Events

Title: The Information Age in Condensed Matter Physics

Speaker: Roger Melko, U Waterloo


Abstract: Monte Carlo simulations have been ubiquitous in efforts to simulate and characterize properties of matter and materials since the advent of computers themselves. In the last decade, condensed matter physicists have turned simulation technology to the study of a new set of phenomena, loosely termed as "emergent", with correlations not manifested in traditional correlation functions. Motivated by this, a new set of tools was recently developed that allows one to probe emergent phenomena in Monte Carlo simulations through their entanglement entropy - a concept borrowed from quantum information theory. Remarkably, since certain scaling terms in the entanglement entropy are universal, this provides a powerful general method to characterize phases and phase transitions in a wide variety of physical theories. Thus, Monte Carlo simulations are beginning to play a central role for physicists who increasingly rely on information quantities to study correlations not only in condensed matter systems and quantum devices, but also in quantum fields, theories of quantum gravity, and more.

Host: David Schwab

Keywords: Physics, Astronomy, colloquium


Title: Exploring nonreciprocity and high throughput sensing with optomechanical interactions

Speaker: Gaurav Bahl, UIUC, EECS Department

Abstract:

Microscale cavities that simultaneously exhibit high-Q optical and mechanical resonances are often employed for studying the coupling between light and vibration. The unique physics of these opto-mechanical systems enables many fundamental experiments in nonlinear optics, with analogies to condensed matter phenomena including cooling and induced transparency, and also for extreme-resolution sensing applications.However, all these systems are generally averse to fluids due to perturbation of refractive indices, scattering, absorption, and mechanical damping. Optomechanical systems have thus remained entirely solid-state till recently.

Our work has focused on two unique areas within optomechanics – (1) using Brillouin scattering for coupling optical fields to traveling acoustic waves in ultra-high-Q resonators [1]; and (2) on developing the first microfluidic optomechanical device [2] capable of high-throughput physical measurements on arbitrary flowing analytes.

In my talk I will discuss the underlying mechanisms of Brillouin Optomechanics and the applications that we have explored in parametric excitation and cooling of acoustic modes, and on induced transparency phenomena that enable nonreciprocal optical transmission[3]. Tangentially, we have also recently been exploring the physics of opto-mechano-fluidic interactions that enable extremely high-speed measurement of the mechanical properties of fluids and nanoparticles[4], only by using light. The new informational degrees-of-freedom provided by such opto-acoustic measurements can lead to surprising new sensor applications in the near future.

 

Refs.

[1] Bahl et al, Nat. Phys. vol.8(3), p.203, 2012

[2] Bahl et al, Nat. Comms. 4:1994, 2013

[3] Kim et al, Nat. Phys. vol.11, p.275, 2015

[4] Han et al, Optica, (in print) vol.3(6), 2016.

 

Bio

Dr. Gaurav Bahl is an Assistant Professor of Mechanical Science and Engineering at the University of Illinois at Urbana-Champaign (UIUC), and an Affiliate Faculty in the Department of Electrical and Computer Engineering. Dr. Bahl received his PhD and MS degrees in EE from Stanford University in 2010 and 2008, and BEng degree in ECE from McMaster University in 2005. He has authored the first experimental papers on parametric excitation and optical cooling through Brillouin Optomechanics, and on Opto-Mechano-Fluidic oscillators. His work on Brillouin systems (cooling and microfluidics) has been featured as a “(top-30) significant development in optics” for two years in a row in the Optics in 2012 and Optics in 2013 special issues of the OSAs monthly Optics & Photonics News magazine. Additional commentary by editors and prominent researchers on the significance of his Brillouin optomechanics work has appeared in Nature Physics, Nature Photonics, and many technical news outlets. Dr. Bahl is also a recipient of the US Air Force Young Investigator Award in 2015.

 

Host: Selim M Shahriar, Brian Odom

Keywords: Physics, Astronomy, AMO


Title: The Birth and Growth of Supermassive Black Holes: Coming of Age with Space Telescope Imaging Spectrograph Surveys


Speaker: Jonathan Trump, Pennsylvania State University


Host: Daniel Angles-Alcazar

Abstract: The past 20 years have revealed that supermassive black holes play an essential role in the formation and growth of galaxies. Every massive galaxy hosts a supermassive black hole in its center, and the black hole's mass is tightly coupled to the mass of the galaxy. Remarkably, the black hole - galaxy connection has been "self-maintained" from the adolescent universe (z~2) to the current epoch, from Milky-Way progenitors to massive cluster galaxies, governed by coupled black hole accretion and galaxy star formation. Until recently the "chicken-or-egg" birth of galaxies and supermassive black holes has remained mysterious. I will show how imaging spectrograph surveys with the Hubble Space Telescope are revolutionizing our understanding of black hole formation, revealing a fossil record of massive black hole seeds in tiny galaxies. Similar imaging spectrographs are flagship survey instruments on the upcoming JWST, WFIRST, and Euclid space telescopes, enabling an exciting future for understanding the birth of primordial galaxies and their black hole seeds.

 

Keywords: Physics, Astronomy, Astrophysics


Title: Dynamics of Magnets: not Landau-Lifshitz vs Bloch, but Landau-Lifshitz AND Bloch


Speaker: Prof. Wayne Saslow, Texas AM University


Abstract: It is well-known that magnets have an equilibrium magnetization M, whose tipping is described by Landau and Lifshitz's 1935 dynamics. In recent years it has been realized that out-of-equilibrium magnets have a ``spin accumulation'' m whose properties have not been fully described. Using spin-dependent Fermi Liquid theory we show that m satisfies a Bloch equation including diffusion. At surfaces M satisfies boundary conditions from micromagnetics, whereas m satisfies spin flux conditions from irreversible thermodynamics. We apply these ideas to spin-pumping (of magnetization from a ferromagnet to a normal metal) and to spin transfer torque (angular momentum from a spin-polarized current in a normal metal to a ferromagnet). The largely forgotten 1979 model of Silsbee, Janossy, and Monod is thereby justified. For spin-pumping the source term is frequency-independent, whereas in the current "paradigm" theory the source term is linear in frequency.

 

Keywords: Physics, Astronomy, CMP


calendar

Yong Chen: TBA

September 13, 2016, 2:00 PM - 3:00 PM

Title: TBA

Speaker: Yong Chen

Abstract: TBA

Host: Brian Odom

Keywords: Physics, Astronomy, AMO

Department Conference Room Calendars

Tech F160    Tech F210     Dearborn 23