  As quantum computing hardware becomes more complex with ongoing design
innovations and growing capabilities, the quantum computing community needs
increasingly powerful techniques for fabrication failure root-cause analysis.
This is especially true for trapped-ion quantum computing. As trapped-ion
quantum computing aims to scale to thousands of ions, the electrode numbers are
growing to several hundred with likely integrated-photonic components also
adding to the electrical and fabrication complexity, making faults even harder
to locate. In this work, we used a high-resolution quantum magnetic imaging
technique, based on nitrogen-vacancy (NV) centers in diamond, to investigate
short-circuit faults in an ion trap chip. We imaged currents from these
short-circuit faults to ground and compared to intentionally-created faults,
finding that the root-cause of the faults was failures in the on-chip trench
capacitors. This work, where we exploited the performance advantages of a
quantum magnetic sensing technique to troubleshoot a piece of quantum computing
hardware, is a unique example of the evolving synergy between emerging quantum
technologies to achieve capabilities that were previously inaccessible.
