Fig. 1: Device layout and photon-assisted quasiparticle generation.
From: Engineering superconducting qubits to reduce quasiparticles and charge noise
a Optical micrograph of a planar-design 6 mm × 6 mm sample chip. The light area indicates the base aluminium layer; the dark area indicates the exposed sapphire substrate. Each qubit (Q1--Q6) has a dedicated charge drive line (straight transmission line) and a dedicated readout resonator (meandering transmission line). The six resonators share a common feed line for a multiplexed readout. b Close-up view of Q1 (blue rectangle in a), showing two aluminium pads (length L and width W) floating inside an aperture. The pad-to-resonator distance is r; the pad-to-ground distance on the other three sides is d; the pad-to-drive-line distance is c; the pad-to-pad distance is q. In the shown case, L = 80 μm, W = 35 μm, r = 23 μm, d = 5 μm, c = 41 μm, q = 10 μm. The qubits shown in a have varying pad-to-ground distances (d = 5 − 30 μm). c Close-up view of the junction area (yellow rectangle in b). Two layers (colour-coded) of aluminium film are deposited on the base layer to form the junction, i.e., the region where the two thin strips (Arm1 and Arm2) overlap. An additional aluminium layer (10 μm × 2 μm rectangular patches) forms the bandage structures that are used to improve the galvanic contact46. The film thicknesses are 100 nm for the pads, 30 nm for Arm1, 40 nm for Arm2, and 200 nm for the bandages. d Schematic of a vertically integrated device with the qubit, resonator and drive line patterned on the bottom die and a square-shaped aluminium pad (purple) on the top die floating above the qubit. The inset on the bottom left shows a cross-sectional view of the device. e Schematic illustrating the quasiparticle processes. Δ0 and Δ are the superconducting energy gaps of the pads and the junction leads, respectively.
