Improving the fidelity of entangling gates via in situ characterization of qubit control lines.

One of the factors limiting the fidelity of entangling gates are control signal distortions arising from non-trivial transfer functions of microwave lines. Distortions can be canceled, in principle, if the complex transfer function of the control line is known, by applying its inverse to the signal before it is transmitted. We have previously developed a method for in-situ measurement of the system function using a qubit as a network vector analyser [1]. I will present the refinement of the method and its experimental application to improve the fidelity of CPHASE gate between two superconducting transmon qutrits. I will also show how our technique can be combined with other recently reported in-situ methods to calibrate low-frequency response of control lines [2,3] to further enhance the fidelity of the two-qubit gates.

[1] M. Jerger et al., arXiv:1706.05829
[2] M. A. Rol K39.00005, APS March Meeting 2018