Stav Zaitsev

Signal amplification in a nanomechanical Duffing resonator via stochastic resonance

The authors experimentally study stochastic resonance in a nonlinear bistable nanomechanical doubly clamped beam resonator, which is capacitively excited by an adjacent gate electrode. The resonator is tuned to its bistability region by an intense pump near a point of equal transition rates between its two metastable states. The pump is amplitude modulated, inducing modulation of the activation barrier between the states. When noise is added to the excitation, resonator’s displacement exhibits noise dependent amplification of the modulation signal. They measure resonator’s response in the time and frequency domains, the spectral amplification, and the statistical distribution of the jump time.

Noise squeezing in a nanomechanical duffing resonator

We study mechanical amplification and noise squeezing in a nonlinear nanomechanical resonator driven by an intense pump near its dynamical bifurcation point, namely, the onset of Duffing bistability. Phase sensitive amplification is achieved by a homodyne detection scheme, where the displacement detectors output, which has a correlated spectrum around the pump frequency, is down-converted by mixing with a local oscillator operating at the pump frequency with an adjustable phase. The down-converted signal at the mixers output could be either amplified or deamplified, yielding noise squeezing, depending on the local oscillator phase.

High intermodulation gain in a micromechanical Duffing resonator

In this work we use a micromechanical resonator to experimentally study small signal amplification near the onset of Duffing bistability. The device consists of a PdAu beam serving as a micromechanical resonator excited by an adjacent gate electrode. A large pump signal drives the resonator near the onset of bistability, enabling amplification of small signals in a narrow bandwidth. To first order, the amplification is inversely proportional to the frequency difference between the pump and the signal. We estimate the gain to be about 15dB for our device.

Quantum nondemolition measurement of discrete Fock states of a nanomechanical resonator

We study theoretically a radio frequency superconducting interference device integrated with a nanomechanical resonator and an LC resonator. By applying adiabatic and rotating-wave approximations, we obtain an effective Hamiltonian that governs the dynamics of the mechanical and LC resonators. Nonlinear terms in this Hamiltonian can be exploited for performing a quantum nondemolition measurement of Fock states of the nanomechanical resonator. We address the feasibility of experimental implementation and show that the nonlinear coupling can be made sufficiently strong to allow the detection of discrete mechanical Fock states.

Forced and self-excited oscillations of an optomechanical cavity.

We experimentally study forced and self-excited oscillations of an optomechanical cavity, which is formed between a fiber Bragg grating that serves as a static mirror and a freely suspended metallic mechanical resonator that serves as a moving mirror. In the domain of small amplitude mechanical oscillations, we find that the optomechanical coupling is manifested as changes in the effective resonance frequency, damping rate, and cubic nonlinearity of the mechanical resonator. Moreover, self-excited oscillations of the micromechanical mirror are observed above a certain optical power threshold. A comparison between the experimental results and a theoretical model that we have recently derived and analyzed yields a good agreement. The comparison also indicates that the dominant optomechanical coupling mechanism is the heating of the metallic mirror due to optical absorption.

Nonlinear dynamics in nanomechanical oscillators

In the present work we investigate nonlinear dynamics in a nanomechanical doubly clamped beam made of PdAu fabricated using bulk nanomachining and e-beam lithography. The beam is driven into nonlinear regime of oscillations and the response is measured by an electron beam displacement detector. In one set of experiments we study the impact of nonlinear damping on the dynamics in the bistable regime of operation. For data analysis we introduce a nonlinear damping term to Duffing equation. The experiment shows conclusively that accounting for nonlinear damping effects is needed for correct modeling of the dynamics. In another set of experiments we study intermodulation mechanical gain near the onset of bistability. As predicted by a theoretical analysis, we find high intermodulation gain when the system is operated close to a bifurcation.

Displacement detection with a vibrating rf superconducting interference device: beating the standard linear limit.

We study a configuration for displacement detection consisting of a nanomechanical resonator coupled to both a radio frequency superconducting interference device and to a superconducting stripline resonator. We employ an adiabatic approximation and rotating wave approximation and calculate the displacement sensitivity. We study the performance of such a displacement detector when the stripline resonator is driven into a region of nonlinear oscillations. In this region the system exhibits noise squeezing in the output signal when homodyne detection is employed for readout. We show that displacement sensitivity of the device in this region may exceed the upper bound imposed upon the sensitivity when operating in the linear region. On the other hand, we find that the high displacement sensitivity is accompanied by a slowing down of the response of the system, resulting in a limited bandwidth.