Simultaneous high Q/V-ratio and optimized far-field emission pattern in diamond slot-bridge nanobeam cavity

Abstract

We present a design for a slot-bridge nanobeam cavity that supports ultrahigh Q/V and optimized far-field emission pattern, and operates at the zero-phonon transition (637nm) of the nitrogen-vacancy color centers in diamond. The slot-bridge cavity is formed by introducing a diamond bridge at the center of the air region of a slotted cavity. As a result of the boundary condition on the parallel component of the electric field, the electric field in the bridge region is the same as that in the slot. This results in a further reduction of the mode volume. Optimized slot-bridge cavities with a calculated Q factor of 6×106 and mode volume of Veff=0.28(λ/n)3have been realized. In comparison to nanobeam cavities, the mode volume is reduced by a factor of 139. The far-field pattern of a slot-bridge cavity is optimized by using the band folding method and by adding small air-slot extensions to the two closest air-holes surrounding the cavity. A high Q of 9.8×105 and a small mode volume of Veff=0.011(λ/n)3 is realized for this design. Therefore, this type of cavities would allow for the realization of efficient single-photon sources. Our results are important for fundamental studies, like cavity quantum electrodynamics, as well as applications in quantum information processing based on diamond where high quality-factor and ultrasmall mode volume are required.