Global optimization of an encapsulated Si/SiO$$_2$$ L3 cavity with a 43 million quality factor

Abstract

We optimize a silica-encapsulated silicon L3 photonic crystal cavity for ultra-high quality factor by means of a global optimization strategy, where the closest holes surrounding the cavity are varied to minimize out-of-plane losses. We find an optimal value of $$Q_c=4.33\times 10^7$$ Q c = 4.33 × 10 7 , which is predicted to be in the 2 million regime in presence of structural imperfections compatible with state-of-the-art silicon fabrication tolerances.

Improved design and experimental demonstration of ultrahigh-Q C${}_\text{6}$-symmetric H1 hexapole photonic crystal nanocavities

“…Thus, our H1 PCNs can be expected to have 𝑄 exp values as high as those ones. In addition, our optimal 𝑄 th /𝑉 opt = 1.9 × 10 8 (𝑛/𝜆) 3 is slightly better than another L3 nanocavity with 𝑄 th /𝑉 = 1.7 × 10 8 (𝑛/𝜆) 3 (𝑄 th = 1.9 × 10 8 and 𝑉 = 1.1(𝜆/𝑛) 3 ) designed by the particle-swarm algorithm [65]. In summary, we showed designs of H1 PCNs based on a manual or brute-force search for extremely high-𝑄 hexapole modes.…”

“…As illustrated in Fig. 1(a), our design uses only four parameters (𝑅 0 , 𝑅 the 𝑄 factor, unlike recent designs based on costly optimizations of many variables [62][63][64][65]. 𝑅 0 determines the filling factor of the PhC, which is related to its photonic band gap and thus the in-plane modal confinement.…”

“…Recent studies have used various automated optimization algorithms to achieve high theoretical 𝑄 factors in PCNs [54,56,[62][63][64][65]. We used the built-in optimization module of COMSOL Multiphysics and found that the performance of the H1 PCN can further be improved.…”

Computational Design of a Split Cavity with Localized Independent Electric Field Tunability

“…The photonic device platform we develop is based on the L3 PhC cavity in a GaAs membrane. L3 cavities have been extensively optimized and have both very high cavity quality factor (high Q ) and low mode volume, both of which are requirements for reaching the strong coupling regime. − The fundamental challenge to applying local electric fields to individual qubits within a cavity such as L3 is that any sort of local electrode that sits proud of the surface necessarily produces a scattering site that destroys the cavity Q . n- and p-electrodes can be incorporated into the membrane to enable application of an electric field within a fully planar structure, eliminating the scattering.…”

“…We first use COMSOL simulations to show that this cut cavity design permits the application of distinct electric fields to the two spatially separated qubits with negligible cross talk. We then use finite difference time domain simulations to adjust the cavity design to achieve a cavity Q of 20,000 while remaining within the parameter space that allows such a device to be fabricated using the existing methods. − We note that we chose a numerical optimization process that allowed us to rapidly determine the viability of this approach, and as a result, there is likely room for significant additional improvement with the application of more sophisticated inverse design, genetic algorithm, or machine learning approaches. − ,− …”