Scientists develop ‘time crystals’ made from light

(ORDO NEWS) — A new, more robust approach to making these strange designs takes them one step closer to being practical. In many ways, scientists are like detectives, solving mysteries by sifting through evidence looking for similar patterns.

For example, any crystal, be it a grain of table salt or a diamond necklace, is simply a collection of atoms arranged in a repeating pattern. With a glimpse of just a few atoms of the crystal, the detective can guess where all the others should be.

But what if this pattern is distributed in time, not in space, and its components are interconnected according to the principle of “when” and not “where”? This counterintuitive concept underlies “time crystals,” quantum systems that exhibit crystal-like, predictably repetitive behavior.

MIT physicist and Nobel laureate Frank Wilczek first suggested their existence in 2012. After many years of hard work, the experimenters managed to finally create such a device only in 2021.

Now, a team of physicists led by engineer Hossein Taheri of the University of California, Riverside, has achieved yet another success by creating a time crystal from light. Their work, published in February in the journal Nature Communications,

Although the time crystal’s behavior repeats itself over time, it cannot be considered a simple ticking clock. In particular, clocks require external energy to keep going, but for a time crystal, “ticking” is its most natural, stable state.

This is the opposite of physicists’ notion of thermodynamic equilibrium, in which energy enters a system only to inevitably dissipate: imagine a pot of water that is brought to a boil and then returned to room temperature.

In this sense, time crystals are like a pot of water that always boils the same and never gets cold. By some definitions, they represent a new and unique state of matter, which is characterized by unshakable persistence in getting out of balance. Like a kind of metronome

“Time crystals have gone from a conceptual idea dictated by purely theoretical considerations to something that people are trying to use in technology,” says Wilczek, who was not involved in the new work.

But researchers have had to go through a long and thorny path in an effort to bring time crystals from the laboratory to the realm of real applications. Usually, in order to determine whether this or that installation is a time crystal at all, complex experimental setups or unique control of powerful quantum computers were required.

The team’s breakthrough was achieved with a comparatively simpler approach, consisting of firing two beams of laser light into a millimeter-wide cavity of a disk-shaped crystal. Inside the cavity, two beams repeatedly ricocheted off its sides and collided in the process.

Crucially, the researchers chose a specific design for the cavity and precisely controlled the properties of the laser beams so that the burst of reflected light created strange patterns that could never have come from light emitted from, for example, ordinary household light bulbs.

Inside the crystalline “jumping house,” the laser light became a parade of “chunks,” each more like a single crest of a wave that never loses its shape than a wide ripple on the surface of an agitated lake.

These solitary waves, or solitons, arose and formed a parade at predictable intervals, marching perfectly in time, thus building a time crystal. Physicists caught this “crystallization” by carefully examining the light that trickled out of the cavity.

If a tiny version of you were to stand at the exit of the cavity, holding a light detector in your hands, Taheri explains, you would first detect periodic changes in the intensity of the output light associated with the properties of lasers.

However, in the end, a pattern of light intensity would spontaneously arise with a completely different periodicity, given by solitons passing through the cavity. It would be like watching a movie on a TV that suddenly started playing it at high speed, with the particular frame rate set by hidden mechanics inside the display, not controlled by you.

“Now we see some features of the [light] wave that are periodic, but their period is actually two or three times or some other integer multiple of the periodicity imprinted [on light] by lasers,” Taheri says. This magnification revealed a quantum system that now naturally maintains its own time – in other words, a light-based time crystal.”

Andrey Matsko, a physicist at NASA‘s Jet Propulsion Laboratory and co-author of the study, compares it to growing salt crystals by hanging a filament in a salty liquid.

“Tuning our lasers is like controlling the structure of a filament that you dip into a [salt] solution,” he says. In any case, a laser or a thread helps the crystals to form, but their periodicity, their structure is completely dependent on themselves.

Previous research has used various building blocks to create time crystals, but the use of light in the new experiment has proven to be a practical advantage. It is important to note that the time crystal created by the team works under relatively normal conditions.

Most of the quantum phases of matter only exhibit their special properties at cryogenic temperatures or other extreme conditions, and become completely normal when they enter the world outside the laboratory.

“From my point of view, this experiment is important because it works at [relatively] high temperatures,” says Berislav Buka, a physicist at the University of Oxford who was not involved in the study. “It makes it closer to the complex processes we see in the real world around us.”

The new time crystal also proved remarkably resistant to the notorious real-world clutter. According to Taheri, random power losses in the system, as well as noise superimposed on it (like your TV getting hot and showing noise in the analogy of watching a movie), actually increased its stability.

Usually, “when these two elements are present, they try to destroy the crystallinity,” he says. To avoid such external disturbances, time crystals usually must be strictly isolated from the environment. “But our system strikes a balance between these opposing players,” Taheri says.

Igor Lesanovsky, a physicist at the University of Nottingham in England, who also did not participate in the experiment, agrees that keeping the time crystal working is without shielding it from the environment can be tricky. “You really need collusion between different effects,” he says.

As dissipation and noise conspire to keep each other’s deleterious effects at bay, the new light time crystal is a promising candidate for integration into practical devices in the future. It also requires a relatively small number of components to build, said Lute Maleki, CEO of photonic technology company OEwaves and co-author of the study.

“It’s a really simple [device] architecture,” he emphasizes. “It should be accessible to many [research] groups.” Maleki hopes that future research will propel this simple but robust design to the center of both fundamental physics research and applied efforts such as precision timekeeping.

As an instrument for measuring time, the light time crystal may be slightly less accurate than modern atomic clocks.

But its stability and ruggedness of components may make it suitable for integration into, for example, communications or computing devices that require very precise timing yet are robust enough to function outside carefully controlled laboratory conditions.

In addition, some common electronics manufacturing technologies may allow the implementation of a time crystal on a chip, making it easier to add the system to existing consumer gadgets.

In addition, physicists could study very large time crystals in the same way that more traditional space crystals have been studied for decades, says study co-author Krzysztof Sasza, a physicist at the Jagiellonian University in Poland.

Here, physicists can swap space for time to investigate whether time crystals, constructed with certain defects or bathed in excess energy, exhibit unexpected behavior. This behavior is usually harder to detect in small crystals, so being able to make their light-based system large potentially gives the team the opportunity to enter a whole new realm.

“I think it really opens up new horizons [for physics research],” Sasha emphasizes. Wilczek agrees. “This is a completely new class of states of matter,” he says.


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