Negative conductances of Josephson junctions: Voltage fluctuations and energetics

We study a resistively and capacitively shunted Josephson junction, which is driven by a combination of time-periodic and constant currents. Our investigations concern three main problems: (A) the voltage fluctuations across the junction; (B) the quality of transport expressed in terms of the Péclet number; and (C) the efficiency of energy transduction from external currents. These issues are discussed in different parameter regimes that lead to: (i) absolute negative conductance; (ii) negative differential conductance; and (iii) normal, Ohmic-like conductance. Conditions for optimal operation of the system are studied.