This work discusses a new kind of wideband, low-temperature superconducting (LTS) filter with multiple finite transmission zeros (TZs). The filters are carried out by using a novel matrix synthesis approach, which can specify a simple and deterministic prototype with coupling pathways and circuit parameters obtained simultaneously to achieve the required filter responses. The prototype is then mapped to lumped inductors and capacitors that are appropriately connected by using a 4-metal layer LTS Niobium process. With an enhancement of out-band attenuation (thanks to the finite TZs), the filter is then implemented with superconducting rapid single-flux-quantum (RSFQ) logics for generating narrow-line-width microwave pulses for qubit control applications. Here, the wideband filter plays an important role in converting SFQ pulse trains (generated by RSFQ digital gates) and output a microwave control pulse. It is shown that the wide bandwidth contributes to a rapid ramp-up time of the generated microwave pulse (to facilitate the quick setup for controlling a qubit), while the attenuation TZs prevent considerable interferences from undesired out-of-band frequencies.
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This work was supported in part by National Natural Science Foundation of China (62101466), Sichuan Science and Technology Program (2022ZYD0119, 2022JDTD0013), the “111” Plan (B18045), and the Fundamental Research Funds for the Central Universities (2682022CX019).