Eyal Buks

Stiction, adhesion energy, and the Casimir effect in micromechanical systems

We measure the adhesion energy of gold using a micromachined cantilever beam. Stress and stiffness of the beam are characterized by measuring the spectrum of mechanical vibrations and the deflection due to external force. We induce stiction between the beam and a nearby surface, employing capillary forces to determine the adhesion energy g. The obtained value g50.06 J/m 2 is a factor of 6 smaller than that predicted by idealized theory. This discrepancy may arise from surface roughness or an adsorbed layer intervening between the contacting surfaces in these mesoscopic structures.

Dephasing in electron interference by a 'which-path'detector

Wave–particle duality, as manifest in the two-slit experiment, provides perhaps the most vivid illustration of Bohrs complementarity principle: wave-like behaviour (interference) occurs only when the different possible paths a particle can take are indistinguishable, even in principle. The introduction of a which-path (welcher Weg) detector for determining the actual path taken by the particle inevitably involved coupling the particle to a measuring environment, which in turn results in dephasing (suppression of interference). In other words, simultaneous observations of wave and particle behaviour is prohibited. Such a manifestation of the complementarity principle was demonstrated recently using a pair of correlated photons, with measurement of one photon being used to determine the path taken by the other and so prevent single-photon interference. Here we report the dephasing effects of a which-path detector on electrons traversing a double-path interferometer. We find that by varying the sensitivity of the detector we can affect the visibility of the oscillatory interference signal, thereby verifying the complementarity principle for fermions.

Metastability and the Casimir effect in micromechanical systems

Electrostatic and Casimir interactions limit the range of positional stability of electrostatically actuated or capacitively coupled mechanical devices. We investigate this range experimentally for a generic system consisting of a doubly clamped Au suspended beam, capacitively coupled to an adjacent stationary electrode. The mechanical properties of the beam, both in the linear and nonlinear regimes, are monitored as the attractive forces are increased to the point of instability. There pull-in occurs, resulting in permanent adhesion between the electrodes. We investigate, experimentally and theoretically, the position-dependent lifetimes of the free state (existing prior to pull-in). We find that the data cannot be accounted for by simple theory; the discrepancy may be reflective of internal structural instabilities within the metal electrodes.

Electrically tunable collective response in a coupled micromechanical array

We employ optical diffraction to study the mechanical properties of a grating array of suspended doubly clamped beams made of Au. The device allows application of electrostatic coupling between the beams that gives rise to formation of a band of normal modes of vibration (phonons). We parametrically excite these collective modes and study the response by measuring the diffraction signal. The results indicate that nonlinear effects strongly affect the dynamics of the system. Further optimization will allow employing similar systems for real-time mechanical spectrum analysis of electrical waveforms.

Mass detection with a nonlinear nanomechanical resonator

Nanomechanical resonators having small mass, high resonance frequency, and low damping rate are widely employed as mass detectors. We study the performance of such a detector when the resonator is driven into a region of nonlinear oscillations. We predict theoretically that in this region the system acts as a phase-sensitive mechanical amplifier. This behavior can be exploited to achieve noise squeezing in the output signal when homodyne detection is employed for readout. We show that mass sensitivity of the device in this region may exceed the upper bound imposed by thermomechanical noise upon the sensitivity when operating in the linear region. On the other hand, we show that the high mass sensitivity is accompanied by a slowing down of the response of the system to a change in the mass.

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.

Performance of Cavity-Parametric Amplifiers, Employing Kerr Nonlinearites, in the Presence of Two-Photon Loss

Two-photon loss mechanisms often accompany a Kerr nonlinearity. The kinetic inductance exhibited by superconducting transmission lines provides an example of a Kerr-like nonlinearity that is accompanied by a nonlinear resistance of the two-photon absorptive type. Such nonlinear dissipation can degrade the performance of amplifiers and mixers employing a Kerr-like nonlinearity as the gain or mixing medium. As an aid for parametric-amplifier design, the authors provide a quantum analysis of a cavity parametric amplifier employing a Kerr nonlinearity that is accompanied by a two-photon absorptive loss. Because of their usefulness in diagnostics, we obtain expressions for the pump amplitude within the cavity, the reflection coefficient for the pump amplitude reflected off of the cavity, the parametric gain, and the intermodulation gain. Expressions by which the degree of squeezing can be computed are also presented. Although the focus here is on providing aids for the design of kinetic-inductance parametric amplifiers, much of what is presented is directly applicable to analogous optical and mechanical amplifiers

Analogue Hawking Radiation in a dc-SQUID Array Transmission Line

We propose the use of a superconducting transmission line formed from an array of direct-current superconducting quantum interference devices for investigating analogue Hawking radiation. Biasing the array with a space-time varying flux modifies the propagation velocity of the transmission line, leading to an effective metric with a horizon. Being a fundamentally quantum mechanical device, this setup allows for investigations of quantum effects such as backreaction and analogue space-time fluctuations on the Hawking process.

Performance of an AuPd micromechanical resonator as a temperature sensor

In this work we study the sensitivity of the primary resonance of an electrically excited microresonator for the possible usage of a temperature sensor. We find a relatively high normalized responsivity factor Rf=|TfdfdT|=0.37 with a quality factor of ∼105. To understand this outcome we perform a theoretical analysis based on experimental observation. We find that the dominant contribution to the responsivity comes from the temperature dependence of the tension in the beam. Subsequently, Rf is found to be inversely proportional to the initial tension. Corresponding to a particular temperature, the tension can be increased by applying a bias voltage.