Quantum Analyzer Setup Tab

The Quantum Analyzer Setup is the main control panel for the qubit measurement unit on the instrument (see functional overview for an overview block diagram). It is available on all UHFQA instruments.

Features

Raw signal deskew
Signal rotation in I/Q plane
10×10 crosstalk suppression matrix
Threshold operation
Qubit-qubit correlation analysis

Description

Table 1. App icon and short description
Control/Tool	Option/Range	Description
QA Setup		Configure the Qubit Measurement Unit

The Quantum Analyzer Setup tab (see Figure 1) is divided into different sections each representing a signal processing step starting from raw signal deskew to the final threshold operation that transforms an analog I/Q signal into a discrete qubit state. This tab represents the interface to the following functional blocks: the integration units, the internal oscillator, the crosstalk suppression matrix, the deskew matrix, the correlation unit, the statistics unit, and the thesholding unit. A block diagram representing the flow of data and trigger signals between the functional blocks is found in Architecture and Signalling .

Figure 1. LabOne UI: Quantum Analyzer Setup tab

Two-element vectors of samples arrive at 1.8 GSa/s from Signal Inputs 1 and 2. In the Deskew section, at this rate, each sample vector is multiplied by a 2×2 Rotation/Gain matrix. The default value is the identity matrix [1, 0; 0, 1] which leaves both input signals unchanged. Changing this to a different value allows the user to compensate for signal imperfections such as analog linear crosstalk, or mixer amplitude imbalance.

In the Integration section, each of the two input signals is demodulated by multiplying with a reference signal and the product is integrated over a fixed time T after reception of a trigger. The user can choose the mode of operation of the weighted integration. In Standard mode, the reference signal is given by the Integration Weights programmed to the instrument memory using the Quantum Analyzer Input Tab . This mode offers the full flexibility to define a custom integration weight to realize a matched filter. In Spectroscopy mode, the reference signal is given by sine and cosine signals generated by the internal digital oscillator controlled from the Inputs/Outputs Tab , which allows for longer integration times and thus higher frequency resolution than the Standard mode. The input signals V~Sig In 1~(t) and V~Sig In 2~(t) of duration T are reduced to a single pair of voltages V_I and V_Q. Since there are 10 separate qubit measurement units, there can be up to 10 pairs (V~I, q~, V~Q, q~ for q=1…10), each corresponding to one frequency component of the signals V~Sig In 1~(t) and V~Sig In 2~(t).

The Rotation section rotates and scales the signal in the complex plane after integration. For each of the 10 channels, the rotation is characterized by a complex number z_q = x_q+iy_q = r_q×exp(iθ_q). The demodulated signal is multiplied with z_q: V'~I, q~ + iV'~Q, q~ = (V~I, q~ + iV~Q, q_)×zq~. The user may specify z_q in polar coordinates in the form "r @ θ" or in Cartesian coordinates in the form "x + y i". Examples are "1@45" for a 45 degree rotation, or "0.0 + 1.0 i" for a 90 degree rotation. The purpose of the rotation step is to ensure that the readout contrast is shifted into the in-phase signal component, i.e., that the state of qubit q only affects V'~I, q~ but not V'~Q, q~.

The Crosstalk section is a graphical representation of the 10×10 crosstalk suppression matrix C that supports systematic minimization of the influence of one qubit’s state on another qubit’s readout signal. The signal processing up to after the rotation step can be abstracted as a 10×10 matrix M that transforms the vector of qubit states (s₁,…,s₁₀), with s_q = 0 or 1, into the vector of signals (V'~I, 1~, … V'~I, 10~). This matrix can be measured systematically by preparing the qubit system in different states of the form (0,…, 0, 1, 0,…, 0), and measuring the resulting signal. Using the Crosstalk Suppression optimally relies on finding the matrix C such that C×M is diagonal. Due to the complexity of this method, setting the elements of the crosstalk suppression matrix C from the graphical UI would be impractical, and its elements can only be set from the API. We denote the signals after crosstalk suppression with a double prime as (V''~I, 1~, … V''~I, 10~) = C×(V'~I, 1~, … V'~I, 10~).

The Correlation section optionally enables the outputs of two readout channels to be multiplied prior to averaging, logging, etc. When enabled, the corresponding channel is multiplied with another channel selected as the Source.

The Thresholds section allows one to define a voltage threshold to transform the in-phase quadrature V''~I, q~ of the readout signal into a discrete qubit state, 0 or 1.

Functional Elements

Table 2. Quantum Analyzer Setup tab
Control/Tool	Option/Range	Description
Rotation/Gain Matrix		Implements a 2×2 matrix multiplication. The two input signals are treated as a vector with two elements and the result is a vector as well.
In-Phase Gain		Gain of in-phase branch
Quadrature Gain		Gain of quadrature branch
In-Phase Phase		Phase of in-phase branch
Quadrature Phase		Phase of quadrature branch
Mode		Application mode.
	Standard	The integration weights are given by the user-programmed filter memory.
	Spectroscopy	The integration weights are generated by a digital oscillator. This mode offers enhanced frequency resolution.
Readout Trigger Selection		Select the source for triggering the readout.
	Trigger In 1	Use the Trigger In 1 as the trigger signal.
	Trigger In 2	Use the Trigger In 2 as the trigger signal.
	Trigger In 3	Use the Trigger In 3 as the trigger signal.
	Trigger In 4	Use the Trigger In 4 as the trigger signal.
	AWG Integration Trigger	Use the AWG Integration Trigger as the trigger signal.
Spectroscopy Trigger Selection		Selects the source for triggering the spectroscopy.
	Trigger In 1	Use the Trigger In 1 as the trigger signal.
	Trigger In 2	Use the Trigger In 2 as the trigger signal.
	Trigger In 3	Use the Trigger In 3 as the trigger signal.
	Trigger In 4	Use the Trigger In 4 as the trigger signal.
	AWG Integration Trigger	Use the AWG Integration Trigger as the trigger signal.
Clear		Empty all Integration Weights memory slots.
Integration Length		The integration time of all weighted integration units specified in units of samples. In Standard mode, a maximum of 4096 samples can be integrated, which corresponds to 2.3 µs. In Spectroscopy mode, a maximum of 16.7 MSa can be integrated, which corresponds to ~10 ms.
Errors		Number of hold-off violations detected in the INTEGRATION unit since last reset.
Delay		A delay time in units of samples that adjusts the time at which the integration starts in relation to the trigger signal of the weighted integration units.
Source		Controls the routing of the input signals to the INTEGRATION units.
	1 → Real, 2 → Imag	Signal input 1 to real part, Signal input 2 to imaginary part.
	2 → Real, 1 → Imag	Signal input 2 to real part, Signal input 1 to imaginary part.
	1 → Real, 1 → Imag	Signal input 1 to real part, Signal input 1 to imaginary part.
	2 → Real, 2 → Imag	Signal input 2 to real part, Signal input 2 to imaginary part.
Rotation		Complex rotation coefficient applied to the signals after integration.
Representation		Select between Cartesian and polar representation of the complex rotation coefficient. Cartesian coordinates are entered in the format "x+iy", polar coordinates in the format "r@a" where x, y, r, and a are real numbers.
Crosstalk		Graphical representation of the 10×10 crosstalk suppression matrix. Positive values are black, negative values are red.
Bypass Crosstalk		Bypass the Crosstalk matrix in order to reduce the latency through the system.
Bypass Rotation		Bypass Rotation in order to reduce the latency through the system.
Bypass Deskew		Bypass Deskew in order to reduce the latency through the system.
En		Enable the correlation mode for the given channel.
Source		Controls the channel with which correlation should be made. Selecting the same channel as the readout channel number corresponds to self-correlation.
Level		The discretization level applied to the output of the Crosstalk Suppression matrix.
Length		Sets the integration length in spectroscopy mode in number of samples. A maximum of 33.5 MSa (2^25 samples) can be integrated, which corresponds to 16.7 ms.
Delay		Sets the delay of the start of the integration in spectroscopy mode with respect to the Trigger Signal.
Offset Frequency		Sets the digital oscillator frequency. The sum of the Offset Frequency and the Center Frequency correspond to the frequency of the microwave tone at the Out connector.
Output Frequency		Displays the carrier frequency of the microwave signal at the Out connector. This frequency corresponds to the sum of the Center Frequency and the Offset Frequency.
Amplitude		Amplitude of the microwave signal relative to the range of the Output.
Set Mode		Set Generator Waveform by parametric generation or CSV Upload.
	Parametric	Generator Waveform are generated by defining sine wave parameters.
	Upload	Generator Waveform are uploaded by the user in a form of a CSV file.
Frequency		Frequency of the complex exponential function.
Phase		Phase of the complex exponential function.
Window Type		Window function to be applied to the complex exponential function.
Window Length		Length of the selected window in samples, starting from 0.
Waveform Memory		Selects the waveform memory for parametric or arbitrary waveform upload.
Set To device		Write the real and imaginary part of the Waveform to the selected Waveform Memory.
Set To Device		Write the real and imaginary part of the Waveform to the selected Waveform Memory.
CSV File		Drag and drop CSV file containing columns of Sequencer Waveform.
Amplitude		Amplitude of the complex exponential function.
Clear		Empty all Readout Waveform memory slots.
Sequencer		Runs the Sequencer.
Status	Running, Idle, Waiting	Displays the status of the sequencer on the instrument. Off: Ready, not running. Green: Running, not waiting for any trigger event. Yellow: Running, waiting for a trigger event. Red: Not ready (e.g., pending elf download, no elf downloaded)