Travelling-wave Parametric Amplifier Induced Qubit Dephasing: Analysis and Mitigation

The mitigation of dephasing poses a significant challenge in improving the performance of error-prone superconducting quantum computing systems. Here, we investigate the dephasing of a transmon qubit in a dispersive readout regime using a Josephson travelling-wave parametric amplifier as the preamplifier. Our findings reveal that the potent pump leakage from the preamplifier may lead to severe dephasing. This issue could be attributed to a mixture of measurement-induced dephasing, ac Stark effect, and heating. We show that pulse-mode readout is a promising measurement scheme to mitigate qubit dephasing while minimizing the need for bulky circulators. Our work provides key insights into mitigating decoherence from microwave-pumped preamplifiers, which will be critical for advancing large-scale quantum computers.