Nonlinear mechanics with photonic crystal nanomembranes

Optomechanical systems close to their quantum ground state and nonlinear nanoelectromechanical systems are two hot topics of current physics research. As high-reflectivity and low mass are crucial features to improve optomechanical coupling towards the ground state, we have designed, fabricated and characterized photonic crystal nanomembranes, at the crossroad of both topics. Here we demonstrate a number of nonlinear effects with these membranes. We first characterize the nonlinear behavior of a single mechanical mode and we demonstrate its nonlocal character by monitoring the subsequent actuation-related frequency shift of a different mode. We then proceed to study the underlying nonlinear dynamics, both by monitoring the phase-space trajectory of the free resonator and by characterizing the mechanical response in presence of a strong pump excitation. We observe in particular the frequency evolution during a ring-down oscillation decay, and the emergence of a phase conjugate mechanical response to a weaker probe actuation. Our results are crucial to understand the full nonlinear features of the PhC membranes, and possibly to look for nonlinear signatures of the quantum dynamics

2D photonic-crystal optomechanical nanoresonator

We present the optical optimization of an optomechanical device based on a suspended InP membrane patterned with a 2D near-wavelength grating (NWG) based on a 2D photonic-crystal geometry. We first identify by numerical simulation a set of geometrical parameters providing a reflectivity higher than 99.8 % over a 50-nm span. We then study the limitations induced by the finite value of the optical waist and lateral size of the NWG pattern using different numerical approaches. The NWG grating, pierced in a suspended InP 265 nm-thick membrane, is used to form a compact microcavity involving the suspended nano-membrane as end mirror. The resulting cavity has a waist size smaller than 10 $\mu$m and a finesse in the 200 range. It is used to probe the Brownian motion of the mechanical modes of the nanomembrane

TET3-Mediated Demethylation in Tomato Activates Expression of a CETS Gene that Stimulates Vegetative Growth

Expression of the mammalian DNA demethylase enzyme TET3 in plants can be used to induce hypomethylation of DNA. In tomato lines that express a TET3 transgene, we observed distinct phenotypes including an increase in the length and number of leaves of primary shoots. As these changes resemble phenotypes observed in plants with strong expression of SELF PRUNING (SP), a member of the PEBP/CETS family, we investigated in TET3 lines the expression levels of members of the PEBP/CETS gene family, which affect shoot architecture and growth of sympodial units in tomato. We did not detect any changes in SP expression in TET3 lines, but for CEN1.1, a putative family member that has not been functionally characterized, we identified changes in gene expression that corresponded to hypomethylation in the upstream region. In tomato wild type, CEN1.1 is expressed in roots, petals, and shoot apices but not in mature leaves. In contrast, in TET3 transformants, the CEN1.1 gene became hypomethylated and activated in leaves. Ectopic expression of CEN1.1 in tomato caused similar phenotypes to those seen in TET3 transformants. Vegetative growth was increased, resulting both in a delay in inflorescence development and in an instability of the inflorescences, which frequently reverted to a vegetative state. Ectopic expression of CEN1.1 in Arabidopsis thaliana also caused floral repression. Our data suggest that the phenotypes observed in TET3 lines are a consequence of ectopic activation of CEN1.1, which promotes vegetative growth, and that CEN1.1 expression is sensitive to DNA methylation changes

Cooling of a mirror by radiation pressure

We describe an experiment in which a mirror is cooled by the radiation pressure of light. A high-finesse optical cavity with a mirror coated on a mechanical resonator is used as an optomechanical sensor of the Brownian motion of the mirror. A feedback mechanism controls this motion via the radiation pressure of a laser beam reflected on the mirror. We have observed either a cooling or a heating of the mirror, depending on the gain of the feedback loop.Comment: 4 pages, 6 figures, RevTe

High-finesse Fabry-Perot cavities with bidimensional Si3_3N4_4 photonic-crystal slabs

Light scattering by a two-dimensional photonic crystal slab (PCS) can result in dramatic interference effects associated with Fano resonances. Such devices offer appealing alternatives to distributed Bragg reflectors or filters for various applications such as optical wavelength and polarization filters, reflectors, semiconductor lasers, photodetectors, bio-sensors, or non-linear optical components. Suspended PCSs also find natural applications in the field of optomechanics, where the mechanical modes of a suspended slab interact via radiation pressure with the optical field of a high finesse cavity. The reflectivity and transmission properties of a defect-free suspended PCS around normal incidence can be used to couple out-of-plane mechanical modes to an optical field by integrating it in a free space cavity. Here, we demonstrate the successful implementation of a PCS reflector on a high-tensile stress Si$_3$N$_4$ nanomembrane. We illustrate the physical process underlying the high reflectivity by measuring the photonic crystal band diagram. Moreover, we introduce a clear theoretical description of the membrane scattering properties in the presence of optical losses. By embedding the PCS inside a high-finesse cavity, we fully characterize its optical properties. The spectrally, angular, and polarization resolved measurements demonstrate the wide tunability of the membrane's reflectivity, from nearly 0 to 99.9470~$\pm$ 0.0025 \%, and show that material absorption is not the main source of optical loss. Moreover, the cavity storage time demonstrated in this work exceeds the mechanical period of low-order mechanical drum modes. This so-called resolved sideband condition is a prerequisite to achieve quantum control of the mechanical resonator with light

Optomechanical characterization of acoustic modes in a mirror

We present an experimental study of the internal mechanical vibration modes of a mirror. We determine the frequency repartition of acoustic resonances via a spectral analysis of the Brownian motion of the mirror, and the spatial profile of the acoustic modes by monitoring their mechanical response to a resonant radiation pressure force swept across the mirror surface. We have applied this technique to mirrors with cylindrical and plano-convex geometries, and compared the experimental results to theoretical predictions. We have in particular observed the gaussian modes predicted for plano-convex mirrors.Comment: 8 pages, 8 figures, RevTe

Isotope effect in superconductors with coexisting interactions of phonon and nonphonon mechanisms

We examine the isotope effect of superconductivity in systems with coexisting interactions of phonon and nonphonon mechanisms in addition to the direct Coulomb interaction. The interaction mediated by the spin fluctuations is discussed as an example of the nonphonon interaction. Extended formulas for the transition temperature Tc and the isotope-effect coefficient alpha are derived for cases (a) omega_np omega_D, where omega_np is an effective cutoff frequency of the nonphonon interaction that corresponds to the Debye frequency omega_D in the phonon interaction. In case (a), it is found that the nonphonon interaction does not change the condition for the inverse isotope effect, i.e., mu^* > lambda_ph/2, but it modifies the magnitude of alpha markedly. In particular, it is found that a giant isotope shift occurs when the phonon and nonphonon interactions cancel each other largely. For instance, strong critical spin fluctuations may give rise to the giant isotope effect. In case (b), it is found that the inverse isotope effect occurs only when the nonphonon interaction and the repulsive Coulomb interaction, in total effect, work as repulsive interactions against the superconductivity. We discuss the relevance of the present result to some organic superconductors, such as kappa-(ET)2Cu(NCS)2 and Sr2RuO4 superconductors, in which inverse isotope effects have been observed, and briefly to high-Tc cuprates, in which giant isotope effects have been observed.Comment: 4 pages, 2 figures, (with jpsj2.cls, ver.1.2), v2:linguistic correction

Macroscopic quantum fluctuations in noise-sustained optical patterns

We investigate quantum effects in pattern formation for a degenerate optical parametric oscillator with walk-off. This device has a convective regime in which macroscopic patterns are both initiated and sustained by quantum noise. Familiar methods based on linearization about a pseudoclassical field fail in this regime and new approaches are required. We employ a method in which the pump field is treated as a c-number variable but is driven by the c-number representation of the quantum subharmonic signal field. This allows us to include the effects of the fluctuations in the signal on the pump, which in turn act back on the signal. We find that the nonclassical effects, in the form of squeezing, survive just above the threshold of the convective regime. Further, above threshold, the macroscopic quantum noise suppresses these effects