Measurement of minuscule forces and displacements with ever greater precision encounters a limit imposed by a pillar of quantum mechanics: the Heisenberg uncertainty principle. A limit to the ...precision with which the position of an object can be measured continuously is known as the standard quantum limit (SQL). When light is used as the probe, the SQL arises from the balance between the uncertainties of photon radiation pressure imposed on the object and of the photon number in the photoelectric detection. The only possibility surpassing the SQL is via correlations within the position/momentum uncertainty of the object and the photon number/phase uncertainty of the light it reflects. Here, we experimentally prove the theoretical prediction that this type of quantum correlation is naturally produced in the Laser Interferometer Gravitational-wave Observatory (LIGO). Our measurements show that the quantum mechanical uncertainties in the phases of the 200 kW laser beams and in the positions of the 40 kg mirrors of the Advanced LIGO detectors yield a joint quantum uncertainty a factor of 1.4 (3dB) below the SQL. We anticipate that quantum correlations will not only improve gravitational wave (GW) observatories but all types of measurements in future.
The oxidation of ferrous ion and the reduction of ceric ion in 0.80 N sulphuric acid by electrons from dissolved P
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and S
35
have been studied. The chemical yields (chemical change per unit energy ...absorbed) obtained agree well with those obtained using X or γ-radiation. The yield is independent of electron energy above about 5 kev. The results show that chemical dosimetry methods may be used for the accurate determination of energy absorption for electron energies as low as 45 kev. or X rays of 200 kev.
The absolute value of the yield of ferric ion on the irradiation of ferrous sulphate in 0.80 N sulphuric acid by γ-rays has been determined using the Bragg–Gray cavity principle. Sources of error in ...the measurements were reduced as much as possible. The yield obtained, 20.8 ± 0.3 ferric ions per 100 ev. absorbed, agrees well with Miller's value of 20.7 molecules per 100 ev.
The Advanced LIGO detectors have recently completed their second observation run successfully. The run lasted for approximately 10 months and lead to multiple new discoveries. The sensitivity to ...gravitational waves was partially limited by correlated noise. Here, we utilize auxiliary sensors that witness these correlated noise sources, and use them for noise subtraction in the time domain data. This noise and line removal is particularly significant for the LIGO Hanford Observatory, where the improvement in sensitivity is greater than 20%. Consequently, we were also able to improve the astrophysical estimation for the location, masses, spins and orbital parameters of the gravitational wave progenitors.
This paper presents an analysis of the transient behavior of the Advanced LIGO suspensions used to seismically isolate the optics. We have characterized the transients in the longitudinal motion of ...the quadruple suspensions during Advanced LIGO's first observing run. Propagation of transients between stages is consistent with modelled transfer functions, such that transient motion originating at the top of the suspension chain is significantly reduced in amplitude at the test mass. We find that there are transients seen by the longitudinal motion monitors of quadruple suspensions, but they are not significantly correlated with transient motion above the noise floor in the gravitational wave strain data, and therefore do not present a dominant source of background noise in the searches for transient gravitational wave signals.
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