Expérimental et théorique
While commercial dilution refrigerators offer a base plate at less than 10 mK, thermalizing the microwave modes themselves turns out to be more challenging than just anchoring the superconducting circuit to the plate. Effectively, superconducting qubits are coupled to a heat bath that is often in the 50-100 mK range, which drastically downgrades their coherence time. A key element to getting lower effective temperatures is the microwave attenuator that is the closest to the quantum circuit. Recent progress has been made by a couple of companies using conductive casing (gold coated copper) instead of stainless steel. However, the dissipative elements are thin films that are not able to evacuate Joule power (up to about 100 nW) well enough into the dilution refrigerator. This is particularly detrimental for quantum error correction or amplification, which both require strong microwave drives. The project consists of removing this current bottleneck by designing, fabricating, and testing better attenuators for superconducting quantum circuits.