Environment optimization for a fast turnaround system to characterize superconducting qubits

A superconducting qubit, such as a transmon, is sensitive to the energy loss coming from the fabrication processes. To achieve a high-quality superconducting qubit, one may conduct a careful check in every step. However, obtaining detailed information about a superconducting qubit is usually a process that takes a week, which delays the iteration of the qubit's characterization. A fast and reliable system is essential for iterative device development and fabrication feedback. A bottom-loading system provides a fast turnaround possibility. However, it is often considered inadequate for a superconducting qubit due to perceived shortcomings in limited space and shielding performance. In this work, we demonstrate that a bottom-loading dilution refrigerator equipped with an optimized IR shielding architecture can serve as a competitive and efficient platform for qubit evaluation. The shielding configuration employs multiple layers of copper, aluminum, and mu-metal to suppress magnetic vortex-related losses. Infrared filtering is applied to block leakage from the coaxial lines, and the inner surface of the copper enclosure is coated with an infrared-absorbing compound to suppress residual radiation, including unintended emission from surrounding materials. We compared the effect of the IR coating shielding. The shielding architecture enables an effective temperature of approximately 20 mK, which is 10 mK lower than before coating. Moreover, we show an improved quasiparticle parity switching rate of about 140 s$^{-1}$ from 1000 s$^{-1}$. while supporting a long relaxation time of up to 319 $\mu$s. A key advantage of the system is its rapid turnaround capability, enabling the measurement of two chips per day on average. Our results indicate that a bottom-loading system is viable and advantageous for fast qubit quality screening, offering a practical alternative to conventional dilution refrigerator setups, particularly in the early-stage validation of superconducting qubit designs.