Multimode optomechanics with a two-dimensional optomechanical crystal

TL;DR

This paper introduces a two-dimensional multimode optomechanical platform that enhances coupling and control of multiple mechanical modes, advancing quantum technology applications beyond previous nanobeam designs.

Contribution

The work designs and experimentally demonstrates a 2D MOM platform with improved optomechanical interactions, mode control, and regenerative oscillations, surpassing limitations of prior nanobeam systems.

Findings

Achieved optical quality factors of ~10^5.

Demonstrated vacuum optomechanical coupling rates of 1.5 MHz.

Observed regenerative optomechanical oscillations involving multiple mechanical modes.

Abstract

Chip-scale multimode optomechanical systems have unique benefits for sensing, metrology and quantum technologies relative to their single-mode counterparts. Slot-mode optomechanical crystals enable sideband resolution and large optomechanical couplings of a single optical cavity to two microwave-frequency mechanical modes. Still, previous implementations have been limited to nanobeam geometries, whose effective quantum cooperativity at ultralow temperatures is limited by their low thermal conductance. In this work, we design and experimentally demonstrate a two-dimensional mechanical-optical-mechanical (MOM) platform that dispersively couples a slow-light slot-guided photonic-crystal waveguide mode and two slow-sound $\sim 7$ GHz phononic wire modes localized in physically distinct regions. We first demonstrate optomechanical interactions in long waveguide sections, unveiling acoustic group velocities below 800 m/s, and then move on to mode-gap adiabatic heterostructure cavities with a tailored mechanical frequency difference. Through optomechanical spectroscopy, we demonstrate optical quality factors $Q \sim 10^5$, vacuum optomechanical coupling rates, $g_o/2\pi$, of 1.5 MHz and dynamical backaction effects beyond the single-mode picture. At larger power and adequate laser-cavity detuning, we demonstrate regenerative optomechanical oscillations involving a single mechanical mode, extending to both mechanical modes through modulation of the input laser drive at their frequency difference. This work constitutes an important advance towards engineering MOM systems with nearly degenerate mechanical modes as part of hybrid multipartite quantum systems.