Position-squared coupling in a tunable photonic crystal optomechanical cavity

TL;DR

This paper reports the design and experimental demonstration of a silicon photonic crystal cavity with significantly enhanced position-squared optomechanical coupling, enabling advanced quantum control applications.

Contribution

It introduces a novel double-slotted photonic crystal structure with tunable supermodes that achieve large quadratic optomechanical coupling, surpassing conventional systems.

Findings

Position-squared vacuum coupling rate of 245 Hz.

Coupling coefficient of 1 THz/nm$^2$.

Coupling is five orders of magnitude larger than in Fabry-Perot systems.

Abstract

We present the design, fabrication, and characterization of a planar silicon photonic crystal cavity in which large position-squared optomechanical coupling is realized. The device consists of a double-slotted photonic crystal structure in which motion of a central beam mode couples to two high-Q optical modes localized around each slot. Electrostatic tuning of the structure is used to controllably hybridize the optical modes into supermodes which couple in a quadratic fashion to the motion of the beam. From independent measurements of the anti-crossing of the optical modes and of the optical spring effect, the position-squared vacuum coupling rate is measured to be as large as 245 Hz to the fundamental in-plane mechanical resonance of the structure at 8.7MHz, which in displacement units corresponds to a coupling coefficient of 1 THz/nm$^2$. This level of position-squared coupling is approximately five orders of magnitude larger than in conventional Fabry-Perot cavity systems.