Quantum noise in ac-driven resonant-tunneling double-barrier structures: Photon-assisted tunneling versus electron antibunching

We study the quantum noise of the electronic current in a double-barrier system with a single resonant level. In the framework of the Landauer formalism, we treat the double barrier as a quantum coherent scattering region that can exchange photons with a coupled electric field, e.g., a laser beam or a periodic ac bias voltage. As a consequence of the manifold parameters that are involved in this system, a complicated steplike structure arises in the nonsymmetrized current-current autocorrelation spectrum and a peaklike structure in the cross-correlation spectrum with and without harmonic ac driving. We present an analytic solution for these noise spectral functions obtained by assuming a Breit-Wigner line shape. In detail, we study how the correlation functions are affected by photoassisted tunneling events and discuss the underlying elementary events of charge transfer, where we identify distinct contributions to the individual shot noise. This enables us to clarify the effects of noncentered irradiation of such a structure with light in terms of contributions originating from different sets of coherent scattering channels. Moreover, we show how the noise is influenced by acquiring a scattering phase due to the complex reflection amplitudes that are crucial in the Landauer approach.