Dual-channel measurement device for KIDs characteristics based on cross-correlation algorithm

Abstract

This invention proposes a dual-channel measurement device for KIDs characteristics based on a cross-correlation algorithm, mainly composed of a signal generator, a dual-channel zero-difference mixing system, a KIDs detector, an ADC data acquisition card, and a control computer. The measurement device obtains four signals by performing zero-difference mixing on the output signals of the KIDs using a dual mixer, and samples these four signals through the ADC data acquisition card. The control computer suppresses measurement noise through cross-correlation calculations to obtain the characteristic parameters of the KIDs. The control computer can perform seven-parameter fitting, resonance characteristic characterization, fast Fourier transform, cross-correlation calculation, and PSD calculation. This invention enables the characteristic measurement and noise readout of terahertz KIDs, and effectively suppresses noise in the measurement system.

Description

Technical Field

[0001] This invention belongs to the field of terahertz technology research, specifically relating to a dual-channel measurement device for KIDs characteristics based on a cross-correlation algorithm. Background Technology

[0002] Kinetic inductance detectors (KIDs) are superconducting devices used to measure electromagnetic radiation. They are microwave detectors based on superconducting materials, detecting electromagnetic radiation by measuring changes in the dynamic inductance within the superconducting material.

[0003] KIDs (Knowledge Inductors) work on the principle that the inductance of superconducting materials changes when exposed to electromagnetic radiation. When an electromagnetic wave interacts with a KID, the wave's energy is absorbed, causing the temperature of the electron and Coulomb pairs in the superconducting material to rise. This leads to a change in the superconducting material's resistance, which in turn alters its inductance. By measuring this change in inductance, the presence and characteristics of the electromagnetic wave can be determined.

[0004] KIDs are highly sensitive to weak electromagnetic radiation, enabling them to detect very low-energy signals. Secondly, KIDs have a wide bandwidth, allowing them to operate over a broad frequency range. Furthermore, KIDs exhibit fast response times and low noise levels, making them widely applicable in fields such as astronomy, spectroscopy, and quantum computing.

[0005] KIDs are used to detect and measure faint microwave and infrared radiation for studying the origin of the universe, interstellar dust, and galaxy evolution. Furthermore, KIDs are used in spectroscopic research, such as particle detection and molecular spectroscopy. In the field of quantum computing, KIDs are used as readout devices for qubits, measuring and controlling the state of superconducting qubits.

[0006] By obtaining the amplitude or phase change information of the microwave resonator through the readout circuit, the information characteristics of the incident photon signal can be indirectly detected. Phase noise is one of the main parameters characterizing the performance of KIDs detectors and directly affecting the overall sensitivity of terahertz imaging systems; its importance is undeniable. Currently, KIDs phase noise measurement hardware systems generally employ microwave quadrature mixers, combined with auxiliary circuit modules such as low-noise amplifiers, power dividers, adjustable attenuators, fixed attenuators, bandpass filters, and low-pass filters, to measure phase noise through homodyne mixing. By processing the data from the I and Q quadrature intermediate frequency output signals, the phase noise θ(f) and amplitude noise A(f) of the KIDs detector can be obtained simultaneously.

[0007] The conventional measurement method consists of a broadband quadrature mixer (generally based on two double-balanced mixers and a 3dB equal-phase power divider) and a 3dB equal-phase directional coupler with a 90° orthogonal phase difference. The RF signal with equal phase and the local oscillator signal with a 90° phase difference are down-mixed in the two double-balanced mixers, resulting in two intermediate frequency (IF) signals, I and Q, with a quadrature phase difference. The ADC processes the acquired I and Q data using software to obtain the noise power spectral density (PSD) of the KIDs.

[0008] Existing conventional KIDs readout circuits have the following problems: the noise acquired by existing measurement systems is not only the noise of the KIDs, but also includes the superposition of noise from amplifiers, attenuators, directional couplers, mixers and other devices in the KIDs readout system. When the noise of the KIDs is very low, the noise generated by the devices in the readout system cannot be ignored, and commonly used noise measurement systems cannot meet the requirements. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a dual-channel measurement device for KIDs characteristics based on a cross-correlation algorithm, which can realize the readout of terahertz KIDs detector characteristics and the noise suppression of the measurement device.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A dual-channel measurement device for KIDs characteristics based on cross-correlation algorithm is characterized by comprising: a signal generator, a dual-channel zero-difference mixer system, a KIDs detector, an ADC data acquisition card, and a control computer.

[0012] The dual-channel zero-difference mixer system includes a directional coupler, a first power divider, a second power divider, a first IQ mixer, and a second IQ mixer. The input of the directional coupler is connected to a signal generator, and the output of the directional coupler is divided into a through-channel and a coupled-channel. The through-channel divides the signal into two signals, LO1 and LO2, by the first power divider, which serve as the local oscillator signals for the first IQ mixer and the second IQ mixer, respectively. The coupled-channel transmits the signal to the KIDs detector.

[0013] The output signal of the KIDs detector is amplified and then divided into two signals RF1 and RF2 by the second power divider, which are used as the radio frequency signals of the first IQ mixer and the second IQ mixer, respectively.

[0014] The first IQ mixer inputs signals LO1 and RF1, and outputs a time-domain DC signal via the difference frequency to the ADC data acquisition card;

[0015] The second IQ mixer inputs signals LO2 and RF2, and outputs a time-domain DC signal via the difference frequency to the ADC data acquisition card;

[0016] The ADC data acquisition card inputs the acquired signals into the control computer;

[0017] The control computer processes the signals acquired by the ADC data acquisition card based on Fourier transform and cross-correlation operations to obtain the characteristic parameters of KIDs.

[0018] To optimize the above technical solution, the specific measures also include:

[0019] Furthermore, the output signal of the KIDs detector is amplified by a low-temperature, low-noise amplifier.

[0020] Furthermore, both the KIDs detector and the low-temperature low-noise amplifier are housed in a Dewar and operate at the superconducting critical temperature.

[0021] Furthermore, the time-domain DC signals output by the first IQ mixer and the second IQ mixer are both filtered by a low-pass filter and an impedance transformer before being input to the ADC data acquisition card.

[0022] Furthermore, the ADC data acquisition card samples the time-domain DC signal output by the first IQ mixer into two orthogonal signals I(t)1 and Q(t)1, and samples the time-domain DC signal output by the second IQ mixer into two orthogonal signals I(t)2 and Q(t)2.

[0023] Furthermore, the control computer executes the following process to obtain the characteristic parameters of the KIDs:

[0024] First, the n sets of signals sampled by the ADC data acquisition card are subjected to seven-parameter fitting and calibration processing. Each set of signals includes I(t)1, Q(t)1 and I(t)2, Q(t)2, to obtain ADC sampling data that meets the ideal resonance characteristics.

[0025] Based on the ADC sampling data after seven-parameter fitting and calibration, n sets of time-domain data for amplitude and phase are obtained;

[0026] Perform a Fast Fourier Transform on n sets of amplitude and phase time-domain data to obtain n sets of amplitude and phase frequency-domain data;

[0027] Cross-correlation is performed on the frequency domain data of each set of amplitude and phase to obtain n sets of amplitude and phase noise data. The average value of the n sets of amplitude and phase noise data is taken, and the noise power spectral density of amplitude and phase is obtained through calculation.

[0028] Furthermore, the seven-parameter fitting is performed based on the S21 curve equation of the resonator that satisfies the ideal resonance characteristics:

[0029]

[0030] In the formula, S 21 (f) represents the transmission coefficient, f represents the detection frequency, fr represents the resonant frequency, and Q l Q represents the load quality factor. c This represents the absolute value of the coupling quality factor. τ represents impedance mismatch, a represents additional amplitude, α represents a phase shift, i represents a complex number, and τ represents the electronic delay caused by cable length and finite speed of light.

[0031] Furthermore, the calculation formulas for the frequency domain data of the amplitude and phase are as follows:

[0032]

[0033] θ(f)=FFT(tan -1 (I(t) / Q(t)))

[0034] In the formula, A(f) and θ(f) represent the amplitude frequency domain data and phase frequency domain data of the same group, respectively. FFT represents the fast Fourier transform. I(t) and Q(t) represent the signal data obtained after seven-parameter fitting and calibration of two orthogonal signals from the same IQ mixer.

[0035] The beneficial effects of this invention are as follows: This invention employs a dual-channel zero-difference mixing structure. The output signal of the KIDs detector is simultaneously split into two paths and mixed by two IQ mixers. The difference frequency after mixing results in two time-domain DC signal outputs, and the ADC samples these into four signals. This effectively measures the characteristics of terahertz KIDs detectors. Simultaneously, the measured time-domain data undergoes cross-correlation processing after frequency domain transformation to further suppress interference signals, resulting in more accurate PSD curves for the KIDs. This invention achieves noise measurement of different test links in dual-channel KIDs and effectively suppresses additional noise generated by different test links through data processing. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structural principle of a dual-channel measurement device for KIDs characteristics based on the cross-correlation algorithm.

[0037] Figure 2 It is a block diagram for controlling the data processing of a computer.

[0038] Figure 3 This is a comparison chart of phase noise and amplitude noise PSDs for commonly used measurements and autocorrelation processing of KIDs resonant points. Detailed Implementation

[0039] The invention will now be described in further detail with reference to the accompanying drawings.

[0040] like Figure 1 As shown, this invention proposes a dual-channel measurement device for KIDs characteristics based on a cross-correlation algorithm. This measurement device can achieve: 1. readout of terahertz KIDs detector characteristics; 2. noise suppression of the measurement device.

[0041] The measuring device mainly includes: a signal generator, a dual-channel zero-difference mixer system, KIDs detectors, an ADC data acquisition card, and a control computer; wherein, the dual-channel zero-difference mixer system includes: a directional coupler, a first power divider, a second power divider, a first IQ mixer, and a second IQ mixer. The specific implementation of the measuring device is as follows.

[0042] I. Hardware Circuit Design - Noise Readout of Terahertz KIDs

[0043] The signal generator outputs a probe signal, which is split into two channels by a directional coupler. The direct-end channel further divides the signal from the signal source into two reference signals, LO1 and LO2, by the first power divider, and these signals serve as the local oscillator signals (LO) for two identical IQ mixers. The signal from the coupled-end channel of the directional coupler is transmitted to the KIDs detector and, after multi-stage amplification, becomes the radio frequency (RF) signal for the IQ mixer. The KIDs detector is located on the cold plate of the Dewar and needs to operate below the superconducting critical temperature (approximately 1.27 K), functioning by detecting changes in the resonant characteristics generated by the probe signal.

[0044] The cryogenic low-noise amplifier (HMET) amplifies the output signal of the KIDs detector within the Dewar flask. Outside the Dewar flask, the HMET output signal is split into two identical signals, RF1 and RF2, via a second power divider. RF1 and LO1, and RF2 and LO2, serve as the input signals to the first and second IQ mixers, respectively. The difference frequency of these mixers produces a DC signal output. These two time-domain DC signals are filtered by a low-pass filter and then input to an ADC data acquisition card via an impedance transformer, where they are sampled as four signals: I(t)1 and Q(t)1, and I(t)2 and Q(t)2. The control computer then converts these two time-domain signals into amplitude or phase noise in the frequency domain using autocorrelation and Fourier transform. A signal generator can generate the frequency of the KIDs resonant point and allows for different input power settings for measurement.

[0045] II. Software Data Processing.

[0046] This part is executed by the control computer, and the specific process is as follows: Figure 2As shown. The signal acquired by the ADC data acquisition card must first undergo seven-parameter fitting. Due to impedance mismatch, standing waves, signal transmission delay of the cable, and the quality factor of the KIDs themselves, the resonant characteristics of the KIDs acquired by the ADC data acquisition card differ somewhat from the ideal resonant characteristics, requiring calibration of these parameters. The equation for the S21 curve of the resonator that satisfies the ideal resonant characteristics is:

[0047]

[0048] In the formula, S 21 (f) represents the transmission coefficient, f represents the detection frequency, fr represents the resonant frequency, and Q l Q represents the load quality factor. c This represents the absolute value of the coupling quality factor. τ represents impedance mismatch, a represents additional amplitude, α represents a phase shift, i represents a complex number, and τ represents the electronic delay caused by cable length and finite speed of light.

[0049] The data acquired by the ADC data acquisition card is fitted with seven parameters using the above formula, and then calibrated to obtain data that meets the general ideal resonance characteristics.

[0050] Then, the amplitude and phase time-domain data of the ADC sampled data, after seven-parameter fitting and calibration, are obtained and subjected to Fast Fourier Transform. The formula for the calculation is shown below:

[0051]

[0052] θ(f)=FFT(tan -1 (I(t) / Q(t)))

[0053] In the formula, A(f) and θ(f) represent the amplitude frequency domain data and phase frequency domain data of the same group, respectively. FFT represents the fast Fourier transform. I(t) and Q(t) represent the signal data obtained after seven-parameter fitting and calibration of two orthogonal signals from the same IQ mixer.

[0054] Finally, a cross-correlation operation is performed on A(f) and θ(f) of the same group using the cross-correlation function Xcor. Then, the average value of the n sets of amplitude and phase noise data is taken, and the amplitude and phase noise power spectral densities are obtained through calculation. The cross-correlation operation can well represent the noise generated by the same KIDs, while the noise generated by the measuring device is suppressed by the cross-correlation operation, thereby enhancing the accuracy of the measurement system.

[0055] Figure 3This is a comparison of the phase noise and amplitude noise PSD of the resonant point of KIDs using common measurements and autocorrelation processing. As can be seen from the figure, the noise curve of the commonly measured method exhibits a large amount of 50Hz interference signal and is also susceptible to high-frequency signal interference from the ADC. In contrast, the autocorrelation-processed curve significantly suppresses these two interference signals, more accurately representing the noise characteristics of KIDs.

[0056] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A KIDs characterization two-channel measurement apparatus based on cross-correlation algorithm, characterized in that, include: Signal generator, dual-channel zero-difference mixer system, KIDs detector, ADC data acquisition card and control computer; The dual-channel zero-difference mixer system includes a directional coupler, a first power divider, a second power divider, a first IQ mixer, and a second IQ mixer. The input of the directional coupler is connected to a signal generator, and the output of the directional coupler is divided into a through-channel and a coupled-channel. The through-channel divides the signal into two signals, LO1 and LO2, by the first power divider, which serve as the local oscillator signals for the first IQ mixer and the second IQ mixer, respectively. The coupled-channel transmits the signal to the KIDs detector. The output signal of the KIDs detector is amplified and then divided into two signals RF1 and RF2 by the second power divider, which are used as the radio frequency signals of the first IQ mixer and the second IQ mixer, respectively. The first IQ mixer inputs signals LO1 and RF1, and outputs a time-domain DC signal via the difference frequency to the ADC data acquisition card; The second IQ mixer inputs signals LO2 and RF2, and outputs a time-domain DC signal via the difference frequency to the ADC data acquisition card; The ADC data acquisition card inputs the acquired signals into the control computer; The control computer processes the signals acquired by the ADC data acquisition card based on Fourier transform and cross-correlation operations to obtain the characteristic parameters of KIDs. The ADC data acquisition card samples the time-domain DC signal output by the first IQ mixer as two orthogonal signals I(t)1 and Q(t)1, and samples the time-domain DC signal output by the second IQ mixer as two orthogonal signals I(t)2 and Q(t)2. The control computer executes the following process to obtain the characteristic parameters of the KIDs: First, the ADC data acquisition card is sampled. n The signals are fitted and calibrated using seven parameters. Each signal group includes I(t)1, Q(t)1 and I(t)2, Q(t)2, to obtain ADC sampling data that meets the ideal resonance characteristics. According to seven parameter fitting and calibration processing after ADC sampling data, obtain n Group amplitude and phase of time domain data; right n The time-domain data of amplitude and phase are subjected to Fast Fourier Transform to obtain... n Frequency domain data of amplitude and phase; Perform cross-correlation on the frequency domain data of each set of amplitude and phase to obtain n Group amplitude and phase noise data, for n The noise power spectral density of amplitude and phase is obtained by averaging the noise data of the group and then calculating it. The seven-parameter fitting is performed based on the S21 curve equation of the resonator that satisfies the ideal resonance characteristics: In the formula, Indicates the transmission coefficient. f Indicates the detection frequency. fr Indicates the resonant frequency. Q l Indicates the load quality factor. Q c This represents the absolute value of the coupling quality factor. φ Indicates impedance mismatch. a Indicates the additional amplitude. α Indicates a phase shift, i Represents the complex number symbol. τ This indicates the electron delay caused by cable length and the finite speed of light.

2. The dual-channel measurement device for KIDs characteristics based on cross-correlation algorithm as described in claim 1, characterized in that: The output signal of the KIDs detector is amplified by a low-temperature, low-noise amplifier.

3. The dual-channel measurement device for KIDs characteristics based on cross-correlation algorithm as described in claim 2, characterized in that: The KIDs detector and the low-temperature low-noise amplifier are both housed in a Dewar and operate at the superconducting critical temperature.

4. The dual-channel measurement device for KIDs characteristics based on cross-correlation algorithm as described in claim 1, characterized in that: The time-domain DC signals output by the first IQ mixer and the second IQ mixer are both filtered by a low-pass filter and an impedance transformer before being input to the ADC data acquisition card.

5. The dual-channel measurement device for KIDs characteristics based on cross-correlation algorithm as described in claim 1, characterized in that: The formulas for calculating the frequency domain data of amplitude and phase are as follows: In the formula, and These represent the amplitude frequency domain data and the phase frequency domain data of the same group, respectively. FFT Represents the Fast Fourier Transform. and These represent the signal data obtained after seven-parameter fitting and calibration processing of two orthogonal signals from the same group output by the same IQ mixer.

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