Hybrid graphene - silver nanoantenna to control THz emission from polar quantum systems

Fluorescent light emission from atomic quantum systems routinely occurs at the illumination frequency. If the system is polar, an additional fluorescence peak appears at a much lower Rabi frequency, which scales with the illumination field amplitude. This opens the possibility of spectrally controlling the emission, promising tunable coherent radiation sources. However, typically the emission occurs in the MHz to GHz regimes, and its intensity from a single quantum system is relatively low. Here, we propose a hybrid nanoantenna combining noble-metal and graphene elements, exploited for an unusual goal: The silver elements spectrally tune the emission frequency of the molecule and shift it to the THz band, where novel sources of coherent radiation are still desired. Additionally, the graphene elements are used to plasmonically enhance the emission intensity. Their tunability allows for adjustment of the operational frequencies of the device to the illumination conditions and to counteract the fluctuations related to the field modulations in space. All these features are discussed based on the real-life example of a polar molecule of barium monofluoride (BaF).