# Shanxi University: position and momentum of rubidium atoms estimated 20% beyond Heisenberg bound

- Published: 2026-11-13 13:30 UTC
- Section: Digital & Computing › Quantum technology
- Tags: Heisenberg uncertainty limit, non-commuting variables, position and momentum, rubidium atoms, weak measurement, quantum sensing, atomic clocks, Shanxi University, arXiv preprint
- URL: https://realtech.media/news/rt-7943bf569b062ee476ed5d73_shanxi_university_position/

**In a preprint, Chinese physicists combined data from before and after a moment to estimate two non-commuting variables of a rubidium atom ensemble more precisely than the Heisenberg bound.**

![Shanxi University: position and momentum of rubidium atoms estimated 20% beyond Heisenberg bound](https://realtech.media/media/2026/11/57edaf887c293f6b.webp)
*sciencealert.com*

Researchers led by a team from Shanxi University in China report that they estimated the position and momentum of a quantum system simultaneously with a precision about 20 percent beyond the Heisenberg uncertainty limit, according to a preprint covered by sciencealert.com. [1] The paper is available on arXiv and has not yet been peer-reviewed. [1] The experiment used 52 billion rubidium atoms in a small glass chamber. [1]

## Measurement with past and future data

The Heisenberg uncertainty principle, introduced by Werner Heisenberg in 1927, says that if one characteristic of a quantum particle is predicted precisely, the paired characteristic becomes less certain. Position and momentum are the best-known pair of such non-commuting variables. [1] This fuzziness complicates measurements of weak signals, from the LIGO gravitational wave detector to the atomic clocks that underpin systems such as GPS. [1]

Instead of predicting the future state, the team took a measurement using data from both before and after the moment of interest. The hypothesis was that this two-way view would remove some of the fuzziness in observations. [1] According to the authors, the approach consistently incorporates past and future measurement information to refine the inference of the system state at a given time. [1]

## Rubidium experiment

A laser aligned the spins of the atoms, which are their magnetic properties, so the atoms behaved as one quantum system. A second laser then measured its momentum and position. [1] Measurements ran continuously for 84 minutes, and the setup allowed both quantities to be measured simultaneously, easing the usual trade-off between them. [1]

The estimates were around 20 percent more precise than the Heisenberg limit allows. [1] The authors say they verified the results using weak measurement. [1]

## Limits of the method

The Heisenberg limit still applies. The study shows that the principle can be circumvented to some extent by working out probabilities in a different way. [1] Because the method uses data from after the moment of interest, it limits real-time monitoring. [1] In many quantum systems, including atomic clocks, retrospective readings are already the norm. [1]

The researchers plan to improve the setup with more precise instrumentation and more accurate readings, and name quantum entanglement as one possible direction. [1] They also write that the work opens prospects for quantum-enhanced sensing that combines trajectory and entanglement strategies. [1]

## Sources

1. [sciencealert.com](https://www.sciencealert.com/physicists-say-theyve-sidestepped-a-nearly-100-year-old-quantum-limit-using-hindsight)
2. [ua.news](https://ua.news/en/dovkolo-svitu/u-kitayi-zaiavili-pro-tochnishe-otsiniuvannia-kvantovikh-velichin-sciencealert)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-7943bf569b062ee476ed5d73_shanxi_university_position/