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Quantum limit on time measurement in a gravitational field
http://hdl.handle.net/2289/6185
Title: Quantum limit on time measurement in a gravitational field<br/><br/>Authors: Sinha, Supurna; Samuel, J.<br/><br/>Abstract: Good clocks are of importance both to fundamental physics and for applications in astronomy, metrology and global positioning systems. In a recent technological breakthrough, researchers at NIST have been able to achieve a stability of one part in 1018 using an ytterbium clock. This naturally raises the question of whether there are fundamental limits to time keeping. In this article we point out that gravity and quantum mechanics set a fundamental limit on the fractional frequency uncertainty of clocks. This limit comes from a combination of the uncertainty relation, the gravitational redshift and the relativistic time dilation effect. For example, a single ion aluminium clock in a terrestrial gravitational field cannot achieve a fractional frequency uncertainty better than one part in 1022. This fundamental limit explores the interaction between gravity and quantum mechanics on a laboratory scale.<br/><br/>Description: Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)Wed, 07 Jan 2015 22:58:59 GMTTwo-step orthogonal-state-based protocol of quantum secure direct communication with the help of order-rearrangement technique
http://hdl.handle.net/2289/6181
Title: Two-step orthogonal-state-based protocol of quantum secure direct communication with the help of order-rearrangement technique<br/><br/>Authors: Yadav, Preeti; Srikanth, R.; Pathank, Anirban<br/><br/>Abstract: The Goldenberg–Vaidman (GV) protocol for quantum key distribution uses orthogonal encoding states of a particle. Its security arises because operations accessible to Eve are insufficient to distinguish the two states encoding the secret bit. We propose a two-particle cryptographic protocol for quantum secure direct communication, wherein orthogonal states encode the secret, and security arises from restricting Eve from accessing any two-particle operations. However, there is a non-trivial difference between the two cases. While the encoding states are perfectly indistinguishable in GV, they are partially distinguishable in the bipartite case, leading to a qualitatively different kind of information-versus-disturbance trade-off and also options for Eve in the two cases.<br/><br/>Description: Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)Fri, 28 Nov 2014 22:58:59 GMTMultimessenger search for sources of gravitational waves and high-energy neutrinos: Initial results for LIGO-Virgo and IceCube
http://hdl.handle.net/2289/6177
Title: Multimessenger search for sources of gravitational waves and high-energy neutrinos: Initial results for LIGO-Virgo and IceCube<br/><br/>Authors: Aartsen, M.G.; Ackermann, M.; Iyer, B.R.; IceCube Collaboration; LIGO Scientific Collaboration and Virgo Collaboration; +800 Co authors<br/><br/>Abstract: We report the results of a multimessenger search for coincident signals from the LIGO and Virgo gravitational-wave observatories and the partially completed IceCube high-energy neutrino detector, including periods of joint operation between 2007–2010. These include parts of the 2005–2007 run and the 2009–2010 run for LIGO-Virgo, and IceCube’s observation periods with 22, 59 and 79 strings. We find no significant coincident events, and use the search results to derive upper limits on the rate of joint sources for a range of source emission parameters. For the optimistic assumption of gravitational-wave emission energy of 10−2 M⊙c2 at ∼150 Hz with ∼60 ms duration, and high-energy neutrino emission of 1051 erg comparable to the isotropic gamma-ray energy of gamma-ray bursts, we limit the source rate below 1.6×10−2 Mpc−3 yr−1. We also examine how combining information from gravitational waves and neutrinos will aid discovery in the advanced gravitational-wave detector era<br/><br/>Description: Open AccessSun, 16 Nov 2014 22:58:59 GMTSearching for stochastic gravitational waves using data from the two colocated LIGO Hanford detectors
http://hdl.handle.net/2289/6157
Title: Searching for stochastic gravitational waves using data from the two colocated LIGO Hanford detectors<br/><br/>Authors: Aasi, J.; Abadie, J.; Abbott, B.P.; Abbott, R.; Iyer, B.R.; LIGO Scientific Collaboration and Virgo Collaboration; +842 Co authors<br/><br/>Abstract: Searches for a stochastic gravitational-wave background (SGWB) using terrestrial detectors typically involve cross-correlating data from pairs of detectors. The sensitivity of such cross-correlation analyses depends, among other things, on the separation between the two detectors: the smaller the separation, the better the sensitivity. Hence, a colocated detector pair is more sensitive to a gravitational-wave background than a noncolocated detector pair. However, colocated detectors are also expected to suffer from correlated noise from instrumental and environmental effects that could contaminate the measurement of the background. Hence, methods to identify and mitigate the effects of correlated noise are necessary to achieve the potential increase in sensitivity of colocated detectors. Here we report on the first SGWB analysis using the two LIGO Hanford detectors and address the complications arising from correlated environmental noise. We apply correlated noise identification and mitigation techniques to data taken by the two LIGO Hanford detectors, H1 and H2, during LIGO’s fifth science run. At low frequencies, 40–460 Hz, we are unable to sufficiently mitigate the correlated noise to a level where we may confidently measure or bound the stochastic gravitational-wave signal. However, at high frequencies, 460–1000 Hz, these techniques are sufficient to set a 95% confidence level upper limit on the gravitational-wave energy density of Ω(f)<7.7×10−4(f/900 Hz)3, which improves on the previous upper limit by a factor of ∼180. In doing so, we demonstrate techniques that will be useful for future searches using advanced detectors, where correlated noise (e.g., from global magnetic fields) may affect even widely separated detectors.<br/><br/>Description: Open AccessWed, 14 Jan 2015 22:58:59 GMT