driving stereotypy and the dynamics exhibit a near-Hamiltonian symmetry. This symmetry holds for different environments and organisms suggesting a general condition of motor control.

Host: Caleb Holt

 

Date:  Thursday, May 31st, 2018
Speaker:  Werner Vogel, University of Rostock

Title: Uncovering the Quantum Nature of Light

Abstract: We consider quantum properties of light, such as nonclassicality, entanglement, and general quantum correlations.  We start by introducing the notions of nonclassical and entangled quantum states and identify their origin in the quantum superposition principle. Some examples for experimental reconstructions of quantum states are given. Properties of nonclassical states are discussed with particular emphasis on squeezed states. We introduce a method to visualize the nonclassicality of such quantum states in experiments by direct sampling of a so-called nonclassicality quasiprobability. The verification of quantum entanglement is considered for complex multipartite scenarios. Our approach allows us to verify entanglement beyond the simple case of bipartitions. Finally we consider general, space-time-dependent quantum correlations of light. Our method uncovers quantum correlations even when other signatures of quantumness fail to do so.

Host: Brian Smith

 

Date:  Thursday, May 24th, 2018
Speaker:  Paul Steinhardt, Princeton University

Title: Once Upon a Time in Kamchatka: The Extraordinary Search for Natural Quasicrystals

Abstract: Quasicrystals are exotic materials with symmetries that were once thought to be impossible for matter.  The first known examples were synthesized in the laboratory over 30 years ago, but could Nature have beaten us to the punch?  This talk will describe the search that took over a dozen years to answer this question, resulting in one of the strangest scientific stories you are ever likely to hear.

Host: John Toner

 

Date: May 17th Physics colloquium CANCELLED

 

Date:  Thursday, May 10th, 2018
Speaker:  Alyson Brooks, Rutgers University

Title: Re-Examining Astrophysical Constraints on the Dark Matter Model

Abstract: The cosmological model based on cold dark matter (CDM) and dark energy has been hugely successful in describing the observed evolution and large scale structure of our Universe. However, at small scales (in the smallest galaxies and at the centers of larger galaxies), a number of observations seem to conflict with the predictions of CDM cosmology, leading to recent interest in alternative dark matter models. I will summarize a number of ways that including baryonic physics (the physics of gas and stars) can resolve the conflict between theory and observations, by significantly altering the structure and evolution of galaxies. Despite all of the successes of baryonic physics in reconciling CDM with observations, I will explain why alternative dark matter models are still viable and interesting.

Host: Graham Kribs

 

Date:  Thursday, May 3rd, 2018
Speaker:  Daniel Blair, Georgetown University

Title: Fluids that Stiffen and Swim

Abstract: In this talk I will discuss our recent results on the microscopic physical origins of shear thickening in sheared colloidal suspensions and the viscoelasticity of active fluids. In the first part of my talk, I will introduce a method we have developed that allows us to resolve the spatial distribution of stresses in sheared soft-materials, known as Boundary Stress Microscopy. We have applied this technique suspensions undergoing continuous and discontinuous shear thickening. I will present our results on the existence of clearly defined dynamically localized regions of substantially increased stress that appear intermittently at stresses well above the applied stress. Surprisingly, we find that these spatially distinct and dynamic phases account quantitatively for the observed shear thickening seen in sheared colloidal dispersions (e.g. Oobleck). In the second part of my talk I will discuss our results on the rheology of active matter. Our system is composed of microtubules and motor kinesin proteins that self-assemble to form complexes that propel themselves through the fluid, resulting in spontaneous “swimming” of the suspended material. What results is an interplay between the internal active stresses and any imposed external stress. I will discuss the impact of the internal flows have on the local and bulk rheological response.

Host: Eric Corwin

 

Date: Thursday, April 26th, 2018
Speaker:  Sean Hartnoll, Stanford University

Title: Quantum Mechanical Bounds on Transport from First Principles

Abstract: Some of hardest theoretical challenges in strongly-interacting many-body systems are concerned with transport. This involves understanding quantities such as the electric resistivity, the thermal conductivity, the viscosity, spin diffusivity etc. of media as diverse as the quark-gluon plasma, unconventional metals and cold atomic gases. I will argue that a handle on these problems can be gained from understanding fundamental limits on the dynamics of many-body systems imposed by quantum mechanics and statistical mechanics themselves. The advantage of this approach is that it does not depend on the presence of weakly interacting quasiparticles.

Host: Tim Cohen

 

Date:  Thursday, April 19th, 2018
Speaker:  Paul Wiggins, University of Washington

Title:  Why Systems Biology Shouldn’t Work but Does and What Heat Capacity Can Explain About Inference

Abstract: Why do systems biology models work in spite of a blizzard of poorly-defined parameters and yet the detection of the Higgs boson required five sigma precision? Scientific and technological innovations are rapidly increasing the size and scope of datasets. Accompanying this growth come new challenges in analysis, interpretation and modeling. Fundamental questions remain about the mechanism of learning. To study the universal principles governing these processes, we expand upon a long-discussed correspondence between thermodynamics and statistics. This correspondence to thermal physics provides some surprising insights into the mechanism of learning. An analogy to heat capacity demonstrates both a universal scaling of learning algorithms as well as how and why these scaling relations fail in many of the most interesting models, including systems biology models. An analogy to the Gibbs entropy provides a new algorithm for efficient inference, well-suited to single-molecule-fluorescence measurements where the number of photons collected is small.

Host: Tristan Ursell

 

Date:  Thursday, April 12th, 2018
Speaker:  Wei R. Chen, University of Central Oklahoma

Title: Laser Immunotherapy for Metastatic Cancers: Interplay of Photons, Molecules, Cells, and Humans

Abstract: The cure for cancer remains elusive because of the ability of cancer cells to disguise themselves as normal “self” cells, thus evading detection and destruction by the host immune system. Metastasis is the major cause of cancer-related death.  We have developed Laser Immunotherapy (LIT) to treat metastatic cancers by using a combination of local laser irradiation and immunological stimulation. In LIT the laser-treated tumor cells become the source of tumor antigens that act as the signals for the immune system to recognize as “foreign” objects. The immune system then proceeds to eradicate both the residual tumor cells at the treatment site and distant metastasized tumors.  Essentially, LIT turns the host immune system around from defending against “foreign” cells to eradicating “domestic” tumor cells.  In this talk the procedures and mechanism of LIT will be introduced.  Our successful clinical results using LIT in patients with late-stage melanoma and breast cancer will be presented.

Host: Rudy Hwa

 

Date:  Thursday, April 5th, 2018
Speaker: Terry Rudolph, Imperial College London

Title: Quantum Quantum-Thermodynamics

Speaker: Terry Rudolph, Imperial College London

Abstract: The thermodynamic implications of quantization of energy were realized before the full quantum theory was even developed. By contrast, the thermodynamic implications of quantum coherence, in the myriad guises it can arise, are still today encountered in a somewhat piecemeal fashion. I will discuss some simple quantum thermodynamic phenomena that rely on the presence of quantum entanglement or quantum coherence, and then discuss progress to a coherent (!) general framework for such phenomena using tools of quantum information theory.

Host: Mike Raymer