A ring-laser-gyro (RLG) is a rotation sensor based on the Sagnac effect. Its ultimate sensitivity is given by the shot-noise. RLG are ring optical cavities where an in-cavity optically active laser volume emits two counter propagating beams. They, if the cavity is rotating and due to the Sagnac effect, show different frequencies. This frequency difference is proportional to the rotation rate of the ring itself. Here we present noise floor measurement for a large ring laser showing that the reached sensitivity level is not consistent with an independent beam model. The measured sensitivity is, indeed, about one order of magnitude better than expected. This is most probably due to coupling of the phases of the two beams mediated by the laser medium and mirror back-scattering. This result paves the way to the use of large RLGs in a wide range of measures in fundamental physics as well as to experimentally investigating quantum effects in non-inertial reference frames. In this contribution, starting from the experimental findings, we will discuss the necessary modifications to the theory and give some hints to understand the role of the above-mentioned mechanisms.
As recently demonstrated [T. Bagci, et al., Nature 507, 81 (2013)], an opto-electro-mechanical system formed by a nanomembrane, capacitively coupled to an LC resonator and to an optical interferometer, may be employed for the high{sensitive optical readout of rf signals. Here we show through a proof of principle device how the bandwidth of such kind of transducer can be increased by controlling the interference between the electromechanical interaction pathways of a two{mode mechanical system. The transducer reaches a sensitivity of 10 nV=Hz1/2 over a bandwidth of 5 kHz and a broader band sensitivity of 300 nV=Hz1/2 over a bandwidth of 15 kHz. We discuss strategies for improving the performance of the device, showing that, for the same given sensitivity, a mechanical multi-mode transducer can achieve a bandwidth significantly larger than that of a single-mode one.
In recent years the interest in the manipulation of quantum systems has furthered new strategies for maintaining
their coherence, continuously threatened by unwanted and uncontrollable interactions with the environment.
Photons interact weakly with the surroundings. Even so decoherence may significantly affect their polarization
state during the propagation within dispersive media because of the unavoidable presence of more than a single
frequency in the envelope of the photon pulse. Here we report on a suppression of the polarization decoherence in
a ring cavity obtained by properly retooling for the photon qubit the "bang-bang" protection technique already
employed for nuclear spins and nuclear-quadrupole qubits. Our results show that bang-bang control can be
profitably extended to all quantum information processes involving flying polarization qubits.
We consider an optical cavity made by two moving mirrors and driven by an intense classical laser field. We
determine the steady state of he optomechanical system and show that two vibrational modes of the mirrors,
with effective mass of the order of micrograms, can be entangled thanks to the effect of radiation pressure. The
resulting entanglement is however quite fragile with respect to temperature.
We study the possibility to reveal a weak coherent force acting on a movable mirror (probe) by coupling it to a radiation field (meter) in a cavityless configuration. We determine the sensitivity of such a model and we show that the use of entangled meter state greatly improves the ultimate detection limit. A comparison of the presented model with that involving optical cavity is also done.
We apply the quantum locking scheme recently proposed by Courty et al. [Phys. Rev. Lett. 90, 083601 (2003)]
for the reduction of back action noise to the realistic case of a gravitational wave interferometer. We show that by applying an active control to each mirror of the interferometer it is possible to improve significatively its sensitivity by reducing the radiation pressure noise.
We present a detailed study of how phase-sensitive feedback schemes
can be used to improve the performance of optomechanical devices.
Considering the case of a cavity mode coupled to an oscillating mirror by the radiation pressure, we show how feedback can be used to reduce the position noise spectrum of the mirror, cool it to its quantum ground state, or achieve position squeezing. Then, we show that even though feedback is not able to improve the sensitivity of stationary position spectral measurements, it is possible to design a
nonstationary strategy able to increase this sensitivity.
We predict the appearance of purely quantum effects within a radiation field upon reflection on a movable mirror. The model of an optical cavity having an oscillating end mirror is employed, and the role of thermal noise associated to this mechanical motion is studied.
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