Probing noisy dynamics at the nanometer scale

When driven by a strong pump, a nonlinear oscillator creates correlations in the frequency domain between signal and idler pairs symmetrically placed about the pump frequency. These correlations result in two-mode squeezing and phase-insensitive amplification of the signal. Not only signals but also noise can be squeezed, leading to measurement sensitivity below the standard limits imposed by thermal or quantum fluctuations. There is currently great interest in demonstrating these effects at the quantum limit, but less attention is paid to the squeezing of thermal noise where there is great potential for practical application. We demonstrate two-mode squeezing in dynamic Atomic Force Microscopy (AFM), where the limiting noise at room temperature is the thermal Brownian motion of the cantilever. Unlike previous work on the mechanical amplification of force, we do not use an 'external' nonlinearity to realize gain. Rather the sample itself is the 'gain medium' which causes a widening of the measurement bandwidth over which dynamic AFM is limited by thermal noise.