Integration Weights Measurement¶

Note

This tutorial is applicable to all SHFQC+ Instruments and no additional instrumentation is needed.

Goals and Requirements¶

LabOne Q is the recommended control software to operate the SHFQC+ for Quantum Technology applications.

The goal of this tutorial is to demonstrate how to use the SHFQC+ Scope to measure integration weights that are needed for high-fidelity single-shot readout using the LabOne User Interface (UI) and Zurich Instruments Toolkit API.

For qubit control with the SHFSG+ Signal Generator, the SHFQC+ Qubit Controller and the HDAWG Arbitrary Wave Generator, and instrument synchronization and feedback with the PQSC Programmable Quantum System Controller, see tutorials in the Online Documentation.

Note

For zhinst-toolkit users, please find the example in https://github.com/zhinst/zhinst-toolkit/blob/main/examples/shfqa_qubit_readout_weights.md, and the zhinst-toolkit documentation.

For LabOne Q users, please find the example in https://github.com/zhinst/laboneq/blob/main/examples/01_qubit_characterization/12_readoutweight_calibration_shfsg_shfqa_shfqc.ipynb, and the LabOne Q User Manual.

Preparation¶

Please follow the preparation steps in Connecting to the Instrument and connect the instrument in a loopback configuration as shown in Figure 1 or to a device under test.

Figure 1: SHFQC+ connection.

Tutorial¶

In the tutorial, readout signals are recorded while the qubit is in ground and excited state. The readout pulse is generated by the SHFQC+ Readout Pulse Generator, and the signal recording is done by the SHFQC+ Scope. The integration weight is derived from the difference of the recorded readout signals.

LabOne UIzhinst-toolkit

This section shows how to use LabOne UI to configure the instrument, run the measurement, monitor the measurement results and calculate the integration weight.

Configure the instrument

Set center frequency and power range of input and output signals

Configure these parameters on the Input and Output Tab as in Figure 2 and in Table 1.

Table 1: Settings of QA Channel 1 on In/Out Tab
Parameter	Setting	Description
QA Channel Selection	All	Select All to display all Channels.
Cent Freq (Hz)	5 GHz	Set center frequency of the frequency sweep of QA Channel 1.
Signal Input 1 On	Enable	Enable the Signal Input 1.
Signal Input 1 Range (dBm)	0 dBm	Set power range of Signal Input 1 to 0 dBm. This setting allows the instrument to acquire a input signal with a power up to 0 dBm.
Signal Input 1 Input Path	RF	Set input path of Signal Input 1 to RF path.
Signal Output 1 On	Enable	Enable the Signal Output 1.
Signal Output 1 Range	0 dBm	Set power range of Signal Output 1 to 0 dBm. This setting allows the instrument to output a signal with a power up to 0 dBm.
Signal Output 1 Output Path	RF	Set output path of the Signal Output 1 to RF path.

Upload and compile measurement sequence

The measurement sequence is defined on the Sequence Sub-Tab of the Readout Pulse Generator Tab, see Table 2.

Table 2: Settings of QA Channel 1 on Readout Pulse Generator Tab.
Parameter	Setting	Description
QA channel Selection	1	Select QA channel 1.
Sub-Tab Display	Sequence	Select Sequence sub-tab and paste the sequence program below. The Waveform Viewer sub-tab displays waveforms saved in Waveform Memory slots and Integration Weight units.
Compile	Click "To Device"	Compile the sequence program by clicking "To Device".
Digital Triggers	Digital Trigger 1	Select Digital Trigger 1.
Digital Trigger 1 Signal	Internal Trigger	Select Internal Trigger as the trigger source of Digital Trigger 1.
Return	Disable	Disable return function.
Run/Stop	Enable	Run the sequence.

Below is the the sequence program for the measurement. In the loop, the waitDigTrigger command waits a trigger (see Table 3) to continue the sequence, the startQA command sends a trigger to generate output waveform and start integration, it also sends a Sequencer Monitor Trigger (third argument of the startQA command) to trigger SHFQC+ Scope to record input signal before integration. The measurement is repeated 100 times to get averaged readout pulses according to qubit prepared in ground and excited state.

// repeat sequence 100 times, i.e. readout qubit in group state and excited state, and then repeat this 50 times
repeat (100) {
    // wait for a trigger over ZSync. Assume the trigger period is longer than the cycle time
    // waitZSyncTrigger();

    // alternatively wait for a trigger from digital trigger 1
    waitDigTrigger(1);

    // play readout waveform stored in Waveform Memory slot 1, send a trigger to start integration, and send a Sequencer Monitor trigger to trigger the Scope
    startQA(QA_GEN_0, QA_INT_0, true);
}

The digital trigger set on the Trigger sub-tab is Internal Trigger. The configuration of the internal is shown in Table 3.

Table 3: Settings of Internal Trigger on DIO Setup Tab, see details on DIO Tab
Parameter	Setting	Description
Repetitions	100	Set number of repetitions.
Holdoff (s)	100u	Set holdoff time to 100 \(\mu\)s.
Synchronization	Disabled	Disable Synchronization.
Run/Stop	Disable	Disable the internal trigger.

Configure signal generation

Signal generation is defined on QA Setup Tab, see Figure 3 and Table 4. Since we are only interested in the signal before integration, the settings for integration weights is not needed.

Figure 3: Configurations on QA Setup Tab.

Table 4: Settings of QA Channel 1 on QA Setup Tab.
Parameter	Setting	Description
QA Channel Selection	1	Select QA Channel 1.
Application Mode	Readout	Use Readout mode for integration weight measurement.
Clear Waveform	Click "Clear"	Clear all waveforms saved in Waveform Memory. Clear all waveforms before uploading new ones to avoid incorrect waveform generation or output overflow.
Waveform Memory 1 Set Mode	Parametric	Generate waveform parametrically in Waveform Memory slot 1. The parametrically generated waveform is \(Ae^{i (2 \pi f t + \frac{\pi}{180}\phi)}\), where \(A\) is the dimensionless amplitude factor of the waveform, \(f\) is the frequency in units of Hz, \(\phi\) is the phase in units of degree.
Amplitude	0.5	Set amplitude factor \(A\) to 0.5.
Frequency (Hz)	10M	Set readout frequency \(f\) to 10 MHz.
Phase (Deg)	0	Set phase \(\phi\) to 0 degree.
Window Length	4096	Set length of the readout waveform in number of samples.
Set To Device	click "Set To Device"	Upload the parametrically generated waveform to Waveform Memory slot 1.

Configure SHFQC+ Scope

The SHFQC+ Scope is configured to record readout pulses before integration, and display averaged readout pulses according to qubit in ground state and excited state, see Figure 4 and Table 5. The figure shows the SHFQA+ Scope configuration for the same measurementNote that the input sources of the first and the second Scope channel are fixed to "Signal Input 1", and only SG channels can be selected as the input sources of the third and the forth Scope channel.

Table 5: Settings on Scope Tab
Parameter	Setting	Description
Horizontal Mode	Time	Display data in time-domain.
Horizontal Length (pts)	4096	Set recording length in number of samples. This setting has to be \(\ge\) readout pulse length.
Channel 1 Signal Selection	Signal Input 1	Monitor signal comes from Signal Input 1 on Scope Channel 1.
Channel 1 Enable	Enable	Enable Scope Channel 1.
HW Averaging	Enable	Enable hardware averaging.
Averages	50	Set number of averages to 50. This setting matches what is defined in the sequence program.
Display Mode	Scope	Display the Scope trace. Enable "2D" if 2D trace is desired.
Add Signal	Scope Wave Channel 1 I and Q	Add Scope Wave Channel 1 I and Scope Wave Channel 1 Q to the plot.
Trigger Mode	Enable	Enable trigger mode so that scope recording starts only after receiving a trigger.
Trigger Signal	Sequencer 1 Monitor Trigger	Select Sequencer 1 Monitor Trigger as the trigger to trigger the Scope.
Trigger Delay (s)	224n	Set trigger delay to 224 ns. The Scope starts to record data 224 ns later after receiving a trigger. This setting must has to match signal propagation delay including internal delay about 224 ns and external delay depending on the signal path between the front panel Signal Output port and Signal Input port.
Segments Enable	Enable	Enable Segments measurement. In Segments measurement, the scope records \(n \times m\) data, where \(n\) is the number of segments, \(m\) is the recording length in number of samples.
Segments	2	Set number of segments to 2. 1 for recording readout pulse when qubit in groud state, another for qubit in excited state.
Run Mode	Single	Using Single mode for the measurement.

Run the measurement

By clicking "Run/Stop" icon on the System Settings sub-tab of DIO tab, the measurement is started and finished in seconds.
Monitor the measurement results and calculate the integration weight

The recorded readout pulses are displayed on the Scope Tab, as shown in Figure 5. The integration weights is calculated by taking the difference of the measured traces according to the qubit is in ground state and excited state.

Figure 5: Recorded readout pulses on Scope Tab.

Connect the instrument

Create a toolkit session to the data server and connect the device with the device ID, e.g. 'DEV12001', see Connecting to the Instrument.

# Load the LabOne API and other necessary packages
from zhinst.toolkit import Session, SHFQAChannelMode, Waveforms
from scipy.signal import gaussian
import numpy as np

DEVICE_ID = 'DEVXXXXX'
SERVER_HOST = 'localhost'

session = Session(SERVER_HOST)              ## connect to data server
device = session.connect_device(DEVICE_ID)  ## connect to device

Generate readout pulses

In the tutorial, the envelope of the readout waveforms is flat-top Gaussian with pulse length of 500 ns and rise and fall time of 10 ns, amplitude factor of 0.9, and 8 readout frequencies span from 32 MHz to 120 MHz. The amplitude factor is not scaled by the number of qubits as in Multiplexed Qubit Readout because the readout output signal is generated from one of the readout waveforms, see the sequence program in the following section. The zhinst-toolkit class Waveforms is for converting waveform data written in Python to data that can be uploaded to the instrument correctly.

NUM_QUBITS = 8
SAMPLING_FREQUENCY = 2e9
RISE_FALL_TIME = 10e-9
PULSE_DURATION = 500e-9

rise_fall_len = int(RISE_FALL_TIME * SAMPLING_FREQUENCY)
pulse_len = int(PULSE_DURATION * SAMPLING_FREQUENCY)
std_dev = rise_fall_len // 10

gauss = gaussian(2 * rise_fall_len, std_dev)
flat_top_gaussian = np.ones(pulse_len)
flat_top_gaussian[0:rise_fall_len] = gauss[0:rise_fall_len]
flat_top_gaussian[-rise_fall_len:] = gauss[-rise_fall_len:]
# Scaling
flat_top_gaussian *= 0.9

readout_pulses = Waveforms()
time_vec = np.linspace(0, PULSE_DURATION, pulse_len)

for i, f in enumerate(np.linspace(2e6, 32e6, NUM_QUBITS)):
    readout_pulses.assign_waveform(
        slot=i,
        wave1=flat_top_gaussian * np.exp(2j * np.pi * f * time_vec)
    )

Configure the channel

Configure center frequency, input and output power range and application mode of the channel using qachannels[n].configure_channel, turn on the Input and Output, and upload the readout waveforms using generator.write_to_waveform_memory.

# configure inputs and outputs
CHANNEL_INDEX = 0 # physical Channel 1

device.qachannels[CHANNEL_INDEX].configure_channel(
    center_frequency=5e9, # in units of Hz
    input_range=0, # in units of dBm
    output_range=-5, # in units of dBm
    mode=SHFQAChannelMode.READOUT, # SHFQAChannelMode.READOUT or SHFQAChannelMode.SPECTROSCOPY
)
device.qachannels[CHANNEL_INDEX].input.on(1)
device.qachannels[CHANNEL_INDEX].output.on(1)

# write waveforms to the Waveform Memory
device.qachannels[CHANNEL_INDEX].generator.write_to_waveform_memory(readout_pulses)

Configure the Scope

Configure the Scope to record 2 segments of data with length of 500 ns which are averaged 50 times using scopes[n].configure. The trigger of the Scope is1 Sequencer 1 Monitor Trigger which is enabled by the startQA command.

SCOPE_CHANNEL = 0
RECORD_DURATION = 500e-9 # in units of second
NUM_SEGMENTS = 2
NUM_AVERAGES = 50
NUM_MEASUREMENTS = NUM_SEGMENTS * NUM_AVERAGES
SAMPLING_FREQUENCY = 2e9 # in units of Hz

device.scopes[0].configure(
    input_select={SCOPE_CHANNEL: f"channel{CHANNEL_INDEX}_signal_input"},
    num_samples=int(RECORD_DURATION * SAMPLING_FREQUENCY),
    trigger_input=f"channel{CHANNEL_INDEX}_sequencer_monitor0", # Sequencer 1 monitor trigger
    num_segments=NUM_SEGMENTS,
    num_averages=NUM_AVERAGES,
    trigger_delay=214e-9, # record the data 214 ns later after receiving a trigger
)

Configure and run the measurement, and calculate the integration weights

In the measurement, the Sequencer is triggered by Internal Trigger using configure_sequencer_trigger.

The integration weights for different qubits are measured sequentially with the for loop. In each loop, the seqc_program is different and is uploaded to the instrument using load_sequencer_program, both Scope and Sequencer run in Single mode set by scopes[n].run and enable_sequencer respectively, the Generator sends 100 pulses to readout 1 of the qubits prepared in ground and excited state, and the Scope acquires 2 segments of data which are averaged 50 times, and the data is downloaded using scopes[n].read, and integration weights are calculated in the end.

results = []

device.qachannels[CHANNEL_INDEX].generator.configure_sequencer_triggering(
    aux_trigger=8,# internal trigger
    play_pulse_delay=0, # 0s delay between startQA trigger and the readout pulse
)
device.system.internaltrigger.repetitions(int(NUM_SEGMENTS * NUM_AVERAGES))
device.system.internaltrigger.holdoff(100e-6)

for i in range(NUM_QUBITS):
    qubit_result = {
        'weights': None,
        'ground_states': None,
        'excited_states': None
    }
    print(f"Measuring qubit {i}.")

    # upload sequencer program
    seqc_program = f"""
        repeat({NUM_MEASUREMENTS}) {{
            waitDigTrigger(1);
            startQA(QA_GEN_{i}, 0x0, true,  0, 0x0); // only QA_GEN_{i} matters for this measurement
        }}
    """
    device.qachannels[CHANNEL_INDEX].generator.load_sequencer_program(seqc_program)

    # Start a measurement
    device.scopes[SCOPE_CHANNEL].run(single=True)
    device.qachannels[CHANNEL_INDEX].generator.enable_sequencer(single=True)
    device.system.internaltrigger.enable(1)

    # get results to calculate weights and plot data
    scope_data, *_ = device.scopes[0].read()

    # Calculates the weights from scope measurements
    # for the excited and ground states
    split_data = np.split(scope_data[SCOPE_CHANNEL], 2)
    ground_state_data = split_data[0]
    excited_state_data = split_data[1]
    qubit_result['ground_state_data'] = ground_state_data
    qubit_result['excited_state_data'] = excited_state_data
    qubit_result['weights'] = np.conj(excited_state_data - ground_state_data)
    results.append(qubit_result)

The following code snippet can be used to plot readout traces (Figure 6) and calculate integration weights (Figure 7) of the last qubit.

Note

In order to achieve the highest possible resolution in the signal after integration, it’s advised to scale the dimensionless readout integration weights with a factor so that their maximum absolute value is equal to 1.

import matplotlib.pyplot as plt

fig, (ax0, ax1) = plt.subplots(nrows = 2, sharex = True)

t = np.linspace(0, RECORD_DURATION, int(RECORD_DURATION * SAMPLING_FREQUENCY/16)*16)
ax0.plot(t/1e-9, ground_state_data.real, '-', label = f'real')
ax0.plot(t/1e-9, ground_state_data.imag, '-', label = f'imag')
ax1.plot(t/1e-9, excited_state_data.real, '-', label = f'real')
ax1.plot(t/1e-9, excited_state_data.imag, '-', label = f'imag')

ax0.set_title('Ground state')
ax1.set_title('Excited state')
ax0.legend(loc='upper right')
ax1.legend(loc='upper right')
ax0.set_ylabel('Amplitude (Vrms)')
ax1.set_ylabel('Amplitude (Vrms)')
ax1.set_xlabel(r'Time (ns)')
plt.tight_layout()

plt.figure()
plt.plot(t/1e-9, results[0]['weights'])
plt.xlabel('Time (ns)')
plt.ylabel('Amplitude (Vrms)')
plt.tight_layout()