Fig. 3: PSDs of the particle’s motion.

PSDs of the motion along z (left), y (middle) and x (right), showing resonance frequencies of Ω_x,y,z/(2π) ≈ (120, 65, 5) kHz. At p = 14 mbar (dark blue), no feedback cooling is applied. At p = 9 × 10⁻⁶ mbar (light blue), active feedback stabilizes the particle’s motion such that the area of the PSD is decreased. At ω ≠ Ω_q (grey), the detection noise dominates.