Oxford physicists have created an unconventional class of quantum superpositions from highly nonclassical states.
Researchers at the University of Oxford have created a new class of quantum superpositions, including Schrödinger’s cat-like states, using building blocks that are themselves strongly nonclassical. The advance could support future quantum computing architectures based on more complex systems than conventional qubits, while also providing new opportunities for sensing and fundamental studies of quantum mechanics.
Unlike classical physics, quantum mechanics allows a system to exist in multiple states simultaneously. This concept is often illustrated by Schrödinger’s cat, a thought experiment in which a cat is considered both alive and dead until it is observed. In laboratory settings, scientists can produce real-world versions of this phenomenon by placing atoms, light, or motion into multiple quantum states at the same time. The ability to create and control these superpositions is central to technologies such as quantum computing and ultra-precise clocks.
One familiar example is a quantum bit, or qubit, which can exist as a combination of both 0 and 1. However, quantum systems are not restricted to two states. Quantum harmonic oscillators can occupy many energy levels, creating far more possibilities. These oscillators describe a wide range of physical systems, including light, vibrations, and the motion of trapped particles.
A well-known example is a “cat state,” where an oscillator exists in a superposition of two wave packets that are displaced in opposite directions. These wave packets, called coherent states, behave as closely to classical motion as quantum mechanics permits.
Building Cat States From Nonclassical Components
The Oxford team developed a new approach for generating quantum superpositions. Rather than constructing cat-like states from coherent-state wave packets, they created them from a broader set of components that are already highly nonclassical. In squeezed-state superpositions, for example, quantum uncertainty is distributed differently across each component of the state.
The experiment centered on the motion of a single trapped ion. Trapped ions combine two types of quantum systems in one platform. Their internal states function like qubits, while their motion acts as a quantum harmonic oscillator that can occupy many different motional states. This makes them especially useful for creating quantum states that extend beyond the capabilities of standard qubits.
To generate the new states, the researchers first entangled the ion’s internal state with several possible motional states through carefully designed interactions. They then performed a mid-circuit measurement of the internal state, causing the ion’s motion to collapse into a selected superposition of nonclassical components.
“This approach gave us a tool to sculpt the quantum superposition into almost any shape,” explains lead author Dr. Sebastian Saner (Department of Physics, University of Oxford).
Confirming Genuine Quantum Behavior
The technique gave the team a high degree of control over the resulting states. By adjusting experimental parameters, they could modify the relative size, orientation, and spacing of the components, producing a wide variety of unusual motional superpositions within the same trapped-ion system.
The researchers then reconstructed the quantum states they had created. These measurements revealed interference patterns and regions of Wigner negativity, both of which indicate behavior that cannot be explained as a simple classical mixture. The results confirmed that the experiment had successfully generated genuine quantum superpositions composed of intrinsically nonclassical motional states.
The team is now working with theorists to better quantify the quantum properties of these states.
“We were really encouraged by our colleagues’ reaction when we showed them what we had made. We believe we’re still scratching the surface of what’s possible, both for practical applications and for understanding these states at a more fundamental level,” says Dr. Raghavendra Srinivas (Department of Physics, University of Oxford), who supervised the work.
The research provides a new pathway toward quantum technologies that rely on quantum oscillators rather than only conventional qubits. One potential application is quantum computing, where these states could offer improved resistance to errors while supporting simpler and more robust error-correction methods. They may also serve as a valuable platform for investigating the boundary between classical and quantum behavior.
Reference: “Generating Arbitrary Superpositions of Nonclassical Quantum Harmonic Oscillator States” by S. Saner, O. Băzăvan, D. J. Webb, G. Araneda, D. M. Lucas, C. J. Ballance and R. Srinivas, 3 June 2026, Physical Review X.
DOI: 10.1103/k1xk-yt42
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