Computer systems born from droplets of DNA computing hold the promise of tackling the most complex problems, yet the very design of these processors provides the developers with a puzzle of their own: how to control the system?
Daniel van der Weide believes he and his German colleagues at the Max Planck Institute and Hannover University have solved a small mystery that may eventually help designers rein in these machines.
The solution is to control the specific activities of a tiny piece of man-made matter called an artificial molecule. Using this technique, van der Weide hopes researchers will be able to apply their knowledge of nature's molecules to understanding the behavior of their artificial brethren. In turn, he wants the artificial molecule to serve as a platform for testing new capabilities, then building them into molecular and biological computers.
"[Controlling the atoms and observing them] are the first baby steps toward understanding how synthetic matter works," said van der Weide, an associate professor of electrical and computer engineering at the University of Delaware.
Artificial atoms are the tiny pockets of electrons nested in the surfaces of semiconductors. Scientists refer to these pockets as atoms -� and two or more together as artificial molecules �- because they bear an uncanny resemblance to their natural counterparts in terms of electronic structure and mechanical behavior. But where the positive and negative charges within an atom hold the natural matter together, the artificial atom counts on special growth techniques and a metal pattern pressed into the two-dimensional semiconductor surface to confine its electrons and define its existence.
Though bigger than its natural counterpart, an artificial molecule is still invisible to the naked eye. An artificial molecule is 1,000 times smaller than the width of human hair, while a real molecule is 500 times smaller than an artificial one. This tiny stature is part of what makes both forms of matter difficult to observe and even more tricky to control.
What van der Weide and his colleagues have done is to take conventional spectroscopy -- a technique used to study real atoms and molecules -- to excite the artificial molecule and observe its actions. A spectroscope is an instrument that can determine the wavelength of a ray of light emitted from an object (a prism is a simple form of a spectroscope). The ray of light captured by the spectroscope is the result of the energy given off during a reaction such as the transfer of electrons between two atoms.
The researchers built an artificial molecule from two adjacent pockets of electrons within the surface of the semiconductor material. The two artificial atoms shared electrons that traveled through a tunnel-like structure linking them together. Researchers then focused high-frequency microwave pulses (ranging from 2 Ghz to 400 Ghz) from two different sources, each tuned to nearly the same frequency. Because the pulsing sources operate at slightly different frequencies, their paths interfered with each other.
This interference created a lower frequency signal which the researchers were able to detect and read. Inside this low-frequency signal lay the clues about the high-frequency response of the artificial molecule. What the researchers saw were movements similar to Rabi oscillations, the pendulum-like movement of electrons between two molecules or atoms in nature.
"We found that the term atom or molecule is even more apt when talking about these [artificial atoms]," said van der Weide. "Now we're trying to take our cues from nature."
The observations have given van der Weide the idea that it is possible to build a better molecule. He and his colleagues want to build larger scale models of molecules to conduct further studies of energy travel and experiments of how they can improve upon Mother Nature. For example, within a model molecule, van der Weide imagines sticking in probes to monitor energy flow and then using the information to tinker with this flow to increase the processing power. In this way, science can imitate nature which can then be used to improve technology.
"By adopting natural architectures to certain problems, we have a much better chance of tackling these problems and putting more horsepower in the computer," said van der Weide.
In a sense, van der Weide and his colleagues are laying the groundwork for a real-life Rabi oscillation. Information about natural matter is used to enhance the technology which is studied. These new lessons are then applied back to nature to build a better, more stable DNA molecule.
