SCIENCE TECHNOLOGY

Tuesday, 19 July 2011

Mantis shrimp eye could improve high-definition CDs, DVDs

ScienceDaily (June 24, 2011) — The eye of the peacock mantis shrimp has led an international team of researchers to develop a two-part waveplate that could improve CD, DVD, blu-ray and holographic technology, creating even higher definition and larger storage density.

Peacock mantis shrimp are one of only a few animal species that can see circularly polarized light -- like the light used to create 3-D movies. Some researchers believe the mantis shrimp's eyes are better over the entire visual spectrum than any artificial waveplates.

A waveplate is a transparent slab that can alter the polarization of light because it is birefringent -- exhibits double refraction. The mineral calcite, which is sometimes used as a waveplate, is birefringent. This print viewed through a calcite lens appears as doubled and slightly offset letters.

"We want to change the polarization without affecting the amount of light that gets through," said Akhlesh Lakhtakia, Charles Godfrey Binder Professor of Engineering Science and Mechanics, Penn State. " We want both transmittance and changing polarization to occur quite independent of frequency. In other words, we do not want to affect the color."

Waveplates restore polarization in devices that require only one polarization of light, but lose polarization within the process. They can also separate light into separate polarizations to carry specific information and can filter light for optical devices.

Typically, waveplates are made from minerals like quartz, calcite or birefringent polymers. In some cases, to create the range and transparency required, two different materials are stacked or joined, but this type of construction sometimes delaminates, coming apart at the seams.

A team of engineers from the National Taipei University of Technology and Lakhtakia developed a method to produce periodically multilayered materials, similar to the lens in the peacock mantis shrimp, that are suitable for waveplates in the visual light spectrum and cannot delaminate because they are manufactured as one piece. The researchers report their work in the current online issue of Nature Communications.

The research team's waveplate is made of two layers of nanorods that are structurally similar to those in the eye of the peacock mantis shrimp. The researchers begin with tantalum pentoxide, but deposit the two layers using different deposition processes creating a multilayered thin film. One method produces a layer of needle-like nanorods that are all parallel to each other and all slanted in the same direction. The second method produces nanorods that are also parallel to each other but are upright.

"The two separate layers are needed so that we can play off one against the other to achieve the desired polarization without significantly reducing transmittance over a broad range of frequencies," said Lakhtakia.

The waveplates consist of a layer of slanted nanorods sandwiched between two layers of upright nanorods. Multiple sandwiches are then stacked to make the required waveplate. Because the size of the nanorods is much less than the wavelengths of visible light, the waveplate is birefringent. Because of the two materials, the waveplate can polarize or repolarize light over the visual spectrum.

The researchers report that "the fabrication technique of the periodically multilayered structures is a workhorse technique in the thin-film industry, does not require expensive lithography equipment and is compatible with … technology commonplace in electronics and optoelectronics industries."

Other researchers on this project were Professor Yi-Jun Jen, post-doctoral researcher Ching-Wei Yu and graduate students Chia-Feng Lin, Meng-Jie Lin, Shih-Hao Wang and Jyun-Rong Lai, Department of Electro-optical Engineering, National Taipei University of Technology.

The National Taipei University of Technology, the National Science Council of the Republic of China and the Charles Godfrey Binder Endowment at Penn State supported this research.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by Penn State.

Journal Reference:

Yi-Jun Jen, Akhlesh Lakhtakia, Ching-Wei Yu, Chia-Feng Lin, Meng-Jie Lin, Shih-Hao Wang, Jyun-Rong Lai. Biologically inspired achromatic waveplates for visible light. Nature Communications, 2011; 2: 363 DOI: 10.1038/ncomms1358

Note: If no author is given, the source is cited instead.

Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.

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New light shed on the private lives of electrons: Lasers allow scientists to observe how electrons become entangled

ScienceDaily (July 3, 2011) — A Princeton researcher and his international collaborators have used lasers to peek into the complex relationship between a single electron and its environment, a breakthrough that could aid the development of quantum computers.

The technique reveals how an isolated electron and its surroundings develop a relationship known as a Kondo state -- a state of matter that is of great interest to physicists and engineers. The results not only yield insights into a long-standing quandary in theoretical physics, but also may help scientists understand how to store information at the smallest possible scales, which would open vast new realms of computing power.

"What we've done is illuminate the private life of a single electron," said Hakan Tureci, an assistant professor of electrical engineering at Princeton and a lead researcher on the project. "It's taken nearly a century to isolate, control and probe a single electron in this way -- an extraordinary feat enabled by quantum theory, cryogenics and nanotechnology."

The research was conducted by an international team of scientists from the United States, Germany and Switzerland. The researchers on the project included Tureci, Atac Imamoglu, a professor at Swiss Federal Institute of Technology Zurich in Switzerland, Jan von Delft, a professor at LMU Munich, and Leonid Glazman, a professor at Yale University.

The key theoretical results and a proposal for testing the ideas experimentally were published March 11 in the journal Physical Review Letters.

These theoretical projections were recently confirmed in experiments led by Imamoglu, which were published June 29 in the journal Nature.

The research brings fresh insight to the study of the Kondo problem, a phenomenon first observed in the 1930s, when researchers were surprised to find that resistance to electricity flowing through certain metals increases at very low temperatures. Normally, resistance through metals decreases as temperature is lowered, but that was not the case with these metals.

The phenomenon was explained 30 years later by Japanese scientist, Jun Kondo, as resulting from the presence of cobalt or other magnetic impurities in the metals.

Scientists have further realized that the Kondo effect results from a relationship between electrons known as "entanglement" in which the quantum state of one electron is tied to those of neighboring electrons, even if the particles are later separated by considerable distances. In the case of Kondo effect, a trapped electron is entangled in a complex manner with a cloud of surrounding electrons.

Researchers have been intrigued by the Kondo effect in part because understanding how a trapped electron becomes entangled with its environment could help overcome barriers to quantum computing, which could lead to far more powerful computers than currently exist.

Previous observation methods allowed scientists to make measurements of the Kondo state, but could not provide information on how electrons developed such a relationship with their surroundings.

To better understand how an electron gradually becomes entangled in this manner with its environment, Tureci and his collaborators investigated the idea of using a laser to probe electrons evolving into the Kondo state. They first developed a theory about how laser light scattered off electrons could carry information about this process.

Depending on the state of the electron, they surmised, it should absorb different colors of laser light to varying degrees. The light reflected back would carry a signature of the entangled quantum state, offering a window into the relationship between the trapped electron and its environment.

To isolate the electrons, they proposed using nanostructured devices, small machines built one atom at a time that trap the electrons in small wells. The particles are only provided limited isolation in the wells and so eventually become entangled with a cloud of surrounding electrons in the device.

Tureci's collaborators in Switzerland tested the idea by projecting a laser beam on the device and measuring the light that was transmitted.

The light signature matched theoretical predictions. The researchers also found that they could use the light signatures to confirm when they turned the Kondo state off using a magnetic field.

"By doing this experiment," Tureci said, "we showed that you can extract this information that was previously unavailable in earlier experiments on the Kondo effect."

He said the finding could provide insight into quantum computing because entanglement, depending on its nature, could allow new ways of storing and processing information or could threaten to destabilize the computing process.

Whereas current computers use transistors to store "bits" of information as ones or zeros, scientists believe quantum computers might one day use trapped electrons that are entangled with one another as "qubits," the basic information units of quantum computing, which can have the odd quality of representing a blend of "one" and "zero" simultaneously.

A series of qubits could thus store exponentially more information than the 0 and 1 combination of classical bits.

While quantum computers could theoretically be far smaller and faster than transistor-based machines, using electrons or other sub-atomic particles as storage devices is no trivial feat.

The undesirable entangled relationship between electrons and their environment, such as that seen in the Kondo effect, can destabilize the desired relationship between trapped electrons that form the qubits and gradually destroy the information they store.

"Our technique offers a window into the Kondo state, allowing us a chance to study electrons that are highly entangled with their environments and understand how they got that way," Tureci said.