Applied Physics / Physics Colloquium

The 2018 Robert Hofstadter Memorial Lecture: The Dawn of Gravitational-Wave Astrophysics

Topic: 
The Dawn of Gravitational-Wave Astrophysics
Abstract / Description: 

In the past two years the gravitational-wave detections enabled by the LIGO detectors have launched a new field in observational astronomy allowing us to study compact object mergers involving pairs of black holes and neutron stars. I will discuss what current results reveal about compact object astrophysics, from binary black hole formation to short gamma-ray bursts and nuclear matter physics. I will also highlight what we can expect in the near future as detectors' sensitivity improves and multi-messenger astronomy further advances.

Date and Time: 
Tuesday, April 3, 2018 - 4:30pm
Venue: 
Hewlett 201

The 2018 Robert Hofstadter Memorial Lecture: Cosmic Collisions Reveal Einstein's Gravitational-Wave Universe

Topic: 
Cosmic Collisions Reveal Einstein's Gravitational-Wave Universe
Abstract / Description: 

For the first time, scientists have observed ripples in the fabric of spacetime called gravitational waves, arriving at the earth from a cataclysmic event in the distant universe. This confirms a major prediction of Albert Einstein's 1915 general theory of relativity and opens an unprecedented new window onto the cosmos. Gravitational waves carry unique information about their dramatic origins and about the nature of gravity that cannot otherwise be obtained. Detected gravitational waves were produced during the final fraction of a second of the mergers of two black holes but also during the last hundred seconds of the collision of two neutron stars. The latter is the first ever cosmic event to be observed both in gravitational waves and in electromagnetic waves, shedding light on several long-standing puzzles, like the production of gold in nature and the physics origins of brief gamma-ray flashes. I will review the beginnings of this exciting field of cosmic exploration and the unprecedented technology and engineering that made it possible.

Date and Time: 
Monday, April 2, 2018 - 7:30pm
Venue: 
Hewlett 200

Applied Physics/Physics Colloquium: Topological Quantum Chemistry

Topic: 
Topological Quantum Chemistry
Abstract / Description: 

The past decade has seen tremendous success in predicting and experimentally discovering distinct classes of topological insulators (TIs) and semimetals. We review the field and we propose an electronic band theory that highlights the link between topology and local chemical bonding, and combines this with the conventional band theory of electrons. Topological Quantum Chemistry is a description of the universal global properties of all possible band structures and materials, comprised of a graph theoretical description of momentum space and a dual group theoretical description in real space. We classify the possible band structures for all 230 crystal symmetry groups that arise from local atomic orbitals, and show which are topologically nontrivial. We show how our topological band theory sheds new light on known TIs, and demonstrate the power of our method to predict a plethora of new TIs.

Date and Time: 
Tuesday, February 27, 2018 - 4:15pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: Magic Angle Graphene: A New Platform for Strongly Correlated Physics

Topic: 
Magic Angle Graphene: A New Platform for Strongly Correlated Physics
Abstract / Description: 

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 Mott-like insulator arising from electrons localized in the moiré superlattice. 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. I will end my talk with an unconventional experimental surprise.

Date and Time: 
Tuesday, February 13, 2018 - 4:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: Sloppy models, Differential geometry, and How Science Works

Topic: 
Sloppy models, Differential geometry, and How Science Works
Abstract / Description: 

Models of systems biology, climate change, ecosystems, and macroeconomics have parameters that are hard or impossible to measure directly. If we fit these unknown parameters, fiddling with them until they agree with past experiments, how much can we trust their predictions? We have found that predictions can be made despite huge uncertainties in the parameters – many parameter combinations are mostly unimportant to the collective behavior. We will use ideas and methods from differential geometry to explain what sloppiness is and why it happens so often. We show that physics theories are also sloppy – that sloppiness may be the underlying reason why the world is comprehensible.

Date and Time: 
Tuesday, February 20, 2018 - 4:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: Extrasolar Planets

Topic: 
Extrasolar Planets
Abstract / Description: 

Over the past two decades, thousands of planets have been discovered orbiting nearby stars, and our perspective on the universe has changed. We now know planets are not rare. We also know planets are diverse - with our biased measurements, a vast range of planetary types and system architectures have been discovered, from systems containing hot Jupiter-like planets orbiting incredibly close to their star, to densely-packed systems of "super-Earth" planets in dynamically complex configurations. Most known systems are radically different than our own; to what extent this is a measurement bias remains unclear, and the question of the frequency of habitable planets is not yet settled. I will review key discoveries over the past decade, by both the Kepler mission and ground-based facilities, and provide perspective on the uncertainties. I will also focus on results from the Gemini Planet Imager, which has produced high-SNR images and spectra of giant planets orbiting far (10-100 AU) from young (10-300 million year) stars. Finally, I will review prospects from the near future (the James Webb Space Telescope) to potential Earth-characterizing missions.

Date and Time: 
Tuesday, February 6, 2018 - 4:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: Searches for new Physics with Nuclear Spin Precession

Topic: 
Searches for new Physics with Nuclear Spin Precession
Abstract / Description: 

Prof. Mike Romalis of Princeton University will give the Applied Physics/Physics colloquium on Jan. 23, 2018, entitled "Searches for new Physics with Nuclear Spin Precession."

Date and Time: 
Tuesday, January 23, 2018 - 4:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: Symmetries of Time

Topic: 
Symmetries of Time
Abstract / Description: 

Time is a basic element in our models of the physical world, as is symmetry. Several issues at the frontiers of modern physics concern the interplay of those concepts. Elaborating on this theme, I will survey the current state of axions and time crystals, including very recent work.

Date and Time: 
Tuesday, January 16, 2018 - 4:30pm
Venue: 
Hewlett 201

Applied Physics/Physics Colloquium: Quantum vs. Classical optimization: A Status Update on the Arms Race

Topic: 
Quantum vs. Classical optimization: A Status Update on the Arms Race
Abstract / Description: 

Can quantum computers meet the tantalizing promise of solving complex calculations - such as optimization problems or database queries - faster than classical computers based on transistor technologies? Although IBM recently opened up their five-qubit programmable quantum computer to the public to tinker with, the holy grail of a useful large-scale programmable universal quantum computer is decades away. While working mid-scale programmable special-purpose quantum optimization machines exist, a conclusive detection of quantum speedup remains controversial despite recent promising results. In this talk, a head-to-head comparison between quantum and classical optimization approaches is given. Current quantum annealing technologies must outperform classical devices to claim the crown in the race for quantum speedup.

Date and Time: 
Tuesday, January 9, 2018 - 4:15pm
Venue: 
Hewlett 201

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