



October 15, 2015
MIT Physics Colloquium
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 physicsand, increasingly, technologyin
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 fluctuationinduced interactionsCasimir
forces and London dispersion forcesdate 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 methodsboth analytical and
numericalthat have transformed the science of predicting
Casimir forces on complexshaped 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 nonequilibrium fluctuations, with applications
including nearfield radiative heat transfer and thermal
selfpropulsion of nanoscale bodies. I will discuss stateoftheart
computational approaches for tackling these formidable problems,
then present new predictions for spontaneous selfpropulsion and
selfrotation of warm asymmetric bodiesphoton torpedoes
and QED pinwheelsin 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.
Content 
File 
Talk Slides, 10/15/2015

PDF

Audio recording, 10/15/2015

MP3



January 23, 2013
Determinants that Count
The Kastelyn method for counting dimer configurations
and graph matchings and the GesselViennot
method for counting vertexdisjoint path systems

How many ways can you cover a chessboard with dominoes? How many ways can
4 salesmen visit 17 cities without overlapping? How many ways can a grid
of microscopic magnets align or misalign with each other? Astonishingly,
all of these questions can be answered by writing down a simple matrix
of integers and computing its determinant. This talk, prepared for
the undergraduate math lecture series during MIT's Independent
Activities Period, introduces you to these powerful methods of
counting, explains what they have to do with the physics of
ferromagnetics and diatomic molecules, and shows you some elegant
tricks for computing certain large determinants analytically
to yield compact closedform expressions.
Content 
PDF 
Talk Slides, 1/23/2013

PDF



December 9, 2010
PhD Thesis Defense
Fluctuating Surface Currents:
A New Algorithm for Efficient Prediction of
Casimir Interactions among Arbitrary Materials in
Arbitrary Geometries

They said the day would never come. (They were almost right.)
But I finally defended my
PhD thesis
and lived to tell the tale.
Content 
PDF 
Thesis Defense Slides, 12/09/2010

PDF



January 17, 2008
On The Number Of Primes Below A Given Magnitude:
The Riemann Zeta Function and How To Use It

Here's an informal talk I put together for our studentled group talk
series on various topics of interest in the ``higher mathematics.''
Riemann discovered in 1867 how to use complex analysis to solve an
ageold problem in number theory, namely, how to write down an analytical
formula for the number of primes below a given magnitude. The ideas
involved in this development are just so totally amazingly cool,
and the techniques one learns along the way of such immense
practical utility, as entirely to overwhelm whatever humiliation
we physicists and engineers might feel at putting time and effort
into what would otherwise seem a purely abstract esoteric mathematical
pursuit.
Content 
PDF 
Audio Recording 
A first definition of the Riemann Zeta function
What does Zeta(s) have to do with the primes?
A second definition of the Riemann Zeta function
The number of primes below a given magnitude

PDF

WAV



February 9, 2006
Quantum Chemistry, DFT, Quantum Transport,
and Nanoscale Device Modeling For Nonspecialists

This was a threepart series of talks in which I attempted to
explain my research to the other members of my research group.
The idea was to extract the central physical ideas of
nonrelativistic quantum mechanics, to introduce them
 with some motivating background  to an
audience of extensive mathematical maturity but no
knowledge of post1867 physics, and to present the
most uptodate mathematical formulations of the problems
as they are attacked by computational physicists today.
My assessment of the success of this program is
pessimistic. I don't think I did very well by the
audience, succeeding in conveying neither a sense of
how enticingly simple these problems really are to
formulate, nor an appreciation of how profound would
be the impact on society (health care! energy sources!)
of any progress on efficient solvers. Still, for my
own selfish purposes I found it a useful exercise
to think through what are the key, irreducible,
necessary and sufficient physical ideas of quantum mechanics
without which nothing works and from which all else flows (I
claim to have reduced it all to two principles?!), and
maybe other physicists who need to give this kind of
talk might get some ideas, perhaps on what not
to do, from the slides.
Part 
Content 
PDF 
Audio Recording 
1 
 Invitation: Why Hydrogen Sticks Together
 Quantum Mechanics: Classical Physics Plus Two
New Ideas
 Quantum Mechanics Of Multielectron Systems
 Hartree Method

PDF


2 
 HartreeFock, Configuration Interaction, Quantum Monte Carlo
 Homogeneous Electron Gas
 Density Functional Theory
 Practical DFT Calculations

PDF


3 
 Invitation: Quantized Conductance in QPCs
 Landauer Conductance Theory
 Computing the Transmission Coefficient
 Putting It All Together: Modern Device Modeling

PDF


Let me also give shoutouts to some of the astounding
freeware tools that enable this and all other work I
ever do:
,
,
,
latexbeamer,
and
speex.
Here's the
poster version of my
memo on modeling
carbon nanotube FETS,, compiled for an IFC/MARCO
workshop in December '05.
Here are the
slides from the first talk I gave on nanoscale device modeling
to my new research group.
