This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: 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. 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.
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