Nanotechnology Used To Find Marjorana Fermion

Researchers at TU Delft’s Kavli Institute and the Foundation for Fundamental Research on Matter (FOM Foundation) have succeeded for the first time in detecting the Majorana particle. In the 1930s, the brilliant Italian physicist Ettore Majorana reasoned from quantum theory the possibility of the existence of a very special particle, a particle that is its own anti-particle: the Majorana fermion. The ‘Majorana’ borders between matter and anti-matter.

The Italian physicist Ettore Majorana was a brilliant theorist who showed great insight into physics at a young age. He discovered a hitherto unknown solution to the equations from which quantum scientists deduce elementary particles: the Majorana fermion. Practically all theoretic particles that are predicted by quantum theory have been found in the last decades, with just a few exceptions, including the enigmatic Majorana particle and the well-known Higgs Boson.

Nanoscientist Leo Kouwenhoven already caused great excitement among scientists in February by presenting the preliminary results at a scientific congress. On 12 April, the scientists published their research in Science.

Majorana fermions are very interesting – not only because their discovery opens up a new and uncharted chapter of fundamental physics, but they may also play a role in cosmology.

A proposed theory assumes that the mysterious dark matter, which forms the greatest part of the universe, is composed of Majorana fermions. Furthermore, scientists view the particles as potential building blocks for a quantum computer. Such a computer would be far more powerful than the best supercomputer, but only functionally exists in theory so far (or until very recently). Contrary to an ‘ordinary’ quantum computer, a quantum computer based on Majorana fermions is exceptionally stable and barely sensitive to external influences.

For the first time, scientists in Leo Kouwenhoven’s research group managed to create a nanoscale electronic device in which a pair of Majorana fermions ‘appear’ at either end of a nanowire. They did this by combining an extremely small nanowire, made by colleagues from Eindhoven University of Technology, with a superconducting material and a strong magnetic field. ‘The measurements of the particle at the ends of the nanowire cannot otherwise be explained than through the presence of a pair of Majorana fermions’, says Leo Kouwenhoven.

It is theoretically possible to detect a Majorana fermion with a particle accelerator such as Large Hadron Collider at CERN. The current Large Hadron Collider appears to be insufficiently sensitive for that purpose but, according to physicists, there is another possibility: Majorana fermions can also appear in properly designed nanostructures.

"What’s magical about quantum mechanics is that a Majorana particle created in this way is similar to the ones that may be observed in a particle accelerator, although that is very difficult to comprehend", explains Kouwenhoven.

"In 2010, two different groups of theorists came up with a solution using nanowires, superconductors and a strong magnetic field. We happened to be very familiar with those ingredients here at TU Delft through earlier research." Microsoft approached Leo Kouwenhoven to help them lead a special FOM programme in search of Majorana fermions, resulting in a successful outcome.

MIT Creates 'Smart Sand' Replicator Concept Microrobotic System

Image Source: M. Scott Brauer

In the future, you may have a big box of sand in which you bury a tiny model of a chair. A few seconds later, you reach into the box and pull out a full-size version, ready to use. The "smart sand" will have assembled itself into a large-scale replica of the model.

That may sound like a scene from a science fiction novel, but it’s the vision animating a research project at the Distributed Robotics Laboratory (DRL) at MIT’s Computer Science and Artificial Intelligence Laboratory. At the IEEE International Conference on Robotics and Automation in May — the world’s premier robotics conference — DRL researchers will present a paper describing algorithms that could enable such “smart sand.” They also describe experiments in which they tested the algorithms on somewhat larger particles — cubes about 10 millimeters to an edge, with rudimentary microprocessors inside and very unusual magnets on four of their sides.


Unlike many other approaches to reconfigurable robots, smart sand uses a subtractive method, akin to stone carving, rather than an additive method, akin to snapping toy blocks together. A heap of smart sand would be analogous to the rough block of stone that a sculptor begins with. The individual grains would pass messages back and forth and selectively attach to each other to form a three-dimensional object; the grains not necessary to build that object would simply fall away. When the object had served its purpose, it would be returned to the heap. Its constituent grains would detach from each other, becoming free to participate in the formation of a new shape.


Technically the, the main software challenge in developing smart sand is that the individual grains would have very few computational resources. “How do you develop efficient algorithms that do not waste any information at the level of communication and at the level of storage?” asks Daniela Rus, a professor of computer science and engineering at MIT and a co-author on the new paper, together with her student Kyle Gilpin. If every grain could simply store a digital map of the object to be assembled, “then I can come up with an algorithm in a very easy way,” Rus says. “But we would like to solve the problem without that requirement, because that requirement is simply unrealistic when you’re talking about modules at this scale.” Furthermore, Rus says, from one run to the next, the grains in the heap will be jumbled together in a completely different way. “We’d like to not have to know ahead of time what our block looks like,” Rus says.

To attach to each other, to communicate and to share power, the cubes use 'electropermanent magnets,' materials whose magnetism can be switched on and off with jolts of electricity.


Conveying shape information to the heap with a simple physical model — such as the tiny chair — helps address both of these problems. To get a sense of how the researchers’ algorithm works, it’s probably easiest to consider the two-dimensional case. Picture each grain of sand as a square in a two-dimensional grid. Now imagine that some of the squares — say, in the shape of a footstool— are missing. That’s where the physical model is embedded.


According to Gilpin-author on the new paper, the grains first pass messages to each other to determine which have missing neighbors. (In the grid model, each square could have eight neighbors.) Grains with missing neighbors are in one of two places: the perimeter of the heap or the perimeter of the embedded shape.


Once the grains surrounding the embedded shape identify themselves, they simply pass messages to other grains a fixed distance away, which in turn identify themselves as defining the perimeter of the duplicate. If the duplicate is supposed to be 10 times the size of the original, each square surrounding the embedded shape will map to 10 squares of the duplicate’s perimeter. Once the perimeter of the duplicate is established, the grains outside it can disconnect from their neighbours.


The same algorithm can be varied to produce multiple, similarly sized copies of a sample shape, or to produce a single, large copy of a large object. “Say the tire rod in your car has sheared,” Gilpin says. “You could duct tape it back together, put it into your system and get a new one.”  The technology might therefore be used in the future as a form of rapid prototyping.


The cubes — or “smart pebbles” — that Gilpin and Rus built to test their algorithm enact the simplified, two-dimensional version of the system. Four faces of each cube are studded with so-called electropermanent magnets, materials that can be magnetized or demagnetized with a single electric pulse. Unlike permanent magnets, they can be turned on and off; unlike electromagnets, they don’t require a constant current to maintain their magnetism. The pebbles use the magnets not only to connect to each other but also to communicate and to share power. Each pebble also has a tiny microprocessor, which can store just 32 kilobytes of program code and has only two kilobytes of working memory.


The pebbles have magnets on only four faces, Gilpin explains, because, with the addition of the microprocessor and circuitry to regulate power, “there just wasn’t room for two more magnets.” But Gilpin and Rus performed computer simulations showing that their algorithm would work with a three-dimensional block of cubes, too, by treating each layer of the block as its own two-dimensional grid. The cubes discarded from the final shape would simply disconnect from the cubes above and below them as well as those next to them.


True smart sand, of course, would require grains much smaller than 10-millimeter cubes. But according to Robert Wood, an associate professor of electrical engineering at Harvard University, that’s not an insurmountable obstacle. “Take the core functionalities of their pebbles,” says Wood, who directs Harvard’s Microrobotics Laboratory. “They have the ability to latch onto their neighbors; they have the ability to talk to their neighbors; they have the ability to do some computation. Those are all things that are certainly feasible to think about doing in smaller packages.”


“It would take quite a lot of engineering to do that, of course,” Wood cautions. “That’s a well-posed but very difficult set of engineering challenges that they could continue to address in the future.”

MIT News




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Nanotechnology Research Aims To Create Artificial Photosynthesis

Image Source: Wang Research Group, UC San Diego Jacobs School of Engineering

Electrical engineers at the University of California, San Diego are building a forest of tiny nanowire trees in order to cleanly capture solar energy without using fossil fuels and harvest it for hydrogen fuel generation. Reporting in the journal Nanoscale, the team said nanowires, which are made from abundant natural materials like silicon and zinc oxide, also offer a cheap way to deliver hydrogen fuel on a mass scale.

“This is a clean way to generate clean fuel,” said Deli Wang, professor in the Department of Electrical and Computer Engineering at the UC San Diego Jacobs School of Engineering.

The trees’ vertical structure and branches are keys to capturing the maximum amount of solar energy, according to Wang. That’s because the vertical structure of trees grabs and adsorbs light while flat surfaces simply reflect it, Wang said, adding that it is also similar to retinal photoreceptor cells in the human eye. In images of Earth from space, light reflects off of flat surfaces such as the ocean or deserts, while forests appear darker.

Wang’s team has mimicked this structure in their “3D branched nanowire array” which uses a process called photoelectrochemical water-splitting to produce hydrogen gas. Water splitting refers to the process of separating water into oxygen and hydrogen in order to extract hydrogen gas to be used as fuel. This process uses clean energy with no green-house gas byproduct. By comparison, the current conventional way of producing hydrogen relies on electricity from fossil fuels

Schematic shows the light trapping effect in nanowire arrays. Photons on are bounced between single nanowires and eventually absorbed by them (R). By harvesting more sun light using the vertical nanotree structure, Wang’s team has developed a way to produce more hydrogen fuel efficiently compared to planar counterparts where they are reflected off the surface (L). Image Credit: Wang Research Group, UC San Diego Jacobs School of Engineering.

“Hydrogen is considered to be clean fuel compared to fossil fuel because there is no carbon emission, but the hydrogen currently used is not generated cleanly,” said Ke Sun, a PhD student in electrical engineering who led the project.

“We are trying to mimic what the plant does to convert sunlight to energy,” said Sun. “We are hoping in the near future our ‘nanotree’ structure can eventually be part of an efficient device that functions like a real tree for photosynthesis."

The team is also studying alternatives to zinc oxide, which absorbs the sun’s ultraviolet light, but has stability issues that affect the lifetime usage of the nanotree structure.

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IBM Scientists Image Charge Distribution in a Single Molecule

Researchers at IBM were able to measure for the first time how charge is distributed within a single molecule.

This achievement promises to enable fundamental scientific insights into single-molecule switching and bond formation between atoms and molecules for future applications such as solar photoconversion, energy storage, or molecular scale computing devices, says IBM.

They directly imaged the charge distribution within a single naphthalocyanine molecule using a special kind of atomic force microscopy called Kelvin probe force microscopy at low temperatures and in ultrahigh vacuum.

“This work demonstrates an important new capability of being able to directly measure how charge arranges itself within an individual molecule”, states Michael Crommie, Professor for Condensed Matter Physics at the University of Berkeley. “Understanding this kind of charge distribution is critical for understanding how molecules work in different environments. I expect this technique to have an especially important future impact on the many areas where physics, chemistry, and biology intersect.”

In fact, the new technique together with STM and AFM provides complementary information about the molecule, showing different properties of interest. This is reminiscent of medical imaging techniques such as X-ray, MRI, or ultrasonography, which yield complementary information about a person’s anatomy and health condition.

“The technique provides another channel of information that will further our understanding of nanoscale physics. It will now be possible to investigate at the single-molecule level how charge is redistributed when individual chemical bonds are formed between atoms and molecules on surfaces. This is essential as we seek to build atomic and molecular scale devices,” explains Fabian Mohn of the Physics of Nanoscale Systems group at IBM Research- Zurich.

The technique could for example be used to study charge separation and charge transport in “charge-transfer complexes,” which consist of two or more molecules and are subject of intense research activity because they hold great promise for applications such as energy storage or photovoltaics.


IBM

X-Ray Lasers Produced at LLNL

Lawrence Livermore Lab (LLNL) researchers and international collaborators have created the shortest, purest X-ray laser pulses ever achieved, realizing a 45-year-old prediction and ultimately opening the door to new medicines, devices and materials.


The researchers aimed radiation from the Linac Coherent Light Source (LCLS), located at the Stanford Linear Accelerator Center (SLAC), at a cell containingneon gas, setting off an avalanche of femtosecond-duration X-ray emissions to create a new “atomic X-ray laser” in the kiloelectronvolt energy regime.


“X-rays give us a penetrating view into the world of atoms and molecules,” said physicist Nina Rohringer, a former LLNL postdoc, now a group leader at Max Planck Society’s Advanced Study Group. She collaborated with researchers from SLAC, LLNL and Colorado State University.


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