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(Color online) The quality factors of four halfwave coplanar waveguide Al resonators versus sample stage temperature, measured in a setup without effort to shield stray infrared light (open symbols) and with an improved light-tight sample stage (closed symbols). Right axis shows the corresponding quasiparticle density n qp. Resonance frequencies lie between 3.8 and 4.5 GHz. Eq. (1) is plotted for an exponentially decreasing quasiparticle density (dashed line), excess quasiparticle density of 230 μm−3 (bottom solid line) and 10 μm−3 (top solid line). Kinetic inductance fraction α = 0.28 for these devices (Ref. 14). Inset shows a halfwave resonator capacitively coupled to a feedline.
(Color online) Schematic representation of the light-tight sample stage: the sample box is mounted inside a larger box on the 50 mK stage, closed off by an outer can. The inner surfaces of the sample box lid and outer can are coated with a blackbody absorber (blue). Coaxial readout lines are filtered using 50 Ω matched metal powder filters (green). The entire sample stage lies within a magnetic shield (grey), attached to the cryostat’s 4 K stage. The radiator is used for Fig. 4.
(Color online) The loss of an Al resonator versus cryostat temperature, showing the influence of different shielding techniques when going from no infrared shielding (▪) to fully shielded (★). Right axis shows the corresponding quasiparticle density. The sample stage temperature is kept below 150 mK. Variations in the presence of a coated sample box lid and coax filters (closed symbols, red colors): no can present (•), sample box covered with Al tape (▴) and uncoated can present (▾). Variations in the presence of a coated outer can (open symbols, purple and blue colors): coated can floating on 0.5 mm spacers (⋄), uncoated sample box lid and no coax filters (⬠), uncoated lid and filters (◃), coated lid and no filters (▹). Influence of a hot blackbody (solid), hot blackbody filtered with a cut-off frequency at 1 THz (dashed), filtered with a cut-off frequency at 100 GHz (dotted), and no dependence (dash dotted).
(Color online) Phase qubit energy relaxation rate measured in the light-tight setup versus cryostat temperature (★) and measured without the presence of a coated outer can versus temperature of a radiator (▪) (see Fig.2). The sample stage temperature is kept below 150 mK.
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