Posted: May 11, 2016

Scientists take a major leap toward a ‘perfect’ quantum metamaterial (Nanowerk News) Scientists have devised a way to build a “quantum metamaterial”—an engineered material with exotic properties not found in nature—using ultracold atoms trapped in an artificial crystal composed of light. The theoretical work represents a step toward manipulating atoms to transmit information, perform complex simulations or function as powerful sensors.

The research team, led by scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley, proposes the use of an accordion-like atomic framework, or “lattice” structure, made with laser light to trap atoms in regularly spaced nanoscale pockets. Such a light-based structure, which has patterned features that in some ways resemble those of a crystal, is essentially a “perfect” structure—free of the typical defects found in natural materials.

Researchers believe they can pinpoint the placement of a so-called “probe” atom in this crystal of light, and actively tune its behavior with another type of laser light (near-infrared light) to make the atom cough up some of its energy on demand in the form of a particle of light, or photon.

This photon, in turn, can be absorbed by another probe atom (in the same or different lattice site) in a simple form of information exchange—like spoken words traveling between two string-connected tin cans.

The wavelike pattern at the top shows the accordion-like structure of a proposed quantum material—an artificial crystal made of light—that can trap atoms in regularly spaced nanoscale pockets. These pockets can be made to hold a large collection of ultracold “host” atoms (green), slowed to a standstill by laser light, and individually planted “probe” atoms (red) that can be made to transmit quantum information in the form of a photon (particle of light). The lower panel shows how the artificial crystal can be reconfigured with light from an open (hyperbolic) geometry to a closed (elliptical) geometry, which greatly affects the speed at which the probe atom can release a photon.

“Our proposal is very significant,” said Xiang Zhang, director of Berkeley Lab’s Materials Sciences Division who led the related research paper, published in April in Physical Review Letters („Coherence-Driven Topological Transition in Quantum Metamaterials”). “We know that the enhancement and ultrafast control of single-photon emission lies at the heart of quantum technologies, in particular quantum information processing, and this is exactly what we have achieved here. Previous proposals can do one or the other but not both simultaneously.”

Zhang is also a professor at UC Berkeley, director of the National Science Foundation’s Center for Scalable and Integrated Nanomanufacturing and a member of the Kavli Energy NanoScience Institute at Berkeley Lab and UC Berkeley.

Pankaj K. Jha, a UC Berkeley postdoctoral researcher who is the lead author of the paper and works in Zhang’s group, said, “Now we have control over the speed of the release of a photon, so we can optically process information much faster, and efficiently transfer it from one point to another.” Other scientists who contributed to this work include Michael Mrejen, Jeongmin Kim, Chihhui Wu, Yuan Wang and Yuri V. Rostovtsev.

This ability to release a photon at fast rates, and to transmit it with low losses from one atom to another, is a vital step in processing information for quantum computation, which could use an array of these controlled photon releases to carry out complex calculations far more rapidly than is possible in modern computers.

A quantum computer, which the tech industry and scientific community are hotly pursuing because of its potential to perform more complex calculations than are possible using modern supercomputers, could tap into the bizarre quantum realm in which ordinary physics rules don’t apply.

While today’s computers can store information as binary bits—either ones or zeroes—a quantum compter would use “qubits” in which an individual bit of information can simultaneously exist in multiple states. These qubits could take the form of atoms, photons, electrons, or even as an individual fundamental property of a particle, and would exponentially increase the number of calculations a computer could perform in an instant.

The non-uniform distribution of the ultracold atoms in the artificial crystal is a key to this latest study, said Jha. “It makes the crucial difference for creating a ‘perfectly’ lossless and reconfigurable quantum metamaterial,” he said, allowing the optical structure of the artificial crystal to be reconfigured from an open geometry (hyperbolic-shaped) to a closed one (elliptical) at the same frequency and with ultrafast timing. This controllable shape-change dramatically changes the speed at which a probe atom in the artificial crystal releases a photon.

The latest proposal suggests that it is possible to speed up the rate at which a probe atom can emit a photon from nanoseconds, or billionths of a second, to picoseconds, or trillionths of a second. Also, this process is importantly considered „lossless,” meaning the photons would not lose any of their energy to their surrounding structure as they likely would in a traditional material. This overcomes one hurdle toward quantum computing and information processing.

Atoms planted in the artificial crystal could also possibly be induced to hop from one place to another. In this case, the atoms could themselves serve as the information carriers in a quantum computer or be arranged as quantum sensors, Jha said.

Jha noted that this latest study marries metamaterials research with the science of “cold atoms,” which are atoms that have been slowed and even brought to a standstill using laser light, which in the process chills them to supercool temperatures. He said, “This integration has solved some of the outstanding challenges for metamaterial platforms and outperforms other designs in several key aspects crucial for quantum technologies.”

The researchers found that rubidium atoms are ideally suited for this study, however barium, calcium and cesium atoms can also be trapped or planted in the artificial crystal, as they exhibit similar energy levels. While the artificial crystal used in the study is described as one-dimensional, Jha said the same approach could be easily extended to create 2-D and 3-D quantum metamaterial crystal structures out of light.

To realize the proposed metamaterial in an actual experiment, Zhang and Jha said the research team would need to trap several atoms per lattice site in the artificial crystal, and to hold those atoms in the lattice even when they are excited to higher energy states.

Zhang said, “Berkeley Lab has been a leader in groundbreaking research in metamaterials, and this work could open new realms of opportunities for quantum light-matter interactions, with enticing applications in quantum information science.”

Jha added, “We believe that the combination of these two contemporary realms of science will help to address key challenges in both fields and open an entirely new research direction at the interface of quantum photonics and artificial materials.”

Read more: Scientists take a major leap toward a ‘perfect’ quantum metamaterial

Posted: May 11, 2016

New research shows how silver could be the key to gold-standard flexible gadgets (Nanowerk News) Research published in the journals Materials Today Communications and Scientific Reports („Predicting the optoelectronic properties of nanowire films based on control of length polydispersity”) has described how silver nanowires are proving to be the ideal material for flexible, touch-screen technologies while also exploring how the material can be manipulated to tune its performance for other applications. Currently, touch screen devices mainly rely on electrodes made from indium tin oxide (ITO), a material that is expensive to source, expensive to process and very brittle.

Silver nanowires are an ideal material for current and future flexible touch-screen technologies.

A team from the University of Surrey, led by Professor Alan Dalton and in collaboration with M-SOLV Ltd, a touch-sensor manufacturer based in Oxford, looked to alternative materials to overcome the challenges of ITO, which is suffering from supply uncertainty. Alternative materials investigated as ITO replacements have included graphene, carbon nanotubes and random metal nanowire films. This study showed how silver nanowire films have emerged as the strongest competitor, due to transmittances and conductivities which can match and readily exceed those of ITO. This is a material that consists of wires which are over a thousand times thinner than a human hair, that form an interconnected conductive network.

Showcasing a new process

Matthew Large, the first author on the research published in Scientific Reports described the importance of these latest results. “Our research hasn’t just identified silver nanowires as a viable replacement touchscreen material, but has gone one step further in showing how a process called ‘ultrasonication’ can allow us to tailor performance capabilities. By applying high frequency sound energy to the material we can manipulate how long the nanosized ‘rods’ of silver are. This allows us to tune how transparent or how conductive our films are, which is vital for optimising these materials for future technologies like flexible solar cells and roll-able electronic displays.”

In a paper published last month in Materials Today Communications, the same team, showed how silver nanowires can be processed using the same laser ablation technique commonly used to manufacture ITO devices. Using this technique, the team produced a fully operating five inch multi-touch sensor, identical to those typically used in smartphone technology. They found it performed comparably to one based on ITO but used significantly less energy to produce.

“Not only does this flexible material perform very well, we have shown that it is a viable alternative to ITO in practical devices,” concluded Professor Dalton. “The fact we are able to produce devices using similar methods as currently in use, but in a less energy-intensive way is an exciting step towards flexible gadgets that do not just open the door for new applications, but do so in a much greener way.”

An easy to deploy alternative

Maria Cann, a technologist from M-SOLV and first author on the Materials Today Communications paper added ““We are seeing a lot of interest from our customers in silver nanowire films as an ITO replacement in devices. This work is a really important step in establishing exactly which sensor designs can make good nanowire products. The fact that the nanowire films are processed by the same laser techniques as ITO makes the transition from ITO to nanowires really straightforward. It won’t be long before we are all using nanowires in our electronic devices.”

The team, now based at the University of Sussex is now looking to develop the scalability of the process to make it more industrially viable. One limiting factor is the current cost of silver nanowires.

Read more: New research shows how silver could be the key to gold-standard flexible gadgets

Posted: Mar 11, 2016

New fuel cell design powered by graphene-wrapped nanocrystals

(Nanowerk News) Hydrogen is the lightest and most plentiful element on Earth and in our universe. So it shouldn’t be a big surprise that scientists are pursuing hydrogen as a clean, carbon-free, virtually limitless energy source for cars and for a range of other uses, from portable generators to telecommunications towers–with water as the only byproduct of combustion.While there remain scientific challenges to making hydrogen-based energy sources more competitive with current automotive propulsion systems and other energy technologies, researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a new materials recipe for a battery-like hydrogen fuel cell–which surrounds hydrogen-absorbing magnesium nanocrystals with atomically thin graphene sheets–to push its performance forward in key areas.The graphene shields the nanocrystals from oxygen and moisture and contaminants, while tiny, natural holes allow the smaller hydrogen molecules to pass through. This filtering process overcomes common problems degrading the performance of metal hydrides for hydrogen storage.Thin sheets of graphene oxide (red sheets) have natural, atomic-scale defects that allow hydrogen gas molecules to pass through while blocking larger molecules such as oxygen (O2) and water (H2O). Berkeley Lab researchers encapsulated nanoscale magnesium crystals (yellow) with graphene oxide sheets to produce a new formula for metal hydride fuel cells. (Image: Jeong Yun Kim)These graphene-encapsulated magnesium crystals act as „sponges” for hydrogen, offering a very compact and safe way to take in and store hydrogen. The nanocrystals also permit faster fueling, and reduce the overall „tank” size.”Among metal hydride-based materials for hydrogen storage for fuel-cell vehicle applications, our materials have good performance in terms of capacity, reversibility, kinetics and stability,” said Eun Seon Cho, a postdoctoral researcher at Berkeley Lab and lead author of a study related to the new fuel cell formula, published recently in Nature Communications („Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage”).In a hydrogen fuel cell-powered vehicle using these materials, known as a „metal hydride” (hydrogen bound with a metal) fuel cell, hydrogen gas pumped into a vehicle would be chemically absorbed by the magnesium nanocrystaline powder and rendered safe at low pressures.Jeff Urban, a Berkeley Lab staff scientist and co-author, said, „This work suggests the possibility of practical hydrogen storage and use in the future. I believe that these materials represent a generally applicable approach to stabilizing reactive materials while still harnessing their unique activity–concepts that could have wide-ranging applications for batteries, catalysis, and energetic materials.”The research, conducted at Berkeley Lab’s Molecular Foundry and Advanced Light Source, is part of a National Lab Consortium, dubbed HyMARC (Hydrogen Materials–Advanced Research Consortium) that seeks safer and more cost-effective hydrogen storage, and Urban is Berkeley Lab’s lead scientist for that effort.The U.S. market share for all electric-drive vehicles in 2015, including full-electric, hybrids and plug-in hybrid vehicles, was 2.87 percent, which amounts to about 500,000 electric-drive vehicles out of total vehicle sales of about 17.4 million, according to statistics reported by the Electric Drive Transportation Association, a trade association promoting electric-drive vehicles.Hydrogen-fuel-cell vehicles haven’t yet made major in-roads in vehicle sales, though several major auto manufacturers including Toyota, Honda, and General Motors, have invested in developing hydrogen fuel-cell vehicles. Indeed, Toyota released a small-production model called the Mirai, which uses compressed-hydrogen tanks, last year in the U.S.A potential advantage for hydrogen-fuel-cell vehicles, in addition to their reduced environmental impact over standard-fuel vehicles, is the high specific energy of hydrogen, which means that hydrogen fuel cells can potentially take up less weight than other battery systems and fuel sources while yielding more electrical energy.A measure of the energy storage capacity per weight of hydrogen fuel cells, known as the „gravimetric energy density,” is roughly three times that of gasoline. Urban noted that this important property, if effectively used, could extend the total vehicle range of hydrogen-based transportation, and extend the time between refueling for many other applications, too.More R&D is needed to realize higher-capacity hydrogen storage for long-range vehicle applications that exceed the performance of existing electric-vehicle batteries, Cho said, and other applications may be better suited for hydrogen fuel cells in the short term, such as stationary power sources, forklifts and airport vehicles, portable power sources like laptop battery chargers, portable lighting, water and sewage pumps and emergency services equipment.Cho said that a roadblock to metal hydride storage has been a relatively slow rate in taking in (absorption) and giving out (desorption) hydrogen during the cycling of the units. In fuel cells, separate chemical reactions involving hydrogen and oxygen produce a flow of electrons that are channeled as electric current, creating water as a byproduct.The tiny size of the graphene-encapsulated nanocrystals created at Berkeley Lab, which measure only about 3-4 nanometers, or billionths of a meter across, is a key in the new fuel cell materials’ fast capture and release of hydrogen, Cho said, as they have more surface area available for reactions than the same material would at larger sizes.Another key is protecting the magnesium from exposure to air, which would render it unusable for the fuel cell, she added.Working at The Molecular Foundry, researchers found a simple, scalable and cost-effective „one pan” technique to mix up the graphene sheets and magnesium oxide nanocrystals in the same batch. They later studied the coated nanocrystals’ structure using X-rays at Berkeley Lab’s Advanced Light Source. The X-ray studies showed how hydrogen gas pumped into the fuel cell mixture reacted with the magnesium nanocrystals to form a more stable molecule called magnesium hydride while locking out oxygen from reaching the magnesium.”It is stable in air, which is important,” Cho said.Next steps in the research will focus on using different types of catalysts–which can improve the speed and efficiency of chemical reactions–to further improve the fuel cell’s conversion of electrical current, and in studying whether different types of material can also improve the fuel cell’s overall capacity, Cho said.
Source: Lawrence Berkeley National Laboratory
Read more: New fuel cell design powered by graphene-wrapped nanocrystals

Posted: May 09, 2016

Novel functionalized nanomaterials for carbon dioxide capture (Nanowerk News) Climate change due to excessive CO2 levels is one of the most serious problems mankind has ever faced. This has resulted in abrupt weather patterns such as flood and drought, which are extremely disruptive and detrimental to life, as we have been witnessing in India in recent years. Mitigating rising CO2 levels is of prime importance. In a new development, scientists at the Tata Institute of Fundamental Research, Mumbai, have developed a novel design of CO2 sorbents that show superior CO2 capture capacity and stability over conventional materials.

The immobilization of functional amines on a porous solid support can result in stable and efficient CO2 sorbent materials compared to similar liquid sorbents. A critical disadvantage however, is a drastic decrease in the textural properties of these supports (i.e., their surface area and pore volume), leading to a decrease in the CO2 capture capability.

To overcome this challenge, scientists at TIFR Mumbai, have designed novel functionalised nanomaterials that allows higher amine loading with a minimal decrease in surface area.

2 Capture” border=”0″ align=”middle”>

Novel functionalized nanomaterials for CO2 capture. (© RSC)

„Our fibrous nanosilica (KCC-1) should be a good candidate for use as a support to design efficient CO2 sorbents that would allow better capture capacity, kinetics and recylability”, says Dr Vivek Polshettiwar, the lead scientist of this study. A unique feature of KCC-1 is its high surface area, which originates from its fibrous morphology and not from its mesoporous channels (unlike in other well studied materials like SBA-15 or MCM-41).

This study, published recently in the Journal of Materials Chemistry A („Design of CO2 sorbents using functionalized fibrous nanosilica (KCC-1): insights into the effect of the silica morphology (KCC-1 vs. MCM-41)”), demonstrates the usefulness of the fibrous morphology of KCC-1 compared to conventional ordered mesoporous silica. This work is in continuation of the teams efforts to develop sustainable catalysts and sorbents.

The KCC-1-based sorbents showed several advantages over conventional silica-based sorbents, including i) high amine loading, ii) minimum reduction in surface area after functionalization and iii) more accessibility of the amine sites to enhance CO2 capture efficiency (i.e., capture capacity, kinetics and recyclability), due to the fibrous structure and high accessible surface area of KCC-1.

The demand for such efficient sorbents is on the rise since CO2 capture is one of the best solutions to mitigate the rising levels of CO2. Solid sorbents exhibit better efficiency with greater potential to overcome the shortcomings of liquid sorbents.

The use of mesoporous silica materials functionalized with various amino groups is well reported. Although materials like SBA-15 and MCM-41, for example, have attracted significant attention because their large pore sizes can accommodate a variety of amine molecules and the high surface area allows for a higher loading of these functional molecules, they suffer from the disadvantages of a decrease in textural properties, thus making KCC-1 a suitable candidate for more efficient CO2 capture.

Read more: Novel functionalized nanomaterials for carbon dioxide capture

Posted: Apr 05, 2016

Changing the color of single photons in a diamond quantum memory (Nanowerk News) Researchers from the Institute for Quantum Computing at the University of Waterloo and the National Research Council of Canada (NRC) have, for the first time, converted the colour and bandwidth of ultrafast single photons using a room-temperature quantum memory in diamond.

Shifting the colour of a photon, or changing its frequency, is necessary to optimally link components in a quantum network. For example, in optical quantum communication, the best transmission through an optical fibre is near infrared, but many of the sensors that measure them work much better for visible light, which is a higher frequency. Being able to shift the colour of the photon between the fibre and the sensor enables higher performance operation, including bigger data rates.

This is an artist’s impression of quantum frequency conversion in a diamond quantum memory. Researchers from the Institute for Quantum Computing at the University of Waterloo and the National Research Council of Canada (NRC) have, for the first time, converted the colour and bandwidth of ultrafast single photons using a room-temperature quantum memory in diamond. (Image: Dr. Khabat Heshami, National Research Council Canada)

The research, published in Nature Communications („Frequency and bandwidth conversion of single photons in a room-temperature diamond quantum memory”), demonstrated small frequency shifts that are useful for a communication protocol known as wavelength division multiplexing. This is used today when a sender needs to transmit large amounts of information through a transmission so the signal is broken into smaller packets of slightly different frequencies and sent through together. The information is then organized at the other end based on those frequencies.

In the experiments conducted at NRC, the researchers demonstrated the conversion of both the frequency and bandwidth of single photons using a room-temperature diamond quantum memory.

„Originally there was this thought that you just stop the photon, store it for a little while and get it back out. The fact that we can manipulate it at the same time is exciting,” said Kent Fisher a PhD student at the Institute for Quantum Computing and with the Department of Physics and Astronomy at Waterloo. „These findings could open the door for other uses of quantum memory as well.”

The diamond quantum memory works by converting the photon into a particular vibration of the carbon atoms in the diamond, called a phonon. This conversion works for many different colours of light allowing for the manipulation of a broad spectrum of light. The energy structure of diamond allows for this to occur at room temperature with very low noise. Researchers used strong laser pulses to store and retrieve the photon. By controlling the colours of these laser pulses, researchers controlled the colour of the retrieved photon.

„The fragility of quantum systems means that you are always working against the clock,” remarked Duncan England, researcher at NRC. „The interesting step that we’ve shown here is that by using extremely short pulses of light, we are able to beat the clock and maintain quantum performance.”

The integrated platform for photon storage and spectral conversion could be used for frequency multiplexing in quantum communication, as well as build up a very large entangled state – something called a cluster state. Researchers are interested in exploiting cluster states as the resource for quantum computing driven entirely by measurements.

„Canada is a power-house in quantum research and technology. This work is another example of what partners across the country can achieve when leveraging their joint expertise to build next-generation technologies,” noted Ben Sussman, program leader for NRC’s Quantum Photonics program.

Source: University of Waterloo

Read more: Changing the color of single photons in a diamond quantum memory