Design and characterization of a light-tight, compact magnetic shield for superconducting qubits

A light-tight magnetic shield is essential for protecting superconducting circuits, as these devices are extremely sensitive to external magnetic fields and stray electromagnetic radiation. Even minimal magnetic flux or light leakage can break Cooper pairs, induce quasiparticles, and introduce noise or decoherence, significantly degrading circuit performance. Designing a shield that combines high magnetic permeability with opacity at microwave, optical, and infrared frequencies allows for the suppression of ambient magnetic fields while preventing photon-induced excitations, ensuring stable superconducting operation. The characterization of such a shield by measuring its magnetic field attenuation, light leakage, and thermal compatibility at cryogenic temperatures, is fundamental to verify that it meets the strict requirements for superconducting circuit experiments.