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DTSTAMP:20261020T233838Z
LAST-MODIFIED:20141208T154813Z
DTSTART:20141210T143000Z
DTEND:20141210T153000Z
UID:event1345@bu.edu
URL:http://physics.bu.edu/internal/events/show/1345
SUMMARY:Phase Transitions\, Algorithms\, and the Applications to Quantum Co
	mputing
DESCRIPTION:Featuring Cheng-Wei Liu\n\nPart of the PhD Final Oral Exams.\n\
	nExamining Committee:  Anders Sandvik\, Anatoli Polkovnikov\, Claudio Chamo
	n\, Robert Carey\, Shyamsunder Erramilli\n\nAbstract:\nPhase transitions an
	d their associated critical phenomena are of\nfundamental importance and pl
	ay a crucial role in the development of\nstatistical physics for both class
	ical and quantum systems. Phase\ntransitions embody diverse aspects of phys
	ics and also have numerous\napplications outside physics\, e.g.\, in chemis
	try\, biology\, and\ncombinatorial optimization problems in computer scienc
	e. Many problems can\nbe reduced to a system consisting of a large number o
	f interacting agents\,\nwhich under some circumstances (e.g.\, changes of e
	xternal parameters)\nexhibit collective behavior; this type of scenario als
	o underlies phase\ntransitions.\n\nThe theoretical understanding of equilib
	rium phase transitions was put on\na solid footing with the establishment o
	f the renormalization group. In\ncontrast\, non-equilibrium phase transitio
	n are relatively less understood\nand currently a very active research topi
	c. One important milestone here\nis the Kibble-Zurek (KZ) mechanism\, which
	 provides a useful framework for\ndescribing a system with a transition poi
	nt approached through a\nnon-equilibrium quench process.\n\nI developed two
	 efficient Monte Carlo techniques for studying phase\ntransitions\, one is 
	for classical phase transition and the other is for\nquantum phase transiti
	ons\, both are under the framework of KZ scaling.\n\nFor classical phase tr
	ansition\, I develop a non-equilibrium quench (NEQ)\nsimulation that can co
	mpletely avoid the critical slowing down problem.\nFor quantum phase transi
	tions\, I develop a new algorithm\, named\nquasi-adiabatic quantum Monte Ca
	rlo (QAQMC) algorithm for studying quantum\nquenches. I demonstrate the uti
	lity of QAQMC quantum Ising model and\nobtain high-precision results at the
	 transition point\, in particular\nshowing generalized dynamic scaling in t
	he quantum system.\n\nTo further extend the methods\, I study more complex 
	systems such as\nspin-glasses and random graphs. The techniques allow us to
	 investigate the\nproblems efficiently. From the classical perspective\, us
	ing the NEQ\napproach I verify the universality class of the 3D Ising spin-
	glasses. I\nalso investigate the random 3-regular graphs in terms of both c
	lassical\nand quantum phase transitions. I demonstrate that under this simu
	lation\nscheme\, one can extract information associated with the classical 
	and\nquantum spin-glass transitions without any knowledge prior to the\nsim
	ulation.\n\n![Cheng-Wei](/resources/event-image/1345/8bef000_small)
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
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