(Color online) (a) Layout of a basic dc-SQUID, referred to as “device A,” used for measuring the mutual inductance between two superconducting strip lines (Nb2 and Nb4) with a shield layer (Nb3). A superconducting ground plane (Nb1) lies beneath the device. The shield layer (Nb3) is electrically floating. The Josephson junctions are shunted by external resistors and grounded through the ground contacts (GCs). (b) Cross-sectional schematic view of a FASTHENRY model along the A–A′ line section. All layers are assumed to be flat.
(Color online) Layouts of three devices with different grounding positions. The dimensions of the contact holes are designed to be and for the Nb1–Nb2 and Nb2–Nb3 contacts, respectively. Virtual contact pillars with cross sections of are used for the FASTHENRY models (see Fig. 3). (a) One ground contact at the center of the lower side of the shield layer (device B). (b) Two ground contacts located perpendicular to the strip lines (device C). (c) Two ground contacts located parallel to the strip lines (device D).
(Color online) Cross-sectional views of grounding structures. (a) A virtual contact pillar is employed in the FASTHENRY models. (b) The shield layer (Nb3) is contacted to the ground plane (Nb1) via the Nb2 layer in a real device.
(Color online) Current distributions in the shielding layer (Nb3) mapped in arbitrary unit. The shield layer is divided by . (a) Current in the direction for device A. (b) Current in the direction for device A. (c) Current in the direction for device D. (d) Current in the direction for device D.
Experimental and numerical results of the mutual inductance for devices A–D. Numerical results for the self-inductances and the coupling coefficient are also listed.
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