Quantum correlations over a large bandwidth in cascaded optical parametric system

Abstract

The availability of quantum entanglement and EPR steering over a large frequency will bring further flexibility to the linking of quantum processes at different wavelengths, especially related to quantum memory. In this paper, a cascaded optical parametric system, with three interacting modes spanning two octaves of frequency difference, is investigated. This process combine degenerate optical parametric oscillation (OPO) and second harmonic generation (SHG), which is shown to be a useful way to obtain the quantum entanglement and EPR steering at three differing frequencies. The results are shown that compared to the normal only SHG, the existence of the OPO interaction eliminates the selfpulsing effect, and the threshold conditions of single OPO interaction is also changed due to the presence of the SHG. Above or below threshold, the system exhibits different quantum correlations features. The tripartite entanglement are only violated above threshold. The entanglement and EPR steering are both present in two conditions, but the system behaves totally different at the threshold. The effect of the ratio of loss rates of the three modes on the quantum correlations is also investigated. It is shown that the symmetric property of the quantum EPR steering is controlled by these ratios. This system is flexible to be adjusted and controlled, which potentially provides a significant resource for quantum correlations over a large bandwidth.