1,470 research outputs found
Continuous variable entanglement using cold atoms
We present experimental demonstration of quadrature and polarization
entanglement generated via the interaction between a coherent linearly
polarized field and cold atoms in a high finesse optical cavity. The non linear
atom-field interaction produces two squeezed modes with orthogonal
polarizations which are used to generate a pair of non separable beams, the
entanglement of which is demonstrated by checking the inseparability criterion
for continuous variables recently derived by Duan et al. [Phys. Rev. Lett. 84,
2722 (2000)] and calculating the entanglement of formation [Giedke et al.,
Phys. Rev. Lett. 91, 107901 (2003)]
Entanglement storage in atomic ensembles
We propose to entangle macroscopic atomic ensembles in cavity using
EPR-correlated beams. We show how the field entanglement can be almost
perfectly mapped onto the long-lived atomic spins associated with the ground
states of the ensembles, and how it can be retrieved in the fields exiting the
cavities after a variable storage time. Such a continuous variable quantum
memory is of interest for manipulating entanglement in quantum networks
Self-cooling of a movable mirror to the ground state using radiation pressure
We show that one can cool a micro-mechanical oscillator to its quantum ground
state using radiation pressure in an appropriately detuned cavity
(self-cooling). From a simple theory based on Heisenberg-Langevin equations we
find that optimal self-cooling occurs in the good cavity regime, when the
cavity bandwidth is smaller than the mechanical frequency, but still larger
than the effective mechanical damping. In this case the intracavity field and
the vibrational mechanical mode coherently exchange their fluctuations. We also
present dynamical calculations which show how to access the mirror final
temperature from the fluctuations of the field reflected by the cavity.Comment: 4 pages, 3 figure
Cooling of a mirror by radiation pressure
We describe an experiment in which a mirror is cooled by the radiation
pressure of light. A high-finesse optical cavity with a mirror coated on a
mechanical resonator is used as an optomechanical sensor of the Brownian motion
of the mirror. A feedback mechanism controls this motion via the radiation
pressure of a laser beam reflected on the mirror. We have observed either a
cooling or a heating of the mirror, depending on the gain of the feedback loop.Comment: 4 pages, 6 figures, RevTe
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
High-sensitivity optical monitoring of a micro-mechanical resonator with a quantum-limited optomechanical sensor
We experimentally demonstrate the high-sensitivity optical monitoring of a
micro-mechanical resonator and its cooling by active control. Coating a
low-loss mirror upon the resonator, we have built an optomechanical sensor
based on a very high-finesse cavity (30000). We have measured the thermal noise
of the resonator with a quantum-limited sensitivity at the 10^-19 m/rootHz
level, and cooled the resonator down to 5K by a cold-damping technique.
Applications of our setup range from quantum optics experiments to the
experimental demonstration of the quantum ground state of a macroscopic
mechanical resonator.Comment: 4 pages, 5 figure
Sensitivity of a cavityless optomechanical system
We study the possibility of revealing a weak coherent force by using a
pendular mirror as a probe, and coupling this to a radiation field, which acts
as the meter, in a cavityless configuration. We determine the sensitivity of
such a scheme and show that the use of an entangled meter state greatly
improves the ultimate detection limit. We also compare this scheme with that
involving an optical cavity.Comment: 4 pages, RevTex file, 2 eps figures, provisionally accepted by Phys.
Rev.
Optomechanical characterization of acoustic modes in a mirror
We present an experimental study of the internal mechanical vibration modes
of a mirror. We determine the frequency repartition of acoustic resonances via
a spectral analysis of the Brownian motion of the mirror, and the spatial
profile of the acoustic modes by monitoring their mechanical response to a
resonant radiation pressure force swept across the mirror surface. We have
applied this technique to mirrors with cylindrical and plano-convex geometries,
and compared the experimental results to theoretical predictions. We have in
particular observed the gaussian modes predicted for plano-convex mirrors.Comment: 8 pages, 8 figures, RevTe
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
Creating and Verifying a Quantum Superposition in a Micro-optomechanical System
Micro-optomechanical systems are central to a number of recent proposals for
realizing quantum mechanical effects in relatively massive systems. Here we
focus on a particular class of experiments which aim to demonstrate massive
quantum superpositions, although the obtained results should be generalizable
to similar experiments. We analyze in detail the effects of finite temperature
on the interpretation of the experiment, and obtain a lower bound on the degree
of non-classicality of the cantilever. Although it is possible to measure the
quantum decoherence time when starting from finite temperature, an unambiguous
demonstration of a quantum superposition requires the mechanical resonator to
be in or near the ground state. This can be achieved by optical cooling of the
fundamental mode, which also provides a method to measure the mean phonon
number in that mode. We also calculate the rate of environmentally induced
decoherence and estimate the timescale for gravitational collapse mechanisms as
proposed by Penrose and Diosi. In view of recent experimental advances,
practical considerations for the realization of the described experiment are
discussed.Comment: 19 pages, 8 figures, published in New J. Phys. 10 095020 (2008);
minor revisions to improve clarity; fixed possibly corrupted figure
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