CAVITY-MODIFIED SPONTANEOUS EMISSION - FROM RABI OSCILLATIONS TO EXPONENTIAL DECAY

We revisit the problem of spontaneous emission by a two-level system i n a cavity, concentrating in particular on those aspects associated wi th the finite propagation time of light between the atom and the cavit y boundaries. We find that spontaneous emission always occurs first at the free space rate and there is then an abrupt change in these dynam ics when light reflected by the cavity mirrors returns to the atom, le ading to interference effects that result either in an enhancement or a reduction of this rate or in a periodic exchange of excitation betwe en the atom and the cavity field. From this point of view, reversible spontaneous emission in terms of single-mode ''vacuum Rabi oscillation s'' can be interpreted as resulting from the interference between the multimode partial waves reflected at the cavity mirrors and the instan taneously radiated light.