Superconducting qubit control using cryogenic frequency conversion

Expanding to higher qubit frequencies introduces the challenge of routing >20 GHz signals into a dilution refrigerator without adding excess thermal load or frequency-dependent loss. In this work, we demonstrate a solution to this problem by using a frequency multiplier to drive the qubit with room-temperature control pulses at half or one third of the qubit frequency fQB. The control pulses are up-converted inside the cryogenic environment using a frequency multiplier based on a high-kinetic inductance nonlinear transmission line. We evaluated the success of the upconversion technique by comparing the randomized benchmarking error-per-gate metrics to that of a standard direct qubit driving technique. The fQB/2 drive technique achieved error rates consistent with the direct drive, with a minimum error per gate of 3.5×10−3 ± 0.4×10−3. The fQB/3 drive technique resulted in a minimum error per gate of 7.6×10−3 ± 0.81×10−3. While this demonstration is based around a fQB=4.836 GHz qubit so that a direct drive comparison is possible, this technique will allow higher-frequency qubits to be tested using existing radio frequency infrastructure.