An off-board quantum point contact as a sensitive detector of cantilever motion

Recent advances in the fabrication of microelectromechanical systems (MEMS) and their evolution into nanoelectromechanical systems (NEMS) have allowed researchers to measure extremely small forces, masses, and displacements. In particular, researchers have developed position transducers with resolution approaching the uncertainty limit set by quantum mechanics. The achievement of such resolution has implications not only for the detection of quantum behavior in mechanical systems, but also for a variety of other precision experiments including the bounding of deviations from Newtonian gravity at short distances and the measurement of single spins. Here we demonstrate the use of a quantum point contact (QPC) as a sensitive displacement detector capable of sensing the low-temperature thermal motion of a nearby micromechanical cantilever. Advantages of this approach include versatility due to its off-board design, compatibility with nanoscale oscillators, and, with further development, the potential to achieve quantum limited displacement detection.Comment: 5 pages, 5 figure

Back-action Evading Measurements of Nanomechanical Motion

When performing continuous measurements of position with sensitivity approaching quantum mechanical limits, one must confront the fundamental effects of detector back-action. Back-action forces are responsible for the ultimate limit on continuous position detection, can also be harnessed to cool the observed structure, and are expected to generate quantum entanglement. Back-action can also be evaded, allowing measurements with sensitivities that exceed the standard quantum limit, and potentially allowing for the generation of quantum squeezed states. We realize a device based on the parametric coupling between an ultra-low dissipation nanomechanical resonator and a microwave resonator. Here we demonstrate back-action evading (BAE) detection of a single quadrature of motion with sensitivity 4 times the quantum zero-point motion, back-action cooling of the mechanical resonator to n = 12 quanta, and a parametric mechanical pre-amplification effect which is harnessed to achieve position resolution a factor 1.3 times quantum zero-point motion.Comment: 19 pages (double-spaced) including 4 figures and reference

Regulation of the proteasome: Evaluating the lung proteasome as a new therapeutic target.

Significance: Lung diseases are on the second rank worldwide with respect to morbidity and mortality. For most respiratory diseases no effective therapies exist. While the proteasome has been successfully evaluated as a novel target for therapeutic interventions in cancer, neurodegenerative, and cardiac disorders, there is a profound lack of knowledge on the regulation of proteasome activity in chronic and acute lung diseases. Recent advances have identified various means of how the amount of active proteasome complexes in the cell can be regulated such as transcriptional regulation of proteasomal subunit expression, association with different regulators, assembly and half-life of proteasomes and regulatory complexes, as well as posttranscriptional modifications. It also becomes increasingly evident that proteasome activity is fine-tuned and depends on the state of the cell. We propose here that 20S proteasomes and their regulators can be regarded as dynamic building blocks, which assemble or disassemble in response to cellular needs. The composition of proteasome complexes in a cell may vary depending on tissue, cell type and compartment, stage of development, or pathological context. Critical Issues and Future Directions: Dissecting the expression and regulation of the various catalytic forms of 20S proteasomes, such as constitutive, immuno-, and mixed proteasomes, together with their associated regulatory complexes will not only greatly enhance our understanding of proteasome function in lung pathogenesis but will also pave the way to develop new classes of drugs that inhibit or activate proteasome function in a defined setting for treatment of lung diseases

Motion-induced localization bias in an action task

DeValois and DeValois (Vis Research, 31, 1619-1626) have shown that a moving carrier behind a stationary window can cause a perceptual misplacement of this envelope in direction of motion. The authors also found that the bias increased with increasing carrier speed and eccentrcity. Yamagishi et al. (2001, Proceedings of the Royal Society, 268, 973-977) showed that this effect can also be found in visuo-motor tasks. To see whether variables such as eccentricity and grating speed increase the motion-induced perceptual shift of a motion field also in an action task, a motor-control experiment was created in which these variables were manipulated (eccentricity values: 0 deg, 8.4 deg and 16.8; speed values: 1.78 deg/sec, 4.45 deg/sec and 7.1 deg/sec). Participants had to keep a downward-sliding path aligned with a motion field (stationary Gaussian and horizontally moving carrier) by manipulating the path with a joystick. The perceptual bias can be measured by comparing the average difference between correct and actual path position. Both speed and eccentricty had a significant impact on the bias size. Similarly to the recognition task, the bias size increased with increasing carrier speed. Contrary to DeValois and DeValois’ finding, here the perceptual shift decreased with increasing eccentricity. There was no interaction of the variables. If we assume an ecological reason for the existence of a motion-induced bias, it might be plausible to see why the bias is smaller in an unnatural task such as actively manipulating an object that is in an eccentric position in the visual field (hence the decrease of bias magnitude in the periphery). Contrary to this, recognition tasks carried out in the periphery of the visual field are far more common and therefore might “benefit” from the existence of a motion-induced localization bias. As expected, task difficulty increased with increasing speed and eccentricity. It seems interesting to further compare action and perception tasks in terms of factors influencing the localization bias in these different task types

Motion-Induced Shift and Navigation in Virtual Reality

De Valois and De Valois [1] showed that moving Gabors (cosine gratings windowed by a stationary 2-dimensional Gaussian envelope) are locally misperceived in their direction of motion. In a pointing task, Yamagishi, Anderson and Ashida [2] reported even stronger visuo-motor localization error especially when participants had to make a speeded response. Here, we examined motion-induced bias in the context of an active navigation task, a situation in which perception and action are tightly coupled. Participants were presented with a birds-eye view of a vertically moving contour that simulated observer motion along a path. Observers centrally fixated while the path and a moving Gabor target were presented peripherally. The task was to follow the path with the moving Gabor, whose position (left/right) and direction(towards left/right) were varied in separate blocks. Gabor eccentricity was constant relative to fixation, with observers adjusting their simulated position with a joystick. Deviations from the path were analyzed as a function of Gabor direction. We found large and consistent misalignment in the direction of the moving Gabor, indicating that global position/motion judgments during action can be strongly affected by irrelevant local motion signals

Bruit thermique et effets quantiques dans une cavité optique de grande finesse

Nous nous intéressons aux bruits dans les mesures optiques de très grande sensibilité et aux limites associées. Une des limitations fondamentales des mesures interférométriques, telles que les détections d'ondes gravitationnelles, est liée aux fluctuations de la pression de radiation exercée par la lumière sur les miroirs. Celle-ci induit des corrélations quantiques entre la position des miroirs et les fluctuations de la lumière. L'observation de ces effets quantiques ouvrirait de nombreuses perspectives: étude de la limite quantique standard, production d'états comprimés, réalisation d'une mesure quantique non destructive $\ldots

Optomechanical coupling in high-finesse cavities: towards the observation of quantum effects

In quantum mechanics, every measurement induces a back-action on the measured system which usually implies a limit in the sensitivity of the measurement. Our goal is to demonstrate such quantum effects, with an experimental setup based on a high-finesse optical cavity to detect very small displacements of the mirrors. We recently observed a cancellation of the back-action induced by the radiation pressure exerted on the mirrors. Such a cancellation effect may greatly enhance the sensitivity of gravitational-waves detection by dual resonators

Proteasome function is not impaired in healthy aging of the lung.

Aging is the progressive loss of cellular function which inevitably leads to death. Failure of proteostasis including the decrease in proteasome function is one hallmark of aging. In the lung, proteasome activity was shown to be impaired in age-related diseases such as chronic obstructive pulmonary disease. However, little is known on proteasome function during healthy aging. Here, we comprehensively analyzed healthy lung aging and proteasome function in wildtype, proteasome reporter and immunoproteasome knockout mice. Wildtype mice spontaneously developed senile lung emphysema while expression and activity of proteasome complexes and turnover of ubiquitinated substrates was not grossly altered in lungs of aged mice. Immunoproteasome subunits were specifically upregulated in the aged lung and the caspase-like proteasome activity concomitantly decreased. Aged knockout mice for the LMP2 or LMP7 immunoproteasome subunits showed no alteration in proteasome activities but exhibited typical lung aging phenotypes suggesting that immunoproteasome function is dispensable for physiological lung aging in mice. Our results indicate that healthy aging of the lung does not involve impairment of proteasome function. Apparently, the reserve capacity of the proteostasis systems in the lung is sufficient to avoid severe proteostasis imbalance during healthy aging

Quantum optics with micromirrors

Recent progress in high-finesse optical cavities and micro-mechanical resonators allows one to reach a new regime in which both mechanical and optical dynamics are governed by the radiation pressure exerted by light on mirrors. This optomechanical coupling leads to the existence of fundamental quantum limits in ultrasensitive interferometric measurements, and also to very efficient cooling mechanisms of micromirrors. We experimentally study these effects by monitoring in a very high-finesse cavity the displacements of a mirror coated on a micro-resonator. We have in particular observed a self-cooling of the mirror induced by the intracavity radiation pressure. Improvements of the experimental setup would open the way to the optical observation of the quantum ground state of a macroscopic resonator