Estimation method for noise figure of circuit of dilution refrigerator, and control system

Abstract

An estimation method for a noise figure of a circuit of a dilution refrigerator, and a control system. The method comprises: a measurement and control system outputting a microwave signal to a dilution refrigerator at a first temperature, and calculating a noise figure by means of a first calculation model; calculating, by means of a second calculation model, noise parameters and noise factors when the microwave signal enters several cold plates; and calculating, by means of a third calculation model, a noise factor of the microwave signal passing through the entire dilution refrigerator, substituting the noise factor into the first calculation model and converting same into a noise figure, determining a compensation amount on the basis of electronic components at the cold plates, and performing summation to obtain a total estimated value of the noise figure. In the method, a noise figure of an internal circuit of a dilution refrigerator is estimated by using the derivation of noise figures of a microwave signal passing through different temperature intervals of the dilution refrigerator, such that the noise figure of the internal circuit of the entire dilution refrigerator can be obtained, thereby solving the problem of it being difficult to measure a signal-to-noise ratio of a microwave signal at a quantum chip inlet under a low-temperature environment of a dilution refrigerator.

Description

Method for estimating noise factor of dilution refrigerator circuit and control system TECHNICAL FIELD

[0001] The present application relates to the field of quantum computer system design, and particularly relates to a method for estimating noise factor of dilution refrigerator circuit and a control system. BACKGROUND

[0002] The microwave cable and low-temperature device of the dilution refrigerator are important components of the low-temperature environment system of the quantum computer, and are used for transmitting quantum state control signals and measurement signals. However, the noise factor needs to consider the cascade and temperature change effects because the internal temperature of the dilution refrigerator decreases from room temperature to low temperature. Therefore, in order to measure the noise characteristics in the dilution refrigerator, it is necessary to evaluate the noise factor introduced by the signal attenuation in the dilution refrigerator.

[0003] The existing noise factor detection method uses a noise tester. This detection method is the most direct, and the signal-to-noise ratio of the microwave signal at the output end of the arbitrary waveform generator of the room temperature environment measurement and control system can be measured. However, it is difficult to measure the microwave signal parameter characteristics at the entrance of the quantum chip in the low-temperature environment of the dilution refrigerator. In the dilution refrigerator, the temperature decreases step by step with the cooling disc. The room temperature noise tester has a large error when used for detection at low temperature, which further affects the system design of the quantum computer. SUMMARY

[0004] The purpose of the present application is to solve the problems in the prior art, and to provide a method for estimating the noise factor of a dilution refrigerator circuit and a control system.

[0005] In order to achieve the above purpose, the present application adopts the following technical scheme: a method for estimating the noise factor of a dilution refrigerator circuit, comprising the steps of:

[0006] S1: The measurement and control system monitors the noise factor of the microwave signal input to the dilution refrigerator at a first temperature, and calculates the noise factor of the microwave signal through a first calculation model;

[0007] S2: The measurement and control system calculates the noise parameters and noise factors of the electronic components at the cooling disc of the dilution refrigerator through a second calculation model at the first temperature, and controls the microwave signal to enter the cooling discs with decreasing temperature in the dilution refrigerator. The noise parameters and noise factors of the microwave signal at several temperatures are calculated through the second calculation model;

[0008] S3: According to the obtained several noise parameters and noise factors, the noise factor of the microwave signal through the dilution refrigerator is calculated through a third calculation model, which is substituted into the first calculation model to convert into the noise factor, and the compensation amount is determined according to the electronic components at the cooling disc, and the total estimated value of the noise factor is obtained by summation.

[0009] As a further description of the above technical solution: in step S1, comprising:

[0010] S11: connecting a noise generator at the input end of the measurement and control system, comparing the signal-to-noise ratio of the waveform generator output in the measurement and control system with the signal-to-noise ratio input by the noise generator, obtaining the noise factor of the microwave signal, and substituting into the first calculation model to calculate the noise coefficient of the microwave signal.

[0011] As a further description of the above technical solution: in step S2, comprising:

[0012] S21: the measurement and control system monitors the microwave signal at the entrance of the quantum chip of the dilution refrigerator, at the first temperature, according to the configuration model and index parameters of the electronic components on each cold plate of the dilution refrigerator, the noise parameters and noise factors of the cold plate microwave control channel are calculated through the second calculation model;

[0013] S22: the microwave signal enters the cold plate of the dilution refrigerator, judges whether it is the coldest cold plate, if yes, the noise parameters and noise factors are calculated through the second calculation model and output,

[0014] S23: if not, the microwave signal enters the next cold plate, returns to step S22 to judge again, and obtains the noise parameters and noise factors generated by the microwave control channel of the microwave signal through several cold plates of the dilution refrigerator.

[0015] As a further description of the above technical solution: the microwave control channel comprises at least one attenuator or filter, and the measurement and control system determines the attenuation coefficient of the microwave signal passing through according to the attenuation index of the attenuator or the filter.

[0016] As a further description of the above technical solution: in step S3, comprising:

[0017] S31: the noise factor of the dilution refrigerator is calculated through the third calculation model, and the first estimated value of the noise coefficient of the microwave signal in the whole dilution refrigerator is obtained by substituting into the first calculation model;

[0018] S32: judging the signal-to-noise ratio of the quantum chip control end signal according to the obtained noise factor, and determining the compensation amount according to the configuration model and index parameters of the electronic components, as the second estimated value of the noise coefficient introduced by the electronic components;

[0019] S33: summing the first estimated value and the second estimated value to obtain the total estimated value of the noise coefficient of the signal-to-noise ratio at the entrance of the dilution refrigerator of the measurement and control system, which ensures the normal work of the whole quantum computer.

[0020] As a further description of the above technical solution: the type of noise factor introduced by the electronic component includes additional noise or thermal noise.

[0021] As a further description of the above technical solution: the first calculation model calculates the noise factor of the microwave signal, and the algorithm formula is as follows: NF(dB) = 10log(F);

[0022] Wherein, SNR represents the signal-to-noise ratio of the input signal, SNR out represents the signal-to-noise ratio of the output signal, NF(dB) is the noise factor, and F is the noise factor of the dilution refrigerator.

[0023] As a further description of the above technical solution: the second calculation model calculates the noise parameter and noise factor of the electronic component, and the algorithm formula is as follows: N i = (a) 器件 + (KT i B i ) 环境 = KT i B i ;

[0024] Wherein, N i is the introduced noise parameter, T i is the temperature, F i is the noise factor of the cold plate at T i , G i is the attenuation coefficient of the electronic component, K is the Boltzmann constant, B i is the equivalent signal bandwidth of the introduced noise at T i temperature, a is the additional noise of the electronic component, and the value of the additional noise containing is 1, and the value of the additional noise not containing is 0, n in is the input noise, and i is the number of temperature reduction.

[0025] As a further description of the above technical solution: the third calculation model calculates the noise factor of the microwave signal through the dilution refrigerator, and the algorithm formula is as follows:

[0026] Wherein, F i is the noise factor of the cold plate at T i , G i is the attenuation coefficient of the electronic component, and i is the number of temperature reduction.

[0027] Also includes a control system, the control system is used for executing any of the above technical solutions in the estimation method, including:

[0028] a control module, which controls the amount of a microwave signal output by the noise generator and the waveform generator to be transmitted to the quantum chip inlet end of the dilution refrigerator;

[0029] a monitoring module, which monitors the noise generated by the microwave signal at the cold plate of the dilution refrigerator and feeds back to the control module;

[0030] a calculation module, which calculates the total estimated value of the noise factor and the noise coefficient according to the configuration model and the index parameter of the electronic component and the monitored noise.

[0031] The above technical solution has the following advantages or beneficial effects:

[0032] 1. The present application uses the noise coefficient of the microwave signal passing through different temperature intervals of the dilution refrigerator to design a method for estimating the noise coefficient of the internal circuit of the dilution refrigerator. This method solves the problem of difficult measurement of the signal-to-noise ratio of the microwave signal at the quantum chip inlet under the low-temperature environment of the dilution refrigerator, and can obtain the noise coefficient of the entire internal circuit of the dilution refrigerator, thereby providing a system design direction for determining the optimization scheme of each link in the transmission path. BRIEF DESCRIPTION OF DRAWINGS

[0033] Fig. 1 is a flowchart of the estimation method according to the present application;

[0034] Fig. 2 is a flowchart of the estimation method according to the present application;

[0035] Fig. 3 is a flowchart of the estimation method according to the present application;

[0036] Fig. 4 is a flowchart of the estimation method according to the present application;

[0037] Fig. 5 is a structural schematic diagram of the control system according to the present application.

[0038] Legend: 1, control module; 2, monitoring module; 3, calculation module. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0040] Referring to Fig. 1, the present application provides an embodiment: a dilution refrigerator circuit noise coefficient estimation method, comprising the steps of:

[0041] S1: The measurement and control system monitors the noise factor of the microwave signal input to the dilution refrigerator at a first temperature, and calculates the noise factor of the microwave signal by a first calculation model;

[0042] S2: The measurement and control system calculates the noise parameters and noise factors of the electronic components at the cold plates of the dilution refrigerator at the first temperature by a second calculation model, and controls the microwave signal to enter the cold plates of the dilution refrigerator in turn, and calculates the noise parameters and noise factors of the microwave signal at several temperatures by the second calculation model;

[0043] S3: According to the obtained several noise parameters and noise factors, the noise factor of the microwave signal passing through the dilution refrigerator is calculated by a third calculation model, which is converted into the noise coefficient by substituting into the first calculation model, and the compensation amount is determined according to the electronic components at the cold plates, and the total estimated value of the noise coefficient is obtained by summation.

[0044] In this embodiment, the measurement and control system controls the noise generator and the waveform generator to be connected to the input end of the dilution refrigerator at a first temperature, introduces a microwave signal and noise into the dilution refrigerator, calculates the noise coefficient of the microwave signal by a first calculation model, monitors the noise generated by the microwave signal entering different temperature intervals of the cold plates in the dilution refrigerator, calculates the noise parameters and noise factors, and calculates the noise factor of the dilution refrigerator by a third calculation model, which is converted into the noise coefficient by substituting into the first calculation model, to obtain the first estimated value of the noise coefficient, and the compensation amount is determined according to the internal electronic components as the second estimated value, and the total estimated value of the noise coefficient is obtained by summation, which ensures that the entire quantum computer works normally, and the noise coefficient of the internal circuit of the dilution refrigerator is obtained, which provides a system design direction for determining the optimization scheme of each link in the transmission path, and the first temperature is room temperature (298.15K).

[0045] Referring to FIG. 2, in step S1, it includes:

[0046] S11: Connect the noise generator to the input end of the measurement and control system, compare the signal-to-noise ratio output by the waveform generator in the measurement and control system with the signal-to-noise ratio input by the noise generator, obtain the noise factor of the microwave signal, and substitute it into the first calculation model to calculate the noise coefficient of the microwave signal.

[0047] In this embodiment, the noise generator is connected to the output end of the measurement and control system, and the test noise is introduced. The waveform generator in the measurement and control system outputs a microwave signal to the quantum chip interface of the dilution refrigerator. By comparing the signal-to-noise ratio at the output end of the waveform generator in the measurement and control system with the signal-to-noise ratio input by the noise generator, the noise factor of the microwave signal can be obtained, and the noise coefficient of the microwave signal is calculated by the first calculation model.

[0048] The calculation formula of the first model is: NF(dB)=10log(F);

[0049] wherein, SNR in represents the signal-to-noise ratio of the input signal, SNR out represents the signal-to-noise ratio of the output signal, NF(dB) is the noise factor, and F is the noise factor of the dilution refrigerator.

[0050] Referring to FIG. 3, in step S2, the following steps are included:

[0051] S21: The measurement and control system monitors the microwave signal at the quantum chip inlet of the dilution refrigerator, and under the first temperature, according to the configuration model and index parameters of the electronic components on each cold plate of the dilution refrigerator, the noise parameters and noise factors of the cold plate microwave control channel are calculated through the second calculation model;

[0052] S22: The microwave signal enters the cold plate of the dilution refrigerator, and it is judged whether it is the coldest cold plate. If yes, the noise parameters and noise factors are calculated through the second calculation model and outputted.

[0053] S23: If no, the microwave signal enters the next cold plate, and the judgment is returned to step S22 to obtain the noise parameters and noise factors generated by the microwave control channel of the microwave signal through the several cold plates of the dilution refrigerator.

[0054] In this embodiment, the number of cold plates is set to five, and the measurement and control system estimates the noise factor of the microwave control channel (XY channel) according to the configuration model and index parameters of the electronic components on each cold plate of the dilution refrigerator, and calculates the noise parameters and noise factors of the microwave control channel under the current cold plate temperature through the second calculation model.

[0055] The types of noise factors introduced by electronic components include additional noise or thermal noise. For passive electronic components, additional noise will not be generated in addition to thermal noise, and in the dilution refrigerator, the main electronic components are passive, and additional noise will not be generated. However, as the temperature gradually decreases with the cold plate in the dilution refrigerator, the thermal noise is also gradually reduced. For passive electronic components at T i temperature, the device will not generate additional noise in addition to thermal noise, so it can be considered that the device together with the environment introduces noise, which is calculated by the second calculation model as: N i =(a) 器件 +(KT i B i ) 环境 =KT i B i

[0056] Noise factor:

[0057] where N i is the introduced noise parameter, T i is the temperature, F i is the noise factor of the cold plate at T i , G i is the electronic component attenuation coefficient, K is the Boltzmann constant, B i is the equivalent signal bandwidth of the introduced noise at T i , a is the electronic component additional noise, and n in is the input noise, i is the number of times of temperature reduction.

[0058] Let the input noise n in be at the equivalent signal bandwidth B i at the temperature T in , that is, n in = KT in B in .

[0059] The noise factor is calculated as:

[0060] According to the analysis results, the microwave control channel is calculated, and the Kelvin temperature at room temperature is taken as 298.15 K. Since it is the lower limit of the estimated noise coefficient attenuation, and considering that the filter eliminates most of the stray signals on the wide frequency spectrum, it can be approximately assumed that the equivalent noise bandwidth B i introduced by each level of device is B in .

[0061] Assuming that in the room temperature environment (25°C), a pure microwave signal is generated by a microwave source and an AWG or a vector network analyzer and other equipment (here, the noise brought by the instrument itself is not considered, that is, only the noise introduced by the environment at room temperature is considered at the beginning, if the noise of the instrument is considered, it can be converted into an equivalent bandwidth and added to B in ), the equivalent temperature T in of the initial input noise is room temperature 298.15 K; then the microwave signal enters the second temperature T1=40 K, and the attenuation coefficient G1=1, so the noise factor at this time is:

[0062] Determine whether this is the coldest cold plate, if not, the microwave signal enters the T2=4 K temperature interval, and the attenuation coefficient is G2=10 -2.03 =0.009332543, so the noise factor at this time is:

[0063] The microwave signal enters the third temperature T3=0.8 K temperature interval, and the attenuation coefficient is

[0064] G3=10 -2.03 = 0.009332543, so the noise factor at this time is:

[0065] The microwave signal enters the fourth temperature T4=0.1K temperature interval, the attenuation coefficient G4=1, so the noise factor at this time is:

[0066] Finally, the microwave signal enters the fifth temperature T5=0.01K temperature interval, the attenuation coefficient is:

[0067] G5=10 -0.093 ·10 -0.019 = 10 -0.112 = 0.77268, so the noise factor at this time is:

[0068] Determine whether it is the lowest temperature cold plate, yes, output noise factor and noise parameters, get the noise factor at each cold plate.

[0069] The microwave control channel includes at least one attenuator or filter, and the measurement and control system determines the attenuation coefficient when the microwave signal passes through according to the attenuation index of the attenuator or filter.

[0070] In this embodiment, the electronic components at the cold plate are selected to use a 6dB attenuator, a 10dB attenuator, a 20dB attenuator, an 8GHz filter or an infrared filter, and the specific distribution is shown in Table 1:

[0071] Table 1

[0072] The calculation results of the second calculation model are analyzed with the configuration model and index parameters of the electronic components, and the results are shown in Table 2:

[0073] Table 2

[0074] Referring to FIG. 4, in step S3, it includes:

[0075] S31: Calculate the noise factor of the dilution refrigerator by the third calculation model, substitute it into the first calculation model to convert it into a noise coefficient, and obtain a first estimated value of the noise coefficient of the microwave signal in the dilution refrigerator;

[0076] S32: Determine the signal-to-noise ratio of the quantum chip control end signal according to the obtained noise factor, and determine the compensation amount according to the configuration model and index parameters of the electronic components as a second estimated value of the noise coefficient introduced by the electronic components;

[0077] S33: summing the first estimated value and the second estimated value to obtain the total estimated value of the noise factor under the condition that the signal-to-noise ratio of the microwave signal entering the dilution refrigerator is ensured to be greater than or equal to 36 dB.

[0078] In the embodiment, the noise factor calculated according to the second calculation model is used to calculate the noise factor of the microwave signal passing through the entire dilution refrigerator through the third calculation model, and the algorithm formula is as follows:

[0079] wherein F is the noise factor of the entire dilution refrigerator, F i is the noise factor of the cold plate at T i , G i is the attenuation coefficient of the electronic component, i is the number of times of temperature reduction, and is converted into dB form by being substituted into the first calculation model to obtain: 10*log(36.7283)=15.65dB≈16dB.

[0080] According to the result of the second calculation model, it is determined that the signal reaching the control end of the quantum chip should be greater than or equal to 20 dB to obtain better polar angle precision and fidelity indexes, so the signal-to-noise ratio of the microwave signal entering the dilution refrigerator should be greater than or equal to (16+20)dB=36dB. According to the configuration model and index parameters of the electronic component, the compensation amount is determined, the error range of the signal attenuation is different according to the parameters of the electronic component at the cold plate, in order to ensure that the signal-to-noise ratio after actual attenuation is still in the effective and usable range, the compensation amount is determined to be in the range of 1-4dB, preferably designed as 3dB, as the second estimated value, and the total estimated value of the noise factor is calculated as 36+3=39dB. The signal-to-noise ratio of the microwave signal entering the dilution refrigerator should be greater than or equal to 39dB to ensure the normal operation of the entire quantum computer.

[0081] Referring to FIG. 5, the application further provides an embodiment of a control system for executing any of the estimation methods in the above technical solutions, which comprises:

[0082] a control module 1 for controlling the noise generator and the waveform generator to output a microwave signal to the quantum chip entrance end of the dilution refrigerator;

[0083] a monitoring module 2 for monitoring the noise generated by the microwave signal at the cold plate of the dilution refrigerator and feeding back to the control module 1;

[0084] a calculation module 3 for calculating the noise factor and the total estimated value of the noise factor according to the configuration model and index parameters of the electronic component and the monitored noise.

[0085] In the embodiment, the control module 1 controls the noise generator and the waveform generator to output a microwave signal to the quantum chip inlet end of the dilution refrigerator, performs microwave signal noise factor monitoring calculation, monitors the noise at each cold plate of the dilution refrigerator through the monitoring module 2, and calculates the noise of the microwave signal when passing through the cold plate through the calculation module 3, calculates the total estimated value of the noise factor and the noise factor, and obtains the noise factor of the whole dilution refrigerator, which can effectively solve the problem that the microwave signal characteristics at the quantum chip inlet of the dilution refrigerator in the low-temperature environment are difficult to measure, and provide support for the establishment of the whole superconducting quantum computer index system.

[0086] Finally, it should be noted that: the above only for the preferred embodiments of the present application, and not for limiting the present application, although the foregoing embodiments of the present application are described in detail, for those skilled in the art, it still can be modified, or part of the technical features of the equivalent replacement, within the spirit and principles of the present application, any modification, equivalent replacement, improvement, etc., should be included in the protection scope of the present application.

Claims

1. A method of estimating the noise figure of a dilution refrigerator circuit, characterized by, The method comprises the steps of: S1: The measurement and control system monitors the noise factor of the microwave signal input to the dilution refrigerator at a first temperature, and calculates the noise factor of the microwave signal by a first calculation model; S2: The measurement and control system calculates the noise parameters and noise factors of the electronic components at the cold plate of the dilution refrigerator at the first temperature by a second calculation model, and controls the microwave signal to enter the cold plates of the dilution refrigerator in turn, and calculates the noise parameters and noise factors of the microwave signal at several temperatures by the second calculation model; S3: According to the obtained several noise parameters and noise factors, the noise factor of the microwave signal through the dilution refrigerator is calculated by a third calculation model, which is substituted into the first calculation model to convert into the noise factor, and the compensation amount is determined according to the electronic components at the cold plate to obtain the total estimated value of the noise factor.

2. The estimation method of claim 1, characterized in that: In step S1, it comprises: S11: Connect the noise generator to the input end of the measurement and control system, compare the signal-to-noise ratio output by the waveform generator in the measurement and control system with the signal-to-noise ratio input by the noise generator, obtain the noise factor of the microwave signal, and substitute it into the first calculation model to calculate the noise factor of the microwave signal.

3. The estimation method of claim 1, wherein: In step S2, it comprises: S21: The measurement and control system monitors the microwave signal at the entrance of the quantum chip of the dilution refrigerator, and at the first temperature, calculates the noise parameters and noise factors of the microwave control channel of the cold plate according to the configuration model and index parameters of the electronic components on each cold plate of the dilution refrigerator by a second calculation model; S22: The microwave signal enters the cold plate of the dilution refrigerator, and judges whether it is the cold plate with the lowest temperature, if yes, the noise parameters and noise factors are calculated by the second calculation model and output; S23: If not, the microwave signal enters the next cold plate, and returns to step S22 for judgment again to obtain the noise parameters and noise factors generated by the microwave control channel of the microwave signal through the several cold plates of the dilution refrigerator.

4. The estimation method of claim 3, characterized in that: The microwave control channel comprises at least one attenuator or filter, and the measurement and control system determines the attenuation coefficient of the microwave signal passing through according to the attenuation index of the attenuator or the filter.

5. The estimation method of claim 1, wherein: In step S3, it comprises: S31: Calculate the noise factor of the dilution refrigerator by a third calculation model, substitute it into the first calculation model to convert into the noise factor, and obtain the first estimated value of the noise factor of the microwave signal in the dilution refrigerator; S32: According to the obtained noise factor, judge the signal-to-noise ratio of the quantum chip control end signal, and determine the compensation amount according to the configuration model and index parameters of the electronic components, as the second estimated value of the noise factor introduced by the electronic components; S33: Sum the first estimated value and the second estimated value to obtain the total estimated value of the noise factor of the signal-to-noise ratio at the entrance of the dilution refrigerator of the measurement and control system under the condition of ensuring the normal operation of the entire quantum computer.

6. The estimation method of claim 5, characterized in that: The type of noise factor introduced by the electronic components includes additional noise or thermal noise.

7. The method of estimating of claim 2, wherein: The first calculation model calculates the noise figure of the microwave signal, and the algorithm formula is as follows: NF(dB)=10log(F); Among them, SNR in The signal-to-noise ratio (SNR) of the input signal. out The signal-to-noise ratio of the output signal is represented by NF(dB), the noise figure is represented by F, and the overall noise factor of the dilution chiller is represented by F.

8. The estimation method of claim 6, wherein: The second calculation model calculates the noise parameter and noise factor of the electronic component, and the algorithm formula is as follows: N i = (a) 器件 + (KT i B i ) 环境 = KT i B i ; Where N i is the introduced noise parameter, T i is the temperature, F i is the noise factor of the cold plate at T i , G i is the electronic component attenuation coefficient, K is the Boltzmann constant, B i is the equivalent signal bandwidth of the introduced noise at T i , a is the electronic component additional noise, and contains the additional noise value 1, and does not contain 0, n in is the input noise, and i is the number of times of temperature reduction.

9. The estimation method of claim 8, characterized in that: The third calculation model calculates a noise factor of the microwave signal passing through the whole dilution refrigerator, and an algorithm formula is as follows: Wherein, F is the noise factor of the whole dilution refrigerator, F i is the noise factor of the cold plate with temperature at T i , G i is the attenuation coefficient of the electronic components, and i is the number of temperature reduction.

10. A control system characterized by, The control system is used to execute the estimation method of any one of claims 1-9, comprising: A control module controls the amount of microwave signal output by the noise generator and the waveform generator to be transmitted to the quantum chip inlet end of the dilution refrigerator; A monitoring module monitors the noise generated by the microwave signal at the cold plate of the dilution refrigerator and feeds back to the control module; A calculation module calculates the total estimated value of the noise factor and the noise coefficient according to the configuration model and the index parameters of the electronic components and the monitored noise.

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