Atom in a damped cavity

Consider two possible states of an atom, the ground state |g> and an excited state |e>, separated by an energy E. In free space, the state |e> would decay to |g> by spontaneous emission of a photon of energy E, leading to a lifetime t. Now imagine placing the atom in a cavity which only has a single mode of the electromagnetic field close to energy E. This is the problem of a two-level system coupled to a "harmonic oscillator": an atom initially in state |e> would undergo Rabi oscillations, in which the energy would oscillate between the atom and single photon mode in the cavity. In any realistic situation, however, these oscillations would eventually be damped by dissipation in the walls of the cavity, associated with the finite Q of the cavity mode. This paper described the influence of this dissipation on the Rabi oscillations. When the cavity Q becomes smaller than (Et)1/2, the Rabi oscillations disappear, and the energy of the atom simply decays into the cavity walls: this happens at a rate which is Q times faster than the decay rate of the atom in free space.

These results are reviewed, using the methods of the paper below, in the text book Quantum Optics by Marlan O. Scully and M. Suhail Zubairy, published by Cambridge University Press (1997). This work was recognized by the LeRoy Apker Award.


  1. Atom in a damped cavity by S. Sachdev, Physical Review A 29, 2627 (1984).