Oxford Physicists Build a New Family of Schrödinger's Cat States From Highly Non-Classical Components
Using a single trapped strontium-88 ion, an Oxford group built cat states whose components are themselves squeezed and trisqueezed states, reporting Wigner negativity and greater quantum resourcefulness than standard cat or Fock states.
Overview
Researchers at the University of Oxford have demonstrated a new family of quantum superpositions in which each component is itself a highly exotic quantum state, according to the University of Oxford Department of Physics. The work, published in Physical Review X on 3 June 2026, extends the standard recipe for Schrödinger-cat states by superposing components that are themselves highly non-classical, rather than the near-classical wave packets used in earlier experiments.
The result is a more flexible toolkit for encoding and protecting quantum information, with the team reporting that the new states carry more “quantum resourcefulness” than the cat states physicists have relied on until now.
What We Know
The textbook Schrödinger-cat state is a superposition of two coherent states. As the Oxford release explains, coherent states are “quantum wave packets that behave as classically as quantum mechanics allows,” per the University of Oxford Department of Physics. What sets the new work apart is that the researchers “demonstrate a method for creating superpositions from a broad range of components that are themselves highly non-classical,” the same source reports — components that include squeezed, trisqueezed or quadsqueezed states.
The experiment was carried out on a single trapped ion. According to Phys.org, the team used “the motion of a single trapped ion,” where “its internal state acts like a qubit, while its motion behaves like a quantum harmonic oscillator.” The University of Oxford Department of Physics specifies that the experiment “used a single ion of strontium-88 confined in an ion trap.”
To confirm that the engineered states were genuinely quantum, the team reconstructed them and looked at their Wigner function, a standard phase-space representation. The reconstructed states “displayed interference patterns and regions of negative values in a mathematical representation called the Wigner function,” the University of Oxford Department of Physics reports. As Phys.org puts it, the reconstructions “revealed interference patterns and regions of Wigner negativity—signatures that the states could not be described as ordinary classical mixtures.” Wigner negativity is widely treated as a marker of non-classicality and a resource for quantum computation.
The team frames the advance in terms of quantum resourcefulness. “For a given average energy, the new superpositions were found to exhibit greater quantum resourcefulness than standard cat states or Fock states,” according to the University of Oxford Department of Physics.
Dr Sebastian Saner, the lead author, described the degree of control the method offers. “This approach gave us a tool to sculpt quantum superpositions into almost any shape. The states we produced exhibit rotational symmetries and form striking geometric interference patterns,” Saner said, as quoted by the University of Oxford Department of Physics.
Dr Raghavendra Srinivas, who supervised the work, signaled that the result is an opening rather than an endpoint. “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,” Srinivas said, according to SciTechDaily.
Why It Matters
The practical interest in cat states comes from quantum error correction. Bosonic codes encode a logical qubit in the many states of a single oscillator rather than in a register of physical qubits, and cat states are one of the canonical building blocks for that approach. By widening the set of components available for these superpositions, the Oxford method gives experimentalists more shapes to work with when designing such codes.
The team links the new states directly to that goal. The states “can be more resilient to errors while enabling simpler and more robust error-correction protocols,” according to Phys.org, and could “offer improved resistance to errors while supporting simpler and more robust error-correction methods,” per SciTechDaily. The University of Oxford Department of Physics frames the work as extending the toolkit for quantum computing, sensing, and error correction, including bosonic quantum error correction.
The experiment also continues a line of trapped-ion oscillator-control work from the same Oxford group. The exotic components used here — squeezed, trisqueezed and quadsqueezed states — build on the group’s earlier demonstration of higher-order squeezing on a single trapped ion, previously reported by The Machine Herald.
What We Don’t Know
The announcements describe the states and their non-classical signatures but do not, in the fetchable releases, quantify how much error-correction advantage the new states would deliver in a working logical-qubit demonstration, nor how the approach scales beyond a single ion. The full technical claims — including the detailed resourcefulness comparisons and the fidelity of the reconstructed states — are contained in the Physical Review X paper itself (DOI 10.1103/k1xk-yt42), which carries the complete experimental results. Whether these sculpted superpositions translate into a measurable improvement in a deployed bosonic code remains to be demonstrated, a point the researchers themselves underscore in describing the work as an early step.