Kalman-based IQ Mixer Calibration for Circuit QED

Quantum measurements with superconducting circuits require the generation and detection of signal frequencies in the 2 - 12 GHz range, where frequency conversion is performed by analog devices known as IQ mixers. These mixers generate unwanted image signals upon upconversion, which crowd the already limited frequency spectrum, and become superimposed with the desired signal upon downconversion. Image signals are particularly problematic for frequency-multiplexed qubits [1] as they are a possible source of dephasing when accidentally driving another qubit. These detrimental effects can be minimized by calibrating the IQ mixers.

In this talk we present some simple but elegant methods which do not require a spectrum analyzer, to calibrate both up and downconversion mixers in situ (i.e. without disconnecting the device under test). The downconversion mixer is calibrated with a Kalman filter, providing a minimally distorted estimate of the image-to-signal power ratio. This ratio is then used to calibrate the up-conversion mixer. These techniques, originally developed for wide-band digital communication [2], are well suited for frequency-multiplexed experiments in circuit QED.

[1] Johannes Heinsoo et. al., Phys. Rev. Applied (2018).
[2] Marcus Windisch, PhD thesis, TU Dresden (2007).