Next weeks' seminars

[ICTP info point]

From: cm at ictp.it


									06/02

JOINT ICTP/SISSA CONDENSED MATTER SEMINARS
Academic Year 2005/06



SEMINAR ROOM - MAIN BUILDING   (first floor)



Wednesday, 15 March -     4:00 p.m.



S.N. MAYBUROV    (Lebedev Institute of Physics, Moscow )



" Quantum information, measurements and their applications in molecular 
biology "


	Abstract

The information-theoretical, dynamical and statistical aspects of 
quantum measurements are reviewed.  An example of dynamics of system is 
considered which includes the measured object S,  the information 
storing device O and its environment E.  From the 
information-theoretical viewpoint, the measurement is the transfer of 
information J from S to O with the possible J losses, due to O,E 
decoherent interactions.  It’s shown that the principal constraints, 
induced by Heisenberg commutation relations, restrict significantly the 
amount of  information J about S state which can be transferred to O in 
the individual event.  As a result an  ability of O to discriminate the 
different  S states is much weaker compared to the  predictions from 
the purely dynamical theory.  Such restrictions may explain 
experimentally observed stochasticity of measurement outcomes, i.e. the 
collapse of  quantum state.  The possible applications to molecular 
biology, bioelectronics and theory of brain functions are discussed.


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CONDENSED MATTER AND STATISTICAL PHYSICS SECTION
	
INFORMAL SEMINAR on

Disorder and strong electron correlations






Thursday, 16 March    -    11:00 a.m.




Room 239,  Main Bldg.- II floor



G. MUSSARDO    (International School for Advanced Studies, Trieste )



"Quantum spin chain and O(3) non-linear sigma model with theta-term"


	Abstract

Quantum anti-ferromagnetic chains admit a continuum formulation in 
terms of O(3) non-linear sigma model with topological theta term.  The 
massive (theta=0)  or massless (theta=pi) nature of this field theory 
is referred in the literature as Haldane conjecture.  Both values of 
theta correspond to integrable model, while for all other values the 
corresponding theory is not integrable.   In this talk we discuss the 
evolution of the spectrum by varying theta.  We show that the massless 
particles (spinons) present at theta=pi get confined once theta moves 
away from this value and that the spectrum consists of a stable triplet 
of massive particles for all values of theta and a singlet state of 
higher mass.  The singlet, however, is a stable particle only in an 
interval of values of theta close to pi, whereas it becomes a resonance 
below a critical value theta_c.