Physics and Astronomy Calendar

Week of Monday, October 16th 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
To be announced.

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
To be announced.
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:
To be announced.
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.
Refreshments to be served in the MIfA Interaction Area (Tate 285-11) following the colloquium.
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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