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DTSTAMP:20260814T100259Z
LAST-MODIFIED:20121116T203436Z
DTSTART:20110429T160000Z
DTEND:20110429T170000Z
UID:event784@bu.edu
URL:http://physics.bu.edu/internal/events/show/784
SUMMARY:Elucidating the quantum measurement problem
DESCRIPTION:Featuring Theo Nieuwenhuizen\, Institute for Theoretical Physic
	s\, UvA\, Amsterdam\, The Netherlands\nHosted by: Paul Krapivsky\n\nPart of
	 the Biophysics/Condensed Matter Seminar Series.\n\nAbstract\nTextbooks des
	cribe ideal quantum measurements by two postulates: the collapse of the wav
	e packet and Born's rule for the probabilities of outcomes. The quantum evo
	lution of a system then has two components: unitary (Hamiltonian) in betwee
	n measurements and non-unitary when a measurement is performed. This split 
	was considered as unsatisfactory by many people\, including Einstein\, Bohr
	\, de Broglie\, von Neumann and Wigner. \nThe quantum measurement problem\,
	 that is\, understanding why a unique outcome is obtained in each individua
	l run of an experiment\, is tackled by solving a Hamiltonian model for a qu
	antum measurement within standard quantum statistical mechanics. The model 
	describes the measurement of the z-component of a spin through interaction 
	with a magnetic memory. The latter apparatus is modeled by a Curie-Weiss ma
	gnet having N >> 1 spins weakly coupled to a phonon bath. \nThe Hamiltonian
	 evolution exhibits several time scales. The reduction\, a rapid decay of t
	he off-diagonal blocks of the system-apparatus density matrix\, arises from
	 the many degrees of freedom of the pointer (the magnetization). The regist
	ration occurs due to a phase transition from the initial metastable state t
	o one of the final stable states\, triggered by the tested system. It yield
	s a stationary state in which the apparatus and the system are correlated. 
	Under proper conditions the process satisfies all features of ideal measure
	ments\, including collapse and Born's rule. The irreversibility of the meas
	urement is ensured by the large size of the apparatus. Nothing else than th
	e usual quantum statistical mechanics and Schrodinger equation is needed\, 
	and the results support a specific version of the statistical interpretatio
	n. The solution of the quantum measurement problem requires a combination o
	f the reduction and the registration\, the properties of which arise from t
	he irreversible dynamics. \nThis talk summarizes work done in last decade i
	n collaboration with Armen Allahverdyan of the Yerevan Physics Institute an
	d Roger Balian of the IPhT\, CEA Saclay.
LOCATION:SCI 352\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
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