BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//RLASKEY//CALENDEROUS//EN
CALSCALE:GREGORIAN
METHOD:PUBLISH
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170728T165201Z
DTSTART:20170801T193000Z
DTEND:20170801T203000Z
UID:event1775@bu.edu
URL:http://physics.bu.edu/events/show/1775
SUMMARY:Investigating Effects of Morphology and Flagella Dynamics on Swimmi
ng Kinematics of Different Helicobacter Species Using Single Cell Imaging
DESCRIPTION:Featuring Maira Constantino\n\nPart of the PhD Final Oral Exams
.\n\nExamining Committee: Rama Bansil\, Shyam Erramilli\, Kirill Korolev\,
Karl Ludwig\, Kevin Black\n\nAbstract:\n\nThis work explores the effects o
f body shape and configuration of flagella on motility of Helicobacter pylo
ri\, a helical-shaped bacterium that inhabits the viscoelastic gastric muco
sa and causes gastritis\, ulcers and gastric cancer. Although it is well kn
own that different shapes produce different hydrodynamic drag thus altering
the speed and that helical shapes generate additional thrust this has not
been quantitatively established for flagellated bacteria. Using fast time-r
esolution and high-magnification two-dimensional phase-contrast microscopy
to simultaneously image and track individual helical-shaped H. pylori and i
ts rod-shaped isogenic mutant in broth and mucin solutions\, the shape as w
ell as rotational and translational speed can be determined. Henry Fu and M
ehdi Jabbarzadeh used the experimental data to validate the method of regul
arized Stokeslets by directly comparing the observed speeds to numerical ca
lculations. The results show that due to relatively slow body rotation rate
s\, the helical shape makes at most a 15% contribution to speeds. In order
to explore the effects of flagella configuration on motility\, three membe
rs of the Helicobacter species were examined: H. suis (bipolar\, multiple f
lagella)\, H. cetorum (bipolar\, single flagellum) and H. pylori (unipolar\
, multiple flagella). Due to the large number of flagella in each pole\, th
e flagellar bundle of H. suis could be visualized while it swam in broth an
d mucin. Results show that regardless of media\, the flagella bundles can a
ssume one of two configurations interchangeably: extended away from the bod
y or wrapped around it. H. suis predominantly swims with the lagging flagel
la extended behind the body and the leading flagella wrapped around it\, bu
t cases where both bundles are extended or both are wrapped have also been
observed. Using the same experimental technique described earlier\, the res
ults show that bipolar bacteria gain a speed advantage over unipolar bacter
ia. In addition\, the effects of pH on motility of H. suis in broth and muc
in were investigated. Similarly to previous findings on H. pylori\, the res
ults show that H. suis swims faster in mucin than broth at same pH and that
it stops swimming in mucin at pH4 due to gelation.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170906T184607Z
DTSTART:20170808T190000Z
DTEND:20170808T200000Z
UID:event1780@bu.edu
URL:http://physics.bu.edu/events/show/1780
SUMMARY:Pseudoparticle approach to strongly correlated systems
DESCRIPTION:Featuring Garry Goldstein\, University of Cambridge \nHosted by
: Claudio Rebbi\n\nPart of the Condensed Matter Theory Seminar Series.\n\nI
n the ﬁrst part we present a slave-particle meanﬁeld study of the mixed
boson+fermion quantum dimer model introduced by Punk\, Allais\, and Sachde
v [PNAS 112\, 9552 (2015)] to describe the physics of the pseudogap phase i
n cuprate superconductors. Our analysis naturally leads to four charge e fe
rmion pockets whose total area is equal to the hole doping p\, for a range
of parameters consistent with the t−J model for high temperature supercon
ductivity. Here we ﬁnd that the dimers are unstable to d-wave superconduc
tivity at low temperatures. The region of the phase diagram with d-wave rat
her than s-wave superconductivity matches well with the appearance of the f
our fermion pockets. In the superconducting regime\, the dispersion contain
s eight Dirac cones along the diagonals of the Brillouin zone. \n\nIn the s
econd part we present an approach for studying systems with hard constraint
s such that certain positive semideﬁnite operators must vanish. The diﬃ
culty with mean-ﬁeld treatments of such cases is that imposing that the c
onstraint is zero only in average is problematic for a quantity that is alw
ays non-negative. We reformulate the hard constraints by adding an auxiliar
y system such that some of the states to be projected out from the total sy
stem are at ﬁnite negative energy and the rest at ﬁnite positive energy
\, we dubbed this method the soft constraint. This auxiliary system comes w
ith an extra coupling that we are free to vary and that parametrizes a whol
e family of mean-ﬁeld theories. We argue that this variational-type param
eter for the family of mean-ﬁeld theories should be ﬁxed by matching a
given experimental observation\, with the quality of the resulting mean-ﬁ
eld approximation measured by how it ﬁts other data. We test these ideas
in the well-understood single-impurity Kondo problem\, where we ﬁx the pa
rameter via the TK (Kondo temperature) obtained from the magnetic susceptib
ility value\, and score the quality of the approximation by its predicted W
ilson ratio. We also study a continuum version of the soft constraint metho
d. To show its usefulness we study the Laughlin fractional quantum Hall sta
tes at ﬁlling fraction ν = 1 2m+1. We produce the Landau Ginzburg Cherns
Simons theory for hard core bosons(arising in this formulation of the Laug
hlin functions0 for these ﬁlling fractions. We handle the hard core const
raint explicitly and show that to leading order it is equivalent to a theor
y of soft core bosons with an eﬀective density density interaction betwee
n the particles of the form of a Coulomb interaction coming from the electr
ons in the original theory and an eﬀective interaction coming from the ha
rd core constraint that can be tuned by hand which we denote by λ(q\,ω).
We show that we can use this eﬀective interaction to reproduce the known
spectra of both inter Landau level and intra Landau level neutral excitatio
ns for the Laughlin states as well as the energy gap to charged excitations
and the electromagnetic response tensor.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170906T184620Z
DTSTART:20170810T150000Z
DTEND:20170810T160000Z
UID:event1781@bu.edu
URL:http://physics.bu.edu/events/show/1781
SUMMARY:The many body localization transition: A dynamical phase transition
triggered by a quantum avalanche
DESCRIPTION:Featuring Marcus Muller\, Paul Scherer Institute\, Villigen Swi
tzerland\nHosted by: Claudio Rebbi\n\nPart of the Condensed Matter Theory S
eminar Series.\n\nI will review recent progress on the understanding of man
y-body localization\, i.e.\, the phenomenon of absence of thermalization in
interacting\, disordered quantum systems. After discussing the restricted
domain of existence of strict many body-localization and the role of rare e
vents\, I will present a real space renormalization group analysis which of
fers a microscopic scenario for the unusual dynamical phase transition whic
h occurs as a localized system is tuned into an ergodic regime. While the t
ransition is associated with a diverging time scale for thermalization\, mo
st spatial correlators remain short range at the critical point. The latter
goes hand in hand with the discontinuous evolution of expectation values o
f local observables. These features distinguish the transition sharply from
standard critical phenomena.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170906T184708Z
DTSTART:20170811T150000Z
DTEND:20170811T170000Z
UID:event1782@bu.edu
URL:http://physics.bu.edu/events/show/1782
SUMMARY:Out-of-equilibrium states and quantum annealing speed up in non-con
vex optimization and learning problems
DESCRIPTION:Featuring Riccardo Zecchina\n\nPart of the Condensed Matter The
ory Seminar Series.\n\nQuantum annealers aim at solving non-convex optimiza
tion problems by exploiting cooperative tunneling effects to escape local m
inima. A key challenge is to identify classes of non-convex optimization pr
oblems for which this scheme can induce an exponential speed up compared t
o thermal annealing. We show that this happens for a wide class of optimiza
tion problems which are also central to machine learning. Their energy land
scape is exponentially dominated by local minima that trap classical therma
l annealers\, while quantum annealing converges efficiently to rare dense r
egions of optimal solutions. For non convex problems\, these will not in g
eneral correspond to configuration dominating the Gibbs measure.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170724T132556Z
DTSTART:20170811T161500Z
DTEND:20170811T181500Z
UID:event1779@bu.edu
URL:http://physics.bu.edu/events/show/1779
SUMMARY:Statistical Physics\, Financial and Complex Systems and Networks
DESCRIPTION:Featuring Asher Mullokandov\n\nPart of the PhD Final Oral Exams
.\n\nExamining Committee: H.E. Stanley\, William Skocpol\, Kirill Korolev\,
Irena Vodenska\, Raj Mohanty
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170814T133931Z
DTSTART:20170816T150000Z
DTEND:20170816T160000Z
UID:event1783@bu.edu
URL:http://physics.bu.edu/events/show/1783
SUMMARY:Entanglement entropy of finite-temperature pure quantum states and
thermodynamic entropy as a Noether invariant
DESCRIPTION:Featuring Sho Sugiura\, University of Tokyo\nHosted by: Anatoli
Polkovnikov\n\nPart of the Condensed Matter Theory Seminar Series.\n\nEntr
opy is a fundamental concept in statistical mechanics. In this talk\, I inv
estigate two aspects of entropy. First\, we reveal a universal behavior of
entanglement entropy of the pure quantum states which are in thermal equili
brium states. Second\, we characterize thermodynamic entropy as a Noether i
nvariant under a non-uniform time translation. \n\nIn the first part\, we f
ocus on the size dependence of the entanglement entropy of the pure quantum
states which can fully describe thermal equilibrium as long as one focuses
on local observables. The thermodynamic entropy can also be recovered as t
he entanglement entropy of small subsystems. When the size of the subsystem
increases\, however\, quantum correlations break the correspondence and ma
ndate a correction to this simple volume-law. The elucidatione of the size
dependence of the entanglement entropy is thus of essential importance in l
inking quantum physics with thermodynamics\, and in analyzing recent experi
ments on ultra-cold atoms. In this talk\, we derive an analytic formula of
the entanglement entropy for a class of pure states called cTPQ states repr
esenting thermal equilibrium. We find that our formula applies universally
to any sufficiently scrambled pure state representing thermal equilibrium\,
i.e.\, general energy eigenstates of non-integrable models and states afte
r quantum quenches. Our universal formula can be exploited as a diagnostic
tool for chaotic systems; we can distinguish integrable models from chaotic
modelsand detect many-body localization with high accuracy. \n\nIn the sec
ond part\, we investigate a thermally isolated quantum many-body system wit
h an external control represented by a time-dependent parameter. We formula
te a path integral in terms of thermal pure states and derive an effective
action for trajectories in a thermodynamic state space\, where the entropy
appears with its conjugate variable. In particular\, for quasi-static opera
tions\, the symmetry for the uniform translation of the conjugate variable
emerges in the path integral. This leads to the entropy as a Noether invari
ant.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170816T125347Z
DTSTART:20170817T190000Z
DTEND:20170817T200000Z
UID:event1776@bu.edu
URL:http://physics.bu.edu/events/show/1776
SUMMARY:Continuum limits of Quantum Walks
DESCRIPTION:Featuring Michael Manighalam\n\nPart of the Preliminary Oral Ex
am.\n\nExamining Committee: Mark Kon\, Alex Sushkov\, Chris Laumann\, Claud
io Rebbi\n\n\nThe quantum analog of a random walk is known as the quantum w
alk. Just as random walks have been used in computer science\, quantum walk
s have been used in many areas of quantum computing. Quantum walks have bee
n shown to match the Grover’s search algorithm speedup over classical ora
cle search algorithms\, to provide exponential speedup compared to any clas
sical algorithms in various graph traversal problems\, and more generally t
o be universal quantum computational primitives. \n\nTwo-state quantum walk
s exist as canonical discretizations of the Dirac equation\, as demonstrate
d originally by Feynman; these walks can be shown rigorously to recapture t
he Dirac equation in their continuum limit. Since their original use\, much
work has been done investigating the properties of continuum limits of qua
ntum walks. The goal of my PhD research is to address the question of wheth
er (or not) quantum scattering can be used as a universal quantum computer\
, and I plan primarily to approach this problem by connecting theorems abou
t quantum walks and their universality to scattering theory via continuum l
imits. \n\nIn this talk I will present results I have obtained about contin
uum limits of some quantum walks on the integers which are interesting in t
heir own right\, and may also give an entrée into the larger question of c
ontinuum limits of walks on graphs. In particular I will give an overview
of quantum walks and their relationships to the Dirac and Schrodinger equat
ions\, motivation for computational universality of scattering theory\, and
discuss my various results on continuum limits of quantum walks.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170828T185042Z
DTSTART:20170830T130000Z
DTEND:20170830T140000Z
UID:event1800@bu.edu
URL:http://physics.bu.edu/events/show/1800
SUMMARY:Comprehensive Exams - Part 1
DESCRIPTION:Featuring Ami Katz\n\nPart of the Comprehensive Exams.\n\n
LOCATION:SCI B58\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170814T154723Z
DTSTART:20170831T120000Z
DTEND:20170831T160000Z
UID:event1793@bu.edu
URL:http://physics.bu.edu/events/show/1793
SUMMARY:Incoming Graduate Students Orientation
DESCRIPTION:Featuring Kevin Black/Mirtha Cabello\n\n
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170821T155945Z
DTSTART:20170901T130000Z
DTEND:20170901T160000Z
UID:event1801@bu.edu
URL:http://physics.bu.edu/events/show/1801
SUMMARY:Comprehensive Exams - Part 2
DESCRIPTION:Featuring Ami Katz\n\nPart of the Comprehensive Exams.\n\n
LOCATION:SCI B58\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170827T143849Z
DTSTART:20170907T160000Z
DTEND:20170907T180000Z
UID:event1802@bu.edu
URL:http://physics.bu.edu/events/show/1802
SUMMARY:Special Systems Biology Seminar: A Conversation About Climate Chang
e
DESCRIPTION:Featuring Charles DeLisi\, Metcalf Professor of Science and Eng
ineering \, Dean Emeritus\, College of Engineering - Boston University\n\nT
he complexity and uncertainties of climate science leave an enormous openin
g for political controversy\, and amplify the environmental and economic co
nsequences associated with possible courses of action---which range from do
ing nothing\, to the Gore proposal to reduce emissions 90% by 2050. \n\nCon
troversy notwithstanding\, scientists have uncovered some hard facts\, and
have also drawn plausible inferences\, with varying levels of confidence\,
about the past and future climate of our planet. Before opening the meetin
g to conversation\, \nI’ll spend about thirty minutes briefly reviewing w
hat’s known about the contribution of human activity to changes in greenh
ouse gases\, average global temperature\, sea levels\, the predicted conseq
uences of allowing change to continue unabated\, and the confidence levels
of the predictions. I’ll also briefly indicate proposed mitigation strate
gies\, including my own views about the potential use of biotechnology for
regulating atmospheric carbon dioxide and other greenhouse gases.
LOCATION:LSE 103\, 24 Cummington Mall\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170815T205644Z
DTSTART:20170911T170000Z
DTEND:20170911T180000Z
UID:event1798@bu.edu
URL:http://physics.bu.edu/events/show/1798
SUMMARY:COUPLED WIRE CONSTRUCTION OF NON-ABELIAN CHIRAL SPIN LIQUIDS
DESCRIPTION:Featuring Po-Hao Huang\n\nPart of the PhD Final Oral Exams.\n\n
Dissertation Committee: Claudio Chamon\, Andrei Ruckenstein\, Anatoli Polk
ovnikov\, Emanuel Katz\, Michael El-Batanouny\n\nAbstract:\n\nTopologically
ordered states of matter have attracted much interest in the past decade.\
nThe search for emergent point-like non-Abelian anyons electronic systems i
s one of the\nmost exciting problems in condensed matter physics\, since it
opens many possibilities for\ntopological quantum computing. In this talk\
, I will construct two-dimensional non-Abelian\ntopologically ordered state
s by strongly coupling arrays of one-dimensional quantum wires\nvia interac
tions. In our scheme\, all charge degrees of freedom are gapped\, so the co
n-\nstruction can use either quantum wires or quantum spin chains as buildi
ng blocks\, with\nthe same end result. Hence\, the resulting non-Abelian sp
in liquid states have vanishing\nquantum Hall conductivities\, but nonzero
thermal ones. The construction gaps the degrees\nof freedom in the bulk\, w
hile leaving decoupled states at the edges that are described by\nconformal
eld theories (CFT) in (1 + 1)-dimensional space and time. We prescribe\, i
n\nparticular\, how to arrive at all the edge states described by the unita
ry CFT minimal\nmodels with central charges c < 1.
LOCATION:SCI TBA\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170911T162601Z
DTSTART:20170912T190000Z
DTEND:20170912T200000Z
UID:event1826@bu.edu
URL:http://physics.bu.edu/events/show/1826
SUMMARY:Constructing Ultra-Slow Glasses in Lattice Models for Reversible Co
mputing
DESCRIPTION:Featuring Lei Zhang\n\nPart of the Preliminary Oral Exam.\n\nEx
amining Committee: Andrei Ruckenstein\, Claudio Chamon\, Michael El-Batano
uny\, Richard Brower\n\nAbstract:\n\nWe construct a two-dimensional lattice
model that lacks any finite temperature phase transition and yet displays
relaxation times that grow as a double exponential of the inverse temperatu
re. The model has bulk translational invariance\, only broken by the presen
ce of the boundaries. The lattice model is associated to a reversible circu
it that can multiply or factorize integers\, depending on the boundary cond
itions. When the lattice model reaches its ground state\, all computations
are performed without error. The ultra-slow (double exponential in inverse
temperature) glassy dynamics is associated with the difficulty of the syste
m to heal computational errors that cost little energy but flip a volumetri
c number of bits in the system.\n\n![Lei](/resources/event-image/1826/af5ae
ef_small)
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170906T183707Z
DTSTART:20170913T150000Z
DTEND:20170913T160000Z
UID:event1816@bu.edu
URL:http://physics.bu.edu/events/show/1816
SUMMARY:Correlations in driven-dissipative quantum systems
DESCRIPTION:Featuring Michiel Wouters\, University of Antwerp\nHosted by: A
natoli Polkovnikov\, Dries Sels\n\nPart of the Condensed Matter Theory Semi
nar Series.\n\nRecent advances in experimental platforms for photonic quant
um simulators (microcavity polaritons and superconducting circuits) have sp
urred the interest in the theory of driven-dissipative quantum systems. The
long time steady state of such systems is not given by a Boltzmann-Gibbs d
istribution\, but has to be found by solving a Lindblad master equation. \n
\nIn this talk\, I will discuss two topics: for weakly interacting systems\
, the imprint of Landau-Beliaev scattering on the steady state distribution
of a 1D photonic Hubbard model in the weakly interacting regime and the fa
ilure of the truncated Wigner approximation to capture this feature. For st
rongly interacting systems\, I will present results obtained within the Gut
zwiller approximation to the quantum trajectories of a dissipative XYZ mode
l. We show that a ferromagnetic to paramagnetic phase transition\, that is
missing within a mean field treatment\, is recovered within our approach.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170901T145009Z
DTSTART:20170913T180000Z
DTEND:20170913T190000Z
UID:event1817@bu.edu
URL:http://physics.bu.edu/events/show/1817
SUMMARY:Numerical Signatures of Conformal Field Theory
DESCRIPTION:Featuring Pranay Patil\n\nPart of the Preliminary Oral Exam.\n\
nAbstract: Conformal Field theory has important consequences for quantum ph
ase transitions and dynamical response of lattice models and as it is not a
lways possible to analytically determine if a lattice model has a low energ
y conformal description\, we need to find numerical signatures which can re
liably help us identify a CFT. Here we look at how entanglement entropy and
correlation functions fare as candidates for CFT signatures using some exa
mples of established CFTs such as the 2d classical Ising model and 1d Heise
nberg chain. We also explore some interesting properties of the 1d Heisenbe
rg chain using these numerics.\n\nDissertation committee: Anders Sandvik\,
Claudio Chamon\, Emanuel Katz\, Alex Sushkov \n\n![Pranay](/resources/event
-image/1817/00307ec_small)
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170912T161810Z
DTSTART:20170915T160000Z
DTEND:20170915T173000Z
UID:event1833@bu.edu
URL:http://physics.bu.edu/events/show/1833
SUMMARY:"Resonant x-ray spectroscopy of topological semimetals"
DESCRIPTION:Featuring Stefanos Kourtis\, Boston University\, Physics Depart
ment\n\nPart of the Condensed Matter Theory Seminar Series.\n\nAngle-resolv
ed photoemission spectroscopy (ARPES) has so far been the definitive method
for the characterization of materials as topological Weyl or Dirac semimet
als\, via direct visualization of band touchings in the bulk and nontrivial
states at the boundary. However\, the unconventional and potentially usefu
l properties of these materials are a consequence of a singular Berry curva
ture distribution\, which cannot be resolved in ARPES. Furthermore\, contro
l over the number and position of Weyl nodes -- the most important property
from an application standpoint -- can only be achieved with sizable electr
omagnetic fields\, which curtail the resolving power of ARPES\, thereby ren
dering the band structure inaccessible to this technique. We show how reson
ant x-ray scattering (RXS) offers a viable path for (a) deducing the band s
tructure of materials in arbitrarily large magnetic fields and (b) visualiz
ing the Berry curvature distribution in momentum space via polarization con
trol of incoming and outgoing x-ray beams. By low-energy modeling of specif
ic material candidates based on ab initio band structure calculations\, we
derive the corresponding RXS spectra and highlight the salient features ste
mming from topological nontriviality. The proposed measurements are within
the resolving capabilities of current instrumentation.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170907T140232Z
DTSTART:20170918T160000Z
DTEND:20170918T180000Z
UID:event1828@bu.edu
URL:http://physics.bu.edu/events/show/1828
SUMMARY:Physics Department Annual BBQ
DESCRIPTION:\nPart of the Departmental Seminars.\n\nPlease join the Physics
Department for our annual BBQ on Monday\, September 18th from 12:00PM-2PM
at the SCI Front Plaza\, 590 Commonwealth Avenue. The BBQ food will include
hot dogs\, hamburgers\, veggie burgers\, chips\, watermelon\, and cookies.
Refreshments will be provided.\n\nWe look forward to seeing you there!
LOCATION:SCI Plaza\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170907T183607Z
DTSTART:20170918T173000Z
DTEND:20170918T183000Z
UID:event1799@bu.edu
URL:http://physics.bu.edu/events/show/1799
SUMMARY:Market Bubbles: Collective Behavior in the Financial Market
DESCRIPTION:Featuring Chon Kit Pun\n\nPart of the Preliminary Oral Exam.\n\
nExamining Committee: William Klein\, Harvey Gould\, Kirill Korolev\, Chris
topher Grant\, Alex Sushkov\n\nAbstract:\n\n\nFrom the stock bubbles in the
1920s\, which eventually led to the Great Depression in the 1930s\, to the
recent boom and bust of the real estate bubbles in 2007-2009\, market bubb
les have been the main source of instability in the financial market. While
speculators and momentum traders are blamed to have driven the price away
from the reasonable level during the formation of a bubble\, value investor
s like the fund managers may sometimes fail to correct the price and instea
d join 'riding the bubble'\, which help growing the bubble further.\n\nIn t
his talk I will present an agent-based model of how the collective behavior
of traders give rise to a bubble. In this model traders learn which assets
to invest by using the Experience Weighted Attraction (EWA) learning algor
ithm\, which has its root in both behavioral psychology and game theory and
has seen applications in social science and economics. I will show that wh
en traders tend to invest in the `winning' asset\, memory and liquidity pla
y an important role in the formation\nof bubbles. The discussion of the res
ult will be emphasized on the implication to the real market\, and on the c
omparison with statistical physics.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170919T145442Z
DTSTART:20170922T160000Z
DTEND:20170922T173000Z
UID:event1836@bu.edu
URL:http://physics.bu.edu/events/show/1836
SUMMARY:"Interfering directed paths & the sign phase transition"
DESCRIPTION:Featuring Christopher Baldwin\, Boston University\, Physics Dep
artment\n\nPart of the Condensed Matter Theory Seminar Series.\n\nWe consid
er the problem of interfering directed paths in disordered media\, and disc
uss the physical contexts in which this problem arises. An important proper
ty of the path sum is the statistics of its sign. The average sign may tend
to zero ("sign-disordered") or remain finite ("sign-ordered") at long dist
ance\, depending on dimensionality and the concentration of negative scatte
ring sites x. We discuss the analogy with a dynamical out-of-equilibrium Is
ing field. We further show that the sign-ordered phase is always unstable f
or any non-zero x in 2D by identifying rare destabilizing events\, and pres
ent numerical evidence that it is stable in 3D. These results have conseque
nces for several different physical systems\, which we conclude by describi
ng.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170911T151308Z
DTSTART:20170925T150000Z
DTEND:20170925T163000Z
UID:event1829@bu.edu
URL:http://physics.bu.edu/events/show/1829
SUMMARY:"Lieb-Schultz-Mattis Theorem and its generalizations from the Persp
ective of the Symmetry Protected Topological Phase"
DESCRIPTION:Featuring Cenke Xu \, University of California - Santa Barbara\
nHosted by: Anders Sandvik\n\nPart of the Condensed Matter Theory Seminar S
eries.\n\nWe ask whether a local Hamiltonian with a featureless (fully gapp
ed and\nnondegenerate) ground state could exist in certain quantum spin sys
tems. \nWe address this question by mapping the vicinity of certain quantum
critical point (or gapless phase) of the d−dimensional spin system under
study to the boundary of a (d+1)−dimensional bulk state\, and the lattic
e symmetry of the spin system acts as an on-site symmetry in the field theo
ry that describes both the selected critical point of the spin system\, and
the corresponding boundary state of the (d+1)−dimensional bulk. If the c
orresponding bulk state is a trivial state instead of a bosonic symmetry pr
otected topological (SPT) state\, then a featureless ground state of the sp
in system is allowed; if the corresponding bulk state is indeed a nontrivia
l SPT state\, then it likely excludes the existence of a featureless ground
state of the spin system. From this perspective we identify the spin syste
ms with SU(N) and SO(N) symmetries on one\, two and three dimensional latti
ces that permit a featureless ground state. We also verify our conclusions
by other methods\, including an explicit construction of these featureless
spin states.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170908T135842Z
DTSTART:20170927T150000Z
DTEND:20170927T160000Z
UID:event1830@bu.edu
URL:http://physics.bu.edu/events/show/1830
SUMMARY:"Iterative Compression-Decimation Scheme for Tensor Network Optimiz
ation"
DESCRIPTION:Featuring Zhicheng Yang\, Boston University\, Physics Departmen
t\n\nPart of the Condensed Matter Theory Seminar Series.\n\nMotivated by st
atistical physics models connected to computation problems\, we devise a te
nsor network technique that is suited to problems with or without translati
on invariance and with arbitrary boundary conditions. We introduce a compre
ssion-decimation algorithm as an efficient iterative scheme to optimize ten
sor networks that encode generalized vertex models on regular lattices. The
algorithm first propagates local constraints to longer ranges via repeated
contraction-decomposition sweeps over all lattice bonds\, thus achieving c
ompression on a given length scale. It then decimates the lattice via coars
e-graining tensor contractions. Repeated iterations of these two steps allo
w us to gradually collapse the tensor network while keeping the tensor dime
nsions under control\, such that ultimately the full tensor trace can be ta
ken for relatively large systems. As a benchmark\, we demonstrate the effic
iency of the algorithm by computing the ground state entropy density of the
planar ice model and the eight-vertex model. We then apply it to reversibl
e classical computational problems based on a recently proposed vertex mode
l representation of classical computations [Nat. Commun. {\bf8}\, 15303 (20
17)]. Our protocol allows us to obtain the exact number of solutions for co
mputations where a naive enumeration would take astronomically long times\,
suggesting that the algorithm is a promising practical tool for the soluti
on of a plethora of problems in physics and computer science.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170928T130857Z
DTSTART:20170928T140000Z
DTEND:20170928T150000Z
UID:event1842@bu.edu
URL:http://physics.bu.edu/events/show/1842
SUMMARY:Exploring Strain Physics in 2D Systems
DESCRIPTION:Featuring Jason Christopher\n\nPart of the Departmental Seminar
s.\n\nDissertation Committee: Bennett Goldberg\, Anna Swan\, David Bishop\
, David Campbell\, Kenneth Lane \n\nAbstract: Two dimensional (2D) materia
ls can withstand an order of magnitude more strain than their bulk counterp
arts which can be used to dramatically change electrical\, thermal and opti
cal properties or even cause unconventional behavior such as generating pse
udo-magnetic fields (PMF). In this seminar I will discuss the origin of PMF
s and several experimental methods I am pursuing to experimentally realize
controllable PMFs using micro-electromechanical systems (MEMS) and neon ato
m intercalation.\n\n![Jason](/resources/event-image/1842/e76821b_small)
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170925T130542Z
DTSTART:20170928T193000Z
DTEND:20170928T203000Z
UID:event1837@bu.edu
URL:http://physics.bu.edu/events/show/1837
SUMMARY:SOLUTIONS TO LINEAR PROBLEMS IN ABERRATED OPTICAL SYSTEMS
DESCRIPTION:Featuring William Shain\n\nPart of the PhD Final Oral Exams.\n\
nExamining Committee: Bennett Goldberg\, Jerome Mertz\, David Campbell\, St
eve Ahlen\, Thomas Bifano\n\nAbstract:\n\nOne of the greatest challenges in
understanding any physical system is extracting as much information as pos
sible. In optics\, the laws that govern the interaction of a system with li
ght are frequently linear: Maxwell’s equations lead to linear wave equati
ons\, and in general one can write the evolution of the quantities of inter
est as a linear propagation in space and time. This linearity imposes a con
straint on how one recovers information about an object of interest; for ex
ample\, one can expand the field-of-view by taking multiple images (reducin
g the total framerate) or by lowering the numerical aperture (reducing the
resolution). In each case\, one aspect of information is sacrificed for ano
ther. Therefore\, one can efficiently probe a system through optical means
by carefully choosing what aspects of the light are measured\, depending on
the problem of interest. This can be attained through direct manipulation
of the optical propagator\, by using a Spatial Light Modulator to perform p
hysical linear transformations on the light field. In this thesis\, I demon
strate the usefulness of a MEMS Deformable Mirror (DM) in implementing the
necessary linear transformation\, and apply the methodology to three system
s of interest: recovering imaging capabilities in porous rock\, expanded im
aging of neuronal activity in brain tissue\, and high-throughput particle i
dentification in label-free flow cytometry. In each case\, I show how caref
ul control of the light travelling through the microscope allows for optimi
zed recovery of the desired information.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170912T160128Z
DTSTART:20171004T150000Z
DTEND:20171004T160000Z
UID:event1832@bu.edu
URL:http://physics.bu.edu/events/show/1832
SUMMARY:"Stability of quantum statistical ensembles with respect to local m
easurements"
DESCRIPTION:Featuring Walter Hahn\, Skolkovo Institute of Science and Techn
ology\, Moscow\nHosted by: Anatoli Polkovnikov\n\nPart of the Condensed Mat
ter Theory Seminar Series.\n\nWe introduce a stability criterion for quantu
m statistical ensembles describing macroscopic systems. An ensemble is call
ed "stable" when a small number of local measurements cannot significantly
modify the probability distribution of the total energy of the system. We a
pply this criterion to lattices of spins-1/2\, thereby showing that the can
onical ensemble is nearly stable\, whereas statistical ensembles with much
broader energy distributions are not stable. In the context of the foundati
ons of quantum statistical physics\, this result justifies the use of stati
stical ensembles with narrow energy distributions such as canonical or micr
ocanonical ensembles.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171006T140420Z
DTSTART:20171006T160000Z
DTEND:20171006T173000Z
UID:event1820@bu.edu
URL:http://physics.bu.edu/events/show/1820
SUMMARY:"Diabatic approach to creating ground states of certain critical mo
dels"
DESCRIPTION:Featuring Kartiek Agrawal\, Princeton University\nHosted by: An
atoli Polkovnikov\n\nPart of the Condensed Matter Theory Seminar Series.\n\
nWe propose a spatio-temporal quench protocol that allows for the fast prep
aration of ground states of gapless models with Lorentz invariance. Assumin
g the system initially resides in the ground state of a corresponding massi
ve model\, we show that a supersonically-moving ‘front’ that locally qu
enches the mass\, leaves behind it (in space) a state arbitrarily close to
the ground state of the gapless model. Importantly\, our protocol takes tim
e O (L) to produce the ground state of a system of size ∼ Ld (d spatial d
imensions)\, while a fully adiabatic protocol requires time ∼ O( L2) to p
roduce a state with exponential accuracy in L. We provide proof-of-concept
by solving the proposed quench exactly for a system of free bosons in arbit
rary dimensions\, and for free fermions in d = 1. We also discuss the role
of interactions and UV effects on the free-theory idealization\, before num
erically illustrating the usefulness of the approach using simulations on c
lassical phonons and on the quantum Heisenberg spin-chain with a mass induc
ed by local magnetic fields.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171002T180812Z
DTSTART:20171013T160000Z
DTEND:20171013T173000Z
UID:event1821@bu.edu
URL:http://physics.bu.edu/events/show/1821
SUMMARY:"Coherent optical control and nonlinear probing of strongly correla
ted materials"
DESCRIPTION:Featuring Roman Mankowsky\, Paul Scherrer Institute \nHosted by
: Wanzheng Hu\n\nPart of the Condensed Matter Theory Seminar Series.\n\nMid
-infrared optical pulses can resonantly drive selected vibrational modes in
solids to deform their crystal structure. In strongly correlated materials
\, this method has been used to melt electronic and magnetic order\, drive
insulator-to-metal transitions\, and transiently induce superconductivity.
Free Electron Lasers have been key in identifying the lattice dynamics unde
rlying these transitions.\n\nIn this talk\, I will first review nonlinear p
hononics and discuss its role in the phenomenon of light-induced supercondu
ctivity. I will then present recent studies\, in which resonant lattice exc
itation was used to control the polarization of ferroelectric materials on
femtosecond timescales. These studies are a first step toward ultrafast rev
ersible switching. In the last part of the lecture\, I will focus on the ex
citation of highly nonlinear lattice dynamics\, a new technique which allow
ed us to reconstruct the interatomic lattice potential of a solid and bench
mark first principle calculations.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170925T150524Z
DTSTART:20171016T163000Z
DTEND:20171016T173000Z
UID:event1840@bu.edu
URL:http://physics.bu.edu/events/show/1840
SUMMARY:"Physicochemical Conditions for Self-Replication"
DESCRIPTION:Featuring Sumantra Sarkar\, Massachusetts Institute of Technolo
gy\nHosted by: Robert Marsland\n\nPart of the Biophysics Seminars.\n\n
LOCATION:CILSE 106C\, 610 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20170913T200604Z
DTSTART:20171018T150000Z
DTEND:20171018T160000Z
UID:event1814@bu.edu
URL:http://physics.bu.edu/events/show/1814
SUMMARY:"Cluster Synchronization of Chaotic Systems in Large Networks"
DESCRIPTION:Featuring Louis Pecora\, United States Naval Research Laborator
y\nHosted by: David Campbell\n\nPart of the Condensed Matter Theory Seminar
Series.\n\nSynchronization of two chaotic systems is a well-known phenomen
on\, although it still seems like an oxymoron. But when many oscillators (c
haotic or not) are linked together in a network causing them to interact\,
they can synchronize to other oscillators in the network\, but not necessar
ily all of them. The network can break up into clusters of synchronized sy
stems where the oscillators in the same cluster synchronize\, but not to os
cillators in other clusters even though all clusters are interconnected and
influence each other. I show that such patterns of synchronization can be
related to the symmetries of the network. One can use computational group
theory to find all the symmetries and hence\, clusters. Such symmetries ca
n be huge in number (e.g. 10^66 symmetries in a network of 100 oscillators)
\, but can be found in short time. I'll show how to analyze such systems\,
determine the stability of the cluster patterns\, and find interesting patt
erns of desynchronization bifurcations. I'll show how one can generate such
patterns in an electro-optical system. The methods I present will include
the construction of synchronization patterns that do not arise from symmetr
ies\, but can be built up from symmetry clusters make symmetries the fundam
ental concept in many cluster patterns.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171017T174315Z
DTSTART:20171020T160000Z
DTEND:20171020T170000Z
UID:event1847@bu.edu
URL:http://physics.bu.edu/events/show/1847
SUMMARY:"Kibble-Zurek Dynamics of a Driven Dissipative System: Universality
Beyond the Markovian Regime"
DESCRIPTION:Featuring Tamiro Villazon\, Boston University\, Physics Departm
ent\n\nPart of the Condensed Matter Theory Seminar Series.\n\nPhase transit
ions in open systems provide a rich avenue for the study of many-body non-e
quilibrium phenomena. These systems exhibit unique properties depending on
the detailed nature of their system-bath interactions\, which may nontrivia
lly alter their critical dynamics\, and which in turn are amenable to study
by slow ramps across the critical point. In this talk\, I will discuss Kib
ble-Zurek dynamics in a paradigmatic two-mode driven-dissipative system of
a pair of non-degenerate parametrically coupled\, optomechanical oscillator
s. I will detail the key theoretical aspects of the model and it's predicti
ons on universality\, which have been confirmed in experiments by our colla
borators in the Vengalattore group at Cornell University.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171011T143333Z
DTSTART:20171023T163000Z
DTEND:20171023T173000Z
UID:event1825@bu.edu
URL:http://physics.bu.edu/events/show/1825
SUMMARY:"On Growth and Form of Range Expansions at Liquid Interfaces"
DESCRIPTION:Featuring Severine Atis\, Harvard University\nHosted by: Kirill
Korolev\n\nPart of the Biophysics Seminars.\n\nTransport phenomena shape a
nd constantly reorganize materials at every scale. In presence of hydrodyna
mical flows\, the Lagrangian advection of individual particles strongly inf
luences their dispersion\, segregation and clustering. Range expansions of
living cells resting on liquid substrates is of great importance in underst
anding the organization of microorganism populations. However\, combining g
rowth dynamics of an expanding assembly of cells with hydrodynamics leads t
o challenging problems\, which involve the coupling of nonlinear dynamics\,
stochasticity and transport. In this talk\, I will present laboratory expe
riments\, combined with numerical modelling\, focused on the collective dyn
amics of genetically labelled microorganisms undergoing division and compet
ition in the presence of a variety of flows. We have created an extremely v
iscous medium that allows us to grow cells on a controlled liquid interface
over macroscopic scales. I will show that an expanding population of micro
organisms can itself generate a radial flow\, leading to an accelerated pro
pagation and fragmentation of the initial colony. I will show how the dynam
ics and morphology of these microbial populations is affected by the fluid
dynamics triggered by this metabolically generated flow. I will conclude by
discussing the potential influence of transport and mixing on evolutionary
dynamics\, and how the control of cell assemblies on liquid interfaces can
lead to a wide range of phenomena at the intersection between cellular bio
logy and physics.
LOCATION:CILSE 106C\, 610 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171020T191831Z
DTSTART:20171023T180000Z
DTEND:20171023T190000Z
UID:event1841@bu.edu
URL:http://physics.bu.edu/events/show/1841
SUMMARY:Boosted Dark Matter at Super-Kamiokande
DESCRIPTION:Featuring Christopher Kachulis\n\nPart of the Departmental Semi
nars.\n\nDissertation Committee: Kearns\, Katz\, Sushkov\, Carey\, Grant\n
\nAbstract: \n\nThere has long been ample evidence for the existence of da
rk matter. Based on observation of the Cosmic Microwave Background\, dark
matter accounts for about 25% of the energy density of the Universe. Beyon
d this\, however\, little is known about the properties of dark matter. Di
rect and indirect detection searches\, as well as searches for dark matter
produced at particle accelerators\, have thus far all produced null results
. I will present a brief history of dark matter experimental results\, and
then discuss a class of dark matter models called "boosted" dark matter.
In these models\, some small fraction of dark matter is produced at late ti
mes at relativistic energies\, thus the name "boosted". I will then presen
t the results of a search for boosted dark matter from the Galactic Center
and the Sun at Super-Kamiokande.
LOCATION:PRB 595\, 3 Cummington Mall\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171018T193831Z
DTSTART:20171024T153000Z
DTEND:20171024T163000Z
UID:event1848@bu.edu
URL:http://physics.bu.edu/events/show/1848
SUMMARY:"Exciting dynamics in multiple time dimensions"
DESCRIPTION:Featuring Ivar Mar\, Argonne National Lab\n\nPart of the Conden
sed Matter Theory Seminar Series.\n\nExternally driving a dynamical system\
, be it quantum or classical\, effectively increases the number of its time
dimensions. In this talk I will describe how these extra time dimensions
can be harnessed to synthesize topological insulators purely in time domain
\, describe their possible applications for energy conversion and quantum e
ngineering\, and point out connections to localization and chaos.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171011T140140Z
DTSTART:20171025T150000Z
DTEND:20171025T163000Z
UID:event1823@bu.edu
URL:http://physics.bu.edu/events/show/1823
SUMMARY:"Nearly deconfined spinon excitations in the square-lattice spin-1/
2 Heisenberg antiferromagnet"
DESCRIPTION:Featuring Hui Shao\, Beijing Computational Science Research Cen
ter\nHosted by: Anders Sandvik\n\nPart of the Condensed Matter Theory Semin
ar Series.\n\nWe study the spin excitation spectrum of the spin-1/2 square-
lattice\nHeisenberg antiferromagnet with QMC and an improved stochastic\na
nalytic continuation method. The spectra are in excellent agreement\nwith r
ecent neutron scattering experiments on Cu(DCOO)2·4D2O\, where a\nbroad sp
ectral-weight continuum at wavevector q = (\pi\,0) was\ninterpreted as deco
nfined spinons. Our results show a similar\nreduction of the magnon weight
and a large continuum. Upon turning on\nthe Q interaction in the J-Q model\
, we observe a rapid reduction of\nthe magnon weight to zero\, well before
the system undergoes a\ndeconfined quantum phase transition into a non-magn
etic spontaneously\ndimerized state. Based on these results\, we re-interpr
et the picture\nof deconfined spinons at (\pi\,0) in the experiments as nea
rly\ndeconfined spinons—a precursor to deconfined quantum criticality. We
\nalso introduce an effective model of the excitations (one magnon or\ntwo
spinons) which can reproduce the reduction of magnon weight and\nlowered ex
citation energy at (\pi\,0) in the Heisenberg model\, as well\nas the rapid
loss of the (\pi\,0) magnon with increasing Q in the J-Q\nmodel.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171026T153829Z
DTSTART:20171027T154500Z
DTEND:20171027T173000Z
UID:event1844@bu.edu
URL:http://physics.bu.edu/events/show/1844
SUMMARY:Physics Department Annual Pumpkin Drop
DESCRIPTION:\nJoin us on Friday\, October 27th for our 13th Annual Pumpkin
Drop!\n\nThe main event starts at 12:30PM in front of the Metcalf Science C
enter (SCI\, 590 Commonwealth Ave)\, but show up early to guess the weight
of the largest pumpkin and snack on some Halloween treats!\n\nYou can also
enter our costume contest for your chance at a prize! Extra points will be
awarded for creativity and detail. Enter to win at the contest table by 11:
45AM.\n\nThe Pumpkin Fall will be at 12:30pm.
LOCATION:SCI Plaza\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171023T193234Z
DTSTART:20171027T160000Z
DTEND:20171027T173000Z
UID:event1835@bu.edu
URL:http://physics.bu.edu/events/show/1835
SUMMARY:"Putting hydrodynamic into solid state"
DESCRIPTION:Featuring Kin Chung Fong\, Raytheon BBN Technologies and Harvar
d University\nHosted by: Scott Bunch\n\nPart of the Condensed Matter Theory
Seminar Series.\n\nDespite of the strong Coulomb interaction\, electrons i
n simple metal behave as a non-interacting Fermi gas with long-lived quasi-
particle excitation. However\, weak screening near the charge neutrality po
int of the massless Dirac fermions in graphene can lead to a new collective
behavior described by hydrodynamics. By listening to the Johnson noise of
the electrons\, we are able to probe simultaneously the thermal and electri
cal transport of the Dirac fluid and observe how it departs from Fermi liqu
id physics. At high temperature near the neutrality point\, we find a stron
g enhancement of the thermal conductivity and breakdown of Wiedemann-Franz
law in graphene. This is attributed to the non-degenerate electrons and hol
es forming a strongly coupled Dirac fluid.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:TENTATIVE
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171027T182312Z
DTSTART:20171103T160000Z
DTEND:20171103T173000Z
UID:event1838@bu.edu
URL:http://physics.bu.edu/events/show/1838
SUMMARY:"When and why is a simpler model better?"
DESCRIPTION:Featuring Ben Machta\, Princeton University\nHosted by: Robert
Marsland\n\nPart of the Biophysics Seminars.\n\nScience is filled with toy
models: abstractions of complicated systems that ignore microscopic details
even when they are known. For a special class of models in physics\, the
renormalization group rigorously justifies the use of effective theories co
ntaining just a small number of relevant parameters. This philosophy seems
to apply more broadly\, even when the renormalization group cannot be used
. But why? In this talk I will discuss an information theory approach to
answering this question\, or at least towards quantifying it. I will first
review that typical models are sloppy\, defined by a hierarchy in paramete
r importance (1). I will argue that sloppiness is both necessary and suffi
cient for a microscopic system to be amenable to description by a simpler e
ffective theory. I will then show how renormalizable models become sloppy
as their data is coarse-grained (2). Finally I will discuss our recent eff
orts to use the structure of these models to choose simpler effective theor
ies automatically (3). \n\n(1) Transtrum\, MK\, et al. Perspective: Sloppin
ess and emergent theories in physics\, biology\, and beyond. The Journal of
chemical physics 143.1 (2015) link\n\n(2) Machta\, BB\, Chachra\, R\, Tran
strum\, MK and Sethna\, JP. Parameter space compression underlies emergent
theories and predictive models. Science 342\, no. 6158 (2013). link\n\n(3)
Mattingly\, HH\, Transtrum\, MK\, Abbott\, MC\, & Machta\, BB. Rational ig
norance: simpler models learn more from finite data. (2017) arxiv.org/abs/
1705.01166
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171101T142607Z
DTSTART:20171103T180000Z
DTEND:20171103T190000Z
UID:event1854@bu.edu
URL:http://physics.bu.edu/events/show/1854
SUMMARY: Learning and Optimizing Quantum Control Landscapes
DESCRIPTION:Featuring Alexandre Day\n\nPart of the Preliminary Oral Exam.\n
\nAbstract:\nThe ability to prepare quantum states rapidly and with high fi
delity is a crucial step towards\nfully scalable quantum computers. In this
talk I will discuss the existence of phase transitions in the quantum stat
e preparation problem as a function of the constraint parameters (field str
engths and ramp time). We study the different phases and discuss their sign
ificance in terms of complexity and robustness for the quantum state prepar
ation problem.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171031T145208Z
DTSTART:20171106T160000Z
DTEND:20171106T170000Z
UID:event1853@bu.edu
URL:http://physics.bu.edu/events/show/1853
SUMMARY:"Polarization\, Large Gauge Invariance\, and Quantum Hall Effect on
Lattice"
DESCRIPTION:Featuring Masaki Oshikawa\, University of Tokyo\nHosted by: And
ers Sandvik\n\nPart of the Condensed Matter Theory Seminar Series.\n\nQuant
um systems on a non-simply connected space possess a\n"large" gauge invaria
nce. Laughlin utilized this to explain quantum\nHall effect. Later\, it was
applied to elucidate a universal relation\nbetween filling factor and ener
gy spectrum in quantum many-body\nsystems on periodic lattices (Lieb-Schult
z-Mattis-M.O.-Hastings).\nSomewhat surprisingly\, the large gauge invarianc
e is also deeply\nrelated to modern theory of electric polarization develop
ed by\nResta et al. Combining these ideas together\, we can derive a constr
aint\non the Hall conductivity of a many-particle system on a periodic\nlat
tice\, with a given magnetic flux per plaquette and particle density.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171023T160747Z
DTSTART:20171108T160000Z
DTEND:20171108T170000Z
UID:event1850@bu.edu
URL:http://physics.bu.edu/events/show/1850
SUMMARY:"Instabilities of the Sachdev-Ye-Kitaev Model"
DESCRIPTION:Featuring Zhen Bi\, Pappalardo Fellow\, Massachusetts Institute
of Technology\nHosted by: Zhicheng Yang\n\nPart of the Condensed Matter Th
eory Seminar Series.\n\nThe Sachdev-Ye-Kitaev (SYK) model is an intriguing
0+1d strongly interacting disordered model of non-Fermi liquid states with
exact solution and possible holographic duality. In this talk\, I will cons
ider a series of perturbations on the SYK model. We show that the maximal c
haotic non-Fermi-liquid phase described by the ordinary SYK model has margi
nally relevant or irrelevant (depending on the sign of the coupling constan
ts) four-fermion perturbations allowed by symmetry. Changing the sign of on
e of these four-fermion perturbations leads to a continuous chaotic-nonchao
tic quantum phase transition of the system accompanied by a spontaneous tim
e-reversal symmetry breaking. We also studied a generalized 0+1d interactin
g disordered fermion model which has a series of new fixed points with cont
inuously varying exponents. If time permits\, I will talk about a 1+1d mode
l built out of SYK clusters\, which exhibits a continuous transition betwee
n thermal metal and insulator phase at low temperature.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171013T200332Z
DTSTART:20171113T170000Z
DTEND:20171113T180000Z
UID:event1846@bu.edu
URL:http://physics.bu.edu/events/show/1846
SUMMARY:Magnetic Field Effects in Low-Dimensional Quantum Magnets
DESCRIPTION:Featuring Adam Iaizzi\n\nPart of the PhD Final Oral Exams.\n\nE
xamining Committee: Anders Sandvik\, David Campbell\, Robert Carey\, Shyam
Erramilli\, Claudio Chamon\n\nAbstract:\n\nWe present a comprehensive study
of a low-dimensional spin-half quantum antiferromagnet\, the J-Q model\, i
n the presence of an external (Zeeman) magnetic field using numerical \nm
ethods\, chiefly stochastic series expansion quantum Monte Carlo with dire
cted loop updates and \nquantum replica exchange. The J-Q model is a many
-body Hamiltonian acting on a lattice of \nlocalized spin-half degrees of f
reedom; it augments the Heisenberg exchange with a \nfour-spin interaction
of strength Q. This model has been extensively studied at zero field\, whe
re \nthe Q term drives a quantum phase transition from a Neel-like state
to a valence-bond solid (a nonmagnetic state consisting of a long-range-
ordered arrangement of local singlet bonds \nbetween sites). This transiti
on is believed to be an example of deconfined quantum criticality\, \nwhere
the excitations are spinons—exotic spin-half bosons. We study the J-Q m
odel in the presence \nof a magnetic field in both one and two dimensions.
In one dimension\, there is metamagnetism above \na critical coupling rati
o (Q/J )min. Metamagnetism is a first-order quantum phase transition \ncha
racterized by discontinuities in the magnetization as a function of field (
magnetization jumps). \n We derive an exact expression for (Q/J)min = 2/9\
, and show that the metamagnetism is caused by \nthe onset of attractive in
teractions between magnons (flipped spins on a polarized\nbackground). We
predict that the same mechanisms will produce metamagnetism in the unfrus
trated \nantiferromagnetic J1-J2 model with anisotropy. Below (Q/J)min\,\n
the saturation transition is continuous and we show that it is governed by
the expected zero-scale-factor universality. In two dimensions\, we also f
ind metamagnetism above a \ncritical coupling ratio (Q/J)min=0.417\, caused
by the same mechanism as in the one-dimensional \ncase. In two dimension
s we also show evidence of an anomalous temperature dependence of specific
\nheat arising from field-induced Bose-Einstein condensation of spinons at
the deconfined quantum \ncritical point.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171031T151501Z
DTSTART:20171113T173000Z
DTEND:20171113T183000Z
UID:event1827@bu.edu
URL:http://physics.bu.edu/events/show/1827
SUMMARY:"Fate and Chance in Microbial Communities"
DESCRIPTION:Featuring Zak Frentz\, Columbia University\nHosted by: Robert M
arsland\n\nPart of the Biophysics Seminars.\n\nMicrobial ecosystems are inf
luenced by random processes over many scales\, such as mutagenesis at the m
olecular scale\, phenotypic switching at the organismal scale\, and fluctua
tions in the external environment which can affect entire populations. It
is not generally known how strongly these random processes induce randomnes
s in population dynamics within communities. To separate deterministic tre
nds from random fluctuations requires making measurements over many replica
te systems\, with well controlled environmental and initial conditions. I'
ll discuss such measurements we made in the lab\, studying microbial ecosys
tems with three different experimental setups\, and the potentially surpris
ing implications for the role of randomness in microbial ecology.
LOCATION:CILSE 106C\, 610 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171114T161116Z
DTSTART:20171117T170000Z
DTEND:20171117T180000Z
UID:event1859@bu.edu
URL:http://physics.bu.edu/events/show/1859
SUMMARY:"A Bosonization Puzzle in Non-linear Transport"
DESCRIPTION:Featuring Carlos Bolech\, University of Cincinnati\n\nPart of t
he Condensed Matter Theory Seminar Series.\n\nIn this talk\, we will critic
ally reexamine the bosonization-debosonization procedure for systems includ
ing localized features or boundaries. First\, by focusing on the case of a
tunneling junction out of equilibrium\, we will show that the conventional
bosonization approach can give results that are not consistent with a direc
t solution of the problem even at the qualitative level when higher-order p
rocesses are considered. Thus highlighting possible inconsistencies that ca
n adversely affect the results of all types of calculations. We will subseq
uently report on a "consistent bosonization-debosonization" procedure that
we have developed to resolve this non-linear transport puzzle and argue tha
t it should be widely applicable [1]. This new framework takes the form of
additional considerations\, related to the regularization of fermionic bili
nears\, that supplement the conventional bosonization procedure and it can
be carried over to the study of other systems. We will then discuss its app
lication to the two-lead Kondo junction [2]\, that besides being a key theo
retical prototype of a non-equilibrium strongly correlated system is also o
f continuing experimental relevance. The discussion will be focused on the
Toulouse limit of that problem. \n\nReferences:\n[1] Nayana Shah and C. J.
Bolech\, Phys. Rev. B 93\, 085440 (2016).\n[2] C. J. Bolech and Nayana Sha
h\, Phys. Rev. B 93\, 085441 (2016).
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171113T145328Z
DTSTART:20171120T173000Z
DTEND:20171120T183000Z
UID:event1856@bu.edu
URL:http://physics.bu.edu/events/show/1856
SUMMARY:"A Quantitative View of RTK Signaling"
DESCRIPTION:Featuring Adrian Whitty\, Boston University\, Chemistry Departm
ent\nHosted by: Maria Kamenetska\n\nPart of the Biophysics Seminars.\n\n
LOCATION:CILSE 106C\, 610 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171116T215342Z
DTSTART:20171120T184500Z
DTEND:20171120T194500Z
UID:event1855@bu.edu
URL:http://physics.bu.edu/events/show/1855
SUMMARY:Kibble-Zurek Dynamics of a Driven Dissipative System: Universality
Beyond the Markovian Regime
DESCRIPTION:Featuring Renzo Tamiro Villazon Scholer\n\nPart of the Prelimin
ary Oral Exam.\n\nExamining Committee: Anushya Chandran\, Anatoli Polkovni
kov\, Wanzheng Hu\, and Liam Fitzpatrick\n\nAbstract:\n\n\nDriven-disipativ
e phase transitions in open systems provide a rich avenue for the study of
many-body non-equilibrium phenomena. These systems exhibit unique propertie
s depending on the detailed nature of their system-bath interactions\, whic
h may nontrivially alter their critical dynamics\, and which are amenable t
o study by slow ramps across the critical point. In this talk\, I will disc
uss Kibble-Zurek dynamics in a paradigmatic two-mode driven-dissipative sys
tem of a pair of non-degenerate parametrically coupled\, optomechanical osc
illators. I will detail the key theoretical aspects of the model and it's p
redictions on universality\, which have been confirmed in experiments by ou
r collaborators in the Vengalattore group at Cornell University.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171121T204744Z
DTSTART:20171127T213000Z
DTEND:20171127T230000Z
UID:event1862@bu.edu
URL:http://physics.bu.edu/events/show/1862
SUMMARY:PY 107 Physics of Food/Cooking Guest Lecture
DESCRIPTION:Featuring Janine Sciarappa\, Pastry Chef\nHosted by: Rama Bansi
l\, Karl Ludwig\nPoster: http://physics.bu.edu//files/download/Rama-Poster1
.pdf\n\nJanine Sciarappa is a pastry chef / instructor with over 20 years o
f experience in the food business. She teaches pastry classes in Boston Un
iversity’s Certificate Program in the Culinary Arts and the Graduate Prog
ram in Gastronomy at Metropolitan College\, and the School of Hospitality A
dministration.
LOCATION:SCI 117\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171120T184031Z
DTSTART:20171128T173000Z
DTEND:20171128T183000Z
UID:event1834@bu.edu
URL:http://physics.bu.edu/events/show/1834
SUMMARY:"Design\, control\, and applications of DNA nanomechanical devices"
DESCRIPTION:Featuring Carlos Castro \, Ohio State University \nHosted by: M
aria Kamenetska\n\nPart of the Biophysics Seminars.\n\nStructural DNA nanot
echnology is a rapidly emerging field with exciting potential for applicati
ons such as single molecule sensing\, drug delivery\, and manipulating mole
cular components. However\, realizing the functional potential of DNA nanom
achines\, and ultimately nanorobots\, requires the ability to design dynami
c mechanical behavior such as complex motion\, conformational dynamics\, or
force generation. Our lab has developed approaches to design and construct
DNA nanostructures with programmable 1D\, 2D\, and 3D motion as well as dy
namic nanostructures with programmed or externally controlled conformationa
l dynamics. We have also recently developed methods to manipulate dynamic D
NA nanodevices via external magnetic fields. This approach relies on coupli
ng the motion of micron-scale magnetic beads to nanoscale DNA machines via
a long mechanical lever arm made from an array of highly stiff DNA origami
structures. We demonstrated the ability to drive continuous or oscillating
rotational motions of nanoscale devices up to several Hz. Moving forward\,
we aim to develop devices where nanoscale dynamic behavior (i.e. motion\, c
onformational distributions\, and kinetics) can be exploited to probe physi
cal properties or manipulate nanoscale components or molecular interactions
in real time. I will also highlight two ongoing projects in our lab implem
enting DNA nanodevices to probe the structure and dynamics of nucleosomes a
nd to engineer cell surface functions such as intercellular adhesion and bi
omolecule sensing.
LOCATION:CILSE 106B\, 610 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171129T180150Z
DTSTART:20171201T170000Z
DTEND:20171201T180000Z
UID:event1863@bu.edu
URL:http://physics.bu.edu/events/show/1863
SUMMARY:"Learning and optimizing quantum control landscapes"
DESCRIPTION:Featuring Alexandre Day\, Boston University\, Department of Phy
sics\n\nPart of the Condensed Matter Theory Seminar Series.\n\nThe ability
to prepare quantum states rapidly and with high fidelity is crucial for qua
ntum technologies. In this talk I will discuss the control problem of a cha
in of coupled qubits. In particular we will see that there exist phase tran
sitions in the quantum state preparation problem and a possible mapping to
a spin-glass model. We will also touch on how various optimization methods\
, including reinforcement learning\, can help discover novel preparation pr
otocols and in particular we will consider their robustness and their resou
rce requirements.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171120T195143Z
DTSTART:20171201T183000Z
DTEND:20171201T193000Z
UID:event1861@bu.edu
URL:http://physics.bu.edu/events/show/1861
SUMMARY:Asset Contagion as a Source of Systemic Risk in Banking Networks
DESCRIPTION:Featuring Alexander Becker\n\nPart of the Departmental Seminars
.\n\nCommittee: H. Eugene Stanley\, Irena Vodenska\, Kevin Black\, Bill Kle
in\, Manher Jariwala\n\nAbstract:\n\nWe study the European banking system b
y constructing a bipartite network of banks and assets\, observing that the
banks form a core-periphery structure with strong regional bias. We model
how common exposures\, for example portfolio overlap\, influence shock prop
agation through the banking system. We show that the system as currently re
gulated is robust to exogenous shocks as long as market participants are ra
tional. However\, the current framework fails to protect the banking networ
k from big losses if market participants become risk-averse. In fact\, the
system undergoes a phase transition in which the perceived asset risk is th
e critical parameter.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171201T164740Z
DTSTART:20171204T153000Z
DTEND:20171204T163000Z
UID:event1864@bu.edu
URL:http://physics.bu.edu/events/show/1864
SUMMARY:"Quantum Hall Ferromagnetism in $\nu=0$ Bilayer Graphene"
DESCRIPTION:Featuring Ganpathy Murthy\, University of Kentucky\nHosted by:
Anushya Chandran\n\nPart of the Condensed Matter Theory Seminar Series.\n\n
In the presence of a quantizing magnetic field\, the lowest energy manifold
of bilayer graphene (BLG) has spin\, valley\, and a two-fold orbital degen
eracy. Experimentally\, it can be tuned by applying a parallel magnetic fie
ld and by applying a perpendicular electric field\, which tends to polarize
the layers. At charge neutrality\, which corresponds to $\nu=0$\, the syst
em can choose among a rich set of possible ground states based on the effe
ctive interactions and external tuning parameters. We will set up a simple
model Hamiltonian containing symmetry-allowed terms and analyze it in the H
artree-Fock approximation to obtain several potential ground states\, some
of which have been obtained before (such as the canted antiferromagnet and
the fully layer polarized phase) and one which has not. This new ground sta
te breaks two different U(1) symmetries spontaneously\, and could appear as
an intermediate phase between the canted antiferromagnet and the fully lay
er polarized phases.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171204T143213Z
DTSTART:20171204T173000Z
DTEND:20171204T183000Z
UID:event1843@bu.edu
URL:http://physics.bu.edu/events/show/1843
SUMMARY:"Simulating electron transfer in biomolecules: magnetosensing by cr
yptochromes"
DESCRIPTION:Featuring Ksenia Bravaya \, Boston University\, Chemistry Depar
tment\nHosted by: Maria Kamenetska\n\nPart of the Biophysics Seminars.\n\nC
ryptochromes are a diverse class of flavoproteins involved in a variety of
biological processes\, e.g. circadian clock regulation\, phototropism. An i
ntriguing question concerning these protoreceptors is their possible involv
ement in a light-dependent magnetoreception in insects and animals. Using c
omputational chemistry tools we explore the mechanism of cryptochromes’ p
hotoactivation and analyze the effect of the Earth’s magnetic field on th
eir photophysics. To this aim\, we are interested in developing ab initio t
echniques for perturbative treatment of spin-spin\, spin-orbit\, and hyperf
ine interactions based on the EOM-CC family of methods.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171204T215759Z
DTSTART:20171206T133000Z
DTEND:20171206T140000Z
UID:event1860@bu.edu
URL:http://physics.bu.edu/events/show/1860
SUMMARY:RIVETING TWO-DIMENSIONAL MATERIALS: EXPLORING STRAIN PHYSICS IN ATO
MICALLY THIN CRYSTALS WITH MICROELECTROMECHANICAL SYSTEMS
DESCRIPTION:Featuring Jason Christopher\, Boston University\, Department of
Physics\n\nPart of the PhD Final Oral Exams.\n\nABSTRACT\nTwo dimensional
(2D) materials can withstand an order of magnitude more strain than their b
ulk counterparts\, which results in dramatic changes to electrical\, therma
l and optical properties. These changes can be harnessed for technological
applications such as tunable light emitting diodes or field effect transis
tors\, or utilized to explore novel physics like exciton confinement\, pseu
do-magnetic fields (PMFs)\, and even quantum gravity. However\, current te
chniques for straining atomically thin materials offer limited control over
the strain field\, and require bulky pressure chambers or large beam bendi
ng equipment. This dissertation describes the development of micro-electrom
echanical systems (MEMS) as a platform for precisely controlling the magnit
ude and orientation of the strain field in 2D materials. MEMS are a versat
ile platform for studying strain physics. Mechanical\, electrical\, thermal
and optical probes can all be easily incorporated into their design. Furt
her\, because of their small size and compatibility with electronics manufa
cturing methods\, there is an achievable pathway from the laboratory bench
to real-world application. Nevertheless\, the incorporation of atomically
thin crystals with MEMS has been hampered by fragile\, non-planer structure
s and low friction interfaces. We have innovated two techniques to overcom
e these critical obstacles: micro-structure assisted transfer to place the
2D materials on the MEMS gently and precisely\, and micro-riveting to creat
e a slip-free interface between the 2D materials and MEMS. With these advan
cements\, we were able to strain monolayer molybdenum disulfide (MoS2) to g
reater than 1% strain with a MEMS for the first time. The dissertation dev
elops the theoretical underpinnings of this result including original work
on the theory of operation of MEMS chevron actuators\, and strain generated
PMFs in transition metal dichalcogenides\, a large class of 2D materials.
We conclude the dissertation with a roadmap to guide and inspire future ph
ysicists and engineers exploring strain in 2D systems and their application
s. The roadmap contains ideas for next-generation fabrication techniques t
o improve yield\, sample quality\, and add capabilities. We have also incl
uded in the roadmap proposals for experiments such as a speculative techniq
ue for realizing topological quantum field theories that mimics recent theo
retical wire construction methods.\n\n![Jason](/resources/event-image/1860/
c555177_small)
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171205T143400Z
DTSTART:20171206T173000Z
DTEND:20171206T183000Z
UID:event1871@bu.edu
URL:http://physics.bu.edu/events/show/1871
SUMMARY:"The mode and predictability of intra-tumour evolution"
DESCRIPTION:Featuring Rob Noble\, ETH Zürich\n\nPart of the Biophysics Sem
inars.\n\nIntra-tumour genetic heterogeneity is a product of evolution in s
patially structured populations of cells. Whereas genetic heterogeneity has
been proposed as a prognostic biomarker in cancer\, its spatially dynamic
nature makes accurate prediction of tumor progression challenging. Progress
ing from the Eden growth model to spatial versions of the Moran process\, I
will characterize how tissue architecture influences the potential for sub
clonal population growth\, the prevalence of clonal sweeps\, and the result
ing pattern of intratumour heterogeneity. Based on computational simulation
s\, I will further describe the conditions under which genetic diversity is
most predictive of future tumour states. These findings help explain the m
ultiformity of tumour evolution and contribute to establishing a theoretica
l foundation for predictive oncology.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171204T215818Z
DTSTART:20171206T200000Z
DTEND:20171206T210000Z
UID:event1866@bu.edu
URL:http://physics.bu.edu/events/show/1866
SUMMARY:Nucleation in Supercooled Liquids
DESCRIPTION:Featuring Rashi Verma\, Boston University\, Department of Physi
cs\n\nPart of the Departmental Seminars.\n\nDissertation Committee: William
Klein\, Thomas Keyes\, Harvey Gould\, Rama Bansil and Kevin Black\n\nAbstr
act:\n\nNucleation is the process by which the metastable phase decays into
the stable phase. It is widely observed in nature\, and is responsible for
many phenomena like cloud formation and crystal growth. The classical theo
ry of nucleation predicts that the objects that initiate the decay from the
metastable to the stable phase are compact droplets of the stable phase. F
or quenches deep into the metastable phase\, however\, the droplets may be
ramified\, with a structure very different from the stable phase. This has
significant implications for material properties.\n\nI study nucleation via
molecular dynamics simulation of Lennard-Jonesium\, a model system for liq
uid-solid transformations. The system is quenched from a high temperature\,
where the liquid is stable\, to a lower temperature\, where the liquid is
metastable\, and allowed to nucleate via fluctuation-driven clusters referr
ed to as critical droplets. I will present a study of the structure of the
critical droplet\, and my attempts to probe it using indirect methods. I wi
ll show evidence that the presence of a hitherto unstudied 'planar' structu
re has a significant influence on the nucleation and growth of the critical
droplet.\n\n![Rashi](/resources/event-image/1866/9b03dac_small)
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171207T160336Z
DTSTART:20171208T170000Z
DTEND:20171208T180000Z
UID:event1872@bu.edu
URL:http://physics.bu.edu/events/show/1872
SUMMARY:"The Cluster Truncated Wigner Approximation in Strongly Interacting
Quantum Systems"
DESCRIPTION:Featuring Jonathan Wurtz\, Boston University\, Department of Ph
ysics\n\nPart of the Condensed Matter Theory Seminar Series.\n\nQuantum man
y-body systems exhibit a rich set of interesting behavior\, from many body
localization to thermalization. However\, existing methods are lacking a w
ay to describe generic out-of-equilibrium dynamics of such systems\, mainly
due to the exponential complexity of large systems. In this seminar\, I de
scribe work done on describing non-equilibrium dynamics of strongly interac
ting quantum systems from the perspective of phase space. Within this persp
ective\, linear quantum dynamics with exponential DoF is replaced with appr
oximate nonlinear classical dynamics with polynomial DoF. I will also descr
ibe some results and behavior of the method\, including entanglement growth
and spreading\, and the change between quantum and classical behavior.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171128T165801Z
DTSTART:20171211T170000Z
DTEND:20171211T180000Z
UID:event1865@bu.edu
URL:http://physics.bu.edu/events/show/1865
SUMMARY:DYNAMICAL PROPERTIES OF CLASSICAL AND QUANTUM SPIN SYSTEMS
DESCRIPTION:Featuring Na Xu\n\nPart of the PhD Final Oral Exams.\n\nExamini
ng Committee: Anders Sandvik\, Anatoli Polkovnikov\, Claudio Chamon\, Alex
Sushkov\, Robert Carey\n\nAbstract:\n\nThe Kibble-Zurek mechanism (KZM) wa
s originally proposed to describe the evolution\nand "freezing" of defects
in the early universe\, but later it was generalized to study other\nquantu
m and classical systems driven by a varying parameter. The basic idea behin
d the\nKZM is that\, as long as the changing rate (velocity) of the paramet
er is below a certain\ncritical velocity\, the system will remain adiabatic
(for quantum systems) or quasi-static\n(for classical systems). The non-eq
uilibrium finite-size scaling (FSS) method based on KZM\nhas been exploited
systematically. Through applying the scaling hypothesis\, we can extract\n
the critical exponents and study the dynamic properties of the system.\nIn
the rest few chapters of this dissertation\, we discuss the applications of
KZM in several\nclassical systems: first\, we study the dynamics of 2D and
3D Ising model under a varying\ntemperature as well as a varying magnetic
eld. Secondly\, we examine the classical Z2 gauge\nmodel\, in which we show
that KZM also works for topological phase transitions. Moreover\,\nwe also
investigate the dynamics of other models with topological ordering only at
T = 0\,\nwhere KZM cannot be applied. Lastly\, we explore the 2D Ising spi
n glass with bimodal\nand gaussian couplings. With bimodal couplings\, we f
ind dual time scales associated with\nthe order parameter and the energy co
rrespondingly\, while in the gaussian case one unique\ntime scale is involv
ed.\nThe systems mentioned above are all classical and the dynamics are app
roached through\nsimulated annealing (SA)\, in which thermal uctuations dri
ves systems to explore the energy\nlandscape in finding the ground state. I
n the last chapter\, we explore the efficiency of Quantum Annealing (QA) \n
on a fully-connected spin glass (or Sherington-Kirkpatrick model)\nwith a t
ransverse field. QA is the counterpart of SA\, where quantum fluctuations d
rive the\nsystem toward the ground state when the quantum terms are reduced
. QA is currently\nwidely explored as a paradigm for quantum computing to s
olve optimization problems.\nHere we compare the scaling of the dynamics (w
ith system size) of the fully-connected spin\nglass through QA versus SA.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171214T152756Z
DTSTART:20171214T210000Z
DTEND:20171214T220000Z
UID:event1874@bu.edu
URL:http://physics.bu.edu/events/show/1874
SUMMARY:Holiday Party - Skit Event 2017
DESCRIPTION:Featuring Grad Council\n\nPart of the Graduate Student Council
Events.\n\n
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171214T175111Z
DTSTART:20171215T150000Z
DTEND:20171215T160000Z
UID:event1869@bu.edu
URL:http://physics.bu.edu/events/show/1869
SUMMARY:Alexander Sherman
DESCRIPTION:Featuring Alex Sherman\n\nPart of the Departmental Seminars.\n\
nDissertation Committee: Kevin Black\, John Butler\, Kenneth Lane\, Edward
Kearns\, Karl Ludwig\n\nAbstract:\n\nIn this talk I present findings for t
he measurement of a previously unconfirmed Standard Model (SM) process\, pr
oviding further evidence that the electroweak sector of the SM is well beha
ved. In order to study more rare and exotic particle behavior at the LHC\,
SM background processes must be searched out\, measured\, and understood. T
o identify new signals\, all of the backgrounds for a process must be under
stood\, and one of the largest background sources remaining to be measured
is a weakly produced single top quark produced in association with a Z boso
n. The measurement of such a process can be used in searches for flavor cha
nging neutral currents as well as possible direct production of yet undisco
vered particles. Here I present initial studies and results of such a searc
h and measurement.
LOCATION:PRB 595\, 3 Cummington Mall\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171127T161247Z
DTSTART:20171215T160000Z
DTEND:20171215T170000Z
UID:event1822@bu.edu
URL:http://physics.bu.edu/events/show/1822
SUMMARY:"Properties of Topological semimetals: Chiral magnetic effect and i
nstability under magnetic field"
DESCRIPTION:Featuring Xi Dai\, Hong Kong University of Science and Technolo
gy\nHosted by: Wanzheng Hu\n\nPart of the Condensed Matter Theory Seminar S
eries.\n\nIn the present talk\, I will introduce two important physical pro
perties of topological semimetals. The first one is the chiral magnetic eff
ect\, which is the direct consequence of the presence of Weyl points in the
band structures. I will introduce that the chiral magnetic effect can be d
etected by its coupling to certain phonon modes\, which behave like pseudo
scalars under point group transformations. Such coupling can generate reson
ance between the intrinsic plasmon oscillation and the corresponding phonon
modes\, leading to dramatic modification of the optical response by the ex
ternal magnetic field. The second one is the instability of topological sem
imetal phase under strong magnetic field. In Dirac semi-metal\, the quantum
limit can be easily reached under the magnetic field leading to two types
of phase instability caused by the high degeneracy of the topological zerot
h Landau bands (LBs)\, namely the charge density wave (CDW) phase and polar
ized nematic phase formed by exciton condensation. We also propose that bo
th the DC transport measurement and Raman scattering can be used to disting
uish the above two phases.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171211T160928Z
DTSTART:20171220T143000Z
DTEND:20171220T153000Z
UID:event1870@bu.edu
URL:http://physics.bu.edu/events/show/1870
SUMMARY:Constraints on Flavored 2d CFT Partition Functions
DESCRIPTION:Featuring Yuan Xin\n\nPart of the Preliminary Oral Exam.\n\nExa
mining Committee: Liam Fitzpatrick\, Ami Katz\, Robert Carey\, Christopher
Laumann\n\nAbstract:\n\nConformal Field Theory (CFT) relates to many open
questions in high-energy physics and condensed matter theory\, and brings u
s important insights into Quantum Gravity via the AdS/CFT correspondence. T
he conformal bootstrap is a powerful approach to CFT that allows one to stu
dy such theories beyond the weakly coupled regime\, using only basic univer
sal principles. In this project\, we perform a bootstrap analysis on all 2
dimensional CFTs with a conserved charge\, using the transformation law for
the modular transformation of the CFT’s partition function in the presen
ce of a chemical potential\, i.e. flavored partition function. First\, we u
se this law to put constraints on the CFT’s "mass-to-charge" ratio\, as w
ell as the weight of charged states in the theory. Then\, we apply the extr
emal functional method to extract the partition functions of the CFTs that
saturate the bounds. In several cases we find the prediction of the occupat
ion numbers are precisely integers\, which is necessary for a physical theo
ry. Our bounds provide a solid proof of the 3-dimensional Quantum Gravity c
ase of the Weak Gravity Conjecture\, and we find some previously inaccessib
le partition functions.
LOCATION:PRB 595\, 3 Cummington Mall\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20171215T101140Z
LAST-MODIFIED:20171211T142327Z
DTSTART:20171220T160000Z
DTEND:20171220T170000Z
UID:event1873@bu.edu
URL:http://physics.bu.edu/events/show/1873
SUMMARY:"Propagation of an impurity through a quantum medium"
DESCRIPTION:Featuring Mikhail Zvonarev\, LPTMS\, CNRS\, Orsay\, France\n\nP
art of the Condensed Matter Theory Seminar Series.\n\nI will report on rece
nt theoretical and experimental progress in understanding the dynamics of a
n impurity particle injected into a one-dimensional quantum liquid. I will
show that the momentum distribution of the impurity subject to a constant e
xternal force exhibits characteristic Bragg reflections at the edge of an e
mergent Brillouin zone. As a consequence\, the impurity exhibits periodic d
ynamics that is interpreted as Bloch oscillations\, which arise even though
the quantum liquid is translationally invariant. I will also discuss a qua
ntum flutter phenomenon\, whose essence is that the impurity injected into
a liquid with some initial momentum sheds only a part of it to the backgrou
nd gas\, and forms a correlated state that no longer decays in time; furthe
rmore\, if the initial momentum is large enough\, the impurity undergoes lo
ng-lived oscillations. The value of the impurity's velocity at infinite tim
e lies between zero and the speed of sound in the gas\, and is determined b
y the injection protocol. This way\, the impurity's frictionless motion is
a dynamically emergent phenomenon whose description goes beyond accounting
for the kinematic constraints of Landau's approach to superfluidity.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
END:VCALENDAR