This metaphorical cat is both dead and alive – and it will help quantum engineers find computing errors

Calgary, AB – A team led by quantum engineers at the University of New South Wales in Sydney, Australia – that includes two UCalgary researchers – has demonstrated a well-known quantum thought experiment in the real world.

It has created a “Schrödinger’s cat” inside a silicon chip.

Their findings, published in the journal Nature Physics, deliver a new and more robust way to perform quantum computations – and they have important implications for error correction, one of the biggest obstacles standing between them and a working quantum computer.

Quantum mechanics has puzzled scientists and philosophers for more than a century. One of the most famous quantum thought experiments is that of the “Schrödinger’s cat” – a cat whose life or death depends on the decay of a radioactive atom.

According to quantum mechanics, unless the atom is directly observed, it must be considered to be in a superposition – that is, being in multiple states at the same time – of decayed and not decayed. This leads to the troubling conclusion that the cat is in a superposition of dead and alive.

“No one has ever seen an actual cat in a state of being both dead and alive at the same time, but people use the Schrödinger’s cat metaphor to describe a superposition of quantum states that differ by a large amount.”

Dr. Andrea Morello, PhD., team lead and professor at the University of New South Wales in Australia

The researchers used an atom of antimony, which is much more complex than standard ‘qubits,’ or quantum building blocks. Antimony is a heavy atom, which possesses a large nuclear spin, meaning a large magnetic dipole. The spin of antimony can take eight different directions, instead of just two. This changes the behaviour of the system. A superposition of the antimony spin pointing in opposite directions is not just a superposition of ‘up’ and ‘down’, because there are multiple quantum states separating the two branches of the superposition.

“My dream of a spin cat state on a single isolated particle, proposed 35 years ago, has come true by exquisitely controlling a single atomic nucleus that has been isolated from the rest of the universe.”

Dr. Barry Sanders, PhD. physics professor and Scientific Director of Quantum City at UCalgary

This research has profound consequences for scientists working on building a quantum computer using the nuclear spin of an atom as the basic building block. This breakthrough opens the door to a new way to perform quantum computations. The information is still encoded in binary code, ‘0’ or ‘1’, but there is more ‘room for error’ between the logical codes.

This work was the result of an international collaboration. Several authors from UNSW Sydney, plus colleagues at the University of Melbourne, fabricated and operated the quantum devices. Theory collaborators in the United States, at Sandia National Laboratories and NASA Ames, and at the University of Calgary, provided important ideas on how to create the cat, and how to assess its complicated quantum state.

Media inquiries

Colette Derworiz
Senior External Communications Specialist, Faculty of Science
University of Calgary
403-815-1556
colette.derworiz@ucalgary.ca

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