Researchers at the University of Oxford have demonstrated a new type of quantum interaction using a single trapped ion. By carefully generating and controlling increasingly complex forms of ‘squeezing’, including a fourth-order effect called quad-squeezing, we are now able to harness quantum behavior that was previously out of reach. This research also introduces new ways to engineer these interactions, with potential applications in quantum simulation, sensing, and computing. The results of this survey were announced today (May 1st). natural physics.
Many physical systems behave like small vibrating objects, similar to springs or pendulums. In quantum physics, these are known as quantum harmonic oscillators. This explanation applies to a wide range of systems, including light waves, molecular vibrations, and even the motion of trapped single atoms.
Controlling these oscillations is essential for modern quantum technology. Applications range from extremely high-precision measurement tools to developing next-generation quantum computers.
The limits of compression and quantum precision
One of the most common techniques for controlling quantum oscillators is called squeezing. Quantum mechanics places strict limits on the precision with which certain pairs of properties, such as position and momentum, can be measured simultaneously. Squeezing redistributes this uncertainty by making one property more accurate and increasing the uncertainty in the other.
This concept is not just theoretical. Squeezed light is already used in gravitational wave detectors such as LIGO to increase sensitivity.
Beyond standard squeezing
Standard squeezing is only part of a wide range of possible interactions. Physicists have long sought to create more complex versions, known as tri-squeezes and quad-squeezes. These higher-order effects are much more difficult to achieve because they are inherently much weaker and quickly overwhelmed by noise.
As a result, observing these advanced quantum interactions remains a major challenge.
A new method using non-commuting ability
The Oxford team developed a solution by combining two precisely controlled forces acting on a single trapped ion. This approach is based on a theory proposed by Dr. Raghavendra Srinivas and Dr. Robert Tyler Sutherland in 2021.
Each force by itself produces a simple and predictable effect. However, when applied together, they produce stronger and more complex interactions. This is caused by noncommutativity, a quantum effect in which the order and combination of actions change outcomes and forces amplify each other.
Lead author Dr Oana Bazavan, from the University of Oxford’s Department of Physics, said: “In the laboratory, non-commutative interactions are often seen as a nuisance because they give rise to undesirable dynamics. Here we took the opposite approach and exploited their properties to generate stronger quantum interactions.”
First ever quad squeezing demonstration
Using the same experimental setup, the researchers were able to switch between different levels of squeezing. They were able to generate a standard squeeze, a tri-squeeze, and for the first time on any platform, a quad-squeeze, a fourth-order interaction.
By adjusting the frequency, phase, and strength of the applied force, they were able to control which interactions appeared while minimizing undesirable effects.
Dr. Oana Băzăvan said, “This result goes beyond the creation of new quantum states. It is a demonstration of a new way to engineer previously inaccessible interactions. Fourth-order quad-squeezing interactions were generated more than 100 times faster than expected using traditional approaches. This makes previously inaccessible effects practically accessible.”
Confirmation of quantum effects
To verify the results, the team reconstructed the quantum motion of the trapped ions. Measurements revealed distinct patterns corresponding to secondary, tertiary, and quaternary squeezing. These patterns provided clear evidence that each type of interaction was successfully created.
Future applications of quantum technology
The researchers are now extending this method to more complex systems with multiple modes of operation. Because this technique relies on tools already available on many quantum platforms, it has the potential to become a widely useful method for exploring advanced quantum behavior.
This approach has already been combined with intermediate circuit measurements of ion spins to generate flexible combinations of squeezed states to simulate lattice gauge theory.
Study co-author Dr Raghavendra Srinivas (Department of Physics, University of Oxford), who oversaw the study, said: “Essentially, we have demonstrated a new type of interaction that allows us to explore quantum physics in uncharted territory, and we are really excited about the discoveries to come.”
