55 research outputs found
Room-temperature quantum optomechanics using an ultra-low noise cavity
Ponderomotive squeezing of light, where a mechanical oscillator creates
quantum correlations between the phase and amplitude of the interacting light
field, is a canonical signature of the quantum regime of optomechanics. At room
temperature, this has only been reached in pioneering experiments where an
optical restoring force controls the oscillator stiffness, akin to the
vibrational motion of atoms in an optical lattice. These include both levitated
nanoparticles and optically-trapped cantilevers. Recent advances in engineered
mechanical resonators, where the restoring force is provided by material
rigidity rather than an external optical potential, have realized ultra-high
quality factors (Q) by exploiting `soft clamping'. However entering the quantum
regime with such resonators, has so far been prevented by optical cavity
frequency fluctuations and thermal intermodulation noise. Here, we overcome
this challenge and demonstrate optomechanical squeezing at room temperature in
a phononic-engineered membrane-in-the-middle system. By using a high finesse
cavity whose mirrors are patterned with phononic crystal structures, we reduce
cavity frequency noise by more than 700-fold. In this ultra-low noise cavity,
we introduce a silicon nitride membrane oscillator whose density is modulated
by silicon nano-pillars, yielding both high thermal conductance and a localized
mechanical mode with Q of 1.8e8. These advances enable operation within a
factor of 2.5 of the Heisenberg limit, leading to squeezing of the probing
field by 1.09 dB below the vacuum fluctuations. Moreover, the long thermal
decoherence time of the membrane oscillator (more than 30 vibrational periods)
allows us to obtain conditional displaced thermal states of motion with an
occupation of 0.97 phonon, using a multimode Kalman filter. Our work extends
quantum control of engineered macroscopic oscillators to room temperature
Clamp-tapering increases the quality factor of stressed nanobeams
Stressed nanomechanical resonators are known to have exceptionally high
quality factors () due to the dilution of intrinsic dissipation by stress.
Typically, the amount of dissipation dilution and thus the resonator is
limited by the high mode curvature region near the clamps. Here we study the
effect of clamp geometry on the of nanobeams made of high-stress
. We find that tapering the beam near the clamp - and locally
increasing the stress - leads to increased of MHz-frequency low order modes
due to enhanced dissipation dilution. Contrary to recent studies of
tethered-membrane resonators, we find that widening the clamps leads to
decreased despite increased stress in the beam bulk. The tapered-clamping
approach has practical advantages compared to the recently developed
"soft-clamping" technique. Tapered-clamping enhances the of the fundamental
mode and can be implemented without increasing the device size
Prometeu contra Hermes: o lugar do design no imaginário contemporâneo
This article proposes a reflection on the contemporary imaginary, taking the design as a central vector and two mythical figures, Hermes and Prometeu, as main coordinates. First, we make some considerations about the theoretical bases that support the approach proposed here, and then we indicate the way in which the figures of Prometeu and Hermes lead much of the sociocultural dynamics. Next, we analyze the post-Promethean paradigm that Bruno Latour identifies from five connotations of the term design. We conclude, finally, that the myths of Hermes and Prometheus are implied in each other and that the design expresses, in the contemporary imaginary, this correlation.Este artigo propõe uma reflexĂŁo sobre o imaginário contemporâneo, tomando o design como vetor central e duas figuras mĂticas, Hermes e Prometeu, como coordenadas principais. De inĂcio, tecemos algumas considerações acerca dasbases teĂłricas que amparam a abordagem aqui proposta e, em seguida, indicamos o modo como as figuras de Prometeu e Hermes conduzem boa parte da dinâmica sociocultural. Na sequĂŞncia, analisamos o paradigma pĂłs-prometeico que BrunoLatour identifica a partir de cinco conotações do termo design. ConcluĂmos, por fim, que os mitos de Hermes e Prometeu se encontram implicados um no outro e que o design expressa, no imaginário contemporâneo, essa correlação
Thermal intermodulation noise in cavity-based measurements
Thermal frequency fluctuations in optical cavities limit the sensitivity of
precision experiments ranging from gravitational wave observatories to optical
atomic clocks. Conventional modeling of these noises assumes a linear response
of the optical field to the fluctuations of cavity frequency. Fundamentally,
however, this response is nonlinear. Here we show that nonlinearly transduced
thermal fluctuations of cavity frequency can dominate the broadband noise in
photodetection, even when the magnitude of fluctuations is much smaller than
the cavity linewidth. We term this noise "thermal intermodulation noise" and
show that for a resonant laser probe it manifests as intensity fluctuations. We
report and characterize thermal intermodulation noise in an optomechanical
cavity, where the frequency fluctuations are caused by mechanical Brownian
motion, and find excellent agreement with our developed theoretical model. We
demonstrate that the effect is particularly relevant to quantum optomechanics:
using a phononic crystal membrane with a low mass, soft-clamped
mechanical mode we are able to operate in the regime where measurement quantum
backaction contributes as much force noise as the thermal environment does.
However, in the presence of intermodulation noise, quantum signatures of
measurement are not revealed in direct photodetectors. The reported noise
mechanism, while studied for an optomechanical system, can exist in any optical
cavity
Hierarchical tensile structures with ultralow mechanical dissipation
Structural hierarchy is found in myriad biological systems and has improved
man-made structures ranging from the Eiffel tower to optical cavities.
Hierarchical metamaterials utilize structure at multiple size scales to realize
new and highly desirable properties which can be strikingly different from
those of the constituent materials. In mechanical resonators whose rigidity is
provided by static tension, structural hierarchy can reduce the dissipation of
the fundamental mode to ultralow levels due to an unconventional form of soft
clamping. Here, we apply hierarchical design to silicon nitride nanomechanical
resonators and realize binary tree-shaped resonators with quality factors as
high as at 107 kHz frequency, reaching the parameter regime of levitated
particles. The resonators' thermal-noise-limited force sensitivities reach
at room temperature and $\mathrm{90\
zN/\sqrt{Hz}}$ at 6 K, surpassing state-of-the-art cantilevers currently used
for force microscopy. We also find that the self-similar structure of binary
tree resonators results in fractional spectral dimensions, which is
characteristic of fractal geometries. Moreover, we show that the hierarchical
design principles can be extended to 2D trampoline membranes, and we fabricate
ultralow dissipation membranes suitable for interferometric position
measurements in Fabry-P\'erot cavities. Hierarchical nanomechanical resonators
open new avenues in force sensing, signal transduction and quantum
optomechanics, where low dissipation is paramount and operation with the
fundamental mode is often advantageous.Comment: 19 pages, 11 figures. Fixed link to Zenodo repositor
DHFR Inhibitors Display a Pleiotropic Anti-Viral Activity against SARS-CoV-2: Insights into the Mechanisms of Action
During the COVID-19 pandemic, drug repurposing represented an effective strategy to obtain quick answers to medical emergencies. Based on previous data on methotrexate (MTX), we evaluated the anti-viral activity of several DHFR inhibitors in two cell lines. We observed that this class of compounds showed a significant influence on the virus-induced cytopathic effect (CPE) partly attributed to the intrinsic anti-metabolic activity of these drugs, but also to a specific anti-viral function. To elucidate the molecular mechanisms, we took advantage of our EXSCALATE platform for in-silico molecular modelling and further validated the influence of these inhibitors on nsp13 and viral entry. Interestingly, pralatrexate and trimetrexate showed superior effects in counteracting the viral infection compared to other DHFR inhibitors. Our results indicate that their higher activity is due to their polypharmacological and pleiotropic profile. These compounds can thus potentially give a clinical advantage in the management of SARS-CoV-2 infection in patients already treated with this class of drugs
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