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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 SHFQA+ Instruments.

Features

  • Continuous or pulsed resonator spectroscopy
  • Multiplexed qubit readout
  • Weighted integration
  • Multistate discrimination
  • Power spectral density

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 is divided into 2 sub-tab groups for resonator spectroscopy (see LabOne GUI: QA Setup Tab - Spectroscopy Mode) and qubit readout (see LabOne GUI: QA Setup Tab - Readout Mode) application. By selecting Application Mode, Spectroscopy or Readout, the corresponding sub-tabs provide all configurations of readout pulse generation and acquired data processing (see LabOne GUI: Readout Pulse Generator Tab - Waveform Viewer). The main differences of the Application Modes are listed below.

Figure 1: LabOne GUI: QA Setup Tab - Spectroscopy Mode

Figure 2: LabOne GUI: QA Setup Tab - Readout Mode

Figure 3: LabOne GUI: Readout Pulse Generator Tab - Waveform Viewer

Table 2: Main differences of Spectroscopy and Readout mode
Parameters Spectroscopy mode Readout mode
Waveform generation Digital oscillator and envelope Sample by Sample
Waveform output mode Continuous or pulsed Pulsed
Waveform length Continuous
or up to 16 μs or 32 μs
Up to 2 μs
Number of qubits per channel 1 Up to 8 or 16
Integration length Up to 16.7 ms Up to 2 μs
Integration weight unit per channel Not applicable Up to 8 or 16
Result normalization after integration Normalized by integration length in samples Not normalized
Real-time state discrimination Not applicable Yes
Multistate discrimination Not applicable Qubits, qutrits and ququads

Spectroscopy Mode

Spectroscopy mode is mainly used for resonator spectroscopy and power spectral density measurement. The SHFQA+ has 1 Digital Oscillator per channel. In Spectroscopy mode, the Digital Oscillator is used for readout waveform generation and integration. The SHFQA+ Sweeper class (API) is the central controller for the Spectroscopy mode, see tutorial Resonator Spectroscopy.

There are 2 operation modes for readout waveform generation, Continuous and Pulsed. In Continuous mode, signal from the Digital Oscillator is routed to the digital IQ mixing stage (see Functional Overview) for readout waveform generation in the output path, and to multiply the input signal for readout waveform integration in the input path. signal from the Digital Oscillator modulates the envelope from the Waveform Memory and then is routed to the output and input paths same as in Continuous mode. The pulse envelope can be displayed on the Waveform Viewer sub-tab of the Readout Pulse Generator tab. The main differences of the 2 operation modes are listed in Table 3.

Figure 4: Readout waveform generation and integration in Spectroscopy mode

Table 3: Main differences of Continuous and Pulsed mode in Spectroscopy
Parameters Continuous mode Pulsed mode
Readout pulse length Continuous wave Up to 16 μs or 32 μs
(up to 32 kSa or 64 kSa)
Envelope delay Not applicable Up to 131.1 μs
Readout pules amplitude Controlled by output range and gain factor of the Digital Oscillator Controlled by output range, gain factor of the Digital Oscillator and the envelope

Readout Waveform Output In Spectroscopy Mode

The readout waveform on the Instrument output can be expressed as

Eoutput(t)=CPARe[A(t)goscei2π(f0+fosc)t+iϕoutput], \begin{equation}\tag{1} E_{\mathrm{output}}(t) = C_{P\rightarrow A}\operatorname{Re}[A(t)g_{\mathrm{osc}}e^{i2\pi (f_0 + f_{\mathrm{osc}}) t + i\phi_{\mathrm{output}}}], \end{equation}

where CPA=10Prange, output1020C_{P\rightarrow A} = 10^{\frac{P_{\mathrm{range,\ output}}-10}{20}} is the conversion factor converting the power range Prange, outputP_{\mathrm{range,\ output}} of the output signal in units of dBm to the amplitude in units of V, , A(t)A(t) is the complex readout envelope in Pulsed mode and A(t)=1A(t) = 1 in Continuous mode, goscg_{\mathrm{osc}} is the amplitude gain factor of the baseband Digital Oscillator. The frequency foscf_{\mathrm{osc}} is the offset frequency set by the baseband Digital Oscillator and ϕoutput\phi_{\mathrm{output}} is the global phase, which can be reset by resetting the phase of the baseband Digital Oscillator. The frequency f0f_0 is the RF center frequency set in the Input/Output tab. Note: when using the LF path the center frequency from the Input/Output tab does not apply and one has to set f0=0f_0 = 0 in the above formula.

The readout waveform envelope A(t)A(t) in Pulsed mode can be displayed on the Waveform Viewer.

Readout Results In Spectroscopy Mode

The readout input signal after analog frequency down-conversion before the ADC is

Ebefore ADC(t)=Re(Ainput(t)ei2πfbefore ADCt+iϕinput) =Ainput(t)cos(2πfbefore ADCt+ϕinput) =Ainput(t)ei2πfbefore ADCt+iϕinput+ei2πfbefore ADCtiϕinput2, \begin{equation}\tag{2} \begin{aligned} E_{\mathrm{before\ ADC}}(t) & = \operatorname{Re}(A_{\mathrm{input}}(t)e^{i2\pi f_{\mathrm{before\ ADC}} t + i\phi_{\mathrm{input}}})\\\ & = A_{\mathrm{input}}(t)\cos({2\pi f_{\mathrm{before\ ADC}} t + \phi_{\mathrm{input}}})\\\ & = A_{\mathrm{input}}(t)\frac{e^{i2\pi f_{\mathrm{before\ ADC}} t + i\phi_{\mathrm{input}}} + e^{-i2\pi f_{\mathrm{before\ ADC}} t - i\phi_{\mathrm{input}}}}{2}, \end{aligned} \end{equation}

where Ainput(t)A_{\mathrm{input}}(t) is the amplitude of input signal on the front panel of the instrument, fbefore ADCf_{\mathrm{before\ ADC}} is the frequency of the input signal before ADC, ϕinput\phi_{\mathrm{input}} is the global phase of the input signal on the front panel of the instrument. After the ADC, it becomes

Ei, after ADC=CscalingAi, input2(ei2πfafter ADCti+iϕinput+ei2πfafter ADCtiiϕinput), \begin{equation}\tag{3} E_{i,\ \mathrm{after\ ADC}} = \frac{C_{\mathrm{scaling}}A_{i,\ \mathrm{input}}}{2}(e^{i2\pi f_{\mathrm{after\ ADC}} t_i + i\phi_{\mathrm{input}}} + e^{-i2\pi f_{\mathrm{after\ ADC}} t_i - i\phi_{\mathrm{input}}}), \end{equation}

where CscalingC_{\mathrm{scaling}} is the conversion factor depending on gain factor, ADC range and bit resolution, fafter ADCf_{\mathrm{after\ ADC}} is the frequency after the ADC, ii means the ii-th sample. The signal Ei, after ADCE_{i,\ \mathrm{after\ ADC}} is then down-converted by a digital oscillator at frequency finput, LO2f_{\mathrm{input,\ LO2}} of 1 GHz (0 Hz) when using RF (LF) path and filtered the high frequency components, as

Ei, before integration=Ei, after ADCei2πfafter, LO2ti =CscalingAi, input2(ei2πfafter ADCti+iϕinput+ei2πfafter ADCtiiϕinput)ei2πfinput, LO2ti, =CscalingAi, input2(ei2πfbasebandti+iϕinput+ei2πfsumtiiϕinput) =filter{CscalingAi, input2ei2πfbasebandti+iϕinput,RF path, CscalingAi, inputcos(2πfbasebandti+ϕinput),LF path, \begin{equation}\tag{4} \begin{aligned} E_{i,\ \mathrm{before\ integration}} & = E_{i,\ \mathrm{after\ ADC}}e^{-i2\pi f_{\mathrm{after,\ LO2}}t_i}\\\ & = \frac{C_{\mathrm{scaling}}A_{i,\ \mathrm{input}}}{2}(e^{i2\pi f_{\mathrm{after\ ADC}} t_i + i\phi_{\mathrm{input}}} + e^{-i2\pi f_{\mathrm{after\ ADC}} t_i - i\phi_{\mathrm{input}}})e^{-i2\pi f_{\mathrm{input,\ LO2}}t_i},\\\ & = \frac{C_{\mathrm{scaling}}A_{i,\ \mathrm{input}}}{2}(e^{i2\pi f_{\mathrm{baseband}} t_i + i\phi_{\mathrm{input}}} + e^{-i2\pi f_{\mathrm{sum}} t_i - i\phi_{\mathrm{input}}})\\\ & \stackrel{\mathrm{filter}}{=} \begin{cases} \frac{C_{\mathrm{scaling}}A_{i,\ \mathrm{input}}}{2}e^{i2\pi f_{\mathrm{baseband}} t_i + i\phi_{\mathrm{input}}}, & \mathrm{RF\ path,} \\\ C_{\mathrm{scaling}} A_{i,\ \mathrm{input}}\cos{(2\pi f_{\mathrm{baseband}} t_i + \phi_{\mathrm{input}})}, & \mathrm{LF\ path,} \end{cases} \end{aligned} \end{equation}

where fbaseband=fafter ADCfinput, LO2=foscf_{\mathrm{baseband}} = f_{\mathrm{after\ ADC}}-f_{\mathrm{input,\ LO2}} = f_{\mathrm{osc}} is the differential frequency, fsum=fbefore ADC+finput, LO2f_{\mathrm{sum}} = f_{\mathrm{before\ ADC}}+f_{\mathrm{input,\ LO2}} is the sum frequency. The signal at fsumf_{\mathrm{sum}} is filtered out by the digital filter. The baseband signal Ei, before integrationE_{i,\ \mathrm{before\ integration}} can be monitored by the SHFQA+ Scope as

EScope={2CscalingEi, before integration=Ai, input2ei2πfbasebandti+iϕinput,RF path, 1CscalingEi, before integration=Ai, inputcos(2πfbasebandti+ϕinput),LFpath. \begin{equation}\tag{5} E_{\mathrm{Scope}} = \begin{cases} \frac{\sqrt{2}}{C_{\mathrm{scaling}}} E_{i,\ \mathrm{before\ integration}} = \frac{A_{i,\ \mathrm{input}}}{\sqrt{2}}e^{i2\pi f_{\mathrm{baseband}} t_i + i\phi_{\mathrm{input}}}, & \mathrm{RF\ path,} \\\ \frac{1}{C_{\mathrm{scaling}}} E_{i,\ \mathrm{before\ integration}} =A_{i,\ \mathrm{input}}\cos{(2\pi f_{\mathrm{baseband}} t_i + \phi_{\mathrm{input}})}, & \mathrm{LF path.} \end{cases} \end{equation}

Note that the conversion factor 2/Cscaling\sqrt{2}/C_{\mathrm{scaling}} is used for the RF path, and 1/Cscaling1/C_{\mathrm{scaling}} is used for LF path. The signal Ei, before integrationE_{i,\ \mathrm{before\ integration}} is then demodulated with the signal ei2πfosctie^{-i2\pi f_{\mathrm{osc}} t_i} (fosc=fbasebandf_{\mathrm{osc}} =f_{\mathrm{baseband}}) from the baseband Digital Oscillator, integrated and normalized by the number of integration samples NN,

Eafter integration=1Ni=1NEi, before integrationei2πfoscti, ={Cscaling2Ni=1NAi, inputeiϕinput,RF path, Cscaling2Ni=1NAi, input(eiϕinput+ei4πfbasebandtiiϕinput),LF path. \begin{equation}\tag{6} \begin{aligned} E_{\mathrm{after\ integration}} & = \frac{1}{N}\sum_{i = 1}^{N}E_{i,\ \mathrm{before\ integration}}e^{-i2\pi f_{\mathrm{osc}} t_i},\\\ & = \begin{cases} \frac{C_{\mathrm{scaling}}}{2N}\sum_{i = 1}^{N} A_{i,\ \mathrm{input}}e^{i\phi_{\mathrm{input}}}, & \mathrm{RF\ path,}\\\ \frac{C_{\mathrm{scaling}}}{2N}\sum_{i = 1}^{N} A_{i,\ \mathrm{input}}(e^{i\phi_{\mathrm{input}}}+e^{-i 4 \pi f_{\mathrm{baseband}} t_i - i\phi_{\mathrm{input}}}), & \mathrm{LF\ path.} \end{cases} \end{aligned} \end{equation}

If Ai, input=AinputA_{i,\ \mathrm{input}} = A_{\mathrm{input}} is constant (and integration length is much longer than 1/(2fosc)1/(2 f_{\mathrm{osc}}) with LF path), then Eafter integration=CscalingAinput2eiϕinputE_{\mathrm{after\ integration}}=\frac{C_{\mathrm{scaling}}A_{\mathrm{input}}}{2}e^{i\phi_{\mathrm{input}}}. By multiply the factor of 2/Cscaling\sqrt{2}/C_{\mathrm{scaling}}, the units of the results is converted to Ainput2eiϕinput\frac{A_{\mathrm{input}}}{\sqrt{2}}e^{i\phi_{\mathrm{input}}}, and then can be downloaded from the instrument via the Instrument node /dev.../qachannels/n/spectroscopy/result/data/wave, see Device Node Tree. The power of input signal is then derived as

Pinput=10log10Eafter integration250+30. \begin{equation}\tag{7} \begin{aligned} P_{\mathrm{input}} & = 10\log_{10}\frac{|E_{\mathrm{after\ integration}}|^2}{50} + 30. \end{aligned} \end{equation}

The power and phase of the input signal can also be calculated and plotted using the Sweeper class.

Power spectral density

Power Spectral Density (PSD) measurements are generally required to characterize an amplification chain. In Spectroscopy mode, a PSD measurement can be performed using the SHFQA+ Sweeper, see GitHub zhinst-toolkit example or zhinst-toolkit Online Documentation, or using instrument nodes, see Device Node Tree.

Here, the PSD is calculated on the hardware as Sxx(f)=limN(Δt)2Tn=Nn=Nxnei2πfnΔt2S_{xx}(f) = \lim_{N\to\infty} \frac{(\Delta t)^2}{T}|\sum_{n = -N}^{n = N} x_ne^{-i2\pi f n\Delta t}|^2 (see Spectral density Wikipedia), where Δt=1/fs\Delta t = 1/f_\mathrm{s} is the time step, fsf_\mathrm{s} is the sampling rate, T=(2N+1)ΔtT = (2N+1)\Delta t is the integration length in seconds, 2N+12N+1 is the integration length in samples, xnx_n is the nn-th complex data of the input signal, ei2πfnΔte^{-i2\pi f n\Delta t} is the integration weight. This calculation is done by the Instrument, and it returns the real-valued PSD in units of Vrms2/Hz\mathrm{Vrms}^2/\mathrm{Hz}. The applicable ranges of the PSD measurement are listed in the table below.

Note that the measurement bandwidth is determined by the inverse of integration time, and the frequency step should be less than or equal to the measurement bandwidth. Typically, the PSD measurement requires many averages to be accurate. Setting the number of averages ≥ 1000 is recommended.

Table 4: Applicable ranges of PSD measurements
Parameters Values
LabOne version ≥ 23.02
Number of channels 2 or 4 for SHFQA+;
1 for SHFQC+
Input frequency range RF: 0.5 - 8.5 GHz
LF: DC - 800 MHz
Input Power Range RF: -50 to +10 dBm
LF: -30 to +10 dBm
Input waveform length continuous or pulsed (> 2 ns)
Measurement bandwidth (1 / integration time) 60 Hz to 500 MHz (16.7 ms to 2 ns)
Number of averages 1 to 131k
Input voltage noise density see Specifications
Input spurious free dynamic range (excluding harmonics) see Specifications

Readout Mode

Readout mode is mainly used for multi qubit readout. The SHFQA+ has 8 or 16 readout Waveform Memory slots, and 8 or 16 integration weight units per channel. In readout mode, these memory slots are used for readout pulse generation and weighted integration. The SHFQA+ Readout Pulse Generator is the central controller in Readout mode, see utorial Multiplexed Qubit Readout.

Figure 5: Readout waveform generation, integration and discrimination in Readout mode.

There are 2 state discrimination modes, 2-state discrimination (default, see tutorial Multiplexed Qubit Readout and multistate discrimination (see tutorial Multistate discrimination). Both modes are based on the linear Support Vector Machine and one versus one classification. Note that multistate discrimination can only be configured via LabOne APIs.

Base features in the Readout mode support multiplexed readout with integration length \le 2 μs. For longer integration up to 32 μs, the Long Readout Time (LRT) option is required, see the functional diagram below. Three functions are added by the LRT option.

  • added 3 oscillators per channel for modulation and demodulation
  • added Waveform Hold function for readout signal generation
  • added downsampling function for weighted integration

Figure 6: Readout waveform generation, integration and discrimination in Readout mode when modulation is enabled with the LRT option.

Readout Waveform Generation In Readout Mode

The readout waveform can be generated parametrically by LabOne GUI and APIs, and then uploaded and saved in the Waveform Memory. All readout waveforms saved in the Waveform Memory can be erased by clicking Clear on LabOne GUI or using LabOne APIs. Each readout waveform can be used for a single qudit readout, and up to 8 or 16 qubits can be readout simultaneously using a sum of the readout waveforms saved in the Waveform Memory. The Readout Waveform Generator controls which and how readout waveforms are played, see the Readout Pulse Generator Tab.

The readout waveform saved in the jj-th (jj\le 8 or 16) Waveform Memory slot is complex data, which can be expressed as

Ei, j, readout=Ai, j, readoutei2πfj, offsetti+iϕj, readout \begin{equation}\tag{8} \begin{aligned} E_{i,\ j,\ \mathrm{readout}} & = A_{i,\ j,\ \mathrm{readout}}e^{i2\pi f_{j,\ \mathrm{offset}}t_{i} + i\phi_{j,\ \mathrm{readout}}} \end{aligned} \end{equation}

where Ai, j, readout (0Ai, j, readout1)A_{i,\ j,\ \mathrm{readout}}\ (0\le A_{i,\ j,\ \mathrm{readout}}\le 1) is the amplitude factor of the readout waveform at the ii-th sample, fj, offsetf_{j,\ \mathrm{offset}} is the offset frequency, ϕj, readout\phi_{j,\ \mathrm{readout}} is the global phase.

Without the LRT option, or with the LRT option and both the modulation of numerical oscillators and the waveform hold function are disabled, the output signal on the front panel is

Eoutput(t)=Re[jAj, readout(t)ei2π(fj, offset+f0)t+iϕj, readout] \begin{equation}\tag{9} \begin{aligned} E_{\mathrm{output}}(t) & = \operatorname{Re}[\sum_j A_{j,\ \mathrm{readout}}(t)e^{i2\pi (f_{j,\ \mathrm{offset}}+f_0)t + i\phi_{j,\ \mathrm{readout}}}] \end{aligned} \end{equation}

where Aj, readout(t)A_{j,\ \mathrm{readout}}(t) is the waveform envelope from waveform memory slot jj. The output signal is sum of selected waveforms saved in the waveform memory. Note that the maximum amplitude factor of the sum of all waveforms in use should not exceed 1.

With the LRT option and the modulation of numerical oscillators is enabled, the output signal on the front panel is

Eoutput(t)=Re[jAj, readout(t)ei2π(fj, offset+foscj+f0)t+i(ϕj, readout+ϕoscj)Aoscj] \begin{equation}\tag{10} \begin{aligned} E_{\mathrm{output}}(t) & = \operatorname{Re}[\sum_j A'_{j,\ \mathrm{readout}}(t)e^{i2\pi (f_{j,\ \mathrm{offset}}+f_{\mathrm{osc}_j}+f_0)t + i(\phi_{j,\ \mathrm{readout}}+\phi_{\mathrm{osc}_j})}A_{\mathrm{osc}_j}] \end{aligned} \end{equation}

where Aj, readout(t)A'_{j,\ \mathrm{readout}}(t) is the waveform envelope from waveform memory slot jj which is extendable by a hold function with configurable hold index and hold length, fj, offsetf_{j,\ \mathrm{offset}} is set to 0 so the offset frequency is defined by the oscillator jj only (foscjf_{\mathrm{osc}_j}), AoscjA_{\mathrm{osc}_j} is the oscillator gain, , ϕoscj\phi_{\mathrm{osc}_j} is the oscillator phase. The output signal is sum of all oscillator-modulated waveforms, i.e. j3j \le 3 limited by the number of available oscillators.

Integration Weights

The integration weights can be parametrically generated or measured with the SHFQA+ Scope for the best SNR (see tutorial Integration Weights Measurement), and uploaded to the integration weight units. All integration weights saved in the memory can be erased by clicking Clear on LabOne GUI Integration Weights sub-tab or using LabOne APIs. The length of the integration weight is automatically extended to 4096 Samples once it’s uploaded, and integration length is used to configure how long it integrates. The Readout Waveform Generator controls which and how integration weights are used, see Readout Pulse Generator Tab.

The integration weights saved in the kk-th integration weight unit is complex data, can be expressed as

Ei, k, weights=Ai, k, weightei2πfk, weighttiiϕk, weight, \begin{equation}\tag{11} \begin{aligned} E_{i,\ k,\ \mathrm{weights}} & = A_{i,\ k,\ \mathrm{weight}}e^{-i2\pi f_{k,\ \mathrm{weight}}t_{i} - i\phi_{k,\ \mathrm{weight}}}, \end{aligned} \end{equation}

where Ai, k, weight (0Ai, k, weight1)A_{i,\ k,\ \mathrm{weight}}\ (0\le A_{i,\ k,\ \mathrm{weight}}\le 1) is the amplitude factor of the integration weight at ii-th sample, fk, weightf_{k,\ \mathrm{weight}} is the frequency of the integration weight, ϕk, weight\phi_{k,\ \mathrm{weight}} is the global phase of the integration weight. Without the LRT option, or with the LRT option and the modulation is disabled, fk, weightf_{k,\ \mathrm{weight}} equals one of the offset frequencies defined in readout waveform generation. With the LRT option and the modulation is enabled, fk, weightf_{k,\ \mathrm{weight}} equals 0 because the signal before weighted integration is already demodulated by the corresponding oscillator.

In 2-state discrimination mode, 1 qubit requires 1 integration weight, i.e. the conjugated difference of readout input signal while qubit is prepared in state |0> and |1>. In multistate discrimination mode, 1 qudit with nn states requires n(n1)/2n(n-1)/2 integration weighs (one vs one classification), i.e. the conjugated differences of any 2 readout input signal while qudit is prepared in state |ii> and |jj>, where i (0in2)i\ (0\le i\le n-2) and j (1jn1)j\ (1\le j\le n-1) are integer and iji \neq j. Only n1n-1 integration weights need to be uploaded, and the integration results from the rest of integration weights are calculated by the Instrument automatically.

Real-time multistate discrimination is not available for long (> 2 μs and \le 32 μs) multiplexed readout experiments that supported by the LRT option.

All integration weights saved in the integration weight units can be displayed on the Waveform Viewer, see Waveform Viewer.

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.

Thresholding

Thresholding sub-tab is used to configure thresholds for state discrimination in 2-state discrimination mode. In multistate discrimination mode, thresholds and assignment matrix are configured by LabOne APIs.

The input signal before integration is

Ei, before integration={CscalingjAi, j, input2ei2πfj, basebandti+ϕj, input,RF path, CscalingjAi, j, inputcos(2πfj, basebandti+ϕj, input),LF path, \begin{equation}\tag{12} \begin{aligned} E_{i,\ \mathrm{before\ integration}} = \begin{cases} C_{\mathrm{scaling}}\sum_j \frac{A_{i,\ j,\ \mathrm{input}}}{2}e^{i2\pi f_{j,\ \mathrm{baseband}}t_i+\phi_{j,\ \mathrm{input}}}, & \mathrm{RF\ path},\\\ C_{\mathrm{scaling}}\sum_j A_{i,\ j,\ \mathrm{input}}\cos{(2\pi f_{j,\ \mathrm{baseband}}t_i+\phi_{j,\ \mathrm{input}}}), & \mathrm{LF\ path}, \end{cases} \end{aligned} \end{equation}

where ii indicates the ii-th sample of the input signal, jj indicates the jj-th component of the input signal for a qubit or qudit, Ai, j, inputA_{i,\ j,\ \mathrm{input}} is the amplitude of jj-th components of the input signal, fj, basebandf_{j,\ \mathrm{baseband}} is the frequency of jj-th component of the input signal, ϕj, input\phi_{j,\ \mathrm{input}}, is the phase of jj-th component of input signal. The signal can be monitored by the SHFQA+ Scope with the same conversion factors as in Spectroscopy mode,

EScope={ΣjAi, j, input2ei2πfj, basebandti+iϕj, input,RF path, ΣjAi, j, inputcos(2πfj, basebandti+ϕj, input),LF path. \begin{equation}\tag{13} E_{\mathrm{Scope}} = \begin{cases} \Sigma_j\frac{A_{i,\ j,\ \mathrm{input}}}{\sqrt{2}}e^{i2\pi f_{j,\ \mathrm{baseband}} t_i + i\phi_{j,\ \mathrm{input}}}, & \mathrm{RF\ path,} \\\ \Sigma_j A_{i,\ j,\ \mathrm{input}}\cos{(2\pi f_{j,\ \mathrm{baseband}} t_i + \phi_{j,\ \mathrm{input}})}, & \mathrm{LF\ path.} \end{cases} \end{equation}

Without the LRT option, or with the LRT option and the modulation is disabled, this signal is then integrated with integration weights Ai, j, weightei2πfj, weighttiiϕj, weightA_{i,\ j,\ \mathrm{weight}}e^{-i2\pi f_{j,\ \mathrm{weight}}t_i-i\phi_{j,\ \mathrm{weight}}} (fj, weight=fj, basebandf_{j,\ \mathrm{weight}} = f_{j,\ \mathrm{baseband}}) simultaneously. With the LRT option and the modulation is enabled, this signal is demodulated by the oscillators first and then integrated with integration weights Ai, j, weighteiϕj, weightA_{i,\ j,\ \mathrm{weight}}e^{-i\phi_{j,\ \mathrm{weight}}} (fj, weight=0f_{j,\ \mathrm{weight}} = 0) with a downsampling factor of NN (NN is an integer from 1 to 16).
The jj-th integration result after weighted integration is

Ej, after integration=Σi=1NEi, j, before integrationAi,j, weightei2πfj, basebandtiiϕj, weight ={Cscaling2i=1NAi, j, inputAi,j, weightei(ϕj, inputϕj, weight),RF path, Cscaling2i=1NAi, j, inputAi,j, weight× (ei(ϕj, inputϕj, weight)+ei4πfj, basebandtiiϕj, weightiϕj, weight),LF path. \begin{equation}\tag{14} \begin{aligned} E_{j,\ \mathrm{after\ integration}} &= \Sigma_{i=1}^N {E_{i,\ j,\ \mathrm{before\ integration}}A_{i, j,\ \mathrm{weight}}e^{-i2\pi f_{j,\ \mathrm{baseband}}t_i-i\phi_{j,\ \mathrm{weight}}}}\\\ &= \begin{cases} \frac{C_{\mathrm{scaling}}}{2}\sum_{i=1}^N A_{i,\ j,\ \mathrm{input}}A_{i, j,\ \mathrm{weight}}e^{i(\phi_{j,\ \mathrm{input}}-\phi_{j,\ \mathrm{weight}})}, & \mathrm{RF\ path,}\\\ \frac{C_{\mathrm{scaling}}}{2}\sum_{i=1}^N A_{i,\ j,\ \mathrm{input}}A_{i, j,\ \mathrm{weight}}\times\\\ (e^{i(\phi_{j,\ \mathrm{input}}-\phi_{j,\ \mathrm{weight}})} + e^{-i 4 \pi f_{j,\ \mathrm{baseband}}t_i-i\phi_{j,\ \mathrm{weight}}-i\phi_{j,\ \mathrm{weight}}}), & \mathrm{LF\ path.} \end{cases} \end{aligned} \end{equation}

If ϕj, input=ϕj, weight\phi_{j,\ \mathrm{input}}=\phi_{j,\ \mathrm{weight}}, Ai, j, input=Aj, inputA_{i,\ j,\ \mathrm{input}} = A_{j,\ \mathrm{input}} is a constant, Ai, j, weights=1A_{i,\ j,\ \mathrm{weights}} = 1, and integration length is much longer than 1/(2fj, baseband)1/(2 f_{j,\ \mathrm{baseband}}) with LF path, the result after integration can be simplified as Ej, after integration=NCscalingAj, input2E_{j,\ \mathrm{after\ integration}} = \frac{NC_{\mathrm{scaling}}A_{j,\ \mathrm{input}}}{2}. This result with RF (LF) path is complex data, and can be downloaded and displayed on the Quantum Analyzer Result Tab with a conversion factor of 2/Cscaling\sqrt{2}/C_{\mathrm{scaling}} (1/Cscaling1/C_{\mathrm{scaling}}), as NAj, input2\frac{NA_{j,\ \mathrm{input}}}{\sqrt{2}} (NAj, input2\frac{NA_{j,\ \mathrm{input}}}{2}).

To achieve the best SNR, the largest separation of qubit states and discriminate states with real data, one can apply optimal weights (Ej, b, ScopeEj,a, Scope)/Anorm(E_{j,\ |b\rangle,\ \mathrm{Scope}} - E_{j,\, |a\rangle,\ \mathrm{Scope}})^*/A_{\mathrm{norm}}, where Ej,b, ScopeE_{j,\, |b\rangle,\ \mathrm{Scope}} (Ej,a, ScopeE_{j,\, |a\rangle,\ \mathrm{Scope}}) is the readout signal when qubit in state b|b\rangle (a|a\rangle) before integration recorded by the scope, "*" is a conjugate operation, AnormA_{\mathrm{norm}} is a factor to normalize the optimal weights. The readout signal Eb , after integrationE_{|b\rangle\ ,\ \mathrm{after\ integration}} of a single qubit after weighted integration with the optimal weights is

Eb , after integration ={Cscaling2Σi=1NAi, bAi, normeiϕb(Ai, beiϕbAi, aeiπa),RF path, CscalingΣi=1NAi, bAi, normcosϕb(Ai, bcosϕbAi, acosϕa),LF path, ={Cscaling2Σi=1NAi, bAi, norm[Ai, bAi, acos(ϕbϕa)iAi, asin(ϕbϕa)],RF path, CscalingΣi=1NAi, bAi, normcosϕb(Ai, bcosϕbAi, acosϕa),LF path, \begin{equation}\tag{15} \begin{aligned} &E_{|b\rangle\ ,\ \mathrm{after\ integration}}\\\ &= \begin{cases} \frac{C_{\mathrm{scaling}}}{2}\Sigma_{i=1}^N\frac{A_{i,\ |b\rangle}}{A'_{i,\ \mathrm{norm}}}e^{i\phi_{|b\rangle}}(A_{i,\ |b\rangle}e^{i\phi_{|b\rangle}} - A_{i,\ |a\rangle}e^{i\pi_{|a\rangle}})^*,& \mathrm{RF\ path},\\\ C_{\mathrm{scaling}}\Sigma_{i=1}^N\frac{A_{i,\ |b\rangle}}{A''_{i,\ \mathrm{norm}}}\cos{\phi_{|b\rangle}}(A_{i,\ |b\rangle}\cos{\phi_{|b\rangle}} - A_{i,\ |a\rangle}\cos{\phi_{|a\rangle}}), & \mathrm{LF\ path}, \end{cases}\\\ &= \begin{cases} \frac{C_{\mathrm{scaling}}}{2}\Sigma_{i=1}^N\frac{A_{i,\ |b\rangle}}{A'_{i,\ \mathrm{norm}}}[A_{i,\ |b\rangle}-A_{i,\ |a\rangle}\cos{(\phi_{|b\rangle}-\phi_{|a\rangle})-i A_{i,\ a}\sin{(\phi_{|b\rangle}-\phi_{|a\rangle})}}], & \mathrm{RF\ path},\\\ C_{\mathrm{scaling}}\Sigma_{i=1}^N\frac{A_{i,\ |b\rangle}}{A''_{i,\ \mathrm{norm}}}\cos{\phi_{|b\rangle}}(A_{i,\ |b\rangle}\cos{\phi_{|b\rangle}} - A_{i,\ |a\rangle}\cos{\phi_{|a\rangle}}), & \mathrm{LF\ path}, \end{cases} \end{aligned} \end{equation}

where Ai, norm=Ai, b2+Ai, a22Ai, aAi, bcos(ϕaϕb)A'_{i,\ \mathrm{norm}}=\sqrt{A_{i,\ |b\rangle}^2+A_{i,\ |a\rangle}^2-2 A_{i,\ |a\rangle}A_{i,\ |b\rangle}\cos{(\phi_{|a\rangle}-\phi_{|b\rangle})}} (Ai, norm=Ai, bcosϕbAi, acosϕaA''_{i,\ \mathrm{norm}}=A_{i,\ |b\rangle}\cos{\phi_{|b\rangle}} - A_{i,\ |a\rangle}\cos{\phi_{|a\rangle}}) is a normalization factor, Ai, bA_{i,\ |b\rangle} (Ai, aA_{i,\ |a\rangle}) and ϕb\phi_{|b\rangle} (ϕa\phi_{|a\rangle}) is the amplitude and phase of the signal in state b|b\rangle (a|a\rangle), respectively. Similarly, the readout signal Ea , after integrationE_{|a\rangle\ ,\ \mathrm{after\ integration}} after weighted integration with the optimal weights is

Ea , after integration ={Cscaling2Σi=1NAi, aAi, norm[Ai, a+Ai, bcos(ϕaϕb)+iAi, bsin(ϕaϕb)],RF path, CscalingΣi=1NAi, aAi, normcosϕa(Ai, bcosϕbAi, acosϕa),LF path, \begin{equation}\tag{16} \begin{aligned} &E_{|a\rangle\ ,\ \mathrm{after\ integration}}\\\ &=\begin{cases} \frac{C_{\mathrm{scaling}}}{2}\Sigma_{i=1}^N\frac{A_{i,\ |a\rangle}}{A'_{i,\ \mathrm{norm}}}[-A_{i,\ |a\rangle}+A_{i,\ |b\rangle}\cos{(\phi_{|a\rangle}-\phi_{|b\rangle})+i A_{i,\ |b\rangle}\sin{(\phi_{|a\rangle}-\phi_{|b\rangle})}}], & \mathrm{RF\ path},\\\ C_{\mathrm{scaling}}\Sigma_{i=1}^N\frac{A_{i,\ |a\rangle}}{A''_{i,\ \mathrm{norm}}}\cos{\phi_{|a\rangle}}(A_{i,\ |b\rangle}\cos{\phi_{|b\rangle}} - A_{i,\ |a\rangle}\cos{\phi_{|a\rangle}}), & \mathrm{LF\ path}, \end{cases} \end{aligned} \end{equation}

Take the real part of the integrated results, and the 2 states can be discriminated by a threshold as

Re[Eb , after integration]+Re[Ea , after integration]2 ={Cscaling2Σi=1N1A_i, norm(Ai, b2Ai, a2),RF path, CscalingΣi=1N1Ai, norm(Ai, b2cos2ϕbAi, a2cos2ϕa),LF path. \begin{equation}\tag{17} \begin{aligned} &\frac{\operatorname{Re}[E_{|b\rangle\ ,\ \mathrm{after\ integration}}]+\operatorname{Re}[E_{|a\rangle\ ,\ \mathrm{after\ integration}}]}{2}\\\ &=\begin{cases} \frac{C_{\mathrm{scaling}}}{2}\Sigma_{i=1}^N\frac{1}{A'\_{\mathrm{i,\ norm}}}(A_{i,\ |b\rangle}^2 - A_{i,\ |a\rangle}^2), & \mathrm{RF\ path},\\\ C_{\mathrm{scaling}}\Sigma_{i=1}^N\frac{1}{A''_{\mathrm{i,\ norm}}}(A_{i,\ |b\rangle}^2\cos^2{\phi_{|b\rangle}} - A_{i,\ |a\rangle}^2\cos^2{\phi_{|a\rangle}}), & \mathrm{LF\ path}. \end{cases} \end{aligned} \end{equation}

The separation between state b|b\rangle and state a|a\rangle can be calculated directly as Σi=1N(Ai, b2+Ai, a22Ai, aAi, bcos(ϕbϕa))\sqrt{\Sigma_{i=1}^N(A_{i,\ |b\rangle}^2 + A_{i,\ |a\rangle}^2-2 A_{i,\ |a\rangle}A_{i,\ |b\rangle}\cos{(\phi_{|b\rangle}-\phi_{|a\rangle})}}), and it is the same as calculated from

Re[Eb , after integration]Re[Ea , after integration]. \begin{equation}\tag{18} \begin{aligned} |\operatorname{Re}[E_{|b\rangle\ ,\ \mathrm{after\ integration}}]-\operatorname{Re}[E_{|a\rangle\ ,\ \mathrm{after\ integration}}]|. \end{aligned} \end{equation}

In 2-state discrimination mode, all integration weights can be uploaded via LabOne GUI and APIs, and all integration results saved in the result logger can be displayed on the Quantum Analyzer Result Tab if integration is selected as result source. In multistate discrimination mode, all integration weights can only be uploaded via LabOne APIs, and only n1n-1 integration results are saved in the result logger if integration is selected as result source, the rest are calculated automatically in the pairwise difference units.

Before state discrimination, threshold TjT_j for each qudit has to be estimated and uploaded to the Instrument with an internal conversion factor 2Cscaling\frac{2}{C_{\mathrm{scaling}}} (1Cscaling\frac{1}{C_{\mathrm{scaling}}}) in RF (LF) path, see tutorial Multistate discrimination). During thresholding, the real part of the result after integration is compared with a threshold, and it returns 0 or 1. Qubit state discrimination can be done in both 2-state and multistate discrimination modes. The readout result of qubit after thresholding is

Ej, after thresholding={0Re[Ej, after integration]Tj, 1Re[Ej, after integration]>Tj, \begin{equation}\tag{19} \begin{aligned} E_{j,\ \mathrm{after\ thresholding}}= \begin{cases} 0 & \mathrm{Re}[E_{j,\ \mathrm{after\ integration}}] \le T_j,\\\ 1 & \mathrm{Re}[E_{j,\ \mathrm{after\ integration}}] \gt T_j, \end{cases} \end{aligned} \end{equation}

where TjT_j is the threshold of the jj-th qubit. The result after thresholding and state assignment can represent qubit state directly.

Figure 7: Readout data processing for qubits. The green blocks are used for both state discrimination modes and the blue blocks are used for multistate discrimination mode only configured by LabOne APIs. xix_i is the readout input signal at the ii-th sample, w1, iw_{1,\ i} is the optimal integration weight calculated from the difference while qubit is prepared in state |0> and |1>, T1T_1 is the threshold for the integrated result, b1=0b_1 = 0 or 11 is the binary value after thresholding. The assignment matrix is defined such that if the b1=0 (1)b_1 = 0\ (1) the result after discrimination is 1 (0), i.e. state |1> (|0>).

For a qutrit, 3 thresholds are used, 2 for the integration results in the weighted integration units and 1 for the integration result in the pairwise difference units. After thresholding, the 3-bit data is assigned to 0, 1 or 2 by the assignment matrix, and the discriminated results can be displayed in the Quantum Analyzer Result Tab. The state assignment can be customized by uploading 8 integer numbers (0, 1 or 2) for a single qutrit via API. The discriminated result represented by 2-bit data can be transferred to control instruments via DIO and ZSync for feedback experiment.

Figure 8: Readout data processing for qutrits. The green blocks are used for both state discrimination modes and the blue blocks are used for multistate discrimination mode only configured by LabOne APIs. xix_i is the readout input signal at the ii-th sample,w1, iw_{1,\ i} and w2, iw_{2,\ i} are the integration weights measured by calculating the readout pulse difference when the qutrit is prepared in state |0> and |1>, and state |0> and |2>, respectively. "r2r1r_2 - r_1" calculated by the instrument is the pairwise difference of the integration results, T1T_1, T2T_2 and T3T_3 are the thresholds for the 3 integration results, b1b_1, b2b_2 and b3b_3 are the binary value after the thresholding. The assignment matrix is defined such that the result after discrimination is 0, 1 or 2, i.e. state |0>, |1> or |2>, respectively. Result with "*" is assigned ambiguously because all states are equally likely.

For a ququad, 6 thresholds are used, 3 for the integration results in the weighted integration units and 3 for the integration results in the pairwise difference units. After thresholding, the 6-bit data is assigned to 0, 1, 2 or 3 by the assignment matrix, and the discriminated results can be displayed in the Quantum Analyzer Result Tab. The state assignment can be customized by uploading 64 decimal numbers (0, 1, 2 or 3) for a single ququad via API. The discriminated result represented by 2-bit data can be transferred to control instruments via DIO and ZSync for feedback experiment.

Figure 9: Readout data processing for ququads. xix_i is the readout input signal at the ii-th sample, w1, iw_{1,\ i}, w2, iw_{2,\ i} and w3, iw_{3,\ i} are the integration weights measured by calculating the readout pulse difference when the ququad is prepared in state |0> and |1>, state |0> and |2>, and state |0> and |3>, respectively. "r2r1r_2 - r_1", "r3r1r_3 - r_1", "r3r2r_3 - r_2" calculated by the instrument are the pairwise differences of the integration results, T1T_1, T2T_2, T3T_3, T4T_4, T5T_5 and T6T_6 are the thresholds for 6 integration results, b1b_1, b2b_2, b3b_3, b4b_4, b5b_5 and b6b_6 are the binary value after thresholding. The assignment matrix is defined such that the result after discrimination is 0, 1, 2 or 3, i.e. state |0>, |1>, |2> or |3>, respectively. Result with "*" is assigned ambiguously because 2 or more states are equally likely.

Functional Elements

Table 5: QA setup settings
Control/Tool Option/Range Description
Application Mode Spectroscopy Using internal digital oscillator for waveform generation and integration.
  Readout Using uploaded waveform for output signal generation and customized weights for integration.
Spectroscopy    
Trigger Signal Selects the source of the trigger for the integration and envelope in Spectroscopy mode.
Integration Length 2^2 to 2^25 Sets the integration length in Spectroscopy mode in number of samples. Up to 33.5 MSa (2^25 samples, with granularity of 4 Samples ) can be recorded, which corresponds to 16.7 ms.
Integration Delay -4 ns to 131.1 μs Sets the delay of the integration in Spectroscopy mode with respect to the trigger signal. The resolution is 2 ns.
Power Spectral Density Enable/Disable Enable or disable power spectral density mode.
Center Frequency RF: 1 - 8 GHz
LF: 0 Hz
Display center frequency in Spectroscopy mode.
Offset Frequency - 1 to +1 GHz Set offset frequency to the internal digital oscillator in Spectroscopy mode.
Output Frequency DC - 8.5 GHz Display frequency of the output signal in Spectroscopy mode.
Amplitude 0 to 1 Set gain of the internal digital oscillator in Spectroscopy mode. The recommended range is from 0.01 to 1 in pulsed mode.
Waveform Mode Continuous The output of the internal digital oscillator is used directly for frequency up-conversion.
  Pulse The waveform envelope is modulated by the internal digital oscillator before frequency up-conversion.
Length 4 to 32 kSa or 64 kSa (with 16W option) Indicate the length of uploaded envelope waveform in units of Samples. The granularity is 4 Samples.
Delay 0 ns to 131.1 μs Set a delay between readout pulse playback trigger and the first sample of the readout pulse (in Pulsed mode). The resolution is 2 ns.
File Upload CSV file Drop CSV file to upload the envelope waveform.
Readout    
Integration Delay 0 ns to 131.1 μs Sets a common delay for the start of the readout integration for all Integration Weights with respect to the time when the trigger is received. The resolution is 2 ns.
Errors Number Number of hold-off errors detected since last reset.
Modulation (LRT option) Enable/Disable Enable or disable modulation.
Frequency (LRT option) -1 GHz to 1 GHz Set oscillator frequency.
Gain (LRT option) 0 to 1 Set oscillator gain.
Sequencer Run/Stop Run or Stop Enables the Sequencer.
Waveforms Clear Empty all readout Waveform Memory slots or Integration weight Units.
Waveform/Weight Generation Mode Parametric or Upload Select the way to generate waveform.
Parametric Amplitude 0 to 1 Set amplitude factor for parametric readout pulse and integration weight generation.
Parametric Frequency -1 to +1 GHz Set offset frequency for parametric readout pulse or integration weight generation.
Parametric Phase -180 to 180 degree Set phase for parametric readout pulse and integration weight generation.
Parametric Window Type Rectangular Display window function to be applied in complex exponential function for parametric readout pulse and integration weight generation.
Parametric Window Length 4 to 4096 Length of the selected window in samples for parametric readout pulse and integration weight generation.
Waveform/Weight Set To Device Yes or No Set parametrically generated readout pulse and integration weight to waveform memory slot and integration memory slot, respectively.
Hold (LRT option) Enable/Disable Enable or disable hold function.
Hold Start Index (LRT option) 4 to 4092 Set an index of waveform data that the corresponding value will be hold for a defined period.
Hold Length (LRT option) 8 to 4194300 Set hold length in number of samples.
Integration Length 4 to 4096 Sets the length of all Integration Weights in number of samples. A maximum of 4096 samples can be integrated, which corresponds to 2.05 μs. The granularity is 4 Samples.
Downsampling Factor (LRT option) 1 to 16 Set downsampling factor to extend integration length.
Thresholding -14.51 kV to 14.51 kV Set threshold for quantum state discrimination. Note that the data before thresholding is not normalized by the integration length.