Resonator Spectroscopy as a function of the coupler current

The qubit spectroscopy as a function of the coupler current is one of the initial steps in characterizing a coupler and preparing for two-qubit gate implementation. This spectroscopy is conducted by varying the current applied to the coupler and measuring the resonator response at each current value. The result is a two-dimensional map typically showing regions with a “U” or \(\bigcap\) shape when analyzing the minimum values of the resonator spectroscopies. These shapes indicate changes in coupling and are key to identifying crossing points between the resonator and the coupler.

Measurement class: ResonatorSpectroscopyMeasurement

Desctibed in resonator spectroscopy.

Analysis classes:

The ResonatorSpectroscopyVsCurrentNodeAnalysis class handles the analysis of all selected couplers and manages the associated plots. In addition to the preview plot that is displayed at run time, the analysis saves a file for each qubit containing all the resonator spectroscopies for debugging purposes.

The ResonatorSpectroscopyVsCurrentCouplerAnalysis combines the results of the two qubits in a coupler and the saving of the QOI so that the information of the crossing points is saved per qubit per coupler as described in the base class documentation.

The ResonatorSpectroscopyVsCurrentQubitAnalysis performs the analysis of a qubit combining the results of all resonator spectroscopy measurements looking primarely for the crossing points, i.e. the values of the currents at which there is a change of region from U to \(\bigcap\); these are the point at which the coupler cross the resonator frequency and can be used to study the properties of the coupler. The main function used is find_crossing_currents, which: * Cleans the data by removing isolated zeros (representing missing or invalid data) and outliers. * Scans the data from left to right, comparing consecutive non-zero values to detect transitions based on a predefined threshold. * Groups transitions occurring within a minimum range to mitigate the effect of noise or spurious detections. * Determines the crossing point as the average position within each grouped transition region.

In cases where the resonator frequency is high and no “U” shape appears—resulting instead in two connected \(\bigcap\) regions—the transition point is inferred from where the two regions meet. The current thresholds and interval ranges are optimized for a current step size of 50uA.

Each individual resonator spectroscopy is performed by the standard ResonatorSpectroscopyQubitAnalysis class described in the resonator spectroscopy node.