The quantum cat state is probably one of the most famous – the idea that a quantum system can exist in the superposition of two different states. It was exemplified by Erwin Schrodinger’s famous thought experiment where an imaginary cat is trapped in a box with a vial of poison activated by a quantum process. Since we do not know when the process will happen, without checking the box, we have to imagine the cat being simultaneously dead and alive.
Real quantum cat states do not involve any danger to real cats – although the states can be as fussy as some felines. Quantum cat states usually need extremely low temperatures, with the system starting from the lowest possible energy: the ground state. Higher temperatures can lead to the collapse of the state. New work has shown that you can make a quantum cat even in warmer, less perfect conditions.
This is the first time that scientists have shown that it is possible to create quantum superpositions from thermally excited states. In a microwave cavity, almost at absolute zero, researchers were able to use a qubit – a quantum bit – to create the hot quantum state. The state was at 1.8 Kelvin (-271.35°C/-456.4°F), which is still extremely cold, but it was 60 times hotter than the cavity itself.
“Our results show that it is possible to generate highly mixed quantum states with distinct quantum properties,” lead author Ian Yang, who performed the experiments reported in the study, said in a statement.
“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,” added Thomas Agrenius, who helped develop the theoretical understanding of the experiment. “Our measurements confirm that quantum interference can persist even at high temperature”.
The protocol designed to create the hot quantum cat state was the same as the protocol to get the quantum cat from the cold ground state. The fact that the same approach is not actually limited by temperature, at least to a certain point, might allow for a lot of new applications of the quantum cat.
“It turned out that adapted protocols also work at higher temperatures, generating distinct quantum interferences,” explained co-author Oriol Romero-Isart, Director of the Institute of Photonic Sciences in Barcelona. “This opens up new opportunities for the creation and use of quantum superpositions, for example in nanomechanical oscillators, for which achieving the ground state can be technically challenging.”
Quantum superposition is key to a whole array of technical applications from sensors to quantum computing. The possibility that temperature constraints might not be as stringent could be revolutionary.
“Our work reveals that it is possible to observe and use quantum phenomena even in less ideal, warmer environments,” emphasized Gerhard Kirchmair. “If we can create the necessary interactions in a system, the temperature ultimately doesn’t matter.”
The work is published in the journal Science Advances.
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