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 Study offers new theoretical approach to describing non-equilibrium phase transitions
27.04.2017 | DOE/Argonne National Laboratory

nachricht SwRI-led team discovers lull in Mars' giant impact history
26.04.2017 | Southwest Research Institute

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: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Fighting drug resistant tuberculosis – InfectoGnostics meets MYCO-NET² partners in Peru

28.04.2017 | Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

 
Latest News

Wireless power can drive tiny electronic devices in the GI tract

28.04.2017 | Medical Engineering

Ice cave in Transylvania yields window into region's past

28.04.2017 | Earth Sciences

Nose2Brain – Better Therapy for Multiple Sclerosis

28.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>