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Register a new userOn testing quantum gravity with interactive information sensing
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Onur Hosten
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We show that the atom interferometric coherence revival test suggested in [arXiv:2101.11629 [quant-ph] (2021)] does not test the quantum nature of the gravitational field when the atoms are coupled to a mechanical oscillator prepared in a thermal state. Specifically we clarify that the same coherence revivals take place in a model where the atoms are coupled to a classical oscillator through a classical gravitational field. We further elucidate the quantum mechanical calculation, showing that entanglement is not the source of the revivals. The suggested test is thus only relevant for pure initial quantum states of the oscillator. In this regime, numerical estimates show that it is unfeasible to do a test of the proposed type.
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We challenge the analysis and conclusions of the paper Phys. Rev. Lett. 109, 141103 (2012) by V. Gharibyan on the tests of Planck-scale gravity with accelerators. The main objective of the Comment is the observation that the explored domain of quantum gravity parameters is already ruled out experimentally from, e.g., absence of the vacuum Cherenkov radiation.
According to quantum mechanics, the informational content of isolated systems does not change in time. However, subadditivity of entropy seems to describe an excess of information when we look at single parts of a composite systems and their correlations. Moreover, the balance between the entropic contributions coming from the various parts is not conserved under unitary transformations. Reasoning on the basic concept of quantum mechanics, we find that in such a picture an important term has been overlooked: the intrinsic quantum information encoded in the coherence of pure states. To fill this gap we are led to define a quantity, that we call coherent entropy, which is necessary to account for the missing information and for re-establishing its conservation. Interestingly, the coherent entropy is found to be equal to the information conveyed in the future by quantum states. The perspective outlined in this paper may be of some inspiration in several fields, from foundations of quantum mechanics to black-hole physics.
We use the cosmic shear data from the Canada-France-Hawaii Telescope Lensing Survey to place constraints on $f(R)$ and {it Generalized Dilaton} models of modified gravity. This is highly complimentary to other probes since the constraints mainly come from the non-linear scales: maximal deviations with respects to the General-Relativity + $Lambda$CDM scenario occurs at $ksim1 h mbox{Mpc}^{-1}$. At these scales, it becomes necessary to account for known degeneracies with baryon feedback and massive neutrinos, hence we place constraints jointly on these three physical effects. To achieve this, we formulate these modified gravity theories within a common tomographic parameterization, we compute their impact on the clustering properties relative to a GR universe, and propagate the observed modifications into the weak lensing $xi_{pm}$ quantity. Confronted against the cosmic shear data, we reject the $f(R)$ ${ |f_{R_0}|=10^{-4}, n=1}$ model with more than 99.9% confidence interval (CI) when assuming a $Lambda$CDM dark matter only model. In the presence of baryonic feedback processes and massive neutrinos with total mass up to 0.2eV, the model is disfavoured with at least 94% CI in all different combinations studied. Constraints on the ${ |f_{R_0}|=10^{-4}, n=2}$ model are weaker, but nevertheless disfavoured with at least 89% CI. We identify several specific combinations of neutrino mass, baryon feedback and $f(R)$ or Dilaton gravity models that are excluded by the current cosmic shear data. Notably, universes with three massless neutrinos and no baryon feedback are strongly disfavoured in all modified gravity scenarios studied. These results indicate that competitive constraints may be achieved with future cosmic shear data.
Weak equivalence principle (WEP) is one of the cornerstones of the modern theories of gravity, stating that the trajectory of a freely falling test body is independent of its internal structure and composition. Even though WEP is known to be valid for the normal matter with a high precision, it has never been experimentally confirmed for relativistic matter and antimatter. We make an attempt to constrain possible deviations from WEP utilizing the modern accelerator technologies. We analyze the (absence of) vacuum Cherenkov radiation, photon decay, anomalous synchrotron losses and the Compton spectra to put limits on the isotropic Lorentz violation and further convert them to the constraints on the difference between the gravitational and inertial masses of the relativistic electrons/positrons. Our main result is the 0.1% limit on the mentioned difference.
Bells inequality is a strong criterion to distinguish classic and quantum mechanical aspects of reality. Its violation is the net effect of the non-locality stored in the Heisenberg uncertainty principle (HUP) generalized by quantum gravity scenarios, called generalized uncertainty principle (GUP). Here, the effects of GUP on Bell-like operators of two, and three outcomes, as well as continuous cases, are studied. The achievements claim that the violation quality of Bells and Bell-like inequalities may be a proper tool to get better understanding of the quantum features of gravity and its effects on reality. Indeed, it is obtained that the current accuracy of Stern-Gerlach experiments implies $beta_0ll10^{23}$.
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