Fig. 2: Transmission measurements of PT-symmetric micromechanical resonators.

a Output amplitude as a function of frequency under various perturbation voltage. b Output amplitude as a function of frequency without perturbation. The transmission is reciprocal. c Output amplitude as a function of frequency with perturbation (δ = 0.003). The transmission is nonreciprocal. All measured results were obtained at μ = γ = 9 × 10−4 with input amplitude of 15 mV.