Qubit as a reflectometer

Microwave pulse distortion due to signal reflections is a major source of gate errors in superconducting qubits. We extend previous pulse-sequence techniques to characterize both in-phase and quadrature components of such reflections [1]. Through analytical modeling of the sequences, we identify that microwave reflections with a relatively long round trip time lead to a long tail of the microwave pulse causing gate error. We then demonstrate that by pre-distorting the waveforms to compensate for the reflection-induced tail, we significantly reduce the coherent error of single qubit gates. Our characterization method is general and can be applied to other types of signal distortion.

[1] Gustavsson et al., Phys. Rev. Lett. 110, 040502 (2013)