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We investigate under what conditions a uniform quench of a superfluid atomic Fermi gas leads to the emergence of spatial inhomogeneities. We demonstrate that, if the system is larger than the coherence length, the superfluid order parameter becomes spatially nonuniform. Spatial modulations develop through a parametric excitations of pairing modes with opposite momenta. Their growth is eventually suppressed by nonlinear effects resulting in a state characterized by a random superposition of wave packets of the superfluid order parameter. This state can be probed by measuring the molecular momentum distribution following a fast sweep to the BEC side of the Feshbach resonance.

This paper proposes simple and precise nonlinear simulation techniques for surface acoustic wave (SAW) duplexers, especially for the in-band 3rd order nonlinear distortion, the socalled 'triple beat'. The simulation model is based on the nonlinearity of SAW stress vs. strain (nonlinear elasticity of SAW), and needs just one nonlinear parameter, which represents the 3rd order nonlinear coefficient for the elastic constant. The simulation results of the triple beat for 1.9 GHz Personal Communications Service (PCS) SAW duplexers demonstrate fairly good agreement with the measurements with an accuracy of less than 1 dB.

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This paper describes a circuit model for the analysis of nonlinearity in the filters based on radiofrequency (RF) bulk acoustic wave (BAW) resonators. The nonlinear output is expressed by a current source connected parallel to the linear resonator. Amplitude of the nonlinear current source is programmed proportional to the product of linear currents flowing in the resonator. Thus, the nonlinear analysis is performed by the common linear analysis, even for complex device structures. The analysis is applied to a ladder-type RF BAW filter, and frequency dependence of the nonlinear output is discussed. Furthermore, this analysis is verified through comparison with experiments.