Physicists Move One Step Closer to Quantum Computer

In his quest to create a "topological insulator," Rice graduate student Ivan Knez spent hundreds of hours modifying tiny pieces of semiconductors in Rice University's clean room. (Credit: Jeff Fitlow/Rice University)

Rice University physicists have created a tiny "electron superhighway" that could one day be useful for building a quantum computer, a new type of computer that will use quantum particles in place of the digital transistors found in today's microchips.

In a recent paper in Physical Review Letters, Rice physicists Rui-Rui Du and Ivan Knez describe a new method for making a tiny device called a "quantum spin Hall topological insulator." The device, which acts as an electron superhighway, is one of the building blocks needed to create quantum particles that store and manipulate data.

Today's computers use binary bits of data that are either ones or zeros. Quantum computers would use quantum bits, or "qubits," which can be both ones and zeros at the same time, thanks to the quirks of quantum mechanics.

This quirk gives quantum computers a huge edge in performing particular types of calculations, said Du, professor of physics and astronomy at Rice. For example, intense computing tasks like code-breaking, climate modeling and biomedical simulation could be completed thousands of times faster with quantum computers.

"In principle, we don't need many qubits to create a powerful computer," he said. "In terms of information density, a silicon microprocessor with 1 billion transistors would be roughly equal to a quantum processor with 30 qubits."

In the race to build quantum computers, researchers are taking a number of approaches to creating qubits. Regardless of the approach, a common problem is making certain that information encoded into qubits isn't lost over time due to quantum fluctuations. This is known as "fault tolerance."

The approach Du and Knez are following is called "topological quantum computing." Topological designs are expected to be more fault-tolerant than other types of quantum computers because each qubit in a topological quantum computer will be made from a pair of quantum particles that have a virtually immutable shared identity. The catch to the topological approach is that physicists have yet to create or observe one of these stable pairs of particles, which are called "Majorana fermions" (pronounced MAH-yor-ah-na FUR-mee-ons).

The elusive Majorana fermions were first proposed in 1937, although the race to create them in a chip has just begun. In particular, physicists believe the particles can be made by marrying a two-dimensional topological insulator -- like the one created by Du and Knez -- to a superconductor.

Topological insulators are oddities; although electricity cannot flow through them, it can flow around their narrow outer edges. If a small square of a topological insulator is attached to a superconductor, Knez said, the elusive Majorana fermions are expected to appear precisely where the materials meet. If this proves true, the devices could potentially be used to generate qubits for quantum computing, he said.

Knez spent more than a year refining the techniques to create Rice's topological insulator. The device is made from a commercial-grade semiconductor that's commonly used in making night-vision goggles. Du said it is the first 2-D topological insulator made from a material that physicists already know how to attach to a superconductor.

"We are well-positioned for the next step," Du said. "Meanwhile, only experiments can tell whether we can find Majorana fermions and whether they are good candidates for creating stable qubits."

The research was funded by the National Science Foundation, Rice University, the Hackerman Advanced Research Program, the Welch Foundation and the Keck Foundation.

Researchers Transform iPhone Into High-Quality Medical Imaging Device

In a feat of technology tweaking that would rival MacGyver, a team of researchers from the University of California, Davis has transformed everyday iPhones into medical-quality imaging and chemical detection devices. With materials that cost about as much as a typical app, the decked-out smartphones are able to use their heightened senses to perform detailed microscopy and spectroscopy. The team will present their findings at the Optical Society's (OSA) Annual Meeting, Frontiers in Optics (FiO) 2011, taking place in San Jose, Calif. Oct. 16-20.

The enhanced iPhones could help doctors and nurses diagnose blood diseases in developing nations where many hospitals and rural clinics have limited or no access to laboratory equipment. In addition to bringing new sensing capabilities where they are needed most, the modified phones are also able transmit the real-time data to colleagues around the globe for further analysis and diagnosis.

"Field workers could put a blood sample on a slide, take a picture, and send it to specialists to analyze," says Sebastian Wachsmann-Hogiu, a physicist with UC Davis' Department of Pathology and Laboratory Medicine and the Center for Biophotonics, Science and Technology, and lead author of the research to be presented at FiO.

Microscope Makeover

The group is not the first to build a smartphone microscope. "But we thought we could make something simpler and less expensive," Wachsmann-Hogiu says.

His first attempt took simplicity too far. "We started with a drop of water on the camera's lens," he says. "The water formed a meniscus, and its curved surface acted like a magnifying lens. It worked fine, but the water evaporated too fast."

Then the team turned to ball lenses. These are finely ground glass spheres that act as low-powered magnifying glasses. The team used a 1-millimeter-diameter ball lens that costs $30-40 USD in their prototype, but mass-produced lenses could be substituted to reduce the price.

To build the microscope's lens, Kaiqin Chu, a post-doctoral researcher in optics, inserted a ball lens into a hole in a rubber sheet, then simply taped the sheet over the smartphone's camera.

At 5x magnification, the ball lens is no more powerful than a child's magnifying glass. Yet when paired with the camera of a smartphone, the microscope could resolve features on the order of 1.5 microns, small enough to identify different types of blood cells.

There are two reasons why such low magnification produces such high-resolution images. First, ball lenses excel at gathering light, which determines resolution. Second, the camera's semiconductor sensor consists of millions of light-capturing cells. Each cell is only about 1.7 microns across. This is small enough to capture precisely the tiny high-resolution image that comes through the ball lens.

Ball lenses pose some unique problems. The curvature of their sphere bends light as it enters the ball, distorting the image, except for a very small spot in the center. The researchers used digital image processing software to correct for this distortion. They also used the software to stitch together overlapping photos of the tiny in-focus areas into a single image large enough for analysis.

Even though smartphone micrographs are not as sharp as those from laboratory microscopes, they are able to reveal important medical information, such as the reduced number and increased variation of cells in iron deficiency anemia, and the banana-shaped red blood cells characteristic of sickle cell anemia.

Wachsmann-Hogiu's team is working with UC Davis Medical Center to validate the device and determine how to use it in the field. They may also add features, such as larger lenses to diagnose skin diseases and software to count and classify blood cells automatically in order to provide instant feedback and perhaps recognize a wider range of diseases.

Simple Spectrometer

When researchers need additional diagnostic tools, the microscope could be swapped for a simple spectrometer that also uses light collected by the iPhone's camera.

Spectrometers smear out light from an object, separating it into its composite wavelengths in much the way a prism breaks up white light in the familiar colors of the rainbow. Since atoms and molecules absorb very specific wavelengths when exposed to light, it is possible to tease out the chemical signature of materials by studying their spectra.

Like the microscope, the iPhone's spectrometer takes advantage of smartphone imaging capabilities. "We had worked with spectrometers for diagnostics, and didn't think it would be too far a stretch," Wachsmann-Hogiu says.

The spectrometer that the researchers added to the iPhone is easy to build. It starts with a short plastic tube covered at both ends with black electrical tape. Narrow slits cut into the tape allow only roughly parallel beams of light from the sample to enter and exit the tube. It is this grating that smears, or spreads, the light into a spectrum of colors that scientists can use like a fingerprint to identify various molecules.

"If you didn't have the slits, light would come in from all different angles and you could never separate it properly," explains Zachary Smith, an optics post-doctoral researcher in the lab.

Though the spectrometer is still in its early stages, the researchers believe it could measure the amount of oxygen in the blood and help diagnose chemical markers of disease.

Because smartphone instruments are powerful and cheap, Wachsmann-Hogiu believes schools could use them to enrich science classes. Spectrometers could help illustrate lessons about light and energy. Microscopes could unveil an invisible world of sugar crystals, pollen grains, and microscopic organisms.

By intelligently exploiting smartphone features, Wachsmann-Hogiu's group promises to both save lives and illuminate science.

Dementia with Lewy bodies

Dementia with Lewy bodies is the second most frequent cause of hospitalization for dementia, after Alzheimer's disease.


Current estimates are that about 60 to 75% of diagnosed dementias are of the Alzheimer's and mixed (Alzheimer's and vascular dementia) type, 10 to 15% are Lewy Bodies type, with the remaining types being of an entire spectrum of dementias including frontotemporal, Pick's disease, alcoholic dementia, pure vascular dementia, etc.

Dementia  :- Dementia is progressive decline in cognitive function due to damage or disease in the brain beyond what might be expected from normal aging

Particularly affected areas may be memory, attention, language and problem solving, although particularly in the later stages of the condition, affected persons may be disoriented in time (not knowing what day, week, month or year it is), place (not knowing where they are) and person (not knowing who they are).

Multi-infarct dementia :- Multi-infarct dementia, also known as vascular dementia, is a form of dementia resulting from brain damage caused by stroke or transient ischemic attacks (also known as mini-strokes)..

Multi-infarct dementia is one type of vascular dementia. Vascular dementia is the second most common form of dementia after Alzheimer's disease (AD) in older adults. Multi-infarct dementia (MID) is thought to be an irreversible form of dementia, and its onset is caused by a number of small strokes or sometimes, one large stroke preceded or followed by other smaller strokes. The term refers to a group of syndromes caused by different mechanisms all resulting in vascular lesions in the brain. Early detection and accurate diagnosis are important, as vascular dementia is at least partially preventable.

 

The main subtypes of this disease are: mild cognitive impairment, multi-infarct dementia, vascular dementia due to a strategic single infarct (affecting the thalamus, the anterior cerebral artery, the parietal lobes or the cingulate gyrus), vascular dementia due to hemorrhagic lesions, and mixed Alzheimer's and vascular dementia.

Vascular lesions can be the result of diffuse cerebrovascular disease or focal lesions; usually both. Mixed dementia is diagnosed when patients have evidence of AD and cerebrovascular disease, either clinically or based on neuroimaging evidence of ischemic lesions. In fact vascular dementia and Alzheimer's disease often coexist, especially in older patients with dementia.

Parkinson's disease :- Parkinson's disease (paralysis agitans or PD) is a neurodegenerative disease of the substantia nigra, an area in the basal ganglia of the brain.

The disease involves a progressive disorder of the extrapyramidal system, which controls and adjusts communication between neurons in the brain and muscles in the human body.

It also commonly involves depression and disturbances of sensory systems.

Hallucination :- A hallucination is a sensory perception experienced in the absence of an external stimulus, as distinct from an illusion, which is a misperception of an external stimulus.    

Hallucinations may occur in any sensory modality - visual, auditory, olfactory, gustatory, tactile, or proprioceptive (sense of balance and position in space).

Psychological research has presented the idea that hallucinations may result from biases in what are known as metacognitive abilities.

These are abilities that allow us to monitor or draw inferences from our own internal psychological states (such as intentions, memories, beliefs and thoughts).

The ability to discriminate between self-generated and external sources of information is considered to be an important metacognitive skill and one which may break down to cause hallucinatory experiences.