Figure 1: (Top) A sketch of the system, which is a pair of $6\times 0.5\times 0.2$ $\mu$$\text{m}$ doubly clamped nanobeams with $400\text{nm}$ separation. The beams were illuminated by an infrared laser focused to a spot of $10$ $\mu$$\text{m}$ and the reflected signal was detected. (Bottom) The effective potential for the slow coordinate $q_2$ of the higher-frequency nanobeam for different values of the modulation frequency ${\omega }_p$; |$q_2$| gives the scaled amplitude of the vibrations at frequency ${\omega }_p/2$, whereas the sign of $q_2$ determines their phase.