Physicists at the University of Oxford have pulled off a quantum trick that researchers have been chasing for years. By tightly controlling the motion of a single trapped ion, they produced the first ever demonstration of "quadsqueezing" — a fourth-order quantum effect so subtle it had eluded every previous attempt to capture it. The work was published on May 1 in Nature Physics.
Quantum mechanics imposes a hard rule on the universe: you can never know certain pairs of properties — such as a particle''s position and momentum — with perfect precision at the same time. "Squeezing" is a clever workaround. It doesn''t break the rule; it simply redistributes the uncertainty, sharpening one property while accepting more fuzziness in the other. The trick already powers some of the most sensitive instruments humans have ever built. LIGO, the gravitational-wave detector that listens for ripples in spacetime, uses squeezed light to push past what would otherwise be the noise floor of physics itself.
But standard squeezing is just the beginning. Theorists have long predicted a hierarchy of higher-order effects — trisqueezing, quadsqueezing, and beyond — each more delicate than the last. The trouble is that these interactions are vanishingly weak in practice, and they tend to drown in environmental noise long before they can be measured.
The Oxford team, led by Dr. Oana Băzăvan in the Department of Physics, found a way around the problem. Building on a 2021 theoretical proposal by Dr. Raghavendra Srinivas and Dr. Robert Tyler Sutherland, they applied two precisely tuned forces to a single trapped ion at the same time. On their own, each force produced a familiar, predictable quantum effect. Together, however, the forces interfered in a way that amplified each other — a phenomenon known as non-commutativity, where the order in which actions are applied changes the outcome.
"In the lab, non-commuting interactions are often seen as a nuisance because they introduce unwanted dynamics," Dr. Băzăvan said. "Here, we took the opposite approach and used that feature to generate stronger quantum interactions."
The payoff was striking. With a single experimental setup, the team was able to dial through different orders of squeezing on demand — first generating standard squeezing, then trisqueezing, and finally, for the first time on any platform, full quadsqueezing. By tweaking the frequencies of their two driving forces, the researchers could effectively choose which slice of the quantum world they wanted to see.
Why does it matter? Because squeezed states are the engine behind a generation of emerging quantum technologies. Quantum sensors that can measure tiny changes in magnetic fields, gravity, or time. Quantum simulators that model molecules too complex for classical computers. And quantum computers that may one day crack problems no supercomputer can touch. The richer the toolkit of squeezing operations available to researchers, the more powerful these machines become.
Quadsqueezing in particular gives physicists a new way to engineer the behaviour of quantum oscillators — the mathematical building blocks that describe everything from a vibrating molecule to a single photon of light. It''s a level of control that was, until now, theoretical at best.
The Oxford method is also notable for its simplicity. Rather than requiring exotic new hardware, the team showed that careful orchestration of existing tools — the same kinds of forces routinely used in trapped-ion labs around the world — is enough to unlock these higher-order effects. That makes the technique relatively easy to adopt, and it suggests that other research groups will be able to build on the result quickly.
For now, the practical applications of quadsqueezing are still being explored. But that''s often how big leaps in physics work: a strange new effect is demonstrated, the toolkit grows, and engineers eventually find uses no one anticipated. Squeezing itself was once a curiosity; today it sharpens the eyes of gravitational-wave observatories. Quadsqueezing may follow a similar trajectory — quietly, then suddenly, becoming indispensable.
