Synopsis

A Test of Gravity’s Quantum Side

Physics 10, s138
Two proposals describe how to test whether gravity is inherently quantum by measuring the entanglement between two masses.
G. W. Morley/University of Warwick and APS/Alan Stonebraker

Quantum theory and general relativity work exceptionally well on their own but stubbornly refuse to play nicely together. Mathematical attempts to reconcile these theories have made some progress, but most proposed experiments for directly seeing quantum gravitational effects are unlikely to pan out because the expected effects are exceedingly small. However, there may be a way to measure these effects indirectly. Two groups in the UK—Sougato Bose at University College London and colleagues, and Chiara Marletto and Vlatko Vedral at the University of Oxford—lay out similar proposals for how to test whether gravity is truly quantum at heart.

The researchers describe similar thought experiments where two masses—microspheres, for example—interact only via their mutual gravitational attraction. If these masses become quantum-mechanically entangled, then gravity must be the culprit. To become entangled by gravity, the masses must be in a superposition of quantum states. Each mass is therefore placed into one of two neighboring interferometers, which create the superposition. If the masses are entangled when they exit the interferometers, this would imply that gravity is inherently quantum, since only a quantum field can induce entanglement.

The experiments are fraught with technical hurdles—not least how to ensure that gravity is the only way for the masses to interact. But they are closer to being realized than other proposed methods, such as directly detecting gravitons. To make these experiments happen, researchers need to figure out how to create and maintain quantum superpositions of relatively massive objects and how to reduce the effects of forces other than gravity.

This research is published in Physical Review Letters.

–Christopher Crockett

Christopher Crockett is a freelance writer based in Montgomery, Alabama.


Subject Areas

GravitationQuantum Physics

Related Articles

Hidden Behavior of Quantum Quasicrystals
Quantum Physics

Hidden Behavior of Quantum Quasicrystals

A new theory unveils the exotic low-energy excitations of quasicrystals formed of quantum particles. Read More »

Quantum Milestones, 1995: Correcting Quantum Computer Errors
Quantum Physics

Quantum Milestones, 1995: Correcting Quantum Computer Errors

Researchers proposed methods to preserve the integrity of quantum bits—techniques that may become the key to practical quantum computing on a large scale. Read More »

Flipping a Metasurface’s Chirality
Quantum Physics

Flipping a Metasurface’s Chirality

Illuminating a metasurface with a laser can enable the rapid modulation of the polarization of terahertz light transmitted through the metasurface. Read More »

More Articles