Fiber-Cavity optomechanics with hexagonal boron nitride drum resonators

In an effort to overcome the limits imposed by the inherently weak radiation pressure interaction, the field of optomechanics aims to miniaturize both the mechanical elements and the mode volume of the optical cavities involved.
Like this, the interaction can be boosted, and the quantum regime comes within reach.
The possibility of introducing additional elements into the system, such as quantum emitters, offers alternative ways to move past current experimental limitations.
This calls for versatile experimental platforms with a small footprint that allow for the integration and exploration of novel materials and experimental protocols.
Here we present a fiber based Fabry-Perot cavity that can be operated under atmospheric conditions, under vacuum, and at 4K.
We demonstrate our ability to stabilize the cavity length within the cavity linewidth while maintaining full tunability and a high finesse.
We fabricate mechanical drum resonators by suspending flakes of hexagonal boron-nitride over holes in a high-stress $Si_{3}N_{4}$ membrane.
By imaging their motion and measuring their thermal displacement spectra, we characterize these drums and their hybridization with the underlying $Si_{3}N_{4}$ membrane.
The observed mode shapes are consistent with theoretical models and finite-element simulations of an ideal drum, revealing that our fabrication procedure introduce little imperfections.
The analysis of the thermal spectra reveals that hybridization with the $Si_{3}N_{4}$ membrane can shift the quality factor and effective mass of the drum modes by several orders of magnitude.
This could be an important tool in the endeavor to improve the moderate mechanical quality factors of 2D material oscillators, and further enhance their sensitivity.
Combining our cavity with our hBN drum resonator yields an optomechanical platform with a single-photon coupling of up to $g_0=230\,\mbox{kHz}$, several orders of magnitude higher than previous implementations employing mechanical resonators made of 2D materials.
This high value is made possible by the small mode volume of our microscale cavity, as well as the low effective mass of our hBN drum resonator.
Finally, the combination of the high stability of our system with this strong interaction allowed us to measure the optomechanically induced transparency effect, highlighting the potential of our experimental platform.