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February 14, 2010

Diamond-based nanowire devices advance quantum science at Harvard

Illustration by Jay Penni. Researchers used a top-down nanofabrication technique to embed color centers into a variety of machined structures. By creating large device arrays rather than just "one-of-a-kind" designs, the realization of quantum networks and systems, which require the integration and manipulation of many devices in parallel, is more likely.

By creating diamond-based nanowire devices, a team at Harvard University has taken another step toward making applications based on quantum science and technology possible.

The new device offers a bright, stable source of single photons at room temperature, an essential element in making fast and secure computing with light practical.

The finding could lead to a new class of nanostructured diamond devices suitable for quantum communication and computing, as well as advance areas ranging from biological and chemical sensing to scientific imaging.



The performance of a single photon source based on a light-emitting defect (color center) in a diamond could be improved by nanostructuring the diamond and embedding the defect within a diamond nanowire.

Scientists, in fact, first began exploiting the properties of natural diamonds after learning how to manipulate the electron spin, or intrinsic angular momentum, associated with the nitrogen vacancy (NV) color center of the gem. The quantum (qubit) state can be initialized and measured using light.

The color center “communicates” by emitting and absorbing photons. The flow of photons emitted from the color center provides a means to carry the resulting information, making the control, capture, and storage of photons essential for any kind of practical communication or computation. Gathering photons efficiently, however, is difficult since color centers are embedded deep inside the diamond.

“This presents a major problem if you want to interface a color center and integrate it into real-world applications,” explains Loncar. “What was missing was an interface that connects the nano-world of a color center with the macro-world of optical fibers and lenses.”

The diamond nanowire device offers a solution, providing a natural and efficient interface to probe an individual color center, making it brighter and increasing its sensitivity. The resulting enhanced optical properties increase photon collection by nearly a factor of ten relative to natural diamond devices.

“Our nanowire device can channel the photons that are emitted and direct them in a convenient way,” says lead author Thomas Babinec, a graduate student at SEAS.

Further, the diamond nanowire is designed to overcome hurdles that have challenged other state-of-the-art systems — such as those based on fluorescent dye molecules, quantum dots, and carbon nanotubes — as the device can be readily replicated and integrated with a variety of nano-machined structures.

The researchers used a top-down nanofabrication technique to embed color centers into a variety of machined structures. By creating large device arrays rather than just “one-of-a-kind” designs, the realization of quantum networks and systems, which require the integration and manipulation of many devices in parallel, is more likely.

“We consider this an important step in enabling technology towards more practical optical systems based on this exciting material platform,” says Loncar. “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.”

Nature Nanotechnology - A diamond nanowire single-photon source

The development of a robust light source that emits one photon at a time will allow new technologies such as secure communication through quantum cryptography. Devices based on fluorescent dye molecules, quantum dots and carbon nanotubes have been demonstrated, but none has combined a high single-photon flux with stable, room-temperature operation. Luminescent centres in diamond have recently emerged as a stable alternative, and, in the case of nitrogen-vacancy centres, offer spin quantum bits with optical readout. However, these luminescent centres have thus far been realized only in bulk diamond, and have low photon out-coupling. Here, we demonstrate a single-photon source composed of a nitrogen-vacancy centre in a diamond nanowire, which produces ten times greater flux than bulk diamond devices, while using ten times less power. This result enables a new class of devices for photonic and quantum information processing based on nanostructured diamond, and could have a broader impact in nanoelectromechanical systems, sensing and scanning probe microscopy.

FURTHER READING
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