Information content of the gravitational field of a quantum superposition

Belenchia, Alessio; Wald, Robert M.; Giacomini, Flaminia; Castro-Ruiz, Esteban; Brukner, Časlav; Aspelmeyer, Markus

doi:10.1142/s0218271819430016

Cited by 47 publications

(75 citation statements)

References 9 publications

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“…Understanding the consequences of replacing gravitating classical matter by gravitating quantum systems in general relativity is at the heart of the problem of quantum gravity 1,2 . At the moment, a fully satisfactory and broadly accepted theory of quantum gravity is lacking, and it is far from clear how, if at all, the essential notions of quantum mechanics and general relativity will be modified in the more fundamental theory 3,4 .…”

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confidence: 99%

Quantum clocks and the temporal localisability of events in the presence of gravitating quantum systems

et al. 2020

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The standard formulation of quantum theory relies on a fixed space-time metric determining the localisation and causal order of events. In general relativity, the metric is influenced by matter, and is expected to become indefinite when matter behaves quantum mechanically. Here, we develop a framework to operationally define events and their localisation with respect to a quantum clock reference frame, also in the presence of gravitating quantum systems. We find that, when clocks interact gravitationally, the time localisability of events becomes relative, depending on the reference frame. This relativity ia a signature of an indefinite metric, where events can occur in an indefinite causal order. Even if the metric is indefinite, for any event we can find a reference frame where local quantum operations take their standard unitary dilation form. This form is preserved when changing clock reference frames, yielding physics covariant with respect to quantum reference frame transformations.

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confidence: 99%

Quantum clocks and the temporal localisability of events in the presence of gravitating quantum systems

et al. 2020

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“…Masses below this will lead to a violation of the bound set by Eq. (14). The resulting minimum mass correspond to the lowest mass seen in Fig.…”

Section: B Casimir Screeningmentioning

confidence: 71%

“…, (14) during the free fall, the inner states will travel a distance s inwards during the time interval t. Note that the center of mass distance d is a "tunable" distance in an experiment, controlled by the parameter N as given in Eq. (11).…”

Section: B Casimir Screeningmentioning

confidence: 99%

Quantum gravity witness via entanglement of masses: Casimir screening

et al. 2020

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A recently proposed experimental protocol for quantum gravity induced entanglement of masses (QGEM) requires in principle realizable, but still very ambitious, set of parameters in matter-wave interferometry. Motivated by easing the experimental realization, in this paper, we consider the parameter space allowed by a slightly modified experimental design, which mitigates the Casimir potential between two spherical neutral test masses by separating the two macroscopic interferometers by a thin conducting plate. Although this setup will reintroduce a Casimir potential between the conducting plate and the masses, there are several advantages of this design. First, the quantum gravity induced entanglement between the two superposed masses will have no Casimir background. Secondly, the matter-wave interferometry itself will be greatly facilitated by allowing both the mass 10 −16-10 −15 kg and the superposition size x ∼ 20 μm to be a one-two order of magnitude smaller than those proposed earlier, and thereby also two orders of magnitude smaller magnetic field gradient of 10 4 Tm −1 to create that superposition through the Stern-Gerlach effect. In this context, we will further investigate the collisional decoherences and decoherence due to vibrational modes of the conducting plate.

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“…[1] (supplementary material) and Refs. [2,20,[31][32][33][34][35][36][37]. There have also been noise analysis [38], as well as related independent suggestions [39,40] and paradox resolutions [41,42] which point toward the necessity of gravity to be quantum in nature.…”

Section: Introductionmentioning

confidence: 99%

Locality and entanglement in table-top testing of the quantum nature of linearized gravity

2020

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This paper points out the importance of the assumption of locality of physical interactions, and the concomitant necessity of propagation of an entity (in this case, off-shell quanta-virtual gravitons) between two nonrelativistic test masses in unveiling the quantum nature of linearized gravity through a laboratory experiment. At the outset, we will argue that observing the quantum nature of a system is not limited to evidencing O(h) corrections to a classical theory: it instead hinges upon verifying tasks that a classical system cannot accomplish. We explain the background concepts needed from quantum field theory and quantum information theory to fully appreciate the previously proposed table-top experiments, namely forces arising through the exchange of virtual (off-shell) quanta, as well as local operations and classical communication (LOCC) and entanglement witnesses. We clarify the key assumption inherent in our evidencing experiment, namely the locality of physical interactions, which is a generic feature of interacting systems of quantum fields around us, and naturally incorporate microcausality in the description of our experiment. We also present the types of states the matter field must inhabit, putting the experiment on firm relativistic quantum-field-theoretic grounds. At the end, we use a nonlocal theory of gravity to illustrate how our mechanism may still be used to detect the qualitatively quantum nature of a force when the scale of nonlocality is finite. We find that the scale of nonlocality, including the entanglement entropy production in local and nonlocal gravity, may be revealed from the results of our experiment.

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Information content of the gravitational field of a quantum superposition

Cited by 47 publications

References 9 publications

Quantum clocks and the temporal localisability of events in the presence of gravitating quantum systems

Quantum clocks and the temporal localisability of events in the presence of gravitating quantum systems

Quantum gravity witness via entanglement of masses: Casimir screening

Locality and entanglement in table-top testing of the quantum nature of linearized gravity

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