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METHOD:PUBLISH
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190122T154151Z
DTSTART:20190130T210000Z
DTEND:20190130T220000Z
UID:event2070@bu.edu
URL:http://physics.bu.edu/events/show/2070
SUMMARY:How to Understand the Magic of Twisted Bilayer Graphene
DESCRIPTION:Featuring Noah F. Q. Yuan\, MIT\nHosted by: Zhicheng Yang\n\nPa
rt of the Biophysics/Condensed Matter Seminar Series.\n\nTwo layers of grap
hene rotated with respect to each other will form the twisted bilayer graph
ene (TBG). A year ago\, Pablo Jarillo-Herrero’s group at MIT found that T
BG at the so-called "magic angle" could become superconducting and insulati
ng. Since then\, more experimental data are accumulated. In this talk\, I w
ill try to understand how superconductivity and insulating phase emerge in
TBG at magic angle. Through weak coupling approach\, the so-called high-ord
er van Hove singularity (VHS) is found near magic angle\, which would lead
to unconventional superconductivity and density wave phases in the presence
of Coulomb repulsion. Through strong coupling approach\, the Wannier orbit
als are obtained for magic angle TBG\, whose nontrivial shape induces the e
xotic effective tight-binding model and extended Hubbard model.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190206T141653Z
DTSTART:20190208T170000Z
DTEND:20190208T180000Z
UID:event2071@bu.edu
URL:http://physics.bu.edu/events/show/2071
SUMMARY:Exciting bulk topological modes in photonic graphene
DESCRIPTION:Featuring Adrian Menssen\, University of Oxford\nHosted by: Cla
udio Chamon\n\nPart of the Biophysics/Condensed Matter Seminar Series.\n\nT
opological photonics sheds light on some of the surprising phenomena seen i
n condensed matter physics that arise with the appearance of topological in
variants. Optical waveguides provide a well-controlled platform to investig
ate effects that relate to different topological phases of matter\, providi
ng insight into phenomena such as topological insulators by direct simulati
on of the states that are protected by the topology of the system. Previous
work has largely focussed on the investigation of states that appear at th
e edge of domains which have different topological invariants. Here\, we o
bserve a mode associated with a topological defect in the bulk of a 2+1D ph
otonic material by introducing a vortex distortion to an hexagonal lattice
and analogous to graphene. Our photonic crystal is fabricated by writing wa
veguides in a glass substrate with a femtosecond laser using adaptive optic
s aberration correction. In order to excite the topological mode\, we devel
oped a method based on a SLM (Spatial Light Modulator) to simultaneously il
luminate multiple waveguides. This allows us to excite an optical mode cons
isting of more than a dozen waveguides with beams of independently controll
ed phase\, amplitude and mode-shape.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190207T181150Z
DTSTART:20190213T210000Z
DTEND:20190213T220000Z
UID:event2072@bu.edu
URL:http://physics.bu.edu/events/show/2072
SUMMARY:Gauge theory for the cuprates near optimal doping
DESCRIPTION:Featuring Harley Scammell\, Harvard University\nHosted by: Juli
an Ingham\n\nPart of the Biophysics/Condensed Matter Seminar Series.\n\nWe
describe a 2+1 dimensional SU(2) gauge theory for the hole-doped cuprates.
The gauge theory emerges upon fractionalization of the fluctuating incommen
surate spin density waves. Our primary assumption is that all low energy fe
rmionic excitations are gauge neutral and electron-like\, while the spin de
nsity wave order is fractionalized into Higgs fields transforming as adjoin
ts of the gauge SU(2). Under this assumption\, we argue that the SU(2) adjo
int Higgs theory is sufficiently rich to account for many key properties of
the cuprates observed experimentally. In particular\, this talk will focus
on the elusive psuedogap phase and offer a description in terms of deconfi
ned gauge theory.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190212T155414Z
DTSTART:20190215T170000Z
DTEND:20190215T180000Z
UID:event2085@bu.edu
URL:http://physics.bu.edu/events/show/2085
SUMMARY:Topological order: new states and new probes
DESCRIPTION:Featuring Gunnar Möller\, University of Kent\nHosted by: Claud
io Chamon\n\nPart of the Biophysics/Condensed Matter Seminar Series.\n\nSin
ce the identification of quantum Hall states as topological states of matte
r\, the search for new topological states of matter has been a central ende
avour. I will present the composite fermion theory of fractional quantum Ha
ll states in the Hofstadter model of interacting particles on a lattice exp
osed to a (synthetic) magnetic field [1]\, providing the numerical evidence
for Chern insulators [1\,2]. In this model\, new types of fractional quant
um Hall states can be formed due to the presence of higher Chern number ban
ds in the single-particle spectrum [2\,3].\n\nAnother crucial question rema
ins how to best probe topologically ordered phases in experiment\, besides
macroscopic properties such as quantised Hall conductance. I will discuss t
he topological marker [4] as an interesting local probe for topological ord
er\, and discuss how to use the marker to probe the critical properties of
topological phase transitions\, as well as its non-equilibrium dynamics aft
er a quantum quench through the transition [5]. Finally\, I will show how t
he topological marker can be inferred from measurements of the single-parti
cle density matrix [5].\n\n1.Möller\, G. & Cooper\, N. R. Composite Fermio
n Theory for Bosonic Quantum Hall States on Lattices. Phys. Rev. Lett. 103\
, 105303 (2009).\n2.Möller\, G. & Cooper\, N. R. Fractional Chern Insulato
rs in Harper-Hofstadter Bands with Higher Chern Number. Phys. Rev. Lett. 11
5\,\n126401 (2015).\n3.Andrews\, B. & Möller\, G. Stability of fractional
Chern insulators in the effective continuum limit of Harper-Hofstadter band
s with Chern number |C|>1. Phys. Rev. B 97\, 035159 (2018).\n4.Bianco\, R.
& Resta\, R. Mapping topological order in coordinate space.\nPhys. Rev. B 8
4\, 241106 (2011).\n5.Caio\, M. D.\, Möller\, G.\, Cooper\, N. R. & Bhasee
n\, M. J. Topological Marker Currents in Chern Insulators\, Nature Physics
315\, 1 (2019).
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190208T160156Z
DTSTART:20190220T210000Z
DTEND:20190220T220000Z
UID:event2073@bu.edu
URL:http://physics.bu.edu/events/show/2073
SUMMARY:Logarithmic growth of entanglement entropy in long-range systems
DESCRIPTION:Featuring Silvia Pappalardi\, SISSA\, Trieste Italy\nHosted by:
Anatoli Polkovnikov\n\nPart of the Biophysics/Condensed Matter Seminar Ser
ies.\n\nA number of recent studies of out-of-equilibrium quantum spin syste
ms with long-range interactions have reported numerical evidence of logarit
hmic growth in time of bipartite entanglement entropy [1\,2]. However\, an
analytical understanding of this observation is apparently lacking. In this
talk\, I will derive the analytical relation between bipartite entanglemen
t entropy and collective spin-squeezing in long-range spin systems in and o
ut of equilibrium\, and use it to elucidate the mechanism responsible for t
he logarithmic growth in time of entanglement entropy after a quench\, whic
h has been numerically observed in a number of recent studies. I will furth
er discuss the special cases of quenches to dynamical critical points\, in
which entanglement entropy increases linearly in time rather than logarithm
ically\, and relate these behaviors to the structure of the underlying semi
classical trajectories. All our analytical results agree with exact numeric
al computations\, and extend to systems with algebraically-decaying interac
tions with exponent α ≤ d\, where d is the system dimensionality. Our fi
ndings also provide access to experimental measurements of entanglement ent
ropy in this class of systems. \n\n[1] J Schachenmayer\, BP Lanyon\, CF Roo
s\, AJ Daley - Physical Review X\, 2013\n[2] A. S. Buyskikh\, M. Fagotti\,
J. Schachenmayer\, F. Essler\, and A. J. Daley\, Phys. Rev. A 93\, 053620 (
2016).\n[3] A.Lerose and S. Pappalardi. "Logarithmic growth of entanglement
entropy in out-of-equilibrium long-range systems." arXiv preprint arXiv:18
11.05505(2018).
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190221T165711Z
DTSTART:20190225T164500Z
DTEND:20190225T174500Z
UID:event2119@bu.edu
URL:http://physics.bu.edu/events/show/2119
SUMMARY:Aspects of entanglement growth after a quantum quench
DESCRIPTION:Featuring Tibor Rakovszky\, TU Munich\n\nPart of the Biophysics
/Condensed Matter Seminar Series.\n\nThe growth of entanglement plays a fun
damental role in the process of thermalization in closed quantum systems an
d has recently become amenable to experimental detection\, through the meas
urement of so-called higher Rényi entropies. In this talk I will show that
the behavior of such Rényi entropies can be qualitatively different from
that of the theoretically more studied von Neumann entropy; in particular I
will argue that the former grow sub-ballistically\, as the square root of
time\, in systems with diffusive transport. I provide evidence for this in
both a U(1) symmetric random circuit model and in a non-integrable spin cha
in\, where energy is the sole conserved quantity\, and interpret the result
s as a consequence of local quantum fluctuations in conserved densities. \n
In the second part of the talk I will discuss the dynamics of the entanglem
ent spectrum of small subsystems and use it to identify signatures of the d
ifferent dynamical velocities that control thermalization. In particular I
will show how the onset of level repulsion in the spectrum occurs at differ
ent timescales depending on the 'entanglement energy'\, and relate this to
the problem of operator spreading.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190225T215915Z
DTSTART:20190227T193000Z
DTEND:20190227T203000Z
UID:event2121@bu.edu
URL:http://physics.bu.edu/events/show/2121
SUMMARY:Spin-gapped phases in nanowires
DESCRIPTION:Featuring Tommy Li\, Niels Bohr Institute Copenhagen\nHosted by
: Julian Ingham\n\nPart of the Condensed Matter Theory Seminar Series.\n\nO
ne dimensional fermionic models with gapped collective spin modes have been
studied theoretically for decades\, but their physical realization in semi
conductor systems has remained elusive. These phases exhibit intriguing phy
sical properties more reminiscent of superconductors than ordinary metals.
I will propose some simple physical setups in semiconductor nanowires in wh
ich spin-gapped phases appear naturally due to the interplay between the or
bital physics of the wire and the three-dimensional Coulomb interaction\, a
nd are protected by the spatial symmetries of the wire. I will also discuss
phases occurring in multiband systems which exhibit topological properties
and host Majorana edge modes.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190226T213940Z
DTSTART:20190227T210000Z
DTEND:20190227T220000Z
UID:event2074@bu.edu
URL:http://physics.bu.edu/events/show/2074
SUMMARY:Steady-state superconductivity in electronic materials with repulsi
ve interactions
DESCRIPTION:Featuring Ollie Hart\, University of Cambridge\nHosted by: Clau
dio Chamon\n\nPart of the Biophysics/Condensed Matter Seminar Series.\n\nWe
study the effect of laser driving on a minimal model for a hexagonal two-d
imensional material with broken inversion symmetry.\nThrough the applicatio
n of circularly polarised light and coupling to a thermal free electron bat
h\, the system is driven into a nonequilibrium steady state with asymmetric
\, nonthermal carrier populations in the two valleys. We show that\, in thi
s nonequilibrium state\, interband superconducting correlations between ele
ctrons can develop both for attractive and repulsive electron-electron inte
ractions. We discuss how our results apply\, for example\, to a topical cla
ss of materials: the transition metal dichalcogenides (TMDs). This work ope
ns the door to inducing superconductivity in a range of materials that were
hitherto precluded from it.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190228T144552Z
DTSTART:20190228T160000Z
DTEND:20190228T170000Z
UID:event2122@bu.edu
URL:http://physics.bu.edu/events/show/2122
SUMMARY:Seeing beyond the light: Vison and photon electrodynamics in quantu
m spin ice
DESCRIPTION:Featuring Attila Szabó\, University of Cambridge\nHosted by: S
iddhardh Morampudi\n\nPart of the Condensed Matter Theory Seminar Series.\n
\nUnderstanding the nature and behaviour of excitations in quantum spin liq
uids\, and in topological phases of matter in general\, is of fundamental i
mportance and has proved crucial for experimental detection and characteris
ation of candidate materials. Current theoretical and numerical techniques\
, however\, have limited capabilities\, especially when it comes to studyin
g gapped excitations. In this talk\, I will discuss a semiclassical numeric
al method\, based on large-$S$ path integral approach\, to study a wide cla
ss of systems whose spin liquid behaviour is underpinned by perturbative ri
ng-exchange Hamiltonians. Our method can readily access both thermodynamic
and spectral properties.\n\nI will focus in particular on quantum spin ice
and its photon and vison excitations. After benchmarking the method against
existing results on photons\, we used it to characterise visons and their
thermodynamic behaviour. We find that visons form a weak electrolyte -- in
contrast to spinons in classical spin ice --\, that is\, vison pairs are th
e dominant population at low temperatures. This is reflected in the behavio
ur of thermodynamic quantities\, such as pinch point motifs in the relevant
correlators. Moreover\, visons appear to strongly hybridise with the photo
n background\, a phenomenon that gravely affects the way these quasiparticl
es may show up in inelastic response measurements.\n\nWe believe that gener
alisations of our method can substantially extend our understanding of quas
iparticles and their interplay in quantum spin ice and other quantum spin l
iquids\, quantum dimer models\, and lattice gauge theories in general.
LOCATION:PRB 261\, 3 Cummington Mall\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190130T143357Z
DTSTART:20190228T190000Z
DTEND:20190228T200000Z
UID:event2105@bu.edu
URL:http://physics.bu.edu/events/show/2105
SUMMARY:Onset of thermalization in the Hilbert space of isolated many-body
systems
DESCRIPTION:Featuring Felix Izrailev\, University of Puebla (Mexico) and Mi
chigan State University (USA)\nHosted by: David Campbell\n\nPart of the Bio
physics/Condensed Matter Seminar Series.\n\nWe study analytically and numer
ically the onset of thermalization in isolated quantum systems with interac
ting Bose and Fermi particles. To do this\, we use two models: one is the m
odel of N bosons interacting via two-body random interactions\, and the oth
er is the 1D integrable model of N spins-1/2. We show that in both models t
he thermalization emerges due to strong quantum chaos quantified in terms o
f chaotic structure of many-body eigenstates. One of the important results
is that in the quench dynamics the number of components in the wave functio
n (in the Hilbert space)\, increases exponentially in time provided the eig
enstates are strongly chaotic. We have developed an analytical approach all
owing one to show that the time scale of the exponential increase (which is
the same as the time scale for a complete thermalization) is proportional
to the number of particles. We also studied how the Bose-Einstein distribut
ion in the first model emerges in time\, thus demonstrating the creation of
quantum correlations in the process of a complete relaxation. We discuss h
ow this process can be described with the use of the Kolmogorov-Sinai entro
py for the systems with a well-defined classical limit. The results allow u
s to suggest a new approach to the problem of quantum-classical corresponde
nce for many-body systems.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190214T152517Z
DTSTART:20190301T170000Z
DTEND:20190301T180000Z
UID:event2087@bu.edu
URL:http://physics.bu.edu/events/show/2087
SUMMARY:Topological spin excitations in a three-dimensional antiferromagnet
DESCRIPTION:Featuring Yuan Li\, Peking University\, International Center fo
r Quantum Materials\, China\nHosted by: Wanzheng Hu\n\nPart of the Biophysi
cs/Condensed Matter Seminar Series.\n\nThe recent discovery of topological
semimetals\, which possess distinct electron-band crossing in the bulk and
novel surface states\, has stimulated intense research interest. By extendi
ng the notion of symmetry-protected band crossing into one of the simplest
magnetic groups\, namely by including the symmetry of time-reversal followe
d by space-inversion\, we predict the existence of topological magnon-band
crossing in three-dimensional antiferromagnets [1]. The crossing may take t
he forms of Dirac points and nodal lines\, in the presence and absence\, re
spectively\, of the conservation of the total spin along the ordered-moment
direction. In a concrete example of a Heisenberg spin model for a "spin-we
b" compound\, Cu3TeO6\, we theoretically demonstrate the presence of Dirac
magnons over a wide parameter range using linear spin-wave approximation. I
nelastic neutron scattering experiments have been carried out to detect the
bulk magnon-band crossing in a single-crystal sample [2]. The highly inter
connected nature of the spin-1/2 network suppresses quantum fluctuations an
d facilitates our experimental observation\, leading to remarkably clean ex
perimental data with very good agreement with the theoretical calculations.
The predicted topological Dirac points are confirmed. Further studies will
be discussed\, including determination of non-collinear spin canting in th
e magnetic ground state of Cu3TeO6 and search for the topological magnon su
rface states.\n\n[1] K. Li et al.\, PRL 119\, 247202 (2017).\n[2] W. Yao et
al.\, Nature Physics 14\, 1011 (2018).
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190214T155832Z
DTSTART:20190308T170000Z
DTEND:20190308T180000Z
UID:event2065@bu.edu
URL:http://physics.bu.edu/events/show/2065
SUMMARY:Quantum Materials: Full of Frustration and Correlations
DESCRIPTION:Featuring Martin Dressel\, University of Stuttgart\nHosted by:
Wanzheng Hu\nPoster: http://physics.bu.edu//files/download/M.-Dressel.pdf\n
\nPart of the Biophysics/Condensed Matter Seminar Series.\n\nThe pioneering
work on geometrical frustration dates back to the 1920s\, when Linus Pauli
ng realized that the hydrogen bonds between H2O molecules in ice can be all
ocated in multiple ways. A given oxygen atom in water ice is situated at th
e vertex of a diamond lattice and has four nearest-neighbor oxygen atoms\,
each connected via an intermediate proton according to the ice rule "two-in
two-out". Although these considerations used electric dipoles\, Phil Ander
son mapped them to a spin model possessing an extensive degeneracy of state
s.\nQuantum spin liquids attract great interest due to their exceptional ma
gnetic properties characterized by the absence of long-range order down to
low temperatures despite the strong magnetic interaction. Commonly these co
mpounds are strongly correlated electrons systems\, and their electrodynami
c response is governed by the Mott gap in the excitation spectrum. \nHere w
e will summarize and discuss the optical properties of several two-dimensio
nal quantum spin liquid candidates with different degrees of effective corr
elations. Placing organic molecules on a triangular lattice\, a spin liquid
ground state can be realized which allows us to investigate the genuine Mo
tt state in the absence of magnetic order. Combining our optical data with
pressure-dependent transport studies and theoretical calculations\, we can
construct a universal phase diagram of the correlation-controlled Mott insu
lator. \nBut how important is the coupling of the fluctuating magnetic mome
nts? How important is disorder for the electronic properties? If this resem
bles a quantum phase transition\, is there a superconducting phase found in
the vicinity and what is the superconducting glue? Can our findings be gen
eralized\, when going to a kagome or hexagonal lattice\, realized in Herber
t-smithites or -RuCl3 for instance?
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190125T180035Z
DTSTART:20190320T200000Z
DTEND:20190320T210000Z
UID:event2075@bu.edu
URL:http://physics.bu.edu/events/show/2075
SUMMARY:CM Seminar TBA
DESCRIPTION:Featuring Ian Mondragon-Shem\, Yale University\nHosted by: Phil
ip Crowley\n\nPart of the Biophysics/Condensed Matter Seminar Series.\n\n
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190207T184030Z
DTSTART:20190322T160000Z
DTEND:20190322T170000Z
UID:event2088@bu.edu
URL:http://physics.bu.edu/events/show/2088
SUMMARY:Study of protein corona for polymeric drug delivery systems
DESCRIPTION:Featuring Sergey Filippov\, Harvard University\nHosted by: Rama
Bansil\n\nPart of the Biophysics/Condensed Matter Seminar Series.\n\nPolym
er drug carriers based on N-(2-Hydroxypropyl)methacrylamide (HPMA) copolyme
rs bearing cholesterol moieties have been studied extensively over the past
few years\, to understand the aggregation behavior and shape of the copoly
mers in dilute aqueous solutions [1\,2]. Above certain concentration\, mice
lle-like nanoparticles (NPs) having ellipsoidal shape are observed. However
\, there is a lack of knowledge on the behavior of these drug carriers in h
uman blood environment. Human serum albumin (HSA)\, fibrinogen\, Imunoglobu
lin G\, and apolipoproteins A-E were chosen for this study as basic protein
s\, which are the main component of human blood plasma. We use fluorescence
life-time correlation spectroscopy (FLCS)\, Electron Paramagnetic Resonanc
e (EPR)\, isothermal titration calorimetry (ITC)\, nuclear magnetic resonan
ce (NMR)\, and small angle X-ray scattering (SAXS) to investigate HPMA cop
olymers that are dissolved in an aqueous solution of proteins to reveal the
interaction between the NPs and proteins [3\,4].\n\n[1] S. K. Filippov\, e
t al.\, Biomacromolecules\, 2012\, 13\, 2594\n[2] S. K.Filippov\, et al.\,
Biomacromolecules\, 2013\, 14\, 4061\n[3] Xiaohan Zhang\, \,\,\, Sergey K
. Filippov\, Christine M. Papadakis\, Langmuir\, 2018\, 34 (27)\, 7998-8006
.\n[4] Damir Klepac\,\,\,\,\, Sergey K. Filippov\, Nanoscale\, 2018\, 10
(13)\, 6194-6204.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190325T171407Z
DTSTART:20190403T200000Z
DTEND:20190403T210000Z
UID:event2077@bu.edu
URL:http://physics.bu.edu/events/show/2077
SUMMARY:Floquet-engineering counterdiabatic protocols in quantum many-body
systems
DESCRIPTION:Featuring Pieter Claeys \, Boston University\, Physics Departme
nt\n\nPart of the Biophysics/Condensed Matter Seminar Series.\n\nCounterdia
batic driving is a way of generating adiabatic dynamics at arbitrary pace\,
where excitations due to non-adiabaticity can be exactly compensated using
the adiabatic gauge potential. However\, obtaining and implementing this g
auge potential in many-body systems is a formidable task\, requiring knowle
dge of the spectral properties of the instantaneous Hamiltonians and contro
l of highly nonlocal multibody interactions. We show how an approximate gau
ge potential can be built up as a series of nested commutators\, which can
be easily obtained and used to systematically suppress excitations. This ga
uge potential can then be generated up to arbitrary order using tools from
periodically-driven (Floquet) systems through resonant oscillations of the
instantaneous Hamiltonian with the driving term\, such that approximate cou
nterdiabatic driving protocols can be realized without leaving the availabl
e control space. This is illustrated on few- and many-body quantum systems\
, where the resulting Floquet protocols provide a drastic increase in fidel
ity and suppressed dissipation.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190411T172615Z
DTSTART:20190412T160000Z
DTEND:20190412T170000Z
UID:event2091@bu.edu
URL:http://physics.bu.edu/events/show/2091
SUMMARY:Fault-Tolerant Dynamic Hamiltonian Engineering of Spin Ensembles
DESCRIPTION:Featuring Joonhee Choi\, Harvard University\nHosted by: Alexand
er Sushkov\n\nPart of the Biophysics/Condensed Matter Seminar Series.\n\nRo
bust control of quantum dynamics lies at the heart of many applications of
quantum physics\, ranging from quantum metrology to many-body quantum simul
ations. Periodic (Floquet) driving is a powerful tool for engineering bare
system Hamiltonians into desired target Hamiltonians while suppressing unwa
nted coupling to the environment. However\, the fidelity of such Hamiltonia
n engineering is typically limited due to imperfections and inhomogeneities
both in the system itself and in the manipulation of the quantum state. Ro
bust ensemble spin engineering in disordered systems with strong interactio
n and imperfect spin control thus remains an open challenge. We introduce a
powerful framework for the design of pulse sequences that are fault-tolera
nt to imperfections\, for reliable and efficient quantum control of interac
ting many-body systems. Our formalism treats leading order imperfection eff
ects in a simple fashion and uses a description of the system based on time
-domain transformations of the S^z Pauli spin operator. We use the formalis
m to design control sequences for the protection of quantum coherence\, for
optimal quantum sensing and for the simulation of engineered many-body Ham
iltonians\, all realized in the presence of interactions and imperfections.
Our method is applicable to a wide range of physical systems with differen
t dominant energy scales and we demonstrate its efficacy by implementing ro
bust sequences in a dense ensemble of nitrogen-vacancy centers in diamond.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190409T215043Z
DTSTART:20190417T200000Z
DTEND:20190417T210000Z
UID:event2079@bu.edu
URL:http://physics.bu.edu/events/show/2079
SUMMARY:Measurement-driven entanglement transition in hybrid quantum circui
ts
DESCRIPTION:Featuring Xiao Chen\, KITP\n\nPart of the Biophysics/Condensed
Matter Seminar Series.\n\nIn this talk we explore "hybrid" quantum circuit
models in one-dimension with both unitary and measurement gates\, focussing
on the entanglement properties of wavefunction trajectories at long times\
, in the steady state. We simulate a large class of Clifford circuits\, inc
luding models with or without randomness in the unitary gates\, and with or
without randomness in the locations of measurement gates\, using stabilize
r techniques to access the long time dynamics of systems up to 512 qubits.
In all models we find a volume law entangled phase for low measurement rate
s\, which exhibits a sub-dominant logarithmic behavior in the entanglement
entropy\, S_A = {\alpha} \log |A| + s|A|\, with sub-system size |A|. With i
ncreasing measurement rate the volume law phase is unstable to a disentangl
ed area law phase\, passing through a single entanglement transition at a c
ritical rate of measurement. At criticality we find a purely logarithmic en
tanglement entropy\, S_A = {\alpha}(p_c) \log|A|\, a power law decay and co
nformal symmetry of the mutual information\, with exponential decay off cri
ticality. Various spin-spin correlation functions also show slow decay at c
riticality\, providing possible experimental access. Critical exponents are
consistent across all models\, indicative of a single universality class.
These results suggest the existence of an effective underlying statistical
mechanical model for the entanglement transition. Beyond Clifford circuit m
odels\, numerical simulations of up to 20 qubits give consistent results.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190411T170956Z
DTSTART:20190419T160000Z
DTEND:20190419T170000Z
UID:event2092@bu.edu
URL:http://physics.bu.edu/events/show/2092
SUMMARY:Quantum fluctuations and uncertainty relations in NLS solitons and
breathers
DESCRIPTION:Featuring Oleksandr Marchukov\, Tel Aviv University and UMASS B
oston\nHosted by: Anatoli Polkovnikov\n\nPart of the Biophysics/Condensed M
atter Seminar Series.\n\nWe consider the quantum fluctuations of the macros
copic variables associated with a breather\, \na second-order soliton solut
ion of nonlinear Schrödinger equation. Linearizing the evolution \nof the
bosonic quantum field around the Bose condensate in a breather state\,\nwe
express the quantum fluctuations of the macroscopic variables through the f
luctuations \nof the full quantum field. We evaluate the initial quantum un
certainties of the macroscopic parameters and\ntheir time evolution. We fin
ally describe how the macroscopic fluctuations affect the time evolution of
the \natomic density and estimate the propagation time needed for an expe
rimental detection of the predicted effects.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190422T185120Z
DTSTART:20190424T200000Z
DTEND:20190424T210000Z
UID:event2080@bu.edu
URL:http://physics.bu.edu/events/show/2080
SUMMARY:Propagation of an impurity through a quantum medium
DESCRIPTION:Featuring Mikhail Zvonarev \, Paris Saclay\nHosted by: Anatoli
Polkovnikov\n\nPart of the Biophysics/Condensed Matter Seminar Series.\n\nI
will discuss the equilibrium momentum distribution function of a single di
stinguishable impurity particle immersed in a gas of either free fermions o
r Tonks-Girardeau bosons in one spatial dimension. I will construct a Fred
holm determinant representation for exactly solvable model of a repulsive a
nd attractive impurity-gas $\delta$-function interaction potential\, at zer
o temperature. The resulting distribution is characterized by fourth power
decay at a large momentum\, and a weakly divergent (quasi-condensate) peak
at a finite momentum. I will also discuss the steady state of the impurity
past the injection into the gas. I will show that the value of the impurity
's velocity at infinite time lies between zero and the speed of sound in th
e gas\, and is determined by the injection protocol. This way\, the impurit
y's frictionless motion is a dynamically emergent phenomenon whose descript
ion goes beyond accounting for the kinematic constraints of Landau's approa
ch to superfluidity.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190425T171957Z
DTSTART:20190426T160000Z
DTEND:20190426T170000Z
UID:event2094@bu.edu
URL:http://physics.bu.edu/events/show/2094
SUMMARY:A journey through magnetic memory
DESCRIPTION:Featuring Karine Chesnel\, Brigham Young University\nHosted by:
Karl Ludwig\n\nPart of the Biophysics/Condensed Matter Seminar Series.\n\n
Magnetic memory is a key component in the development of magnetic storage n
anotechnologies. Magnetic domain memory (MDM) is the ability exhibited by c
ertain ferromagnetic thin films to reproduce the exact same nanoscale magne
tic domain pattern after it has been erased by an external magnetic field.
I will review the various circumstances under which this unusual phenomenon
occurs. We will see how MDM was first observed in rough Co/Pt multilayers
as a result of disorder. I will then describe how 100 % MDM can be achieved
even in smooth ferromagnetic films\, by coupling the film to an antiferrom
agnetic template through exchange interactions at low temperature (1). I wi
ll review the persistence of MDM through field cycling and through warming.
Additionally\, we will discuss the spatial dependence of MDM\, highlightin
g intriguing oscillatory behaviors revealing magnetic correlations and rota
tional symmetries at the nanoscopic and microscopic scales.(2) Finally\, we
will review the dependence of MDM on cooling conditions\, revealing how MD
M can be fully controlled\, turned on and off\, by adjusting the magnitude
of the cooling field.(3) \n \n \n(1) K. Chesnel\, E.E Fullerton\, J.B. Kort
right & S. Kevan\, PRB 78\, 132409 (2008) (2) K. Chesnel\, J. Nelson\, S. K
evan & E.E. Fullerton\, PRB 83\, 054436 (2011) (3) K. Chesnel\, A. Safsten\
, M. Rytting & E.E Fullerton\, Nature Comm\, 7\, 11648 (2016)
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190205T211445Z
DTSTART:20190503T160000Z
DTEND:20190503T170000Z
UID:event2106@bu.edu
URL:http://physics.bu.edu/events/show/2106
SUMMARY:The last jigsaw piece of phase diagrams of polymer solutions – Th
e Universal Scaling
DESCRIPTION:Featuring Prof. Chi Wu\, Wei Lun Professor of Chemistry; The Ch
inese University of Hong Kong\nHosted by: Ophelia Tsui\nPoster: http://phys
ics.bu.edu//files/download/5-3-2019BPCM.pdf\n\nPart of the Biophysics/Conde
nsed Matter Seminar Series.\n\n
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
BEGIN:VEVENT
DTSTAMP:20190619T032410Z
LAST-MODIFIED:20190506T194254Z
DTSTART:20190508T150000Z
DTEND:20190508T160000Z
UID:event2135@bu.edu
URL:http://physics.bu.edu/events/show/2135
SUMMARY:Local constraints can globally shatter Hilbert space
DESCRIPTION:Featuring Vedika Khemani\, Harvard University\nHosted by: Anato
li Polkovnikov\n\nPart of the Biophysics/Condensed Matter Seminar Series.\n
\nThe dynamics of constrained systems is a subject of much recent interest.
In this talk\, I will show how local constraints can globally "shatter" Hi
lbert space into subsectors\, leading to an unexpected dynamics with featur
es reminiscent of both many body localization and quantum scars. A crisp ex
ample of this phenomenon is provided by a "fractonic circuit" - a model of
quantum circuit dynamics in one dimension constrained to conserve both char
ge and dipole moment. I will show how the Hilbert space of the fractonic ci
rcuit dynamically fractures into disconnected emergent subsectors within a
particular charge and dipole symmetry sector. A large number of the emergen
t subsectors\, exponentially many in the size of the system\, have dimensio
n one and exhibit strictly localized quantum dynamics---even in the absence
of spatial disorder and in the presence of temporal noise. I will prove th
at exponentially large localized subspaces exist for any one dimensional fr
actonic circuit with finite spatial range\, providing a potentially new rou
te for the robust storage of quantum information. The shattering of a part
icular symmetry sector into a distribution of dynamical subsectors with var
ying sizes leads to the coexistence of high and low entanglement states\, i
.e. this provides a general mechanism for the production of quantum many bo
dy scars. I will discuss the detailed pattern of fracturing and its implica
tions.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
END:VEVENT
END:VCALENDAR