600 research outputs found
Back-action cancellation in interferometers by quantum locking
We show that back-action noise in interferometric measurements such as
gravitational-waves detectors can be completely suppressed by a local control
of mirrors motion. An optomechanical sensor with an optimized measurement
strategy is used to monitor mirror displacements. A feedback loop then
eliminates radiation-pressure effects without adding noise. This very efficient
technique leads to an increased sensitivity for the interferometric
measurement, which becomes only limited by phase noise. Back-action
cancellation is furthermore insensitive to losses in the interferometer.Comment: 4 pages, 3 figures, RevTe
Direct Measurement of the Photon Statistics of a Triggered Single Photon Source
We studied intensity fluctuations of a single photon source relying on the
pulsed excitation of the fluorescence of a single molecule at room temperature.
We directly measured the Mandel parameter Q(T) over 4 orders of magnitude of
observation timescale T, by recording every photocount. On timescale of a few
excitation periods, subpoissonian statistics is clearly observed and the
probablility of two-photons events is 10 times smaller than Poissonian pulses.
On longer times, blinking in the fluorescence, due to the molecular triplet
state, produces an excess of noise.Comment: 4 pages, 3 figures, 1 table submitted to Physical Review Letter
Quantum fluctuations for drag free geodesic motion
The drag free technique is used to force a proof mass to follow a geodesic
motion. The mass is protected from perturbations by a cage, and the motion of
the latter is actively controlled to follow the motion of the proof mass. We
present a theoretical analysis of the effects of quantum fluctuations for this
technique. We show that a perfect drag free operation is in principle possible
at the quantum level, in spite of the back action exerted on the mass by the
position sensor.Comment: 4 pages, 1 figure, RevTeX, minor change
Beating quantum limits in interferometers with quantum locking of mirrors
The sensitivity in interferometric measurements such as gravitational-wave
detectors is ultimately limited by quantum noise of light. We discuss the use
of feedback mechanisms to reduce the quantum effects of radiation pressure.
Recent experiments have shown that it is possible to reduce the thermal motion
of a mirror by cold damping. The mirror motion is measured with an
optomechanical sensor based on a high-finesse cavity, and reduced by a feedback
loop. We show that this technique can be extended to lock the mirror at the
quantum level. In gravitational-waves interferometers with Fabry-Perot cavities
in each arms, it is even possible to use a single feedback mechanism to lock
one cavity mirror on the other. This quantum locking greatly improves the
sensitivity of the interferometric measurement. It is furthermore insensitive
to imperfections such as losses in the interferometer
Quantum noise in ideal operational amplifiers
We consider a model of quantum measurement built on an ideal operational
amplifier operating in the limit of infinite gain, infinite input impedance and
null output impedance and with a feddback loop. We evaluate the intensity and
voltage noises which have to be added to the classical amplification equations
in order to fulfill the requirements of quantum mechanics. We give a
description of this measurement device as a quantum network scattering quantum
fluctuations from input to output ports.Comment: 4 pages, 2 figures, RevTe
The Waveform Digitiser of the Double Chooz Experiment: Performance and Quantisation Effects on PhotoMultiplier Tube Signals
We present the waveform digitiser used in the Double Chooz experiment. We
describe the hardware and the custom-built firmware specifically developed for
the experiment. The performance of the device is tested with regards to
digitising low light level signals from photomultiplier tubes and measuring
pulse charge. This highlights the role of quantisation effects and leads to
some general recommendations on the design and use of waveform digitisers.Comment: 14 pages, 8 figures, accepted for publication in JINS
MidâHolocene site formation, diagenesis and human activity at the foothills of Serra da Estrela (Portugal)
UIDB/00749/2020 UIDP/00749/2020The Neolithic occupation of Penedo dos Mouros in the foothills of Serra da Estrela, PortugalÊŒs highest mountain, dates to the 5th to 4th millennia cal B.C. The siteÊŒs faunal assemblage is extremely rare in the regional prehistoric archaeological record, due to the acidity of the granitic geology. This underlines Penedo dos Mouros importance as a reference site for understanding early pastoralism in the region. Due to the insufficient survival of bone collagen for radiocarbon dating and the homogeneity of the stratigraphy, where most visible contacts are due to postdepositional processes, we chose micromorphology to address the reasons behind the bone preservation and to assess the stratigraphic integrity of the prehistoric deposit. Reworking of eroding saprolitic soils was a major factor in the sediment accumulation, with remains of short human occupation events. Possible evidence for clearance fires linked to the first occurrences of pastoralism practised in the region, creating open spaces for grazing, was identified. Postâdepositional carbonate cementation derived from ashes, identifiable at the microscopic scale, enabled bone preservation. Carbonate and spodicâlike features document water saturation once the sedimentation ceased. This sedimentary dynamic has broader geomorphological implications, such as an inferred postâNeolithic incision of the stream valley adjacent to the site.publishersversionpublishe
On testing the violation of the Clausius inequality in nanoscale electric circuits
The Clausius inequality, one of the classical formulations of the second law,
was recently found to be violated in the quantum regime. Here this result is
formulated in the context of a mesoscopic or nanoscale linear RLC circuit
interacting with a thermal bath. Previous experiments in this and related
fields are analyzed and possibilities of experimental detection of the
violation are pointed out. It is discussed that recent experiments reached the
range of temperatures, where the effect should be visible, and that a part of
the proposal was already confirmed.Comment: 5 pages revtex 4. No figure
Reverse Automatic Differentiation for Optimum Design: from Adjoint State Assembly to Gradient Computation
The utilization of reverse mode Automatic Differentiation to the adjoint method for solving an Optimal Design problem is described. Using the reverse mode, we obtain the adjoint system residual in a rather efficient way. But memory requirements may be very large. The family of programs to differentiate involves many independant calculations, typically in parallel loops. Then we propose to apply a reverse differentiation «by iteration». This demands much less memory storage. This methods is used for the computing of the adjoint state and gradient related to the Optimal Design problem
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