Qualifying qubit shielding with an ultra-high quality factor superconducting 3D resonator

Excess quasiparticles generated by either thermal or ionizing radiation are a known problem for coherence of superconducting qubits and necessitate advanced radiation shielding inside and around the dilution refrigerator [1,2]. In this talk, we first establish a sensing technique to study sources of excess quasiparticles and then compare varying levels of shielding including infrared-absorbing coatings. Specifically, we use an ultra-high quality (Q > 10^6) superconducting aluminum cavity [3] as a radiation sensor and track the resonance frequency around 4 GHz with a lock-in technique. Our apparatus also includes a free-space thermal radiation source which, weakly thermalized to the 1 K plate, can be heated up to tens of kelvins without affecting the temperature of the sample space and thus allows emulating remote hot spots inside the refrigerator. The method we present demonstrates potential for qualifying shielding for quantum processors and opens doors to study time-dependent effects in superconductors such as two-level systems.



[1] Appl. Phys. Lett. 99, 113507 (2011)

[2] Nature 584, 551–556 (2020)

[3] Appl. Phys. Lett. 117, 070601 (2020)