Editor's Summary
23 August 2007
Count photons with atoms
Quantum measurement projects a microscopic system into a state in which the observed quantity — previously uncertain — becomes precisely known. Its value is random, with a probability determined by the system's initial state. Such 'state collapse' can be progressive, accumulating the effects of elementary state changes. A step-by-step collapse of that type has now been observed by using light as the object of investigation, repeatedly interrogated by a stream of atoms that measures its photon number non-destructively. The procedure has all characteristics predicted for a quantum measurement and should facilitate studies of non-classical electromagnetic fields trapped in cavities.
News and Views: Quantum physics: Wave goodbye
When measuring photons, it's a case of 'wanted, dead' — catching them alive is not an option. But we can observe how a superposition of many photon waves progressively collapses as it interacts with a beam of atoms.
Luis A. Orozco
doi:10.1038/448872a
Article: Progressive field-state collapse and quantum non-demolition photon counting
Christine Guerlin, Julien Bernu, Samuel Deléglise, Clément Sayrin, Sébastien Gleyzes, Stefan Kuhr, Michel Brune, Jean-Michel Raimond & Serge Haroche
doi:10.1038/nature06057
