Nanoscale cavity strongly links quantum particles

Scientists have created a crystal structure that boosts the interaction between tiny bursts of light and individual electrons, an advance that could be a significant step toward establishing quantum networks in the future.

Today’s networks use electronic circuits to store information and optical fibers to carry it, and quantum networks may benefit from a similar framework. Such networks would transmit qubits – quantum versions of ordinary bits – from place to place and would offer unbreakable security for the transmitted information. But researchers must first develop ways for qubits that are better at storing information to interact with individual packets of light called photons that are better at transporting it, a task achieved in conventional networks by electro-optic modulators that use electronic signals to modulate properties of light.

Now, researchers in the group of Edo Waks, a fellow at JQI and an Associate Professor in the Department of Electrical and Computer Engineering at the University of Maryland, have struck upon an interface between photons and single electrons that makes progress toward such a device. By pinning a photon and an electron together in a small space, the electron can quickly change the quantum properties of the photon and vice versa. The research was reported online Feb. 8 in the journal Nature Nanotechnology.

“Our platform has two major advantages over previous work,” says Shuo Sun, a graduate student at JQI and the first author of the paper. “The first is that the electronic qubit is integrated on a chip, which makes the approach very scalable. The second is that the interactions between light and matter are fast. They happen in only a trillionth of a second – 1,000 times faster than previous studies.”

CONSTRUCTING AN INTERFACE

The new interface utilizes a well-studied structure known as a photonic crystal to guide and trap light. These crystals are built from microscopic assemblies of thin semiconductor layers and a grid of carefully drilled holes. By choosing the size and location of the holes, researchers can control the properties of the light traveling through the crystal, even creating a small cavity where photons can get trapped and bounce around.

”These photonic crystals can concentrate light in an extremely small volume, allowing devices to operate at the fundamental quantum limit where a single photon can make a big difference,” says Waks.

The results also rely on previous studies of how small, engineered nanocrystals called quantum dots can manipulate light. These tiny regions behave as artificial atoms and can also trap electrons in a tight space. Prior work from the JQI group showed that quantum dots could alter the properties of many photons and rapidly switch the direction of a beam of light.

The new experiment combines the light-trapping of photonic crystals with the electron-trapping of quantum dots. The group used a photonic crystal punctuated by holes just 72 nanometers wide, but left three holes undrilled in one region of the crystal. This created a defect in the regular grid of holes that acted like a cavity, and only those photons with only a certain energy could enter and leave.

Inside this cavity, embedded in layers of semiconductors, a quantum dot held one electron. The spin of that electron – a quantum property of the particle that is analogous to the motion of a spinning top – controlled what happened to photons injected into the cavity by a laser. If the spin pointed up, a photon entered the cavity and left it unchanged. But when the spin pointed down, any photon that entered the cavity came out with a reversed polarization – the direction that light’s electric field points. The interaction worked the opposite way, too: A single photon prepared with a certain polarization could flip the electron’s spin.

Both processes are examples of quantum switches, which modify the qubits stored by the electron and photon in a controlled way. Such switches will be the coin of the realm for proposed future quantum computers and quantum networks.

QUANTUM NETWORKING

Those networks could take advantage of the strengths that photons and electrons offer as qubits. In the future, for instance, electrons could be used to store and process quantum information at one location, while photons could shuttle that information between different parts of the network.

Such links could enable the distribution of entanglement, the enigmatic connection that groups of distantly separated qubits can share. And that entanglement could enable other tasks, such as performing distributed quantum computations, teleporting qubits over great distances or establishing secret keys that two parties could use to communicate securely.

Before that, though, Sun says that the light-matter interface that he and his colleagues have created must create entanglement between the electron and photon qubits, a process that will require more accurate measurements to definitively demonstrate.

“The ultimate goal will be integrating photon creation and routing onto the chip itself,” Sun says. “In that manner we might be able to create more complicated quantum devices and quantum circuits.”

In addition to Waks and Sun, the paper has two additional co-authors: Glenn Solomon, a JQI fellow, and Hyochul Kim, a post-doctoral researcher in the Department of Electrical and Computer Engineering at the University of Maryland.

Joint Quantum Institute

Learn Engineering from Nature

Surface Structure of a Springtail

Christian Thaulow, NTNU, Norway 

Biomimetics is the imitation of the models, systems, and elements of nature for the purpose of solving complex human problems. The terms biomimicry and biomimetics come from the Greek words bios, meaning life, and mimesis, meaning to imitate. A closely related field is bionics.

Over the last 3.6 billion years, nature has gone through a process of trial and error to refine the living organisms, processes, and materials on Earth. The emerging field of biomimetics has given rise to new technologies created from biologically inspired engineering at both the macro scale and nanoscale levels. Biomimetics is not a new idea. Humans have been looking at nature for answers to both complex and simple problems throughout our existence. Nature has solved many of today's engineering problems such as self-healing abilities, environmental exposure tolerance and resistance, hydrophobicity, self-assembly, and harnessing solar energy through the evolutionary mechanics of selective advantages.

No, this isn't something out of horror movie. These are the gears - a remarkable feat of "organic engineering" - of aIssus coleaptratus nymph (photo courtesy of The University of Cambridge).

Nature turns out to be as prodigious an engineer as human beings. The University of Cambridge recently discovered that a European plant-hopping insect called the Issus coleaptratus possesses natural, biological gears not unlike those found in bicycles, transmissions, and automobile differentials. Adding to the surprise of this discovery, the Issus has been living comfortably in European gardens for decades. Only ornamental “gears” have been spotted in nature prior to this discovery; those of the Issus, however, play an essential role in the insect’s survival.

This is a micrograph of a rainbow butterfly's microstructure. The arrangement of the grooves gives rise to a dull blue color that can be observed with the naked eye.

There are many displays of iridescence in nature, found in many different climates, for presumably, many different reasons. Iridescence is simply coloration due to a microscopic physical geometry, rather than the pigments that are usually considered to be sources of coloration. The wings of Blue Morpho butterfly,the Urania ripheus butterfly, the Rainboy Butterfly, and the surface of the mother of pearl, sea shell, all share a similar mode of coloration: iridescence. The apparent bend of the light comes from interference caused by small surface grooves on the surface. There are approximately 4 striations on one micrometer of Blue Morpho wing, and they are supposed to be made of chitin, the same material marine creature's shells are made of. Looking at objects of this size is well within the magnification range of the microscope.

Scanning electron microscope image of the eye on a leaf miner moth. 

(Image:Dartmouth College)

Using the compound eyes of the humble moth as their inspiration, an international team of physicists from the City University of New York and Tongji University in Shanghai applied biomimicry to develop new nanoscale materials that could someday increase the resolution of the resulting X-ray images without the need for larger radiation dosages which occur due to amplification of input radiation.

Moths have large compound eyes which consist out of many thousands of ommatidia-structures which form a primitive cornea and lens that are connected to photoreceptor cells. Their eyes are also anti-reflective and bounce back very little of the light that strikes them in order to help the insects be stealthier and less visible to predators during their nocturnal flights. Because of this feature, engineers have looked to the moth eye to help design more efficient coatings for solar panels and displays.

Led by Yasha Yi, a professor of the City University of New York, who is also affiliated with MIT and New York University, the researchers took another path and used the moth eye as a model for a new class of materials that improve the light-capturing efficiency of X-ray machines and similar medical imaging devices.

Glass spheres among microhairs that are mushroom-shaped to improve adhesive force. 

(SEM: Michael Röhrig, KIT)

Geckos outclass adhesive tapes in one respect: Even after repeated contact with dirt and dust do their feet perfectly adhere to smooth surfaces. Researchers of the KIT and the Carnegie Mellon University, Pittsburgh, have now developed the first adhesive tape that does not only adhere to a surface as reliably as the toes of a gecko, but also possesses similar self-cleaning properties. Using such a tape, food packagings or bandages might be opened and closed several times.

Through the study of nanobiomimicry, key components of nanodevices like nanowires, quantum dots, and nanotubes have been produced in an efficient and simple manner when compared to more conventional lithographic techniques. Many of these biologically derived structures are then developed into applications for photovoltaics, sensors, filtration, insulation, and medical uses. The field of nanobiomimetics is highly multidisciplinary, and requires collaboration between biologists, engineers, physicists, material scientists, nanotechnologists and other related fields. In the past century, the growing field of nanotechnology has produced several novel materials and enabled scientists to produce nanoscale biological replicas.

Scientists scale terahertz peaks in nanotubes

Rice U. researchers find plasmonic root of terahertz signals in some carbon nanotubes 

Carbon nanotubes carry plasmonic signals in the terahertz range of the electromagnetic spectrum, but only if they’re metallic by nature or doped.

In new research, the Rice University laboratory of physicist Junichiro Kono disproved previous theories that dominant terahertz response comes from narrow-gap semiconducting nanotubes.

Knowing that metallic or doped nanotubes respond with plasmonic waves at terahertz frequencies opens up the possibility that the tubes can be used in a wide array of optoelectronic amplifiers, detectors, polarizers and antennas.

The work by Kono and his Rice colleagues appeared online recently in the American Chemical Society journal Nano Letters.

Scientists have long been aware of a terahertz peak in nanotubes, the tiny cylinders of rolled-up carbon that show so much promise for advanced materials. But experiments on batches of nanotubes, which generally grow in a willy-nilly array of types, failed to reveal why it was there.

The origin of the peak was not explainable because researchers were only able to experiment on mixed batches of nanotube types, said Qi Zhang, a graduate student in Kono’s group and lead author of the paper. “All the previous work was done with a mixture of semiconducting and metallic tubes. We are the first to clearly identify the plasmonic nature of this terahertz response,” he said.

Rice’s growing expertise in separating nanotubes by type allowed Kono and his group to test for terahertz peaks in batches of pure metallic nanotubes known as “armchairs” as well as nonmetallic, semiconducting tubes.

“Metallic carbon nanotubes are expected to show plasmon resonance in the terahertz and infrared range, but no group has clearly demonstrated the existence of plasmons in carbon nanotubes,” Zhang said. “Previously, people proposed one possible explanation — that the terahertz peak is due to interband absorption in the small band gaps in semiconducting nanotubes. We rejected that in this paper.”

Plasmons are free electrons on the surface of metals like gold, silver or even aluminum nanoparticles that, when triggered by a laser or other outside energy, ripple like waves in a pond. Strong waves can trigger plasmon responses in adjacent nanoparticles. They are being investigated at Rice and elsewhere for use in sophisticated electronic and medical applications.

The Kono group’s research showed plasmons rippling at terahertz frequencies only along the length of a nanotube, but not across its width. “The only way charge carriers can move around is in the long direction,” Kono said. The researchers previously used this fact to demonstrate that aligned carbon nanotubes act as an excellent terahertz polarizer with performance better than commercial polarizers based on metallic grids.

Nanotubes can be thousands of times longer than they are wide, and the ability to grow them (or cut them) to specific lengths or to dope semiconducting nanotubes to add free carriers would make the tubes highly tunable for terahertz frequencies, Kono said.

“This paper only clarifies the origin of this effect,” he said. “Now that we understand it, there’s so much to do. We will be making various terahertz devices, architectures and systems based on carbon nanotube plasmons.”

Rice alumni Erik Hároz, now a postdoctoral researcher at Los Alamos National Laboratory, and Lei Ren, a researcher at TGS, co-authored the paper with undergraduate student Zehua Jin, postdoctoral researcher Xuan Wang, senior research scientist Rolf Arvidson and Andreas Lüttge, a research professor of Earth science and chemistry, all of Rice. Kono is a professor of electrical and computer engineering and of physics and astronomy and of materials science and nanoengineering.

The Department of Energy, the National Science Foundation and the Robert A. Welch Foundation supported the research.

Source: http://news.rice.edu/2013/12/09/scientists-scale-terahertz-peaks-in-nanotubes/