IQST Grad School Project

A solid-state quantum voltage reference

Project Description:

There is no existing portable reliable voltage standard. Existing voltage references are derived from hybrid diode arrangements. Those structures are specified in terms of their initial output voltage accuracy, their temperature coefficients and their short and long-term drifts. Despite tremendous progress in fabrication techniques, temperature compensation and drift correction over almost a century, current devices achieve accuracies on the order of 10-4, temperature coefficients of 10-5/K, drift of 10-5/kh and relative noise levels of 10-6, and they are usually shipped uncalibrated. Yet, there is a growing need for calibration-free voltage references as, e.g. all digital to analogue conversion requires a reliable base voltage.

The project aims at exploring optically accessible spin defects in silicon carbide (SiC) and diamond as quantum voltage standards. The electric field generated by the voltage to be referenced should be measured via a precision measurement of the spin splitting of such atomic scale defects, which arises from spin orbit coupling. Superior functionality is expected mainly because of four facts. First, electric fields effectively break defect or lattice symmetry and therefore can be uniquely identified. Second, compared to current devices they do not rely on the Boltzman factor (E/kBT) and are therefore much less prone to temperature variation. Particularly the defect center electric field measurement are largely immune against temperature effects for symmetry reason. Third, proper functionality is envisaged beyond certain limits of crystal quality, whereas current devices have to precisely match certain criteria, e.g. doping levels. Fourth, the long-term stability is expected to be superior because the applied electric fields in the envisaged quantum standards are well below the discharge field strength whereas state-of-the-art devices work close to or above these fields, which causes avalanches and ageing. Interestingly, such a quantum voltage standard can reference a continuously tuneable voltage.