Researchers at the University of Oxford have achieved a landmark breakthrough in quantum physics: the first-ever experimental demonstration of “quadsqueezing” — a fourth-order quantum interaction previously thought to be out of reach. The findings were published on May 1 in the journal Nature Physics.

What is ‘Squeezing’?

In quantum physics, “squeezing” is a technique for redistributing quantum uncertainty. According to the Heisenberg uncertainty principle, certain pairs of physical quantities — such as position and momentum — cannot be precisely measured simultaneously. Squeezing works by increasing the precision of one measurement while accepting greater uncertainty in the other.

The technology is already in practical use — for example, LIGO’s gravitational wave detectors employ squeezed light to enhance their sensitivity.

Going Beyond Standard Squeezing

Standard squeezing represents only one part of a broader spectrum of possible interactions. Physicists have long pursued more complex forms known as “trisqueezing” and “quadsqueezing.” These higher-order effects have proven exceptionally difficult to achieve because they are naturally very weak and quickly overwhelmed by noise.

The Oxford team’s solution builds on a theory proposed in 2021 by Dr. Raghavendra Srinivas and Robert Tyler Sutherland. They combined two precisely controlled forces acting on a single trapped ion. Each force alone produces a simple, predictable effect. But when applied together, due to “non-commutativity” — a quantum phenomenon where the order and combination of actions change the outcome — the forces amplify each other, creating a stronger and more complex interaction.

Breakthrough Results

Using the same experimental setup, the researchers were able to switch between different levels of squeezing. They successfully produced standard squeezing, trisqueezing, and — for the first time on any platform — quadsqueezing.

Lead author Dr. Oana Băzăvan of Oxford’s Department of Physics said: “In the lab, non-commuting interactions are often seen as a nuisance because they introduce unwanted dynamics. We took the opposite approach and used that feature to generate stronger quantum interactions.”

Dr. Băzăvan added: “The result is more than the creation of a new quantum state. It is a demonstration of a new method for engineering interactions that were previously out of reach. The fourth-order quadsqueezing interaction was generated more than 100 times faster than expected using conventional approaches. This makes effects that were previously inaccessible achievable in practice.”

Applications and Future Directions

The technique has broad applications in quantum simulation, sensing, and computing. The team is now extending the method to more complex systems with multiple modes of motion. Because the approach relies on tools already available in many quantum platforms, it could become a widely useful way to explore advanced quantum behavior.

The method has already been combined with mid-circuit measurements of the ion’s spin to generate flexible combinations of squeezed states and to simulate a lattice gauge theory.

Study co-author Dr. Srinivas said: “Fundamentally, we have demonstrated a new type of interaction that lets us explore quantum physics in uncharted territory, and we are genuinely excited for the discoveries to come.”

Source: ScienceDaily, Nature Physics