Anti-interference measurement system for Josephson junction resistance

Abstract

The invention discloses an anti-interference measurement system for Josephson junction resistance, and belongs to the technical field of quantum chips. In the system, an alternating current source for generating n alternating current electric signals with different frequencies, a Josephson junction and a current measuring unit are connected in series to form a loop; the voltage measuring unit is connected in parallel with the Josephson junction; and the resistance measuring and calculating unit is used for measuring the Josephson junction for m times under the action of each alternating-current electric signal to obtain n * m resistance measured values, and determining a resistance calculated value of the Josephson junction based on the n * m resistance measured values. In the system, the resistance of the Josephson junction is measured for multiple times under the action of the alternating current electric signals with different frequencies generated by the alternating current source, so that the proportion of the resistance measurement values with errors caused by noise coupling in the environment to all the resistance measurement values is reduced, and the resistance measurement accuracy of the Josephson junction can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of quantum chip, and particularly relates to an anti-interference measurement system for the resistance of Josephson junctions. Background Art

[0002] The key structure on a superconducting quantum chip is a superconducting qubit, and the key structure of a superconducting qubit is a Josephson junction. To ensure the performance of a superconducting quantum chip, it is necessary to strictly control the frequency parameters of the superconducting qubit. The room-temperature resistance characterization of a superconducting qubit is important information reflecting the frequency parameters, and the resistance of a Josephson junction is the key to the room-temperature resistance characterization of a superconducting qubit.

[0003] Since a Josephson junction is very fragile, in order to avoid burning it out during the measurement process, a small voltage is often used when measuring the resistance of a Josephson junction at room temperature. However, during the existing measurement of the small voltage signal corresponding to a Josephson junction, it is very susceptible to electromagnetic noise in the environment, resulting in a reduction in the accuracy of the measured voltage result of the Josephson junction, and further causing a large error in the calculated resistance value. Summary of the Invention

[0004] The purpose of the present invention is to provide an anti-interference measurement system for the resistance of Josephson junctions to solve the deficiencies in the prior art. It can reduce the influence of environmental noise during the measurement process and effectively and accurately characterize the resistance value of a Josephson junction.

[0005] The solution of the example of the present application is implemented through the following content.

[0006] The example of the present application proposes an anti-interference measurement system for the resistance of Josephson junctions, and the system includes:

[0007] An AC source, a Josephson junction, and a current measurement unit connected in series to form a loop, where the AC source is used to generate n AC signals with different frequencies;

[0008] A voltage measurement unit connected in parallel with the Josephson junction; and

[0009] A resistance calculation unit connected to the current measurement unit and the voltage measurement unit respectively, and is used to perform m measurements on the Josephson junction under the action of each of the AC signals, and obtain n*m resistance measurement values through the current measurement value output by the current measurement unit and the voltage measurement value output by the voltage measurement unit;

[0010] The resistance calculation unit is further used to determine the resistance calculation value of the Josephson junction based on the n*m resistance measurement values.

[0011] According to some examples of the present application, the resistance measurement unit is also connected to the AC source and is used to control the AC source to generate n AC signal with different frequencies.

[0012] According to some examples of the present application, the resistance measurement unit is also used to control the frequency of each of the AC signals according to the frequency threshold condition, and the frequency threshold condition is determined by the frequency distribution range of the ambient noise.

[0013] According to some examples of the present application, the resistance measurement unit is also used to control the amplitudes of each of the AC signals generated by the AC source to be equal.

[0014] According to some examples of the present application, the resistance measurement unit is also used to:

[0015] Based on the numerical values of each resistance measurement value and the number of occurrences in the n*m resistance measurement values, determine the weights corresponding to each numerical value;

[0016] Using each numerical value and the corresponding weight, determine the calculated resistance value of the Josephson junction.

[0017] According to some examples of the present application, the voltage measurement unit is also connected to the AC source and is used to output voltage measurement result information to the resistance measurement unit according to the frequency of the AC signal, and the voltage measurement result information includes the voltage measurement value.

[0018] According to some examples of the present application, the series circuit further includes:

[0019] A preset resistor, the resistance value of the preset resistor is greater than the resistance value of the Josephson junction, and the preset resistor is used to control the current in the series circuit to be constant.

[0020] According to some examples of the present application, the current measurement unit is a lock-in amplifier.

[0021] According to some examples of the present application, the voltage measurement unit is a lock-in amplifier.

[0022] According to some examples of the present application, the AC source and the voltage measurement unit are two working units of the same lock-in amplifier.

[0023] In the anti-interference measurement system for the Josephson junction resistance in the foregoing example of the present application, an AC source that generates n AC signals with different frequencies, a Josephson junction, and a current measurement unit are connected in series to form a loop; a voltage measurement unit is connected in parallel with the Josephson junction; a resistance calculation unit is connected to the current measurement unit and the voltage measurement unit respectively. Under the action of each AC signal, the Josephson junction is measured m times. Through the current measurement value output by the current measurement unit and the voltage measurement value output by the voltage measurement unit, n*m resistance measurement values are obtained, and based on the n*m resistance measurement values, the resistance calculation value of the Josephson junction is determined. In the above system, under the action of different-frequency AC signals generated by the AC source, the resistance of the Josephson junction is measured multiple times. The resistance calculation unit calculates the resistance of the Josephson junction according to the obtained multiple resistance measurement values, reduces the proportion of the resistance measurement values with errors caused by noise coupling in the environment among all the resistance measurement values, and thus can effectively improve the accuracy of the Josephson junction resistance measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] For a clearer illustration, the drawings required for the description will be briefly introduced below.

[0025] Figure 1 It is a structural block diagram of the anti-interference measurement system for the Josephson junction resistance in an example of the present application;

[0026] Figure 2 It is a structural block diagram of the anti-interference measurement system for the Josephson junction resistance in another example of the present application;

[0027] Figure 3 It is a structural block diagram of the anti-interference measurement system for the Josephson junction resistance in another example of the present application;

[0028] Figure 4 It is a structural block diagram of the anti-interference measurement system for the Josephson junction resistance in another example of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] The specific embodiments of the present invention will be described in more detail below with reference to the schematic diagrams. According to the following description and claims, the advantages and features of the present invention will be clearer. It should be noted that the drawings are all in a very simplified form and use non-precise scales, only for the purpose of facilitating and clearly assisting in explaining the embodiments of the present invention.

[0030] In the description of the present invention, it should be understood that the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0031] In the field of quantum chip manufacturing technology, the key structure on a superconducting quantum chip is the Josephson junction; to ensure the performance of the superconducting quantum chip, it is necessary to strictly control the frequency parameters of the superconducting qubits, and the normal temperature resistance characterization of the superconducting qubits is important information reflecting the frequency parameters, where the key to the normal temperature resistance of the superconducting qubits is the resistance of the Josephson junction. Since the Josephson junction is very fragile, in order to avoid burning it during the measurement process, a small current and a small voltage are often used to measure it at normal temperature. However, the measurement of a small-magnitude voltage signal is very susceptible to magnetic noise in the environment, resulting in a reduction in the accuracy of the measurement result (i.e., during the process of measuring the voltage of the Josephson junction, the noise signal in the environment may be coupled with the voltage signal of the Josephson junction in the circuit, causing an error in the measured voltage value).

[0032] Based on this, as Figure 1 shown, an embodiment of the present invention provides an anti-interference measurement system for the resistance of a Josephson junction, and the system includes:

[0033] An AC source 110, a Josephson junction 120, and a current measurement unit 130 connected in series to form a loop, where the AC source 110 is used to generate n AC signals with different frequencies;

[0034] A voltage measurement unit 140 connected in parallel with the Josephson junction 120; and

[0035] A resistance calculation unit 150, connected to the current measurement unit 130 and the voltage measurement unit 140 respectively, and used to perform m measurements on the Josephson junction 120 under the action of each AC signal, and obtain n*m resistance measurement values through the current measurement value output by the current measurement unit 130 and the voltage measurement value output by the voltage measurement unit 140;

[0036] The resistance calculation unit 150 is further used to determine the resistance calculation value of the Josephson junction 120 based on the n*m resistance measurement values.

[0037] Among them, the AC source 110 can be a frequency-hopping signal source, or stores instructions for outputting signals with different frequencies, and can output AC signals with different frequencies when the signal source is started. The AC source 110 only needs to output AC signals with different frequencies, and this application does not limit information such as the amplitude of the AC signal.

[0038] In one embodiment of the present application, as Figure 2 shown, the series circuit includes a preset resistor 160, the resistance value of the preset resistor 160 is greater than the resistance value of the Josephson junction 120, and the preset resistor 160 is used to control the current in the series circuit to be constant. Since the AC signal output by the AC source 110 is a signal with different frequencies and the same amplitude, therefore, when the resistance value of the preset resistor 160 is much greater than the resistance value of the Josephson junction 120, the current in the series circuit is constant.

[0039] Specifically, the current measurement unit 130 connected in series in the circuit is used to measure the current measurement value in the circuit, and the voltage measurement unit 140 is used to measure the voltage measurement value corresponding to the Josephson junction 120 in the series circuit.

[0040] However, due to the existence of noise in the environment, there will be noise coupling resulting in errors. When the voltage measurement unit 140 outputs the voltage measurement value of the voltage measurement signal (this voltage measurement signal is the AC signal divided in series by the Josephson junction 120) with the same frequency as the AC signal, if the environmental noise and the AC signal are of the same frequency, there will be noise coupling, resulting in the voltage measurement value measured by the voltage measurement unit 140 being the voltage measurement value of the voltage measurement signal of the Josephson junction 120 and the voltage measurement value of the coupled environmental noise; if the environmental noise and the AC signal are of different frequencies, there will be no noise coupling, and the voltage measurement value measured by the voltage measurement unit 140 is the voltage measurement value of the voltage measurement signal of the Josephson junction 120.

[0041] Based on this, the resistance calculation unit 150 measures the Josephson junction 120 multiple times under the action of each AC signal, and determines the resistance calculation value of the Josephson junction 120 based on the obtained multiple resistance measurement values. When the resistance calculation unit 150 measures the Josephson junction 120 multiple times under the action of AC signals with different frequencies, the proportion of the resistance measurement values with noise coupling in all resistance measurement values can be reduced, and thus the accuracy of the resistance measurement of the Josephson junction 120 can be improved.

[0042] It should be noted that the present application does not specifically limit the AC source 110, the current measurement unit 130, the voltage measurement unit 140, the resistance calculation unit 150, and the preset resistor 160, and only needs to meet the corresponding functions.

[0043] In one embodiment of the present application, as Figure 3 shown, the resistance calculation unit 150 is also connected to the AC source 110 and is used to control the AC source 110 to generate n AC signals with different frequencies.

[0044] Specifically, the AC power source 110 can be connected to or communicate with the resistance measurement unit 150, receive the control instructions of the resistance measurement unit 150, and output n AC power signals with different frequencies that meet the frequency threshold conditions according to the control instructions to act on the series circuit.

[0045] In an embodiment of the present application, the resistance measurement unit 150 is further configured to control the frequency of each AC power signal according to the frequency threshold conditions, and the frequency threshold conditions are determined by the frequency distribution range of the ambient noise.

[0046] The resistance measurement unit 150 also sets the frequency of the AC power signal according to the ambient noise distribution range, and controls that there is no overlap between the frequency range corresponding to the AC power signal generated by the AC power source 110 and the ambient noise distribution range. Since the noise in the environment is randomly distributed, when the frequency distribution of the AC power signal is wide enough and the number is large enough, the probability of the resistance measurement values affected by ambient noise coupling among the n*m resistance measurement values obtained by the resistance measurement unit 150 will decrease. For example, in a certain laboratory, the ambient electrical noise frequency band is concentrated around 2.5 MHz and 6.5 MHz. The bandwidth is set according to actual needs to obtain the distribution range of the ambient noise. The resistance measurement unit 150 can determine the frequency threshold conditions including the frequency threshold range (there is no overlap between the frequency threshold distribution range and the ambient noise distribution range) according to the distribution range of the ambient noise, so as to set the frequency of the AC power signal.

[0047] Since the frequency of the AC power signal meets the frequency threshold conditions, the possibility of the ambient noise and the AC power signal being of the same frequency is reduced. Furthermore, the proportion of the resistance measurement values with noise coupling in all resistance measurement values can be effectively reduced, so that the proportion of the obtained resistance measurement values being true values is increased, and the accuracy of the resistance measurement of the Josephson junction 120 is improved.

[0048] In an embodiment of the present application, the resistance measurement unit 150 is further configured to control that the amplitudes of each AC power signal generated by the AC power source 110 are equal.

[0049] Specifically, when the resistance measurement unit 150 is connected to the AC power source 110, it controls the AC power source 110 to generate AC power signals with equal amplitudes and different frequencies. Since the preset resistance 160 in the series circuit is greater than the resistance value of the Josephson junction 120, the current in the series circuit is constant.

[0050] In an embodiment of the present application, the resistance measurement unit 150 is further configured to:

[0051] Based on the number of times each resistance measurement value appears among the n*m resistance measurement values, determine the weight value corresponding to each value;

[0052] Use each value and the corresponding weight value to determine the resistance calculation value of the Josephson junction 120.

[0053] Specifically, for each resistance measurement value, the terminal can determine the weight value corresponding to the resistance measurement value based on the number of times the resistance measurement value appears among the n*m resistance measurement values and the corresponding number of the n*m resistance measurement values, and then determine the resistance calculation value based on the weighted average algorithm.

[0054] The weight value can include a single-frequency weight value and a multi-frequency weight value. The resistance calculation unit 150 can also:

[0055] When a certain value appears in the measurement at a certain frequency, determine the single-frequency weight value corresponding to the value according to the number of occurrences.

[0056] Determine the multi-frequency weight value corresponding to the value according to the number of frequencies corresponding to the frequency measurement where the value appears.

[0057] Based on the weighted average algorithm, determine the resistance calculation value of the Josephson junction 120 according to the single-frequency weight value and multi-frequency weight value corresponding to each value.

[0058] Among them, each resistance measurement value has a single-frequency weight value and a multi-frequency weight value.

[0059] When the value of a resistance measurement value appears at least twice at a certain frequency, the number of occurrences can be used as the single-frequency weight value a of the value of the resistance measurement value at that frequency R,f (where a R,f represents the single-frequency weight value of the resistance measurement value R at the frequency f). When the value of a resistance measurement value appears only once at a certain frequency, determine that the single-frequency weight value of the value of the resistance measurement value at that frequency is 0. Further, a resistance measurement value can have multiple single-frequency weight values. For example, for a value (i.e., the resistance measurement value R), when the resistance measurement value R appears in multiple frequencies, for the number of times the resistance measurement value R appears at each frequency, determine the single-frequency weight value corresponding to the resistance measurement value R at each frequency. Based on this, the resistance calculation needs to be performed based on the single-frequency weight value at each frequency corresponding to each resistance measurement value.

[0060] When a value (i.e., the resistance measurement value R) appears in the measurements at at least two frequencies, according to the number of frequencies where the value appears, the calculation formula for the multi-frequency weight value corresponding to the value is: b R = 2 N-1 , where b R represents the multi-frequency weight value of the resistance measurement value R, and N is the number of frequencies where the resistance measurement value R appears; when a value (i.e., the resistance measurement value R) appears only once in the measurement at a certain frequency, determine that the multi-frequency weight value of the resistance measurement value is 0. For a resistance measurement value, there is only one multi-frequency weight value.

[0061] Specifically, based on the weighted average algorithm, the terminal determines the calculation formula for the resistance calculation value of the Josephson junction 120 according to the single-frequency weight and multi-frequency weight corresponding to each value, as follows:

[0062]

[0063] Among them, is the resistance calculation value, R f is the resistance measurement value R at frequency f, a R,f is the single-frequency weight of the resistance measurement value R at frequency f, b R represents the multi-frequency weight of the resistance measurement value R.

[0064] It should be noted that the method for determining the weight and calculating the resistance value in this application is only an illustrative example and is not specifically limited, and can be selected according to actual needs.

[0065] In an embodiment of the present application, as Figure 4 shown, the voltage measurement unit 140 is also connected to the AC source 110, and is used to output voltage measurement result information to the resistance measurement unit 150 according to the frequency of the AC signal, and the voltage measurement result information includes the voltage measurement value.

[0066] Specifically, the voltage measurement unit 140 is connected to the AC source 110, and is used to output the voltage measurement value of the voltage measurement signal (the voltage measurement signal is the AC signal divided in series by the Josephson junction 120) with the same frequency as the AC signal to the resistance measurement unit 150 according to the frequency of the AC signal.

[0067] In an embodiment of the present application, the current measurement unit 130 is a lock-in amplifier.

[0068] In an embodiment of the present application, the voltage measurement unit 140 is a lock-in amplifier.

[0069] In an embodiment of the present application, the AC source 110 and the voltage measurement unit 140 are two working units of the same lock-in amplifier.

[0070] Among them, the current measurement unit 130, the voltage measurement unit 140, and the AC source 110 can all be lock-in amplifiers capable of realizing the corresponding functions. Specifically, the current measurement unit 130, the voltage measurement unit 140, and the AC source 110 can be SR830 digital lock-in amplifiers. The voltage measurement unit 140 and the AC source 110 can also be two working units in the SR830 digital lock-in amplifier. Based on this, the voltage measurement unit 140 can lock the frequency of the AC signal output by the AC source 110 in real time to output the voltage measurement value of the voltage measurement signal with the same frequency.

[0071] It should be noted that the current measurement unit 130, the voltage measurement unit 140, and the AC source 110 can each be a device that independently implements its function, or they can be different working units of the same device.

[0072] In an embodiment of the present application, multiple functions can be simultaneously implemented through a lock-in amplifier (or other multifunctional device) by setting and changing the wiring. For example, simultaneously generating AC signals of different frequencies and measuring voltage. At this time, the AC source 110 and the voltage measurement unit 140 are two working units of the same lock-in amplifier (or other multifunctional device); simultaneously generating AC signals of different frequencies and measuring current. At this time, the AC source 110 and the current measurement unit 130 are two working units of the same lock-in amplifier (or other multifunctional device); simultaneously generating AC signals of different frequencies, measuring current, and measuring voltage. At this time, the AC source 110, the current measurement unit 130, and the voltage measurement unit 140 are three working units of the same lock-in amplifier (or other multifunctional device).

[0073] In the description of this specification, the description with reference to terms such as "an embodiment", "some embodiments", "example", or "specific example" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0074] The above are only the preferred embodiments of the present invention and do not impose any limiting effect on the present invention. Any person skilled in the art within the technical field, without departing from the technical solution of the present invention, makes any form of equivalent replacement or modification and other changes to the technical solution and technical content disclosed in the present invention, all of which belong to the content that does not depart from the technical solution of the present invention and still falls within the protection scope of the present invention.

Claims

1. An anti-interference measurement system for Josephson junction resistance, characterized in that Including: An AC source, a Josephson junction, and a current measurement unit connected in series to form a loop, where the AC source is used to generate n AC electrical signals with different frequencies; A voltage measurement unit connected in parallel with the Josephson junction; And A resistance calculation unit, connected to the current measurement unit and the voltage measurement unit respectively, for performing m measurements on the Josephson junction under the action of each of the AC electrical signals, and obtaining n*m resistance measurement values through the current measurement value output by the current measurement unit and the voltage measurement value output by the voltage measurement unit; The resistance calculation unit is further used to determine a resistance calculation value of the Josephson junction based on the n*m resistance measurement values.

2. The system according to claim 1, wherein The resistance calculation unit is further connected to the AC source for controlling the AC source to generate n AC electrical signals with different frequencies.

3. The system according to claim 2, characterized in that, The resistance calculation unit is further used to control the frequency of each of the AC electrical signals according to a frequency threshold condition, and the frequency threshold condition is determined by the frequency distribution range of ambient noise.

4. The system according to claim 2, wherein The resistance calculation unit is further used to control the amplitudes of each of the AC electrical signals generated by the AC source to be equal.

5. The system according to claim 1, wherein The resistance calculation unit is further used for: Based on the numerical value of each resistance measurement value and the number of times it appears among the n*m resistance measurement values, determining the weight value corresponding to each numerical value; Using each numerical value and the corresponding weight value to determine the resistance calculation value of the Josephson junction.

6. The system according to claim 1, wherein The voltage measurement unit is further connected to the AC source for outputting voltage measurement result information to the resistance calculation unit according to the frequency of the AC electrical signal, and the voltage measurement result information includes the voltage measurement value.

7. The system according to claim 1, wherein The series loop further includes: A preset resistor, the resistance value of the preset resistor is greater than the resistance value of the Josephson junction, and the preset resistor is used to control the current in the series loop to be constant.

8. The system according to claim 1, wherein The current measurement unit is a lock-in amplifier.

9. The system according to claim 1, wherein The voltage measurement unit is a lock-in amplifier.

10. The system according to claim 1, wherein The AC source and the voltage measurement unit are two working units of the same lock-in amplifier.

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