The term quantum gravity attempts to explain how gravity works on the universe’s smallest particles. Tabletop tests of quantum gravity (QG) have long been thought to be practically impossible.

Using cutting-edge research in quantum computation and quantum technology, scientists ed by the University of Nottingham proposed a new approach to determine how the universe works at its most fundamental level.

Scientists demonstrated that only quantum and not classical gravity could create a certain informatic ingredient needed for quantum computation.

Dr. Richard Howl led the research during his time at the University of Nottingham’s School of Mathematics said, *“For more than a hundred years, physicists have struggled to determine 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, they have come up with two fundamentally contrasting approaches, called ‘quantum gravity’ and ‘classical gravity.’ However, a complete lack of experimental evidence means that physicists do not know which approach the overarching theory takes; our research provides an experimental approach to solving this.”*

In this study, scientists found an unexpected connection between the fields of quantum computing and quantum gravity. Using this, they proposed a new way to test that there is quantum, not classical gravity experimentally.

For the experiment, scientists cooled billions of atoms in a millimeter-sized spherical trap to shallow temperatures such that they enter a new phase of matter, called a Bose-Einstein condensate, and start to behave like a single large, quantum atom. They then applied a magnetic field to this atom so that it feels only its gravitational pull. With this all in place, if the single gravitating bit demonstrates the key ingredient needed for quantum computation, which is curiously associated with “negative probability,” nature must take the quantum gravity approach.

To conduct this experiment, scientists used a current technology that involves a single quantum system, the gravitating “atom,” and does not rely on assumptions concerning the interaction’s locality, 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, physicists would finally have information on the true overarching, fundamental theory of nature.

Dr. Marios Christodoulou, from the University of Hong Kong, who was part of the collaboration, added: *“This research is fascinating as the experiment proposed would also connect with the more philosophical idea that the universe is behaving as an immense quantum computer that is calculating itself, by demonstrating that quantum fluctuations of spacetime are a vast natural resource for quantum computation.”*

##### Journal Reference:

- Richard Howl, Vlatko Vedral, Devang Naik, Marios Christodoulou, Carlo Rovelli, Aditya Iyer. Non-Gaussianity as a Signature of a Quantum Theory of Gravity. PRX Quantum, 2021; 2 (1) DOI: 10.1103/PRXQuantum.2.010325