Defect Control Yields More Reliable Qubits

Enhancing the fluorescent light emission from atomic defects in diamond could be a key step toward creating reliable qubits for quantum computers.

A team of researchers from several institutions has demonstrated photonic cavities with Q factors of up to 24,000 by carefully controlling the nitrogen vacancy (NV) centers within.

NV centers contain an unpaired electron that can store information in its spin. That information can be read by observing the intensity of particular frequencies of the light that the NV center emits when illuminated by a laser.

A scanning electron microscope image of a diamond photonic cavity shows nanoscale holes etched through the layer containing NV centers. The scale bar indicates 200 nm. Courtesy of Evelyn Hu/Harvard University.

At room temperatures, this emission includes multiple sideband frequencies, making it difficult to interpret. The photonic cavity, which consists of a pattern of nanoscale holes, amplifies the most important element of the signal.

“A photonic cavity that is properly matched to the NVs can substantially augment their capabilities,” said Harvard University professor Dr. Evelyn Hu. “Strong spatial overlap is the hardest (task) to achieve in designing and fabricating a photonic cavity for NV centers.”

The team used delta doping to control the vertical position of the atomic defects, enhancing the intensity of photonic cavity emissions by roughly a factor of 30.

The technique confines NV centers to a layer approximately 6 nm thick, sandwiched inside a diamond membrane approximately 200 nm thick. The researchers then etched holes into the membrane to create the photonic cavities.

Further enhancement could come from also controlling the horizontal position of the defects. The team is now working on ways to achieve full 3-D control.

The work was published in Applied Physics Letters (doi: 10.1063/1.4904909).

For more information, visit www.harvard.edu.