A typically fragile quantum superposition has been made to last exceptionally long, and could eventually be used as a probe for discovering new physics.
Quantum superpositions are typically fragile and fleeting, but one such state has now been maintained for a record-breaking 23 minutes. Keeping quantum states stable for this long could help make more robust quantum devices, or lead to discoveries of strange new effects in quantum physics.
 |
| The unknowable aliveness of Schrödinger’s cat is key to more stable quantum devices Olivia ZZ/Getty Images |
This long-lived phenomenon is known as a cat state, named for Erwin Schrödinger’s famous thought experiment where a cat is placed in a box under such peculiar circumstances that it becomes impossible to tell whether it is living or dead. Cat states are superpositions where a quantum object can be in several mutually exclusive states, but it is impossible to tell which one it actually occupies – it effectively simultaneously occupies them all.
Researchers have been able to create cat states with particles of light and even tiny crystals in labs for years, but these states would always quickly lose their special character and collapse into a single, well-determined one. Now, Zheng-Tian Lu at the University of Science and Technology of China and his colleagues have used atoms trapped by light to sustain a cat state for an exceptionally long time.
They used about 10,000 atoms of ytterbium, which they cooled down to a few thousandths of a degree above absolute zero and trapped with the electromagnetic forces of laser light. Under these conditions, the atoms’ quantum states could be very precisely controlled – the researchers leveraged this to put each atom into a superposition of two states that had two very different spins.
Typically, disturbances from the atoms’ environment would collapse them into a single spin state in a matter of seconds or milliseconds, but the researchers tuned their lasers just right to make the cat states last an unprecedented 1400 seconds – or the length of the average sitcom episode.
“It’s a big deal because they’re making this beautiful cat state in an atomic system and it’s stable,” says Barry Sanders at the University of Calgary in Canada.
Such a state is very sensitive to everything that happens in its environment, so it could be used to detect and study subtle magnetic forces or to probe new and exotic effects in fundamental physics, he says. “A probe gets jiggled and pushed and nudged and prodded, and then by seeing what happens, you learn about the things that interact with it.”
The researchers showed that the cat states’ sensitivity for measuring magnetic fields is already very close to the fundamental sensitivity limits set forth by the laws of quantum mechanics. Because it lasts so long, the cat state would not only be a sensitive probe but also one that can keep collecting data past a single snapshot, possibly capturing effects that happen both very quickly and more slowly, says Sanders.
Cat states may become useful for quantum information processing where they could be used as a very stable memory that could store extra information. This could be used in a device like a quantum computer to course-correct whenever it makes an error.
Reference: