Atomic feline: Engineers use ‘cat with 7 lives’ to prevent quantum computing errors

Known as superposition, this exponentially speeds up calculation speeds since quantum computers can work on multiple possibilities simultaneously. Although extremely beneficial, the approach is also prone to rapidly accumulating errors, which must be corrected. Scientists have been working on different approaches to achieve effective error correction. This has been a major hurdle in the large-scale adoption of quantum computers so far.  

Metaphorical Schrödinger’s cat

Devised by Austrian physicist Erwin Schrödinger, Schrödinger’s Cat is a famous thought experiment in quantum mechanics that tries to explain the conception of superposition. The experiment involves a cat sealed in a box with a mechanism that can potentially kill it. 

An observer cannot know if the cat is dead or alive inside the box unless they open it. However, until the box is opened, the cat is dead and alive at the same time or in a state of superposition. 

In a real-world experiment, Andrea Morello, a professor of Quantum Engineering at UNSW, used the atom of the heavy element of antimony as a qubit and the metaphorical Schrödinger’s cat. 

Using nuclear spins of ‘up’ and ‘down’ as the two quantum states of ‘on’ and ‘off’ is common in quantum computing. However, when the spin suddenly changes, a quantum system faces a logical error. 

Antimony, though, has a large nuclear spin that can take any of the eight directions available to it. So, if ‘0’ is a dead cat and ‘1’ is an alive cat, a change in spin direction will not introduce logical errors immediately. 

“Our metaphorical ‘cat’ has seven lives: it would take seven consecutive errors to turn the ‘0’ into a ‘1’! ” explained Morello in a press release. 

Scalable error detection 

With technical inputs from researchers at the University of Melbourne, Morello’s team embedded the antimony atom inside a silicon quantum chip. This allowed them to encode information in classical binary code while providing large room for error when using logical codes. If an error occurs, the team can spot it and correct it before it accumulates. 

“To continue the ‘Schrödinger cat’ metaphor, it’s as if we saw our cat coming home with a big scratch on his face,” added Morello in the press release. “He’s far from dead, but we know that he got into a fight; we can go and find who caused the fight, before it happens again and our cat gets further injuries.”

This opens up a new way of quantum error correction that can be easily scaled and help deploy quantum computing for real-world applications. 

The research findings were published in the journal Nature Physics.