Temperature Performance of Magnetic Shielding for Multi-Qubit Chip Carrier

Quantum error correction for fault tolerant quantum computing will require dense one- and two-qubit gate sequences with minimal generation of noise and heating effects. Flux-tunable superconducting qubits have recently been implemented in a surface-code-inspired geometry [1], utilizing frequency tuning and short gate operations at the cost of increased flux-bias noise [2]. Overall, microwave and magnetic shielding is considered crucial for achieving high coherence and fidelity in a wide variety of superconducting qubit experiments.

In this work we introduce a magnetic shielding for our multi-qubit chip carrier: QCage.24[3]. The shielding is a fully EMC tight assembly composed of layers of mu-metal and bulk aluminum. Since thermalization of the qubit chip is of the utmost importance to increase coherence times, we show that our solution enables cooling down below 50 mK with a minimal time delay. Optimal heat sinking to the mixing chamber plate is achieved, showing recovery times of about 15 minutes after induced heating is applied. Eventually, no heating effects were observed at the sample mount inside the shielding when inducing magnetic heating in the outer mu-metal shield.

[1] Krinner, S. et al., Nature 605, 669 (2022)

[2] Kjaergaard, M. et al., Annual Review of Condensed Matter Physics 11, 369 (2020)

[3] https://qdevil.com/qcage-microwave-cavity-sample-holder/