A JOSEPHSON JUNCTION MEASUREMENT SYSTEM AND MEASUREMENT METHOD

Abstract

The present invention provides a Josephson measurement system and a measurement method, comprising an excitation coil, a sample superconducting loop and a superconducting detector structure; the excitation coil is connected to an excitation current and generates an excitation magnetic flux, and the sample superconducting loop generates a phase between two ends of the sample Josephson junction and a superconducting current of the sample superconducting loop according to the excitation magnetic flux; the superconducting detector structure obtains an output voltage according to the superconducting magnetic flux output; wherein, based on the relationship between the excitation magnetic flux and the excitation current and the relationship between the excitation magnetic flux and the phase between two ends of the sample Josephson junction, the relationship between the phase of the sample Josephson junction and the excitation current can be obtained; and the relationship between the phase of the sample Josephson junction and the superconducting current can be obtained according to the output voltage, the excitation current, the superconducting current and the relationship between the phase of the sample Josephson junction and the excitation current. The present invention can accurately obtain complete information of the Josephson junction.

Description

Technical Field

[0001] The present invention relates to the field of superconducting technology, and in particular to a Josephson junction measurement system and a measurement method. Background Art

[0002] With the rapid development of superconducting quantum bits and superconducting integrated circuits, superconducting circuits may become an important part of future information technology. The superconducting Josephson junction is the basic unit in superconducting circuits. There is a functional relationship between the superconducting current in the junction and the phase difference of the wave function in the superconductors at both ends of the junction, which is a manifestation of the macroscopic quantum effect of superconductivity. The current-phase relationship (CPR) of an ideal Josephson junction presents a sinusoidal function I s =I c sinθ, where I s is the superconducting current flowing through the junction, I c is the critical current of the junction, and θ is the phase difference between the two ends of the junction, which is the basic DC Josephson effect. However, in reality, due to the influence of material defects and boundary effects, CPR often deviates from the sine function. For electronic devices based on Josephson junctions, slight deviations will have an impact on the performance of the device. In addition, with the advancement of superconducting material science and nano-manufacturing technology, various new Josephson junctions have emerged. Many of these junction models are no longer just deviating from the ideal sinusoidal function current-phase relationship, but will have a more complex current-phase relationship. Therefore, accurate measurement of the current-phase relationship is of great fundamental significance for studying the basic properties of quantum materials, verifying the physical model of unconventional Josephson junctions, and further developing the performance of superconducting Josephson devices.

[0003] Since the phase of the superconducting wave function is not a physical quantity that can be measured directly, the current-phase relationship is currently measured indirectly. There are mainly two measurement methods.

[0004] One method is to connect the sample Josephson junction to a superconducting loop, change the magnetic flux in the loop by means of magnetic field or current excitation, and then the magnetic flux of the loop can be changed into the phase at both ends of the junction, and the induced current generated by the change of magnetic flux in the superconducting loop is measured by a readout SQUID. Although this method can measure the main characteristics of the current-phase relationship, the SQUID measures the magnetic flux of the induced current coupled to the SQUID loop, so it is impossible to accurately measure the exact current value in the loop.

[0005] Another measurement method is to use an asymmetric SQUID composed of a Josephson junction to be tested and a reference junction with a very large critical current. This method can directly obtain the current value passing through the junction. However, it requires that the critical current of the junction to be tested must be much smaller than the critical current of the reference junction, and the reference junction is assumed to be an ideal Josephson junction. At this time, the flux modulation relationship of the SQUID can be approximated to the current-phase relationship of the junction to be tested. This measurement method based on the asymmetric SUID is also less accurate in obtaining approximate results. Summary of the invention

[0006] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a Josephson junction measurement system and a measurement method, so as to solve the problem of inaccurate Josephson junction measurement in the prior art.

[0007] To achieve the above-mentioned object and other related objects, the present invention provides a Josephson junction measurement system, comprising:

[0008] An excitation coil, wherein the excitation coil is connected to an excitation current and generates an excitation magnetic flux according to the excitation current;

[0009] A sample superconducting loop, the sample superconducting loop comprising a superconducting loop and a sample Josephson junction, the sample Josephson junction being connected in series in the superconducting loop; the sample superconducting loop generates a phase between two ends of the sample Josephson junction and a superconducting current of the sample superconducting loop according to the excitation magnetic flux;

[0010] A superconducting detector structure, wherein the superconducting detector structure comprises a superconducting quantum interference device loop, wherein the superconducting quantum interference device loop detects a superconducting magnetic flux coupled to the superconducting quantum interference device loop according to the superconducting current, and the superconducting detector structure obtains an output voltage according to the superconducting magnetic flux output;

[0011] Wherein, based on the relationship between the excitation magnetic flux and the excitation current and the relationship between the excitation magnetic flux and the phase between the two ends of the sample Josephson junction, the relationship between the phase of the sample Josephson junction and the excitation current can be obtained;

[0012] The relationship between the phase of the sample Josephson junction and the superconducting current is obtained according to the output voltage, the excitation current, the superconducting current and the relationship between the phase of the sample Josephson junction and the excitation current.

[0013] Preferably, the sample Josephson junctions include two, the two sample Josephson junctions are connected in series in a superconducting ring, and the superconducting ring is divided into two superconductors connected by the sample Josephson junctions.

[0014] Preferably, the superconducting loop is provided with a positive current test terminal, a negative current test terminal, a positive voltage test terminal and a negative voltage test terminal; the positive voltage test terminal and the positive current test terminal are connected to one of the superconductors, and the negative voltage test terminal and the negative current test terminal are connected to the other superconductor; wherein, the excitation current is controlled to obtain the critical current of the current test terminal, and the superconducting current is obtained according to the relationship between the critical current and the superconducting current and the excitation current.

[0015] Preferably, the superconducting detector structure further includes a comparison amplifier, a feedback resistor and a feedback coil;

[0016] The input end of the comparison amplifier is connected to a superconducting quantum interference device loop, and the comparison amplifier obtains the output voltage according to the current and bias current of the superconducting quantum interference device loop;

[0017] One end of the feedback resistor is connected to one end of the feedback coil, and the other end of the feedback coil is grounded;

[0018] The output end of the comparison amplifier and the other end of the feedback resistor are both connected to the output end of the superconducting detector structure.

[0019] Preferably, the superconducting quantum interference device loop includes a first branch and a second branch;

[0020] The first branch includes a first induction coil and a first reference Josephson junction connected in series;

[0021] The second branch includes a second induction coil and a second reference Josephson junction connected in series;

[0022] The first induction coil and the second induction coil are connected to form a first connection point, and the first connection point is connected to the input end of the comparison amplifier;

[0023] The first reference Josephson junction and the second reference Josephson junction are connected to form a second connection point, and the second connection point is grounded.

[0024] To achieve the above object and other related objects, the present invention also provides a Josephson junction measurement method, which at least includes the following steps:

[0025] Conducting a test experiment based on a Josephson junction measurement system and obtaining a test result; the test experiment outputs different output voltages by controlling the excitation current; the test result includes the excitation current, the superconducting current, the output voltage and the critical current;

[0026] The test results are processed to obtain the relationship between the phase and the excitation current of the sample Josephson junction;

[0027] The test results are processed to obtain the relationship between the excitation current and the superconducting current;

[0028] The relationship between the phase of the sample Josephson junction and the superconducting current is obtained according to the relationship between the excitation current and the superconducting current and the relationship between the phase of the sample Josephson junction and the excitation current.

[0029] Preferably, the test results are processed to obtain the relationship between the phase and the excitation current of the sample Josephson junction, including:

[0030] The relationship between the critical current and the excitation current of the test results is processed to obtain the mutual inductance between the sample Josephson junction and the excitation coil;

[0031] The relationship between the phase of the sample Josephson junction and the excitation current is obtained according to the mutual inductance between the sample Josephson junction and the excitation coil and the relationship between the phase of the Josephson junction and the excitation current.

[0032] Preferably, processing the test results to obtain the relationship between the excitation current and the superconducting current includes:

[0033] The relationship between the output voltage and the superconducting current is obtained according to the test results;

[0034] The relationship between the output voltage and the excitation current is obtained according to the test results;

[0035] The relationship between the excitation current and the superconducting current is obtained according to the relationship between the output voltage and the superconducting current and the relationship between the output voltage and the excitation current.

[0036] Preferably, the relationship between the voltage and current of the superconducting Josephson junction of the sample is also obtained according to the test results.

[0037] As described above, the Josephson junction measurement system and measurement method of the present invention have the following beneficial effects:

[0038] Compared with the existing measurement methods, the Josephson junction measurement system and method of the present invention can obtain the exact current value and phase value and the current-voltage curve representation of the junction in situ while achieving the process of measuring the relationship between the phase and current of a superconducting Josephson junction, while processing the trend of the current-phase relationship, thereby obtaining complete information about the Josephson junction. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Shown is a schematic structural diagram of a Josephson junction measurement system in an embodiment of the present invention.

[0040] Figure 2 Shown is a schematic flow chart of a Josephson junction measurement method according to an embodiment of the present invention.

[0041] Figure 3 Shown is a schematic diagram of a test system integrated circuit board according to an embodiment of the present invention.

[0042] Figure 4 Shown is a schematic diagram of the current-voltage relationship curve of the sample Josephson junction in an embodiment of the present invention.

[0043] Figure 5 It is a schematic diagram of the magnetic flux modulation curve when two sample Josephson junctions are connected in parallel in an embodiment of the present invention.

[0044] Figure 6 It is a schematic diagram showing the relationship between the output voltage and the excitation current in an embodiment of the present invention.

[0045] Figure 7 Shown is a schematic diagram of the relationship between the phase and current of a sample Josephson junction in an embodiment of the present invention.

[0046] Component number description

[0047] 1 Sample superconducting loop

[0048] 11 Sample Josephson junction

[0049] 12 Superconducting Ring

[0050] 2 Superconducting quantum interference device loop DETAILED DESCRIPTION

[0051] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0052] See also Figure 1-7 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0053] The present invention can accurately obtain the superconducting current of the sample superconducting loop based on the designed sample superconducting loop, and can obtain the relationship between the phase of the sample Josephson junction and the excitation current according to the regulation and control of the excitation current in the measurement system, and then can finally accurately obtain the relationship between the phase of the sample Josephson junction and the superconducting current through the output voltage obtained in the measurement system. Based on the above technical concept, the present invention proposes a Josephson junction measurement system and a measurement method.

[0054] System Example:

[0055] In order to achieve the above technical objectives and technical concepts, the present invention proposes a Josephson junction measurement system. In an embodiment of the present invention, the structural schematic diagram of the Josephson junction measurement system is as follows: Figure 1 As shown, the Josephson junction measurement system includes:

[0056] Excitation coil coil 1, the excitation coil coil 1 is connected to the excitation current I in , according to the excitation current I in Generates excitation flux Ф in ;

[0057] A sample superconducting loop 1, wherein the sample superconducting loop 1 comprises a superconducting loop 12 and a sample Josephson junction 11, wherein the sample Josephson junction 11 is connected in series in the superconducting loop 12; the sample superconducting loop 1 is connected in series according to the excitation magnetic flux Φ in The phase θ between the two ends of the sample Josephson junction 11 and the superconducting current I of the sample superconducting loop 1 are generated. S ;

[0058] A superconducting detector structure, wherein the superconducting detector structure includes a superconducting quantum interference device loop 2 (DC SQUID), wherein the superconducting quantum interference device loop 2 detects and obtains a superconducting current I S coupled to the superconducting flux Φ in the SQUID loop 2 S The superconducting detector structure is based on the superconducting magnetic flux Φ S The output voltage V out ;

[0059] Wherein, based on the excitation flux Φ in With the excitation current I in The relationship between the excitation flux Φ in The relationship between the phase θ between the two ends of the sample Josephson junction can be obtained by comparing the phase θ of the sample Josephson junction with the excitation current I in relationship;

[0060] According to the output voltage V out , the excitation current I in 、the superconducting current IS and the phase θ of the sample Josephson junction versus the excitation current I in The relationship between the phase θ of the sample Josephson junction and the superconducting current I S The relationship between.

[0061] The sample Josephson junction 11 in the embodiment of the present invention includes two, and the two sample Josephson junctions are connected in series in the superconducting ring, and the superconducting ring is divided into two superconductors connected by the sample Josephson junction. In order to accurately describe the structural relationship of the sample superconducting loop 1, the two sample Josephson junctions 11 are defined as the first sample Josephson junction and the second sample Josephson junction respectively; because the two sample Josephson junctions 11 are connected in series in the superconducting ring 12, the superconducting ring 12 is understood to be divided into the first superconductor and the second superconductor, then, the two ends of the first superconductor are respectively connected to the first end of the first sample Josephson junction and the first end of the second sample Josephson junction, and the two ends of the second superconductor are respectively connected to the second end of the first sample Josephson junction and the second end of the second sample Josephson junction.

[0062] The superconducting loop of the present invention is provided with a positive current test terminal I+, a negative current test terminal I-, a positive voltage test terminal V+ and a negative voltage test terminal V-; the positive voltage test terminal V+ and the positive current test terminal I+ are connected to one of the superconductors, i.e., the first superconductor, and the negative voltage test terminal V- and the negative current test terminal I- are connected to another superconductor, i.e., the second superconductor; wherein, the critical current Ic of the current test terminal (I+, I-) is obtained by controlling the excitation current, and the critical current Ic is obtained according to the difference between the critical current Ic and the superconducting current I S The relationship between the excitation current I in Get the superconducting current I S .

[0063] The relationship between the phase of the Josephson junction and the excitation current is:

[0064]

[0065] Among them, θ is the phase of the sample Josephson junction, Ф0 is the magnetic flux quantum, M in-s is the mutual inductance between the excitation coil 1 and the sample superconducting loop 1, I in is the excitation current of the excitation coil 1.

[0066] Since the mutual inductance between the sample superconducting loop 1 and the excitation coil 1 is unknown in the embodiment of the present invention, it is necessary to first determine the mutual inductance M between the excitation coil 1 and the sample superconducting loop 1. in-s , in order to accurately obtain the phase θ and excitation current I of the sample Josephson junction in the test system in relationship.

[0067] In the embodiment of the present invention, the mutual inductance M between the excitation coil 1 and the sample superconducting loop 1 is in-s The determination method is as follows: first, a limited number of test experiments are carried out based on the Josephson junction measurement system; specifically, different excitation currents are controlled to make the excitation flux a multiple of the constant Ф0, and the superconducting current I is obtained through the current test terminals (I+, I-) S Different critical current I C , that is, controlling different excitation currents I in Make the current test end (I+, I-) get different critical current I C , draw the excitation current I in and critical current I C The relationship between the excitation current I in and critical current I C The relationship between and conforms to the sinusoidal relationship (the sinusoidal relationship contains the phase). According to any excitation current I in and critical current I C The corresponding phase θ can be obtained by measuring the size of the excitation current I. in The mutual inductance M between the excitation coil 1 and the sample superconducting loop 1 can be determined based on the relationship between the phase of the Josephson junction and the excitation current. in-s .

[0068] According to the determined mutual inductance M between the excitation coil 1 and the sample superconducting loop 1 in-s The relationship between the phase of the Josephson junction and the excitation current is obtained in the test system to determine the phase θ of the sample Josephson junction and the excitation current I in The relationship between.

[0069] Among them, the critical current I C It is superconducting current I S The current in the critical state, therefore, the present invention is based on the superconducting current I S Each critical current I in the critical state C With the excitation current I in Determine the phase θ of the sample Josephson junction and the excitation current I in The relationship between.

[0070] As a preferred embodiment of the present invention, a test current is applied to the current test terminal (I+, I-), and then the voltage of the sample Josephson junction can be obtained through the voltage test terminal, that is, the current and voltage relationship (I~V) of the Josephson junction can be obtained.

[0071] The superconducting detector structure of the present invention further includes a comparison amplifier D, a feedback resistor R F and feedback coil coil2;

[0072] The input end of the comparison amplifier D is connected to the superconducting quantum interference device loop. The comparison amplifier D is based on the current of the superconducting quantum interference device loop and the bias current I B The output voltage V out ;

[0073] The feedback resistor R F One end of the feedback coil 2 is connected to one end of the feedback coil 2, and the other end of the feedback coil 2 is grounded;

[0074] The output end of the comparison amplifier D and the feedback resistor R F The other end of each is connected to the output end of the superconducting detector structure.

[0075] The superconducting quantum interference device loop 2 of the superconducting detector structure of the present invention first senses the superconducting magnetic flux Φ of the sample superconducting loop. S , and in the superconducting magnetic flux Ф S The current is generated under the action of the SQID, and then the current of the SQID loop and the bias current I are compared by the amplifier D. B After comparison and amplification, the output voltage V out Then the SQUID loop 2 simultaneously senses the feedback flux Φ generated by the feedback coil 2 f , in the feedback flux Ф f Under the feedback regulation, the superconducting quantum interference device loop 2 adjusts the output current and realizes the output voltage V out Dynamically adjust the output to meet control requirements.

[0076] In an embodiment of the present invention, the superconducting quantum interference device loop 2 includes a first branch and a second branch;

[0077] The first branch includes a first induction coil and a first reference Josephson junction connected in series;

[0078] The second branch includes a second induction coil and a second reference Josephson junction connected in series;

[0079] The first induction coil and the second induction coil are connected to form a first connection point, and the first connection point is connected to the input end of the comparison amplifier;

[0080] The first reference Josephson junction and the second reference Josephson junction are connected to form a second connection point, and the second connection point is grounded.

[0081] In the embodiment of the present invention, the first reference Josephson junction and the second reference Josephson junction are the same as the sample Josephson junction, that is, they are manufactured using the same process to simplify and reduce the complexity of the manufacturing process of the devices used in the overall measurement system.

[0082] Method Example:

[0083] In order to achieve the above technical objectives and technical concepts, the present invention proposes a Josephson junction measurement method, which is applicable to the above Josephson junction measurement system. The process of the Josephson junction measurement method of the present invention is as follows: Figure 2 As shown, the measuring method shown includes at least the following steps:

[0084] S1, performing a test experiment based on a Josephson junction measurement system and obtaining a test result; the test experiment outputs different output voltages by controlling the excitation current;

[0085] The test results include excitation current, superconducting current, output voltage and critical current;

[0086] like Figure 3 The test circuit board shown is formed by connecting the sample Josephson junction 11 in series to the superconductor 12 by micro-nano processing means on an insulating substrate, and the sample superconducting loop 1 including the superconducting quantum interference device loop 2 (DC SQUID) is integrated on-chip with the sample superconducting loop 1 and the excitation coil to facilitate measurement.

[0087] The test experiments are:

[0088] 1. Apply different excitation currents I to the excitation coil 1. in , adjust to produce different excitation magnetic field Ф in ;

[0089] 2. Adjusting the symmetry between the first sample Josephson junction and the second sample Josephson junction. Specifically, when the magnetic flux modulation curve of the superconducting quantum interference device loop 2 is completely symmetrical, it can be considered that the first sample Josephson junction and the second sample Josephson junction are symmetrical. Therefore, the present invention adjusts the symmetry of the two sample Josephson junctions through the symmetry of the magnetic flux modulation curve.

[0090] 3. At different excitation current I in The magnetic field of the sample superconducting loop 1 is changed under the action of, and the superconducting current Is of the sample superconducting loop 1 and the critical current Ic of the sample Josephson junction are obtained;

[0091] Then in the flux modulation curve I c Maximum value, measured critical current I of the SQUID c is the critical current of a single junction I c-junction When measuring the current-phase relationship, when only the superconducting current Is generated by the external magnetic field exists in the loop, the two sample Josephson junctions are connected in series in the superconducting ring. At this time, the current flowing through each sample Josephson junction is the same, and the phase difference at both ends of each sample Josephson junction is also equal.

[0092] Specifically, when the excitation current I in The change makes the external magnetic flux Ф e =n×Ф0, the critical current Ic of the sample superconducting loop 1 reaches the maximum value Ic-max; when the excitation current Iin changes so that the external magnetic flux When the critical current Ic of the sample superconducting loop 1 reaches the minimum value Ic-min, Ф0 represents the magnetic flux quantum and is a fixed constant, and n is a natural number; different excitation currents I in and the corresponding critical current Ic, thus obtaining Figure 5 The relationship curve between the critical current and the excitation current is shown in FIG. 1 ; in the embodiment developed in Japan, the modulation depth is 25.7%, and the critical current I of the double junction parallel connection is obtained. c value, through the exciting coil I in Apply magnetic flux to the sample ring to obtain the magnetic flux modulation curve, and get I c The maximum value is 14.67μA, and the critical current I of the Josephson junction of a single sample c / 2=7.335μA,

[0093] 4. By adjusting the symmetry of feedback coil 2 and SQUID loop 2, the influence of feedback coil 2 on SQUID loop 2 can be reduced to zero, so that SQUID loop 2 senses the superconducting magnetic flux generated by the superconducting current of sample superconducting loop 1, so the excitation currents I of different excitation currents can be accurately obtained. in And the corresponding different output voltage V out size.

[0094] In addition, the test experiment can also directly measure the current and corresponding voltage, critical current and corresponding excitation flux of the sample Josephson junction through the current test terminal (I+, I-) and voltage test terminal (V+, V-) set in the sample superconducting loop 1, so as to obtain the current and voltage relationship (IV) of the sample Josephson junction. Figure 4 As shown in the figure, the relationship between critical current and excitation flux (Ic-Ф in ).

[0095] S2, processing the test results to obtain the relationship between the phase and the excitation current of the sample Josephson junction;

[0096] S21, processing the relationship between the critical current and the excitation current of the test results to obtain the mutual inductance between the sample Josephson junction and the excitation coil;

[0097] For the excitation current I in the test results in and the corresponding critical current Ic, so as to obtain Figure 5The relationship curve diagram between the critical current and the excitation current is shown in FIG. in and critical current I C The corresponding phase θ can be obtained by measuring the size of the excitation current I. in The mutual inductance M between the excitation coil 1 and the sample superconducting loop 1 can be determined based on the relationship between the phase of the Josephson junction and the excitation current. in-s In the embodiment of the present invention, the mutual inductance M between the excitation coil 1 and the sample superconducting loop 1 is determined. in-s The pH is 2.25.

[0098] The relationship between the phase of the Josephson junction and the excitation current is:

[0099]

[0100] Among them, θ is the phase of the sample Josephson junction, Ф0 is the magnetic flux quantum, M in-s is the mutual inductance between the excitation coil 1 and the sample superconducting loop 1, I in is the excitation current of the excitation coil 1.

[0101] S22, obtaining the relationship between the phase of the sample Josephson junction and the excitation current according to the mutual inductance between the sample Josephson junction and the excitation coil and the relationship between the phase of the Josephson junction and the excitation current.

[0102] The mutual inductance M between the excitation coil 1 and the sample superconducting loop 1 obtained in step S21 is in-s By bringing the relationship between the phase and the excitation current of the Josephson junction into the relationship between the phase and the excitation current of the sample Josephson junction in the test system of the present invention, the relationship between the phase and the excitation current can be obtained, that is, θ = k0 × I in .

[0103] S3, processing the test results to obtain the relationship between the excitation current and the superconducting current;

[0104] The relationship between the phase of the sample Josephson junction and the superconducting current is obtained according to the excitation current, the superconducting current, the output voltage and the relationship between the phase of the sample Josephson junction and the excitation current in the test results.

[0105] S31, obtain the output voltage V according to the test results out With superconducting current I s the relationship between;

[0106] First, substitute the output voltage and superconducting current in the test results into the following formula to obtain The value of

[0107]

[0108] Among them, Φ f is the feedback flux, M f is the mutual inductance between the feedback coil and the DC SQUID, RF is the feedback resistance, M S is the mutual inductance between the superconducting sample loop and the DC SQUID.

[0109] Then, Substituting the value of into the formula, the output voltage V in the test system can be obtained. out With superconducting current I s The relationship between out =k1×I s .

[0110] S32, obtain the output voltage V according to the test results out With the excitation current I in the relationship between;

[0111] The output voltage and excitation current in the test results are processed to obtain the output voltage V out With the excitation current I in The relationship between Figure 6 As shown; can be regarded as V out =k2×I in

[0112] S33, according to the output voltage V out With superconducting current I μ The relationship between the output voltage V out With the excitation current I in The relationship between the excitation current I in With superconducting current I μ the relationship between;

[0113] Specifically, according to V out =k1×I s and V out =k2×I in Get I in =k3×I s . That is, the excitation current I in With the superconducting current I S between.

[0114] S4, obtaining the relationship between the phase of the sample Josephson junction and the superconducting current according to the relationship between the excitation current and the superconducting current and the relationship between the phase of the sample Josephson junction and the excitation current.

[0115] According to the above, the relationship between the phase of the sample Josephson junction and the excitation current is θ = k0 × Iin ; The relationship between the excitation current and the superconducting current is I in =k3×I s ; Derivation of the two relationships yields θ=k4×I S . That is, the relationship between the phase of the sample Josephson junction and the superconducting current in the test system can be accurately obtained. Figure 7 shown.

[0116] As a preferred embodiment of the present invention, because the superconducting sample loop is provided with a current test terminal and a voltage test terminal, the current and voltage of the superconducting sample loop can also be measured. According to the current and voltage, the relationship between the voltage and current of the sample superconducting Josephson junction can be accurately obtained, thereby achieving a more comprehensive understanding and mastery of the sample Josephson junction information.

[0117] In summary, in the process of measuring the relationship between the phase and current of a superconducting Josephson junction, the Josephson junction measurement system and the Josephson junction measurement method of the present invention can obtain the exact current value and phase value and obtain the current-voltage curve characterization of the junction in situ, compared with the existing measurement method, in addition to obtaining the trend of the current-phase relationship, thereby obtaining complete information about the Josephson junction. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

[0118] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A Josephson junction measurement system, characterized in that: include: An excitation coil, wherein the excitation coil is connected to an excitation current and generates an excitation magnetic flux according to the excitation current; A sample superconducting loop, the sample superconducting loop comprising a superconducting loop and a sample Josephson junction, the sample Josephson junction being connected in series in the superconducting loop; the sample superconducting loop generates a phase between two ends of the sample Josephson junction and a superconducting current of the sample superconducting loop according to the excitation magnetic flux; A superconducting detector structure, wherein the superconducting detector structure includes a superconducting quantum interference device loop, wherein the superconducting quantum interference device loop detects a superconducting magnetic flux coupled to the superconducting quantum interference device loop according to the superconducting current, and the superconducting detector structure obtains an output voltage according to the superconducting magnetic flux output; the superconducting detector structure also includes a comparison amplifier, a feedback resistor and a feedback coil; the input end of the comparison amplifier is connected to the superconducting quantum interference device loop, and the comparison amplifier obtains the output voltage according to the current and bias current of the superconducting quantum interference device loop; Wherein, based on the relationship between the excitation flux and the excitation current and the relationship between the excitation flux and the phase between the two ends of the sample Josephson junction, the relationship between the phase of the sample Josephson junction and the excitation current can be obtained; based on the Josephson junction measurement system, a test result is obtained, and the test result includes the output voltage, the excitation current and the critical current; the test result is processed to obtain the relationship between the phase of the sample Josephson junction and the excitation current; the test result is processed to obtain the relationship between the excitation current and the superconducting current; the relationship between the phase of the sample Josephson junction and the superconducting current is obtained according to the relationship between the excitation current and the superconducting current and the relationship between the phase of the sample Josephson junction and the excitation current; and the relationship between the output voltage and the superconducting current is obtained according to the test result, the relationship between the output voltage and the excitation current is obtained according to the test result, and the relationship between the excitation current and the superconducting current is obtained according to the relationship between the output voltage and the superconducting current and the relationship between the output voltage and the excitation current; The relationship between the phase of the sample Josephson junction and the superconducting current is obtained according to the output voltage, the excitation current, the superconducting current and the relationship between the phase of the sample Josephson junction and the excitation current.

2. The Josephson junction measurement system according to claim 1, characterized in that: The sample Josephson junctions include two sample Josephson junctions, which are connected in series in a superconducting ring and divide the superconducting ring into two superconductors connected by the sample Josephson junctions.

3. The Josephson junction measurement system according to claim 2, characterized in that: The superconducting loop is provided with a positive current test terminal, a negative current test terminal, a positive voltage test terminal and a negative voltage test terminal; the positive voltage test terminal and the positive current test terminal are connected to one of the superconductors, and the negative voltage test terminal and the negative current test terminal are connected to the other superconductor; wherein the excitation current is controlled to obtain the critical current of the current test terminal, and the superconducting current is obtained according to the relationship between the critical current and the superconducting current and the excitation current.

4. The Josephson junction measurement system according to claim 1, characterized in that: One end of the feedback resistor is connected to one end of the feedback coil, and the other end of the feedback coil is grounded; The output end of the comparison amplifier and the other end of the feedback resistor are both connected to the output end of the superconducting detector structure.

5. The Josephson junction measurement system according to claim 4, characterized in that: The superconducting quantum interference device loop includes a first branch and a second branch; The first branch includes a first induction coil and a first reference Josephson junction connected in series; The second branch includes a second induction coil and a second reference Josephson junction connected in series; The first induction coil and the second induction coil are connected to form a first connection point, and the first connection point is connected to the input end of the comparison amplifier; The first reference Josephson junction and the second reference Josephson junction are connected to form a second connection point, and the second connection point is grounded.

6. A Josephson junction measurement method, applicable to the Josephson junction measurement system according to any one of claims 1 to 5, characterized in that: At least the following steps are included: Conducting a test experiment based on a Josephson junction measurement system and obtaining test results; the test experiment outputs different output voltages by controlling the excitation current; the test results include the excitation current, the superconducting current, the output voltage and the critical current; The test results are processed to obtain the relationship between the phase and the excitation current of the sample Josephson junction; The test results are processed to obtain the relationship between the excitation current and the superconducting current; The relationship between the phase of the sample Josephson junction and the superconducting current is obtained according to the relationship between the excitation current and the superconducting current and the relationship between the phase of the sample Josephson junction and the excitation current.

7. The Josephson junction measurement method according to claim 6, characterized in that: The relationship between the phase and excitation current of the sample Josephson junction obtained by processing the test results includes: The relationship between the critical current and the excitation current of the test results is processed to obtain the mutual inductance between the sample Josephson junction and the excitation coil; The relationship between the phase of the sample Josephson junction and the excitation current is obtained according to the mutual inductance between the sample Josephson junction and the excitation coil and the relationship between the phase of the Josephson junction and the excitation current.

8. The Josephson junction measurement method according to claim 6, characterized in that: The relationship between the excitation current and the superconducting current obtained by processing the test results includes: The relationship between the output voltage and the superconducting current is obtained according to the test results; The relationship between the output voltage and the excitation current is obtained according to the test results; The relationship between the excitation current and the superconducting current is obtained according to the relationship between the output voltage and the superconducting current and the relationship between the output voltage and the excitation current.

9. The Josephson junction measurement method according to claim 6, characterized in that: According to the test results, the relationship between the voltage and current of the superconducting Josephson junction of the sample is also obtained.

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