Multiple junction biasing of superconducting tunnel junction detectors
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Circuit schematic for magnetic-field free detector biasing. The X’s represent junctions. Applied current splits between the two branches; the same current flows through junctions 2 and 3. The pulse amplifier is shown AC coupled to junction 3. Photon-excited quasiparticles can be read out through junctions 2, 3, or both.
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(a) Hysteretic dynamics for the circuit shown in Fig. 1. is plotted against the voltage for junctions 1 (dotted line), 2, and 3 (both solid lines). is initially increased until the three junctions switch to nonzero voltage; then the current is decreased. At the bias current, junctions 2 and 3 are in the subgap region where they can function as photon detectors; here nearly all the current is flowing through junction 1. (b) I-V curves showing the subgap current for junctions 2 and 3. is plotted versus , solid line, and () dotted line. The two lower curves are for a temperature () and the two upper curves are for (). At the lower temperature, the intersection of the two curves gives the operating point. The heat from a photon coupled to both junctions causes the system to move from A to B, straight up. Heat only coupled to one of the junctions causes it to move to the left.
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