Charge relaxation and dephasing in Coulomb-coupled conductors

The dephasing time in coupled mesoscopic conductors is caused by the fluctu ations of the dipolar charge permitted by the long-range Coulomb interactio n. We relate the phase breaking time to elementary transport coefficients t hat describe the dynamics of this dipole: the capacitance, an equilibrium c harge relaxation resistance, and in the presence of transport through one o f the conductors a nonequilibrium charge relaxation resistance. The discuss ion is illustrated for a quantum point contact in a high magnetic field in proximity to a quantum dot.