World’s First Quantum Metamaterial Unveiled (TechnologyReview.com)

Quantum isn’t just for abstract theories anymore. It’s now comes in a working “metamaterial” variety.


German researchers have designed, built, and tested the first metamaterial made out of superconducting quantum resonators.

In recent years, physicists have been excitedly exploring the potential of an entirely new class of materials known as metamaterials. This stuff is built from repeating patterns of sub-wavelength-sized structures that interact with photons, steering them in ways that are impossible with naturally occuring materials.

The first metamaterials were made from split-ring resonators (C-shaped pieces of metal) the size of dimes that were designed to interact with microwaves with a wavelength of a few centimetres. These metamaterials had exotic properties such as a negative refractive index that could bend light “the wrong way”.

But they were far from perfect, not least because the split-ring resonators introduced losses because of their internal resistance.

It doesn’t take much imagination to think of a solution to this problem: use superconducting resonators that have zero internal resistance.

And that’s a good idea in theory. In practice, however, it is hugely challenging. Apart from the obvious difficulty of operating at superconducting temperatures just above absolute zero, the main problem is that superconducting resonators are quantum devices with strange  quantum properties that are fragile and difficult to handle.

In particular, these properties are exponentially sensitive to the physical shape of the resonator. So tiny differences between one resonator and another can lead to huge differences in their resonant frequency.

And since metamaterials are periodic arrays of structures with identical properties,  that’s a problem. Indeed, nobody has ever made a quantum metamaterial for precisely this reason.

Today that changes thanks to the work of Pascal Macha at the Karlsruhe Institute of Technology in Germany and a few pals. These guys have built and tested the first quantum metamaterial, which they constructed as an array of 20 superconducting quantum circuits embedded in a microwave resonator.

This experiment is a significant challenge. These guys fabricated their quantum circuits out of aluminium in a niobium resonator, which they operated below 20 milliKelvin.

Their success comes from two factors. The first was in minimising the differences between each quantum circuit  so there was less than a 5 per cent difference in the current passing through each.

The second was in clever design. A quantum circuit influences an incoming photon by interacting with it. To do this as a group, the quantum circuits must also interact with each other.

The problem in the past is that physicists had arranged the circuits in series so that the combined state must be a superposition of the states of all the circuits. So if a single circuit was out of kilter, the entire experiment failed.

Macha and co got around this by embedding the quantum circuits inside a microwave resonator – a chamber about a wavelength long in which the microwaves become trapped.

To interact with a photon, each quantum circuit need only couple with the resonator itself and its nearest neighbours. That’s much easier to do with a large ensemble of quantum circuits.

And the results  show that it worked, at least in part.

The interaction with the quantum circuits changes the phase of the outgoing photons in subtle but measurable ways. So by studying this change, Macha and co were able to work out exactly what kind of interaction was occurring.

What they saw was that eight of the circuits formed a coherent group that influenced the photons. But over time, this dissociated into two separate groups of four quantum circuits.

That raises the tantalising question of why the large ensemble dissociated into two smaller ones, something that Macha and co will surely be investigating in future work.

It also raises the prospect of a new generation of devices. “Quantum circuits…based on this proof-of-principle experiment offer a wide range of prospects, from detecting single microwave photons to phase switching, quantum birefringence and superradiant phase transitions,” say Macha and co.

All in all, a significant first step for quantum metamaterials.

First Planet Discovered Orbiting a Brown Dwarf (TechnologyReview.com)

This is really interesting. Using a different detection technique, astronomers aren’t required to search for planets and stars based on brightness alone. I’d expect to see dozens of new brown dwarf planets to be found in the near future due to this discovery.

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Astronomers have long supposed that planets can form around brown dwarfs just as they do around ordinary stars. Now they’ve found the first example.

Astrophysical calculations show that any star that is smaller than about 1/10th of the mass of the sun cannot sustain hydrogen fusion reactions at its core. These failed stars never light up. Instead they wander the galaxy as warm, dark balls of hydrogen known as brown dwarfs.

Brown dwarfs probably form through the same process that lead to ordinary stars but merely on a smaller scale. If that’s correct, planets should also form in the protoplanetary disks of gas and dust around brown dwarfs. Indeed, astronomers have seen a number of protoplanetary disks of this type.

Until now, however, they’ve never seen a planet orbiting a brown dwarf. That’s not really surprising.

The standard methods for detecting planets look for the way a star wobbles as a planet orbits or at how its magnitude changes as a planet passes in front. But given that brown dwarfs are dim and difficult to see, these methods have yet to produce fruit.

All that changes today with the announcement by an international team of astronomers that they’ve discovered a planet orbiting a brown dwarf the first time. These guys have made their discovery using an entirely different method of detection called gravitational lensing. This occurs when one body passes in front of another and its gravity focuses light from the more distant object towards Earth. That works regardless of the brightnesses involved.

The brown dwarf in question is almost 6000 light years from Earth in the Fish Hook constellation. Astronomers first noticed an unusual change in its brightness in April 2012. Further investigation showed that this was indeed a lensing event.

These guys conclude that the brown dwarf is being orbited by a planet about twice the mass of Jupiter at a distance of just under one astronomical unit. The brown dwarf itself is about 10 times larger than its companion.

That’s the first time astronomers have found an object orbiting a brown dwarf that can be truly described as a planet. The technical definition of a planet is that it must have formed in the parent object’s protoplanetary disk.

Astronomers have seen other planet-sized objects orbiting brown dwarfs but only at distances of several tens of astronomical units. That’s too far to have been part of the protoplanetary disk. “Thus,…,they are not bona fide planets,” say the team.

So that’s a modest first for this team. It raises the question of what kind of conditions exist on such a planet and, of course, whether these could support life.

This planet almost certainly does not fall into that category but where there is one planet, there are almost certainly others. Astronomers can now have some fun speculating on the Goldilocks zones around brown dwarfs where conditions are just right for life and how to spot the interesting planets inside them.

Ref: arxiv.org/abs/1307.6335 : Microlensing Discovery Of A Tight, Low Mass-Ratio Planetary-Mass Object Around An Old, Field Brown Dwarf

Contact Lens Computer: Like Google Glass, Without Glasses (TechnologyReview.com)

Bottom Line: Soft contact lenses could display information to the wearer and provide continuous medical monitoring.

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WHY IT MATTERS

A computer embedded into a contact lens could make for the ultimate heads-up display.

soft contact lenses on finger
(We’ve made contact: Researchers embedded a light-emitting diode into this contact lens.)

For those who find Google Glass indiscreet, electronic contact lenses that outfit the user’s cornea with a display may one day provide an alternative. Built by researchers at several institutions, including two research arms of Samsung, the lenses use new nanomaterials to solve some of the problems that have made contact-lens displays less than practical.

A group led by Jang-Ung Park, a chemical engineer at the Ulsan National Institute of Science and Technology, mounted a light-emitting diode on an off-the-shelf soft contact lens, using a material the researchers developed: a transparent, highly conductive, and stretchy mix of graphene and silver nanowires. The researchers tested these lenses in rabbits—whose eyes are similar in size to humans’—and found no ill effects after five hours. The animals didn’t rub their eyes or grow bloodshot, and the electronics kept working. This work is described online in the journal Nano Letters.

A handful of companies and researchers have developed electronic contact lenses over the past five years. Sensimed, of Switzerland, makes a lens for 24-hour monitoring of eye pressure in glaucoma patients, and other researchers, including University of Washington professor and Google Glass project founderBabak Parviz, have built contact-lens displays. But these devices have used rigid or nontransparent materials.

Park wants to make contact lenses that have all the functions of a wearable computer but remain transparent and soft. “Our goal is to make a wearable contact-lens display that can do all the things Google Glass can do,” he says. To make it work, they needed a transparent, highly conductive material that was also flexible. The transparent conductor of choice in conventional rigid electronics, indium tin oxide, is brittle, and it must be deposited at high temperatures that would melt a contact lens. Organic conductors, graphene, and nanowires are flexible and transparent, but they’re not conductive enough.

Park, working with Sung-Woo Nam of the University of Illinois at Urbana-Champaign, found that sandwiching silver nanowires between sheets of graphene yielded a composite with much lower electrical resistance than either material alone. The industry standard for a transparent conductor is a resistance of 50 ohms per square or less, says Nam; their material has a resistance of about 33 ohms per square. The material also transmits 94 percent of visible light, and it stretches. The researchers make these conductive sheets by depositing liquid solutions of the nanomaterials on a spinning surface, such as a contact lens, at low temperatures.

Working with researchers at Samsung, they coated a contact lens with the stretchy conductor, then placed a light-emitting diode on it. Although it would be an exaggeration to call this a display, since there is just one pixel, it’s possible this kind of material will be a necessary component in future contact-lens displays, says Herbert De Smet, who works on electronic contact lenses at Ghent University in Belgium but was not involved with the work.

Nam believes medical applications of electronic contact lenses may be even more promising than eyeball-mounted displays. He is currently using the graphene-nanowire conductors to make biosensors that could monitor health conditions by sampling the chemistry of the eye’s tear film. And De Smet’s group is developing lenses that can actively filter light to compensate for vision problems.

Original TechnologyReview.com Article

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