Rydberg atoms and cavities: measurements and manipulations of quantum fields

S. Haroche

Circular Rydberg atoms, detected by the very sensitive and state selective field ionization method, can be used to measure and manipulate quantum fields stored in a cavity. The method is based on an interferometric detection of the dispersive energy shifts experienced by these atoms when they interact with a slightly off‐resonant field mode sustained by a cavity which the atoms cross one at a time. These shifts give rise to a translation of the Ramsey fringe pattern observed in the field ionization signal of the atoms. The method consitutes a non‐destructive way of photon counting. In this experiment, non local correlations between the atom and the cavity field are created, which could be used to perform new types of Einstein‐Podolsky‐Rosen experiments. Non classical fields could also be generated, which would display some of the properties discussed by Schrödinger in his famous ‘‘cat paradox.’’ We present the theory of these experiments which until very recently would have been considered as mere ‘‘gedanken’’ ones and we describe the operation of a Rydberg atom interferometer which has already enabled us to detect subphoton fields and to measure vacuum field effects in a cavity.

Mary R. Kutteruf

Santosh Kumar, Charles Ewel, Jonathon A. Sedlacek +1 more

J. M. Raimond, M. Brune, Ferdinand Schmidt‐Kaler +1 more

The dispersive interaction between a circular Rydberg atom and a superconducting millimeter-wave cavity creates an entangled quantum state of these two systems. Due to the long lifetime of the atomic levels and of the field, this correlation survives a long time after the atom has crossed the cavity mode. This situation is reminiscent of the EPR paradox, with non-local correlations between two subsystems. A quantum measurement performed on one part of this entangled state yields thus information on the other part.

Eugene Oks

J. M. Raimond, M. Brune, S. Haroche +6 more

Long lived circular Rydberg atoms interacting with high finesse superconducting cavities offer unique opportunities to perform tests on fundamental quantum mechanics. “Schrödinger cats”, multiparticle nonlocal correlations, “quantum teleportation” offer striking illustrations of the less intuitive aspects of quantum mechanics. At the heart of these experiments is the dispersive atom‐cavity interaction. We present its experimental manifestations, with the measurement of single photons light shifts and of Lamb shifts due to a single, empty, cavity mode. We then describe some possible extensions of this experiment, some of which being under way in our laboratory.