A Quantum Twist: Scientists Create “Hot” Schrödinger’s Cat States

Quantum physics has long required extreme precision and ultra-cold temperatures to observe its most mind-bending phenomena. But a breakthrough from researchers in Innsbruck, Austria, challenges that assumption—revealing that quantum states can persist even in warmer, less controlled environments.

In a new study published in Science Advances, a team from the University of Innsbruck and the Institute of Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences has successfully generated “hot” Schrödinger cat states—a type of quantum superposition—inside a superconducting microwave resonator.

What Are Schrödinger Cat States?

Named after Erwin Schrödinger’s famous thought experiment where a cat is both alive and dead at the same time, cat states represent the quantum reality where a system exists in two distinct states simultaneously. While such effects have previously been observed in carefully prepared cold systems, this new research marks the first time they’ve been created from thermally excited—or “hot”—states.

“Schrödinger assumed a living, or hot, cat in his thought experiment,” says Gerhard Kirchmair, co-lead author of the study. “We wanted to know if quantum effects could still emerge without starting from the ‘cold’ ground state.”

The Experiment: Heating Things Up

The researchers used a transmon qubit inside a superconducting microwave resonator to craft their quantum states. Instead of cooling the system to near absolute zero (the usual method), they created cat states at temperatures up to 1.8 Kelvin—around 60 times hotter than the surrounding environment in the cavity.

Their team employed two specialized protocols—previously only used for cold systems—to produce superpositions in this warmer setup. Remarkably, these adapted methods worked, generating distinct quantum interferences despite the added heat.

Rethinking Quantum Temperature Limits

“Many scientists were skeptical at first,” says Thomas Agrenius, a theoretical physicist on the team. “Because temperature is typically seen as a quantum killer—it tends to destroy delicate quantum states. But our measurements show that quantum interference can survive, even at elevated temperatures.”

Lead experimentalist Ian Yang adds: “What we’ve demonstrated is that highly mixed quantum states with genuine quantum properties can still be engineered under these conditions.”

A New Path for Quantum Technologies

The implications of this research could ripple across the world of quantum science. Cooling a system to its ground state is often one of the biggest technical challenges in quantum experiments. This new method may pave the way for quantum technologies that function in less-than-perfect conditions, especially in complex systems like nanomechanical oscillators where achieving ultra-cold temperatures is tough.

“This opens new doors,” says Oriol Romero-Isart, who led the theoretical part of the project and is now Director at ICFO in Barcelona. “We’ve shown that with the right interactions, temperature isn’t necessarily a barrier.”

The Takeaway

Far from a mere academic curiosity, this achievement challenges a key assumption in quantum science: that heat and quantum behavior don’t mix. As Kirchmair puts it, “If we can design the right interactions within a system, temperature might no longer matter.”

That could be a game-changer for the future of quantum computing, sensing, and other next-generation technologies—bringing us one step closer to harnessing quantum effects in the real, imperfect world.

Read the Original Article: Phys.org

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