Magnetic shield integration for a chip-scale atomic clock

We introduce a miniaturized magnetic shield integrated into the physics package of a chip-scale atomic clock. The primary shield, which is formed by a stack of precision-machined high-permeability plates, compactly sits inside the package as it is designed to be the internal supporting frame. Further improved by a Kovar lid, the best frequency sensitivity to a longitudinal external field is 1.1(3) × 10−11/μT, which is consistent with the measured shielding factor, while the transverse sensitivity is well below 10−12/μT. The sealed unit on a chip carrier alone allows stable clock operation with a frequency instability of 4.8(2) × 10−12 at 1000 s.