Resonance fluorescence assisted by plasmonic nanostructures

The interaction between plasmonic nanostructures and fluorescent molecules is a field of intense research that spans from chemistry to nanosciences. Within a collaboration with Peking University, we are trying to develop more accurate models to describe this interaction in a way such that quantum effects can be described. In a recent publication, the resonance fluorescence of a two-level single molecular system interacting with a plasmonic nanostructure is investigated. Specific regions of space are identified, where a balance exists between the near-field enhancement and the modification of the decay rate, such that the fluorescence spectrum of the molecule exhibits the Mollow triplet and the emission photons are antibunched. The utilization of such quantum phenomena at the vicinity of custom-designed plasmonic nanostructures paves the way for applications in nanoscale quantum devices and quantum information processing.

(a) Schematic and (b) absorption of a silver nanostructure composed of four nanostrips. Each nanostrip has dimensions 110x50x40 nm3 and each gap is 50 nm wide. The electric field is propagating along the x direction and is polarized along the z direction. The plasmon resonance wavelength is at λ=590 nm. (c) Dressed states diagram for a two-level DBATT molecule with Rabi splitting ΩR. The resonance wavelength between excited and ground levels is also λ=590 nm and matches the plasmon resonance wavelength. (d) Fluorescence spectra for single molecules with and without plasmonic structure, computed in the middle of the xy plane 50 nm above the metal surface.

We have found conditions where the Mollow triplet and photon antibunching of molecular fluorescence can be realized in plasmonic nanostructures. These effects require a subtle balance between the near-field enhancement and the modification of the lifetime caused by the nanostructure. In order to obtain high-quality resonance fluorescence spectra of single molecules, the designed system must satisfy two conditions: (i) the resonance wavelength of plasmonic structure must be similar to that of the molecules; (ii) the molecules must be located within optimal regions with a large near-field enhancement and a small modification of the decay rate. Let us mention that this is the first attempt to use the near-field enhancement of plasmonic nanostructures realize quantum effects. This work shall pave the way for applications in nanoscale quantum devices and quantum information processing.

Check the corresponding publication: PDF External link: doi: 10.1103/PhysRevB.81.193103