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arXiv:2410.05184 · Physical review. D/Physical review. D.

Quantum nature of gravity in a Bose-Einstein condensate

Soham Sen, Sunandan Gangopadhyay

Published Mar 3, 2025• 0 citations
arXivHTMLPDF

Abstract

The effect of noise induced by gravitons on a Bose-Einstein condensate has been explored in Sen and Gangopadhyay [Probing the quantum nature of gravity using a Bose-Einstein condensate, ]. In the previous paper, we investigated the effects of graviton while detecting a gravitational wave using a Bose-Einstein condensate. In this work, we shall explicitly calculate the decoherence due to the noise of gravitons for maximally entangled momentum states of the Bose-Einstein condensate. This decoherence happens due to bremsstrahlung from the Bose-Einstein condensates due to the effect of the noise induced by gravitons. It is observed that the maximally entangled state becomes entangled with the graviton state and it decays over time as a result of this gravitational bremsstrahlung. This new entangled state is termed as a Bose-Einstein supercondensate. Using this property of the Bose-Einstein condensate in a quantum gravity background, we propose an experimental test via the use of atom lasers (generated from the condensate) which would, in principle, help to detect gravitons in future generations of very advanced ultracold temperature experiments.

DOI
10.1103/physrevd.111.066002

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The effect of noise induced by gravitons on a Bose-Einstein condensate has been explored in Sen and Gangopadhyay [Probing the quantum nature of gravity using a Bose-Einstein condensate, ]. In the previous paper, we investigated the effects of graviton while detecting a gravitational wave using a Bose-Einstein condensate. In this work, we shall explicitly calculate the decoherence due to the noise of gravitons for maximally entangled momentum states of the Bose-Einstein condensate. This decoherence happens due to bremsstrahlung from the Bose-Einstein condensates due to the effect of the noise induced by gravitons. It is observed that the maximally entangled state becomes entangled with the graviton state and it decays over time as a result of this gravitational bremsstrahlung. This new entangled state is termed as a Bose-Einstein supercondensate. Using this property of the Bose-Einstein condensate in a quantum gravity background, we propose an experimental test via the use of atom lasers (generated from the condensate) which would, in principle, help to detect gravitons in future generations of very advanced ultracold temperature experiments.
The eigenstates of two test-masses (where each test-mass is placed inside of a harmonic trap) separated by a distance, can get entangled where gravity acts as the mediator of entanglement and it has been argued in \href{https://doi.org/10.48550/arXiv.2511.07348}{arXiv:2511.07348 [quant-ph]} that this entanglement of masses cannot be generated without the underlying quantum nature of gravity. In this work, we consider two non-relativistic Bose-Einstein condensates (formed inside of harmonic trap potentials with identical trapping frequencies) separated by a distance. We take a linearized quantum gravity model and investigate the generation of entanglement while gravitons serve as the mediator of entanglement. The entanglement is generated between the phonon modes of the two condensates, and we observe that for very low separation distance, the entanglement generated is significantly higher than that observed for the quantum gravity induced entanglement of masses or QGEM protocol; however, the fall of entanglement is faster than the two-particle case for two separated Bose-Einstein condensates. We observe that when the number of particles in the condensate is increased, the degree of entanglement for a smaller separation distance becomes substantially higher compared to the case discussed in \href{https://doi.org/10.1103/PhysRevD.105.106028}{Phys. Rev. D 105 (2022) 106028}, which allows for a more robust experimental proposal using this quantum gravity induced entanglement of phonons or QGEP protocol.
We investigate the interference of two-dimensional Bose-Einstein condensates in micro-gravity, which influenced by the interaction strength, initial momentum, gravitational potential and phase difference. We demonstrate that the gravitational potential from the Earth can change the density distribution and phase distribution of the condensate's wave function. As time evolves, a portion of the gravitational potential energy of the microscopic particles can be converted into kinetic energy, which changes the motion of the microscopic particles, and leads to the varying of the density and phase distribution of the wave function. Nevertheless, the influences of the Earth's gravity on the wave function can be eliminated by the micro-gravity environment, which confirmed by many micro-gravity cold atom experiments. Our results present the influences of gravity and other parameters on interference of Bose-Einstein condensates, which help us to reveal the intrinsic natures of the related theoretical predictions and experimental phenomena. Furthermore, our work builds a bridge between the related physical phenomena and our physical intuition about the Bose-Einstein condensates in micro-gravity environment.
We investigate the interface between quantum mechanics and gravity employing techniques from quantum information theory. The focus is primarily on investigating the gravitationally mediated entanglement (measured here by the concurrence) between two probe qubits created by two-level atoms with a reservoir consisting of thermally equilibrated homogeneous three-dimensional Bose-Einstein condensates. Our results demonstrate that below a certain temperature, the gravitational contribution to the qubit-reservoir interaction may strongly modify their coherence and entanglement dynamics even at large interqubit distance. By analyzing multi-parameter estimation techniques such as the quantum Fisher information, and quantum signal-to-noise ratio as a metric for certifying quantum effects and sensing performance, we show that the spatial separation between qubits and gravitational interaction may enhance estimation efficiency, providing a high-precision quantum gravity sensor.
Abstract Despite almost a century’s worth of study, it is still unclear how general relativity (GR) and quantum theory (QT) should be unified into a consistent theory. The conventional approach is to retain the foundational principles of QT, such as the superposition principle, and modify GR. This is referred to as ‘quantizing gravity’, resulting in a theory of ‘quantum gravity’. The opposite approach is ‘gravitizing QT’ where we attempt to keep the principles of GR, such as the equivalence principle, and consider how this leads to modifications of QT. What we are most lacking in understanding which route to take, if either, is experimental guidance. Here we consider using a Bose–Einstein condensate (BEC) to search for clues. In particular, we study how a single BEC in a superposition of two locations could test a gravitizing QT proposal where wavefunction collapse emerges from a unified theory as an objective process, resolving the measurement problem of QT. Such a modification to QT due to general relativistic principles is testable near the Planck mass scale, which is much closer to experiments than the Planck length scale where quantum, general relativistic effects are traditionally anticipated in quantum gravity theories. Furthermore, experimental tests of this proposal should be simpler to perform than recently suggested experiments that would test the quantizing gravity approach in the Newtonian gravity limit by searching for entanglement between two massive systems that are both in a superposition of two locations.
Light-pulse atom interferometers are highly sensitive to inertial and gravitational effects. As such they are promising candidates for tests of gravitational physics. In this article the state-of-the-art and proposals for fundamental tests of gravity are reviewed. They include the measurement of the gravitational constant GGG, tests of the weak equivalence principle, direct searches of dark energy and gravitational-wave detection. Particular emphasis is put on long-time interferometry in microgravity environments accompanied by an enormous increase of sensitivity. In addition, advantages as well as disadvantages of Bose-Einstein condensates as atom sources are discussed.
The Bose-Marletto-Vedral experiment is a proposal for testing the quantum nature of gravity with entanglement due to Newtonian gravity. This proposal has stimulated controversy on how the entanglement due to Newtonian gravity is related to the essence of quantum gravity and the existence of gravitons. Motivated by this, we analyze the entanglement generation between two charged particles coupled to a photon field. We assume that each particle is in a superposition of two trajectories and that the photon field is initially in a coherent state. Based on covariant quantum electrodynamics, the formula for the entanglement negativity of the charged particles is derived for the first time. Adopting simple analytic trajectories of the particles, we demonstrate the entanglement between them. It is observed that the entanglement is suppressed by the decoherence due to the vacuum fluctuations of the photon field. We also find that the effect of quantum superposition of bremsstrahlung appears in the entanglement negativity formula. The similar structures between the gravity theory and electromagnetic theory suggests that a similar feature may be observed in the entanglement generation by quantum gravitational radiation.