Warm and hot conditions are believed to destroy quantum effects. However, for the first time, a team of researchers has shown that quantum states can exist even at high temperatures.
They created and measured Hot Schrödinger cat states at temperatures as high as 1.8 Kelvin (-271.3°C). This may seem extremely cold to you, but the researchers say it is way higher than the milli-Kelvin temperatures at which quantum superposition is typically observed.
“Many of our colleagues were surprised when we first told them about our results because we usually think of temperature as something that destroys quantum effects. Our measurements confirm that quantum interference can persist even at high temperature,” Thomas Agrenius, one of the study authors and a PhD student at the University of Innsbruck, said.
Cold quantum states in a big limitation
Schrödinger’s cat is a thought experiment in quantum physics that was proposed by Erwin Schrödinger in 1935. It describes a cat placed in a sealed box with a device that can kill the cat.
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Schrödinger suggested that until the box is opened and observed, the cat is considered both alive and dead at the same time. This experiment illustrates a quantum state in which particles can exist in multiple states simultaneously until measured—also known as quantum superposition.
Until now, scientists believed that Schrödinger cats could only be created by first bringing down the energy of an object at its lowest (i.e., the ground state) by cooling it. This required extremely low temperatures (near millikelvin levels) to minimize thermal noise.
This limitation restricts many quantum technologies to lab conditions and prevents their use on a large scale. However, the study authors found a way to solve this problem to a great extent.
They adopted two special protocols to achieve hot Schrödinger cats.
Hot Schrödinger’s cat experiment
The study authors placed a transmon qubit in a superconducting microwave resonator, a special container or box made of superconducting material designed to trap and store microwave energy with minimal loss.
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They used modified versions of two protocols: echoed conditional displacement (ECD) and quantum control mapping (qcMAP). The former involves displacing a quantum state in one direction and then applying a quantum echo to refine the displacement, helping create a desired quantum state with reduced errors.
The latter involves a continuous interaction that entangles one quantum object with another, enabling controlled manipulation of quantum states.
Together, these protocols allowed the study authors to create Schrödinger cats at 1.8 Kelvin while the ambient temperature of the microwave resonator remained at 0.03 Kelvin.
“Our work reveals that it is possible to observe and use quantum phenomena even in less ideal, warmer environments. If we can create the necessary interactions in a system, the temperature ultimately doesn’t matter.” Gerhard Kirchmair, one of the study authors and an experimental physicist at the University of Innsbruck, said.
The study is published in the journal Science Advances.
