539 research outputs found
Feedback Enhanced Sensitivity in Optomechanics: Surpassing the Parametric Instability Barrier
The intracavity power, and hence sensitivity, of optomechanical sensors is
commonly limited by parametric instability. Here we characterize the parametric
instability induced sensitivity degradation in a micron scale cavity
optomechanical system. Feedback via optomechanical transduction and electrical
gradient force actuation is applied to suppress the parametric instability. As
a result a 5.4 fold increase in mechanical motion transduction sensitivity is
achieved to a final value of .Comment: 4 pages, 4 figure
Minimum requirements for feedback enhanced force sensing
The problem of estimating an unknown force driving a linear oscillator is
revisited. When using linear measurement, feedback is often cited as a
mechanism to enhance bandwidth or sensitivity. We show that as long as the
oscillator dynamics are known, there exists a real-time estimation strategy
that reproduces the same measurement record as any arbitrary feedback protocol.
Consequently some form of nonlinearity is required to gain any advantage beyond
estimation alone. This result holds true in both quantum and classical systems,
with non-stationary forces and feedback, and in the general case of
non-Gaussian and correlated noise. Recently, feedback enhanced incoherent force
sensing has been demonstrated [Nat. Nano. \textbf{7}, 509 (2012)], with the
enhancement attributed to a feedback induced modification of the mechanical
susceptibility. As a proof-of-principle we experimentally reproduce this result
through straightforward filtering.Comment: 5 pages + 2 pages of Supplementary Informatio
Thin film superfluid optomechanics
Excitations in superfluid helium represent attractive mechanical degrees of
freedom for cavity optomechanics schemes. Here we numerically and analytically
investigate the properties of optomechanical resonators formed by thin films of
superfluid He covering micrometer-scale whispering gallery mode cavities.
We predict that through proper optimization of the interaction between film and
optical field, large optomechanical coupling rates kHz
and single photon cooperativities are achievable. Our analytical model
reveals the unconventional behaviour of these thin films, such as thicker and
heavier films exhibiting smaller effective mass and larger zero point motion.
The optomechanical system outlined here provides access to unusual regimes such
as and opens the prospect of laser cooling a liquid into its
quantum ground state.Comment: 18 pages, 6 figure
Modelling of vorticity, sound and their interaction in two-dimensional superfluids
Vorticity in two-dimensional superfluids is subject to intense research
efforts due to its role in quantum turbulence, dissipation and the BKT phase
transition. Interaction of sound and vortices is of broad importance in
Bose-Einstein condensates and superfluid helium [1-4]. However, both the
modelling of the vortex flow field and of its interaction with sound are
complicated hydrodynamic problems, with analytic solutions only available in
special cases. In this work, we develop methods to compute both the vortex and
sound flow fields in an arbitrary two-dimensional domain. Further, we analyse
the dispersive interaction of vortices with sound modes in a two-dimensional
superfluid and develop a model that quantifies this interaction for any vortex
distribution on any two-dimensional bounded domain, possibly non-simply
connected, exploiting analogies with fluid dynamics of an ideal gas and
electrostatics. As an example application we use this technique to propose an
experiment that should be able to unambiguously detect single circulation
quanta in a helium thin film.Comment: 23 pages, 8 figure
Estimates of tropical bromoform emissions using an inversion method
Abstract. Bromine plays an important role in ozone chemistry in both the troposphere and stratosphere. When measured by mass, bromoform (CHBr3) is thought to be the largest organic source of bromine to the atmosphere. While seaweed and phytoplankton are known to be dominant sources, the size and the geographical distribution of CHBr3 emissions remains uncertain. Particularly little is known about emissions from the Maritime Continent, which have usually been assumed to be large, and which appear to be especially likely to reach the stratosphere. In this study we aim to reduce this uncertainty by combining the first multi-annual set of CHBr3 measurements from this region, and an inversion process, to investigate systematically the distribution and magnitude of CHBr3 emissions. The novelty of our approach lies in the application of the inversion method to CHBr3. We find that local measurements of a short-lived gas like CHBr3 can be used to constrain emissions from only a relatively small, sub-regional domain. We then obtain detailed estimates of CHBr3 emissions within this area, which appear to be relatively insensitive to the assumptions inherent in the inversion process. We extrapolate this information to produce estimated emissions for the entire tropics (defined as 20° S–20° N) of 225 Gg CHBr3 yr−1. The ocean in the area we base our extrapolations upon is typically somewhat shallower, and more biologically productive, than the tropical average. Despite this, our tropical estimate is lower than most other recent studies, and suggests that CHBr3 emissions in the coastline-rich Maritime Continent may not be stronger than emissions in other parts of the tropics.
M. Ashfold thanks the Natural Environment
Research Council (NERC) for a research studentship, and is
grateful for support through the ERC ACCI project (project
number 267760). N. Harris is supported by a NERC Advanced
Research Fellowship. This work was supported through the EU
SHIVA project, through the NERC OP3 project, and NERC
grants NE/F020341/1 and NE/J006246/1. We also acknowledge
the Department of Energy and Climate Change for their support
in the development of InTEM (contract GA0201). For field site
support we thank S.-M. Phang, A. A. Samah and M. S. M. Nadzir
of Universiti Malaya, S. Ong and H. E. Ung of Global Satria,
Maznorizan Mohamad, L. K. Peng and S. E. Yong of the Malaysian
Meteorological Department, the Sabah Foundation, the Danum
Valley Field Centre and the Royal Society. This paper constitutes
publication no. 613 of the Royal Society South East Asia Rainforest
Research Programme.This is the final published version. It first appeared at http://www.atmos-chem-phys.net/14/979/2014/acp-14-979-2014.html
Emergent Error Correcting States in Networks of Nonlinear Oscillators
Networks of nonlinear oscillators can exhibit complex collective behaviour
ranging from synchronised states to chaos. Here, we simulate the dynamics of
three coupled Duffing oscillators whose multiple equilibrium states can be used
for information processing and storage. Our analysis reveals that even for this
small network, there is the emergence of an error correcting phase where the
system autonomously corrects errors from random impulses. The system has
several surprising and attractive features, including dynamic isolation of
resonators exposed to extreme impulses and the ability to correct simultaneous
errors. The existence of an error correcting phase opens the prospect of
fault-tolerant information storage, with particular applications in
nanomechanical computing
Engineered entropic forces allow ultrastrong dynamical backaction
When confined within an optical cavity, light can exert strong radiation
pressure forces. Combined with dynamical backaction, this enables important
processes such as laser cooling, and applications ranging from precision
sensors to quantum memories and interfaces. However, the magnitude of radiation
pressure forces is constrained by the energy mismatch between photons and
phonons. Here, we overcome this barrier using entropic forces arising from the
absorption of light. We show that entropic forces can exceed the radiation
pressure force by eight orders of magnitude, and demonstrate this using a
superfluid helium third-sound resonator. We develop a framework to engineer the
dynamical backaction from entropic forces, applying it to achieve phonon lasing
with a threshold three orders of magnitude lower than previous work. Our
results present a pathway to exploit entropic forces in quantum devices, and to
study nonlinear fluid phenomena such as turbulence and solitons.Comment: Main text is 10 pages, 5 figures. Supplements is 21 pages, 11 figure
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