Time domain measurement of on-chip flux waveforms for superconducting qubits

Implementing high fidelity entangling gates between frequency-tunable superconducting qubits often requires ad hoc optimization of control waveforms on a per-channel basis due to signal path irregularities. To better model these irregularities and more efficiently optimize control waveforms, we have developed a method of directly measuring flux waveforms on-chip using a low Q tunable resonator. This device may be operated in two regimes--one with a high sensitivity to flux, used to characterize DC to ~500 MHz current waveforms, and another which can can provide an estimate of the worst standing wave amplitude in a microwave chain. Through A/B comparisons, this technique provides an avenue for measuring the transfer function of specific signal chain components in a cryogenic environment avoiding both the complication of measuring qubits and the limits of their coherence time.