Researchers at the University of Oxford have created a new type of quantum superposition, a phenomenon often associated with Schrödinger’s famous cat thought experiment. Unlike previous versions, these newly described states are based on largely non-classical quantum components. This breakthrough could help advance quantum computing beyond traditional binary systems, improve sensing technologies, and provide new insights into the foundations of quantum physics.
One of the most surprising features of quantum mechanics is that objects can exist in multiple states simultaneously. This concept is usually illustrated by Schrödinger’s Cat, a virtual cat that is both alive and dead until it is observed.
Although the thought experiment is fictional, scientists routinely create real quantum superpositions in the laboratory. Atoms, light, and even motion can be put into multiple quantum states simultaneously. The ability to generate and control these states is crucial for technologies such as quantum computers and ultra-precise clocks.
A familiar example is a quantum bit, or qubit, which can exist in a combination of 0 and 1 at the same time. However, quantum systems are capable of much more than just two-state behavior.
Quantum harmonic oscillators, which can occupy many energy levels, provide a richer set of possibilities. These oscillators describe a wide range of physical systems, including light, vibrations, and the motion of trapped particles. Scientists have used it to create different types of quantum superpositions. One well-known example is the “cat state,” where the oscillator exists as a superposition of two wave packets moving in opposite directions. These wave packets are called coherent states, and they are the closest quantum equations to classical motion.
Constructing quantum states from non-classical components
The Oxford team has now demonstrated an entirely new family of quantum superpositions.
Instead of constructing cat-like states from wave packets with a coherent state, researchers have developed a technique that combines a wide range of quantum components that are already highly non-classical. In the case of a compact state superposition, for example, quantum uncertainty is distributed differently across each part of the state.
The experiment was based on the movement of a single trapped ion. The trapped ion combines two distinct quantum systems into a single platform. Its internal state behaves like a qubit, while its motion acts as a quantum harmonic oscillator that can occupy many different kinetic states. This combination makes trapped ions particularly useful for creating quantum states that extend beyond conventional qubits.
To generate the new states, the researchers first designed interactions that link the internal state of the ion with different potential states of motion. They then performed a mid-circle quantum measurement of the internal state, collapsing the ion’s motion into the desired superposition of the nonclassical components.
“This approach has given us a tool to sculpt quantum superposition into almost any shape,” explains lead author Dr. Sebastian Sanner (Department of Physics, University of Oxford).
Programmable control of exotic quantum states
The new method gave the team a high degree of control over the quantum states they produced.
By adjusting experimental parameters, they were able to modify the relative size, orientation, and separation of components within the superposition. This flexibility has allowed them to create a wide range of unusual kinetic quantum states using the same system of trapped ions.
The researchers then reconstructed the quantum states directly. Their measurements revealed interference patterns and regions of Wegener negativity, clear signs that the states cannot be described as ordinary classical mixtures. These observations confirmed that the experiment had succeeded in producing real quantum superpositions consisting of truly non-classical kinetic states.
The team is now working with theorists to better understand how these newly created states are “quantum.”
“We were really encouraged by the reaction of our colleagues when we showed them what we had made,” says Dr Raghavendra Srinivas (Department of Physics, University of Oxford), who supervised the work. “We believe we are still scratching the surface of what is possible, both for practical applications and for understanding these cases at a more fundamental level.”
Potential impact on quantum computing
The research points to future quantum technologies that rely on quantum oscillators rather than just simple qubits.
One particularly promising application is quantum computing. These types of instances may be more error-resistant while also supporting simpler and more effective debugging strategies. Beyond computing, they provide a new experimental platform for investigating one of physics’ biggest questions: where the boundaries lie between the classical world we experience and the fundamental quantum reality that governs it.
