Experiment shows when quantum 'cat' states stop bouncing back

October 23, 2026 report Experiment shows when quantum 'cat' states stop bouncing back Ingrid Fadelli Author Lisa Lock Scientific Editor Robert Egan Senior Editor Quantum systems can occupy superpositions, quantum states that combine different possibilities. For instance, a microwave field can be prepared in a superposition of an empty state and a state that contains microwave light. These two components can interfere, reinforcing or canceling each other's contributions to the probabilities of measurement outcomes. This interference distinguishes a superposition from a situation in which the microwave field is simply empty or contains light. A quantum system's interactions with the surrounding environment can cause interference to fade, a process known as decoherence. Researchers at Fuzhou University in China recently investigated whether interference can return after fading and whether this depends on the size of the environment. Their findings, published in Physical Review Letters, showed that expanding an artificial environment from one qubit (i.e., a unit of quantum information) to eight qubits progressively suppressed the return of interference. Monitoring the disappearance and return of interference The researchers prepared a microwave field in a "cat state." This is a superposition of distinguishable states named after Schrödinger's cat, a famous thought experiment in which a cat's fate depends on a quantum event, placing it in a superposition of being alive and dead. The microwave field was in a superposition of an empty state and a light-containing state. It was stored inside a superconducting resonator, a circuit component that can hold an oscillating electromagnetic field. Information about its states could become encoded in correlations between the field and its environment via entanglement, a quantum relationship between the systems. Notably, this information does not need to be read by a person to affect interference and cause decoherence. The researchers reconstructed Wigner maps, representations of the field's quantum state, with a single qubit (embodied in a controllable circuit element) acting as the environment. Alternating positive and negative fringes in these maps revealed interference between the empty and light-containing states. As distinguishing information became encoded in the qubit, these fringes faded. Around 38 nanoseconds (i.e., 38 billionths of a second) after the interaction began, the qubit nearly completed an oscillation and interference returned. At this point, "the quantum coherence is nearly revived," as the researchers explained in their paper. In this scenario, continued interactions could erase the environment's distinguishing record without the need to perform a separate erasure operation. How a larger environment retains information The researchers gradually increased the number of environmental qubits in their setup from one to eight. By measuring individual qubits, they could estimate how well the combined environment distinguished the microwave field's two superposition components. The distinguishability measure they used ranged from zero, indicating no distinguishing information, to one, indicating an unambiguous distinction between the two states. As they included more qubits, oscillations in this measure weakened. The researchers found that with eight qubits, the distinguishability measure approached one after approximately 15 nanoseconds and remained close to this value during measurements that extended to 80 nanoseconds. Separate Wigner maps showed that interference faded without reviving between 0 and 30 nanoseconds. The findings of this study show suppression of the return of interference during the experiment's observation period, rather than establishing that it could never return. Specifically, the team found that different environmental qubits exchanged energy with the microwave field at different rates. To remove their combined record of information, the qubits had to collectively return to states that could no longer distinguish between the field's two superposition components. Adding more qubits made this coordinated return less likely. The experiment performed by the authors provides a controlled setting for investigating apparently irreversible decoherence, which may inform future efforts aimed at developing quantum computers and precision measurement tools. Cat states are useful in both fields, but their vulnerability to decoherence is a known challenge. While the researchers did not demonstrate a method for overcoming it, their experimental platform could help to investigate it further. Written for you by our author Ingrid Fadelli, edited by Lisa Lock, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you. Publication details Ri-Hua Zheng et al., Observation of the Transition from Reversible to Irreversible Decoherence of Mesoscopic Quantum Superpositions, Physical Review Letters (2026). DOI: 10.1103/t2yx-9bqh. On arXiv: arxiv.org/abs/2510.15730v2 Journal information: Physical Review Letters , arXiv Key concepts Quantum correlations, foundations & formalism© 2026 Science X Network