Defects in silicon – old story or new horizons ?

Coherence and relaxation times of defects in silicon have been studied for more than six decades and contributed to the breaktrough of the semiconductors including the the advent of quantum information processing (QIP).
However, in modern implementations of quantum devices coherence times can still suffer from or be limited by the properties of the materials, e.g. defects at interfaces or the coherence properties of the atomic qubits themselves.

We present the investigation of the coherence and relaxation times of various defects in silicon such as the Pb centers at the Si/SiO₂ interface as well as phosphorus donors. We employ pulsed electron spin resonance techniques using superconducting niobium lumped element microwave resonators in the temperature regime below 0.5 K, the relevant temperature regime for QIP. We will highlight the challenges and benefits of using superconducting planar structures for electron spin resonance. Typical coherence times for the systems studied are of the order of a few milliseconds. The relaxation times observed are in the seconds range and are likely limited by the coupling to the microwave circuit.