Here’s what you’ll learn when you read this story:

  • Schrödinger’s Cat is a famous thought experiment that explains the non-classical weirdness of quantum superposition.

  • For decades, physicists have theorized that more Schrödinger’s Cat states exist beyond simple position or velocity, but these theories haven’t been recreated in a lab.

  • Now, scientists at Oxford University say they’ve created new exotic superpositions by capturing a single ion of strontium-88 confined in an ion trap, a breakthrough that could help improve quantum computing and error correction.

Quantum physics is the ultimate challenge to humanity’s classical intuition. During a 1964 lecture at MIT, physicist Richard Feynman famously remarked, “I can safely say that nobody understands quantum mechanics.” It’s precisely this unintuitive weirdness that’s driven physicists over the decades to rely on handy metaphors when explaining one of quantum mechanics’ core principles: superposition.

The most famous of these metaphors is Schrödinger’s Cat, a thought experiment first put forward by Austrian theoretical physicist Erwin Schrödinger in which a cat, a radioactive isotope with a 50/50 chance of decaying, a Geiger counter, a flask of poison, and a triggering mechanism are placed in a sealed box. If the Geiger counter detects radioactive decay, the flask is broken, the poison is released, and the cat dies (disclaimer: no felines were actually harmed in the making of this thought experiment). If the radioactive isotope doesn’t decay, the cat lives.

The significance of this metaphorical setup is that it’s mathematically similar to the idea of quantum superposition and the quantum collapse of the wave function. Until the box is opened, we can’t know whether the radioactive isotope has decayed, so the cat in the box is therefore both alive and dead from our perspective. But once an observer makes a measurement (i.e. opens the box), the “wave function” of this superposition of states collapses. After the box is opened, the cat can only be in one state or the other—it’s either dead or alive.

The seeming paradox of Schrödinger’s cat being both alive and dead is analogous to the problem of superposition in subatomic particles, which can appear to be in two states at once until they’re measured. For decades, however, scientists have theorized that more complex variations of Schrödinger’s famous thought experiment might exist beyond the simple “alive or dead” scenario. Now, a study led by scientists at Oxford University has successfully demonstrated these exotic variations in the lab by using a single ion of strontium-88 confined in an ion trap. By manipulating both the ion’s internal quantum state (i.e., its spin) and its motion—the latter behaving as a quantum oscillator—the researchers created superpositions involving multiple quantum properties, not just two opposing states. The results of the study were published in the journal Physical Review X.

“This approach gave us a tool to sculpt quantum superpositions into almost any shape,” Oxford physicist Sebastian Saner, lead author of the study, said in a press statement. “The states we produced exhibit rotational symmetries and form striking geometric interference patterns.”

These different states primarily arise from how the uncertainty of the quantum structure is distributed or how it’s placed in phase space, according to the press statement. With two degrees of freedom—provided by the internal quantum state and the ion’s motion—researchers could essentially sculpt the motional state of the ion. The authors explain that this allowed them to tune the size, phase, and separation of the varying components while also switching between other non-classical states, including squeezed, trisqueezed, or quadsqueezed states in a single superposition.

This isn’t just an interesting theoretical discovery. These new quantum states could improve upon the two-level quantum bits found in current quantum technologies while also improving methods for quantum error correction.

“The textbook image of a quantum system being in two places at once is only the beginning,” Saner told Gizmodo. “There is a much larger landscape of possible quantum states, and we are still learning how to access it experimentally.”

Quantum physics continues to challenge the human mind’s ability to understand the inherent weirdness of reality. But the more we learn, the more we release the immense potential of a future powered by these unintuitive ideas.

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