Physics and Astronomy Calendar

Week of Monday, October 23rd 2017

Monday, October 23rd 2017
12:15 pm:
Speaker: Colin Hill, Department of Physics, Columbia University
Subject: New Information in Ancient Photons: Novel Approaches to CMB Foregrounds and Secondary Anisotropies

Studies of the cosmic microwave background (CMB) radiation have driven the current era of precision cosmology. The tightest cosmological constraints to date have been derived from the primary CMB anisotropies, which predominantly probe the universe in its infancy. However, CMB experiments have recently entered a new regime in which constraints derived from the secondary anisotropies -- sourced by effects between our vantage point and the surface of last scattering -- substantially improve upon those derived from the primary anisotropies alone. Moreover, the secondary anisotropies contain valuable astrophysical information about the distribution and thermodynamic properties of baryons and dark matter at late times. I will describe new approaches to extract information from these signals, highlighting recent results related to the thermal (tSZ) and kinematic Sunyaev-Zel'dovich (kSZ) effects, which refer to the Compton-scattering of CMB photons off ionized gas with high temperature or non-zero bulk momentum, respectively. In particular, I will show how the kSZ effect probes the abundance of ionized gas in and around modern-day galaxies, which I have used to resolve the long-standing "missing baryon problem". I will then discuss new methods for combining multi-frequency CMB data to extract these signals in the presence of large (and correlated) foregrounds, with additional applications to CMB polarization analyses. I will conclude with a look ahead to such measurements with the Simons Observatory (SO), focusing on methods to determine the optimal frequency coverage of the large-aperture SO telescope for secondary anisotropy science, including CMB lensing.

Faculty Host: Shaul Hanany

Tuesday, October 24th 2017
12:20 pm:
Space Physics Seminar in Tate 301-20
There will be no seminar this week. Please attend Stuart Bale's MIFA Colloquium.

Wednesday, October 25th 2017
1:25 pm:
Speaker: Cindy Regal, University of Colorado-Boulder
Subject: Prospects for an optical link to superconducting qubits via engineered micromechanical motion
Faculty Host: Clement Pryke
Speaker: Doug Glenzinski, Fermilab
Subject: The Mu2e Experiment
4:30 pm:
CM Journal Club in Tate 201-20
Speaker: Ruiqi Xing
Subject: Machine Learning circumvents sign problem in Quantum Monte Carlo

The journal club talk will be about the paper [1]. I will first introduce the famous fermion sign problem [2] in Determinantal Quantum Monte Carlo(DQMC) [3], and then discuss how to circumvent it using a method developed in machine learning community, convolutional neural networks. Introduction to neural networks [4] will be given. In the end, A successful application of this method to distinguish phases and to identify quantum phase transitions will be presented.

[1]Machine learning quantum phases of matter beyond the fermion sign problem
[2]Sign problem in the numerical simulation of many-electron systems
[3]Monte Carlo calculations of coupled boson-fermion systems. I
[4]Neural Networks and Deep Learning

Thursday, October 26th 2017
10:10 am:
Biophysics Seminar in 120 PAN
Speaker: Hao Wu, University of Minnesota
Subject: To be announced.
10:30 am:
Thesis Defense in 110 PAN
Speaker: Qianhui Shi, University of Minnesota
Subject: Quantum Hall stripes under in-plane magnetic fields
This is the public portion of Ms. Shi's thesis defense. Her advisor is Michael Zudov.
Speaker: Micaela Bagley
3:35 pm:
Speaker: Cindy Regal, University of Colorado-Boulder
Subject: Interferometry in a Strong Light

Optical interferometry is at the heart of many precise measurements from gravitational wave searches to microscopy. Generally one improves interferometer precision by increasing the light intensity, as well as by calming the many technical sources of noise that can perturb the mirrors or optical path. However, at extreme levels of light strength where radiation forces are significant, a new and interesting disturbance should appear – the quantum shaking associated with random arrival of individual photons at a mirror of the interferometer. This quantum backaction of light has been long foreseen and played a formative role in quantum optics theory. In this talk I will discuss an experiment in which we used a particularly compliant micro-scale drum to observe backaction in an interferometer, and demonstrate how quantum correlations can improve measurement in the presence of backaction. In this strong-light limit, interferometer mirrors can also be used as a nonlinear medium to manipulate light – for example to make squeezed light.

Faculty Host: Clement Pryke

Friday, October 27th 2017
10:10 am:
Nuclear Physics Seminar in Tate 301-20
There will be no seminar this week.
12:20 pm:
Speaker: Yilikal Ayino, University of Minnesota
Subject: Superconductivity in NdxSr1-xTiO3 Thin Films

Superconductivity in SrTiO3(STO) has remained an open question for more than half a century. In this talk I will present experimental results showing superconductivity in Nd doped STO thin flims (50-250 nm), where Nd is expected to carry a net magnetic moment. All the samples we studied show an anisotropic resistance along the two in-pane orthogonal directions, where the normal state resistances along the two directions differ by more than several factors. Although the normal state resistances between the channels seem to be qualitatively similar, the resistive superconducting transition is drastically different. Along the channel with larger normal state resistance we observe a smooth transition from metallic to superconducting state with decreasing temperature (“normal channel”), but along the channel with smaller normal state resistance we observe an insulating state (resistance rising by up to an order of magnitude in a narrow temperature range) between the metallic and superconducting states. The onset of the insulating state is closely related to superconductivity and that its behavior is qualitatively different from known effects of granularity or superconducting fluctuations in an insulating matrix. For the “normal channel” the out of plane upper critical field as a function of temperature shows opposite curvature from what would be expected based on WHH theory and that the critical field doesn’t seem to saturate with decreasing temperature. I will present possible explanations for such anomalous behavior, including effects related to magnetic impurities and two-band superconductivity.

Speaker: Gustavo Marques Tavares (Stanford)
Subject: "Detecting dark matter from Supernovae

The central region of Supernovae are one of the hottest and densest regions in the Universe. Due to the high temperatures, particles with masses below hundreds of MeV can be copiously produced if they have non-negligible couplings to the Standard Model. In this talk I will show that in a wide range of dark sector models, the dark matter flux from past Supernovae could be sufficiently large enough to be detected in dark matter direct detection experiments.

Speaker: Stuart Bale, Berkeley Space Science Lab.
Subject:  Plasma kinetics in the inner heliosphere and the NASA Parker Solar Probe mission
Refreshments to be served in the MIfA Interaction Area (Tate 285-11) following the colloquium.

I will describe measurements of velocity distribution functions and waves in the solar wind at 1 AU using instruments on NASA's WIND spacecraft and at 0.3 AU using Helios spacecraft. Plasma velocity distributions at 1 AU suggest the evolution by Coulomb collisions from nonthermal states to collisional equilibrium. Measurements at 0.3 AU are generally more nonthermal. This Coulomb coupling relationship can be used probe the plasma distributions of the inner heliosphere and suggests that the coronal population will be highly nonthermal. Furthermore, measurements of plasma waves at 1 AU suggest nonlinear evolution from a population of intense Alfven waves in the inner
heliosphere. Taken together, these observations suggest that the coronal plasma
environment is highly nonthermal and perhaps permeated by impulsive jets or waves. I will also describe the NASA Solar Probe Plus mission which will launch in summer 2018 and orbit the Sun with a final perihelion altitude of 9.8 solar radii, well within the predicted Alfven surface. Parker Solar Probe will make the first ever in situ measurements of plasma heating processes in the solar corona.

Faculty Host: Cynthia Cattell
Speaker: C. Kenneth Waters, Department of Philosophy - University of Calgary
Subject: An Epistemology of Scientific Investigation
Refreshments served at 3:15 p.m.

Basic accounts of scientific knowledge typically present it as a system for representing the world, often as a system that represents the fundamental structure of the world. This talk presents science as a system centered on investigating the world. It begins by posing the metaphysical possibility that the world has no fundamental structure. The world seems to have lots of structures, but perhaps it has no overall, general structure that spans scales. The talk continues by examining how geneticists and allied biologists systematically investigate, manipulate, and explain aspects of such a world. It shows that the systematicity of these investigations depends on strategies for manipulating and learning about aspects of parts of the world; it does not depend on scientists having a representation of the overall structure of these parts. The talk concludes that we can dispense with the assumption that the parts of the world investigated by these scientists have a general overall structure to be represented. These parts of the world have lots of structure, and investigation depends on them having lots of structure, but it does not depend on them having a general, overall structure.

4:40 pm:
Speaker: Jian-Ping Wang, University of Minnesota
Subject: To be announced.

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