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Quantum Optics Group
Norman Bridge Laboratory of Physics
California Institute of Technology

With recent developments in optical cavity QED pioneered in the Quantum Optics Group at Caltech, optical physics has progressed to a domain wherein processes are driven by single atoms interacting with optical fields with average energy corresponding to much less than one photon. This unique situation opens doors for new and exciting phenomena which manifestly rely on the quantum nature of the atom-field interaction. The system that we have developed to access this realm consists of an atom strongly coupled to a single mode of a high finesse optical cavity (mirror reflectivity R = 0.9999984), for which a single atom can profoundly effect the cavity characteristics and the field associated with less than a single photon can saturate the atomic response.

Current research efforts:

Pictured is part of this experiment - a cesium MOT dropping onto a high-finesse cavity. The large white areas are mirror substrates, while the gap between mirrors which forms the cavity (an 8 micron gap) cannot be seen at this resolution. [For scale, the diameter of the mirrors at the narrow 'notch' is 1mm.]

Trapping single atoms with single photons
By making the coupling energy of the atom to the cavity, g, greater than kinetic energy of the atom, it has been possible for the first time to trap single atoms with a single-photon strength laser field. Visit more subpages for further details of the "atom-cavity microscope" and Quicktime movies of individual atom trajectories.
One exciting prospect is that by observing atoms passing through the standing wave structure of the cavity mode, it should be possible to approach the standard quantum limit for measurement of the atomic position.

Far off-resonant traps: a tool for confining atoms in cavities

Single atoms have been trapped inside a strongly-coupled cavity using a classical standing-wave dipole force trap, with a trap lifetime of 2-3 seconds obtained.
Having thus confined an atom so that it is available for interaction with a series of photons, we open up the possibility for interesting new experiments, such as the synthesis of single-photon states. This trapped atom is also a strong candidate for use in quantum computation schemes; for example, the two-level atomic structure could be used as a "qubit" to store information, or the nonlinear response of the atom-cavity system could be exploited as a "quantum phase gate."

Past research directions

Cavity QED with squeezed vacuum

Microsphere Cavities
Driven by the quest for yet higher cavity finesse in combination with small mode volume, we have also investigated microsphere cavities as a possible setting for extending our work with cold atoms. Shown on the right is a microsphere during fabrication. We have measured microsphere resonator quality factors of 2 to 3 billion.

Further information:

Overview: "Real-time Cavity QED with single atoms: Experiments in the strong coupling domain" (a short poster)

Tutorial: "Cavity QED with Strong Coupling -- Toward the Deterministic Control of Quantum Dynamics"(a long presentation)