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CATEGORIES:Scott Lectures
SUMMARY:Scott Lecture I - Quantum Interference - Prof Clau
 de Cohen-Tannoudji\, Laboratoire Kastler Brossel\,
  Département de Physique de l'ENS
DTSTART;TZID=Europe/London:20110307T160000
DTEND;TZID=Europe/London:20110307T170000
UID:TALK27255AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/27255
DESCRIPTION:Linear superpositions of states play a central rol
 e in quantum physics. We will show in these lectur
 es that atomic physics offers the possibility to c
 learly explain with examples of increasing complex
 ity how these linear superpositions of states\, al
 so called atomic coherences\, give rise to quantum
  interference effects. In the first optical pumpin
 g experiments performed a few decades ago\, it was
  observed that the pumping light could not only po
 larize the atoms by concentrating them in a certai
 n Zeeman sublevel\, but also prepare them in linea
 r superpositions of Zeeman sublevels. Several inte
 resting effects involving these Zeeman coherences 
 were discovered\, like quantum beats\, coherent mu
 ltiple scattering\, level crossing resonances in a
 tomic ground states\, dark resonances and coherent
  population trapping. These effects were revisited
  a few decades later in different contexts and fou
 nd to play a crucial role in new fields\, like fem
 tochemistry\, laser cooling\, and light induced tr
 ansparency. \nWhen laser cooling techniques gave t
 he possibility to achieve large de Broglie wavelen
 gths for the atomic centre of mass variables\, it 
 became possible to study the role of spatial coher
 ences which are related to the existence of linear
  superpositions of states localized at different p
 oints in space. Several well-known experiments in 
 wave optics\, like Young's double slit interferenc
 es\, could be extended to atomic de Broglie waves.
  Furthermore by playing with the atomic internal v
 ariables\, it was possible to realize atomic inter
 ferometers\, where the two paths of the interferom
 eter differ\, not only by the external variables o
 f the centre of mass\, but also by the atomic inte
 rnal variables. These interferometers are presentl
 y the most precise devices for building atomic clo
 cks and for measuring inertial fields\, like those
  associated with gravity or rotation. \nFinally\, 
 one can consider linear superpositions of states o
 f two subsystems 1 and 2. When such linear superpo
 sitions cannot be written as a product of a state 
 of system 1 by a state of system 2\, the two syste
 ms are in an entangled state\, which can exhibit q
 uantum correlations\, impossible to understand wit
 h the concepts of classical physics. Several quant
 um effects related to entangled states will be des
 cribed and it will be shown how they are now playi
 ng an important role in discussions concerning qua
 ntum non separability\, the measurement process\, 
 the decoherence due to the coupling with the envir
 onment\, the possibility to use quantum correlatio
 ns for transmitting and processing information\n
LOCATION:Pippard Lecture Theatre\, Cavendish Laboratory\, D
 epartment of Physics
CONTACT:Leona Hope-Coles
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