Events at Physics |
Events on Wednesday, April 9th, 2008
- Atomic Physics Seminar
- Reconstructing the Wigner function of a photonic Schrodinger cat in a cavity: a movie of decoherence
- Time: 11:00 am
- Place: 5310 Chamberlin
- Speaker: Serge Haroche, Laboratoire Kastler Brossel
- Abstract: The development of super-high finesse cavities made of pairs of mirrors which bounce microwave photons back and forth for times up to a few tenths of a second has opened a new domain in quantum optics. It is now possible to "look" at stored light without destroying it, to prepare by quantum non-demolition (QND) measurements well-defined photons number states and to observe the quantum jumps between them(1). One can also generate and study mesoscopic non-classical states containing several photons, which survive long enough to be measured and fully characterized. We will describe how a single atom passing between mirrors trapping a coherent field prepares a superposition of photonic states with opposite phases. This state is called a "Schroedinger cat" by reference to the feline that the founding father of quantum physics imagined to be suspended in a superposition of life and death. This highly non-classical state is represented in phase space by a quasi-probability distribution, called Wigner function, which exhibits Gaussian peaks corresponding to its classical components (the "dead" and "alive" parts of the cat) along with interference fringes describing its quantum coherence. By performing QND measurements of the photon number parity, we have reconstructed these Wigner function and recorded the progressive disappearance of their interference features. Movies of the decoherence process are realized in this way, which directly illustrate how a mesoscopic system evolves from quantum to classical.
- Host: Deniz Yavuz