Microscopic Origin of Excess Quasiparticles in Superconducting Detectors

Determine the microscopic origin of the residual excess quasiparticle population that limits the resolution of superconducting pair-breaking detectors, including kinetic-inductance devices and superconducting qubits.

Background

Residual quasiparticles generate excess generation–recombination noise in kinetic-inductance devices and background tunneling events in superconducting qubits. Their density remains above the equilibrium BCS prediction even in well-isolated cryogenic systems, and candidate sources include readout power, blackbody radiation, ionizing radiation, low-energy excess events, and disorder-induced fluctuations of the superconducting gap.

The paper notes that the relative contributions of these mechanisms are not settled. Identifying the microscopic origin of the excess quasiparticles is important because dark-matter signals must exceed the associated parasitic excitation background to be detectable.