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Controlling Qubits in Silicon at Picosecond Speeds

Among the many candidates for storing quantum bits, or qubits, are electrons, atoms, molecules and quantum dots. However, over the last few years, researchers have been focusing on storing quantum bits in silicon as a promising avenue towards realizing a quantum computer. Now, researchers from the University of Surrey, University College London, Heriot-Watt University in Edinburgh, the Radboud University in Nijmegen, and ETH Zürich/EPF Lausanne/Paul Scherrer Institute in Switzerland have reported the ability to control the quantum state of qubits embedded in silicon and readout the result by a simple electrical measurement. A paper describing their findings appears in the 20 March edition of Nature Communications

The qubits are phosphorus atoms trapped inside the silicon layer. Because the spin state of the outer electron of these atoms can remain in a state of superposition of the two possible spin states, these qubits are therefore called “orbital qubits.” They can retain a superposition state for a fraction of a millisecond before they are disrupted. The researchers demonstrated that they could switch the quantum state of the phosphorus atoms with laser pulses in about a picosecond (10-12 s), which is a thousand times faster than achieved with previous similar experiments. The advantage of these short pulses is that in future computers, operations could be performed easier on qubits that retain their quantum state for a very short time, says Ben Murdin, a physicist at the University of Surrey and corresponding author of the paper.

The researchers also reported that they could determine the quantum state of a qubit by measuring the amount of current passing through the silicon. The point of the experiment, says Murdin, is to show that it’s possible to use completely standard commercial silicon, and a simple voltmeter for the readout of quantum superpositions. "It's the first electrical detection of orbital qubits in silicon,” he says. And the only piece of fancy equipment that’s required is the laser.

Murdin notes that electrical readouts of quantum states have advantages for other quantum technologies too. "I don't know how to make a quantum computer, but this method would help enormously if you want an atomic clock or a quantum magnetometer,” the Surrey professor says.

Solid State Refrigerators

Materials that cool and heat when stress is applied and released could led to new solid-state refrigerators that are more efficient and environmentally friendly than conventional fridges, researchers say.

Air conditioners, refrigerators, and freezers burn through energy, accounting for roughly one-third of all electricity that U.S. homes use. A normal cooler uses a pump to squeeze refrigerant gas, turning it into a liquid. This liquid then expands in tubes lining the cooler, taking heat with it. Unfortunately, the most effective refrigerant gases are freon-based compounds banned internationally 15 years ago because they destroy the ozone layer. Freon’s replacements are hardly better; they are environmentally unfriendly global warming gases more than 1,000 times worse than carbon dioxide.

To sidestep these environmental effects entirely, scientists at the Technical University of Denmark explored so-called elastocaloric materials that change temperature when they are compressed and when they decompress. They detailed their findings in the 24 March online edition of the Journal of Applied Physics

When squeezed, the materials’ crystal structures change, they heat up, and subsequently expel this heat into their surroundings. When the stress is removed, and the crystal structure of the elastocaloric material reverts, the material cools down and draw heat away from the compartment that is to be cooled. The researchers basically turned the shape memory effect, where a change in temperature can make a material change its shape, on its head.

The Danish researchers found that wires made from a super-elastic alloy that was 48.9 percent nickel and 51.1 percent titanium could be repeatedly compressed and decompressed with a reproducible elastocaloric effect over a wide range of temperatures. They added that a 2014 U.S. Department of Energy report suggested that elastocaloric cooling shows the most potential among all non-vapor-compression cooling technologies.

The scientists noted that over the expected lifetime of 10 years, an elastocaloric material has to stand up to 100 million cycles of compression and decompression. Although no elastocaloric material is currently this durable, the Danish group says that recent nickel-titanium thin films doped with copper and cobalt have shown promise. That formula has withstood more than one million cycles, while showing good levels of cooling function and no fatigue.

The scientists say the next step is to build a prototype to demonstrate the potential of these materials. 

Scientists Want to Mine Sewage For Technologically Important Metals

Human waste is a useful source of energy. Schemes abound for converting treated waste into biogas for heat, generating electricity, or conversion into biofuels for cars and rockets.

Apparently, the contents of your toilet are also a goldmine. Solid waste can contain copper, silver, gold as well as rare-earth elements like palladium and vanadium that are used in electronics. Scientists at the US Geological Survey are now trying to find out just how much of these useful metals Americans are flushing down their toilets every year, and how they could be recovered. They are presenting details at the American Chemical Society national meeting this week.

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Light Emitting Fibers for Crazy Clothes

Thin light-emitting fibers that can be woven into textiles could be made into glowing clothes and other wearable electronics, researchers at Fudan University in Shanghai say.

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First Prototype of a Working Tricorder Unveiled at SXSW

“Don’t worry, I’m not going to take off all my clothes,” said Robert Kaul, president and CEO of Cloud DX, as he unbuttoned his shirt in front of a crowd at SXSW Interactive last week.

Kaul was showing off the components of his entry in the Tricorder Xprize, the $10-million competition that requires teams to develop a sci-fi medical scanner worthy of Star Trek. Each device must be able to diagnose 15 different medical conditions and monitor vital signs for 72 hours.

Cloud DX was ready to unveil its prototype at SXSW, but all ten finalist teams must be nearly done tinkering with their devices. They’re required to turn in their entries on 1 June in preparation for a six-month round of consumer testing.

The XPrize is partnering with the medical center at the University of California, San Diego on that consumer testing, since it requires recruiting more than 400 people with a variety of medical conditions. Grant Campany, director of the Tricorder XPrize, said he’s looking forward to getting those devices into hands of real patients. “This will be a practical demonstration of what the future of medicine will be like,” said Campany at that same SXSW talk, “so we can scale it up after competition.” 

Around his neck, Kaul revealed a sort of electronic collar that forms one component of the Cloud DX system; the other pieces of hardware sat on a table before him. In a one-on-one with Spectrum just before the talk, Kaul gave me a closer look at his Tricorder prototype, which has four pieces:

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NASA's LEAPTech X-plane Will Fly with 18 Electric Motors and Tiny Wings

NASA’s X-plane program has, for the past 70 years, demonstrated some of the most exciting and innovative aircraft ever flown, including rockets and robots, scramjets and spacecraft (and lots more). It’s always worth paying attention when a new X-plane is announced, and NASA has just given us a hint of what the X-57 might beLEAPTech, an experimental demonstrator that replaces the single large motor on light aircraft with 18 (!) tiny ones, all mounted on an impossibly skinny little wing.

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Rand Paul Woos the Tech Crowd at SXSW Interactive

There were a number of surprising attendees at the high-tech geek fest that is SXSW Interactive: Grumpy Cat, the U.S. Postal Service, and Rand Paul, to name just a few. 

Paul, the junior U.S. senator from Kentucky and a presumptive presidential candidate, came to SXSW to sell himself to tech libertarian types. In an on-stage discussion with a Texas journalist, Paul pitched himself as the only (presumptive!) presidential candidate who would fight for civil liberties online.

But his opposition to government meddling also makes him an opponent of government regulations on net neutrality, he said. Paul has been making a big play for support from the tech community with trips to Silicon Valley and field offices coming to Austin and the Bay Area, but his net neutrality stance may limit his geek appeal.

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Liquid 3-D Printing

Giant leaps have been made in recent years with 3-D printing. Though most 3-D printed items are made of plastic, more exotic ingredients have included sugar, mashed potatoes, and living cells. A 3-D printer commonly works by depositing a layer of material much like an ordinary printer and then printing out another layer once the material below has solidified. This procedure has a built-in problem: Even small objects take way too long to produce.

An object just several centimeters high can take hours to print. But now scientists at Carbon3D in Redwood City, Calif., and the University of North Carolina at Chapel Hill (UNC) say they can slash printing times by two orders of magnitude. Instead of printing an item step by step and layer by layer, the new technique prints objects in a continuous manner.

A 3-D printer often uses ultraviolet light to harden resins, but oxygen in the air often slows this hardening down. Instead of treating oxygen as an obstacle they had to overcome, the researchers used it to their advantage.

The new 3-D printer starts with a basin filled with a pool of liquid resin. Ultraviolet rays can emerge from beneath through a hole at the bottom of this basin. (Imagine a sink filled with resin where ultraviolet light can shine up from the drain.)

In the hole between the basin and ultraviolet rays, where a stopper might fill the hole at the bottom of a sink, is a layer of oxygen-rich liquid tens of micrometers thick. This layer serves as a transparent window for the ultraviolet rays. Solidification cannot occur in this "dead zone."

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To print an object, a metal plate is lowered down onto the surface of the resin pool. Ultraviolet rays are then fired upward at the metal plate. The ultraviolet rays make the resin harden only in specific zones within this pool above the dead zone. The resulting solid object is attached to the metal plate. When enough of the object has solidified, the 3-D printer slowly pulls the metal plate upward. As the hardening item rises from the liquid resin, it creates suction forces that pull liquid resin into the basin to replace what was lost to the solidified object.

Using this new method, the scientists printed objects at speeds of up to more than 1 meter per hour, generating complex solid objects such as a 10-centimeter-tall version of the Eiffel Tower. By slowing down print speeds, they could also print features less than 100 µm wide, or thinner the average human hair.

One of the senior researchers on this work, UNC’s Joseph DeSimone, gave a TEDTalk on this project on 16 March. The scientists will detail their findings in the 20 March issue of the journal Science.

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Why International Engineering and Science Students Stay or Go

Foreign-born talent has fueled many Silicon Valley startups and contributed heavily to U.S. leadership in in science and engineering for decades. But national data shows that just half of science and engineering doctoral recipients who were born overseas end up staying in the U.S. to pursue their post-graduation careers. A new study has teased out several reasons why students choose to stay in the U.S. or go back to their home countries.

The limitations of U.S. immigration policy and H-1B work visas are one of the biggest challenges for foreign students interested in pursuing U.S. careers. That’s according to a survey of 166 international graduate students conducted by the Center for Nanotechnology in Society at the University of California, Santa Barbara. Many students who participated in the survey pointed to uncertainty about obtaining permanent resident status after graduation as a major deterrent to both studying in the U.S. and trying to work in the U.S. after graduation. For the study, which appeared in the 11 March 2015 issue of the journal PLOS One, one mechanical engineering student summed up the frustrations of many peers thusly:

The fact that you don’t have a green card at the end of your PhD—it’s a nightmare. For international students, not having a green card, it impacts the job search, everything. The U.S. is welcoming to graduate students to come and study but there doesn’t seem to be a plan for after students graduate. Students settle for jobs that are below them because they work for companies that will provide them with a green card.

But the study also examined how several professional, social and personal factors influenced the decisions of foreign students. The study authors focused on three key decisions: whether to pursue higher education in the home country, whether to stay in the U.S. or return home after graduation, and whether to pursue a career in academia or industry.

One of the strongest predictors of whether a student will stay or leave is whether he or she wants to pursue a career in academia or industry. Students who wanted industry careers had a 90 percent probability of pursuing U.S.-based careers after graduation. By comparison, students who planned to pursue academic careers believed they would receive better treatment from colleagues in their home country. As a result, this group had an 86 percent probability of leaving the U.S. after graduation.

The quality of U.S. mentors and professional networks factored heavily into the decisions of students who wanted to go into academia but decided to leave the United States after earning their degrees. But not in the way one might predict. Many students who believed the U.S. offered higher quality mentors or professional networks were more likely to return to their home countries.

“We were most surprised by the role mentorship and networking played in whether a student decided to stay or leave,” said Xueying (Shirley) Han, lead author on the study and a postdoctoral scholar in marine biology at the University of California, Santa Barbara, in a press release. “Individuals who felt they had strong mentorships and networking actually felt more comfortable leaving the U.S.”

It’s possible that foreign students who had forged strong relationships with U.S. mentors or professional networks were more confident about returning home to work, according to Han and her colleagues. Students who had weaker U.S. relationships might be more interested in staying longer in order to strengthen professional ties.

One important thing to note is the study’s relatively small sample size. Of the 166 students surveyed, about 73 percent were engineers and the rest studied life and physical sciences. But the demographics of the survey respondents did generally match the national distribution of international students studying in the U.S.; the largest groups hailed from China and India.

Such foreign talent continues to drive much of U.S. innovation. About 44 percent of Silicon Valley startups currently include a foreign founder. Foreign born scientists and engineers also contributed more than half of the international patents filed by multinational corporations based in the United States. But the United States can’t assume it will continue to attract the world’s best talent without addressing these students’ concerns. Many international students pointed to Europe as an increasingly competitive choice for studying science and engineeringin large part because of more relaxed immigration policies.

In order for policymakers to craft smart policy, they need to consider the complex interaction of factors that go into foreign students’ career decisions,” Han said. “And if the U.S. wants to maintain its competitive economic edge, it needs to provide an alternative for highly skilled scientists and researchers to stay.”

Laser Bug Zapper Inches To Market

If it’s over-the-top crazy to swat a fly with a sledgehammer, what are we to say of vaporizing one with a laser?

How about: good riddance. We need new weapons for the war on bugs, particularly disease-bearing mosquitoes, which are quick to evolve resistance to poisons and are hardly fazed by traps that lure them to their deaths. That’s because there are just too many of the little bloodsuckers out there, particularly in the malarial regions of Africa. 

After years in the blue-sky area of speculative inquiry, the laser bug zapper took its first solid step toward commercialization last week, when Intellectual Ventures, the patent-holding giant, announced that it had licensed the manufacturing of the system to Lighting Science Group of Melbourne, Florida, a maker of LEDs.

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