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The Colella–Overhauser–Werner experiment observed a gravitationally induced relative quantum phase in a neutron interferometer. The 1975 primary report identifies the measured signal as a phase shift caused by the interaction of neutron matter waves with Earth's gravitational field.^[ref]

An idealized two-path model explains the sensitivity. If equal-speed horizontal segments of length $L$ are separated vertically by $h$, their gravitational potential energy difference is $mgh$ and their common traversal time is approximately $L/v$. The corresponding phase-difference magnitude isThe sign depends on path orientation and phase convention. Recombination converts this difference into matter-wave interference, making a tiny potential-energy difference measurable through phase accumulation. The rectangular equal-speed expression is a leading explanatory model, not a complete precision correction for real crystal diffraction, bending and rotation effects.