How-to Guides - Qubit Characterization¶

The following guides are intended to help you help you become familiar with how different experiments can be written in LabOne Q. Depending on your specific use case and architecture, you will likely wish to modify these experiments and adapt them to your own workflow. Please get in touch at info@zhinst.com and we will be happy discuss your application.

How to readout raw data¶

In the how-to readout raw data guide, you'll see how you can access the raw time traces of the readout integration unit for both UHFQA and SHFQA. This is useful for optimizing the readout fidelity when designing matched filter functions for the readout integration weights.

How to do resonator spectroscopy¶

These notebooks shows you how to perform resonator spectroscopy, i.e., you'll find the resonance frequency of the qubit readout resonator by looking at the transmission or reflection of a probe signal applied through the readout line. The first guide shows how you can do this with a continuous wave (CW) mode with the SHFQA or the quantum analyzer channels of a SHFQC, here, with readout pulses here or with either method with the UHFQA.

Example data from resonator spectroscopy. The absolute value of the transmission (not
normalized) is plotted as a function of the oscillator frequency. The resonance
frequency of the resonator shows as a dip in the transmission with a
Lorentzian line shape, whose width is given by the photon decay rate of
the oscillator. — Figure 1: Example data from resonator spectroscopy. The absolute value of the transmission (not normalized) is plotted as a function of the oscillator frequency. The resonance frequency of the resonator shows as a dip in the transmission with a Lorentzian line shape, whose width is given by the photon decay rate of the oscillator.

How to do resonator spectroscopy vs power: "punchout"¶

This notebook shows you how to perform a pulsed resonator spectroscopy vs power, a "punchout", experiment with a SHFQA or the quantum analyzer channels of a SHFQC. Here, you'll find the perform a 2D sweep of the frequency vs power on the qubit readout resonator to find the optimal settings at which to drive it.

How to measure propagation delay: time-of-flight¶

This notebook shows you how to perform a propagation delay experiment to calibrate the time-of-flight, or round trip time, that the measurement signal requires to come back to the quantum analyzer. To do this, you'll sweep the delay of the qantum analyzer integration and find the maximum result.

How to measure qubit spectroscopy¶

The qubit spectroscopy notebook shows you how to find the resonance frequency of the qubit by measuring the change in resonator transmission when sweeping the frequency of a qubit excitation pulse.

Example qubit spectroscopy data with the absolute value of the readout
resonator response as a function of the qubit drive excitation
frequency. The response changes when the qubit drive is in
resonance with the qubit transition.
Data courtesy of Dr. Daniel J. Weigand, PGI13, FZ Jülich. — Figure 2: Example qubit spectroscopy data with the absolute value of the readout resonator response as a function of the qubit drive excitation frequency. The response changes when the qubit drive is in resonance with the qubit transition. Data courtesy of Dr. Daniel J. Weigand, PGI13, FZ Jülich.

How to do an amplitude Rabi experiment¶

The amplitude Rabi notebook shows you how to measure the readout resonator response as a function of the qubit excitation pulse amplitude. You can fit the resulting data to a sinusoid to determine the periodicity of the response, which allows you to calibrate the pulse amplitudes necessary for bringing the qubit to the equator of the Bloch sphere (π/2-pulse) and for flipping the qubit state (π-pulse).

Figure 3: Example data from Rabi amplitude calibration courtesy of Dr. Daniel J. Weigand, PGI13, FZ Jülich.

How to perform a Ramsey experiment¶

This notebook shows you how to perform a Ramsey experiment: you'll sweep the delay between two π/2-pulses played on the qubit drive line and readout the result. Note that you can artificially detune the qubit excitation pulse frequency, which, for a perfectly calibrated qubit, this artificial detuning will ensure that the measured signal shows oscillations over the delay time. Any additional frequency contribution in the data can therefore be attributed to a prior miscalibration of the qubit frequency. The Ramsey experiment is often used to fine-tune the qubit resonance frequency.

Ramsey experiment data. In addition to oscillations, the
measured signal will typically also decay over time with a
characteristic timescale called the Ramsey dephasing time, or T<sub>2</sub>. This
timescale carries information about the low frequency part of the noise
acting on the qubit. The data can be fit to a decaying oscillating function that is used to determine the qubit excitation
frequency as well as the dephasing time of the qubit quantum state. Courtesy Dr. Daniel J. Weigand, PGI13, FZ Jülich — Figure 4: Ramsey experiment data. In addition to oscillations, the measured signal will typically also decay over time with a characteristic timescale called the Ramsey dephasing time, or T₂. This timescale carries information about the low frequency part of the noise acting on the qubit. The data can be fit to a decaying oscillating function that is used to determine the qubit excitation frequency as well as the dephasing time of the qubit quantum state. Courtesy Dr. Daniel J. Weigand, PGI13, FZ Jülich

How to perform e-f transition spectroscopy¶

In the e-f transition spectroscopy notebook, you'll learn how to to perform spectroscopy of higher qubit levels.

How to perform e-f gate tune-up¶

In this notebook you'll learn how to tune-up the π-pulse acting on the e-f transition of a superconducitng transmon qubit.

How to perform cross-resonance (CR) gate tune-up¶

The CR gate tune-up notebook, you'll sweep the pulse length of a qubit drive pulse at the difference frequency of two qubits to determine the ideal parameters for a CR gate.

Additional experiments¶

The basic experiments notebook contains some of the above experiments, as well as:

How to do a length Rabi experiment¶

In the length Rabi section, you'll measure the readout resonator response as a function of the qubit excitation pulse length, in contrast to the Rabi amplitude experiment.

How to do a T₁ Experiment¶

This T₁ section will show you how to measure the lifetime T₁ of the qubit. You'll bring the qubit to its excited state and then wait a variable time before measuring its state. Averaging over many measurements will yield the probability of finding the qubit in its excited state after this time. The experimental parameters for a T₁ experiment are the range of delay times and the number of steps to iterate the delay over. You'll also define the pulse used to drive the qubit from the ground to its excited state, using the waveform and π-pulse parameters given in your Rabi experiment.

Data from a T<sub>1</sub> experiment. The probability of the qubit to be in its
excited state decays exponentially with the delay between excitation and
measurement. The decay time constant can be retrieved from fitting the
data and is the inverse of the qubit lifetime T<sub>1</sub>. Data courtesy of Dr. Daniel J. Weigand, PGI13, FZ Jülich. — Figure 5: Data from a T₁ experiment. The probability of the qubit to be in its excited state decays exponentially with the delay between excitation and measurement. The decay time constant can be retrieved from fitting the data and is the inverse of the qubit lifetime T₁. Data courtesy of Dr. Daniel J. Weigand, PGI13, FZ Jülich.

How to do a Ramsey experiment with a sampled pulse¶

The Ramsey experiment (and other experiments) can use a user-defined sampled pulse, as shown here.

How to measure flux-dependent qubit spectroscopy¶

In this section you'll measure resonator transmission while performing a 2D sweep of the frequency of a qubit excitation pulse and the flux bias.

How to perform a flux-scope experiment¶

Here, you'll perform a flux-scope experiment to characterise the distortions of flux pulses due to the imperfect signal lines. See Chapter 4.4.3 for further information on this experiment.

How to perform a cryoscope experiment¶

In the cryoscope section, you'll learn an alternative method to characterise pulse distortions from line impedance, as shown in this reference. The experiment consists of a Ramsey sequence with fixed timing and variable flux pulse in between, where both the flux pulse length and amplitude are swept.