  We examine the resonant activation of a current-biased Josephson junction
near the crossover temperature in order to show the way in which the device
transitions from the classical regime to the quantum regime. We use microwaves
to probe the quantum energy states that exist in the potential well. The
quantum features are visible until the junction is heated up to the crossover
temperature, at which point the line widths of the energy levels overlap and
become indistinguishable from one another. When well above this temperature,
the junction behaves classically when resonantly activated with microwaves.
