UC Santa Barbara physicists have discovered that silicon carbide (carborundum), widely used as a semiconductor, contains crystal imperfections that can be controlled at room temperature at a quantum-mechanical level.

The UCSB team discovered that electrons that become trapped by certain imperfections in silicon carbide do so in a way that allows their quantum states to be initialized, precisely manipulated, and measured using a combination of light and microwave radiation. This means that each of these defects meets the requirements for use as a quantum bit (qubit).

Before this research, the only system known to possess these same characteristics was a flaw in diamond known as the nitrogen-vacancy center, which can function as a qubit at room temperature, while many other quantum states of matter require an extremely cold temperature, near absolute zero. However, the nitrogen-vacancy center exists in a material that is difficult to grow and challenging to manufacture into integrated circuits.

In contrast, high-quality crystals of silicon carbide, multiple inches in diameter, are commonly produced for commercial purposes. They can be readily fashioned into a multitude of intricate electronic, optoelectronic, and electromechanical devices. In addition, the defects studied by Awschalom and his group are addressed using infrared light that is close in energy to the light used widely throughout modern telecommunications networks.

The combination of these features makes silicon carbide an attractive candidate for future work seeking to integrate quantum mechanical objects with sophisticated electronic and optical circuitry, according to the researchers.

While defects in silicon carbide may offer many technologically attractive qualities, an immense number of defects in other semiconductors are still left to be explored.

Ref.: William F. Koehl, et al., Room temperature coherent control of defect spin qubits in silicon carbide, Nature, 2011; 479 (7371): 84 [DOI: 10.1038/nature10562]