Constant motion without energy.
For months now, there’s been speculation that researchers might have finally created time crystals – strange crystals that have an atomic structure that repeats not just in space, but in time, putting them in constant oscillation without energy.
Now it’s official – researchers have just reported in detail how to make and measure these bizarre crystals. And two independent teams of scientists claim they’ve actually created time crystals in the lab based off this blueprint, confirming the existence of an entirely new phase of matter.
The discovery might sound pretty abstract, but it heralds in a whole new era in physics – for decades we’ve been studying matter that’s defined as being ‘in equilibrium’, such as metals and insulators.
But it’s been predicted that there are many more strange types of matter out there in the Universe that aren’t in equilibrium that we haven’t even begun to look into, including time crystals. And now we know they’re real.
The fact that we now have the first example of non-equilibrium matter could lead to breakthroughs in our understanding of the world around us, as well as new technology such as quantum computing.
“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,” said lead researcher Norman Yao from the University of California, Berkeley.
“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.”
Let’s take a step back for a second, because the concept of time crystals has been floating around for a few years now.
First predicted by Nobel-Prize winning theoretical physicist Frank Wilczek back in 2012, time crystals are structures that appear to have movement even at their lowest energy state, known as a ground state.
Usually when a material is in ground state, also known as the zero-point energy of a system, it means movement should theoretically be impossible, because that would require it to expend energy.
But Wilczek predicted that this might not actually be the case for time crystals.
Normal crystals have an atomic structure that repeats in space – just like the carbon lattice of a diamond. But, just like a ruby or a diamond, they’re motionless because they’re in equilibrium in their ground state.
But time crystals have a structure that repeats in time, not just in space. And it keep oscillating in its ground state.
Imagine it like jelly – when you tap it, it repeatedly jiggles. The same thing happens in time crystals, but the big difference here is that the motion occurs without any energy.
A time crystal is like constantly oscillating jelly in its natural, ground state, and that’s what makes it a whole new phase of matter – non-equilibrium matter. It’s incapable of sitting still.
But it’s one thing to predict these time crystals exist, it’s another entirely to make them, which is where the new study comes in.
Yao and his team have now come up with a detailed blueprint that describes exactly how to make and measure the properties of a time crystal, and even predict what the various phases surrounding the time crystals should be – which means they’ve mapped out the equivalent of the solid, liquid, and gas phases for the new phase of matter.
And it’s not just speculation, either. Based on Yao’s blueprint, two independent teams – one from the University of Maryland and one from Harvard – have now followed the instructions to create their own time crystals.
Both of these developments were announced at the end of last year on the pre-print site arXiv.org (here and here), and have been submitted for publication in peer-reviewed journals. Yao is a co-author on both articles.
While we’re waiting for the papers to be published, we need to be skeptical about the two claims. But the fact that two separate teams have used the same blueprint to make time crystals out of vastly different systems is promising.
The University of Maryland’s time crystals were created by taking a conga line of 10 ytterbium ions, all with entangled electron spins.
The key to turning that set-up into a time crystal was to keep the ions out of equilibrium, and to do that the researchers alternately hit them with two lasers. One laser created a magnetic field and the second laser partially flipped the spins of the atoms.
Because the spins of all the atoms were entangled, the atoms settled into a stable, repetitive pattern of spin flipping that defines a crystal.
That was normal enough, but to become a time crystal, the system had to break time symmetry. And observing the ytterbium atom conga line, the researchers noticed it was doing something odd.
The two lasers that were periodically nudging the ytterbium atoms were producing a repetition in the system at twice the period of the nudges, something that couldn’t 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?” said Yao.
“But that is the essence of the time crystal. You have some periodic driver that has a period ‘T’, but the system somehow synchronises so that you observe the system oscillating with a period that is larger than ‘T’.”
Under different magnetic fields and laser pulsing, the time crystal would then change phase, just like an ice cube melting.
The Harvard time crystal was different. The researchers set it up using densely packed nitrogen vacancy centres in diamonds, but with the same result.
“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,” explained Phil Richerme from Indiana University, who wasn’t involved in the study, in a perspective piece accompanying the paper.
“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.”
Update 31 January 2017: We had previously compared the constant oscillation of the time crystals as being in perpetual motion at ground state, which isn’t accurate. We’ve now corrected this explanation.
By: ScienceAlert, Australia
Source: www.sciencealert.comRead More
Harvard scientists report they have succeeded in creating the rarest material on the planet— atomic metallic hydrogen.
Thomas D. Cabot Professor of the Natural Sciences Isaac Silvera and postdoctoral fellow Ranga Dias, have begun to answer some fundamental questions about the nature of matter with the material, which is believed to have a number of applications, including as a room-temperature superconductor.
“This is the Holy Grail of high-pressure physics,” Silvera said in a statement. “It’s the first-ever sample of metallic hydrogen on Earth, so when you’re looking at it, you’re looking at something that’s never existed before.”
Silvera and Dias were able to squeeze a tiny hydrogen sample at 495 gigapascal (GPa) or more than 71.7 million pounds per square inch, which is greater than the pressure at the center of the Earth.
According to Silvera, at such extreme pressures solid molecular hydrogen, which consists of molecules on the lattice sites of the solid, breaks down and the tightly bound molecules dissociate to transform into atomic hydrogen.
In the experiment, the two researchers used two small pieces of carefully polished synthetic diamond and treated them to make them even tougher. They then mounted them opposite each other in a device called a diamond anvil cell.
“Diamonds are polished with diamond powder and that can gouge out carbon from the surface,” Silvera said. “When we looked at the diamond using atomic force microscopy, we found defects, which could cause it to weaken and break.”
They were able to use a reactive ion etching process to shave a tiny layer—just five microns thick—from the diamond’s surface and then coated the diamond with a thin layer of alumina to prevent the hydrogen from diffusing into the crystal structure and embrittling it.
Silvera said the discovery could lead to new materials.
“One prediction that’s very important is metallic hydrogen is predicted to be meta-stable,” Silvera said. “That means if you take the pressure off, it will stay metallic, similar to the way diamonds form from graphite under intense heat and pressure, but remain diamonds when that pressure and heat are removed.”
Silvera said understanding whether the material is stable could suggest that metallic hydrogen could act as a superconductor at room temperatures.
“As much as 15 percent of energy is lost to dissipation during transmission,” he said, “so if you could make wires from this material and use them in the electrical grid, it could change that story.”
Dias explained that a room temperature superconductor could change the transportation system by making magnetic levitation of high-speed trains possible, as well as making electric cars more efficient and improving the performance of many electronic devices.
Other applications for the material could provide major improvements in energy production and storage, because superconductors have zero resistance, making superconducting coils more useful to store excess energy, which could then be used whenever it is needed.
Another application could be as a more powerful rocket propellant.
“It takes a tremendous amount of energy to make metallic hydrogen,” Silvera said. “And if you convert it back to molecular hydrogen, all that energy is released, so that would make it the most powerful rocket propellant known to man, and could revolutionize rocketry.”
Fuels are often measured by a specific impulse—a measure in seconds of how fast a propellant is fired from the back of the rocket.
The most powerful fuels in use today have a specific impulse of about 450 seconds, while the specific impulse for metallic hydrogen is theorized to be 1,700 seconds.
“That would easily allow you to explore the outer planets,” Silvera said. “We would be able to put rockets into orbit with only one stage, versus two and could send up larger payloads, so it could be very important.”
The study was published in Science.
While the Harvard scientists believe they have made the breakthrough that researchers have been trying to discover for several decades, others aren’t so sure.
In a recent article published in Nature, five experts reported doubt on the discovery of metallic hydrogen, saying that the accompanying paper is not convincing.
By: R&D magazine, USA
Source: www.rdmag.comRead More