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BEGIN:VEVENT
DTSTAMP:20171212T175628Z
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
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