Experiments on the influence of infrared photons on superconducting qubits

Superconducting circuits are used in a wide range of ultra-low noise applications. Exceptionally low excitations are observed when operated well below the superconducting gap, e.g. at millikelvin temperatures for aluminium based circuits. Even under such conditions, however, pair-breaking excitations are still observed, caused by numerous processes as for instance the absorption of high energy particles from residual radioactivity, or by stray infrared radiation. The latter poses a substantial problem for quantum circuits, since these circuits are conventionally addressed by microwave photons, employing coaxial cables. Here, the dielectric insulator, usually PTFE, is an excellent pathway for the infrared photons originating from elevated temperature stages to the superconductor. One possible solution to this problem is the insertion of a low pass filter with an efficient block for infrared photons and a low loss transmission for microwave signals.
In this contribution we present an experimental setup to test the influence of infrared radiation on superconducting qubits. We discuss the relevant qubit performance quantities in response to a varying incident photon flux and investigate promising infrared filters materials to protect superconducting circuits.