MIT engineers develop “blackest black” material to date

Posted on September 14, 2019 by plug_the_plugger

MIT engineers report today that they have cooked up a material that is 10 times blacker than anything that has previously been reported. The material is made from vertically aligned carbon nanotubes, or CNTs — microscopic filaments of carbon, like a fuzzy forest of tiny trees, that the team grew on a surface of chlorine-etched aluminum foil. The foil captures at least 99.995 percent* of any incoming light, making it the blackest material on record. (from news.mit.edu)

The researchers have published their findings today in the journal ACS-Applied Materials and Interfaces. They are also showcasing the cloak-like material as part of a new exhibit today at the New York Stock Exchange, titled “The Redemption of Vanity.”

The artwork, a collaboration between Brian Wardle, professor of aeronautics and astronautics at MIT, and his group, and MIT Center for Art, Science, and Technology artist-in-residence Diemut Strebe, features a 16.78-carat natural yellow diamond from LJ West Diamonds, estimated to be worth $2 million, which the team coated with the new, ultrablack CNT material. The effect is arresting: The gem, normally brilliantly faceted, appears as a flat, black void.

Wardle says the CNT material, aside from making an artistic statement, may also be of practical use, for instance in optical blinders that reduce unwanted glare, to help space telescopes spot orbiting exoplanets.

“There are optical and space science applications for very black materials, and of course, artists have been interested in black, going back well before the Renaissance,” Wardle says. “Our material is 10 times blacker than anything that’s ever been reported, but I think the blackest black is a constantly moving target. Someone will find a blacker material, and eventually we’ll understand all the underlying mechanisms, and will be able to properly engineer the ultimate black.”

Wardle’s co-author on the paper is former MIT postdoc Kehang Cui, now a professor at Shanghai Jiao Tong University.

Into the void

Wardle and Cui didn’t intend to engineer an ultrablack material. Instead, they were experimenting with ways to grow carbon nanotubes on electrically conducting materials such as aluminum, to boost their electrical and thermal properties.

But in attempting to grow CNTs on aluminum, Cui ran up against a barrier, literally: an ever-present layer of oxide that coats aluminum when it is exposed to air. This oxide layer acts as an insulator, blocking rather than conducting electricity and heat. As he cast about for ways to remove aluminum’s oxide layer, Cui found a solution in salt, or sodium chloride.

At the time, Wardle’s group was using salt and other pantry products, such as baking soda and detergent, to grow carbon nanotubes. In their tests with salt, Cui noticed that chloride ions were eating away at aluminum’s surface and dissolving its oxide layer.

“This etching process is common for many metals,” Cui says. “For instance, ships suffer from corrosion of chlorine-based ocean water. Now we’re using this process to our advantage.”

Cui found that if he soaked aluminum foil in saltwater, he could remove the oxide layer. He then transferred the foil to an oxygen-free environment to prevent reoxidation, and finally, placed the etched aluminum in an oven, where the group carried out techniques to grow carbon nanotubes via a process called chemical vapor deposition.

By removing the oxide layer, the researchers were able to grow carbon nanotubes on aluminum, at much lower temperatures than they otherwise would, by about 100 degrees Celsius. They also saw that the combination of CNTs on aluminum significantly enhanced the material’s thermal and electrical properties — a finding that they expected.

What surprised them was the material’s color.

“I remember noticing how black it was before growing carbon nanotubes on it, and then after growth, it looked even darker,” Cui recalls. “So I thought I should measure the optical reflectance of the sample.

“Our group does not usually focus on optical properties of materials, but this work was going on at the same time as our art-science collaborations with Diemut, so art influenced science in this case,” says Wardle.

Wardle and Cui, who have applied for a patent on the technology, are making the new CNT process freely available to any artist to use for a noncommercial art project.

“Built to take abuse”

Cui measured the amount of light reflected by the material, not just from directly overhead, but also from every other possible angle. The results showed that the material absorbed at least 99.995 percent of incoming light, from every angle. In other words, it reflected 10 times less light than all other superblack materials, including Vantablack. If the material contained bumps or ridges, or features of any kind, no matter what angle it was viewed from, these features would be invisible, obscured in a void of black.

The researchers aren’t entirely sure of the mechanism contributing to the material’s opacity, but they suspect that it may have something to do with the combination of etched aluminum, which is somewhat blackened, with the carbon nanotubes. Scientists believe that forests of carbon nanotubes can trap and convert most incoming light to heat, reflecting very little of it back out as light, thereby giving CNTs a particularly black shade.

“CNT forests of different varieties are known to be extremely black, but there is a lack of mechanistic understanding as to why this material is the blackest. That needs further study,” Wardle says.

The material is already gaining interest in the aerospace community. Astrophysicist and Nobel laureate John Mather, who was not involved in the research, is exploring the possibility of using Wardle’s material as the basis for a star shade — a massive black shade that would shield a space telescope from stray light.

“Optical instruments like cameras and telescopes have to get rid of unwanted glare, so you can see what you want to see,” Mather says. “Would you like to see an Earth orbiting another star? We need something very black. … And this black has to be tough to withstand a rocket launch. Old versions were fragile forests of fur, but these are more like pot scrubbers — built to take abuse.”

*An earlier version of this story stated that the new material captures more than 99.96 percent of incoming light. That number has been updated to be more precise; the material absorbs at least 99.995 of incoming light.

Kofi Annan

Posted on August 18, 2018 by plug_the_plugger

Kofi Atta Annan
8 April 1938 – 18 August 2018
was a Ghanaian diplomat who served as the seventh secretary-general of the United Nations from 1997 to 2006. Annan and the UN were the co-recipients of the 2001 Nobel Peace Prize. He was the founder and chairman of the Kofi Annan Foundation, as well as chairman of The Elders, an international organisation founded by Nelson Mandela.

CMU Artificial Intelligence Is Tough Poker Player. Libratus builds substantial lead in Brains vs. AI competition

Posted on January 4, 2018 by plug_the_plugger

As the “Brains Vs. Artificial Intelligence: Upping the Ante” poker competition nears its halfway point, Carnegie Mellon University’s AI program, called Libratus, is opening a lead over its human opponents — four of the world’s best professional poker players. Libratus had amassed a lead of $459,154 in chips in the 49,240 hands played by the end of Day Nine. (from cmu.edu)

One of the pros, Jimmy Chou, said he and his colleagues initially underestimated Libratus, but have come to regard it as one tough player. “The bot gets better and better every day,” Chou said. “It’s like a tougher version of us.”

Brains Vs. AI, which began Jan. 11 2017 at Rivers Casino in Pittsburgh, pits Chou and three other leading players — Dong Kim, Jason Les and Daniel McAulay — against Libratus in a 20-day contest in which they will play 120,000 hands of Heads-Up, No-Limit Texas Hold’em poker. All four pros specialize in this two-player, unlimited bid form of Texas Hold’em and are considered among the world’s top players of the game.

While the pros are fighting for humanity’s pride — and shares of a $200,000 prize purse — Carnegie Mellon researchers are hoping their computer program will establish a new benchmark for artificial intelligence by besting some of the world’s most talented players.

Libratus was developed by Tuomas Sandholm, professor of computer science, and his Ph.D. student, Noam Brown. Libratus is being used in this contest to play poker, an imperfect information game that requires the AI to bluff and correctly interpret misleading information to win. Ultimately programs like Libratus also could be used to negotiate business deals, set military strategy or plan a course of medical treatment — all cases that involve complicated decisions based on imperfect information.

In the first Brains Vs. AI contest in 2015, four leading pros amassed more chips than the AI, called Claudico. But Sandholm said he’s feeling good about Libratus’ chances as the competition proceeds. “The algorithms are performing great. They’re better at solving strategy ahead of time, better at driving strategy during play and better at improving strategy on the fly,” Sandholm said.

Chou said he and the other pros have shared notes and tips each day, looking for weaknesses they can each exploit.

“The first couple of days, we had high hopes,” Chou said. “But every time we find a weakness, it learns from us and the weakness disappears the next day.”

The change from day to day is not unexpected, Sandholm said. Each night after poker play ends, the Pittsburgh Supercomputing Center’s Bridges computer performs computations to sharpen the AI’s strategy. During the day’s game play, Bridges is used to compute end-game strategies for each hand.

“The people at the Pittsburgh Supercomputing Center have done a great job,” Sandholm said, noting the staff has moved workloads around to enable the computer to be used in the competition. Since the beginning of the contest, the center has increased the number of Bridges’ computer nodes assigned to the poker tournament.

Cosmic rays have revealed a new chamber in Egypt’s Great Pyramid

Posted on November 27, 2017 by plug_the_plugger

Cosmic rays may have just unveiled a hidden chamber within Egypt’s most famous pyramid. An international team led by Kunihiro Morishima at Nagoya University in Japan used muons, the high-energy particles generated when cosmic rays collide with our atmosphere, to explore inside Egypt’s Great Pyramid without moving a stone. (from newscientist.com)

Muons can penetrate deep into rock, and get absorbed at different rates depending on the density of the rock they encounter. By placing muon detectors within and around the pyramid, the team could see how much material the particles passed through.

“If there is more mass, fewer muons get to that detector,” says Christopher Morris at Los Alamos National Laboratory, who uses similar techniques to image the internal structure of nuclear reactors. “When there is less mass, more muons get to the detector.”

By looking at the number of muons that arrived at different locations within the pyramid and the angle at which they were travelling, Morishima and his team mapped out cavities within the ancient structure.

This type of exploration – muon radiography – is perfect for sensitive historical sites as it uses naturally occurring radiation and causes no damage to the structure.

The team mapped the pyramid’s three known chambers – the subterranean chamber, the Queen’s chamber, and the King’s chamber – along with connecting corridors. They also detected a new large void above the Grand Gallery that connects the King and Queen’s chamber. This new void is approximately the same volume as the Grand Gallery. The team believes it’s another oversized tunnel similar in dimensions to the Grand Gallery that is at least 30 metres long.

The team used three different muon detectors, starting with nuclear emulsion film within the Queen’s chamber. Like photographic film is exposed to light to make a photo, the emulsion reacts to muons and makes a record of their paths.

Once their initial findings indicated a potential cavity, they confirmed it by placing an instrument that emits a flash of light when struck by muons within the pyramid. Outside the pyramid, they also used detectors that record muons indirectly when the high-energy particles ionise the gas inside. After several months in position to record muons, all three methods confirmed a void in the same location.

“It’s marvelous,” Morris says, noting that the long exposure times increase the robustness of the results. “What they’ve seen is fairly definitive,” he says, although it will take drilling and cameras to determine if the cavity is a structural chamber, or a void created by a long-forgotten collapse.

A team led by Luis Alvarez first tried using muon radiography to map pyramids in 1970, but they were unable to detect new voids. If confirmed, this would be the first newly rediscovered chamber within the Great Pyramid in more than a century.

“I’d love to be there when they first stick a camera through a drill hole,” Morris admitted. “It’s not every day we discover a chamber in a pyramid.”

Journal reference: Nature, DOI: 10.1038/nature24647

Researchers demonstrate new type of laser

Posted on August 7, 2017 by plug_the_plugger

Lasers are everywhere nowadays: Doctors use them to correct eyesight, cashiers to scan your groceries, and quantum scientist to control qubits in the future quantum computer. For most applications, the current bulky, energy-inefficient lasers are fine, but quantum scientist work at extremely low temperatures and on very small scales. For over 40 years, they have been searching for efficient and precise microwave lasers that will not disturb the very cold environment in which quantum technology works. (from phys.org)

A team of researchers led by Leo Kouwenhoven at TU Delft has demonstrated an on-chip microwave laser based on a fundamental property of superconductivity, the ac Josephson effect. They embedded a small section of an interrupted superconductor, a Josephson junction, in a carefully engineered on-chip cavity. Such a device opens the door to many applications in which microwave radiation with minimal dissipation is key, for example in controlling qubits in a scalable quantum computer.

The scientists have published their work in Science on the 3rd of March.

Lasers have the unique ability to emit perfectly synchronized, coherent light. This means that the linewidth (corresponding to the color) is very narrow. Typically lasers are made from a large number of emitters (atoms, molecules, or semiconducting carriers) inside a cavity. These conventional lasers are often inefficient, and dissipate a lot of heat while lasing. This makes them difficult to operate in cryogenic environments, such as what is required for operating a quantum computer.

Superconducting Josephson junction

In 1911, the Dutch physicist Heike Kamerlingh Onnes discovered that some materials transition to a superconducting state at very low temperatures, allowing electrical current to flow without any loss of energy. One of the most important applications of superconductivity is the Josephson effect: if a very short barrier interrupts a piece of superconductor, the electrical carriers tunnel through this non-superconducting material by the laws of quantum mechanics. Moreover, they do so at a very characteristic frequency, which can be varied by an externally applied DC voltage. The Josephson junction is therefore a perfect voltage to light (frequency) converter.

Josephson junction laser

The scientists at QuTech coupled such a single Josephson junction to a high-quality factor superconducting micro-cavity, no bigger than an ant. The Josephson junction acts like a single atom, while the cavity can be seen as two mirrors for microwave light. When a small DC voltage is applied to this Josephson junction, it emits microwave photons that are on resonance with the cavity frequency. The photons bounce back and forth between two superconducting mirrors, and force the Josephson junction to emit more photons synchronized with the photons in the cavity. By cooling the device down to ultra-low temperatures (< 1 Kelvin) and applying a small DC voltage to the Josephson junction, the researchers observe a coherent beam of microwave photons emitted at the output of the cavity. Because the on-chip laser is made entirely from superconductors, it is very energy efficient and more stable than previously demonstrated semiconductor-based lasers. It uses less than a picoWatt of power to run, more than 100 billion times less than a light globe.

Low-loss quantum control

Efficient sources of high quality coherent microwave light are essential in all current designs of the future quantum computer. Microwave bursts are used to read out and transfer information, correct errors and access and control the individual quantum components. While current microwave sources are expensive and inefficient, the Josephson junction laser created at QuTech is energy efficient and offers an on-chip solution that is easy to control and modify. The group is extending their design to use tunable Josephson junctions made from nanowires to allow for microwave burst for fast control of multiple quantum components. In the future, such a device may be able to generate so-called “amplitude-squeezed” light with has smaller intensity fluctuations compared to conventional lasers, this is essential in most quantum communication protocols. This work marks an important step towards the control of large quantum systems for quantum computing.

New Measurement Will Help Redefine International Unit of Mass

Posted on July 8, 2017 by plug_the_plugger

Using a state-of-the-art device for measuring mass, researchers at the National Institute of Standards and Technology (NIST) have made their most precise determination yet of Planck’s constant, an important value in science that will help to redefine the kilogram, the official unit of mass in the SI, or international system of units. (from nist.gov )

The new NIST measurement of Planck’s constant is 6.626069934 x 10⁻³⁴ kg∙m²/s, with an uncertainty of only 13 parts per billion. NIST’s previous measurement, published in 2016, had an uncertainty of 34 parts per billion.

The kilogram is currently defined in terms of the mass of a platinum-iridium artifact stored in France. Scientists want to replace this physical artifact with a more reproducible definition for the kilogram that is based on fundamental constants of nature.

Planck’s constant enables researchers to relate mass to electromagnetic energy. To measure Planck’s constant, NIST uses an instrument known as the Kibble balance, originally called the watt balance. Physicists widely adopted the new name last year to honor the late British physicist Bryan Kibble, who invented the technique more than 40 years ago.

NIST’s Kibble balance uses electromagnetic forces to balance a kilogram mass. The electromagnetic forces are provided by a coil of wire sandwiched between two permanent magnets. The Kibble balance has two modes of operation. In one mode, an electrical current goes through the coil, generating a magnetic field that interacts with the permanent magnetic field and creates an upward force to balance the kilogram mass. In the other mode, the coil is lifted at a constant velocity. This upward motion induces a voltage in the coil that is proportional to the strength of the magnetic field. By measuring the current, the voltage and the coil’s velocity, researchers can calculate the Planck constant, which is proportional to the amount of electromagnetic energy needed to balance a mass.

There are three major reasons for the improvement in the new measurements, said physicist Stephan Schlamminger, leader of the NIST effort.

First, the researchers have much more data. The new result uses 16 months’ worth of measurements, from December 2015 to April 2017. The increase in experimental statistics greatly reduced the uncertainty in their Planck value.

Second, the researchers tested for variations in the magnetic field during both modes of operation and discovered they had been overestimating the impact the coil’s magnetic field was having on the permanent magnetic field. Their subsequent adjustment in their new measurements both increased their value of Planck’s constant and reduced the uncertainty in their measurement.

Finally, the researchers studied in great detail how the velocity of the moving coil affected the voltage. “We varied the speed that we moved the coil through the magnetic field, from 0.5 to 2 millimeters per second,” explained Darine Haddad, lead author of the NIST results.

In a magnetic field, the coil acts like an electric circuit consisting of a capacitor (a circuit element that stores electric charge), a resistor (an element that dissipates electrical energy) and an inductor (an element that stores electrical energy). In a moving coil, these circuit-like elements generate an electrical voltage that changes over time, said Schlamminger. The researchers measured this time-dependent voltage change to account for this effect and reduced the uncertainty in their value.

This new NIST measurement joins a group of other new Planck’s constant measurements from around the world. Another Kibble balance measurement, from the National Research Council of Canada, has an uncertainty of just 9.1 parts per billion. Two other new measurements use the alternative Avogadro technique, which involves counting the number of atoms in a pure silicon sphere.

The new measurements have such low uncertainty that they exceed the international requirements for redefining the kilogram in terms of Planck’s constant.

“There needed to be three experiments with uncertainties below 50 parts per billion, and one below 20 parts per billion,” Schlamminger said. “But we have three below 20 parts per billion.”

All of these new values of the Planck’s constant do not overlap, “but overall they’re in amazingly good agreement,” Schlamminger said, “especially considering that researchers are measuring it with two completely different methods.” These values will be submitted to a group known as CODATA ahead of a July 1 deadline. CODATA will consider all of these measurements in setting a new value for Planck’s constant. The kilogram is slated for redefinition in November 2018, along with other units in the SI.