Experiments on the Influence of Infrared Photons on Superconducting Qubits

The energy gap of superconductors allows for a large variety of ultra-low noise applications, as for instance, for using them to construct qubits. At sufficiently low temperatures, the number of excitations above the gap is generally low but not zero. Such excitations can be created by numerous external influences, including absorption of high energy particles from radioactive decay or extraterrestrial space. Also stray infrared photons play a role, since their energy is larger than the energy gap of conventional superconductors used for making qubit. One external leakage pathway is the dielectric of a coaxial cable used to manipulate and read out the qubit which connects to room temperature electronics. Here, the combination of the dielectric’s transparency to infrared photons and the high infrared photon flux from elevated cryogenic temperature stages make the insertion of a low-pass filter with a sharp cutoff well below the superconducting gap frequency an important requirement.
In this contribution, we present experimental investigation of the influence of infrared photons on superconducting qubits. We have measured the dephasing and decay times as well as the qubit temperature in response to incident photon flux. ... mehrWe explore usage of various materials for making infrared filters.