Repulsive gravity from quantum interference

A source particle held in a spatial superposition pulls gravitationally on a probe particle. Post-selecting a special outcome of the source can make the net effect on the probe look like repulsion — even though every individual branch was ordinary attraction.

Based on Saldanha, Marletto & Vedral, "Repulsive Gravitational Force as a Witness of the Quantum Nature of Gravity," arXiv:2602.12266 (2026).

The setup

Setup of the source and probe particles A source particle is superposed at two locations A and B, pulling gravitationally on a probe particle. The pull from A is stronger because A is closer. Source (superposition) A B Probe Stronger pull (closer) Weaker pull (farther)

Probe momentum distribution

Probe momentum distribution Chart showing the probe particle's momentum distribution, with and without post-selecting the source particle. p = 0 −1 +1.6 no post-selection post-selected
Show post-selected curve
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