Nonlinear coupling and radiation damping in oscillator-detected magnetic resonance of single spins

We consider the effects of close coupling between magnetic spin systems and oscillator detectors. The scaling of present experiments using both mechanical and electrical oscillator detectors for single-spin detection is examined. We show how nonlinear interactions ignored in previous descriptions may dominate the detector response in single-spin schemes using mechanical detectors. From a generalized form of the coupled Bloch equations, the difference between mechanical and electrical oscillator detection can be readily appreciated. Numerical solution of the coupled system using reasonable experimental parameters shows that complex dynamics may be observed in the single-spin detection scheme when the detector and the spin system are strongly coupled. The interpretation of spin system data obtained from the motion of a mechanical oscillator will require understanding of these detector effects. Chaotic regimes are predicted in extreme cases. These results help both in identifying realistic limits of sensitivity for mechanical oscillator-detected magnetic resonance and in designing experimental methods to realize those limits.