Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Purdue professor puts new spin on quantum computer technology

14.10.2004


Purdue University physicists have built a critical component for the development of quantum computers and spintronic devices, potentially bringing advances in cryptography and high-speed database searches a step closer.


atomic force micrograph



A team of researchers including Leonid P. Rokhinson has created a device that can effectively split a stream of quantum objects such as electrons into two streams according to the spin of each, herding those with "up" spin in one direction and corralling those that spin "down" in another. By producing such "spin-polarized" streams, the tiny device could become a key component in quantum computers, which have not yet left the drawing boards of the computer industry but are highly sought-after for their purported facility at cracking codes and searching large databases.

"For the first time, we have achieved spatial spin separation of the ’holes’ in gallium arsenide, the spaces that electrons leave behind as they travel through this semiconductor," said Rokhinson, who is an assistant professor of physics in Purdue’s School of Science. "These holes also have spin characteristics, just as particles do, and separating them according to their spin has been a great challenge. Producing this effect will be critical for the success of any spin-based electronic device, and this separation method could be one of the missing links necessary for the development of quantum computers and non-volatile memory devices." The research appears in the current issue of the journal Physics Review Letters.


Quantum computers, though still in the early stages of development, are highly desired because of their projected ability to solve particular kinds of difficult problems that often arise in cryptography and database searching. These problems often have a very large number of candidate solutions, most of which are incorrect and must be quickly eliminated from the solution pool.

Even the fastest conventional computers, which must test each potential solution before moving on to another, can take an inordinately long time to winnow out the incorrect candidates. But a quantum computer could theoretically test the solutions simultaneously – a process computer scientists refer to as parallel processing. Rokhinson said this is because of a peculiar quantum physical property of particles called entanglement. "Two electrons – one that has ’up’ spin, the other with ’down’ – can be entangled so that anything that affects one affects the other," he said. "The particles remain entangled even if they are separated by great distances."

The two particles’ respective spins, which are opposite but inextricably linked, allow them to form a ’quantum bit,’ or qubit, that can actually be ’on’ and ’off’ simultaneously, or function as both a one and a zero during digital calculations. This ability to represent two conditions at once, multiplied many times over within a computer chip that uses a large number of qubits, could be a powerful tool for sifting through information.

"The trouble is, you have to find a way to measure the final quantum state of the qubit after the calculations have been made to extract useful information from them," Rokhinson said. "Only once you have separated them can you obtain the answer to your calculations. This measurement issue has been one of the big challenges of the field."

Some of the reason behind this difficulty lies in the very weak coupling of spin with the environment. In semiconductor materials, Rokhinson said, spin is coupled many trillions of times less than charge is, and spin experiences comparatively little influence from nearby matter.

"In practical terms, this means you can try to make a particle flip its spin from ’up’ to ’down,’ but it won’t feel you pushing," he said. "Researchers have tried to polarize the particles using everything from light waves to strong magnetic fields, but nothing was working well enough to separate them."

However, Rokhinson’s team discovered that semiconductors made of highly purified gallium arsenide sandwiched between layers of aluminum gallium arsenide possessed a natural property that, when harnessed, could push the quantum spaces, or ’holes,’ into two different directions according to their spin state.

"Although it may seem counterintuitive, the holes have a spin state as well," Rokhinson said. "The spaces don’t literally spin – the idea of spin is just a loose metaphor anyway, to help physicists imagine what’s going on. In an electric current flowing through a copper wire, we imagine electrons jumping from one copper atom’s orbital hole to another. We could also imagine those holes having a positive charge and flowing in the opposite direction. A similar concept is at work here with spin state – we’re just working with the holes this time, not the particles."

It is a natural property of the holes within the semiconductor that Rokhinson’s group has harnessed to divide them up, which could make life simpler for the chip designers who may someday put this hole-herder to use. "The large magnetic fields needed for other methods of spin measurement are not necessary in this device," Rokhinson said. "However, it requires very low temperatures, a fraction of a degree above absolute zero. We will probably need to reproduce the effect at higher temperatures for chips based on this technology to become commercially worthwhile."

But with further development, Rokhinson said, the device might form a key element in a quantum microprocessor. "All spin-based processors require devices that can inject, detect and manipulate particles," he said. "This device can both inject and detect them, and since we already have some knowledge about manipulating particles, it could mean that a major hurdle in the way of developing spintronics devices has been overcome."

Rokhinson said his team would be concentrating on creating a device that also could manipulate the electron holes as well, thus accomplishing all three necessary tasks with a single component. "That would allow us to create a spin-based transistor," he said. "Because semiconductor transistors have had such a dramatic impact on the last few decades of computer development, we are optimistic that this discovery could be significant for the industry."

This research is supported in part by the Defense Advanced Research Projects Agency and the National Science Foundation.

Rokhinson is affiliated with Purdue’s Birck Nanotechnology Center. The center anchors Purdue’s new Discovery Park, located on the southwestern edge of campus. Programs include undergraduate teaching, graduate research and technology transfer initiatives with industry partners.

Chad Boutin | EurekAlert!
Further information:
http://www.purdue.edu

More articles from Physics and Astronomy:

nachricht Ultra-compact phase modulators based on graphene plasmons
27.06.2017 | ICFO-The Institute of Photonic Sciences

nachricht Smooth propagation of spin waves using gold
26.06.2017 | Toyohashi University of Technology

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Touch Displays WAY-AX and WAY-DX by WayCon

27.06.2017 | Power and Electrical Engineering

Drones that drive

27.06.2017 | Information Technology

Ultra-compact phase modulators based on graphene plasmons

27.06.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>