Quantum control of acoustic waves

A key role in quantum communication technologies is the efficient transport of information between quantum resources (such as spins, superconducting circuits, or light). Typically, one would use microwaves, guided by microwave waveguides, as a transportation mechanism. However, there is recent interest in switching to the acoustic domain through mechanical, or acoustic vibrations. High-frequency acoustic modes in nano- and microresonators are an intriguing alternative as they couple well with quantum resources and carry GHz excitations with low velocities in the km/s range. However, to develop a flexible acoustic quantum communication platform, we need to develop protocols for active control of the dispersion and dissipation of acoustic waves. In the absence of strong acoustic nonlinearities, we propose to address this challenge by implementing protocols, via optical means, to harness control over acoustic waves in diamond hosting an ensemble of negatively charged nitrogen vacancies (NVs). These protocols build on the fact that NVs in diamond experience strain, which opens a channel that is accessible via an optical laser, that interacts with acoustic phonons through strain-orbit coupling. The model we consider consists of a single optically-excited NV coupled to a single acoustic mode. We show through a master equation how the action of the NV modifies the dissipation and dispersion of the mode, and show how this is controlled by the amplitude and resonance of the optical laser. We then utilise the theoretical framework to modify the dispersion and dissipation of acoustic waves propagating in different diamond waveguide geometries by controlling the state of NVs embedded in the material. Lastly, we show the expectation value of the phonon dynamics can be written in terms of the NV spectrum.