The HDIQ is designed for superconducting qubit experiments. The high-quality IQ mixers of the HDIQ allow users to minimize LO leakage and suppress the image sideband. The amplifiers and filters of the HDIQ ensure a reasonable output power with strong suppression of higher-order harmonics and spurs, thus enabling fast and high-fidelity gate operation. Two examples of applications for 4-qubit systems are qubit experiments and mixer calibration, as shown in Figure 1.
To generate the qubit driving pulses, an external LO source and an HDAWG are required. The in-phase (I) and quadrature (Q) input signals come from the HDAWG and the LO input signal is taken from an external microwave source. In default mode, i.e., with both RF switches in logic "low", the RF output signal from the HDIQ Exp. port goes to the physical system for qubit manipulation.
For qubit spectroscopy, wide frequency and amplitude scans are often required. This can be achieved by operating the HDIQ in LO output mode without any cable reconnections.
For qubit readout, the HDIQ can be used for readout pulse generation with the UHFQA Quantum Analyzer and an external LO source. An external RF switch can be used to switch between readout signal analysis and mixer calibration without any additional cabling work.
LO leakage and image sideband suppression of IQ mixers are both frequency-dependent, and any non-negligible LO leakage and image sideband may cause off-resonant and unwanted excitations. To eliminate this effect, all IQ mixers have to be calibrated.
The mixers can be calibrated by measuring the Calib. output signal of the HDIQ in calibration mode with the UHFQA FFT function while scanning the pulse parameters of I and Q signals generated by the HDAWG. Reference Python code for mixer calibration of a single HDIQ and multiple HDIQs using the HDAWG and UHFQA is available upon request by writing to [email protected].