BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Talks.cam//talks.cam.ac.uk// X-WR-CALNAME:Talks.cam BEGIN:VEVENT SUMMARY:Scott Lecture II - Quantum Interference - Prof Claude Cohen-Tannou dji\, Laboratoire Kastler Brossel\, Département de Physique de l'ENS DTSTART:20110309T160000Z DTEND:20110309T170000Z UID:TALK27256@talks.cam.ac.uk CONTACT:Leona Hope-Coles DESCRIPTION:Linear superpositions of states play a central role in quantum physics. We will show in these lectures that atomic physics offers the po ssibility to clearly explain with examples of increasing complexity how th ese linear superpositions of states\, also called atomic coherences\, give rise to quantum interference effects. In the first optical pumping experi ments performed a few decades ago\, it was observed that the pumping light could not only polarize the atoms by concentrating them in a certain Zeem an sublevel\, but also prepare them in linear superpositions of Zeeman sub levels. Several interesting effects involving these Zeeman coherences were discovered\, like quantum beats\, coherent multiple scattering\, level cr ossing resonances in atomic ground states\, dark resonances and coherent p opulation trapping. These effects were revisited a few decades later in di fferent contexts and found to play a crucial role in new fields\, like fem tochemistry\, laser cooling\, and light induced transparency. \nWhen laser cooling techniques gave the possibility to achieve large de Broglie wavel engths for the atomic centre of mass variables\, it became possible to stu dy the role of spatial coherences which are related to the existence of li near superpositions of states localized at different points in space. Seve ral well-known experiments in wave optics\, like Young's double slit inter ferences\, could be extended to atomic de Broglie waves. Furthermore by pl aying with the atomic internal variables\, it was possible to realize atom ic interferometers\, where the two paths of the interferometer differ\, no t only by the external variables of the centre of mass\, but also by the a tomic internal variables. These interferometers are presently the most pre cise devices for building atomic clocks and for measuring inertial fields\ , like those associated with gravity or rotation. \nFinally\, one can cons ider linear superpositions of states of two subsystems 1 and 2. When such linear superpositions cannot be written as a product of a state of system 1 by a state of system 2\, the two systems are in an entangled state\, whi ch can exhibit quantum correlations\, impossible to understand with the co ncepts of classical physics. Several quantum effects related to entangled states will be described and it will be shown how they are now playing an important role in discussions concerning quantum non separability\, the me asurement process\, the decoherence due to the coupling with the environme nt\, the possibility to use quantum correlations for transmitting and proc essing information\n LOCATION:Pippard Lecture Theatre\, Cavendish Laboratory\, Department of Ph ysics END:VEVENT END:VCALENDAR