Optimal Configurations for Normal-Metal Traps in Transmon Qubits

Abstract

In quantum information processing, long qubit coherence times are crucial. In a superconducting qubit, quasiparticles set fundamental limits on coherence, and are generated not just predictably in the course of operation, but also sporadically by unknown sources. While prevent their random appearance is difficult, their number may be controlled and adverse effects mitigated by incorporating normal-metal islands (traps) into the qubit. For the technologically important transmon configuration, the authors provide strategies to optimize such traps by varying their number, size, and location, to evacuate quasiparticles rapidly, and suppress population fluctuations.