Fig. 1
Frequency locking. a A silicon nanorod is optically trapped in a standing wave formed by counterpropagating focussed laser beams at λ = 1550 nm, see “Methods” section. The polarization of the light is controlled using a fiber-EOM driven by a signal generator. We detect the motion of the nanorod via the scattered light collected in a multimode optical fiber. The signal is mixed down with a local oscillator f LO to record the spectrum and the phase of the rotation with respect to the drive frequency f d. Both frequencies f d and f LO are synced to a common clock. b Power spectral density (gray points) of the frequency-locked rotation at 1.11 MHz, taken over 4 continuous days, fit with a Lorentzian (red curve). The upper bound on the FWHM is 1.3 μHz. c Comparison of driven rotation when frequency-locked (“locked rotation”, red, right axis) and un-locked (“threshold rotation”, blue, left axis)
