Qubit and Resonator Spectroscopy at the Speed Limit: Your Measurements. Faster.

June 23, 2022 by Mark Kasperczyk
Qubit Spectroscopy

Figure 1: Representative resonator and qubit spectroscopy measurements, performed with the fast frequency sweeping feature of the SHFQC Qubit Controller.

Getting your measurements up and running as fast as possible is a priority at Zurich Instruments. Together with one of our Application Scientists, researchers at the ETH Zurich - Paul Scherrer Institute (PSI) Quantum Computing Hub were able to install the SHFQC Qubit Controller and perform qubit spectroscopy, Ramsey, and Rabi measurements on 5 qubits in parallel in half a day.

The ability of our instruments to perform fast frequency sweeping was at the heart of the fast qubit tune-up procedures. In the superconducting qubit community, qubit and resonator spectroscopy measurements are typically performed by sweeping the frequency of the signal applied to either the qubit or the readout resonator and measuring the signal transmitted through the readout resonator. The figure above shows an example of a resonator spectroscopy measurement on the left, in which 5 resonators are visible in the sweep. On the right is an example of a typical single qubit spectroscopy measurement. Researchers working with other types of qubits perform their own versions of qubit spectroscopy: in the NV center community, for example, qubit frequencies are measured through optically detected magnetic resonance by monitoring the optical fluorescence signal of the NV center while sweeping the microwave drive frequency.

For many instruments, updating the frequency during a sweep requires communication between the instrument and the host computer for each point of a frequency sweep, leading to slow measurements due to the communication overhead. Thanks to new sequencer commands on our SHFSG Signal Generator, SHFQA Quantum Analyzer, and SHFQC Qubit Controller, a full sweep of the offset frequency can be programmed directly on the instrument. This allows users to perform resonator and qubit spectroscopy measurements with minimal communication overhead, greatly accelerating qubit characterization.

In a typical continuous wave qubit spectroscopy experiment, a sweep could span over 1000 frequency points with 20ms of integration time at each point. This would correspond to a minimum measurement time of 20s. In reality, the measurement at PSI took 20.5s, corresponding to a measurement duty cycle of 97.5%. And this measurement was done in parallel on 5 qubits! Reducing communication overhead and parallelizing measurements are just two examples of how we help our customers perform their measurements faster- and these factors become even more important as researchers scale to larger numbers of qubits.

To make use of this feature yourself, you can start from a selection of Python examples. The ShfSweeper class of the ziPython API supports hardware sweeping for resonator spectroscopy. Its usage is documented in the tutorials section of the SHFQC and of the SHFQA User Manuals. To implement qubit spectroscopy, have a look at the application-specific examples of the zhinst-toolkit package.