Abstract
Tabletop tests of quantum gravity (QG) have long been thought to be practically impossible. However, remarkably, because of rapid progress in quantum information science (QIS), such tests may soon be achievable. Here we uncover an exciting new theoretical link between QG and QIS that also leads to a radical new way of testing QG with QIS experiments. Specifically, we find that only a quantum, not classical, theory of gravity can create non-Gaussianity, a QIS resource that is necessary for universal quantum computation, in the quantum field state of matter. This allows tests based on QIS in which non-Gaussianity in matter is used as a signature of QG. In comparison with previous studies testing QG with QIS where entanglement is used to witness QG when all other quantum interactions are excluded, our non-Gaussianity witness cannot be created by direct classical gravity interactions, facilitating tests that are not constrained by the existence of such processes. Our new signature of QG also enables tests that are based on just a single quantum system rather than a multipartite quantum system, simplifying previously considered experimental setups. We describe a tabletop test of QG that uses our non-Gaussianity signature and that is based on just a single quantum system, a Bose-Einstein condensate, in a single location. In contrast to proposals based on optomechanical setups, Bose-Einstein condensates have already been manipulated into massive nonclassical states, aiding the prospect of testing QG soon.
- Received 30 April 2020
- Accepted 21 January 2021
DOI:https://doi.org/10.1103/PRXQuantum.2.010325
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
We have used recent findings in the field of quantum information science to develop a new approach to determining how our Universe works at its most fundamental level. For more than a hundred years, physicists have struggled to understand how the two foundational theories of science, quantum theory and general relativity, which respectively describe microscopic and macroscopic phenomena, are unified into a single overarching theory of nature. During this time, two fundamentally contrasting approaches have been developed, called ‘quantum gravity’ and ‘classical gravity’. However, a complete lack of experimental evidence means that we do not know which approach the overarching theory actually takes.
Now, a collaboration between researchers in quantum information, quantum gravity, and quantum technology, demonstrates that only quantum and not classical gravity could bring a signature (called non-Gaussianity) that is typically discussed in the context of quantum computation, connecting the fields of quantum gravity, quantum information, and computing.
In particular, we propose a way to test experimentally the quantum character of gravity in a scientific laboratory: billions of atoms are cooled to very low temperatures in a spherical trap such that they enter a new phase of matter, called a Bose-Einstein condensate, and act like a single ‘wave of matter’ inside the trap. This single wave is massive enough to feel its own gravitational pull, and if after a certain period of time it demonstrates non-Gaussianity, then this proves that nature must take the quantum gravity approach. The proposed experiment involves just a single quantum system and does not rely on assumptions concerning the locality of the interaction, making it simpler than previous approaches and potentially expediting the delivery of the first experimental test of quantum gravity. After more than a hundred years of research, having information on the unified theory of nature may be closer.