  Solid-state quantum coherent devices are quickly progressing. Superconducting
circuits, for instance, have already been used to demonstrate prototype quantum
processors comprising a few tens of quantum bits. This development also
revealed that a major part of decoherence and energy loss in such devices
originates from a bath of parasitic material defects. However, neither the
microscopic structure of defects nor the mechanisms by which they emerge during
sample fabrication are understood. Here, we present a technique to obtain
information on locations of defects relative to the thin film edge of the qubit
circuit. Resonance frequencies of defects are tuned by exposing the qubit
sample to electric fields generated by electrodes surrounding the chip. By
determining the defect's coupling strength to each electrode and comparing it
to a simulation of the field distribution, we obtain the probability at which
location and at which interface the defect resides. This method is applicable
to already existing samples of various qubit types, without further on-chip
design changes. It provides a valuable tool for improving the material quality
and nano-fabrication procedures towards more coherent quantum circuits.
