Quantum superposition of massive objects and the quantization of gravity

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

doi:10.1103/physrevd.98.126009

Cited by 198 publications

(247 citation statements)

References 38 publications

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“…It is also worth comparing our scheme to other proposals reported in literature so far, a non-exhaustive list including [47][48][49][50][51][52][53][54][55]57]. Among them, let us mention that [47] is based on the possibility to generate Schrödinger cat states of a mechanical oscillator through the use of a superposition of optical field states with exactly 0 and n excitations, which is very challenging to achieve experimentally, on its own.…”

Section: Revelation Strategiesmentioning

confidence: 99%

Testing the gravitational field generated by a quantum superposition

et al. 2019

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What gravitational field is generated by a massive quantum system in a spatial superposition? Despite decades of intensive theoretical and experimental research, we still do not know the answer. On the experimental side, the difficulty lies in the fact that gravity is weak and requires large masses to be detectable. However, it becomes increasingly difficult to generate spatial quantum superpositions for increasingly large masses, in light of the stronger environmental effects on such systems. Clearly, a delicate balance between the need for strong gravitational effects and weak decoherence should be found. We show that such a trade off could be achieved in an optomechanics scenario that allows to witness whether the gravitational field generated by a quantum system in a spatial superposition is in a coherent superposition or not. We estimate the magnitude of the effect and show that it offers perspectives for observability.Quantum field theory is one of the most successful theories ever formulated. All matter fields, together with the electromagnetic and nuclear forces, have been successfully embedded in the quantum framework. They form the standard model of elementary particles, which not only has been confirmed in all advanced accelerator facilities, but has also become an essential ingredient for the description of the Universe and its evolution.In light of this, it is natural to seek a quantum formulation of gravity as well. Yet, the straightforward procedure for promoting the classical field as described by general relativity, into a quantum field, does not work. Several strategies have been put forward, which turned into very sophisticated theories of gravity, the most advanced being string theory and loop quantum gravity. Yet, none of them has reached the goal of providing a fully consistent quantum theory of gravity.At this point, one might wonder whether the very idea of quantizing gravity is correct [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. At the end of the day, according to general relativity, gravity is rather different from all other forces. Actually, it is not a force at all, but a manifestation of the curvature of spacetime, and there is no obvious reason why the standard approach to the quantization of fields should work for spacetime as well. A future unified theory of quantum and gravitational phenomena might require a radical revision not only of our notions of space and time, but also of (quantum) matter. This scenario is growing in likeliness [18][19][20].From the experimental point of view, it has now been ascertained that quantum matter (i.e. matter in a genuine quantum state, such as a coherent superposition state) couples to the Earth's gravity in the most obvious way. This has been confirmed in neutron [21], atom [22] interferometers and used for velocity selection in molecular interferometry [23]. However, in all cases, the gravitational field is classical, i.e. it is generated by a distribution of matter (the Earth) in a fully classical state. Therefore, the pleth...

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Section: Revelation Strategiesmentioning

confidence: 99%

Testing the gravitational field generated by a quantum superposition

et al. 2019

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“…Due to the large mass of the mechanical element, many * sofiaqvarfort@gmail.com † dennis.raetzel@physik.hu-berlin.de ‡ david.edward.bruschi@gmail.com proposals in fundamental physics could potentially be tested with optomechanical experiments, such as collapse theories [15][16][17]. Furthermore, optomechanical systems have been proposed as the main experimental platform for detection of possible low-energy quantum gravity effects [18][19][20]. In terms of force sensing, microspheres optically trapped in a lattice have been considered [21,22], as well as mesoscopic interferometry for the purpose of gravitational wave detection [23].…”

Section: Introductionmentioning

confidence: 99%

Optimal estimation with quantum optomechanical systems in the nonlinear regime

et al. 2020

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We study the fundamental bounds on precision measurements of parameters contained in a timedependent nonlinear optomechanical Hamiltonian, which includes the nonlinear light-matter coupling, a mechanical displacement term, and a single-mode mechanical squeezing term. By using a recently developed method to solve the dynamics of this system, we derive a general expression for the quantum Fisher information and demonstrate its applicability through three concrete examples: estimation of the strength of a nonlinear light-matter coupling, the strength of a time-modulated mechanical displacement, and a single-mode mechanical squeezing parameter, all of which are modulated at resonance. Our results can be used to compute the sensitivity of a nonlinear optomechanical system to a number of external and internal effects, such as forces acting on the system or modulations of the light-matter coupling.arXiv:1910.04485v1 [quant-ph]

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“…In this essay, we make use of one of these Gedankenexperimente-originally proposed in [3] and previously analyzed by us in [9]-to gain insight into "where and how" quantum information about a quantum superposition of a source particle is stored in its gravitational field, and under what circumstances it can be accessed. We will argue here that a quantum massive particle should be thought of as being entangled with its own Newtonian-like gravitational field, and thus that a Newtonian-like gravitational field can transmit quantum information.…”

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confidence: 99%

Information content of the gravitational field of a quantum superposition

Belenchia

Wald

Giacomini

et al. 2019

Int. J. Mod. Phys. D

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When a massive quantum body is put into a spatial superposition, it is of interest to consider the quantum aspects of the gravitational field sourced by the body. We argue that in order to understand how the body may become entangled with other massive bodies via gravitational interactions, it must be thought of as being entangled with its own Newtonian-like gravitational field. Thus, a Newtonian-like gravitational field must be capable of carrying quantum information. Our analysis supports the view that table-top experiments testing entanglement of systems interacting via gravity do probe the quantum nature of gravity, even if no "gravitons" are emitted during the experiment.

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Quantum superposition of massive objects and the quantization of gravity

Cited by 198 publications

References 38 publications

Testing the gravitational field generated by a quantum superposition

Testing the gravitational field generated by a quantum superposition

Optimal estimation with quantum optomechanical systems in the nonlinear regime

Information content of the gravitational field of a quantum superposition

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