Fast flux control of 3D transmon qubits using a magnetic hose

An important feature in analog quantum simulation experiments with superconducting qubits [1] is the possibility to change the frequency of SQUID-based transmon qubits by applying magnetic flux. Implementing fast flux control on a transmon remains challenging in the 3D cavity architectures due to the presence of a massive metallic cavity. Here we introduce a new approach for fast flux control on 3D transmon qubits. We use a magnetic hose similar to the one proposed by C. Navau et al. [2] to guide a fast flux pulse from the outside to the inside of a microwave cavity. This hose enables us to locally circumvent any magnetic shielding effects such as the appearance of eddy currents in cavities made out of copper or the Meissner effect in superconducting cavities made out of aluminum. First experiments show that the transition frequency of a transmon can be tuned in less than 100 nanoseconds. Besides the high speed, the frequency shift is precise, without showing any ringing or hysteresis. Using a magnetic hose with an aluminum cavity preserves the benefits of a superconducting cavity, like providing magnetic field shielding and a high internal quality factor, along with the possibility to fast-tune individual qubits.
[1] PRL, 112, 253901 (2014)
[2] PRB, 174507 (2015)