GENERATION OF A POPULATION-INVERSION BETWEEN QUANTUM STATES OF A MACROSCOPIC VARIABLE

A population inversion has been created between the two adjacent fluxo id wells (with energy difference epsilon) in an rf SQUID subject to we ak radiation at 100 GHz. The states in the two wells have opposite cur rents, of magnitude similar to 2 mu A, circulating through an inductan ce of 0.2 nH. The steady state population of the upper well n(u)(epsil on) shows local maxima whose positions correspond to calculated photon absorption resonances between the ground state and an intermediate st ate, The maximum n(u)(epsilon) is 0.94 compared to the expected therma l equilibrium value of n(u)(epsilon) = 2 X 10(-9).