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BEGIN:VEVENT
DTSTAMP:20261020T034813Z
LAST-MODIFIED:20180716T170742Z
DTSTART:20180717T160000Z
DTEND:20180717T173000Z
UID:event1961@bu.edu
URL:http://physics.bu.edu/internal/events/show/1961
SUMMARY:Dynamics of quantum measurement and the measurement problem.
DESCRIPTION:Featuring Theo M. Nieuwenhuizen\, Institute for Theoretical Phy
	sics University of Amsterdam\n\nPart of the Condensed Matter Theory Seminar
	 Series.\n\nQuantum mechanics allows ideal measurements to be treated by po
	stulates\, which has led to various postulate-based interpretations of vary
	ing merit.\n \nIn a laboratory a measurement is performed with a physical a
	pparatus.\nMuch can be learned from solving the Curie-Weiss model for quant
	um measurement\, where the z-component of a spin 1/2 is measured with a Cur
	ie-Weiss magnet.\n \nIn this exactly solvable model the which-basis questio
	n and the ready-state of the apparatus find obvious meanings. Three dynamic
	al mechanisms have been identified:\n1) truncation of the density matrix (d
	isappearance of off-diagonal "Schrodinger cat" terms)\n2) registration\, wh
	ere the macroscopic pointer benefits from a first order phase transition\n3
	) subensemble relaxation inside the magnet\, after decoupling it from the s
	pin\n \nWhile 1) and 2) are concordant with the postulates\, 3) is related 
	to the quantum measurement problem:\nhow can one describe individual events
	 in the ensemble approach? While this is trivial classically (a coin lies f
	ace up or down)\, it is considered to be unsolvable within quantum mechanic
	s.\nOur approach nevertheless allows to formulate minimal postulates to con
	nect to the reality in laboratories.\n \nThe Born rule is connected to indi
	cations of the macroscopic magnet\, while the state of the microscopic spin
	 is inferred from it. Most "quantum probabilities" should be left without i
	nterpretation.\nThe frequency interpretation emerges from the addition rule
	 for density matrices.
LOCATION:SCI 328\, 590 Commonwealth Avenue\, 02215
STATUS:CONFIRMED
CLASS:PUBLIC
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