A newly created diamond-based nanowire device offers a bright, stable source of single photons at room temperature – an essential element in making fast and secure computing with light practical. Harvard University researchers led by Marko Loncar, assistant professor of electrical engineering at the Harvard School of Engineering and Applied Sciences (SEAS), found that the performance of a single photon source based on a light-emitting defect (color center) in diamond could be improved by nanostructuring the diamond and embedding the defect within a diamond nanowire. Scientists 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 because color centers are embedded deep inside the diamond. A diamond-based nanowire device. 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. (Illustration by Jay Penni.) "This presents a major problem if you want to interface a color center and integrate it into real-world applications," Loncar said. "What was missing was an interface that connects the nanoworld of a color center with the macroworld 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 10 relative to natural diamond devices. "Our nanowire device can channel the photons that are emitted and direct them in a convenient way," said Tom Babinec, a SEAS graduate student. 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 nanomachined 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 and enabling technology towards more practical optical systems based on this exciting material platform," Loncar said. "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." Babinec is lead author of a study published on the research Feb. 14 in Nature Nanotechnology; Loncar also is an author. Also contributing to the paper were research scholar Birgit Hausmann, graduate student Yinan Zhang and postdoctoral student Mughees Khan, all at SEAS; and graduate student Jero Maze in the department of physics at Harvard; and faculty member Phil R. Hemmer at Texas A&M University. The researchers acknowledge the following support: a Nanoscale Interdisciplinary Research Team grant from the National Science Foundation (NSF), the NSF-funded Nanoscale Science and Engineering Center at Harvard; DARPA; and a National Defense Science and Engineering Graduate Fellowship and a National Science Foundation Graduate Fellowship. All devices have been fabricated at the Center for Nanoscale Systems at Harvard. For more information, visit: www.harvard.edu