  We propose to use an acoustic surface wave as a memory for a photon carrying
orbital angular momentum. We clarify the physical mechanism that enables the
transfer of information, derive the angular momentum selection rule that must
be obeyed in the process, and show how to optimize the optoacoustic coupling.
We theoretically demonstrate that high fidelities can be achieved, using
realistic parameters, for the transfer of a coherent optical Laguerre-Gaussian
state, associated with large angular momentum, to a mechanical shear mode. Our
results add a significant possibility to the ongoing efforts towards the
implementation of quantum information processing using photonic orbital angular
momentum.
