Qubit Flux Spectroscopy#

For flux tunable qubits, the resonance frequency of the qubit depends on the flux. This can be used to find the sweetspot.

[1]:

from __future__ import annotations

import json

import numpy as np
import rich  # noqa:F401
from qcodes.instrument import find_or_create_instrument
from qcodes.parameters import ManualParameter

import quantify_core.data.handling as dh
from qblox_instruments import Cluster, ClusterType
from quantify_core.measurement.control import MeasurementControl
from quantify_core.visualization.pyqt_plotmon import PlotMonitor_pyqt as PlotMonitor
from quantify_scheduler import Schedule
from quantify_scheduler.device_under_test.quantum_device import QuantumDevice
from quantify_scheduler.gettables import ScheduleGettable
from quantify_scheduler.instrument_coordinator import InstrumentCoordinator
from quantify_scheduler.instrument_coordinator.components.qblox import (
    ClusterComponent,
)
from quantify_scheduler.operations.gate_library import Measure, Reset, X

Setup#

In this section we configure the hardware configuration which specifies the connectivity of our system.

The experiments of this tutorial are meant to be executed with a Qblox Cluster controlling a transmon system. The experiments can also be executed using a dummy Qblox device that is created via an instance of the Cluster class, and is initialized with a dummy configuration. When using a dummy device, the analysis will not work because the experiments will return np.nan values.

Configuration file#

This is a template hardware configuration file for a 2-qubit system with a flux-control line which can be used to tune the qubit frequency. We will only work with qubit 0.

The hardware setup is as follows, by cluster slot: - QCM (Slot 2) - Flux line for q0. - QCM-RF (Slot 6) - Drive line for q0 using fixed 80 MHz IF. - QRM-RF (Slot 8) - Readout line for q0 using a fixed LO set at 7.5 GHz.

Note that in the hardware configuration below the mixers are uncorrected, but for high fidelity experiments this should also be done for all the modules.

[2]:

with open("configs/tuning_transmon_coupled_pair_hardware_config.json") as hw_cfg_json_file:
    hardware_cfg = json.load(hw_cfg_json_file)

# Enter your own dataset directory here!
dh.set_datadir(dh.default_datadir())

Data will be saved in:
/root/quantify-data

Scan For Clusters#

We scan for the available devices connected via ethernet using the Plug & Play functionality of the Qblox Instruments package (see Plug & Play for more info).

[3]:

!qblox-pnp list

No devices found

[4]:

cluster_ip = None  # To run this tutorial on hardware, fill in the IP address of the cluster here
cluster_name = "cluster0"

Connect to Cluster#

We now make a connection with the Cluster.

[5]:

cluster = find_or_create_instrument(
    Cluster,
    recreate=True,
    name=cluster_name,
    identifier=cluster_ip,
    dummy_cfg=(
        {
            2: ClusterType.CLUSTER_QCM,
            4: ClusterType.CLUSTER_QRM,
            6: ClusterType.CLUSTER_QCM_RF,
            8: ClusterType.CLUSTER_QRM_RF,
        }
        if cluster_ip is None
        else None
    ),
)

Quantum device settings#

Here we initialize our QuantumDevice and our qubit parameters, checkout this tutorial for further details.

In short, a QuantumDevice contains device elements where we save our found parameters. Here we are loading a template for 2 qubits, but we will only use qubit 0.

[6]:

quantum_device = QuantumDevice.from_json_file("devices/transmon_device_2q.json")
qubit = quantum_device.get_element("q0")
quantum_device.hardware_config(hardware_cfg)

Configure measurement control loop#

We will use a MeasurementControl object for data acquisition as well as an InstrumentCoordinator for controlling the instruments in our setup.

The PlotMonitor is used for live plotting.

All of these are then associated with the QuantumDevice.

[7]:

def configure_measurement_control_loop(
    device: QuantumDevice, cluster: Cluster, live_plotting: bool = False
) -> tuple[MeasurementControl, InstrumentCoordinator]:
    meas_ctrl = find_or_create_instrument(MeasurementControl, recreate=True, name="meas_ctrl")
    ic = find_or_create_instrument(InstrumentCoordinator, recreate=True, name="ic")

    # Add cluster to instrument coordinator
    ic_cluster = ClusterComponent(cluster)
    ic.add_component(ic_cluster)

    if live_plotting:
        # Associate plot monitor with measurement controller
        plotmon = find_or_create_instrument(PlotMonitor, recreate=False, name="PlotMonitor")
        meas_ctrl.instr_plotmon(plotmon.name)

    # Associate measurement controller and instrument coordinator with the quantum device
    device.instr_measurement_control(meas_ctrl.name)
    device.instr_instrument_coordinator(ic.name)

    return (meas_ctrl, ic)


meas_ctrl, instrument_coordinator = configure_measurement_control_loop(quantum_device, cluster)

Configure external flux control#

In the case of flux-tunable transmon qubits, we need to have some way of controlling the external flux. This can be done by setting an output bias on a module of the cluster which is then connected to the flux line. If your system is not using flux-tunable transmons, then you can skip to the next section.

[8]:

flux_settable: callable = cluster.module2.out0_offset
flux_settable.inter_delay = 100e-9  # Delay time in seconds between consecutive set operations.
flux_settable.step = 0.3e-3  # Stepsize in V that this Parameter uses during set operation.
flux_settable()  # Get before setting to avoid jumps.
flux_settable(0.0)

Qubit Flux Spectroscopy#

[9]:

def two_tone_spec_sched_nco(
    qubit,  # noqa: ANN001
    spec_pulse_frequencies: np.array,
    repetitions: int = 1,
) -> Schedule:
    """
    Generate a batched schedule for performing fast two-tone spectroscopy.

    Using the X gate to perform the frequency sweep on the qubit.

    Parameters
    ----------
    qubit
        qubit that should be used.
    spec_pulse_frequencies
        Sample frequencies for the spectroscopy pulse in Hertz.
    repetitions
        The amount of times the Schedule will be repeated.

    """
    sched = Schedule("two-tone", repetitions)

    for acq_idx, spec_pulse_freq in enumerate(spec_pulse_frequencies):
        sched.add(Reset(qubit.name))
        sched.add(X(qubit.name, freq=spec_pulse_freq))
        sched.add(Measure(qubit.name, acq_index=acq_idx), rel_time=200e-9)
    return sched


freqs = ManualParameter(name="freq", unit="Hz", label="Frequency")
freqs.batched = True

qubit_spec_sched_kwargs = dict(
    qubit=qubit,
    spec_pulse_frequencies=freqs,
)

gettable = ScheduleGettable(
    quantum_device,
    schedule_function=two_tone_spec_sched_nco,
    schedule_kwargs=qubit_spec_sched_kwargs,
    real_imag=False,
    batched=True,
)

meas_ctrl.gettables(gettable)

[10]:

quantum_device.cfg_sched_repetitions(400)
center = qubit.clock_freqs.f01()
frequency_setpoints = np.linspace(center - 20e6, center + 20e6, 300)
flux_setpoints = np.linspace(0, 1, 3)
meas_ctrl.settables([freqs, flux_settable])
meas_ctrl.setpoints_grid((frequency_setpoints, flux_setpoints))

qfs_ds = meas_ctrl.run("flux two-tone")
qfs_ds

Starting batched measurement...
Iterative settable(s) [outer loop(s)]:
         out0_offset
Batched settable(s):
         freq
Batch size limit: 900

/usr/local/lib/python3.9/site-packages/quantify_scheduler/backends/types/qblox.py:1220: ValidationWarning: Setting `auto_lo_cal=on_lo_interm_freq_change` will overwrite settings `dc_offset_i=0.0` and `dc_offset_q=0.0`. To suppress this warning, do not set either `dc_offset_i` or `dc_offset_q` for this port-clock.
  warnings.warn(
/usr/local/lib/python3.9/site-packages/quantify_scheduler/backends/types/qblox.py:1235: ValidationWarning: Setting `auto_sideband_cal=on_interm_freq_change` will overwrite settings `amp_ratio=1.0` and `phase_error=0.0`. To suppress this warning, do not set either `amp_ratio` or `phase_error` for this port-clock.
  warnings.warn(

/usr/local/lib/python3.9/site-packages/quantify_scheduler/backends/types/qblox.py:1235: ValidationWarning: Setting `auto_sideband_cal=on_interm_freq_change` will overwrite settings `amp_ratio=1.0` and `phase_error=0.0`. To suppress this warning, do not set either `amp_ratio` or `phase_error` for this port-clock.
  warnings.warn(
/usr/local/lib/python3.9/site-packages/quantify_scheduler/backends/types/qblox.py:1235: ValidationWarning: Setting `auto_sideband_cal=on_interm_freq_change` will overwrite settings `amp_ratio=1.0` and `phase_error=0.0`. To suppress this warning, do not set either `amp_ratio` or `phase_error` for this port-clock.
  warnings.warn(

[11]:

rich.print(quantum_device.hardware_config())

{
    'config_type': 'quantify_scheduler.backends.qblox_backend.QbloxHardwareCompilationConfig',
    'hardware_description': {
        'cluster0': {
            'instrument_type': 'Cluster',
            'modules': {
                '6': {'instrument_type': 'QCM_RF'},
                '2': {'instrument_type': 'QCM'},
                '8': {'instrument_type': 'QRM_RF'}
            },
            'sequence_to_file': False,
            'ref': 'internal'
        }
    },
    'hardware_options': {
        'output_att': {'q0:mw-q0.01': 10, 'q1:mw-q1.01': 10, 'q0:res-q0.ro': 60, 'q1:res-q1.ro': 60},
        'mixer_corrections': {
            'q0:mw-q0.01': {
                'auto_lo_cal': 'on_lo_interm_freq_change',
                'auto_sideband_cal': 'on_interm_freq_change',
                'dc_offset_i': None,
                'dc_offset_q': None,
                'amp_ratio': 1.0,
                'phase_error': 0.0
            },
            'q1:mw-q1.01': {
                'auto_lo_cal': 'on_lo_interm_freq_change',
                'auto_sideband_cal': 'on_interm_freq_change',
                'dc_offset_i': None,
                'dc_offset_q': None,
                'amp_ratio': 1.0,
                'phase_error': 0.0
            },
            'q0:res-q0.ro': {
                'auto_lo_cal': 'on_lo_interm_freq_change',
                'auto_sideband_cal': 'on_interm_freq_change',
                'dc_offset_i': None,
                'dc_offset_q': None,
                'amp_ratio': 1.0,
                'phase_error': 0.0
            },
            'q1:res-q1.ro': {
                'auto_lo_cal': 'on_lo_interm_freq_change',
                'auto_sideband_cal': 'on_interm_freq_change',
                'dc_offset_i': None,
                'dc_offset_q': None,
                'amp_ratio': 1.0,
                'phase_error': 0.0
            }
        },
        'modulation_frequencies': {
            'q0:mw-q0.01': {'interm_freq': 80000000.0},
            'q1:mw-q1.01': {'interm_freq': 80000000.0},
            'q0:res-q0.ro': {'lo_freq': 7500000000.0},
            'q1:res-q1.ro': {'lo_freq': 7500000000.0}
        }
    },
    'connectivity': {
        'graph': [
            ['cluster0.module6.complex_output_0', 'q0:mw'],
            ['cluster0.module6.complex_output_1', 'q1:mw'],
            ['cluster0.module2.real_output_0', 'q0:fl'],
            ['cluster0.module2.real_output_1', 'q1:fl'],
            ['cluster0.module8.complex_output_0', 'q0:res'],
            ['cluster0.module8.complex_output_0', 'q1:res']
        ]
    }
}

[12]:

quantum_device.to_json_file("devices/")

[12]:

'devices/device_2q_2024-09-18_14-58-47_UTC.json'