Ultra-thin Wires for Quantum Computing


Nano Fiber Wires 74804_relWASHINGTON D.C., June 17, 2014 – Take a fine strand of silica fiber, attach it at each end to a slow-turning motor, gently torture it over an unflickering flame until it just about reaches its melting point and then pull it apart. The middle will thin out like a piece of taffy until it is less than half a micron across — about 200 times thinner than a human hair.

That, according to researchers at the Joint Quantum Institute at the University of Maryland, is how you fabricate ultrahigh transmission optical nanofibers, a potential component for future quantum information devices, which they describe in AIP Publishing’s journal AIP Advances.

Quantum computers promise enormous power, but are notoriously tricky to build. To encode information in qubits, the fundamental units of a quantum computer, the bits must be held in a precarious position called a superposition of states. In this fragile condition the bits exist in all of their possible configurations at the same time, meaning they can perform multiple parallel calculations.

Nano Fiber Wires 74804_rel

This image depicts light propagating through an optical nanofiber during the pulling process with a SEM image of the 536 nanometer diameter waist.

The tendency of qubits to lose their superposition state too quickly, a phenomenon known as decoherence, is a major obstacle to the further development of quantum computers and any device dependent on superpositions. To address this challenge, researchers at the Joint Quantum Institute proposed a hybrid quantum processor that uses trapped atoms as the memory and superconducting qubits as the processor, as atoms demonstrate relatively long superposition survival times and superconducting qubits perform operations quickly.

“The idea is that we can get the best of both worlds,” said Jonathan Hoffman, a graduate student in the Joint Quantum Institute who works in the lab of principal investigators Steven Rolston and Luis Orozco. However, a problem is that superconductors don’t like high optical power or magnetic fields and most atomic traps use both, Hoffman said.

This is where the optical nanofibers come in: The Joint Quantum Institute team realized that nanofibers could create optics-based, low-power atom traps that would “play nice” with superconductors. Because the diameter of the fibers is so minute — 530 nanometers, less than the wavelength of light used to trap atoms — some of the light leaks outside of the fiber as a so-called evanescent wave, which can be used to trap atoms a few hundred nanometers from the fiber surface.

Hoffman and his colleagues have worked on optical nanofiber atom traps for the past few years. Their AIP Advances paper describes a new procedure they developed that maximizes the efficiency of the traps through careful and precise fabrication methods.

The group’s procedure, which yields an improvement of two orders of magnitude less transmission loss than previous work, focuses on intensive preparation and cleaning of the pre-pulling environment the nanofibers are created in.

In the fabrication process, the fiber is brushed through the flame to prevent the formation of air currents, which can cause inconsistencies in diameter to arise, as it is pulled apart and tapered down. The flame source is a mixture of hydrogen and oxygen gas in a precise two-to-one ratio, to ensure that water vapor is the only byproduct. The motors are controlled by an algorithm based on the existing work of a group in Vienna, which calculates the trajectories of the motors to produce a fiber of the desired length and profile.

Previous pulling methods, such as carbon dioxide lasing and chemical etching, were limited by the laser’s insufficient diameter and by a lesser degree of control over tapering length, respectively.

Future work includes interfacing the trapped atoms with the superconducting circuits held at 10 mKelvin in a dilution refrigerator, as well as guiding more complicated optical field patterns through the fiber (higher-order modes) and using these to trap atoms.

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The article, “Ultrahigh transmission optical nanofibers,” is authored by J.E. Hoffman, S. Ravets, J.A. Grover, P. Solano, P.R. Kordell, J.D. Wong-Campos, L.A. Orozco and S.L. Rolston. It will be published in AIP Advances on June 17, 2014 (DOI: . After that date, it may be accessed at: http://scitation.aip.org/content/aip/journal/adva/4/6/10.1063/1.4879799

Quantum Dots Shine Even Brighter


 
QDOT images 3Journal reference: Nature Materials Provided by Massachusetts Institute of Technology. This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.
 
Quantum dots—tiny particles that emit light in a dazzling array of glowing colors—have the potential for many applications, but have faced a series of hurdles to improved performance. But an MIT team says that it has succeeded in overcoming all these obstacles at once, while earlier efforts have only been able to tackle them one or a few at a time.
 
The new quantum dots “combine all these attributes that people think are important, at the same time,” says Moungi Bawendi, the Lester Wolfe Professor of Chemistry.
Credit: OU CHEN

 Quantum dots—in this case, a specific type called colloidal quantum dots—are tiny particles of semiconductor material that are so small that their properties differ from those of the bulk material: They are governed in part by the laws of quantum mechanics that describe how atoms and subatomic particles behave. When illuminated with ultraviolet light, the dots fluoresce brightly in a range of colors, determined by the sizes of the particles.

First discovered in the 1980s, these materials have been the focus of intense research because of their potential to provide significant advantages in a wide variety of optical applications, but their actual usage has been limited by several factors. Now, research published this week in the journal Nature Materials by MIT chemistry postdoc Ou Chen, Moungi Bawendi, the Lester Wolfe Professor of Chemistry, and several others raises the prospect that these limiting factors can all be overcome.

The new process developed by the MIT team produces quantum dots with four important qualities: uniform sizes and shapes; bright emissions, producing close to 100 percent emission efficiency; a very narrow peak of emissions, meaning that the colors emitted by the particles can be precisely controlled; and an elimination of a tendency to blink on and off, which limited the usefulness of earlier quantum-dot applications.

Multicolored biological dyes For example, one potential application of great interest to researchers is as a substitute for conventional fluorescent dyes used in medical tests and research. Quantum dots could have several advantages over dyes—including the ability to label many kinds of cells and tissues in different colors because of their ability to produce such narrow, precise color variations. But the blinking effect has hindered their use: In fast-moving biological processes, you can sometimes lose track of a single molecule when its attached quantum dot blinks off.

 

Previous attempts to address one quantum-dot problem tended to make others worse, Chen says. For example, in order to suppress the blinking effect, particles were made with thick shells, but this eliminated some of the advantages of their small size.

The small size of these new dots is important for potential biological applications, Bawendi explains. “[Our] dots are roughly the size of a protein molecule,” he says. If you want to tag something in a biological system, he says, the tag has got to be small enough so that it doesn’t overwhelm the sample or interfere significantly with its behavior.

Quantum dots are also seen as potentially useful in creating energy-efficient computer and television screens. While such displays have been produced with existing quantum-dot technology, their performance could be enhanced through the use of dots with precisely controlled colors and higher efficiency. Combining the advantages So recent research has focused on “the properties we really need to enhance [dots’] application as light emitters,” Bawendi says—which are the properties that the new results have successfully demonstrated.

The new quantum dots, for the first time, he says, “combine all these attributes that people think are important, at the same time.” The new particles were made with a core of semiconductor material (cadmium selenide) and thin shells of a different semiconductor (cadmium sulfide).

They demonstrated very high emission efficiency (97 percent) as well as small, uniform size and narrow emission peaks. Blinking was strongly suppressed, meaning the dots stay “on” 94 percent of the time. A key factor in getting these particles to achieve all the desired characteristics was growing them in solution slowly, so their properties could be more precisely controlled, Chen explains. “A very important thing is synthesis speed,” he says, “to give enough time to allow every atom to go to the right place.”

The slow growth should make it easy to scale up to large production volumes, he says, because it makes it easier to use large containers without losing control over the ultimate sizes of the particles.

Chen expects that the first useful applications of this technology could begin to appear within two years. Taeghwan Hyeon, director of the Center for Nanoparticle Research at Seoul National University in Korea, who was not involved in this research, says, “It is very impressive, because using a seemingly very simple approach—that is, maintaining a slow growth rate—they were able to precisely control shell thickness, enabling them to synthesize highly uniform and small-sized quantum dots.”

This work, he says, solves one of the “key challenges” in this field, and “could find biomedical imaging applications, and can be also used for solid-state lighting and displays.”

 

Cadmium-Free Quantum Dots for High Luminesence & Effciency for QLED’s


InP-QLED-High-Efficiency( Publication Date (Web): September 24, 2013)

While Cd-based materials are under the risk to be completely banned sooner or later, much attention has been paid in the last few years to the development of non-toxic analogues with similarly good performance.

In case of quantum-dots-based light emitting diods (QLED), the maximal brightness and efficiency of luminescence are the most critical parameters determining whether the new technology can be accepted for mass production. The best results up to now have been achieved with QDs of copper-indium-sulfide (max. brightness 2100 cd/m2) and silicon (efficiency of 1.1%).

Now a new breakthrough in the development of Cd-free QLED was reported by a group of scientists from Seoul National University & KIST in an article published online in ACS-Nano describes novel quantum dots made from cadmium-free lnP/ZnSeS core-shell semiconductor nanoparticles.

The special feature of these QDs is the gradient structure of the shell, where selenium resides mostly close to the core, while sulfide enriches the outer part of the shell. The further fine tuning of the shell thickness and of the assembly of the QLED brought its results. The synthesized QDs had the electroluminescence quantum yield of 3.46% (compared to the previous record of 1.1%) and brightness of 3900 cd/m2 while showing the photoluminescence QY of 70%.

Abstract from ACS Nano: http://pubs.acs.org/doi/abs/10.1021/nn403594j

Highly Efficient Cadmium-Free Quantum Dot Light-Emitting Diodes Enabled by the Direct Formation of Excitons within InP@ZnSeS Quantum Dots

 

nn-2013-03594j_0005

We demonstrate bright, efficient, and environmentally benign InP quantum dot (QD)-based light-emitting diodes (QLEDs) through the direct charge carrier injection into QDs and the efficient radiative exciton recombination within QDs. The direct exciton formation within QDs is facilitated by an adoption of a solution-processed, thin conjugated polyelectrolyte layer, which reduces the electron injection barrier between cathode and QDs via vacuum level shift and promotes the charge carrier balance within QDs. The efficient radiative recombination of these excitons is enabled in structurally engineered InP@ZnSeS heterostructured QDs, in which excitons in the InP domain are effectively passivated by thick ZnSeS composition-gradient shells.

The resulting QLEDs record 3.46% of external quantum efficiency and 3900 cd m–2 of maximum brightness, which represent 10-fold increase in device efficiency and 5-fold increase in brightness compared with previous reports. We believe that such a comprehensive scheme in designing device architecture and the structural formulation of QDs provides a reasonable guideline for practical realization of environmentally benign, high-performance QLEDs in the future.

 

Nanotechnology to Provide Better Solar Cells, Optical Devices


Nano Wires Solar 140411102933While we work for the eventual development of a nanotechnology that transforms human life via atomically precise manufacturing, the partial control of the configuration of atoms in important materials that is afforded by current nanotechnology promises great near-term advantages.

 

A decade ago, Foresight focused on progress in nanotechnology to meet six major challenges faced by humanity. Although we haven’t said as much the past several years about these challenges (except for #3, Improving Health and Longevity), recent progress promises great contributions to the other challenges as well.

Challenge #1, Providing Renewable Clean Energy, appears soon to profit from advances in controlling the atomic configuration of gallium arsenide nanowires. Patrick Cox’s Tech Digest reports on “Building a Better Solar Cell One Atom at a Time“. Citing work by researchers at the Norwegian University of Science and Technology working with IBM engineers to grow gallium arsenide nanowires on graphene, he concludes:

… With a better understanding of how, atom by atom, a panel’s composition could be manipulated to achieve maximum output, solar-panel technology of the future promises to become lighter and more portable, as well as easier to manufacture and maintain. …

A hat tip to ScienceDaily for providing more details by reprinting news published by the Norwegian University of Science and Technology “Better Solar Cells, Better LED Light And Vast Optical Possibilities“:

Changes at the atom level in nanowires offer vast possibilities for improvement of solar cells and LED light. NTNU-researchers have discovered that by tuning a small strain on single nanowires they can become more effective in LEDs and solar cells.

 

NTNU researchers Dheeraj Dasa and Helge Weman have, in cooperation with IBM, discovered that gallium arsenide can be tuned with a small strain to function efficiently as a single light-emitting diode or a photodetector. This is facilitated by the special hexagonal crystal structure, referred to as wurtzite, which the NTNU researchers have succeeded in growing in the MBE lab at NTNU. The results were published in Nature Communications [abstract].

… By altering the crystal structure in a substance, i.e. changing the positions of the atoms, the substance can gain entirely new properties. The NTNU researchers discovered how to alter the crystal structure in nanowires made of gallium arsenide and other semiconductors.

With that, the foundation was laid for more efficient solar cells and LEDs.

“Our discovery was that we could manipulate the structure, atom by atom. We were able to manipulate the atoms and alter the crystal structure during the growth of the nanowires. This opened up for vast new possibilities. We were among the first in the world who were able to create a new gallium arsenide material with a different crystal structure,” says Helge Weman at the Department of Electronics and Telecommunications.

… The next big news came in 2012. At that point, the researchers had managed to make semiconductor nanowires grow on the super-material graphene. Graphene is the thinnest and strongest material ever made. This discovery was described as a revolution in solar cell and LED component development.

… The research group has received a lot of international attention for the graphene method. Helge Weman and his NTNU co-founders Bjørn-Ove Fimland and Dong-Chul Kim have established the company CrayoNano AS, working with a patented invention that grows semiconductor nanowires on graphene. The method is called molecular beam epitaxy (MBE), and the hybrid material has good electric and optical properties.

“We are showing how to use graphene to make much more effective and flexible electronic products, initially solar cells and white light-emitting diodes (LED). The future holds much more advanced applications,” says Weman.

… The last couple of years the research group has, among other things, studied the unique hexagonal crystal structure in the GaAs nanowires.

“In cooperation with IBM, we have now discovered that if we stretch these nanowires, they function quite well as light-emitting diodes. Also, if we press the nanowires, they work quite well as photodetectors. This is facilitated by the hexagonal crystal structure, called wurtzite. It makes it easier for us to change the structure to optimise the optical effect for different applications.

“It also gives us a much better understanding, allowing us to design the nanowires with a built-in compressive stress, for example to make them more effective in a solar cell. This can for instance be used to develop different pressure sensors, or to harvest electric energy when the nanowires are bent,” Weman explains.

Because of this new ability to manipulate the nanowires’ crystal structure, it is possible to create highly effective solar cells that produce a higher electric power. Also, the fact that CrayoNano now can grow nanowires on super-light, strong and flexible graphene, allows production of very flexible and lightweight solar cells.

The CrayoNano group will now also start growing gallium nitride nanowires for use in white light-emitting diodes.

“One of our objectives is to create gallium nitride nanowires in a newly installed MBE machine at NTNU to create light-emitting diodes with better optical properties — and grow them on graphene to make them flexible, lightweight and strong.”

This work illustrates beautifully the practical benefits from increasing ability to control the configuration of atoms in materials. This work uses currently available tools to control the atomic configuration of bulk materials. Atomically precise manufacturing, when it is developed, will allow specifying different atomic configurations to produce, if needed, nanometer scale complexity throughout a microscale or macroscale object to manufacture enormously complex systems of materials, devices, and molecular machines.
—James Lewis, PhD

Smart Lighting Moves Beyond Energy Efficiency


id31611Published: May 28, 2014 Category: Smart Technology

NanoMarkets believes that in the past year or so the smart lighting industry has begun to grow up. It has begun to focus on what the opportunities are for its products rather than simply dwelling on technical issues. Our sense of the market is that in the past, next-generation smart lighting firms have been uncourageous about saying how their systems differ from each other and from the previous generation of lighting management systems. We now appear to have reached a stage in the evolution of the smart lighting business, where firms in this space must think hard about what they really have to offer.

Judging from the fact that quite a lot of firms have quit the smart lighting business in the past few years, some smart lighting firms have spent too much money on engineering and not enough on marketing and business development.  At the very least some smart lighting companies may not have thought through entirely how their products are going to make money in the coming years.

In this respect, commercial and industrial buildings are a better bet than residential buildings when it comes to selling smart lighting, because the benefits of smart lighting can, for the most part, be easily quantified for business users.  This fact of life is reflected in NanoMarkets’ most recent forecasts where we show smart lighting for commercial and industrial buildings as generating $5.1 billion by 2019, but residential smart lighting for the same year with revenues of just $820 million.

It is also apparent that smart lighting firms will now have to work to get their products into profitable channels.  For the giant lighting firms—the GEs and Osrams of this world—this is not an issue.  However, for the many smaller firms in this business what this will mean is slogging away trying to build arrangements with local and regional building product and electrical supply outlets/installers.  This takes time.  Selling smart lighting through major national chains is another option—and to some extent a quick fix—but it is not easy to get one’s products into such retailers and may not be optimal given the retail-orientation of many of these outlets.

Beyond this, NanoMarkets believes that there are some trends that have not been recognized widely yet by the smart lighting community, but which will be important going forward. One of these is the necessity for smart lighting suppliers to push their marketing stories well beyond the energy efficiency meme.  Another is the degree to which there are opportunities for smart lighting in markets other than buildings.

As NanoMarkets noted in its 2013 smart lighting report, firms that fail to find effective ways to differentiate themselves in what is already becoming a crowded smart lighting marketplace, will quickly see their business slip away from them. In our 2012 smart lighting report we specifically noted that many of the smart lighting systems from firms that were purportedly innovative start-ups, actually had a certain sameness to them.  They seemed to be offering features and benefits that just weren’t that special and we questioned whether these would be enough to build a sustainable business for smart lighting firms.

Yet in a recent interview with a smart lighting firm, NanoMarkets was told that it was hard enough to design a smart lighting product for energy efficiency without having to worry about functionality beyond energy efficiency.  However, we think that increasingly such comments are going to seem beside the point.

Beyond Efficiency:  Why Smart Mood Lighting is the Next Big Thing 

Possibly, the necessary market differentiation for smart lighting can be achieved simply by offering higher levels of performance; such as quicker response times for lighting systems.  But it seems to us that more will be needed in the era of the Internet-of-Things (IoT), when customers are going to be looking for more than just an extra percentage point on energy efficiency.

IoT raises the stakes.  As a result, we think that manufacturers of smart lighting will switch to a bigger story; one that encompasses “mood lighting” as well as energy efficiency. For our purposes, mood lighting in this context includes lighting designed to influence, not just immediate mood, but long-term health and work performance.  According to NanoMarkets’ forecasts, smart lighting with mood enhancement capability will generate $2.9 billion by 2019.

It has been well understood since the days of the first incandescent light that changes in light can affect health, mood, and human performance.  However, given the nature of lighting technology, there has until recently been a limited amount that could be done to take advantage of what was known about light and human behavior.  With the new solid-state lighting systems—those based on LEDs—a lot more can be done. These systems intrinsically allow for more control, partly precisely because they are based on chips not tubes and bulbs.

As NanoMarkets sees things, there is enough potential in the smart mood lighting concept to allow for substantial differentiation in smart lighting products and systems for most of the eight-year period that is covered in this report.  And when the mood lighting idea begins to run out of steam, smart lighting can tap into smart lighting based visible light communications (VLC).  However, we also expect that smart mood lighting will increasingly be challenged by professional medical opinion which is already saying that the health benefits of lighting are not all that they are cracked up to be.

Thinking Outside of the Building

The other profitable new direction that NanoMarkets sees for smart lighting is in markets outside of traditional building usages.  Non-building sectors in which smart lighting could be deployed include transportation, street lighting and other outdoor lighting. Together, we see these applications for smart lighting as accounting for $4.6 billion in revenues; that is 42 percent of all smart lighting revenues.  These applications will account for just 12 percent of smart lighting in 2014.

What is creating this opportunity for smart lighting outside of buildings is the same factor that is creating opportunities for lighting applications inside buildings; the growing role of LEDs.  LEDs are a key enabler for smart lighting systems because they are chips and therefore inherently more controllable than the types of lighting that went before it.  So with LEDs, smart lighting systems are more of an obvious play than they were with earlier generations of lighting.

Automotive:  NanoMarkets believes that by 2015 we are going to see significant revenues generated by smart lighting systems in the automotive sector.  This may not be all that obvious though, because the impetus for smart lighting in cars and trucks is coming not from the smart lighting community itself, but rather from the automobile firms and it is not always tagged as being “smart” lighting, although this is exactly what it is.  Among the firms that have indicated publicly that they are involved with developing smart lighting are Audi, BMW, Opal and Mercedes-Benz.  (All German car firms, by the way, and more or less the same group that are working with smart windows in their cars.)

One aspect of smart lighting in the automotive segment that interests us especially is that it is another example of smart lighting moving beyond energy efficiency.  Thus, Audi’s Matrix LED headlamps are said to provide more precise lighting for the driver and less blinding light that dazzles drivers in oncoming cars. BMW is working on “laser headlamps” that offer white lighting that can be intelligently modulated.

The general objective of these developments seems to be to provide improved control of the outside lighting on cars for greater safety.  But as NanoMarkets sees things, “smarts” could also be deployed inside a vehicle. Smart mood lighting seems to be especially appropriate in this context; to provide passengers and drivers with greater comfort. This makes sense in cars and internal lighting has also been a specific focus of Boeing and (presumably) other firms that make airliners.

One ongoing advantage to the transportation sector from the perspective of the lighting industry is that once a particular smart lighting product is designed into a popular vehicle, this can guarantee that tens of thousands of lights will be sold.  The flip side of this is that design-in times (i.e., lead times) can be very long.  In the auto industry three years is typical.  In aerospace, it can be seven years.

Street lighting and other outdoor lighting:  Outdoor lighting is in just as much need of energy efficiency as in-building lights; arguably more.  Therefore, we see emerging a significant market for smart outdoor lighting, which can potentially be quite elaborate.  A recent project at the University of California illustrates this well. The University has built a $1-million network of outdoor smart lighting that “talk to each other and adapt to their environment.” According to press reports, the new outdoor lights promise to save the university $100,000 on electricity and make it a safer place after dark.

This University of California smart lighting system can be scheduled and adjusted for increased or decreased levels of activity, such as during sporting events, or to guide pedestrians along preferred routes. The system senses occupants, whether on foot, bicycle or automobile, predicts their direction of travel, and lights the path ahead. The smart network also senses when areas are vacant, then dims lights enough to save energy and reduce light pollution, without compromising safety.

Street lighting is also gradually using more LEDs and consequently is a likely target for smart lighting in the future.  Large individual orders are possible as they are in the transportation sector—street light installations can involve thousands of lights.  But lead times can be a lot more attractive for novel lighting designs than in the transportation sector.  However, smart lighting faces a serious challenge in the street lighting sector—the problem of glare.  The HID lighting that is currently used in street lighting is good on glare, but not easy to make smart.

The converse is apparently true for LED lighting and NanoMarkets believes that this fact may again drive smartness for lighting away from being a pure energy efficiency play. Although we are not entirely clear how this can be done, some form of intelligence might be used to reduce glare.  Meanwhile, we note that Philips is teaming up with Ericsson on a connected street lighting project. It combines LED lighting from Philips with Ericsson’s telecommunications equipment and uses VLC to make street lights into hot spots for mobile devices.

Yet again, this indicates just how far smart lighting can potentially reach beyond the energy efficient lighting label.

– See more at: http://nanomarkets.net/articles/article/smart-lighting-moves-beyond-energy-efficiency#sthash.mVXDGcBv.dpuf