Scientists Created the Fattest Schrodinger's Cat Ever
Researchers have created the world’s biggest “quantum cat.”
Named after Schrödinger’s famous thought experiment, a “quantum cat” can be in superposition—the scientific name for being in two states at the same time.
This research may help explain why we don’t see superposition in macroscopic objects, and could help to develop more reliable qubits for quantum computing.
The thought experiment of Schrödinger’s Cat goes like this: place a cat, a radioactive atom, and a vial of poison in a box and close the lid. At some point, that atom will decay, triggering a mechanism that breaks the vial of poison and kills the cat. Because you don’t know when that atom will decay, at any given moment the vial could be broken or whole and the cat could be alive or dead. So—in a way—until you open the box, the cat is both alive and dead at the same time.
Now, obviously, a cat cannot be both alive and dead. A living creature can’t exist in two states at once like that. But quantum particles play by different rules than cats, and if you’re dealing with a small enough object under special conditions, it really can exist in two states at the same time. Not in a “we-don’t-know-the-state” way like the cat, but in an “it-really-is-in-two-states-at-the-same-time” way.
This mind-bending ability to be in two states at the same time is called superposition, and it’s not entirely uncommon in the quantum world. What is uncommon, though, is something of any substantial size being able to maintain a superposition state. And that’s exactly what a team of researchers from ETH Zurich managed to achieve—the “fattest quantum cat to date.” The researchers recently published their results in the journal Science.
The team didn’t quite get to cat size, or cat biology. “Of course, in the lab we can’t realize such an experiment with an actual cat weighing several kilograms”, Yiwen Chu, the lead researcher on the project, said in a press release. But they did hit 16 micrograms. That might not sound like a lot, but considering most “quantum cats” are the size of a single atoms or molecules, it’s comparatively substantial.
The experiments contained three components: the “cat,” a qubit (the quantum equivalent of a bit found in any standard computer), and a material connecting the two. The “cat” was made from something called an oscillating crystal, which is a crystal that can shift back and forth between two states, changing shape as it goes.
The qubit is where the superposition comes into play. Unlike a standard binary bit that can only be in one state at a time—on or off, 1 or 0—a qubit can be in a combination of those two states—1 and 0—at the same time, achieving superposition. It also produces an electric field.
Finally, a material that generates a separate electric field when the oscillating crystal changes shape connects the “cat” to the qubit. When the electric field from the connecting material interacts with the qubit, it is able to transfer the superposition 1-and-0-at-the-same-time state back to the “cat,” placing it in a true state of being “alive” and “dead” at the same time. Once the team was able to verify that the “cat” was in both states at once, and that “alive” and “dead” were noticeably different states, they were able to declare success.
The whole point of this experiment, pushing the boundaries of “quantum cat” size, is to try and understand why it is that we lose the ability to be in two states at once when we hit a certain size. “This is interesting because it will allow us to better understand the reason behind the disappearance of quantum effects in the macroscopic world of real cats,” Chu said in a news release. The research also has implications for how to make more reliable qubits for future forays into quantum computing—ones that don’t hinge entirely on single atoms or molecules.
Maybe someday we’ll know why real cats don’t behave the same way as quantum ones, but until then, it will remain just another mystery of the quantum realm.
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