Measurement of Quasiparticle Diffusion in a Superconducting Transmon Qubit

Quasiparticles, especially the ones near the Josephson junctions in the superconducting qubits, are known as an important source of decoherence. By injecting quasiparticles into a quantum chip, we characterized the diffusion feature by measuring the energy relaxation time and the residual excited-state population of a transmon qubit. From the extracted transition rates, we phenomenologically modeled the quasiparticle diffusion in a superconducting circuit that contained hot nonequilibrium quasiparticles in addition to low-energy ones.

Automated summary

Quasiparticles near Josephson junctions in superconducting qubits are known to be a significant source of decoherence. We characterized the diffusion feature of quasiparticles in a quantum chip by measuring the energy relaxation time and residual excited-state population of a transmon qubit. Using the extracted transition rates, we phenomenologically modeled the quasiparticle diffusion in a superconducting circuit that contained both low-energy quasiparticles and hot nonequilibrium quasiparticles.