# Universality of Diffractive Collisions and the Quantum Pressure Standard

## TL;DR

This paper demonstrates the universality of quantum diffractive collisions, introduces a quantum pressure standard based on this principle, and validates it experimentally with cold rubidium atoms, achieving high accuracy in pressure measurement.

## Contribution

It introduces a universal function for quantum diffractive collisions and establishes a quantum-based pressure standard applicable to any gas species.

## Key findings

- Universal energy distribution function observed experimentally.
- Quantum pressure standard agrees within 0.5% with traditional methods.
- First quantum definition of the Pascal for vacuum and pressure metrology.

## Abstract

This work demonstrates that quantum diffractive collisions, those that result in very small momentum and energy transfer, are universal. Specifically, the cumulative energy distribution transferred to an initially stationary sensor particle by a quantum diffractive collision follows a universal function that depends only on the sensor particle mass and the thermally-averaged, total collision cross section. The characteristic energy scale corresponds to the localization length associated with the collision-induced quantum measurement, and the shape of the universal function is determined {\it only} by the analytic form of the interaction potential at long range. Using cold $^{87}$Rb sensor atoms confined in a magnetic trap, we observe experimentally the universal function specific to van der Waals collisions, and realize a \emph{self-defining} particle pressure sensor that can be used for any ambient gas. This provides the first primary and quantum definition of the Pascal, applicable to any species and therefore represents a key advance for vacuum and pressure metrology. The quantum pressure standard realized here was compared with a state-of-the-art orifice flow standard transferred by an ionization gauge calibrated for N$_2$. The pressure measurements agreed at the 0.5\% level.