Austrian researchers defy rules of quantum physics with "hot" Schrödinger's cat

Researchers at an Austrian university have achieved a quantum breakthrough that challenges conventional understanding: They've generated Schrödinger cat states not from ultra-cold ground states, but from warm, thermally excited ones previously only described in a thought experiment by fellow countryman Erwin Schrödinger.

In a superconducting qubit setup, the team demonstrated that quantum superpositions can persist even at higher temperatures, defying the long-standing belief that heat disrupts quantum phenomena. An article by SciTechDaily points out that this discovery not only supports Schrödinger's original idea of a "hot cat," but also opens the door to more practical and accessible quantum technologies.

Schrödinger cat states are a fascinating feature of quantum mechanics, where a system exists in two contradictory states at once. The concept originates from the Austrian physicist Erwin Schrödinger's famous thought experiment, where a cat is both alive and dead simultaneously. His scenario explored what happens when a quantum object interacts with something more familiar. He envisioned a box containing a radioactive atom, a vial of poison, and a cat. According to quantum mechanics, the atom can either decay or remain stable at any moment, with no way to predict when it will happen. If the atom decays, it breaks the vial, releases the poison, and kills the cat.

In real experiments, similar quantum superpositions have been seen in atomic positions, molecular states, or electromagnetic resonator vibrations. Traditionally, these superpositions were achieved by cooling the quantum system to its ground state, the lowest energy level. However, a recent breakthrough led by Gerhard Kirchmair and Oriol Romero-Isart in Innsbruck, Austria shows it’s possible to create Schrödinger cat states even from thermally excited, or "hot," systems. "Schrödinger also envisioned a living, or ‘hot’ cat, in his thought experiment," explains Kirchmair from the University of Innsbruck and IQOQI. "We wanted to see if these quantum effects could still occur without starting from the cold ground state."

In their study, published in Science Advances on April 4, the team used a transmon qubit inside a microwave resonator to create the cat states, achieving success at temperatures up to 1.8 Kelvin—about 60 times hotter than the usual operating temperature. "Our results show it's possible to generate highly mixed quantum states with distinct quantum properties," says Ian Yang, who is part of the research team.

"Many were surprised when we first shared our results, as we usually associate temperature with the destruction of quantum effects," adds Thomas Agrenius, who helped develop the theoretical framework. "Our measurements confirm that quantum interference can persist even at higher temperatures."

These findings could accelerate the development of quantum technologies. "Our work shows that quantum phenomena can be observed and utilized even in warmer environments," Kirchmair concludes. "If the necessary interactions are created in a system, temperature becomes less of a concern."

By Nazrin Sadigova