Tunable coupling of a double quantum dot spin system to a mechanical resonator*

Hybrid systems in which a mechanical resonator is coupled to a microscopic quantum system are of strong practical and fundamental interest. Achieving a large interaction strength is vital for many goals in this field, and the ability to tune this coupling is also valuable. This has been challenging in solid state spin systems, where often the coupling is weak and fixed. Here we use pairs of coupled InAs quantum dots embedded within GaAs cantilevers to achieve high spin-mechanical coupling through strain. One electron is injected into each dot, with the tunnel coupling inducing a splitting between the singlet and triplet spin states. While optically driving motion of the cantilever, we measure the time-dependent shifts of the singlet and triplet transitions and find that the spin splitting can be highly sensitive to the motion-induced strain. This sensitivity depends strongly on the electrical bias of the system and can even be tuned to zero. The results can be explained by the difference in strain experienced by the two QDs, due to their different positions in the cantilever, which results in a change in the exchange interaction.