SUPERCONDUCTING JOSEPHSON-JUNCTION OF FINITE CAPACITANCE IN A LOSSLESS CAVITY - A PLAUSIBLE 2-LEVEL SYSTEM WITH A GIANT COUPLING-CONSTANT

We shall present our theoretical studies of a Josephson junction of sm all size in a lossless cavity. When the size of two superconductors ar e at order of micrometres and the Josephson coupling constant is adjus ted to the correct magnitude, the Josephson junction is found to be re duced to a two-level system owing to the finite-size effect and the qu enching of the low-lying single-electronic excitations by the supercon ducting gap. When such a two-level system is placed in a high-quality microwave cavity, the coupling constant with a single photon g may be extremely large, for instance of the order of 10(8) s(-1). On the othe r hand, the damping rate of the cavity field is much less than g. Ther efore, this two-level system may be used to study the quantum nature o f photons and to control the dynamics of quantum fields in the framewo rk of the Jayne-Cummings model much more easily.