Design, Fabrication and Characterization of Si 3 N 4 Photonic Crystal Nanocavities for Diamond-based Quantum Information
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Design, Fabrication and Characterization of Si3N4 Photonic Crystal Nanocavities for Diamond-based Quantum Information Processing Applications Mughees Khan, Murray W. McCutcheon, Thomas Babinec, Parag Deotare and Marko Lončar School of Engineering and Applied Sciences, Harvard University, 9 Oxford St., Cambridge, MA 02138 ABSTRACT In order to improve the efficiency of quantum emitters, in particular nitrogen-vacancy (NV) color centers in diamond nanocrystals (NCs), it is important to enhance their photon production rate as well as the collection efficiency of the emitted photons. This can be achieved by embedding the emitters within optical cavities. Here we describe the design and fabrication of 1-D photonic crystal nanocavities in an air-bridge silicon nitride (SiNx) structure. In spite of the low index of SiNx (n~2), we were able to design optical nanocavities with Quality (Q) factors as high as Q~1 x 106. These nanocavities were designed to operate near 637 nm in order to strongly enhance the zero-phonon line (ZPL) emission of an NV center in a diamond NC while suppressing the in-plane emission into the phonon side-band. Simulation results show that a NV center placed near the top of the cavity would experience a reduction of radiative lifetime from ~15ns to ~2ps (Purcell factor ~7000), thus significantly improving the photon production rate. Experimental results show a cavity resonance at ~630nm, with a linewidth corresponding to Q~1250, limited by the spectrometer resolution. The presented work is an important step towards the realization of diamond-based single photon devices, including switches. INTRODUCTION Diamond nanocrystals (NCs) with single nitrogen-vacancy (NV) [1,2] color centers embedded in the middle have emerged as promising platforms for single photon sources, and quantum systems in general [3]. In order to further improve the efficiency of NV-based quantum-emitters, it is important to enhance the photon production rate as well as the collection efficiency of emitted photons. This can be achieved by embedding NCs within optical cavities. Recently silicon nitride (SiNx) [4-6] has been explored as a material platform for fabrication of photonic crystal (PC) cavities at visible wavelengths. Barth et al. [4, 5] have experimentally reported quality (Q) factors as high as 3400 in a 2-D SiNx PC cavity, and observed cavityenhanced emission from a fluorescent dye spun on top of their PC membrane. Makarova et al. [6] showed Q factors of about 300 in their 2-D Si rich SiNx PC membranes and investigated emission from Si nanocrystals. In this work we first describe the design of an ultrahigh Q photonic crystal nanocavity in an air-bridge SiNx structure. We then report on the fabrication process, test setup and preliminary characterization of the SiNx nanocavities. DESIGN The high Q cavity is formed by spatially modulating the lattice of a 1D PC in a freestanding air-bridge waveguide. In a 1D PC nanocavity, the photonic crystal mirror provides optical confinement in one dimension only, and total i
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