Physicists measured both the momentum and position of the particles without breaking Heisenberg’s symbolic principle of uncertainty.
In quantum mechanics, particles do not have fixed properties like everyday objects. Instead, they exist in the haze of possibilities until they are measured. And when certain properties are measured, other properties become uncertain. According to Heisenberg’s uncertainty, it is not possible to know both the exact location of a particle and its exact momentum at the same time.
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“Heisenberg’s principle of uncertainty cannot be violated,” Christoph Vallaf, a physicist at the University of Sydney and lead author of the study, told Live Science. “What we do is change the uncertainty. We throw away information that is not necessary, so we can measure what we care about with much more accuracy.”
The trick for Valaf and his team was to measure modular momentum and modular position rather than directly measuring momentum and position. This captures the relative shifts of these quantities within the fixed scale, not absolute values.
“Imagine you have a ruler. If you’re just measuring the position of something, you’ll read as many centimeters as you go, and then millimeters past it,” Varaf said. “But with module measurements, I don’t care which centimeters you are. I only care how many millimeters you are from the last mark. I throw away the overall location and track the small shifts.”
Valahu said this type of measurement is important in quantum sensing scenarios. This is because the goal is to detect tiny changes that are often caused by faint forces or fields. Quantum sensing is used to pick up signals that ordinary instruments often miss. That level of accuracy could one day make navigation tools more reliable and make the watch even more accurate.
In the lab, the team relied on a single locked ion. This is the only charged atom held in place by an electromagnetic field. They used a tuned laser to direct ions into a quantum pattern called grid states.
In the grid state, the ion wavefunction spreads to a series of uniformly spaced peaks, like the ruler’s mark. Uncertainty is concentrated in the space between the marks. The researchers used the peak as the reference point. Small forces fine-tune the ions, and the entire grid pattern shifts slightly. Small lateral shifts in the peaks appear as changes in position, while the slope of the grid pattern reflects changes in momentum. Measurements only care about shifts relative to peaks, so both positional changes and momentum changes can be read simultaneously.
That’s where power begins. In physics, forces cause changes in momentum and position. By looking at how the grid patterns moved, researchers measured small pushes acting on ions.
The power of approximately 10 Yoctonnewtons (10-23 Newtons) is not a world record. “People have beaten this about double digits, but they use giant crystals in very large and expensive experiments,” Varav told Live Science. “The reason we’re excited is that it’s not that complicated and can really get good sensitivity using a single atom with a slightly scalable trap.”
The power achieved is not at the lowest, but it proves that scientists can gain very extreme sensitivity from a very basic setup. The ability to sense small changes has broad meaning across science and technology. Ultra-advanced quantum sensors can improve navigation in places where GPS is not reachable, such as underwater, underground, or space. It also potentially enhances biological and medical imaging.
“Just as atomic clocks revolutionized navigation and communications, quantum-enhanced sensors with extreme sensitivity could open the door to a whole new industry,” Valaf said in a statement.
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