Alex Knapp , Forbes Staff I write about the future of science, technology, and culture.
Physicists at the University of New South Wales have created a transistor composed of a single atom, which is an amazing feat of nanoengineering, and could provide a better foundation for scalable quantum computing. The technique and experiment in Nature Nanotechnology.
The transistor itself is composed of a single phosphorous-31 isotope, which has been precisely placed on a base of silicon using a Scanning Tunneling Microscope in an ultra-high vacuum chamber. What's particularly amazing about their technique is that they were able to position the individual phosphorous atoms precisely. The atom was confirmed to be exactly where it needed to be. Considering that most single-atom devices have a positioning margin of error of about 10 nm, that's an impressive accomplishment.
“Our group has proved that it is really possible to position one phosphorus atom in a silicon environment - exactly as we need it - with near-atomic precision, and at the same time register gates," said lead researcher Dr. Martin Fuechsle in a.
Some physicists have conjectured that the two possible nuclear spins of P-31 make it ideal for use as the basis for solid-state quantum computing. That's especially true because if phosphorous and silicon are used, it's conceivable that techniques used are compatible with CMOS systems used in today's computers.
Despite the small size of the transistor, the team was able to confirm that the electrodes present on the silicon were contacting the transistor, and also confirmed that they were able to successfully change the quantum states of the atom - which means that it can be successfully used as a transistor.
As amazing an achievement as this is, this is only the start of providing a basis for either conventional or quantum computing. Researchers will need to build off of this technology to develop chips comprised of many P-31 transistors that are able to be used for computation. Even once that's achieved, we're still a long way from using chips based on this transistor in your home. Scanning Tunneling Microscopy is a pretty powerful tool for positioning individual atoms, but it's also incredibly expensive to use as a basis for manufacturing.
That said, I'm very excited about the trend of potential quantum computing that uses cheap materials, such as silicon and phosphorous, as a base for materials. From an economic standpoint, that obviously has some advantages over more expensive materials such as superconductors or diamonds, which have been used in other quantum computation applications. It'll be interesting to see how this develops over the next few years.
In the meantime, if you want a little more background on the transistor, you can see a that UNSW put together below:
Follow me on or . Read my Forbes blog .
A controllable transistor engineered from a single phosphorus atom has been developed by researchers at the University of New South Wales, Purdue University, and the University of Melbourne. The atom, shown here in the center of an image from a computer model, sits in a channel in a silicon crystal. The atomic-sized transistor and wires might allow researchers to control gated qubits of information in future quantum computers. Image: Purdue University
The smallest transistor ever built—in fact, the smallest transistor that can be built—has been created using a single phosphorous atom by an international team of researchers at the University of New South Wales, Purdue University, and the University of Melbourne.
The single-atom device was described in a paper in Nature Nanotechnology.
Michelle Simmons, group leader and director of the ARC Centre for Quantum Computation and Communication at the University of New South Wales, says the development is less about improving current technology than building future tech.
"This is a beautiful demonstration of controlling matter at the atomic scale to make a real device," Simmons says. "Fifty years ago when the first transistor was developed, no one could have predicted the role that computers would play in our society today. As we transition to atomic-scale devices, we are now entering a new paradigm where quantum mechanics promises a similar technological disruption. It is the promise of this future technology that makes this present development so exciting."
The same research team announced in January (2012) that it had developed a wire of phosphorus and silicon—just one atom tall and four atoms wide—that behaved like copper wire.
Simulations of the atomic transistor to model its behavior were conducted at Purdue using nanoHUB technology, an online community resource site for researchers in computational nanotechnology.
Gerhard Klimeck, who directed the Purdue group that ran the simulations, says this is an important development because it shows how small electronic components can be engineered.
"To me, this is the physical limit of Moore's Law," Klimeck says. "We can't make it smaller than this."
Although definitions can vary, simply stated Moore's Law holds that the number of transistors that can be placed on a processor will double approximately every 18 months. The latest Intel chip, the "Sandy Bridge," uses a manufacturing process to place 2.3 billion transistors 32 nm apart. A single phosphorus atom, by comparison, is just 0.1 nm across, which would significantly reduce the size of processors made using this technique, although it may be many years before single-atom processors actually are manufactured.
The single-atom transistor does have one serious limitation: It must be kept very cold, at least as cold as liquid nitrogen, or -391 F (-196 C).
"The atom sits in a well or channel, and for it to operate as a transistor the electrons must stay in that channel," Klimeck says. "At higher temperatures, the electrons move more and go outside of the channel. For this atom to act like a metal you have to contain the electrons to the channel.
"If someone develops a technique to contain the electrons, this technique could be used to build a computer that would work at room temperature. But this is a fundamental question for this technology."
Although single atoms serving as transistors have been observed before, this is the first time a single-atom transistor has been controllably engineered with atomic precision. The structure even has markers that allow researchers to attach contacts and apply a voltage, says Martin Fuechsle, a researcher at the University of New South Wales and lead author on the journal paper.
"The thing that is unique about what we have done is that we have, with atomic precision, positioned this individual atom within our device," Fuechsle says.
Simmons says this control is the key step in making a single-atom device. "By achieving the placement of a single atom, we have, at the same time, developed a technique that will allow us to be able to place several of these single-atom devices towards the goal of a developing a scalable system."
The single-atom transistor could lead the way to building a quantum computer that works by controlling the electrons and thereby the quantum information, or qubits. Some scientists, however, have doubts that such a device can ever be built.
"Whilst this result is a major milestone in scalable silicon quantum computing, it does not answer the question of whether quantum computing is possible or not," Simmons says. "The answer to this lies in whether quantum coherence can be controlled over large numbers of qubits. The technique we have developed is potentially scalable, using the same materials as the silicon industry, but more time is needed to realize this goal."
Klimeck says despite the hurdles, the single-atom transistor is an important development.
"This opens eyes because it is a device that behaves like metal in silicon. This will lead to many more discoveries."
The research project spanned the globe and was the result of many years of effort.
"When I established this program 10 years ago, many people thought it was impossible with too many technical hurdles. However, on reading into the literature I could not see any practical reason why it would not be possible," Simmons says. "Brute determination and systemic studies were necessary—as well as having many outstanding students and postdoctoral researchers who have worked on the project."
Klimeck notes that modern collaboration and community-building tools such as nanoHUB played an important role.
"This was a trans-Pacific collaboration that came about through the community created in nanoHUB. Now Purdue graduate students spend time studying at the University of New South Wales, and their students travel to Purdue to learn more about nanotechnology. It has been a rewarding collaboration, both for the scientific discoveries and for the personal relationships that were formed."