System Bits: Feb. 20

Stretchable, touch-sensitive electronics; unconventional superconductors; new form of light.


An evolution in electronics
Restoring some semblance to those who have lost the sensation of touch has been a driving force behind Stanford University chemical engineer Zhenan Bao’s decades-long quest to create stretchable, electronically-sensitive synthetic materials.

Zhenan Bao, the K.K. Lee professor of chemical engineering and (by courtesy) of materials science and engineering and (by courtesy) of chemistry. She is also faculty fellow of Stanford ChEM-H, a member of the Stanford Bio-X, the Precourt Institute for Energy and the Stanford Neurosciences Institute, and an affiliate of the Stanford Woods Institute for the Environment. She founded and directs the Stanford Wearable Electronics Initiative (eWEAR).

A breakthrough like this could one day serve as skin-like coverings for prosthetics. But in the near term, this same technology could become the foundation for the evolution of new genre of flexible electronics that are in stark contrast with rigid smartphones that many of us carry, gingerly, in our back pockets, the researchers suggested.

Pixelated electronics built with skin-like materials conform to the complex curves of a hand. Source: Stanford University

To this point, Bao and her team have achieved two technical firsts that could bring this 20-year goal to fruition: the creation of a stretchable, polymer circuitry with integrated touch-sensors to detect the delicate footprint of an artificial ladybug. And while this technical achievement is a milestone, the second, and more practical, advance is a method to mass produce this new class of flexible, stretchable electronics – a critical step on the path to commercialization.

“Research into synthetic skin and flexible electronics has come a long way, but until now no one had demonstrated a process to reliably manufacture stretchable circuits,” Bao said.

Her hope is that manufacturers might one day be able to make sheets of polymer-based electronics embedded with a broad variety of sensors, and eventually connect these flexible, multipurpose circuits with a person’s nervous system. This kind of product would be akin to the vastly more complex biochemical sensory network and surface protection “material” that we call human skin, which can not only sense touch, but temperature and other phenomena, as well. But long before artificial skin becomes possible, the processes created by Bao and her team will enable the creation of foldable, stretchable touchscreens, electronic clothing or skin-like patches for medical applications.

Bao said the production process involves several layers of new-age polymers, some that provide the material’s elasticity and others with intricately patterned electronic meshes. Others serve as insulators to isolate the electronically sensitive material. Interestingly, one step in the production process involves the use of an inkjet printer to, in essence, paint on certain layers.

So far, the team has successfully fashioned its material in squares about two inches on a side containing more than 6,000 individual signal-processing devices that act like synthetic nerve endings. All this is encapsulated in a waterproof protective layer. The prototype can be stretched to double its original dimensions – and back again – all the while maintaining its ability to conduct electricity without cracks, delamination or wrinkles. To test durability, the team stretched a sample more than one thousand times without significant damage or loss of sensitivity. The real test came when the researchers adhered their sample to a human hand.

Stanford postdoctoral scholar Jie Xu said it works great, even on irregularly shaped surfaces. Perhaps most promising of all, the fabrication process could become a platform for evaluating other stretchable electronic materials developed by other researchers that could one day begin to replace today’s rigid electronics.

Still, much work lies ahead before these new materials and processes are as ubiquitous and capable as rigid silicon circuitry. First of all, Bao said, she and her team must improve the electronic speed and performance of their prototype, but this is a promising step. “I believe we’re on the verge of a whole new world of electronics.”

Quantum computers of the future
Chalmers University of Technology researchers have discovered that so called Majorana particles could become stable building blocks of a quantum computer given their insensitivity to decoherence even though they only occur under very special circumstances now that they have succeeded in manufacturing a component that is able to host the sought-after particles.

Aluminum plates were attached to the topological insulator using platinum. The picture (scale bar: 200 nm) shows one of the devices used in the experiment. Because of the stress, induced by various cool downs, a clear buckling feature appears in the nanogap of the device. This modification is causing the characteristics of the superconducting pairs of electron to vary in different directions, a signature of unconventional superconductivity.
Source: Chalmers University of Technology

Elsewhere, researchers are struggling to build a quantum computer with one of the great challenges being to overcome the sensitivity of quantum systems to decoherence, collapse of superpositions.

The Chalmers team pointed out that one track within quantum computer research is to make use of what are known as Majorana particles, which are also called Majorana fermions.

Interestingly, Microsoft is also committed to the development of this type of quantum computer, they said.

In highly simplified terms, Majorana fermions can be seen as half electron. In a quantum computer the idea is to encode information in a pair of Majorana fermions which are separated in the material, which should, in principle, make the calculations immune to decoherence.

In solid state materials Majorana fermions only appear to occur in what are known as topological superconductors – a type of superconductor that is so new and special that it is hardly ever found in practice, but the research team at Chalmers has submitted results indicating that they have actually succeeded in manufacturing a topological superconductor using a topological insulator made of bismuth telluride, Be2Te3. Then, a layer of a conventional superconductor on top, in this case aluminum, was placed on top which conducts current entirely without resistance at really low temperatures. The superconducting pair of electrons then leak into the topological insulator which also becomes superconducting.

However, initial measurements indicated they only had standard superconductivity induced in the Bi2Te3 topological insulator but when they cooled the component down again later, to routinely repeat some measurements, the situation suddenly changed – the characteristics of the superconducting pairs of electrons varied in different directions. Repeated cooling cycles gave rise to stresses in the material (see image) , which caused the superconductivity to change its properties.

After an intensive period of analyses the research team was able to establish that they had probably succeeded in creating a topological superconductor.

Enabling quantum computing with photons
Imagine you have two flashlights into a dark room. Shine them so that their light beams cross. Notice anything peculiar? The answer is, probably not because the individual photons that make up light do not interact. Instead, they simply pass each other by. But what if light particles could be made to interact, attracting and repelling each other like atoms in ordinary matter? One intriguing and positively sci-fi possibility: light sabers: beams of light that can pull and push on each other, making for dazzling confrontations. In a more likely scenario, two beams of light could meet and merge into one single, luminous stream.

A team of researchers from MIT, Harvard University, and elsewhere have demonstrated that photons can be made to interact — an accomplishment that could open a path toward using photons in quantum computing, if not in light sabers. 
Source: MIT

While it may seem that such optical behavior would require bending the rules of physics, in fact, scientists at MIT, Harvard University, the University of Maryland, Princeton University, and the University of Chicago have now demonstrated that photons can be made to interact. This accomplishment could actually open a path toward using photons in quantum computing, if not in light sabers.

In new paper, the team, led by Vladan Vuletic, the Lester Wolfe Professor of Physics at MIT, and Professor Mikhail Lukin from Harvard University, reports that it has observed groups of three photons interacting and, in effect, sticking together to form a completely new kind of photonic matter.

The researchers found in controlled experiments that when they shone a very weak laser beam through a dense cloud of ultracold rubidium atoms, rather than exiting the cloud as single, randomly spaced photons, the photons bound together in pairs or triplets, suggesting some kind of interaction — in this case, attraction — taking place among them.

While photons normally have no mass and travel at 300,000 kilometers per second (the speed of light), the team found that the bound photons actually acquired a fraction of an electron’s mass. These newly weighed-down light particles were also relatively sluggish, traveling about 100,000 times slower than normal noninteracting photons.
Vuletic says the results demonstrate that photons can indeed attract, or entangle each other. And, if they can be made to interact in other ways, photons may be harnessed to perform extremely fast, incredibly complex quantum computations.

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