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The David and Edith Harris Physics Colloquium Series
fall 2015 Schedule
SEPTEMBER 10, 2015
University of Cambridge
Host: MIT Graduate Women in Physics
"Identifying exotic electronic ground states using quantum oscillations"
Electrons traversing momentum space orbits in conducting materials yield classic signatures in transport and thermodynamic properties as a function of magnetic field. These undulatory signatures - known as 'quantum oscillations' - were first predicted and oberved in elemental metals. Since then, this experimental tool has found widespread use in mapping the characteristic electronic structures of strongly correlated materials ranging from heavy fermions to unconventional superconductors. I will present the surprising observation of quantum oscillations in interacting materials with apparently little in common with conventional metals; namely the exotic cuprate high temperature superconductors, and the Kondo insulating material samarium hexaboride. I will demonstrate how quantum oscillations prove a powerful tool to identify exotic ground states in strongly correlated electron systems.
SEPTEMBER 17, 2015
Host: Bolek Wyslouch
"Unveiling the Secrets of Nature: the Post-Higgs Discovery Era"
We found the Higgs boson, but where is everybody else? The first run of the Large Hadron Collider (LHC) at CERN was a remarkable success. Its highlight, the Higgs Boson discovery in 2012, completed the Standard Model of fundamental particle interactions. Yet, with the restart of the LHC in June 2015, the particle physics community expects that the era of even deeper discovery is just beginning. In this talk I will describe the landscape of post-Higgs discovery, explain why LHC physicists are so excited about the potential discoveries of the more powerful LHC, and give insights into a possible roadmap for particle physics beyond the LHC.
SEPTEMBER 24, 2015
Director, National High Magnetic Field Laboratory
Professor of Physics, Florida State University and University of Florida
Host: Patrick Lee
“Materials, Energy and Life: Entertaining Aspects of High Magnetic Field Research”
The MagLab exists to provide its international user community with unique magnets and expertise spanning condensed matter physics, materials research, chemistry, biochemistry, biology, and biomedicine. We generate magnetic fields exceeding two million times the Earth’s magnetic field. This talk seeks to answer the question, “Why would anyone want to do such a thing?” Illustrative examples from the portfolio of user research at the MagLab will include
- MATERIALS: tweaking macroscopic quantum phenomena in two-dimensional square lattices of copper and oxygen to achieve high-temperature superconductivity or magnetic Bose-Einstein condensation;
- ENERGY: analyzing nature’s most complex fluids, including petroleum, to improve utilization and mitigate pollution; and
- LIFE: tracking sodium and gadolinium quantum dots to revolutionize magnetic resonance imaging. During the talk, we anticipate that jokes will very likely be told.
The portion of the talk that surveys my own work on high-temperature superconductivity uses magnetic fields to suppress the superconductivity with a goal of revealing the Wizard who pulls the strings behind the curtain. This work is a collaboration with Scott Riggs, Oskar Vafek and Jon Kemper of the MagLab branch at Florida State University; Jon Betts, Al Bert Migliori and Fedor Balakirev of the MagLab branch at Los Alamos National Laboratory; and W. N. Hardy, Ruixing Liang and Doug Bonn of the University of British Columbia.
OCTOBER 1, 2015
Host: Peter Fisher
"The Gravitational Macro- and Micro-lensing of Quasars and the Ratio of Dark to Baryonic Matter in Galaxies"
In the time since the photons of the cosmic microwave background were last scattered, the universe has grown increasingly inhomogeneous. Dark and baryonic matter, once uniformly mixed, have become progressively more segregated. Observations of the motions of stars and gas in galaxies give total masses, but do not isolate the contributions of the dark and baryonic components. Observations of the micro-lensing of multiply imaged quasars by the stars within those galaxies permits measurement of the stellar mass component. We report results from such micro-lensing observations.
OCTOBER 8, 2015
University of Chicago
Host: Robert Simcoe
"Physics and Cosmology with the Cosmic Microwave Background"
The study of the cosmic microwave background (CMB) has driven spectacular advances in our understanding of the origin, make-up, and evolution of our universe. We now have a standard cosmological model, LCDM, that fits all the cosmological data with only six parameters, although there are some tensions that may hint at cracks in the model. Far from being the last word in cosmology, the model points to exciting times ahead using the CMB to explore new physics, i.e. inflation, dark matter, dark energy, neutrino masses and possible additional relativistic species, or dark radiation. This talk will review the latest results and near term plans for CMB measurements, with emphasis on the South Pole Telescope, and briefly discuss plans for the next generation experimental program CMB-S4.
OCTOBER 15, 2015
Host: MIT Society of Physics Students
"The Upside of Noise: Photon Torpedoes, QED Pinwheels, and the First 70 Years of Fluctuational Electrodynamics"
Noise is the sworn enemy of experimental scientists and a perennial headache for engineers, who spend much of their lives trying to mitigate its effects. It is thus somewhat surprising that there exists a branch of physics—and, increasingly, technology—in which noise plays the role of friend. This is fluctuational electrodynamics, the study of random microscopic fluctuations that mediate macroscopic transfers of energy and momentum. Although the first theoretical studies of fluctuation-induced interactions—Casimir forces and London dispersion forces—date back over 70 years, it has only been in the past 20 years that experimental breakthroughs and theoretical advances have combined to usher in the present golden age of fluctuation physics, a field now wide open for exploration and discovery.
In this talk, I will first review the theoretical underpinnings of fluctuational electrodynamics and briefly trace its history in the 20th century. I will then discuss the rapid progress of the past decade in predictive methods—both analytical and numerical—that have transformed the science of predicting Casimir forces on complex-shaped bodies from a forbidding intellectual challenge into an almost routine modeling procedure. This will bring us to the bleeding edge of the field today: the physics of non-equilibrium fluctuations, with applications including near-field radiative heat transfer and thermal self-propulsion of nanoscale bodies. I will discuss state-of-the-art computational approaches for tackling these formidable problems, then present new predictions for spontaneous self-propulsion and self-rotation of warm asymmetric bodies—photon torpedoes and QED pinwheels—in cold environments. The talk will also cover new theoretical tools, inspired by electrical engineering, for problems in quantum field theory, including entanglement entropy and constrained path integrals.
OCTOBER 22, 2015
Vienna Center for Quantum Science and Technology (VCQ), Atominstitut, TU-Wien
Host: Wolfgang Ketterle
"Does an isolated quantum system relax?"
Interfering two isolated one-dimensional quantum gases, we study how the coherence created between the two many body systems by the splitting process slowly degrades by coupling to the many internal degrees of freedom available . Two distinct regimes are clearly visible: for short length scales the system is characterized by spin diffusion, for long length scales by spin decay . For a sudden quench the system approaches a pre-thermalized state , which is characterized by thermal like correlation functions in the observed interference fringes with an effective temperature over five times lower than the kinetic temperature of the initial system. A detailed study of the time evolution of the correlation functions reveal that these thermal-like properties emerge locally in their final form and propagate through the system in a light-cone-like evolution . Furthermore we demonstrate that the pre-thermalized state is described by a generalized Gibbs ensemble . This is verified through a detailed study of the full non-translation invariant phase correlation functions up to the 10th order. Finally we show two distinct ways for subsequent evolution away from the pre-thermalized state. One proceeds by further de-phasing, the other by higher order phonon scattering processes. In both cases the final state is indistinguishable from a thermally relaxed state. We conjecture that our experiments point to a universal way through which relaxation in isolated many body quantum systems proceed if the low energy dynamics is dominated by long lived excitations (quasi particles).
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 M. Kuhnert et al., Phys. Rev. Lett, 110, 090405 (2013).
 M. Gring et al., Science, 337, 1318 (2012); D. Adu Smith et al. NJP, 15, 075011 (2013).
 T. Langen et al., Nature Physics, 9, 640–643 (2013).
 T. Langen et al., Science 348 207-211 (2015).
OCTOBER 29, 2015
University of California, San Diego
Host: Andrew Friedman
"The Twisted Universe: fundamental physics from the Cosmic Microwave Background's B-mode polarization"
The era of Cosmic Microwave Background (CMB) B-mode polarization cosmology began in March 2014 with two landmark papers released within a week of each other. The BICEP2 telescope observed from the South Pole for three seasons (2010–2012) and released results showing an excess of B-modes, thought to be the signature of inflationary gravitational waves. Despite its minuscule size, the signal could not be explained by instrumental systematic effects and was confirmed in cross-correlation with other instruments. Although a joint analysis with the Planck satellite in early 2015 found that BICEP2 signal was consistent with a galactic dust foreground, it represents the first, heroic foray into cosmic polarimetry at the parts-per-billion level. One week before the BICEP2 announcement, the POLARBEAR telescope (which observed from the Atacama Desert, Chile in 2012 & 2013) announced the detection of the CMB’s B-mode power spectrum at sub-degree scales. This signal, caused by gravitational lensing of the CMB’s E-mode polarization by large scale structure at low-redshift, paves the way towards measuring the absolute masses of neutrinos. Further fundamental physics constraints, including tantalizing bounds on primordial magnetism and cosmic birefringence — the rotation of the polarization plane of cosmic photons — are coming of age. I will describe early attempts to measure cosmic birefringence using distant polarized sources as well as describing state-of the-art measurements made by modern CMB polarimeters.
NOVEMBER 5, 2015
Lawrence Berkeley National Laboratory
Host: Physics Graduate Student Council
"Optimal Thermodynamic Control and the Geometry of Ising Magnets"
A major impediment to a quantitative understanding of molecular-scale machines is that they operate out of thermodynamic equilibrium. However, if the system is not too far from equilibrium, then optimal (minimum dissipation) thermodynamic control is governed by a fiction metric that generates a Riemannian geometry on thermodynamic state space. I’ll discuss the Riemannian geometry of the Ising model, a quintessential model of statistical mechanics that described the thermodynamics of ferromagnetic and fluid systems.
NOVEMBER 12, 2015
Howard Hughes Medical Institute and Harvard University
Host: Ibrahim Cissé
"Illuminating Biology at the Nanoscale with Single-Molecule and Super-Resolution Fluorescence Microscopy"
Dissecting the inner workings of a cell requires imaging methods with molecular specificity, molecular-scale resolution, and dynamic imaging capability such that molecular interactions inside the cell can be directly visualized. Fluorescence microscopy is a powerful imaging modality for investigating cells largely owning to its molecular specificity and dynamic imaging capability. However, the spatial resolution of light microscopy, classically limited by diffraction to a few hundred nanometers, is substantially larger than molecular length scales in cells, making many sub-cellular structures difficult to resolve. We developed a super-resolution fluorescence microscopy method, stochastic optical reconstruction microscopy (STORM), which breaks the diffraction limit by using photo-switchable fluorescent probes to temporally separate the spatially overlapping images of individual molecules. This approach has allowed multicolor and three-dimensional imaging of living cells with nanometer-scale resolution and enabled discoveries of novel sub-cellular structures. In this talk, I will discuss the recent technological advances and biological applications of STORM.
I will also describe a single-cell transcriptome imaging method that we recently developed. System-wide analyses of the abundance and spatial organization of RNAs in single cells promise to transform our understanding in many areas of cell and developmental biology, such as the mechanism of gene regulation, the heterogeneous behavior of cells, and the development and maintenance of cell fate. Single-molecule imaging approaches are powerful tools for counting and mapping RNA; however, the number of RNA species that can be simultaneously imaged in individual cells has been limited, making it challenging to perform transcriptomic analysis of single cells in a spatially resolved manner. To overcome this challenge, we developed a transcriptome imaging approach, multiplexed error-robust fluorescent in situ hybridization (MERFISH), which allows numerous RNA species to be localized and quantified in single cells in situ. In this talk, I will also discuss the technology development and application of MERFISH.
NOVEMBER 19, 2015
Host: Jesse Thaler
"String Theory in The Bathtub"
I will describe the peculiar mechanical properties of certain string-like objects that can exist in fluids and superfluids: vortex lines and vortex rings. I will then show how these properties follow straightforwardly from the principles of effective field theory applied to strings living in a medium.
DECEMBER 3, 2015
CEO, Vibrant Composites Inc.
Host: Peter Fisher
“Manufacturing Insect-scale Machines”
A quick look at the insect world reveals that we are still outclassed by nature when it comes to aspects of machine design and manufacturing. A key challenge is the target device scale of millimeters to centimeters, which exists between the realms of MEMS and conventional manufacturing. To address this challenge, we have developed "µMECS" technology, an additive manufacturing process with the potential for mass production. In this talk, I will discuss our techniques and results in creating high performance insect-scale machines. I will also discuss the practical challenges of building a technology business from research results.
DECEMBER 10, 2015
University of Heidelberg
Host: Martin Zwierlein
"One, Two, Three, Many: Manipulating Quantum Systems One Atom at a Time”
Experiments with ultracold gases have been extremely successful in studying many body systems, such as Bose Einstein condensates or fermionic superfluids. These are deep in the regime of statistical physics, where adding or removing an individual particle does not matter. For a few-body system this can be dramatically different. This is apparent for example in nuclear physics, where adding a single neutron to a magic nucleus dramatically changes its properties. In our work, we deterministically prepare generic model systems containing up to ten ultracold fermionic atoms with tunable short range interaction. In our bottom-up approach, we have started the exploration of such few-body systems with a two-particle system that can be described with an analytic theory. Adding more particles one by one we enter a regime in which an exact theoretical description of the system is exceedingly difficult, until the particle number becomes large enough such that many-body theories provide an adequate approximation.
Our vision is to use our deterministically prepared tunable few-body systems as microscopic building blocks to assemble model systems that might help to gain insight into complex many-body systems in condensed matter or even QCD.
Last updated on November 19, 2015 10:01 AM