Quantum mechanics has long been the playground of paradoxes, a field where atoms behave like both waves and particles, and cats are both alive and dead. Now, researchers at the University of New South Wales (UNSW) have brought a twist to the famous Schrödinger’s cat thought experiment, using a heavy atom and a silicon chip to address one of the biggest hurdles in quantum computing — error correction.
A Quantum Cat With a Safety Net
The new research hinges on the antimony atom. Unlike standard quantum bits, or “qubits,” which are typically limited to two states — like the binary “up” and “down” of a spinning electron — the antimony atom boasts eight spin directions. This expanded set of possibilities makes it a unique playground for exploring quantum superposition.
“In our work, the ‘cat’ is an atom of antimony,” explains Xi Yu, the study’s lead author. The team’s findings, published in Nature Physics, reveal how this “cat” survives multiple errors without the system falling apart.
“As the proverb goes, a cat has nine lives. One little scratch is not enough to kill it. Our metaphorical ‘cat’ has seven lives: it would take seven consecutive errors to turn the ‘0’ into a ‘1’! This is the sense in which the superposition of antimony spin states in opposite directions is ‘macroscopic’ — because it’s happening on a larger scale, and realizes a Schrödinger cat,” explains Yu.
For quantum computing, this resilience is a game changer. Standard qubits are notoriously fragile; a single error can scramble data. But antimony’s spin structure creates a buffer, allowing scientists to detect and correct mistakes before they cascade into a system failure.
“If the qubit is a spin, we can call ‘spin down’ the ‘0’ state, and ‘spin up’ the ‘1’ state. But if the direction of the spin suddenly changes, we have immediately a logical error: 0 turns to 1 or vice versa, in just one go. This is why quantum information is so fragile,” Yu said.
Quantum Leap in Silicon
This “atomic cat” lives inside a silicon quantum chip, the most widely used material in the technology powering smartphones and laptops. Embedding the antimony in silicon is a huge practical leap because all our technology is based on silicon, meaning these new developments can be scaled.
“By hosting the atomic ‘Schrödinger cat’ inside a silicon chip, we gain exquisite control over its quantum state — or, if you wish, over its life and death,” says Dr. Danielle Holmes, a co-author and chip fabricator.
The UNSW team says this scalability is crucial for building a functional quantum computer. Hosting the ‘cat’ in silicon means that, “in the long term, this technology can be scaled up using similar methods as those we already adopt to build the computer chips we have today,” Dr. Holmes adds.
What This Means for Quantum Computing
Quantum computers promise to solve problems that are practically impossible for classical computers, like simulating complex molecules or optimizing vast networks. However, quantum systems are extremely sensitive to errors, a limitation that has hampered their progress. The UNSW study represents a significant step forward, offering a way to encode data that is more resistant to disruption.
“If an error occurs, we detect it straight away, and we can correct it before further errors accumulate,” says Professor Andrea Morello, who led the study. The antimony atom’s capacity to absorb multiple errors without collapsing the quantum code is an essential step toward achieving robust quantum error correction — a long-sought “Holy Grail” of quantum computing.
Schrödinger’s thought experiment is a metaphor to describe the peculiar nature of quantum superposition. In the original scenario, a cat is placed in a sealed box with a radioactive atom, a Geiger counter, and a vial of poison. If the atom decays, the Geiger counter triggers the release of poison, killing the cat. Quantum mechanics suggests that, until we observe the system, the atom exists in a superposition of decayed and not decayed states — and by extension, the cat is both dead and alive.
While the team’s work brings us closer to reliable quantum computation, challenges remain. Scaling the technology and demonstrating error correction in a larger system will require continued innovation. Still, the progress offers a tantalizing glimpse into a future where quantum computers can reliably perform computations that would take classical computers millions of years.
So, while Schrödinger’s thought experiment was purely conceptual, this research brings the idea into reality. The team has created a system where quantum states — like the cat’s “life” or “death” — can coexist and persist even when small disturbances occur. It’s a tangible realization of quantum superposition but with a practical twist: the metaphorical cat has multiple lives, making quantum computations more resilient.
