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Quantum computing breakthrough uses diamond nanowires

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March 12, 2010

A diamond-based nanowire device (Illustrated by Jay Penni)

A diamond-based nanowire device (Illustrated by Jay Penni)

Current computers operate using binary coding; thousands to trillions of small electrical circuits representing a binary digit (bit) of information that represent a "1" when the circuit is switched on and a "0" when switched off by means of an electronic switch. The future of computing is to move this to a quantum scale, where the weird properties of subatomic particles can be used to create much faster computers. A new device developed by Harvard scientists which uses nanostructured diamond wire to provide a bright, stable source of single photons at room temperature represents a breakthrough in making this quantum technology a reality.

Scientists have been exploiting the properties of diamonds since learning how to manipulate the electron spin associated with the nitrogen vacancy (NV) color center of the gem. The color center "communicates" by emitting and absorbing photons. The emitted photon flow provides a means to carry the resulting information conveyed in practical communication or computation, while the quantum (qubit) state can be initialized and measured using light. However, until now gathering photons efficiently has been difficult since the color-centers are embedded deep inside the diamond.

Researchers led by Marko Loncar, Assistant Professor of Electrical Engineering at the Harvard School of Engineering and Applied Sciences (SEAS), found that the emission performance of a diamond color center's single photon source could be improved by nanostructuring the diamond and embedding the color center within a diamond nanowire. The result was a bright, stable source of single photons at room temperature; a natural and efficient interface to probe an individual color center; increased brightness and sensitivity; and enhanced optical properties that increased photon collection by nearly a factor of ten relative to natural diamond devices, all of which have good implications for fast and secure computing using light.

The diamond nanowire device overcomes some of the drawbacks of other approaches (such as those based on fluorescent dye molecules, quantum dots, and carbon nanotubes) because it can be readily replicated and integrated with a variety of nano-machined structures.

Loncar's team suggest it can be applied using a top-down nanofabrication technique capable of embedding the color centers into a wide variety of machined structures, and that it will be more productive to apply the technology to large device arrays as opposed to "one-of-a-kind" designs. They hope it could lead to a new class of nanostructured diamond devices suitable for quantum communication and computing, as well as advanced areas ranging from biological and chemical sensing to scientific imaging.

"What was missing was an interface that connects the nano-world of a color center with macro-world of optical fibers and lenses," explains Loncar. "We consider this an important step and enabling technology towards more practical optical systems based on this exciting material platform. Starting with these synthetic, nanostructured diamond samples, we can start dreaming about the diamond-based devices and systems that could one day lead to applications in quantum science and technology as well as in sensing and imaging."

Loncar and Babinec's co-authors included research scholar Birgit Hausmann, graduate student Yinan Zhang, and postdoctoral student Mughees Khan, all at SEAS; graduate student Jero Maze in the Department of Physics at Harvard; and faculty member Phil R. Hemmer at Texas A&M University. They published their research in the February 14th issue of Nature Nanotechnology.

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