Department Calendar

January 2018

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"The strong CP problem and UV instantons"

"The strong CP problem and UV instantons"

Date: 
Mon, 01/22/2018 - 2:10pm
Location: 
Pupin Hall Theory Center, 8th Floor

Prateek Agrawal

Harvard Univesity

"The strong CP problem and UV instantons"

The absence of sizeable CP violation in the strong sector is a long standing puzzle. A class of solutions to this problem rely on a global U(1) symmetry that is anomalous with QCD. These solutions lead to robust low-energy predictions, for example a massless up quark or a light axion. I will present simple extensions to such solutions which can dramatically change these low-energy predictions. In our models, contributions from small instantons play a significant role in affecting the low-energy physics while preserving the solution to the strong CP problem.

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01/22/2018 - 2:10pm
 
"Unlocking the secrets of the fastest fluid in nature"

"Unlocking the secrets of the fastest fluid in nature"

Date: 
Mon, 01/22/2018 - 4:15pm
Location: 
428 Pupin Hall

Jorge Noronha

University of São Paulo

"Unlocking the secrets of the fastest fluid in nature"

Fluid dynamic behavior is observed in radically different systems, ranging from ordinary fluids (such as water) to their exotic counterparts formed in ultra-relativistic particle collisions and the strongly interacting matter formed in neutron star mergers. Yet, their description defies physicists and mathematicians, especially when the flow velocities involved are near the speed of light. 

This talk will present an introduction to the modern applications of fluid dynamics, focusing on the Quark-Gluon Plasma, the primordial liquid that existed microseconds after the Big Bang. First principles calculations that have challenged the very foundations of fluid dynamics, pushing it towards the far-from-equilibrium regime, will be discussed. A new type of universality is shown to emerge in systems far from equilibrium via non-equilibrium attractor solutions, first found in relativistic liquids. 

About the speaker

Jorge Noronha received his PhD in theoretical physics from Goethe University Frankfurt, Germany, in 2007.  Following his PhD, Jorge worked as a postdoctoral scientist at Columbia University from 2008-2011 before joining the faculty at the University of Sao Paulo, Brazil, where he is currently an Assistant Professor.  
 
Jorge research interests' include, Quantum chromodynamics, String theory and the holographic duality, Quark-gluon plasma, and Fluid dynamics and kinetic theory in curved spacetimes.  
 
 
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01/22/2018 - 4:15pm
 
"Probing spinon nodal structures in Kitaev spin liquids"

"Probing spinon nodal structures in Kitaev spin liquids"

Date: 
Tue, 01/23/2018 - 2:30pm
Location: 
705 Pupin Hall

Natalia Perkins

University of Minnesota

"Probing spinon nodal structures in Kitaev spin liquids"

The quantum spin liquid (QSL) state of matter is very difficult to detect experimentally because it lacks a local order parameter to which common probes couple directly.  The three defining characteristics of a  QSL are  a topological ground-state degeneracy, long-range entanglement, and a fractionalization of the fundamental spin degrees of freedom. While the first two are not easily accessible by experiment, fractionalized excitations can be detected by means of thermodynamic and dynamical scattering measurements. Here we propose that resonant inelastic X-ray scattering (RIXS) is an effective probe of the fractionalized excitations in  2D and 3D Kitaev spin liquids, which are quintessential examples of the QSL state [1,2]. We find that  RIXS channels, the spin-conserving  and the non-spin-conserving  RIXS channels do not interfere and give completely different responses.  The spin-conserving channel picks up exclusively the Majorana sector with a pronounced momentum dispersion.  In all Kitaev spin liquids, as a signature of symmetry fractionalization, the spin-conserving response is strongly  suppressed around the center of the  Brillouin zone. The non-spin-conserving  RIXS channels  additionally  create immobile fluxes, and the  response becomes only weakly momentum dependent.
 
[1] G. Halasz, N.B. Perkins, J. van den Brink, PRL 117, 127203 (2016)
[2] G. Halasz, B. Perreault, N.B. Perkins, PRL 119, 097202 (2017)
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01/23/2018 - 2:30pm
 
 
 
 
 
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Theory seminar: Walter Goldberger, Yale
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01/29/2018 - 2:10pm
 
"Schrödinger Cats, Maxwell’s Demon and Quantum Error Correction (That Works)"

"Schrödinger Cats, Maxwell’s Demon and Quantum Error Correction (That Works)"

Date: 
Mon, 01/29/2018 - 4:15pm
Location: 
428 Pupin Hall

Steven Girvin

Yale University

"Schrödinger Cats, Maxwell’s Demon and Quantum Error Correction (That Works)"

A ‘second quantum revolution’ is underway based on our new understanding of how information can be stored and manipulated using quantum hardware.  Even more remarkable than the concept of quantum computation is the concept of quantum error correction.   We know that measurement disturbs a quantum state.  Nevertheless, it is possible to store an unknown quantum state and if it develops errors due to imperfect hardware, we can measure and correct such errors to recover the original unknown state (without ever knowing what the state is).

A recent experiment at Yale storing quantum information in Schrödinger cat states of microwave photons has successfully demonstrated quantum error correction that for the first time enhances the lifetime of the information. This talk will present an elementary introduction to the field as well as an overview of recent experimental progress.

 

About the speaker

Steven Girvin is a theoretical physicist who studies the quantum mechanics of large collections of atoms, molecules and electrons such as are found in superconductors, magnets and transistors. Of particular current interest to him is the engineering question of whether it is possible to build a quantum computer. He is collaborating with experimentalists Rob Schoelkopf and Michel Devoret in Applied Physics who are constructing superconducting circuit elements which might someday form the basis for a quantum computer. Such a computer could in principle solve problems which are impossible on ordinary computers. However in order to build a quantum computer it is necessary to create circuit devices which behave quantum mechanically (like individual atoms) despite the fact that they are macroscopic and consist of a very large number of atoms. In addition to potential practical applications, this difficult challenge will help us better understand the connections between the microscopic quantum world and the macroscopic classical world of everyday experience.
 
Professor Girvin is interested in quantum many-body physics, and quantum and classical phase transitions, particularly in disordered systems. A quantum phase transition is one which occurs at zero temperature as some parameter in the Hamiltonian is varied. Using path integral techniques, one can often show that a quantum critical point in a d-dimensional system is in the same universality class as some other classical system in (d+1)-dimensions. He is interested in finding quantities that are universal properties of the system near the critical point and are independent of all microscopic details. For example, the electrical conductivity of some two-dimensional conductors at critical points is a universal dimensionless number of order unity times the quantum of conductance, e2/h.
 
Much of his work has been on the quantum Hall effect, but he has also worked on the superconductor-insulator transition, the vortex glass transition in high Tc superconductors, superfluid helium in fractal aerogel, the Anderson localization problem, the Coulomb blockade problem in mesoscopic device physics, and on quantum spin chains.
 
His work is approximately evenly divided between analytical theories and numerical simulations.
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01/29/2018 - 4:15pm
 
 
 
 
 
 
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