'Schrödinger's Cat' in a Lab: Created with 20 Entangled Qubits

The record-breaking research is significant for the future of quantum computers.

Schrödinger's cat, perhaps the most well-known paradox in physics, has now been recreated in a laboratory in a bid to keep improving quantum computers. 

Created by a team of German physicists, the research has set a new record as they built a quantum cat-state out of 20 entangled quantum bits, or qubits as they are widely referred to. 


The findings were published in the journal Science.

What is Schrödinger's cat?

Coined and created by Austrian physicist, Erwin Schrödinger, in 1935, his experiment put forward the quantum cat. The cat is enclosed in a box with a radioactive sample, a detector, and a lethal dosage of poison. 

If the radioactive liquid disintegrates, the detector is triggered, and the poison is released, ultimately killing the cat. But, according to quantum physics, different from everyday life, it's unclear whether or not the cat is dead or alive. 

'Schrödinger's Cat' in a Lab: Created with 20 Entangled Qubits
Experimental sketch: Rubidium atoms are captured by laser beams (red). Another additional laser (blue) excites about half of the atoms to such an extent that their atomic shells merge with the adjacent atoms. Source: Tobias Schlößer/Forschungszentrum Jülich

It's only once the box is opened that the truth is revealed, so until then, it's a suspended state in which the cat would be both dead and alive at the same time.

How is this cat-state recreated in a laboratory?

The 'cat-state' is recreated where two or more particles can be in two different states simultaneously.

This is important in physics, as it plays an integral role in quantum computers, and is the first step in creating a logical operation between two qubits.

As co-author of the study and physicist at the Peter Grünberg Institute of Jülich, Jian Cui, said: "Qubits in the cat state are considered extremely important for the development of quantum technologies."

Cui continued, "The secret of the enormous efficiency and performance expected of future quantum computers is to be found in this superposition of states."

'Schrödinger's Cat' in a Lab: Created with 20 Entangled Qubits
In quantum computing, a cat state - named after the famous analogy of Schrödinger's cat - is a quantum state composed of two diametrically opposed conditions simultaneously. Together with experts from Forschungszentrum Jülich, an international team has now succeeded in placing 20 entangled quantum bits in such a state of superposition. Source: Annette Stettien/Forschungszentrum Jülich

However, these 'cat-states' are very sensitive, with even the smallest interference from the outside enough to 'decohere' them. This would lead to the entangled state to be lost. 

The team of researchers was interested in creating a higher number of entangled cat-state qubits. And that's exactly what they did. 

"We practically inflated some atoms to such an extent that their atomic shells merge with the adjacent atoms to simultaneously form two opposite configurations, namely excitations occupying all even or odd sites," said Cui.

"This goes so far that the wave functions overlap as in the analogy of Schrödinger's cat, and we were able to create the superposition of the opposite configurations."

The way in which the team avoided decoherence? Turning the lasers off and on at the exact right state to increase the preparation process. 


What they've achieved from their 20 entangled cat-state qubits is the equivalent of more than a million superimposed states.

Physicists will keep trying to increase the number of entangled qubits as time goes on. Let's see what the next record will be.

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