Magnetic flux imaging in a 3D superconductor integrated circuit

We present the first direct visualization of magnetic flux maps in a superconductor quantum circuit composed of 8 layers with distinct lithographic patterns of superconducting elements. Using high-sensitivity magneto-optical imaging, we observe the flux penetration, concentration, and trapping in complicated 3D assembly of niobium film microstructures in an external fields. The emerging intricate flux distributions reflect not only the induction modulations in the topmost layer but also contributions from the buried superconducting layers. These patterns can be interpreted as arising from meandering Meissner screening currents and flux occupied regions in different components of the circuit. Our observations reveal specific role of shape and mutual position of the circuit elements in the field screening and flux trapping, which may help in the future designs of multilayer superconducting circuits.