Researchers at the University of Oxford have recently demonstrated a groundbreaking type of quantum interaction using a single trapped ion. By creating and controlling increasingly complex forms of “squeezing”—including a fourth-order effect known as quadsqueezing—the team has rendered previously unreachable quantum effects experimentally accessible for the first time. This approach offers a novel methodology for engineering interactions, with significant potential applications in quantum simulation, sensing, and computation.
Experimental realization of higher-order quadsqueezing in quantum oscillators
In the field of physics, numerous systems behave as microscopic objects vibrating or oscillating back and forth, much like a mechanical spring or a pendulum. In the quantum realm, these systems are identified as quantum harmonic oscillators, and they provide the framework for describing light waves, molecular vibrations, and the motion of individual trapped atoms. Mastering the control of these oscillators is considered essential for the development of advanced quantum technologies, ranging from ultra-precise sensors to innovative computing architectures.
One of the most established methods for controlling a quantum oscillator is a process known as squeezing. Quantum mechanics dictates a fundamental limit on the precision with which certain pairs of physical properties, such as position and momentum, can be known simultaneously. Squeezing effectively reshapes this inherent uncertainty by making one property more defined while the other becomes proportionally more uncertain, a technique already employed to enhance the sensitivity of gravitational wave detectors.
Despite the utility of ordinary squeezing, it represents only one facet of a much larger family of potential squeezing interactions. Physicists have long aspired to move beyond these basic forms to create stronger and more intricate interactions known as trisqueezing and quadsqueezing. Until recently, however, these higher-order interactions have proven exceptionally difficult to realize in practice because their effects are naturally weak and easily obscured by environmental noise.
Engineering non-commutative forces in trapped ions
The Oxford research group has now demonstrated a sophisticated solution to the problem of weak higher-order effects. Rather than attempting to induce a complex interaction directly, the team combined two carefully controlled forces acting on a single trapped ion, a strategy based on a 2021 theory proposed by Dr. Raghavendra Srinivas and Robert Tyler Sutherland. While each force produces a simple linear effect when applied individually, their simultaneous application generates a new interaction that exceeds the sum of its parts.
This phenomenon relies on the principle of non-commutativity, wherein the two applied forces influence each other to generate a stronger interaction within the motion of the ion. In many laboratory settings, non-commutative interactions are viewed as a nuisance because they introduce unwanted dynamics into a system. However, the researchers chose to exploit this characteristic as a tool to engineer stronger quantum interactions that were previously considered unattainable through conventional experimental methods.
By adjusting the frequencies, phases, and intensities of the applied forces, the team was able to toggle between different types of squeezing within the same experimental setup. This flexibility allowed them to generate multiple, triple, and—for the first time on any experimental platform—quadruple squeezing interactions. This fourth-order quadsqueezing was achieved over 100 times faster than expected, making these complex quantum states practically viable for the first time.
Implications for quantum simulation and future research
The researchers confirmed the success of these interactions by reconstructing the quantum states of the trapped ion’s motion. These measurements revealed the distinctive physical signatures associated with second, third, and fourth-order squeezing, providing direct evidence of the different engineered interactions. This verification highlights the robustness of the method and its ability to suppress undesired effects while precisely selecting the intended quantum behavior.
The methodology is currently being extended to more complex systems involving multiple modes of motion. Because the technique relies on components available across a wide range of quantum platforms, it could provide a generalized pathway toward new forms of quantum sensing and computation. Furthermore, the technique has already been combined with mid-circuit ion spin measurements to generate arbitrary superpositions of squeezed states and to simulate lattice gauge theories.
Ultimately, the demonstration of these higher-order interactions allows scientists to explore quantum physics in previously uncharted territory. By providing a new type of interaction for quantum engineering, this work paves the way for future discoveries in quantum simulation and the development of next-generation sensors. The ability to manipulate the fundamental uncertainty of quantum systems with such precision marks a significant milestone in the ongoing evolution of quantum science.
The study is published in the journal Nature.
