60 research outputs found
Active feedback cooling of a SiN membrane resonator by electrostatic actuation
No full textFeedback-based control techniques are useful tools in precision measurements as they allow us to actively shape the mechanical response of high quality factor oscillators used in force detection measurements. In this paper, we implement a feedback technique on a high-stress low-loss SiN membrane resonator, exploiting the charges trapped on the dielectric membrane. A properly delayed feedback force (dissipative feedback) enables the narrowing of the thermomechanical displacement variance in a similar manner to the cooling of the normal mechanical mode down to an effective temperature Teff. In the experiment reported here, we started from room temperature and gradually increasing the feedback gain, we were able to cool down the first normal mode of the resonator to a minimum temperature of about 124mK. This limit is imposed by our experimental setup and, in particular, by the injection of the read-out noise into the feedback. We discuss the implementation details and possible improvements to the technique.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Components, Technology and MaterialsEKL Equipmen
Hypertrophic scar in a dog: histological and clinical features
No full textAn adult male bullmastiff dog was treated for paraparesis and ataxia due to discospondylitis and disc herniation. At this time, the dog had a nonhealing ulcer between the pads of the left hindfoot. At re-evaluation, the dog had developed a large exophitic mass in the previously ulcerated area. Cytological examination revealed occasional spindle cells with mild atypia, and a soft tissue tumour was suspected. The mass was excised and submitted for histology. The lesion was characterized by superficial ulceration, an intermediate layer of granulation tissue and a deep portion containing vertically orientated capillaries and perpendicularly arranged fibroblasts and collagen. The histological features led to a diagnosis of hypertrophic scar. Eight weeks after surgery, the lesion recurred and was treated with an intralesional injection of methylprednisolone acetate. The lesion regressed in 10 days, but recurred after 3 months following severe self-trauma. Hypertrophic scars and keloids are two types of exuberant scarring reported in human beings, the pathogenesis of which is still unclear but seems to involve several cytokines, growth factors and inflammatory cells. The histological features identified in this case paralleled those reported in hypertrophic scars in humans. In this case, intralesional corticosteroid therapy was useful in the management of the lesion, but the severe self-trauma could have influenced the recurrence. Even if uncommon, hypertrophic scar should be included among the differential diagnoses of spindle cell tumours in dogs
Urinary Incontinence and Other Pelvic Floor Dysfunctions as Underestimated Problems in People under Forty Years: What Is Their Relationship with Sport?
No full textUrinary incontinence is still an underestimated problem due to its anatomical complexity and social taboo. Most of the time, it is believed to affect predominantly the elderly female population, and the literature still lacks data on its presence in the younger and male populations. Its relationship with other pelvic floor dysfunctions (PFDs) and sport activity remains an open topic. Thus, the present study surveyed 342 subjects of both genders, ranging from 18 to 39 y/o and with different sport activity levels, to understand the prevalence of PFDs (such as haemorrhoids, anal fissures, involuntary urinary/faecal leakage, and urgency). The results also showed a significative prevalence in younger, sporty, and male people. Approximately one third of the population had urinary incontinence mostly during stress activities (sport activity: 17%, cough/sneeze: 13%). The statistical analysis confirmed a higher prevalence in the cases of a light (32%) and intense (41%) sport activity level and a protective role of sport if practiced between 5 and 10 h/week, with bodybuilding/CrossFit and running seeming to be the riskiest sports. The relationship with the other PFDs showed a statistically significant dependence with most of them, confirming that urinary incontinence cannot be considered a separate problem from the other PFDs
Frequency-noise cancellation in optomechanical systems for ponderomotive squeezing
No full textPonderomotive squeezing of the output light of an optical cavity has been recently observed in the megahertz range in two different cavity optomechanical devices. Quadrature squeezing becomes particularly useful at lower spectral frequencies, for example, in gravitational wave interferometers, despite being more sensitive to excess phase and frequency noise. Here we show a phase and frequency-noise cancellation mechanism due to destructive interference which can facilitate the production of ponderomotive squeezing in the kilohertz range and we demonstrate it experimentally in an optomechanical system formed by a Fabry-P´erot cavity with a micromechanical mirror.MicroelectronicsElectrical Engineering, Mathematics and Computer Scienc
Detection of weak stochastic forces in a parametrically stabilized micro-optomechanical system
No full textMeasuring a weak force is an important task for micromechanical systems, both when using devices as sensitive detectors and, particularly, in experiments of quantum mechanics. The optimal strategy for resolving a weak stochastic signal force on a huge background (typically given by thermal noise) is a crucial and debated topic, and the stability of the mechanical resonance is a further, related critical issue. We introduce and analyze the parametric control of the optical spring, which allows us to stabilize the resonance and provides a phase reference for the oscillator motion, yet conserving a free evolution in one quadrature of the phase space. We also study quantitatively the characteristics of our micro-optomechanical system as detector of stochastic force for short measurement times (for quick, high-resolution monitoring) as well as for the longer-term observations that optimize the sensitivity. We compare a simple strategy based on the evaluation of the variance of the displacement which is a widely used technique) with an optimal Wiener-Kolmogorov data analysis. We show that, due to the parametric stabilization of the effective susceptibility, we can more efficiently implement Wiener filtering, and we investigate how this strategy improves the performance of our system. We finally demonstrate the possibility to resolve stochastic force variations well below 1% of the thermal noise.MicroelectronicsElectrical Engineering, Mathematics and Computer Scienc
Squeezing a Thermal Mechanical Oscillator by Stabilized Parametric Effect on the Optical Spring
No full textWe report the confinement of an optomechanical micro-oscillator in a squeezed thermal state, obtained by parametric modulation of the optical spring. We propose and implement an experimental scheme based on parametric feedback control of the oscillator, which stabilizes the amplified quadrature while leaving the orthogonal one unaffected. This technique allows us to surpass the ?3??dB limit in the noise reduction, associated with parametric resonance, with a best experimental result of ?7.4??dB . While the present experiment is in the classical regime, in a moderately cooled system our technique may allow squeezing of a macroscopic mechanical oscillator below the zero-point motion.MicroelectronicsElectrical Engineering, Mathematics and Computer Scienc
Quantum nondemolition measurement of light intensity fluctuations in an optomechanical experiment
No full textAccording to quantum mechanics, there exists a class of observables for which is possible to confine the perturbation produced by a continuous measurement to the conjugate variable. Therefore, it is possible to devise experimental schemes that allow estimating the observed variable with arbitrary accuracy, or preparing it in a well-known state. Such schemes are referred to as quantum non-demolition measurements (QND). Among these observables there is the amplitude of the light field. Indeed, it is possible to exploit a movable mirror to implement a QND scheme [1]. Intensity fluctuations of an optical field impinging on it are not affected by the interaction. However, the movable mirror is excited by the associated radiation pressure. This, in turn, affects the phase of the field.
We have performed an optomechanical experiment, based on a Fabry-Pérot cavity in which the end mirror is a high Q micro-mechanical device [2], where we have simultaneously measured intensity fluctuations of the field reflected by the cavity and the mirror motion imprinted in the phase fluctuations. By exploiting the correlations between these variables, we demonstrate a reduced uncertainty on intensity fluctuations actually achieving a sub-shot noise level
Quantum motion of a squeezed mechanical oscillator attained via an optomechanical experiment
No full textWe experimentally investigate a mechanical squeezed state realized in a parametrically modulated membrane resonator embedded in an optical cavity. We demonstrate that a quantum characteristic of the squeezed dynamics can be revealed and quantified even in a moderately warm oscillator, through the analysis of motional sidebands. We provide a theoretical framework for quantitatively interpreting the observations and present an extended comparison with the experiment. A notable result is that the spectral shape of each motional sideband provides a clear signature of a quantum mechanical squeezed state without the necessity of absolute calibrations, in particular in the regime where residual fluctuations in the squeezed quadrature are reduced below the zero-point level. </p
Low Noise Opto-Electro-Mechanical Modulator for RF-to-Optical Transduction in Quantum Communications
No full textIn this work, we present an Opto-Electro-Mechanical Modulator (OEMM) for
RF-to-optical transduction realized via an ultra-coherent nanomembrane
resonator capacitively coupled to an rf injection circuit made of a
microfabricated read-out able to improve the electro-optomechanical
interaction. This device configuration can be embedded in a Fabry-Perot cavity
for electromagnetic cooling of the LC circuit in a dilution refrigerator
exploiting the opto-electro-mechanical interaction. To this aim, an optically
measured steady-state frequency shift of 380 Hz was seen with a polarization
voltage of 30 V and a -factor of the assembled device above at room
temperature. The rf-sputtered titanium nitride layer can be made
superconductive to develop efficient quantum~transducers.Comment: 14 pages, 8 figure
Quantum nondemolition measurement of optical field fluctuations by optomechanical interaction
No full textAccording to quantum mechanics, if we keep observing a continuous variable we generally disturb its evolution.
For a class of observables, however, it is possible to implement a so-called quantum nondemolition measurement:
by confining the perturbation to the conjugate variable, the observable is estimated with arbitrary accuracy, or
prepared in a well-known state. For instance, when the light bounces on a movable mirror, its intensity is not
perturbed (the effect is just seen on the phase of the radiation), but the radiation pressure allows one to trace back
its fluctuations by observing the mirror motion. In this work, we implement a cavity optomechanical experiment
based on an oscillating micromirror, and we measure correlations between the output light intensity fluctuations
and the mirror motion. We demonstrate that the uncertainty of the former is reduced below the shot-noise level
determined by the corpuscular nature of light
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