Coupling Plasmonic Cavities to Quantum Emitters

Abstract

Nano-plasmonic devices can have a wide variety of applications that rely on strongly enhanced optical fields confined well below the diffraction limit. The applications could be surface-enhanced Raman scattering, nanoscale nonlinear optics, optical tweezing, large Purcell enhancement and fluorescence enhancement. Here first we demonstrated the fabrication of 10-nm gap silver bowtie apertures based on e-beam lithography and lift-off process, which are conventionally fabricated by lower-throughput focused ion beam. The aperture can have mode area as small as 0.002 (λ/n)$^2$, showing that they are good plasmonic nano-cavities for emitter coupling. Then, due to highly concentrated field, these bowtie apertures were used to optically trap individual, 30 nm silica coated quantum dots (scQD), with a relatively low continuous wave trapping flux of 1.56 MW/cm$^2$ at 1064 nm. This platform might enable single quantum dot absorption spectrum measurements. Last, we applied plasmonic nano-cavities for other quantum emitter, silicon vacancy (SiV) center in diamond. We designed circular plasmonic apertures to have Purcell enhancement on SiV center in diamond. SiV centers inside can have lifetime as short as 0.2 ns, which represents a $\sim$9-fold reduction over a $\sim$1.8 ns value typical for SiV in bulk diamond. Due to low internal quantum efficiency of SiV center, the Purcell enhancement could be larger than the measured lifetime reduction. Also, SiV in the plasmonic apertures can have linewidth as narrow as 330 MHz, which is comparable to the transform-limited linewidth. The spectral diffusion is within the linewidth ($\pm$ 100 MHz), showing that our devices can have applications in quantum optics.