Real World Demonstration of Schrödinger’s Cat Metaphor

Jan. 14 () –

Engineers of the University of New South Wales (UNSW) have demonstrated the well-known quantum thought experiment of Schrödinger’s cat in the real world, specifically on a silicon chip.

His findings, published in ‘Nature Physics’offer a new, more robust way to perform quantum calculations, and have important implications for error correction, one of the biggest obstacles standing between them and a functional quantum computer.

Quantum mechanics has baffled scientists and philosophers for more than a century. One of the most famous quantum thought experiments is that of “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 (i.e., in several states at the same time) of decay and non-decay. This leads to the disturbing conclusion that the cat is in a superposition of life and death.

“No one has ever seen a real cat in a state of being dead and alive at the same time, but people use the metaphor of Schrödinger’s cat to describe a superposition of quantum states that differ by a large amount”, argues UNSW professor Andrea Morello, leader of the team that carried out the research.

For this research work, Professor Morello’s team used an antimony atom, which is much more complex than standard “qubits”, or quantum building blocks. “In our work, the ‘cat’ is an antimony atom,” explains Xi Yu, lead author of the article.

“Antimony is a heavy atom, which has a large nuclear spin, which means a large magnetic dipole. The spin of antimony can take eight different directions, instead of just two. This may not seem like much, but in fact it changes by complete the behavior 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 that separate the two branches of the superposition“adds the expert.

This has profound consequences for scientists working to build a quantum computer using the nuclear spin of an atom as the basic building block. “Typically, people use a quantum bit, or ‘qubit’ (an object described by only two quantum states), as the basic unit of quantum information,” said co-author Benjamin Wilhelm. “If the qubit is a spin, we can call the state “0” “spin down” and the state “1” “spin up.” But if the direction of the spin suddenly changes, we immediately have a logical error: 0 becomes converts to 1 or vice versa, in one go. “That’s why quantum information is so fragile.”

But in the antimony atom, which has eight different spin directions, if the ‘0’ is coded as a ‘dead cat’ and the ‘1’ as a ‘live cat’, A single error is not enough to crack the quantum code.

“As the proverb goes, a cat has nine lives. A small scratch is not enough to kill it. Our metaphorical ‘cat’ has seven lives: it would take seven consecutive mistakes to turn the ‘0’ into a ‘1. This is the meaning in which the superposition of antimony spin states in opposite directions is ‘macroscopic’, because it is happening on a larger scale and makes a Schrödinger’s cat a reality,” explains Yu.

In this way, the antimony cat is embedded in a silicon quantum chip, similar to those we have in our computers and mobile phones, but adapted to give access to the quantum state of a single atom. The importance of this advance is that it opens the door to a new way of performing quantum calculations. The information is still encoded in binary code, “0” or “1”, but there is more “margin for error” between the logical codes.

“If an error occurs, we detect it immediately and can correct it before more errors accumulate. Continuing with the metaphor of “Schrödinger’s cat”, it is as if we saw our cat coming home with a big scratch on its face.. He’s not dead, but we know he’s had a fight; We can go find the cause of the fight, before it happens again and our cat suffers more injuries,” the researchers explain.

Demonstrating quantum error detection and correction – a “Holy Grail” in quantum computing – is the next milestone the team will address.