Physicists Beat a Quantum Fuzziness Limit by Using Hindsight, Study Claims

A team of physicists led by researchers at Shanxi University in China says it has found a way to get around a quantum measurement limit that has stood since 1927, by using information from both before and after the moment being measured, ScienceAlert reported. The result is a preprint on arXiv and has not yet been peer-reviewed, so it still needs scrutiny from other scientists.

In the experiment, the measurements came out about 20 percent more precise than the Heisenberg uncertainty limit would normally allow, according to ScienceAlert.

What is the Heisenberg uncertainty principle?

German physicist Werner Heisenberg introduced the principle in 1927. It describes a built-in fuzziness in physics: if one property of a quantum particle can be predicted precisely, a paired property becomes less certain. Position and momentum are the best-known pair. Knowing where a particle is makes it harder to judge how it is moving, and the reverse is also true.

This fuzziness makes it harder to measure weak signals accurately, ScienceAlert said, in technologies ranging from the LIGO gravitational wave detector to the atomic clocks that underpin systems such as GPS.

What did the researchers do differently?

Normally, a measurement relies on predicting the future state of a system. The team tested another approach: estimating the state at a given moment using data gathered both before and after it. The hypothesis, according to ScienceAlert, was that this two-way view would strip away some of the fuzziness.

For the test, the researchers collected 52 billion rubidium atoms in a small glass chamber and used a laser to line up their spins, a magnetic property. The aligned spins made the atoms behave as a single quantum system. A second laser then measured its position and momentum. Measurements ran continuously for 84 minutes.

The setup allowed the team to measure position and momentum at the same time, easing the usual trade-off between the two. In their preprint, the researchers wrote that the approach consistently combines past and future measurement information to refine the estimate of a system's state at a given time. They said they checked the results with a technique called weak measurement.

Does this overturn Heisenberg's principle?

No. ScienceAlert stressed that the limit still applies, which matters because the principle underpins much of fundamental physics theory. What the study suggests is that the limit can be circumvented to some extent by working out probabilities in a different way.

What are the drawbacks?

Waiting until after an event to measure it limits real-time monitoring, ScienceAlert noted. The outlet said the greater accuracy may outweigh that cost. In many quantum systems, including the atomic clocks mentioned above, readings are taken after the fact anyway, so the new approach would not necessarily slow analysis.

The gain was also modest, and it comes from a single experiment that has not been independently reviewed.

Why does it matter?

For everyday readers, nothing changes right away. The potential payoff is in sensing technology. ScienceAlert said the work points toward more accurate quantum sensors in the future, the kind of instruments used in gravitational wave detection and precision timekeeping.

The researchers wrote that the result opens prospects for further research on quantum measurements and for quantum-enhanced sensing that combines trajectory and entanglement strategies.

What happens next?

The team wants to improve the experiment with more precise instruments and more accurate readings, ScienceAlert reported. Adding quantum entanglement, a link between particles, could be one way forward. Independent peer review and replication by other groups will show whether the 20 percent improvement holds up.

Around Prague, based on reporting by ScienceAlert

Cover photo: 33shaguftansari / Wikimedia Commons, CC BY-SA 4.0, cropped

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