Circuit Models for Small Signal Performance of Spin 1/2 Quantum Systems

Nanocircuits are composed of nanoelements interacting with external electromagnetic fields which are ultimately described in terms of voltages and currents or incident and reflected waves. Hence the necessity of describing their quantum performance in terms of circuit quantities. We present equivalent circuits for the small signal performance of a population of non-interacting spin 1/2 particles about passive and active equilibria induced by external pumping between the ground and the excited state, that describe respectively e.g. nuclear magnetic resonance and reflection amplification.