Software and hardware for improved quantum volume of transmon processors

The quantum volume (arXiv:1811.12926 [quant-ph]) is a single-number metric useful for pragmatic quantification and comparison of performance for NISQ devices. It is affected by the software toolchain as well as the selection and fidelity of available quantum gates. I will discuss improvements on both axes. In particular, we introduced a surprisingly effective circuit rewriting method for approximately decomposing arbitrary target two-qubit SU(4) gates while optimally trading off approximation error against the gate error. Combining this technique with updated hardware achieves the highest quantum volume measured to date.