  We present results for the dynamics of an impurity spin coupled to a magnetic
field and to two ohmic baths which are out-of equilibrium due to the
application of a bias voltage. Both the non-equilibrium steady state and the
rate constants describing the approach to steady state are found to depend
sensitively on the relative strengths of a magnetic field and a voltage
dependent decoherence rate. Computation of physical quantities including the
frequency dependent ratio of response to correlation functions and the
probabilities of the two spin states allows the extraction of voltage dependent
effective temperatures. The temperatures extracted from different quantities
differ from one another in magnitude and their dependence on parameters, and in
general are non-monotonic.

Mesoscale and Nanoscale Physics