System Bits: Dec. 2

A graphene layer reads optical information from nanodiamonds electronically
It is assumed that nitrogen-vacancy centers in diamonds could be used to construct vital components for quantum computers but reading optically-written information electronically from them has not been possible. Now, by using a graphene layer, a team of scientists headed by the Technische Universität München (TUM) has implemented just such a read unit.

Ideally, diamonds consist of pure carbon but natural diamonds always contain defects. The most researched defects are nitrogen-vacancy centers comprising a nitrogen atom and a vacancy that might serve as highly sensitive sensors or as register components for quantum computers.

The team, which includes physicists from TUM and the Institut de Ciencies Fotoniques near Barcelona, has created a technique for reading the stored information that builds on a direct transfer of energy from nitrogen-vacancy centers in nanodiamonds to a directly neighboring graphene layer.

The researchers explained that when laser light shines on a nanodiamond, a light photon raises an electron from its ground state to an excited state in the nitrogen-vacancy center. The system of the excited electron and the vacated ground state can be viewed as a dipole, that in turn induces another dipole comprising an electron and a vacancy in the neighboring graphene layer.

Vision of a future quantum computer with chips made of diamond and graphene.
(Source: NIM)

In contrast to the approximately 100 nanometer large diamonds, in which individual nitrogen-vacancy centers are insulated from each other, the graphene layer is electrically conducting. Two gold electrodes detect the induced charge, making it electronically measurable.

Laboratory set-up measuring the interaction between graphene and nano-diamonds with implanted nitrogen-vacancy centers.
(Source: TUM)

As a result of the extremely fast switching speeds of the nanocircuits developed by the researchers, sensors built using this technology could be used not only to measure extremely fast processes. Integrated into future quantum computers they would allow clock speeds ranging into the terahertz domain.