Physicists unveil new form of matter—time crystals

January 26, 2017, University of California - Berkeley
Following a blueprint created by UC Berkeley physicist Norman Yao, physicists at the University of Maryland made the first time crystal using a one-dimensional chain of ytterbium ions. Each ion behaves like an electron spin and exhibits long-range interactions indicated by the arrows. Credit: Chris Monroe, University of Maryland

Normal crystals, likes diamond, are an atomic lattice that repeats in space, but physicists recently suggested making materials that repeat in time. Last year, UC Berkeley's Norman Yao sketched out the phases surrounding a time crystal and what to measure in order to confirm that this new material is actually a stable phase of matter. This stimulated two teams to build a time crystal, the first examples of a non-equilibrium form of matter.

To most people, crystals mean diamond bling, semiprecious gems or perhaps the jagged amethyst or beloved by collectors.

To Norman Yao, these inert crystals are the tip of the iceberg.

If crystals have an atomic structure that repeats in space, like the carbon lattice of a diamond, why can't crystals also have a structure that repeats in time? That is, a time crystal?

In a paper published online last week in the journal Physical Review Letters, the University of California, Berkeley assistant professor of physics describes exactly how to make and measure the properties of such a crystal, and even predicts what the various phases surrounding the time crystal should be—akin to the liquid and gas phases of ice.

This is not mere speculation. Two groups followed Yao's blueprint and have already created the first-ever time crystals. The groups at the University of Maryland and Harvard University reported their successes, using two totally different setups, in papers posted online last year, and have submitted the results for publication. Yao is a co-author on both papers.

Time crystals repeat in time because they are kicked periodically, sort of like tapping Jell-O repeatedly to get it to jiggle, Yao said. The big breakthrough, he argues, is less that these particular crystals repeat in time than that they are the first of a large class of new materials that are intrinsically out of equilibrium, unable to settle down to the motionless equilibrium of, for example, a diamond or ruby.

"This is a new phase of matter, period, but it is also really cool because it is one of the first examples of non-equilibrium matter," Yao said. "For the last half-century, we have been exploring equilibrium matter, like metals and insulators. We are just now starting to explore a whole new landscape of non-equilibrium matter."

While Yao is hard put to imagine a use for a time crystal, other proposed phases of non-equilibrium matter theoretically hold promise as nearly perfect memories and may be useful in quantum computers.

This phase diagram shows how changing the experimental parameters can 'melt' a time crystal into a normal insulator or heat up a time crystal to a high temperature thermal state. Credit: Norman Yao, UC Berkeley
An ytterbium chain

The time crystal created by Chris Monroe and his colleagues at the University of Maryland employs a conga line of 10 ytterbium ions whose electron spins interact, similar to the qubit systems being tested as quantum computers. To keep the ions out of equilibrium, the researchers alternately hit them with one laser to create an effective magnetic field and a second laser to partially flip the spins of the atoms, repeating the sequence many times. Because the spins interacted, the atoms settled into a stable, repetitive pattern of spin flipping that defines a crystal.

Time crystals were first proposed in 2012 by Nobel laureate Frank Wilczek, and last year theoretical physicists at Princeton University and UC Santa Barbara's Station Q independently proved that such a crystal could be made. According to Yao, the UC Berkeley group was "the bridge between the theoretical idea and the experimental implementation."

From the perspective of quantum mechanics, electrons can form crystals that do not match the underlying spatial translation symmetry of the orderly, three-dimensional array of atoms, Yao said. This breaks the symmetry of the material and leads to unique and stable properties we define as a crystal.

A time crystal breaks time symmetry. In this particular case, the magnetic field and laser periodically driving the ytterbium atoms produce a repetition in the system at twice the period of the drivers, something that would not occur in a normal system.

"Wouldn't it be super weird if you jiggled the Jell-O and found that somehow it responded at a different period?" Yao said. "But that is the essence of the time crystal. You have some periodic driver that has a period 'T', but the system somehow synchronizes so that you observe the system oscillating with a period that is larger than 'T'."

Yao worked closely with Monroe as his Maryland team made the new material, helping them focus on the important properties to measure to confirm that the material was in fact a stable or rigid time crystal. Yao also described how the time crystal would change phase, like an ice cube melting, under different magnetic fields and laser pulsing.

The Harvard team, led by Mikhail Lukin, set up its time crystal using densely packed nitrogen vacancy centers in diamonds.

"Such similar results achieved in two wildly disparate systems underscore that time crystals are a broad new phase of matter, not simply a curiosity relegated to small or narrowly specific systems," wrote Phil Richerme, of Indiana University, in a perspective piece accompanying the paper published in Physical Review Letters. "Observation of the discrete time crystal... confirms that symmetry breaking can occur in essentially all natural realms, and clears the way to several new avenues of research."

Yao is continuing his own work on as he explores the theory behind other novel but not-yet-realized non-equilibrium materials.

Explore further: Time crystals might exist after all (Update)

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16 comments

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Jim4321
4.5 / 5 (2) Jan 26, 2017
I don't understand. How does this differ from a lightly driven pendulum, or a clock or a swing?
Time periodic behavior is the one thing we are best at measuring. ????
salf
Jan 26, 2017
This comment has been removed by a moderator.
Pooua
4 / 5 (1) Jan 26, 2017
I don't understand. How does this differ from a lightly driven pendulum, or a clock or a swing?

I think that part of the answer is that a pendulum, clock or swing do not constitute a bigger system of similar components. They also aren't atomic-level. So, a crystal is a matrix of repeating, symmetrical elements.
Jim4321
not rated yet Jan 26, 2017
A regular crystal is equally spaced (periodic) in space. A time crystal is presumably periodic in time. Isn't a clock the epitome of a time crystal? If not, what is the definition of a time crystal? The news release didn't provide a definition, they only gave examples. So again, what is a time crystal?
Osiris1
1 / 5 (1) Jan 26, 2017
How about getting this to be part of a real time machine or a time-space warping device?
NeilC
1 / 5 (1) Jan 27, 2017
"unable to settle down to the motionless equilibrium of, for example, a diamond or ruby."

Did these guys (or maybe this author) ever study physics? No such motionless equilibrium exists. Only the average position of each ion in a lattice is quasi-motionless. This is a naive notion of the solid state.
antialias_physorg
5 / 5 (1) Jan 27, 2017
While Yao is hard put to imagine a use for a time crystal,


Well, if it works at period T it might also be stable at period T/2. So we might look at way to store memory (or even energy) by kicking it into various stable states .

How about getting this to be part of a real time machine or a time-space warping device?

Why don't you at least try to read the article before posting? This has nothing to do with time manipulatiuon or warping of space.

Did these guys (or maybe this author) ever study physics? No such motionless equilibrium exists.

They clearly say that it's a periodic ground state. Not the kind of ground-state-plus-uncertainty you usually get.
derphys
not rated yet Jan 27, 2017
External energy is necessary from the external system like for a clock at the atomic level in a time crystal.

But it could be a quantum time crystal moving periodically without dissipation in its zero point motion without any external energy and dissipation ?
A superconducting or superfluid current oscillating in time perpetually coherently could be a time crystal without any external stimulation ?
But the size of this system cannot be very large.
http://en.wikiped..._crystal
http://arxiv.org/abs/1410.2143
Da Schneib
not rated yet Jan 28, 2017
A far better definition of a time crystal is necessary to make sense of this article.
Da Schneib
5 / 5 (1) Jan 28, 2017
While Yao is hard put to imagine a use for a time crystal,


Well, if it works at period T it might also be stable at period T/2. So we might look at way to store memory (or even energy) by kicking it into various stable states .
Actually, the more interesting effect is T2, not T/2.
Zarka
1 / 5 (1) Jan 29, 2017
Isn't DNA a "time crystal"? Here's a good example: bald-headedness gene expression skips a generation because it moves through the maternal line. Hence, a response periodicity with 2x the period of excitation.
savvys84
Jan 30, 2017
This comment has been removed by a moderator.
Gigel
not rated yet Jan 30, 2017
Maybe this will help understanding t-crystals: http://physics.ap...es/v10/5
holoverse
1 / 5 (3) Jan 30, 2017
Is it just an assumption that they never achieve equilibrium? If so...then its in a wierd sense kinda like Pi, and the fact that we dont really know if Pi is non-repeating.....we just assume it to be.

How would we ever prove that these crystals keep perfect time over infinite time spans?
SiaoX
not rated yet Jan 30, 2017
Time crystal is essentially a perpetuum mobile - an eternally moving system, which moves periodically (the common quantum chaos doesn't count here). However, it doesn't produce any energy - instead of this it must be pumped with energy from outside for its survival. The ytterbium atoms act like the time crystal just because they're kept along line - this arrangement just needs cooling below temperature of vacuum fluctuations and such a cooling is not for free. In addition, this system works only in certain combination of temperature and distance parameters between atoms: when they're pressed each other too much, they will freeze and when they're released too much, their motion becomes chaotic - and this is just what the above graph illustrates. Note that above certain temperature limit you can never achieve the periodic motion: only mutually locked positions or chaotic motion.
SlartiBartfast
3 / 5 (2) Jan 30, 2017
Is it just an assumption that they never achieve equilibrium? If so...then its in a wierd sense kinda like Pi, and the fact that we dont really know if Pi is non-repeating.....we just assume it to be.


I've been lurking here for ages, but I had to make an account just for you. We _do_ know that the decimal expansion of pi doesn't repeat. We've known so since Johann Lambert proved that pi was irrational in 1761. That's a pretty serious fail.

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