Stochastic resonance in an electron-spin-nuclear-spin system

We report a realization of stochastic resonance, based on the intrinsic bistability of the magnetic resonance of conduction electrons in gallium oxide [E. Aubay and D. Gourier, Phys. Rev. B 47, 15 023 (1993); D. Gerbault and D. Gourier, ibid. 54, 6315 (1996)]. We show that the response to a small periodic magnetic field of the bistable conduction electron-spin-resonance signal can be amplified by the addition of an external random magnetic field. This is experimental evidence of stochastic resonance in the interaction of an electromagnetic field with an ensemble of two-level quantum systems (the Zeeman energy levels of free electrons).