Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session V3: Nonequilibrium Nano-oscillators |
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Sponsoring Units: DCMP Chair: B. Golding, Michigan State University Room: Baltimore Convention Center Ballroom I |
Thursday, March 16, 2006 11:15AM - 11:51AM |
V3.00001: Noise in nonlinear nanomechanical resonators Invited Speaker: Noise limits the sensitivity of linear sensors, in a manner that is well understood, but also limits nonlinear systems in a less trivial way. Nonlinear nanomechanical resonators present interesting possibilities for the sensitive detection of forces and masses, but the noise limitations have not been explored much to date. Here we report on noise effects on nonlinear resonators operated in regimes where they have either one or two stable attractors. We have made quantitative measurements of the nonlinear response of a radiofrequency mechanical resonator with very high quality factor, measuring the noise-free transitions between the two attractors, and find good agreement with theory. We measure the transition rate response to controlled levels of white noise, and extract the basin activation energy. This allows us to obtain precise values for the relevant frequencies and the cubic nonlinearity in the Duffing oscillator, with applications to parametric sensing, in particular mass sensing. References: ``Noise-enabled precision measurements of a Duffing nanomechanical resonator,'' J.S. Aldridge and A.N. Cleland, Phys. Rev. Lett. 94, 156403 (2005). ``Thermomechanical noise limits on parametric sensing with nanomechanical resonators,'' A.N. Cleland, New J. Phys. 7, 235 (2005). [Preview Abstract] |
Thursday, March 16, 2006 11:51AM - 12:27PM |
V3.00002: Noise activated switching in a driven, nonlinear micromechanical torsional oscillator Invited Speaker: We study noise induced switching in an underdamped micromechanical torsional oscillator driven into the nonlinear regime, a system that is far from equilibrium. Within a certain range of driving frequencies, the oscillator possesses two stable dynamical states with different oscillation amplitudes. We induce the oscillator to escape from one dynamical state into the other by introducing noise in the excitation. Close to the birfucation point, the activation energy for switching is expected to display system-independent scaling. By measuring the rate of random transitions at different noise intensities, we deduce the activation energy as a function of frequency detuning and measure a critical exponent that is in good agreement with theoretical predictions. While the oscillator predominately resides in one of the two states for most excitation frequencies, a narrow range of frequencies exist where the occupations of the two states are approximately equal. At these frequencies, the oscillator undergoes `kinetic phase transition' that resembles phase transition of thermal equilibrium systems. We observe a supernarrow peak in the power spectral densities of fluctuations in the measured oscillation amplitude. This peak is centered at the driving frequency and arises as a result of noise-induced transitions between the two dynamic states. [Preview Abstract] |
Thursday, March 16, 2006 12:27PM - 1:03PM |
V3.00003: Multiphoton antiresonance and quantum activation in driven oscillators Invited Speaker: Resonantly modulated oscillators are predicted to display quantum effects, which have no analog in two-level systems. One of them is antiresonance of the coherent nonlinear response: the amplitude of forced vibrations of the oscillator displays a sharp minimum or maximum when the modulation frequency passes adiabatically through multiphoton resonance. The other is escape from metastable states of forced vibrations via quantum diffusion over quasienergy levels. The escape is studied for the cases of resonant and parametric modulation of the oscillator. In both cases, even for zero temperature, the rate of diffusion over quasienergy states is faster than the rate of interstate dynamical tunneling given that the latter is smaller than the relaxation rate. The effective activation energy of escape is a sharp function of temperature in the quantum regime. It displays a power-law dependence on the distance to the bifurcation value of the modulation amplitude or frequency. We show the fragility of the distribution over quasienergy for $T=0$, when the system has detailed balance: it strongly differs from the distribution for $T \to 0$ and from the distribution in the presence of dephasing even where the dephasing rate is small. \newline 1. M. I. Dykman and M. V. Fistul, Phys. Rev. B {\bf 71}, 140508 (R) (2005). \newline 2. M. I. Dykman, “Multiphoton antiresonance and quantum activation in driven systems”, quant-ph/0507261. [Preview Abstract] |
Thursday, March 16, 2006 1:03PM - 1:39PM |
V3.00004: Metastable states in an RF-driven Josephson oscillator Invited Speaker: A superconducting tunnel (Josephson) junction can be viewed as a non-linear, non-dissipative inductor and can be used to construct an oscillator by shunting it with a capacitor. Under certain driving conditions, the non-linear oscillator can adopt one of two possible modes of oscillation with different amplitude and phase. I'll present experimental results which characterize these metastable states, and the transitions between them in the thermal and quantum regime. The dynamical switching between the metastable states can be used to make sensitive detectors. I'll present data demonstrating the successful implementation of such a detector (Josephson Bifurcation Amplifier) to measure superconducting quantum bits. Other implementations of such non-linear oscillators using superconducting transmission line resonators will also be discussed. [Preview Abstract] |
Thursday, March 16, 2006 1:39PM - 2:15PM |
V3.00005: Quantum nano-electromechanics: non-equilibrium cooling and strong feedback effects Invited Speaker: A nano-electromechanical system consists of a micron-scale mechanical resonator coupled to a mesoscopic electronic conductor (e.g. a single-electron transistor, an atomic quantum point contact, etc.). The dissipative quantum mechanics of these systems are particularly interesting. How do the tunneling excitations in the conductor heat and damp the oscillator? To what extent do they act as an effective thermal bath? I will review recent theoretical work which demonstrates how a generic out-of-equilibrium mesoscopic conductor can act as an effective thermal bath. I will also discuss the interesting case where this bath is formed by out-of-equilibrium, incoherently-tunneling Cooper pairs. This is system is remarkable in that significant cooling of the oscillator is possible, as well as a negative-damping instability which leads to a regime of strong-feedback between the oscillator and the Cooper pairs. Both these effects are analogous to ponderomotive effects occurring in a driven optical Fabry-Perot cavity having a moveable mirror; in our case, tunneling Cooper pairs play the role of the cavity photons. \newline \newline [1] A. Clerk, Phys. Rev. B, 70, 245306, 2004. \newline [2] A. Clerk and S. Bennett, New J. Phys. 7 238, 2005. [Preview Abstract] |
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