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METHOD:PUBLISH
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170119T204121Z
DTSTART:20170123T180000Z
DTEND:20170123T190000Z
UID:event1700@bu.edu
URL:http://physics.bu.edu/events/show/1700
SUMMARY:Dissipation\, time asymmetry\, and flux for model biomolecular syst
ems
DESCRIPTION:Featuring Aidan Brown\, Simon Fraser University\n\nPart of the
Condensed Matter Theory Seminar Series.\n\nThermal fluctuations play a sign
ificant role in biomolecular systems\, notably by preventing them from alwa
ys proceeding in a preferred direction. With energy dissipation necessary t
o break detailed balance\, we can ask how best to dissipate energy such tha
t a system is driven in the preferred direction. First\, by considering a m
odel of microscopic energy storage\, the characteristics that allow time-re
versal symmetry to be efficiently broken at fixed energy dissipation are ex
amined. I find that an intermediate energy barrier produces unusually high
asymmetry. Second\, using a biased chemical reaction cycle\, I determine ho
w to optimize the distribution of free energy dissipation to various stages
of a cycle\, to maximize the rate of forward progress. My results show tha
t the flux-maximizing distribution of dissipation depends on the inherent t
imescales of different transition pathways\, as well as the total free ener
gy dissipation available.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170119T150137Z
DTSTART:20170123T203000Z
DTEND:20170123T213000Z
UID:event1699@bu.edu
URL:http://physics.bu.edu/events/show/1699
SUMMARY:Building materials from light: Photonic Landau levels and Rydberg-m
ediated interactions
DESCRIPTION:Featuring Ariel Sommer\, MIT\n\nPart of the Biophysics/Condense
d Matter Seminar Series.\n\nAdvances in the control of light propagation an
d photon-photon interactions have lead to a new notion of photonic material
s -- states of light that resemble material systems. I will describe our ex
perimental approach to photonic materials\, in which we use a degenerate no
n-planar optical resonator to realize a two-dimensional photon gas with an
effective magnetic field. We observe photonic Landau levels\, indicating a
strong effective magnetic field\, and a singularity of spatial curvature ar
ising from the effectively conical geometry of our photon gas. Spatial curv
ature provides a novel probe of quantum Hall states\, allowing us to make t
he first experimental measurement of the mean orbital spin\, which characte
rizes topological phases. To realize photon-photon interactions\, we demons
trate hybridization of photons in an optical resonator with atomic Rydberg
excitations. Future work will aim to realize strongly correlated photonic f
ractional quantum Hall states by combining strong effective gauge fields wi
th photon-photon interactions.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170123T145653Z
DTSTART:20170126T150000Z
DTEND:20170126T160000Z
UID:event1701@bu.edu
URL:http://physics.bu.edu/events/show/1701
SUMMARY:New quantum phases of matter in strongly correlated and spin-orbit-
coupled metals
DESCRIPTION:Featuring John Harter\, California Institute of Technology\n\nP
art of the Biophysics/Condensed Matter Seminar Series.\n\nStrong interactio
ns between electrons are known to drive metallic systems toward a variety o
f well-known symmetry-broken phases\, including superconducting\, electroni
c liquid crystalline\, and charge- and spin-density wave ordered states. In
contrast\, the electronic instabilities of correlated metals with strong s
pin-orbit coupling have only recently begun to be explored. In this talk\,
I will discuss a new class of parity-breaking Fermi liquid instabilities en
abled by spin-orbit coupling. These instabilities are distinguished by the
spontaneous development of a lattice-locked spin texture on the Fermi surfa
ce\, generalizing the notion of itinerant ferromagnetism. I will argue that
nonlinear optical spectroscopy is an ideal experimental tool to search for
these phases in quantum materials\, and I will discuss our recent experime
ntal discovery of one such phase--multipolar electronic nematic order--in a
strongly spin-orbit-coupled metallic pyrochlore.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170123T145927Z
DTSTART:20170130T203000Z
DTEND:20170130T213000Z
UID:event1702@bu.edu
URL:http://physics.bu.edu/events/show/1702
SUMMARY:Grooming Schrodinger's Cat: Improving Superconducting Quantum Elect
ronics
DESCRIPTION:Featuring Eli Levenson-Falk\, Stanford\n\nPart of the Biophysic
s/Condensed Matter Seminar Series.\n\nSuperconducting materials enable the
creation of novel electronics with fundamentally non-classical behavior. T
hese quantum circuits can be used as detectors\, magnetic field sensors\, a
rtificial atoms\, and quantum bits\, with applications ranging from chemist
ry to cryptography to studies of basic quantum mechanics. Fully realizing
this potential requires us to cleverly design our circuits and experiments\
, to improve the performance of basic circuit elements\, and to engineer sc
ale-able systems. This work goes hand-in-hand with fundamental physics res
earch\, as each incremental improvement in performance opens up new experim
ental avenues. In this talk I will present some results from my own work t
ackling these practical challenges for applied and basic research\, includi
ng studies of quasiparticle behavior in superconducting resonators and impr
ovements of quantum-limited parametric amplifiers.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170127T153132Z
DTSTART:20170202T203000Z
DTEND:20170202T213000Z
UID:event1717@bu.edu
URL:http://physics.bu.edu/events/show/1717
SUMMARY:Synthesizing\, controlling\, and probing quantum states through mic
roscopy
DESCRIPTION:Featuring Adam Kaufman\, Harvard University\n\nPart of the Biop
hysics/Condensed Matter Seminar Series.\n\nI will describe two experimental
platforms --- optical tweezer trapping\nof single atoms and quantum gas mi
croscopy --- and how we have used them\nto realize experiments with low-ent
ropy systems of neutral atoms. While\nthese platforms share a common goal
of creating and microscopically\nmanipulating quantum states of neutral ato
ms\, they employ opposite\nstrategies. The optical tweezer approach aims to
assemble quantum\nsystems from single atoms in a bottom-up fashion; quantu
m gas\nmicroscopes employ a top-down strategy\, where smaller many-body sys
tems\nare distilled from larger samples. In describing these ideas\, I will
\nfocus on two experiments we performed that utilize the capabilities of\nt
hese platforms. In one experiment with optical tweezers\, we realized\natom
ic Hong-Ou-Mandel interference with independently prepared atoms. In\na sec
ond experiment with a quantum gas microscope\, we performed studies\nof qua
ntum thermalization\, which leverage this atomic Hong-Ou-Mandel\ninterferen
ce to probe the role of entanglement in thermalization of\nclosed systems.
Lastly\, I will discuss future avenues that draw on the\ncapabilities of th
ese platforms and build on these experimental studies.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170201T162009Z
DTSTART:20170206T193000Z
DTEND:20170206T203000Z
UID:event1718@bu.edu
URL:http://physics.bu.edu/events/show/1718
SUMMARY:Real-space imaging of a nematic quantum liquid
DESCRIPTION:Featuring Ben Feldman\, Princeton University\n\nPart of the Bio
physics/Condensed Matter Seminar Series.\n\nThe wave functions of electroni
c states in solids typically respect the symmetries of the host material. H
owever\, interactions among electrons can give rise to a variety of exotic
correlated phases characterized by broken symmetry. An intriguing example i
s the formation of electron fluids with wave functions that spontaneously b
reak the symmetry of the underlying crystal lattice. These phases are quant
um analogues of classical liquid crystals and have been studied in recent y
ears across disparate platforms ranging from high-temperature superconducto
rs to two-dimensional electron systems. In this talk\, I will describe scan
ning tunneling microscope measurements that allow us to visualize such a qu
antum liquid in real space. We examine the quantum Hall states that arise a
t high magnetic field from anisotropic Fermi pockets on the surface of bism
uth. Our measurements reveal that a combination of strain and exchange inte
ractions lift the Landau level degeneracy and produce valley-polarized stat
es. We image the resulting anisotropic wave functions and find that they ha
ve a different orientation for each broken-symmetry state\, providing a dir
ect spatial signature of a nematic electronic phase.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170203T145412Z
DTSTART:20170209T203000Z
DTEND:20170209T213000Z
UID:event1720@bu.edu
URL:http://physics.bu.edu/events/show/1720
SUMMARY:Shining light on topological insulators and Weyl semimetals
DESCRIPTION:Featuring Liang Wu\, University of California\, Berkeley\n\nPar
t of the Biophysics/Condensed Matter Seminar Series.\n\nThe last decade has
witnessed an explosion of research investigating the role of topology in b
and-structure\, as exemplified by the wealth of recent works on topological
insulators (TIs) and Weyl semimetals (WSMs). In this talk I hope to convin
ce you that optical probes of solids give unique insight into these topolog
ical states of matter. First\, I will discuss how we can probe the special
low-energy electrodynamics of 3D TI thin films of Bi2Se3 using time-domain
THz spectroscopy[1]. I will then discuss our work following the evolution
of the response as a function of magnetic field from a semi-classical trans
port regime [2] to a quantum regime [3]. In the later case\, although DC
transport is still semi-classical\, we find evidence for Faraday and Kerr r
otation angles quantized in units of the fine structure constant [3]. Thi
s is consistent with the long-sought "axion electrodynamics" and the topolo
gical magneto-electric effect of 3D TIs. Among other aspects this give a p
urely solid-state measure of the fine structure constant based on a topolog
ical invariant [3]. I will also discuss how optics can observe quantized Ha
ll conductance without involving the edge states [3]. Finally\, I will pres
ent our most recent discovery of the largest 2nd harmonic generation in tra
nsition monopnictide Weyl semimetals such as TaAs [4] and talk about a new
perspective of nonlinear optics in term of probing the Berry connection/cur
vature in momentum space [4]. (The focus of my talk will be on Refs. [3\, 4
].)\n\n1. Wu\, et al\, Nat. Phys. 9\, 410-414 (2013).\n2. Wu\, et al\, Phy.
Rev. Lett. 115\, 217602 (2015).\n3. Wu\, et al\, Science 354\, 1124-1127
(2016). \n4. Wu\, et al\, Nat. Phys. (2016). doi:10.1038/nphys3969
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170207T150252Z
DTSTART:20170210T171500Z
DTEND:20170210T181500Z
UID:event1719@bu.edu
URL:http://physics.bu.edu/events/show/1719
SUMMARY:Peculiar Thermodynamics of Liquid Polyamorphism
DESCRIPTION:Featuring Prof. M. A. Anisimov\, Univ. of Maryland\nHosted by:
H. Eugene Stanley\n\nPart of the Biophysics/Condensed Matter Seminar Series
.\n\n"Liquid polyamorphism" is the existence of two alternative amorphous s
tructures in a\nsingle-component liquid. Liquid polyamorphism is found or p
redicted in a broad group\nof materials\, such as triphenyl phosphite\, pho
sphorus\, sulfur\, cerium\, germanium\,\nsilicon\, silicon dioxide\, and hy
drogen\, usually at extreme conditions. In particular\, this\nphenomenon is
hypothesized in metastable\, deeply supercooled water. Structure of\nsuper
cooled water is supposed to exhibit two forms\, a low-density liquid or a h
igh-density\nliquid. The existence of these two alternative structures coul
d\, at certain conditions\, result\nin metastable liquid-liquid separation
in pure water. In this presentation a\nphenomenological approach\, based on
a "chemical reaction" between two alternative\namorphous strictures\, is f
ormulated to quantitatively describe the phenomenon of liquid\npolyamorphis
m. The first fundamental question to be addressed is the peculiar interplay
\nbetween thermodynamics and kinetics: a system with two inter-convertible
fluid structures\ncan be viewed as a single-component fluid if the time of
observation is much longer than\nthe time of conversion. In the opposite li
mit (slow conversion) the system can\nthermodynamically be treated as a two
-component fluid mixture. An equation of state\nwith a thermodynamic constr
ain imposed by "chemical- reaction" equilibrium between\ntwo inter-converti
ble fluid structures generically describes\, within the same model\, all th
e\npossible fluid phases (e.g. vapor and two liquids)\, stability limits\,
and thermodynamic\nanomalies. The results are compared with the behavior of
p o p u l a r atomistic waterlike\nmodels.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170210T162753Z
DTSTART:20170210T203000Z
DTEND:20170210T213000Z
UID:event1723@bu.edu
URL:http://physics.bu.edu/events/show/1723
SUMMARY:Coupled spin-1/2 ladders as microscopic models for non-Abelian chir
al spin liquids
DESCRIPTION:Featuring Po-Hao Huang\, Boston University\n\nPart of the Conde
nsed Matter Theory Seminar Series.\n\nTopologically ordered states of matte
r have attracted a much interest in the past decade. The search for emerge
nt point-like non-Abelian anyons in two-dimensional electronic system is on
e of the most exciting problems in condensed matter physics\, since it open
s many possibilities in quantum computing. In this talk\, I will construct
a two- dimensional lattice model that is argued to realize a chiral spin l
iquid with Ising topological order. The logic of the construction is to pr
epare an array of one-dimensional spin ladders with Ising criticality\, the
n couple them into the two-dimensional chiral spin liquid with spin-spin in
teractions that breaks time-reversal symmetry. This coupled wire construct
ion takes advantage of describing the one-dimensional spin system by confor
mal field theory. I will discuss mainly the theoretical proposal while pro
vide some numerical evidence to support it.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170210T212455Z
DTSTART:20170213T203000Z
DTEND:20170213T213000Z
UID:event1725@bu.edu
URL:http://physics.bu.edu/events/show/1725
SUMMARY:Non-equilibrium dynamics of a frustrated Mott insulator
DESCRIPTION:Featuring Zhanybek Alpichshev\, MIT\n\nPart of the Biophysics/C
ondensed Matter Seminar Series.\n\nWhat happens to electrons when both the
spin orbit coupling and inter-particle Coulomb repulsion are very strong? W
hile SOC alone can change the topology of the single particle insulating st
ate\, even short range on-site repulsion by itself can give rise to a Mott
insulator - one of the most mysterious and thought provoking phases in soli
d state physics. In this seminar I will talk about the behaviour of quasipa
rticles in a frustrated Mott insulator in the presence of strong spin-orbit
coupling. Using ultrafast optical spectroscopy to study Na2IrO3 we found t
hat the low energy properties of non-equilibrium charged quasiparticles are
almost entirely determined by their interaction with the magnetic backgrou
nd. We observe that the behaviour of photo-doped electrons and holes is dra
stically different in the magnetically ordered and disordered phases. While
in the ordered phase the spin correlations just renormalize the effective
mass of the quasiparticles\, in the latter they give rise to an effective a
ttraction between charged excitations which grows with distance causing the
m to become trapped within a bound state in a far going analogy with quark
confinement inside hadrons.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170210T211514Z
DTSTART:20170216T203000Z
DTEND:20170216T213000Z
UID:event1726@bu.edu
URL:http://physics.bu.edu/events/show/1726
SUMMARY:Building quantum materials with superconducting circuits
DESCRIPTION:Featuring Angela Kou\, Yale\n\nPart of the Biophysics/Condensed
Matter Seminar Series.\n\nSuperconducting artificial atoms are created by
connecting Josephson junctions\, which are nonlinear\, non-dissipative el
ements\, to simple electrical circuits. Individual artificial atoms can b
e coupled using this same toolbox of inductors\, capacitors\, and Josephson
junc- tions to build novel quantum materials. In this talk\, I will discus
s prospects for using the fluxonium artificial atom as a building block for
topological materials. Topological phases of matter have excitations with
exotic quantum statistics and have been proposed as a plat- form for robust
quantum computation. Building a topological material from the bottom-up\,
however\, requires individual components with degenerate ground states and
strong coupling between these components.\nI will describe two circuits bas
ed on the fluxonium artificial atom that meet these require- ments. The fir
st circuit is an artificial molecule composed of two strongly-coupled fluxo
nium artificial atoms\, which realizes a Hamiltonian with a dominant Ïƒz Ïƒ
z -type interaction between the individual atoms [1]. We find excellent agr
eement between the measured spectroscopy of the circuit and the theoretical
ly-predicted level transitions\, which highlights the suitability of superc
onducting circuits for implementing tailored quantum systems. Instead of th
e cos Ï• energy term characteristic of a Josephson junction\, the second ci
rcuit realizes an unconven- tional cos 2Ï• energy term\, which results in a
nearly-degenerate ground-excited state manifold. Taken together\, these ci
rcuits fulfill the requirements for the building blocks of topological phas
es and we can thus start to realize topological materials using superconduc
ting circuits.\n\n[1] A. Kou\, et al.\, arxiv:1610.01094 (2016).
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170215T142302Z
DTSTART:20170217T183000Z
DTEND:20170217T193000Z
UID:event1729@bu.edu
URL:http://physics.bu.edu/events/show/1729
SUMMARY:Dynamic transition and its structural correlation
DESCRIPTION:Featuring Limei Xu\, Peking University\n\nPart of the Biophysic
s/Condensed Matter Seminar Series.\n\nDynamic transition from Arrhenius to
non-Arrhenius behavior is reported in many glass-forming liquids. The mecha
nism of such phenomenon was extensively debated. Different scenarios\, such
as phase transition\, partial crystallization\, or glass transition\, were
been proposed to understand the dynamic transition. In this presentation\,
I will talk about our recent study on the dynamic crossover in models of m
olecular\, atomic and metallic systems. Our studies show that the structura
l heterogeneity is the origin of the dynamic transition. For instance\, whe
n the size of the largest cluster consisting of densely packed atoms starts
to increase sharply\, the dynamics starts to deviate from the high tempera
ture behavior\, while the largest cluster percolates the entire system and
forms stable 3-dimentional network structures\, it follows the low temperat
ure behavior. The potential energy landscape method study also confirms suc
h scenario. Our study directly link the dynamic crossover with structure in
homogeneity\, thus provide a more general picture for the dynamic transitio
ns in glass-forming liquids.\n\na short CV\n****************\nLimei Xu rece
ived her Ph.D. degree from the Department of Physics\, Boston University an
d did her postdoc in the Chemistry Department\, University of Utah. In 2008
she joined the Advanced Institute of Materials Research (WPI-AIMR) at Toho
ku University as an assistant professor. In 2011 she was selected as the Ju
nior 1000 Talents by the Recruitment Program of Global Experts of China and
took the associate professor position at Peking University in China. She w
as awarded the Distinguished Young Scholars by the National Science Foundat
ion in 2015. Her current research interests include critical and supercriti
cal phenomena in condensed matter physics\, surface science and nonequilibr
ium statistical physics.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170123T210620Z
DTSTART:20170224T203000Z
DTEND:20170224T213000Z
UID:event1703@bu.edu
URL:http://physics.bu.edu/events/show/1703
SUMMARY:Dynamical Materials Control with Light
DESCRIPTION:Featuring Wanzheng Hu\, Max Planck Institute for the Structure
and Dynamics of Matter\n\nPart of the Biophysics/Condensed Matter Seminar S
eries.\n\nUsing ultra-short laser pulses to drive quantum materials out of
equilibrium is an emergent technique for dynamical materials control. On th
e one hand\, unfolding quantum phases in time offers new perspective in und
erstanding fundamental physics. On the other hand\, selectively driving low
-energy excitations using femtosecond laser pulses can achieve novel quantu
m phases inaccessible at equilibrium.\nCombining dynamical light control wi
th ultra-broadband transient optical spectroscopy\, we are able to directly
probe the dynamics of lattice vibrations and electronic excitations over t
he whole far-infrared region\, revealing the physics behind the transient q
uantum phases. In this talk\, I will present two examples: 1) transient sup
erconductivity in multi-layer cuprate superconductors\, and 2) phonon-drive
n insulator-to-metal transition in nickelate heterostructures.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170320T130528Z
DTSTART:20170324T160000Z
DTEND:20170324T170000Z
UID:event1742@bu.edu
URL:http://physics.bu.edu/events/show/1742
SUMMARY:Quantum aging\, universal real-time crossovers\, and the non-equili
brium phase diagram of pre-thermal critical states
DESCRIPTION:Featuring Jamir Marino\, University of Cologne\n\nPart of the B
iophysics/Condensed Matter Seminar Series.\n\nInspired by the phenomenon of
aging occurring in classical statistical physics\, I will discuss the impr
int of similar real-time scaling behaviour in the dynamics of correlation a
nd response functions in a far from equilibrium O(N) interacting field theo
ry\, quenched at its dynamical critical point. Universal pre-thermal dynami
cs after such quantum quench\, first approaches an attractor analog of a fi
xed point dominated by quantum fluctuations\, reaching subsequently a more
stable fixed point with classical thermal-like features due to the energy i
njected by the quench. Solving the RG crossover from quantum to classical f
ixed points and employing the exactly solvable large N limit\, I will show
how static and dynamical critical exponents cross over among the two fixed
points and affect observables of physical interest. Time permitting\, I wil
l briefly discuss the expected phase diagram for this novel type of non-equ
ilibrium criticality occurring during pre-thermalization.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170320T165034Z
DTSTART:20170327T190000Z
DTEND:20170327T200000Z
UID:event1750@bu.edu
URL:http://physics.bu.edu/events/show/1750
SUMMARY:Intermittent Many-Body Dynamics at Equilibrium
DESCRIPTION:Featuring Sergej Flach\, Institute for Basic Science\, Daejeon\
, South Korea\n\nPart of the Condensed Matter Theory Seminar Series.\n\nThe
equilibrium value of an observable defines a manifold in the phase space o
f an ergodic\nand equipartitioned many-body system. A typical trajectory pi
erces that manifold infinitely\noften as time goes to infinity. We use thes
e piercings to measure both the relaxation time of\nthe lowest frequency ei
genmode of the Fermi-Pasta-Ulam chain\, as well as the fluctuations of the
subsequent dynamics in equilibrium. We show that previously obtained scalin
g laws for\nequipartition times are modified at low energy density due to a
n unexpected slowing down of\nthe relaxation. The dynamics in equilibrium i
s characterized by a power-law distribution of\nexcursion times far off equ
ilibrium\, with diverging variance. The long excursions arise from\nsticky
dynamics close to regular orbits in the phase space. Our method is generali
zable to\nlarge classes of many-body systems.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170321T142957Z
DTSTART:20170329T180000Z
DTEND:20170329T190000Z
UID:event1751@bu.edu
URL:http://physics.bu.edu/events/show/1751
SUMMARY:Higher Rank Quantum Spin Liquids: From Fractons to Emergent Gravity
DESCRIPTION:Featuring Michael Pretko\, MIT\n\nPart of the Condensed Matter
Theory Seminar Series.\n\nQuantum spin liquids are well described in the la
nguage of gauge theory. To date\, most theoretical effort has focused on t
he study of models with a familiar vector gauge field. However\, there exi
st stable spin liquids with more complicated gauge structure. In this talk
\, I will focus on three-dimensional spin liquid phases described by symmet
ric tensor ("higher spin") gauge fields. I will show that these models pos
sess exotic conservation laws which restrict the gauge charges to exist in
lower-dimensional subspaces\, as opposed to propagating in three-dimensiona
l space. Some charges are even restricted to a zero-dimensional subspace a
nd are totally immobile\, in a manifestation of the fracton phenomenon. As
a special case\, I will discuss rank 2 symmetric tensor spin liquids\, whi
ch provide us with toy models for emergent gravity.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170403T205802Z
DTSTART:20170404T150000Z
DTEND:20170404T160000Z
UID:event1756@bu.edu
URL:http://physics.bu.edu/events/show/1756
SUMMARY:Training and generalization dynamics in deep linear neural networks
DESCRIPTION:Featuring Andrew Saxe \, Harvard\n\nPart of the Biophysics Semi
nars.\n\nAnatomically\, the brain is deep; and computationally\, deep learn
ing is known to be hard. How might depth impact learning in the brain? To u
nderstand the specific ramifications of depth\, I develop the theory of lea
rning in deep linear neural networks. I will describe exact solutions to th
e dynamics of learning which specify how every weight in the network evolve
s over the course of training. The theory answers fundamental questions suc
h as how learning speed scales with depth\, how structured data sets are em
bedded into hidden neural representations\, and why unsupervised pretrainin
g accelerates learning. Turning to generalization error\, we use random mat
rix theory to analyze the cognitively-relevant "high-dimensional" regime\,
where the number of training examples is on the order of or even less than
the number of adjustable synapses. We find that generalization error can di
verge in certain instances if training is run forever\, but that implicit r
egularization in the form of early stopping and small initial weights subst
antially improves performance. Next\, we turn to the question of how comple
x a model should be for optimal generalization. We describe a counter-intui
tive regime where increasing the complexity of a model can lower both the a
pproximation error and the estimation error of the system\, resulting in su
bstantial generalization benefits. This result may help explain the strikin
g performance of even very large deep network models in practice\, which of
ten have more parameters than training samples. Finally\, if time permits\,
I will describe an example of how these results may begin to inform the dy
namics of nonlinear networks. In particular\, I will describe a setting in
which a nonlinear network can be understood as a collection of linear netwo
rks that learn in parallel\, yielding learning dynamics which are dominated
by the fastest linear network in the collection.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170330T180716Z
DTSTART:20170405T183000Z
DTEND:20170405T193000Z
UID:event1746@bu.edu
URL:http://physics.bu.edu/events/show/1746
SUMMARY:Time-reversal and reflection symmetry in (2+1)-dimensional topologi
cal phases
DESCRIPTION:Featuring Meng Cheng\, Yale University\n\nPart of the Condensed
Matter Theory Seminar Series.\n\nAbstract: There has been immense progress
recently in the understanding of interacting topological phases of matter
in the presence of symmetry. I will discuss recent developments for the cas
e of time-reversal / reflection symmetry-enriched topological (SET) phases.
I will derive a simple formula for the ground state degeneracy of such SET
s on non-orientable manifold. I then use these results to develop an unders
tanding of anomalies associated with time-reversal / reflection SETs. If ti
me permits\, I will discuss explicit constructions of time-reversal/reflect
ion SETs\, including anomalous ones.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:TENTATIVE
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170328T144343Z
DTSTART:20170407T160000Z
DTEND:20170407T170000Z
UID:event1743@bu.edu
URL:http://physics.bu.edu/events/show/1743
SUMMARY:Interacting lattice systems with a model of quantum dissipation fro
m a thermodynamic perspective
DESCRIPTION:Featuring Lode Pollet\n\nPart of the Biophysics/Condensed Matte
r Seminar Series.\n\nQuantum dissipation arises when a large system can be
split in a quantum system and an environment where the energy of the former
flows to. We propose a conceptually simple approach to introduce the dissi
pation into interacting quantum systems (the XXZ model) in a thermodynamica
l context\, in which every site of the 1d lattice is coupled to its own bat
h. In case of Ohmic diagonal coupling\, a bath-induced Bose liquid phase ca
n occur in the ground state phase diagram away from half filling. This phas
e is compressible\, gapless\, and conducting but not superfluid. At haf-fil
ling\, only a Luttinger liquid and a density wave ordered phase are found.
The phase transition between them is of Kosterlitz-Thouless type where the
Luttinger parameter takes a non-universal value. In case of off-diagonal co
upling\, we find a compressible zero-temperature state with spontaneous dis
crete symmetry breaking and a thermal phase transition for a one-dimensiona
l system. Our results are supported by Quantum Monte Carlo path integral s
imulations.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170320T133010Z
DTSTART:20170410T180000Z
DTEND:20170410T190000Z
UID:event1747@bu.edu
URL:http://physics.bu.edu/events/show/1747
SUMMARY:TBD
DESCRIPTION:Featuring Sayan Choudhury\n\nPart of the Condensed Matter Theor
y Seminar Series.\n\n
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170411T130625Z
DTSTART:20170414T150000Z
DTEND:20170414T160000Z
UID:event1758@bu.edu
URL:http://physics.bu.edu/events/show/1758
SUMMARY:Shortcuts to adiabaticity using flow-fields
DESCRIPTION:Featuring Ayoti Patra\, Maryland\n\nPart of the Condensed Matte
r Theory Seminar Series.\n\nAdiabatic invariants â€“ quantities that are pr
eserved under the slow driving of a systemâ€™s external parameters â€“ are
important in classical mechanics\, quantum mechanics and thermodynamics. Sh
ortcuts to adiabaticity are strategies for preserving adiabatic invariants
even under rapid driving. One such strategy utilizes an auxiliary counterdi
abatic term to suppress the non-adiabatic excitations arising due to rapid
driving. I will describe a unified framework for obtaining counterdiabatic
terms using flow-fields. In the flow-fields approach\, an appropriate inte
grated function (IF) is first defined. The flow-field parameters namely the
velocity and acceleration are derived from the IF. Counterdiabatic terms c
an then be constructed using simple equations involving the flow-field para
meters. I will illustrate that the flow-fields framework provides 'shortcut
s' for quantum\, classical as well as stochastic systems.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170411T141554Z
DTSTART:20170419T183000Z
DTEND:20170419T193000Z
UID:event1748@bu.edu
URL:http://physics.bu.edu/events/show/1748
SUMMARY:Chiral Floquet Phases
DESCRIPTION:Featuring Adrian Po\, Harvard University\n\nPart of the Condens
ed Matter Theory Seminar Series.\n\nPeriodically driven quantum systems\, a
ka Floquet problems\, have been recently identified as a prime platform for
the study of topologically nontrivial quantum dynamics. Absent the notion
of ground state(s)\, many-body localization plays a crucial role in the def
inition of such Floquet phases. Strikingly\, some of the discovered phases
are intrinsically dynamical\, in the sense that they do not admit static co
unterparts. In this talk\, I will describe our results on the study of chir
al phases in this context. First\, I will discuss an analog of the integer
quantum Hall phases\, where instead of charge or heat\, quantum information
is pumped along the edge in a unidirectional manner. Next\, I will present
an extension of this phase into one featuring intrinsic topological order\
, where the pumping of emergent Majorana fermions along the edge is\, surpr
isingly\, accompanied by a necessary dynamical anyon transmutation in the b
ulk
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170419T144102Z
DTSTART:20170421T160000Z
DTEND:20170421T170000Z
UID:event1762@bu.edu
URL:http://physics.bu.edu/events/show/1762
SUMMARY:The phase diagram of quantum state preparation : limitations and co
mplexity
DESCRIPTION:Featuring Alexandre Day\, Boston University\n\nPart of the Biop
hysics/Condensed Matter Seminar Series.\n\nPreparing quantum states efficie
ntly and with high fidelity is a key stepping stone towards building a reli
able and scalable quantum computer.\nIn this talk I will present some of th
e fundamental limitations of quantum state preparation. In particular I wil
l discuss how having finite preparation time leads to different phases in t
erms of the difficulty of obtaining optimal fidelity. We find strong eviden
ce for the existence of a generic NP-hard phase analogous to a spin glass\,
where finding the optimal preparation protocol is exponentially hard. We s
upport these findings using different machine learning approaches such as r
einforcement learning and simulated annealing.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170418T131720Z
DTSTART:20170426T150000Z
DTEND:20170426T160000Z
UID:event1745@bu.edu
URL:http://physics.bu.edu/events/show/1745
SUMMARY:Competition between Bose glass and superfluid phases in quantum ant
iferromagnets
DESCRIPTION:Featuring Sylvain Capponi\, Toulouse university & BU\nHosted by
: Anders Sandvik\n\nPart of the Condensed Matter Theory Seminar Series.\n\n
Building on recent NMR experiments [1]\, we theoretically investigate the h
igh magnetic field regime of the disordered quasi-one-dimensional S=1 antif
erromagnetic material DTNX. The interplay between disorder\, chemically con
trolled by Br-doping\, interactions\, and the external magnetic field\, lea
ds to a very rich phase diagram. Beyond the well-known antiferromagneticall
y ordered regime\, analog of a Bose condensate of magnons\, we unveil a res
urgence of phase coherence at higher field\, induced by the doping [2]. Suc
h a ``mini-condensation'' contrasts with previously reported Bose-glass phy
sics in the same regime and should be accessible to future experiments.\n\n
In a second part\, I will discuss recent findings regarding the one-dimensi
onal superfluid-Bose glass transition at T=0 in S=1/2 XXZ chain [3]. As a f
unction of interaction and disorder strength\, we identify a Berezinskii-Ko
sterlitz-Thouless critical line with two different regimes. At small attrac
tion where critical disorder is weak compared to the bandwidth\, the critic
al Luttinger parameter K takes its universal Giamarchi-Schulz value 3/2. Co
nversely\, a non-universal K>3/2 emerges for stronger attraction where weak
-link physics is relevant. In this strong disorder regime\, the transition
is characterized by self-similar power-law distributed weak links with a co
ntinuously varying characteristic exponent.\n\nRefs:\n[1] A. Orlova et al.\
, Phys. Rev. Lett. 118\, 067203 (2017)\n[2] M. Dupont\, S. Capponi\, N. Laf
lorencie\, Phys. Rev. Lett. 118\, 067204 (2017)\n[3] E. Doggen\, G. LemariÃ
©\, S. Capponi\, N. Laflorencie\, arXiv:1704.02257
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170424T172529Z
DTSTART:20170428T160000Z
DTEND:20170428T170000Z
UID:event1744@bu.edu
URL:http://physics.bu.edu/events/show/1744
SUMMARY:Many body localization\, thermalization\, and the localization tran
sition: insights from the entanglement spectrum
DESCRIPTION:Featuring Rahul Nandkishore\n\nPart of the Biophysics/Condensed
Matter Seminar Series.\n\nI discuss universal structure in the pattern of
entanglement of many body localized (MBL) and thermalizing phases. There is
far more universal structure than is captured by the entanglement entropy
- and some if it can be extracted from the entanglement spectrum using diag
nostics inspired by random matrix theory. Examining the thermalizing phase
through this lens\, we discover new universal structure consistent with but
going beyond that predicted by eigenstate thermalization (ETH). In the MBL
phase\, we discover universal structure in the high energy part of the ent
anglement spectrum indicative of a residual `memory of criticality\,â€™ whi
ch persists in the wave functions arbitrarily deep into the localized phase
. Armed with this insight\, we attack the many body localization transition
by working deep within the localized phase\, where finite size effects are
well under control. A consideration of appropriate diagnostics based on th
e entanglement spectrum allows us to identify the MBL-quantum critical cros
sover for the first time in exact numerics. This allows us to place an uppe
r bound on the critical disorder strength for localization\, to complement
the lower bounds that have previously been obtained.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170427T154602Z
DTSTART:20170503T150000Z
DTEND:20170503T160000Z
UID:event1752@bu.edu
URL:http://physics.bu.edu/events/show/1752
SUMMARY:Glassy dynamics as a consequence of the equilibrium liquid to solid
transition
DESCRIPTION:Featuring Zohar Nussinov\, WUSTL\n\nPart of the Condensed Matte
r Theory Seminar Series.\n\nWe will review the underpinning of the micro-ca
nonical ensemble and the\nmore refined (and explicitly quantum) "Eigenstate
Thermalization\nHypothesis". We will then find and apply a simple corollar
y of these to\nanalyze the evolution of a liquid upon supercooling to form
a structural\nglass. Simple\ntheoretical considerations lead to a predictio
ns for general properties of\nsupercooled liquids. Amongst other things\, a
collapse of the viscosity of\nglass formers is predicted from this theory.
This collapse indeed occurs\nover 16 decades of relaxation times for all k
nown types of glass formers.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170502T152157Z
DTSTART:20170508T180000Z
DTEND:20170508T190000Z
UID:event1763@bu.edu
URL:http://physics.bu.edu/events/show/1763
SUMMARY:Topological Phase Transitions: From Duality Web to Symmetric Mass G
eneration
DESCRIPTION:Featuring Yi-Zhuang You\, Harvard University\n\nPart of the Con
densed Matter Theory Seminar Series.\n\nTopological phases of matter is an
active research area of condensed matter physics. Among various topics\, th
e symmetry protected topological (SPT) phases\, which are generalizations o
f topological insulators\, have attracted enormous theoretical interest in
the last few year. Much progress has been made in classifying and character
izing SPT phases. Yet another interesting topic is to study the phase trans
itions between different SPT phases. In this talk\, I will present a lattic
e model for (2+1)D bosonic SPT phases\, which is free of the sign problem a
nd can be explored by quantum Monte Carlo simulations. It turns out that th
e model demonstrates a rich phase diagram with exotic topological quantum p
hase transitions. In particular\, I will focus on two of these transitions
and report our on-going progress to understand them both theoretically and
numerically.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170508T133144Z
DTSTART:20170510T190000Z
DTEND:20170510T200000Z
UID:event1767@bu.edu
URL:http://physics.bu.edu/events/show/1767
SUMMARY:Stochastic Neural Networks for Machine Learning the Many-Body Probl
em
DESCRIPTION:Featuring Roger Melko\n\nPart of the Condensed Matter Theory Se
minar Series.\n\nCondensed matter physicists have a sophisticated array of
numerical\ntechniques that they use to study classical and quantum many-bod
y models. \nIn parallel\, the machine learning community has developed a ve
ry successful\nset of algorithms with the goal of classifying\, characteriz
ing and\ninterpreting complex sets of data\, such as images and natural lan
guage\nrecordings. We briefly show that standard neural networks architectu
res for\nsupervised learning can identify phases and phase transitions in a
variety\nof condensed matter Hamiltonians\, directly from raw state config
urations\nsampled with standard Monte Carlo and treated like images. Then\
, we show\nhow we can use such Monte Carlo configurations to train a stocha
stic variant\nof a neural network\, called a Restricted Boltzmann Machine (
RBM)\, for use in\nunsupervised learning applications. We demonstrate how
RBMs\, once trained\,\ncan be sampled much like a physical Hamiltonian to p
roduce configurations\nuseful for estimating physical observables\, as well
as other applications.\nFinally\, we explore the representational power of
RBMs\, and comment on their\napplication to the simulation of quantum syst
ems.
LOCATION: \, \,
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170509T191056Z
DTSTART:20170512T160000Z
DTEND:20170512T170000Z
UID:event1768@bu.edu
URL:http://physics.bu.edu/events/show/1768
SUMMARY:NEW PHYSICS ON DILUTING WATER WITH IMPURITIES
DESCRIPTION:Featuring Prof. Francesco Mallamace\, Physics Dept\, Univ. of M
essina\nHosted by: H. Eugene Stanley\n\nPart of the Biophysics/Condensed Ma
tter Seminar Series.\n\n
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170515T161618Z
DTSTART:20170516T180000Z
DTEND:20170516T193000Z
UID:event1770@bu.edu
URL:http://physics.bu.edu/events/show/1770
SUMMARY:Qauntum chaos\, (diffusive) transport and random matrixes
DESCRIPTION:Featuring Anatoly Dymarsky\, UKY\nHosted by: Anatoli Polkovniko
v\n\nPart of the Condensed Matter Theory Seminar Series.\n\nAbstract: I wil
l discuss prospects and limitations of using random matrix models to descri
be transport in quantum chaotic systems
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170515T132109Z
DTSTART:20170518T150000Z
DTEND:20170518T160000Z
UID:event1769@bu.edu
URL:http://physics.bu.edu/events/show/1769
SUMMARY:Defect dynamics of the 2D confined active nematic liquid crystals
DESCRIPTION:Featuring Achini Opathalage\, Dogic Lab\, Brandeis University\n
\nPart of the Biophysics Seminars.\n\nBoundaries modify active matter in wa
ys that have no counterpart in equilibrium materials. Presently there is no
universal theory in active matter to account for boundaries\, making it es
sential to proceed experimentally with a well-controlled system. In this ta
lk I will talk about the role of boundary conditions on a simplified experi
mental model of biological active matter system composed of extensile filam
entous bundles of microtubules driven by clusters of kinesin motors. These
bundles form a dense quasi-2D active nematic liquid crystals when sediment
onto a surfactant-stabilized oil-water interface. When this system is furth
er confined onto different boundary conditions\, imposing total topological
charge\, unique dynamical behavior can be observed under high circular con
finement\, in the order of hundred micrometers. The experimental results il
lustrate how this system can serve as a platform for testing theoretical mo
dels of non-equilibrium statistical mechanics and potentially aid in unders
tanding self-organization processes in living biological systems.
LOCATION: \, \,
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20170625T203502Z
LAST-MODIFIED:20170601T181936Z
DTSTART:20170607T150000Z
DTEND:20170607T160000Z
UID:event1773@bu.edu
URL:http://physics.bu.edu/events/show/1773
SUMMARY:Out-of-time-order correlators in disordered quantum systems
DESCRIPTION:Featuring David J. Luitz\n\nPart of the Condensed Matter Theory
Seminar Series.\n\nOut-of-time-order correlators (OTOC) are used\nto study
the propagation of local information in isolated quantum systems.\nI will
discuss recent results using large scale exact time-evolution\nfor up to L=
31 spins 1/2 and show that for\nweakly disordered nonintegrable systems inf
ormation propagates behind\na ballistically moving front\, while the entang
lement entropy growths\nlinearly in time. For stronger disorder the motion
of the information\nfront is algebraic and sub-ballistic with a disorder st
rength\ndependent exponent which depends on the strength of the disorder\,\
nsimilarly to\nthe sublinear growth of the entanglement entropy. The\ndynam
ical exponent associated with the information front coincides\nwith the exp
onent of the growth of the entanglement entropy for both\nweak and strong d
isorder and the temporal\ndependence of the OTOC is characterized by a fast
nonexponential\ngrowth\, followed by a slow saturation after the passage o
f the\ninformation front. Finally\, I will mention the implications of this
\nbehavioral change on the growth of the entanglement entropy.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
END:VCALENDAR