Optomechanical ground-state cooling of a 5 MHz silicon nitride membrane mode in a closed-cycle dilution refrigerator

Ground-state cooled silicon nitride membranes have been used to mediate microwave-to-optical transduction with low added noise and high efficiency [1]. Typical transducers employ a mechanical mode with a resonance frequency near 1 MHz, but pushing to higher frequencies reduces optical pump filtering requirements when transducing within entanglement distribution networks that rely on optical heralding. In this talk, we demonstrate optomechanical ground-state cooling of a 5 MHz silicon nitride membrane mode. We characterize the factors that determine the cooling limit in this regime and discuss improvements in laser noise that enable our sensitive mechanical noise thermometry. In addition, we detail a custom cryogenic vibration isolation system that enables continuous operation of our optomechanical cavities in a commercial closed-cycle dilution refrigerator. This system is useful for any experimental platform that requires stable locking of low-noise lasers to cryogenically cooled, high-finesse cavities.

[1] M. D. Urmey, S. Dickson, K. Adachi, S. Mittal, L. G. Talamo, A. Kyle, N. E. Frattini, S.-X. Lin, K. W. Lehnert, C. A. Regal, High-throughput electro-optic upconversion and downconversion with few-photon added noise, arXiv preprint arXiv:2507.09873 (2025).