[Paper Review] Massive quantum systems as interfaces of quantum mechanics and gravity

Sougato Bose, Ivette Fuentes+8 more|arXiv (Cornell University)|Nov 15, 2023

Atomic and Subatomic Physics Research4 citations

TL;DR

This paper proposes that massive quantum systems—engineered in the lab at masses far exceeding atomic scales—can serve as experimental interfaces between quantum mechanics and gravity. By leveraging advanced quantum control and precision measurement techniques, the authors outline how such systems enable low-energy tests of gravity, including gravitationally induced decoherence, wavefunction collapse, and gravity-mediated entanglement, offering a viable path to probing quantum gravity phenomenologically.

ABSTRACT

The traditional view from particle physics is that quantum gravity effects should only become detectable at extremely high energies and small length scales. Due to the significant technological challenges involved, there has been limited progress in identifying experimentally detectable effects that can be accessed in the foreseeable future. However, in recent decades, the size and mass of quantum systems that can be controlled in the laboratory have reached unprecedented scales, enabled by advances in ground-state cooling and quantum-control techniques. Preparations of massive systems in quantum states pave the way for the explorations of a low-energy regime in which gravity can be both sourced and probed by quantum systems. Such approaches constitute an increasingly viable alternative to accelerator-based, laser-interferometric, torsion-balance, and cosmological tests of gravity. In this review, we provide an overview of proposals where massive quantum systems act as interfaces between quantum mechanics and gravity. We discuss conceptual difficulties in the theoretical description of quantum systems in the presence of gravity, review tools for modeling massive quantum systems in the laboratory, and provide an overview of the current state-of-the-art experimental landscape. Proposals covered in this review include, among others, precision tests of gravity, tests of gravitationally-induced wavefunction collapse and decoherence, as well as gravitymediated entanglement. We conclude the review with an outlook and summary of the key questions raised.

Motivation & Objective

• To explore the feasibility of testing quantum gravity effects in the laboratory using massive quantum systems, circumventing the need for extreme energies or scales.
• To address conceptual challenges in unifying quantum mechanics and gravity, particularly regarding superposition, measurement, and entanglement in gravitational fields.
• To review theoretical frameworks for modeling massive quantum systems, including open-system dynamics and quantum metrology tools.
• To map the current experimental landscape and identify viable pathways for testing gravity using levitated optomechanics, BECs, and hybrid systems.
• To propose and analyze key experimental protocols for detecting gravity-mediated entanglement, gravitational decoherence, and deviations from Newtonian gravity.

Proposed method

• Modeling the coupling of massive mechanical oscillators to quantum probes using optomechanical and spin-based interactions to simulate gravitational effects.
• Applying quantum master equations and Langevin formalisms to describe open quantum systems under gravitational influence and environmental noise.
• Using quantum Fisher information and standard quantum limits to assess the sensitivity of quantum sensors to weak gravitational forces.
• Employing entanglement witnesses and concurrence measures to characterize gravity-induced entanglement in bipartite systems.
• Designing protocols involving spatial superpositions and interferometric setups to test gravity-mediated entanglement between distant massive systems.
• Integrating tools from quantum information theory to analyze decoherence and wavefunction collapse under semi-classical gravity models.

Experimental results

Research questions

• RQ1 Can massive quantum systems in superposition states reveal deviations from Newtonian gravity at low energies?
• RQ2 To what extent can gravity induce decoherence or collapse the wavefunction of a massive quantum system?
• RQ3 Is entanglement between two massive systems mediated solely by gravity, and can it be detected experimentally?
• RQ4 How do non-inertial frames and curved spacetime affect quantum state evolution in massive systems?
• RQ5 Can quantum field theory in curved spacetime be tested using engineered quantum systems in the lab?

Key findings

• Recent advances in ground-state cooling and quantum control now allow preparation of massive systems (beyond atomic mass scale) in coherent superpositions, enabling low-energy tests of gravity.
• Proposed experiments with levitated optomechanical systems can probe gravitational decoherence and test the semi-classical gravity model with sensitivity approaching the Planck scale.
• Gravity-mediated entanglement protocols have been theoretically shown to be feasible with current or near-future technology, offering a direct test of gravity's quantum nature.
• Tests of the equivalence principle and dark matter searches are realizable using massive quantum systems in superpositions, with sensitivity limited only by control and measurement fidelity.
• Quantum metrology tools such as quantum Fisher information and back-action evading measurements can enhance sensitivity to weak gravitational forces below standard quantum limits.
• Theoretical frameworks based on quantum field theory in curved spacetime and perturbative quantum gravity provide consistent descriptions of low-energy gravitational effects on massive quantum systems.