Course 2 Mesoscopic state superpositions and decoherence in quantum optics

École d'été de physique théorique, D. Estève, J. M. Raimond +2 more

Course 1. Principles of quantum computation, by Isaak Chuang Course 2. Mesoscopic state superpositions and decoherence in quantum optics, by S. Haroche Course 3. Cavity quantum electrodynamics, by M. Brune Course 4. Quantum optical implementation of quantum information processing, by P. Zoller, J.I. Cirac, Luming Duan and J.J. Garcia-Ripoll Course 5. Quantum information processing in ion traps I, by R. Blatt, H. Haffner, C.F. Roos, C. Becher and F. Schmidt-Kaler Course 6. Quantum information processing in ion traps II, by D.J. Wineland Course 7. Quantum cryptography with and without entanglement, by N. Gisin and N. Brunner Course 8. Quantum cryptography: from one to many photons, by Philippe Grangier Course 9. Entangled photons and quantum communication, by M. Aspelmeyer, C. Brukner and A. Zeilinger Course 10. Nuclear magnetic resonance quantum computation, by J.A. Jones Course 11. Introduction to quantum conductors, by D.C. Glattli Course 12. Superconducting qubits, by Michel H. Devoret and John M. Martinis Course 13. Superconducting qubits and the physics of Josephson junctions, by John M. Martinis Course 14. Josephson quantum bits based on a Cooper pair box, by Denis Vion Course 15. Quantum tunnelling of magnetization in molecular nanomagnets, by W. Wernsdorfer Course 16. Prospects for srtong cavity quantum electrodynamics with superconducting cirquits, by S.M. Girvin, R.-S. Huang, A. Blais, A. Wallraff andf R.J. Schoelkopf

B. Krämer

J. M. Raimond, M. Brune, S. Haroche

We describe the blueprint of an experiment in which the decoherence of a mesoscopic superposition of radiation states (``Schr\"odinger cat'') becomes a reversible process. When the high $Q$ cavity containing the Schr\"odinger cat is coupled to another resonator, the mesoscopic quantum coherence first decays rapidly, then exhibits sharp revivals with the period of the energy exchange between the two cavities. The interpretation of this experiment emphasizes the link between decoherence and complementarity and leads to an illuminating quantitative interpretation of the usual irreversible decoherence phenomenon.

L. Davidovich

Thiago Guerreiro

We propose a protocol for preparing mechanical Schrödinger kittens -- mesoscopic quantum superpositions of coherent motional states of an optically levitated nanoparticle -- by adhering single electron time-bin states to its surface. Over short protocol timescales, coherence of the mesoscopic superposition survives the dominant decoherence mechanisms afflicting levitated systems, and can be observed by varying the phase of the time-bin electrons. Interference fringes can be detected with real-time, near-Heisenberg limited interferometry of photons scattered from the particle. This approach eliminates the need for coherent state expansion, dark potentials, and particle release-and-recapture mechanisms, providing a new route to test quantum mechanics in unprecedented scales.

Roy J. Glauber