Fluorescent diamond “defect centers” are being used to create efficient single-photon sources that are expected to enable secure optical communications, also known as quantum cryptography.

Defect centers in diamond materials, which function as atomic-scale light sources, are trapped in a transparent material that is large enough to be handled manually. Moreover, unlike quantum dots or trapped atoms, they don't need to be kept at cryogenic temperatures or to be trapped in large electromagnetic fields to be stable.

"Defect centers could also be used as building blocks for solid-state quantum computers, which would use quantum effects to solve problems that are not efficiently solvable with current computer technology," said J.P. Hadden, a PhD candidate at the Centre for Quantum Photonics at the university.

To fulfill the potential of diamond defect centers, it's essential that the light be collected efficiently from the diamond material, but this collection efficiency is dramatically reduced by reflection and refraction of light passing through the diamond-air interface.

"We managed to show an improvement in the brightness of these defect centers of up to 10 times by etching hemispherical 'solid immersion lenses' into the diamond," notes Hadden. "This is an important result, showing how nanofabrication techniques can complement and enhance quantum technologies, and opens the door to diamond-defect-center-based implementations of quantum cryptography and quantum computation."

More recently, Hadden and colleagues developed a technique that allows them to reliably etch these structures over previously characterized defect centers to a precision of about 100 nm — another significant step toward a practical and repeatable combination of nanotechnology and quantum optics.

For more information, visit: apl.aip.org