NOISE IN AN AC BIASED JUNCTION - NONSTATIONARY AHARONOV-BOHM EFFECT

We study excess noise in a quantum conductor in the presence of constant voltage and alternating external field. Because of a two-particle interference effect caused by Fermi correlations the noise is sensitive to the phase of the time-dependent transmission amplitude. We compute spectral density and show that at T = 0 the noise has singular dependence on the dc voltage V and the ac frequency OMEGA with cusplike singularities at integer eV/hOMEGABAR. For a metallic loop with an alternating flux the phase sensitivity leads to an oscillating dependence of the strength of the cusps on the flux amplitude.