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Tinier quantum dots

Photonics Spectra
Apr 2009
Rebecca C. Jernigan,

Quantum dots are fascinating – thousands of atoms, acting together as one, bring us closer and closer to true quantum computing. As amazing as they are, though, they still have their problems, including the need for ultralow operating temperatures.

One possibility is to make them even smaller, thereby enhancing the stability of their electrons and enabling the particles to withstand higher temperatures. But how do you make a quantum dot that’s smaller than a quantum dot? Researchers at the National Institute for Nanotechnology say that you just need to use an atom.

A room-temperature scanning tunneling microscopy image displays two coupled atomic quantum dots that share one electron. When they are left alone (top) the electron is shared equally, but the addition of a control charge changes that. Image courtesy of Robert A. Wolkow.

A team at the institute, led by Robert A. Wolkow, has developed single-atom silicon quantum dots that operate reliably at room temperature. To prevent the atomic dots from merging with nearby atoms, the investigators used a scanning tunneling microscope to sever the bond between the silicon atom and any of its hydrogen neighbors, enabling the modified silicon dots to exist in the bandgap range. The researchers can specify which energy levels the electrons will fill, shifting and tailoring the levels to obtain a desired response.

Although the new dots do not yet offer all aspects of the control that is available with conventional quantum dots, the new approach could bring investigators closer to developing a quantum computing device. Their ability to withstand higher temperatures would make the devices more practical, while the use of silicon in their creation means that they could be compatible with current technology while being inexpensive to produce.

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