A Nanowire Optical Nanocavity For Broadband Enhancement Of Spontaneous Emission

To deliver an optimal performance for photonic quantum technologies, semiconductor quantum dots should be integrated in a carefully designed photonic structure. Here, we introduce a nanowire optical nanocavity designed for free-space emission. Thanks to its ultrasmall mode volume, this simple structure offers a large acceleration of spontaneous emission (predicted Purcell factor of 6.3) that is maintained over a 30-nm bandwidth. In addition, a dielectric screening effect strongly suppresses the emission into the 3D continuum of radiation modes. The fraction of spontaneous emission funneled into the cavity mode reaches 0.98 at resonance and exceeds 0.95 over a 100-nm spectral range. Close-to-optimal collection efficiency is maintained over an equivalent bandwidth and reaches a predicted value of 0.54 at resonance for a first lens with a numerical aperture (NA) of 0.75. As a first experimental demonstration of this concept, we fabricate an Au-SiO2-GaAs device embedding isolated InAs quantum dots. We measure a maximal acceleration of spontaneous emission by a factor as large as 5.6 and a bright quantum dot emission (collection efficiency of 0.35 into NA=0.75). This nanowire cavity constitutes a promising building block to realize advanced sources of quantum light for a broad range of material systems.