The Realisation of a “Time Crystal”
A time crystal, like a perpetual motion machine, cycles between states indefinitely without using energy. Inside a quantum computer, physicists claim to have created this new phase of matter.
For the first time, Google’s quantum computer demonstrated a true “time crystal.” A time crystal is an object whose components move in a predictable, repeating cycle without consuming any energy. Time crystals were also the first objects to break “time-translation symmetry” spontaneously. Over the last five years, researchers have been racing to develop a time crystal, but earlier demonstrations have failed to meet all of the requirements. Google’s quantum computing team completed the first-ever computation that was supposed to be impossible for regular computers to complete in a reasonable amount of time. One of the first instances a quantum computer has found work is with the new time crystal demonstration.
“It’s a brilliant use of Google’s processing,” stated researcher Nayak Nayak. The original concept of a time crystal had a fatal flaw: it violated time-translation symmetry, reverting to its original state at regular intervals. Three Princeton and Columbia physicists demonstrated in 2005 that a one-dimensional chain of quantum particles can experience many-body localization. In calculations and simulations, they discovered that tickling a localised chain of spins with a laser in a specific way causes them to flip back and forth. Khemani joined Sondhi on a sabbatical at the Max Planck Institute in Dresden in the fall of 2014.
He observed that if you flip all of the spins in the system (in our case, yielding down, up, up, and down), you get a new stable state. In March 2016, Khymani Khemani and co-authors submitted a preprint proposing the existence of Floquet time crystals. A Floquet crystal exhibits the type of behaviour predicted by Wilczek, but only when it is pushed by an external energy source on a regular basis. Chris Monroe of the University of Maryland, who employs electromagnetic fields to capture and manipulate ions, collaborated with Nayak’s team. The team announced last month in Science that they had transformed the trapped ions into a “prethermal” time crystal.
Google’s Sycamore quantum computer completed a task that would have taken 10,000 years in the past in just 200 seconds. The cryptography and search algorithms built for full-fledged quantum computers are too error-prone for the machine to run. Google’s engineers needed something to do with their machine, which was too prone to errors to run cryptosystems. They contacted Kostya Kechedzhi, a Google theorist, who agreed to work on the time crystal project with them. According to scientists, time crystals reveal something profound about the nature of time.
“This is the first time I’ve heard of a scenario when it’s only one of the group,” Nayak says. It’s uncertain whether a Floquet time crystal could be useful, but Moessner thinks its stability is encouraging. The discovery gives the divide between time and space a fresh perspective.
