See also

A Jupyter notebook version of this tutorial can be downloaded here.

Resonator Spectroscopy

In a resonator spectroscopy experiment, we sweep the frequency of a microwave tone applied to the readout line. When the drive tone frequency matches the resonator’s resonance frequency, a change in the amplitude and/or phase of the reflected signal is observed.

from qblox_applications.qblox_scheduler.analysis import ResonatorSpectroscopyAnalysis
from qblox_applications.qblox_scheduler.superconducting.transmon import (
    BasicTransmonElement,  # noqa: F401
)
from xarray import open_dataset

from qblox_scheduler import DType, HardwareAgent, IdlePulse, Measure, Schedule, arange, linspace

Setup

The hardware agent manages the connection to the instrument and ensures that pulses and acquisitions happen over the appropriate input and output channels of the Cluster. The cell below creates an instance of the HardwareAgent based on the hardware- and device-under-test configuration files in the ./dependencies/configs folder, allowing us to start doing measurements. We also define some convenient aliases to use throughout our measurements. For a more thorough discussion of the hardware- and device-under-test configuration files, check out this tutorial.

# Set up hardware agent, this automatically connects to the instrument
hw_agent = HardwareAgent(
    hardware_configuration="./dependencies/configs/hw_config.json",
    quantum_device_configuration="./dependencies/configs/dut_config.json",
)

# convenience aliases
q0 = hw_agent.quantum_device.get_element("q0")  # Qubits 0 and 2 are measured using QRM-RF + QCM-RF
q2 = hw_agent.quantum_device.get_element("q2")
q3 = hw_agent.quantum_device.get_element("q3")  # Qubit 3 is measured using QRC

cluster = hw_agent.get_clusters()["cluster"]
hw_options = hw_agent.hardware_configuration.hardware_options
qubit = q0

/.venv/lib/python3.14/site-packages/qblox_scheduler/qblox/hardware_agent.py:603: UserWarning: cluster: Trying to instantiate cluster with ip 'None'.Creating a dummy cluster.
  warnings.warn(

Experiment settings

# Frequency settings
frequency_center = qubit.clock_freqs.readout  # Hz
frequency_width = 5e6  # Hz
frequency_npoints = 300

repetitions = 1000

Experiment schedule

spec_sched = Schedule("resonator_spectroscopy")
with (
    spec_sched.loop(arange(0, repetitions, 1, DType.NUMBER)),
    spec_sched.loop(
        linspace(
            start=frequency_center - frequency_width / 2,
            stop=frequency_center + frequency_width / 2,
            num=frequency_npoints,
            dtype=DType.FREQUENCY,
        )
    ) as freq,
):
    spec_sched.add(Measure(qubit.name, freq=freq, coords={"frequency": freq}, acq_label="S_21"))
    spec_sched.add(IdlePulse(10e-6))  # Let the resonator decay

# Execute the experiment
rs_data = hw_agent.run(spec_sched)
if cluster.is_dummy:
    example_data = open_dataset(
        "./dependencies/datasets/resonator_spectroscopy.hdf5", engine="h5netcdf"
    )
    rs_data.update({"S_21": example_data.S_21})

Analyze the experiment

resspec_analysis = ResonatorSpectroscopyAnalysis(rs_data).run()
resspec_analysis.display_figs_mpl()

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Post-run

# Update device config
qubit.clock_freqs.readout = resspec_analysis.quantities_of_interest["fr"].nominal_value

Update the device configuration file

After measurement, we may store the measured device properties inside a new file to use in future experiments. The time-unique identifier ensures that it is easy to find back previously found measurement results.

hw_agent.quantum_device.to_json_file("./dependencies/configs", add_timestamp=True)

'./dependencies/configs/two_flux_tunable_transmons_2026-10-15_13-58-44_UTC.json'