Abstract
Combining gravity with quantum mechanics remains one of the biggest challenges of physics. In the past years, experiments with optomechanical systems have been proposed that may give indirect clues about the quantum nature of gravity. In a recent variation of such tests [Carney et al., PRX Quantum 2, 030330 (2021)], the authors propose to gravitationally entangle an atom interferometer with a mesoscopic oscillator. The interaction results in periodic drops and revivals of the interferometeric visibility, which under specific assumptions indicate the gravitational generation of entanglement. Here, we study semiclassical models of the atom interferometer that can reproduce the same effect. We show that the core signature---periodic collapses and revivals of the visibility---can appear if the atom is subject to a random unitary channel, including the case where the oscillator is fully classical and situations even without explicit modeling of the oscillator. We also show that the nonclassicality of the oscillator vanishes unless the system is very close to its ground state, and even when the system is in the ground state, the nonclassicality is limited by the coupling strength. Our results thus indicate that deducing entanglement from the proposed experiment is very challenging, since fulfilling and verifying the nonclassicality assumptions constitute a significant challenge in their own right.
Highlights
The search for a full theory of quantum gravity is a major open problem in modern physics
For the case where both the atoms and the oscillator are described fully quantum mechanically, we study the nonclassicality for a thermal harmonic oscillator, showing that it vanishes for low coupling even if the system is in the ground state
The theorem rests on some assumptions, and since we claim to be providing semiclassical models which do not generate any entanglement but display the same collapse and revival signature, we ought to discuss how our models contradict the theorem proved in Ref. [17]
Summary
The search for a full theory of quantum gravity is a major open problem in modern physics. In similar spirit to the latter, a recent paper by Carney, Müller, and Taylor [17] showed that interactions between atoms and massive systems can hint at the quantum nature of gravity. They showed that the coupling results in periodic collapses and revivals of the interferometer visibility of the atomic interferometer. For the case where both the atoms and the oscillator are described fully quantum mechanically, we study the nonclassicality for a thermal harmonic oscillator, showing that it vanishes for low coupling even if the system is in the ground state Such experiments with very low coupling strengths and at finite temperature always allow for a classical description, unless it is explicitly invalidated experimentally
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