The David and Edith Harris Physics Colloquium Series

FALL 2018 Schedule

Thursdays // Socials: 3:30pm in 4-349 (Pappalardo Room) // Talk: 4:00pm in 10-250 (unless otherwise noted)

OCTOBER 25, 2018
RAMESH NARAYAN
Department of Astronomy, Harvard University
Host: Deepto Chakrabarty

PAPPALARDO DISTINGUISHED LECTURE

"Observing Black Holes Up Close and Personal"

Accretion of gas on black holes powers many energetic phenomena in the universe. The accretion power generally comes out as radiation, but sometimes also as relativistic jets. The region close to the black hole, where accreting magnetized gas disappears through the horizon and where the jet originates, involves complex nonlinear physics. In the case of a few nearby supermassive black holes, thanks to the Event Horizon Telescope, this region will soon be amenable to direct observational study. Meanwhile, theoretical study of the nonlinear physics of black hole accretion has become practical with the development of numerical codes to simulate multi-dimensional radiation MHD flows in general relativistic space-times. However, poor understanding of the underlying plasma processes is a severe bottleneck and needs to be addressed before we can expect convergence between theoretical models and observations.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

NOVEMBER 1, 2018
JOCHEN MANNHART
Max Planck Institute for Solid State Research
Host: Riccardo Comin

"Loss-Free Charge Transport without Superconductivity?"

The discovery of superconductivity enabled the transport of electric charge without dissi-pation. Sustained, constructive work to develop sophisticated superconducting materials has led to enormous advances in the performance of superconductors and in raising their critical temperature. Interestingly, dissipation-free charge flow also exists in non-superconducting systems. Atoms, molecules, atomic clusters, and mesoscopic conduc-ting rings may carry such currents. Quantum-Hall systems also transport current loss-free if biased in a quantum-Hall plateau. Loss-free currents have furthermore been found to flow along the edges of topological insulators. In all systems described, dissipation-free transport is based on sustained quantum coherence and the suppression of inelastic scattering. Here, we report on our search for further possibilities to realize loss-free charge flow in non-superconducting devices or wires. We introduce quantum devices that use collapses of the wave functions and a subsequent coherent evolution of quantum states as essen-tial device elements. These devices are candidates to realize astonishing functional pro-perties, including lossless current transport in wires at high temperatures.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

NOVEMBER 8, 2018
DAVID DEMILLE
Yale University
Host: David Pritchard

"A tabletop-scale probe for TeV physics: the electric dipole moment of the electron"

Time-reversal (T) symmetry is observed to be broken in K- and B-meson systems, in a manner consistent with the Standard Model (SM) of particle physics. Violation of T-invariance also allows elementary particles such as the electron to have an electric dipole moment (EDM) along their spin axis. Although the SM prediction for the electron EDM is too small to detect, extensions to the SM with new physics at the TeV scale—or even far above it—can lead to an EDM near the experimental bound. I will describe our ACME experiment, which uses a tabletop-scale apparatus and methods of atomic/molecular/optical physics to detect the electron EDM. Our 2018 result from ACME has sensitivity an order of magnitude better than in any prior work, but the electron EDM remains consistent with zero. I will discuss the impact of this result in the wider context of the search for physics beyond the Standard Model, and prospects for future progress in the search for a nonzero EDM.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

NOVEMBER 15, 2018
NEVIN WEINBERG
MIT
Host: TBA

"When stars go nonlinear: large amplitude tides and stellar oscillations"

Tides significantly impact the structure, evolution, and fate of many types of close binary systems, including short-period exoplanets, stellar binaries, and coalescing binary neutron stars.  In many of these systems, the tide’s amplitude is so large that it cannot be treated as a small, linear perturbation to the background star.  In this talk, I will show that nonlinear effects can greatly enhance the rate of tidal dissipation and thus the rate of binary evolution.  As examples, I will describe how nonlinear tides influence the orbital decay of hot Jupiters and the gravitational-wave signal of coalescing binary neutron stars.  I will also discuss the nonlinearity of oscillation-modes in red giants, which are excited by turbulent motions within the convective envelope of the star.  The rich oscillation spectra observed by the CoRoT and Kepler space missions, and soon TESS, has yielded a wealth of information about the internal and global properties of thousands of red giants.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

NOVEMBER 29, 2018
MIKE WILLIAMS
MIT
Host: TBA

Title and Abstract - TBA

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

DECEMBER 6, 2018
WILLIAM DETMOLD
MIT
Host: TBA

Title and Abstract - TBA

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

PAST FALL 2018 COLLOQUIA

SEPTEMBER 20, 2018
TRACY SLATYER
Host: Washington Taylor

"The Dark Matter Mystery Hunt - Seeking Clues in the Sky"

The nature of dark matter remains one of the great puzzles of fundamental physics, with potential connections to a plethora of deep questions. Interactions between dark and visible matter could have reshaped the history of the cosmos, and left their signatures in light that is only now reaching our telescopes. I will discuss how my group has developed novel theoretical and analytic techniques to predict and identify such signals, with applications ranging from unveiling the nature of a mysterious gamma-ray glow in the Milky Way’s heart, to testing a vast range of possibilities for dark matter using light from the dawn of the universe.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

SEPTEMBER 27, 2018
GEORGE ZWEIG
Signition, LP and RLE@MIT
Host: Robert Jaffe

"Remembering Feynman"

A professional and personal perspective on Richard Feynman is provided based on my interactions with him from 1959 to 1981. Topics include the quantization of gravity, aces, quarks, and the road to partons.

Time: 4:00 pm
Place: Room 34-101 *NOTE ROOM CHANGE
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

OCTOBER 4, 2018
ILA FIETE
Brain and Cognitive Sciences at MIT
Host: Mehran Kardar

"Brain Dynamics and Codes for Navigation"

I will introduce key aspects of the problem of navigation and describe circuits in the brain that participate in navigational computations. These circuits contain cells with remarkable responses to spatial variables, including head-direction cells, grid cells, and place cells. I will describe dynamics in the head direction circuit across species from insects to mammals. I will do the same for mammalian grid cells, then focus on the remarkable theoretical coding properties of the non-local, periodic code of grid-cells for spatial location, a non-periodic, local quantity. Given that spatial computations unfold over time, I will review theoretical and experimental work on understanding the temporal/non-equilibrium dynamics of navigational computations. I will mention open questions throughout. Time permitting, I will end with ideas and experiments on how the grid and place cell circuits might support abstract cognitive computations besides spatial navigation.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

OCTOBER 11, 2018
WASEEM BAKR
Princeton University
Host: Martin Zwierlein

"Quantum gas microscopy of strongly interacting fermions in optical lattices"

Ultracold fermions in optical lattices provide a clean physical realization of the celebrated Fermi-Hubbard model of condensed matter, a minimal model believed to contain the essential ingredients for high-temperature superconductivity. Recent advances in the field of quantum gas microscopy have opened up the possibility to probe and manipulate Fermi-Hubbard systems at the atomic level, enabling quantitative studies at temperatures that are challenging for state-of-the-art simulations on classical computers. In this talk I will report on experiments that probe equilibrium spin and density correlations in the Hubbard model in new regimes, including a repulsive spin-imbalanced system and a doped attractive system, which are related to each other through a mathematical mapping. I will also report on experiments where we measure the transport properties of doped repulsive systems. We find that the resistivity exhibits a linear temperature dependence and shows no evidence of saturation, two characteristic signatures of a bad metal.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

OCTOBER 18, 2018
PABLO JARILLO-HERRERO
MIT
Host: Raymond Ashoori

"Magic Angle Graphene: a New Platform for Strongly Correlated Physics"

The understanding of strongly-correlated quantum matter has challenged physicists for decades. Such difficulties have stimulated new research paradigms, such as ultra-cold atom lattices for simulating quantum materials. In this talk I will present a new platform to investigate strongly correlated physics, based on graphene moiré superlattices. In particular, I will show that when two graphene sheets are twisted by an angle close to the theoretically predicted ‘magic angle’, the resulting flat band structure near the Dirac point gives rise to a strongly-correlated electronic system. These flat bands exhibit half-filling insulating phases at zero magnetic field, which we show to be a correlated insulator arising from electrons localized in the moiré superlattice. Moreover, upon doping, we find electrically tunable superconductivity in this system, with many characteristics similar to high-temperature cuprates superconductivity. These unique properties of magic-angle twisted bilayer graphene open up a new playground for exotic many-body quantum phases in a 2D platform made of pure carbon and without magnetic field. The easy accessibility of the flat bands, the electrical tunability, and the bandwidth tunability though twist angle may pave the way towards more exotic correlated systems, such as quantum spin liquids or correlated topological insulators.

Time: 4:00 pm
Place: Room 10-250
Refreshments @ 3:30 pm in 4-349 (Pappalardo Community Room)

Last updated on October 22, 2018 10:33 AM