First optical rectenna—combined rectifier and antenna—converts light to DC current

 

A carbon nanotube optical rectenna converts green laser light to electricity in the laboratory of Baratunde Cola at the Georgia Institute of Technology. Credit: Rob Felt, Georgia Tech

Using nanometer-scale components, researchers have demonstrated the first optical rectenna, a device that combines the functions of an antenna and a rectifier diode to convert light directly into DC current.

Based on multiwall carbon nanotubes and tiny rectifiers fabricated onto them, the optical rectennas could provide a new technology for photodetectors that would operate without the need for cooling, energy harvesters that would convert waste heat to electricity - and ultimately for a new way to efficiently capture solar energy.

In the new devices, developed by engineers at the Georgia Institute of Technology, the carbon nanotubes act as antennas to capture light from the sun or other sources. As the waves of light hit the nanotube antennas, they create an oscillating charge that moves through rectifier devices attached to them. The rectifiers switch on and off at record high petahertz speeds, creating a small direct current.

Billions of rectennas in an array can produce significant current, though the efficiency of the devices demonstrated so far remains below one percent. The researchers hope to boost that output through optimization techniques, and believe that a rectenna with commercial potential may be available within a year.

"We could ultimately make solar cells that are twice as efficient at a cost that is ten times lower, and that is to me an opportunity to change the world in a very big way" said Baratunde Cola, an associate professor in the George W. Woodruff School of Mechanical Engineering at Georgia Tech. "As a robust, high-temperature detector, these rectennas could be a completely disruptive technology if we can get to one percent efficiency. If we can get to higher efficiencies, we could apply it to energy conversion technologies and solar energy capture."

The research, supported by the Defense Advanced Research Projects Agency (DARPA), the Space and Naval Warfare (SPAWAR) Systems Center and the Army Research Office (ARO), is scheduled to be reported September 28 in the journal Nature Nanotechnology.

Developed in the 1960s and 1970s, rectennas have operated at wavelengths as short as ten microns, but for more than 40 years researchers have been attempting to make devices at optical wavelengths. There were many challenges: making the antennas small enough to couple optical wavelengths, and fabricating a matching rectifier diode small enough and able to operate fast enough to capture the electromagnetic wave oscillations. But the potential of high efficiency and low cost kept scientists working on the technology.

"The physics and the scientific concepts have been out there," said Cola. "Now was the perfect time to try some new things and make a device work, thanks to advances in fabrication technology."

Using metallic multiwall carbon nanotubes and nanoscale fabrication techniques, Cola and collaborators Asha Sharma, Virendra Singh and Thomas Bougher constructed devices that utilize the wave nature of light rather than its particle nature. They also used a long series of tests - and more than a thousand devices - to verify measurements of both current and voltage to confirm the existence of rectenna functions that had been predicted theoretically. The devices operated at a range of temperatures from 5 to 77 degrees Celsius.

Fabricating the rectennas begins with growing forests of vertically-aligned carbon nanotubes on a conductive substrate. Using atomic layer chemical vapor deposition, the nanotubes are coated with an aluminum oxide material to insulate them. Finally, physical vapor deposition is used to deposit optically-transparent thin layers of calcium then aluminum metals atop the nanotube forest. The difference of work functions between the nanotubes and the calcium provides a potential of about two electron volts, enough to drive electrons out of the carbon nanotube antennas when they are excited by light.

In operation, oscillating waves of light pass through the transparent calcium-aluminum electrode and interact with the nanotubes. The metal-insulator-metal junctions at the nanotube tips serve as rectifiers switching on and off at femtosecond intervals, allowing electrons generated by the antenna to flow one way into the top electrode. Ultra-low capacitance, on the order of a few attofarads, enables the 10-nanometer diameter diode to operate at these exceptional frequencies.

"A rectenna is basically an antenna coupled to a diode, but when you move into the optical spectrum, that usually means a nanoscale antenna coupled to a metal-insulator-metal diode," Cola explained. "The closer you can get the antenna to the diode, the more efficient it is. So the ideal structure uses the antenna as one of the metals in the diode - which is the structure we made."

The rectennas fabricated by Cola's group are grown on rigid substrates, but the goal is to grow them on a foil or other material that would produce flexible solar cells or photodetectors.

Cola sees the rectennas built so far as simple proof of principle. He has ideas for how to improve the efficiency by changing the materials, opening the carbon nanotubes to allow multiple conduction channels, and reducing resistance in the structures.

"We think we can reduce the resistance by several orders of magnitude just by improving the fabrication of our device structures," he said. "Based on what others have done and what the theory is showing us, I believe that these devices could get to greater than 40 percent efficiency."

Quantum entanglement: New study predicts a quantum Goldilocks effect

                                                            

          The 'just right' structure that emerges when you drive a system containing light and matter (like the universe), neither too fast nor too slow across a quantum phase transition. It illustrates the findings of the study titled "Enhanced dynamic light-matter entanglement from driving neither too fast nor too slow," published in the journal Physical Review. Credit: Oscar Acevedo, Universidad de los Andes, and Neil Johnson, University of Miami.

A new study has translated "not too hot or too cold, just right" to the quantum world and the generation of quantum entanglement – the binding within and between matter and light – and suggests that the universe started "neither too fast nor too slow."
By studying a system that couples matter and light together, like the universe itself, researchers have now found that crossing a quantum phase transition at intermediate speeds generates the richest, most complex structure. Such structure resembles "defects" in an otherwise smooth and empty space. The findings are published in Physical Review A, the American Physical Society's main journal.
"Our findings suggest that the universe was 'cooked' at just the right speeds," said Neil Johnson, professor of physics in the University of Miami College of Arts & Sciences and one of the authors of the study. "Our paper provides a simple model that can be realized in a lab on a chip, to explore how such defect structure develops as the speed of cooking changes."
The big mystery concerning the origin of the universe is how the star clusters, planetary systems, galaxies, and other objects that we now see managed to evolve out of nothing. There is a widespread belief within the scientific community that the birth of structure in the universe lies in the crossing of a quantum phase transition and that the faster the transition is crossed, the more structure it generates. The current findings contradict that belief.

The study sheds new light on how to generate, control, and manipulate quantum entanglement, since the defects contain clusters of quantum entanglement of all sizes. The findings hold the key to a new generation of futuristic technologies—in particular, ultrafast quantum computing, ultrasafe quantum cryptography, high-precision quantum metrology, and even the quantum teleportation of information.
"Quantum entanglement is like the 'bitcoin' that funds the universe in terms of interactions and information," Johnson said. "It is the magic sauce that connects together all objects in the universe, including light and matter."
In the everyday world, a substance can undergo a phase transition at different temperatures; for example, water will turn to ice or steam when sufficiently cold or hot. But in the quantum world, the system can undergo a phase transition at absolute zero temperature, simply by changing the amount of interaction between the light and matter. This phase transition generates quantum entanglement in the process.
Johnson likes to compare the emergence of highly entangled light-matter structures, as the quantum phase transition is crossed, with the way lumps of porridge appear out of "nothing," when you heat up milk and oats.
"If you cross the transition at the right speed (cook at right speed), the structures (lumps) that appear are far more complex - more 'tasty' - than when crossing fast or slow," said Johnson. "Since it is a quantum phase transition that is being crossed, the structures that appear contain clumps of quantum entanglement."
The results of the study, titled "Enhanced dynamic light-matter entanglement from driving neither too fast nor too slow," are robust for a wide range of system sizes, and the effect is realizable using existing experimental setups under realistic conditions. O.L. Acevedo, from Universidad de los Andes, Colombia, is first author of the study. Other co-authors from Universidad de los Andes are L. Quiroga and F. J. Rodriguez.
"Understanding quantum entanglement in light-matter systems is arguably the fundamental problem in physics," Johnson said.
The current paper opens up a novel line of investigation in this area. In addition, it provides a unique opportunity to design and build new nanostructure systems that harness and manipulate quantum entanglement effects. The researchers are now looking at specifying the precise conditions that experimentalists will need in order to see the enhanced quantum entanglement effect that they predict.
                                                                                                                          

Life 2.0? Synthetic DNA Added to Genetic Code

Well, there’s no way this could go wrong.
According to recent announcements, a small biotech startup in California has successfully added new synthetic components to the genetic alphabet of DNA, potentially creating entirely new kinds of life on Earth.
You’d need a Ph.D. or three to really get into it, but here goes: DNA, the organic molecule that carries genetic information for life, is made from a limited chemical “alphabet.” DNA can be thought of as a molecular code containing exactly four nitrogen-containing nucleobases — cytosine (C), guanine (G), adenine (A), or thymine (T). All known living organisms on the planet, from bacteria to biologists, are based on combinations of this four-letter molecular code: C-G-A-T.

DNA Data Storage Lasts Thousands Of Years
That’s how it’s been for several billion years, but last year the biotech company Synthorx announced development of a synthetic pair of nucleobases — abbreviated X-Y — to create a new and expanded genetic code.

From the company website: “Adding two new synthetic bases, termed X and Y, to the genetic alphabet, we now have an expanded vocabulary to improve the discovery and development of new therapeutics, diagnostics and vaccines as well as create innovative products and processes, including using semi-synthetic organisms….”

The additions to the four letter DNA code effectively raises the number of possible amino acids an organism could use to build proteins from 20 to 172. That opens up entire new vistas of possibilities, including a completely new class of semi-synthetic life forms using a six-letter DNA code instead of a four-letter code.
Brainwaves, Heartbeat, DNA Turned Into Music

Synthorx’s most recent announcement concerns the successful production of proteins containing the new synthetic base pair, building on the research published last year: “Since the publication, Synthorx has developed and validated a protein expression system, employing its synthetic DNA technology to incorporate novel amino acids to create new full-length and functional proteins.”
According to third-party reports, Synthorx has even started creating new organisms with the technology, including a type of E. coli bacteria “never before seen on the face of the Earth.”

The company insists that multiple safeguards are built into the technology, and that organisms created with the synthetic elements can only be produced in the lab. That, of course, is the premise of roughly one million science fiction horror stories, but what can you do? Well, you can read more about it here.

Massive Wall of Fans Converts CO2 to Fuel

This just in from the Why Didn’t We Think Of This Before bureau: A Canadian startup company is working on a plan to deploy massive walls of intake fans that would suck carbon dioxide out of the air and turn it into fuel.

Carbon Engineering, based in Calgary, is hoping that its air capture plants will help to reduce CO2 emissions from all sources, but cars and trucks in paticular. Whereas carbon dioxide from power plants can be captured and filtered at the source, to a degree, emissions from motor vehicles and other moving sources are more difficult to trap.

Tiny Capsules Can Do The Big Job Of Carbon Capture
“Capturing CO2 directly from the air allows emissions originating from any source to be managed with standardized scalable industrial facilities,” reads the description on the company’s product page. “Our full-scale design, for example, could absorb the emissions created by 300,000 typical cars.”
The fans work by pulling air over a carbon-absorbing liquid that turns the CO2 into a salt. That salt can then be stored underground or re-used as a low-carbon synthetic fuel, according to the company.
Carbon Engineering has already constructed a pilot plant in Canada and is preparing to run the system at full capacity this year. After that, the company hopes to build commercial plants in 2017 or 2018 able to produce 10,000 barrels of synthetic fuel a year.
CO2 Milestone Already Passed In 2015


Direct air capture is not a particularly efficient method for reducing emissions, the company concedes, but the technology is scalable and requires a relatively small footprint.
The air capture plants essentially do the same work as trees and other vegetation, but require about 1/1,000th of the space. The company is hoping that its air scrubbers will be part of a larger, coordinated effort in the clean-tech industry.

“We must do something about the rising levels of carbon dioxide in our atmosphere,” says David Keith, Carbon Engineering president and a professor at Harvard University’s School of Engineering, in the company’s demo video. “We can and must transition to sustainable sources of low carbon energy.”

Paralyzed Man Can 'Feel' Again with Brain-Connected Prosthetic Hand

_{DARPA's Revolutionizing Prosthetics program aims to develop technologies that can restore a near-natural sense of touch.}

A prosthetic hand that is connected directly to the brain successfully enabled a paralyzed man to "feel" again, according to researchers at the Defense Advanced Research Projects Agency (DARPA).
The 28-year-old male, who suffered a spinal cord injury and has been paralyzed for more than a decade, was able to control a robotic hand with his brain and reported being able to sense physical sensations.


DARPA researchers attached electrodes to the man's sensory cortex — the area of the brain responsible for identifying tactile sensations, such as pressure. Electrodes were also placed on the patient's motor cortex, the part of the brain that directs body movements.

Wires were run directly from the electrodes to the mechanical hand, which was developed by the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland. Using this connection, the man could control the robotic hand's movements using the same types of thoughts, or neural connections, that the brain uses to move a hand normally. In addition, because the prosthetic hand was connected to the sensory cortex, the patient could sense when the hand was being touched, even when he was blindfolded.


DARPA officials announced the milestone during the agency's three-day "Wait, What? Technology Forum," held last week in St. Louis.
The research is part of DARPA's Revolutionizing Prosthetics program, which aims to develop a prosthetic that can not only be controlled by sending signals for the brain, but can also sense precisely what those devices are touching.


"Prosthetic limbs that can be controlled by thoughts are showing great promise," DARPA program manager Justin Sanchez said in a statement, "but without feedback from signals traveling back to the brain it can be difficult to achieve the level of control needed to perform precise movements. By wiring a sense of touch from a mechanical hand directly into the brain, this shows the potential for seamless bio-technological restoration of near-natural function."


In addition to this technology, DARPA reported preliminary findings from the agency's Restoring Active Memory (RAM) program, which is a dedicated to augmenting memory formation and recall in people suffering from memory loss.
DARPA has tested the program's first few dozen volunteers, who had neurological problems unrelated to memory loss, agency officials said. These volunteers had small electrode arrays placed in brain regions known to be involved in the formation of declarative memory, or simple memory used to recall lists, as well as in regions involved in spatial memory and navigation. These electrodes are giving scientists the ability to "read" the processes involved in memory formation and retrieval, and are even offering insights into when a volunteer is about to make an error in recall.
According to their initial results, it is possible to read and interpret these key signals in memory processing and even improve memory by providing targeted electrical stimulation to the brain, DARPA officials said.


"We still have a lot to learn about how the human brain encodes declarative memory," Sanchez said, "but these early experiments are clarifying issues such as these and suggest there is great potential to help people with certain kinds of memory deficits."

DARPA says the technologies being developed in the Revolutionizing Prosthetics and Restoring Active Memory programs hold great potential for improving brain function.

"As the technology of these fully implantable devices improves, and as we learn more about how to stimulate the brain ever more precisely to achieve the most therapeutic effects, I believe we are going to gain a critical capacity to help our wounded warriors and others who today suffer from intractable neurological problems," Sanchez said.

Quantum Teleportation Sets Distance Record

A record-breaking distance has been achieved in the bizarre world of quantum teleportation, scientists say.
The scientists teleported photons (packets of light) across a spool of fiber optics 63 miles (102 kilometers) long, four times farther than the previous record. This research could one day lead to a "quantum Internet" that offers next-generation encryption, the scientists said.


Teleporting an object from one point in the universe to another without it moving through the space in between may sound like science fiction pulled from an episode of "Star Trek," but scientists have actually been experimenting with "quantum teleportation" since 1998.

Quantum teleportation depends on capturing the fundamental details of an object — its "quantum states" — and instantly transmitting that information from one area to another to recreate the exact object someplace else.

Quantum teleportation relies on the strange nature of quantum physics, which finds that the fundamental building blocks of the universe can essentially exist in two or more places at once.

Specifically, quantum teleportation relies on an odd phenomenon known as "quantum entanglement," in which subatomic particles can become linked and influence each other instantaneously, regardless of how far apart they are. Scientists cannot distinguish the state of either particle until one is directly measured, but because the particles are connected, measuring one instantly determines the state of the other.

Currently, physicists can't instantly transport matter (say, a human), but they can use quantum teleportation to beam information from one place to another. In a recent experiment, scientists at the National Institute of Standards and Technology (NIST) were able to teleport photons farther across an optical fiber than ever before.

"What's exciting is that we were able to carry out quantum teleportation over such a long distance," study co-author Martin Stevens, a quantum optics researcher at the NIST in Boulder, Colorado, told Live Science.

The new distance record was set using advanced single-photon detectors made of superconducting wires of molybdenum silicide that were about 150 nanometers (or billionths of a meter) wide and cooled to about minus 457 degrees Fahrenheit (minus 272 degrees Celsius), or about 1 degree above absolute zero. The experiment involved a near-infrared wavelength commonly used in telecommunications, the researchers said.

"Only about 1 percent of photons make it all the way through 100 kilometers (60 miles) of fiber," Stevens said in a statement. "We never could have done this experiment without these new detectors, which can measure this incredibly weak signal."

The detectors used in this new experiment could record more than 80 percent of arriving photons, according to the scientists. In comparison, the previous record-holder had detectors that operated with about 75 percent efficiency at best. Moreover, the new experiment detected 10 times fewer stray photons than the previous record-holder.

Prior research did achieve quantum teleportation over longer distances over open air — a span of 89 miles (144 kilometers) between the two Canary Islands of La Palma and Tenerife, located off the northwest coast of Africa.

"However, the experiment at the Canary Islands involved a telescope on top of one mountain and a telescope on top of another mountain, with the telescopes pointed at each other at night, since background light during the day would interfere with the experiment," Stevens said. "If you wanted quantum teleportation in the real world — say, from one city to another — you might not necessarily have a direct line-of-sight between two locations, and you wouldn't want to be limited to working at night, so fiber optics might be more feasible."

Quantum teleportation could enable the development of a "quantum Internet" that allows messages to be sent more securely, Stevens said.

"A quantum Internet could allow you to establish communications channels that are much more secure than what we have with the standard encryption protocols we use everyday nowadays," Stevens said.