Nature Physics

Scientists Just Made ‘Superionic Ice’ That’s Solid And Liquid at The Same Time

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“A really strange state of matter.”

Scientists think they’ve finally discovered a totally new type of water ice called superionic water, water that is simultaneously a solid and a liquid, potentially teaching us much more about this most versatile of substances and leading to the development of new materials.

The idea of superionic water has actually been around for several decades – it’s believed to exist inside the mantles of planets like Uranus and Neptune – but until now no one had managed to prove its existence in an experiment.

Step forward the team of researchers behind the new study, who were able to produce superionic water from a high-pressure type of ice and a series of powerful laser pulses.

That combination provided the kinds of temperatures and pressures we don’t get naturally here on Earth, giving us our first real glimpse of this mysterious water.

“These are very challenging experiments, so it was really exciting to see that we could learn so much from the data,” says one of the team, physicist Marius Millot from the Lawrence Livermore National Laboratory (LLNL) in California.

“Especially since we spent about two years making the measurements and two more years developing the methods to analyse the data.”

Water molecules are made from two hydrogen atoms connected to one oxygen atom in a V-shape. Weak forces between the molecules become more obvious as they cool, causing them to push apart when water freezes.

 In superionic water, intense heat breaks the bonds between a water molecule’s atoms, leaving a solid crystal structure of oxygen atoms, and a flow of hydrogen nuclei or ions in between them – creating both a solid and a liquid at the same time.

“That’s a really strange state of matter,” Millot told Kenneth Chang at The New York Times.

To begin with, pressure more than a million times that of Earth was exerted on water by passing it through two diamond layers and creating a special kind of ice called ice VII, which remains solid at room temperature.

At a separate laboratory, laser shock waves lasting 10-20 billionths of a second were then sent through the ice, resulting in conditions extreme enough to generate superionic water.

The initial pre-compression of the ice enabled researchers to push the ice to higher temperatures before everything vaporised.

superionic water 2Laser-driven shock compressions completed the process.

By capturing the optical appearance of the ice, scientists were able to determine that ions rather than electrons were moving around in the material, because of its opaque rather than shiny look.

Now we know that superionic ice actually exists, it could help explain the rather off-centre magnetic fields of Uranus and Neptune, a discrepancy that scientists have put down to shells of superionic ice inside their mantles.

It’s also another valuable example of how molecules act under extremes of temperature and pressure, and further down the line, we could even engineer new materials with specific properties by being able to manipulate how the molecules react.

“Driven by the increase in computing resources available, I feel we have reached a turning point,” says one of the researchers, physicist Sebastien Hamel from LLNL.

“We are now at a stage where a large enough number of these simulations can be run to map out large parts of the phase diagram of materials under extreme conditions in sufficient detail to effectively support experimental efforts.”

The research has been published in Nature Physics.

Reality Doesn’t Exist Until We Measure It, Quantum Experiment Confirms

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Australian scientists have recreated a famous experiment and confirmed quantum physics’s bizarre predictions about the nature of reality, by proving that reality doesn’t actually exist until we measure it – at least, not on the very small scale.

That all sounds a little mind-meltingly complex, but the experiment poses a pretty simple question: if you have an object that can either act like a particle or a wave, at what point does that object ‘decide’?

Our general logic would assume that the object is either wave-like or particle-like by its very nature, and our measurements will have nothing to do with the answer. But quantum theory predicts that the result all depends on how the object is measured at the end of its journey. And that’s exactly what a team from the Australian National University has now found.

“It proves that measurement is everything. At the quantum level, reality does not exist if you are not looking at it,” lead researcher and physicist Andrew Truscott said in a press release.

Known as John Wheeler’s delayed-choice thought experiment, the experiment was first proposed back in 1978 using light beams bounced by mirrors, but back then, the technology needed was pretty much impossible. Now, almost 40 years later, the Australian team has managed to recreate the experiment using helium atoms scattered by laser light.

“Quantum physics predictions about interference seem odd enough when applied to light, which seems more like a wave, but to have done the experiment with atoms, which are complicated things that have mass and interact with electric fields and so on, adds to the weirdness,” said Roman Khakimov, a PhD student who worked on the experiment.

To successfully recreate the experiment, the team trapped a bunch of helium atoms in a suspended state known as a Bose-Einstein condensate, and then ejected them all until there was only a single atom left.

This chosen atom was then dropped through a pair of laser beams, which made a grating pattern that acted as a crossroads that would scatter the path of the atom, much like a solid grating would scatter light.

They then randomly added a second grating that recombined the paths, but only after the atom had already passed the first grating.

When this second grating was added, it led to constructive or destructive interference, which is what you’d expect if the atom had travelled both paths, like a wave would. But when the second grating was not added, no interference was observed, as if the atom chose only one path.

The fact that this second grating was only added after the atom passed through the first crossroads suggests that the atom hadn’t yet determined its nature before being measured a second time.

So if you believe that the atom did take a particular path or paths at the first crossroad, this means that a future measurement was affecting the atom’s path, explained Truscott. “The atoms did not travel from A to B. It was only when they were measured at the end of the journey that their wave-like or particle-like behaviour was brought into existence,” he said.

Although this all sounds incredibly weird, it’s actually just a validation for the quantum theory that already governs the world of the very small. Using this theory, we’ve managed to develop things like LEDs, lasers and computer chips, but up until now, it’s been hard to confirm that it actually works with a lovely, pure demonstration such as this one.

Source: Nature Physics.

Physicists Twist Water into Knots .

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A 3-D-printed vortex-maker may improve understanding of braided fluids in nature, such as in the sun’s outer atmosphere, superconductive materials, liquid crystals and quantum fields

More than a century after the idea was first floated, physicists have finally figured out how to tie water in knots in the laboratory. The gnarly feat, described today in Nature Physics, paves the way for scientists to experimentally study twists and turns in a range of phenomena — ionized gases like that of the Sun’s outer atmosphere, superconductive materials, liquid crystals and quantum fields that describe elementary particles.

Lord Kelvin proposed that atoms were knotted “vortex rings” — which are essentially like tornado bent into closed loops and knotted around themselves, as Daniel Lathrop and Barbara Brawn-Cinani write in an accompanying commentary. In Kelvin’s vision, the fluid was the theoretical ‘aether’ then thought to pervade all of space. Each type of atom would be represented by a different knot.

Kelvin’s interpretation of the periodic table never went anywhere, but his ideas led to the blossoming of the mathematical theory of knots, part of the field of topology. Meanwhile, scientists also have come to realize that knots have a key role in a host of physical processes.

Creating a knot in a fluid bears little resemblance to tying a knot in a shoelace, say Dustin Kleckner and William Irvine, physicists at the University of Chicago in Illinois. The entire three-dimensional (3D) volume of a fluid within a confined region, such as a vortex, must be twisted. Kleckner and Irvine have now created a knotted vortex using a miniature version of an airplane wing built with a 3D printer.

During an airplane’s flight, a wing induces a rotational or vortex-like motion of air currents that gives lift to an airplane. When a wing at rest suddenly accelerates, it creates two vortices of air circulating in opposite directions. The researchers submerged their tiny wings in a tank of water and gave it a sudden acceleration to create a knotted structure (videos below and at top).

Capturing images of the knot was another technical tour-de-force. Fluid dynamicists often use colored dye to trace the motion of fluids, but Kleckner and Irvine injected tiny gas bubbles into the water that were drawn to the center of the knotted vortex by buoyancy forces. A high-speed laser scanner capable of producing CT-scan views of the fluid at 76,000 frames per second enabled the researchers to reconstruct the 3D arrangement of the bubbles, thus revealing the knots.

“The authors have managed a remarkable achievement to be able to images these vortex knots,” says Mark Dennis, an optical physicist at the University of Bristol, UK, who has made knotted vortices from light beams. The new study, he adds, transforms abstract notions about physical processes involving knots into testable ideas in the laboratory.

“Knotted vortices are an ideal model system for allowing us to study the precise way in which knots untie themselves in a real physical field,” says Irvine.

Knotted vortices show up in several branches of physics. Particle physicists, for example, have proposed that ‘glueballs’, hypothetical agglomerations of gluons — the elementary particles that bind quarks to form protons and neutrons — are tightly knotted quantum fields.

And in January, scientists reported evidence of ‘unbraiding’ or relaxation of knotted magnetic fields that may help to transfer heat to the Sun’s corona, or outer atmosphere, explaining why the plasma in this region is much hotter than the Sun’s surface.

Source: Scientific American.