as it appeared in the July 18, 2008 edition of ACM TechNews.
An international research team has taken a step toward the creation of a working quantum computer through a demonstration that the quantum state of a single electron can be controlled in a silicon transistor through the alteration of the voltage applied to the transistor. "This represents a nice step towards future devices where performance is determined by manipulation of quantum states of single atoms," says Lawrence Berkeley National Laboratory researcher Thomas Schenkel. Prefabricated transistors constructed for nanotech research were employed by the researchers, and each transistor was comprised of a pair of crossed nanowires. Electrodes containing arsenic were linked to the bottom nanowire, which when charged would sometimes attract arsenic atoms into the transistor. When the researchers applied voltage across 100 transistors, they discovered a half-dozen transistors that seemed to have individual arsenic atoms embedded in the nanowire, and that the quantum state of one of the atom's electrons could be controlled by varying the voltage across the top nanowire. The researchers were able to draw distinctions between three atomic states in all six devices through the use of scanning tunneling spectroscopy, and one of those states corresponded with the electron being in two places simultaneously, which is essential for quantum computing. The key to a practical quantum computer is the entanglement of its quantum bits (qubits), and Schenkel thinks that adjacent qubits could be coupled by drawing an electron away from its atom. "While this result is an important one, the real challenge to making future single-dopant devices is in figuring out how to position the [arsenic atoms] into the silicon host with the required precision," notes University of Maryland scientist Bruce Kane. Click Here to View Full Article
