The Noise Susceptibility of a Photo-excited Coherent Conductor

We report the theory of the \emph{dynamical response of current fluctuations} of a photo-excited conductor. We have performed the calculation for a coherent conductor described by arbitrary energy-dependent transmissions and for arbitrary frequencies. We consider two experimental setups that correspond to different ways of symmetrizing the current operators, leading to different predictions. Our results are in very good, quantitative agreement with a recent measurement. We demonstrate that the dynamical response of noise that we have calculated is the key concept that relates Dynamical Coulomb Blockade, i.e. the electron-electron correction to the conductance due to the presence of an external impedance, to quantum noise.