Effects of dephasing and dissipation on quantum noise in conductors

We consider the nonequilibrium quantum noise of electrical current in one-dimensional conductors, and clarify the mechanism that distinguishes macroscopic conductors from mesoscopic conductors. The noise does not become of the macroscopic type even when a strong dephasing is introduced. Macroscopic noise is obtained only when the energy of the total electron system is maximally dissipated when each electron traverses the conductor. Energy transfer from the electron system to other systems is therefore essential for noise suppression and for the noise to be macroscopic.