time crystal

Physicists develop highly robust time crystal

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Dortmund physicists develop highly robust time crystal
What looks like a flame is the measurement of the new time crystal: Each point corresponds to an experimental value, resulting in different views of the periodic dynamics of the nuclear spin polarization of the time crystal.

A team from TU Dortmund University recently succeeded in producing a highly durable time crystal that lived millions of times longer than could be shown in previous experiments. By doing so, they have corroborated an extremely interesting phenomenon that Nobel Prize laureate Frank Wilczek postulated around ten years ago and which had already found its way into science fiction movies.

The results have been published in Nature Physics.

Crystals or, to be more precise, crystals in space, are periodic arrangements of atoms over large length scales. This arrangement gives crystals their fascinating appearance, with smooth facets like in gemstones.

As physics often treats space and time on one and the same level, for example in special relativity, Frank Wilczek, physicist at the Massachusetts Institute of Technology (MIT) and winner of the Nobel Prize in Physics, postulated in 2012 that, in addition to crystals in space, there must also be crystals in time.

For this to be the case, he said, one of their physical properties would have to spontaneously begin to change periodically in time, even though the system does not experience corresponding periodic interference.

That such time crystals could be possible was the subject of controversial scientific debate for several years—but quick to arrive in the movie theater: For example, a time crystal played a central role in Marvel Studios’ movie Avengers: Endgame (2019).

From 2017 onward, scientists have indeed succeeded on a handful of occasions in demonstrating a potential time crystal. However, these were systems that—unlike Wilczek’s original idea—are subjected to a temporal excitation with a specific periodicity, but then react with another period twice as long.

A crystal that behaves periodically in time, although excitation is time-independent, i.e. constant, was only demonstrated in 2022 in a Bose-Einstein condensate. However, the crystal lived for just a few milliseconds.

The Dortmund physicists led by Dr. Alex Greilich have now designed a special crystal made of indium gallium arsenide, in which the nuclear spins act as a reservoir for the time crystal. The crystal is continuously illuminated so that a nuclear spin polarization forms through interaction with electron spins. And it is precisely this nuclear spin polarization that then spontaneously generates oscillations, equivalent to a time crystal.

The status of the experiments at the present time is that the crystal’s lifetime is at least 40 minutes, which is 10 million times longer than has been demonstrated to date, and it could potentially live far longer.

It is possible to vary the crystal’s period over wide ranges by systematically changing the experimental conditions. However, it is also possible to move into areas where the crystal “melts,” i.e. loses its periodicity.

These areas are also interesting, as chaotic behavior, which can be maintained over long periods of time, is then manifested.

This is the first time that scientists have been able to use theoretical tools to analyze the chaotic behavior of such systems.

‘Time crystals’ work around laws of physics to offer new era of quantum computing.

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https://www.space.com/time-crystals-quantum-computing?utm_campaign=socialflow

Scientists discover how to use time crystals to power superconductors.

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https://bigthink.com/hard-science/scientists-discover-how-to-use-time-crystals-to-power-superconductors/#Echobox=1654430170

What’s the real science behind Google’s time crystal?

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https://bigthink.com/starts-with-a-bang/time-crystal/?utm_medium=Social&utm_source=Facebook#Echobox=1653083130

Physicists Created the First-Ever Time Crystals

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  • Scientists have pushed through the theoretical and have created the first ever physical time crystal.
  • While the harvesting of energy from such an object would violate physical law, the development may spur new possibilities in quantum computing.

MAKING A TIME CRYSTAL

A time crystal, without going into much detail, is an object appearing to have movement while remaining at its ground state — an idea proposed by theoretical physicist and Nobel laureate Frank Wilczek in 2012. In an article published last month, we featured how “floquet time crystals” were theoretically possible, according to researchers from the University of California, Santa Barbara (UCSB).

This time, a team of scientists from the University of Maryland took the research further by actually building a working time crystal. The experiment involved creating a quantum system, where a group of ions form a ring shape structure cooled to their ground state.

In order to observe the unobservable perpetual spontaneous break in time-translation symmetry of time crystals, the researchers used a quantum system that evolves over time.

They used ytterbium ions, chaining them in an out-of-equilibrium state that localized them in a specific space, with spins interacting with one another. Then, a laser was used to change the spin of certain ytterbium ions, one after the other, creating continuous oscillation.

A STUDY IN STRANGE

The results were surprising: after observing and allowing the quantum system to evolve, the continuous interactions were occurring at twice the original period. “Since there is no driving force with that period, the only explanation is that the time symmetry must have been broken, thereby allowing these longer periods. In other words, [they] had created a time crystal,” according to MIT Technology Review.

Credits: J. Zhang, C. Monroe, et. al/University of Maryland
Spontaneous breaking of time-transaltion symmetry. Credits: J. Zhang, C. Monroe, et. al/University of Maryland

Time crystals exist as some sort of loophole in the law of physics, by existing in motion without energy consumption — a spontaneous break in time-translation symmetry — now made observable in time. However, in as much as the movement made by time crystals do not use consume energy, neither can it produce any. Also according to Tech Review, “Of course, it would never be possible to extract energy from this motion – that would violate the conservation of energy.”

The experiment has been forwarded for peer review where the experiment will hopefully be able to be replicated.

Still, in just a few years, what was first thought to be impossible was explained theoretically probable and then proven really possible. The existence of time crystals can help us work around the problem of quantum memory and push quantum computing research further.

Physicists propose new definition of time crystals—then prove such things don’t exist

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Few years, physicists have been intrigued by a hypothetical system called a “quantum time crystal,” which has the unusual property of exhibiting periodic motion in its ground state, which is its state of lowest energy. This behavior is unexpected, as it suggests that the system can move even when it doesn’t seem to have enough energy to do so. Ever since time crystals were first proposed in 2012 by Frank Wilczek, physicists have raised serious doubts over their existence, with a few studies already disproving their existence in specific cases.

time crystals

Although at this point it seems likely that time crystals are merely hypothetical concepts, physicists want to be as certain as possible that they do not exist before permanently laying the idea to rest.

With this motivation, physicists Haruki Watanabe at the University of California at Berkeley and Masaki Oshikawa at the University of Tokyo have published a paper in Physical Review Letters in which they first propose a precise of time crystals, and then prove a no-go theorem that rules out the possibility of their existence when defined in this way.

“The original proposal of Wilczek was about a , and we proved its impossibility quite generally,” Watanabe told Phys.org. “We also managed to extend the argument for a ground state (at zero temperature) to a more general ‘‘ state (at non-zero temperatures). These two situations are what we usually discuss for spontaneous symmetry breaking. Thus, we would like to stress that, in our opinion, the spontaneous breaking of time translation symmetry in the standard sense has been proven impossible. In this respect, we believe that our result pretty much settles the debate.”

Yet, as the physicists explain more below, a few open questions still remain.

Time crystals and ordinary crystals

Because a precise mathematical definition of time crystals has been lacking until now, it has understandably been difficult to settle the question of their existence. Watanabe and Oshikawa’s general definition of time crystals resembles the definition of ordinary crystals. Both definitions are based on “long-range order,” which refers to a crystal’s characteristic structure of a highly ordered pattern that repeats over long distances. In ordinary crystals, such as diamonds, long-range order accounts for the periodic geometric shape. In time crystals, according to the new definition, long-range order describes the oscillating motion over time.

When investigating whether time crystals defined in this way actually exist, Watanabe and Oshikawa explain that the key criteria is that the term “crystal” should be reserved for systems that exhibit correlated, coherent behavior. However, due to thermodynamic reasons, they show that a system cannot exhibit this type of behavior at any temperature, and so no real system can be considered a time crystal by this definition.

Overall, the results show that, while ordinary crystals can and do exist, time crystals cannot exist. The only difference between the two is that the first involves spatial long-range order while the second involves temporal long-range order. Although space and time are often considered to be closely related, together forming the “fabric of spacetime,” the findings here emphasize a subtle yet fundamental difference between space and time—with a result that allows for the existence of crystals in one dimension, but forbids them in the other.

Time crystals in equilibrium

There is one minor caveat to the physicists’ definition of time crystals: it requires that the system exist in a state of equilibrium, which is basically the state that a system acquires after a long time without any external forces acting on it. It’s well-known that some non-equilibrium systems exhibit spontaneous oscillations, as demonstrated by a swinging pendulum. However, the researchers explain that these systems should not be considered time crystals without further justification.

“The oscillation of a pendulum or the quantum oscillation in the AC Josephson effect have been known for a long time, and they are not surprising because they are not in thermal equilibrium,” Oshikawa explained. “Certainly they should not be regarded as time crystals. This is a trivial example of periodic motion seen when the system is not in a ground state or in thermal equilibrium. The motion of the pendulum with a small amplitude can be described by a harmonic oscillator, and essentially the same behavior can occur in quantum and classical systems. … Ordinary crystals, on the other hand, can certainly be realized in equilibrium at low enough temperatures.”

With that being said, the scientists also explained that it may still be possible to realize true time crystals in a state of non-equilibrium, but doing so would require formulating a new definition and answering several controversial questions.

“Although it is in the textbooks that any state will approach thermal equilibrium after leaving it for a long enough time—and this has been supported in countless numbers of experiments—this is a highly nontrivial statement and is still under active study,” Watanabe said. “Even if it is true after an infinitely long time, if it requires an unrealistically long time (for example, longer than the age of the universe) to reach the equilibrium, it would be rather irrelevant for actual observation.

“We may generalize the definition of to non-thermal/non-equilibrium setups, and we expect more works along this line. For example, we can easily come up with two interesting open questions one can ask: First, can excited eigenstates [quantum mechanical states] show a time-dependent long range order? This question is related to a recent hot topic, the so-called ‘many-body localization.’ Second, can discrete time translation be spontaneously broken? The continuous time translation cannot be spontaneously broken as we explained above. However, when a system is periodically driven (this makes the problem non-equilibrium), the relevant symmetry is discrete time translation.

“Time crystals may be realized in some way in a non-equilibrium setup, but we would need an appropriate definition for that (as we explained above, there are many systems that show periodic motion rather trivially and we should not include them). As far as we are aware of, there is no positive evidence suggesting such a possibility so far, however.”