A Long-lived and Efficient Optomechanical Memory for Light

We demonstrate a memory for light based on optomechanically induced transparency. We achieve a long storage time by leveraging the ultra-low dissipation of a soft-clamped mechanical membrane resonator, which oscillates at MHz frequencies. At room temperature, we demonstrate a lifetime $T_1\approx 23\mathrm{m}\mathrm{s}$ and a retrieval efficiency $\eta \approx 40\mathrm{\%}$ for classical coherent pulses. We anticipate storage of quantum light to be possible at moderate cryogenic conditions ($T\approx 10\mathrm{K}$). Such systems could find applications in emerging quantum networks, where they can serve as long-lived optical quantum memories by storing optical information in a phononic mode.