A method for improving dephasing time based on mutual inductance adjustment and junction asymmetry compensation

Abstract

The application provides a decoherence time improving method based on mutual inductance adjustment and junction asymmetry compensation, and belongs to the technical field of superconducting quantum computation. The method comprises the following steps: constructing a superconducting quantum bit theoretical model comprising a non-equilibrium mutual inductance and a non-symmetrical Josephson junction; determining the core basic parameters and constraint conditions of the double-junction superconducting quantum bit, deducing a mutual inductance balance compensation condition, adjusting a magnetic flux line ground position, changing the numerical relationship of mutual inductances of left and right arms, and eliminating the relaxation caused by mutual inductance imbalance; defining a junction asymmetry parameter and a mutual inductance imbalance degree, deducing a relaxation compensation condition, making the relaxation caused by mutual inductance imbalance and the relaxation caused by junction asymmetry cancel each other out, and improving the decoherence time of the superconducting quantum bit. The application establishes a quantitative relationship between mutual inductance adjustment and junction asymmetry compensation, realizes relaxation cancellation by using the interaction between mutual inductance imbalance and junction asymmetry, and significantly improves the decoherence time and gate fidelity of the quantum bit.

Description

Technical Field

[0001] This invention relates to the field of technology, and in particular to a method for improving decoherence time based on mutual inductance adjustment and junction asymmetry compensation. Background Technology

[0002] Decoherence time is a key performance indicator for superconducting qubits, characterizing the duration for which quantum coherence can be effectively maintained. However, due to the inevitable coupling of qubits with various noises, their decoherence time is typically finite, further reducing the gate fidelity in practical quantum circuits. Low gate fidelity is a major factor limiting the quantum volume of noisy medium-scale quantum (NISQ) circuits. In the long term, fault-tolerant quantum circuits also require sufficiently high gate fidelity to reduce the error rate below a threshold, or even lower, thereby reducing the number of physical qubits required for a single logic qubit to a practical level.

[0003] Currently, in superconducting quantum computing, frequency-tunable transmon qubits (two-junction transmons) have become the mainstream architecture due to their ability to effectively avoid frequency congestion and achieve high-fidelity two-qubit gates. This architecture typically uses a SQUID loop containing two Josephson junctions, and the frequency is tuned by applying an external magnetic field through a flux bias line. However, existing theoretical models and designs usually assume that the coupling between the flux bias line and the two arms of the SQUID is ideal or only focus on the total flux coupling, neglecting the imbalance of mutual inductance. In addition, due to the lack of active compensation methods, there is currently no mechanism to actively address process errors during the layout design stage, resulting in chip performance being limited by process deviations after fabrication, making it difficult to improve yield. Summary of the Invention

[0004] The purpose of this invention is to provide a decoherence time improvement method based on mutual inductance adjustment and junction asymmetry compensation. By adjusting the position of the magnetic flux grounding point to optimize mutual inductance coupling and establishing a compensation relationship between mutual inductance imbalance and junction asymmetry, the relaxation caused by the two is mutually canceled, thereby significantly improving the decoherence time and gate fidelity of superconducting qubits.

[0005] To achieve the above objectives, this invention proposes a method for improving decoherence time based on mutual inductance adjustment and junction asymmetry compensation. This method adjusts the mutual inductance imbalance by utilizing the location of the magnetic flux line grounding point, and simultaneously leverages the interaction between mutual inductance imbalance and junction asymmetry to compensate for the relaxations induced by each, ultimately improving the decoherence time. The method includes the following steps:

[0006] Step S1: Construct a theoretical model of a superconducting quantum bit that includes unbalanced mutual inductance and an asymmetric Josephson junction. The model is based on the double-junction Transmon quantum bit architecture and includes a SQUID loop, a magnetic flux bias line, and a shunt capacitor.

[0007] Step S2: Clarify the mutual inductance of the left arm of the SQUID loop Mutual sensation with the right arm And the Josephson junction energy of the left and right arms of the SQUID loop, adjusting the position of the magnetic flux line grounding, changing the numerical relationship of the mutual inductance of the left and right arms until the two mutual inductances meet the conditions. Eliminate relaxation caused by mutual inductance imbalance;

[0008] Step S3: Define the junction asymmetry parameter and mutual inductance imbalance, adjust the relationship between mutual inductance imbalance and junction asymmetry parameter, derive the relaxation compensation condition, so that the relaxation caused by mutual inductance imbalance and the relaxation caused by junction asymmetry cancel each other out, thereby improving the decoherence time of the superconducting quantum bit. The compensation relationship satisfies the following formula:

[0009] ;

[0010] ;

[0011] in, For mutual inductance imbalance, For the junction asymmetry parameter, For magnetic flux bias, For a unit magnetic flux quantum, For the Josephson knot energy of the left arm of the SQUID loop, For the Josephson knot energy of the right arm of the SQUID loop, It is Planck's constant. For unit charge, and These are the mutual inductions of the left and right arms, respectively. and This is the energy of the Josephson knot.

[0012] Preferably, step S1 includes the following steps:

[0013] Step S11: Establish the circuit Lagrangian quantities including unbalanced mutual inductance and asymmetric Josephson junctions. Derive the system Hamiltonian based on the Lagrangian quantities. The formula is:

[0014] ;

[0015] ;

[0016] ;

[0017] ;

[0018] in, For circuit Lagrange quantities, For the Josephson potential operator under interaction, The magnetic flux generated by the current in the branch at node 1. The magnetic flux generated by the current in the branch at node 2. For the flux of the left arm of the SQUID loop, For the flux of the right arm of the SQUID loop, Angular frequency, For distributed inductance, For the system Hamiltonian, For capacitor The charge on it, It is a shunt capacitor. For annihilation operators, To reduce Planck's constant;

[0019] Step S12: Decompose the Josephson junction potential energy into symmetric and antisymmetric potential energy, corresponding to the energy contributions from the symmetry and asymmetry of the junction parameters, respectively. The formula is as follows:

[0020] ;

[0021] ;

[0022] ;

[0023] in, For the Josephson potential operator under interaction, For the flux operator passing through the left arm of the SQUID ring under the interaction, For the flux operator passing through the right arm of the SQUID ring under the interaction, For symmetrical potential energy, To counterbalance potential energy, The sum of Josephson's energies. For the core node magnetic flux, The sum of magnetic flux. This is the difference in magnetic flux;

[0024] Step S13: Decompose the sum and difference of magnetic flux into classical and quantum components, using the following formula:

[0025] ;

[0026] ;

[0027] in, This is the classical component of the sum of the magnetic flux of the two arms of the Squid ring. The classical component of the difference in magnetic flux passing through the SQUID ring. Let be the quantum component of the sum of the magnetic flux of the two arms of the SQUID ring. The quantum component is the difference in magnetic flux passing through the SQUID ring.

[0028] Preferably, step S2 includes the following steps:

[0029] Step S21: Based on the double-junction Transmon architecture, define the mutual inductance between the flux lines and the left arm of the SQUID loop. Mutual sensation with the right arm The physical coupling location is determined, and a theoretical model incorporating non-equilibrium mutual inductance is constructed. Based on the circuit Lagrangian and Hamiltonian, the physical coupling location is clearly defined. , The logical connection with relaxation;

[0030] Step S22: Locate the grounding point adjustment area and set the grounding point to... and On the coupling path between them, the physical position of the grounding point is shifted step by step, and the position of the GND node is finely adjusted along the coupling direction of the magnetic flux line and the SQUID loop, with the initial position as the reference.

[0031] Step S23: Real-time monitoring and The numerical change was measured by synchronously collecting mutual inductance data of the two arms at different grounding point locations using testing equipment, until it reached... The equilibrium coupling condition.

[0032] Preferably, step S3 includes the following steps:

[0033] Step S31: Define the junction asymmetry parameters and mutual inductance imbalance. Based on the established circuit model including unbalanced mutual inductance and an asymmetric Josephson junction, and the double-junction Transmon architecture, clarify the circuit Lagrangian and Hamiltonian quantities, incorporate the coupling relationship between the symmetric and antisymmetric potential energies of the Josephson junction, and derive the relaxation rate formula, which is:

[0034] ;

[0035] ;

[0036] ;

[0037] in, The relaxation rate, The product's vertical coupling coefficient. The frequency of a quantum bit;

[0038] Step S32: Determine the core condition for relaxation cancellation as the longitudinal coupling coefficient. The compensation relationship is derived, and the formula is:

[0039] ;

[0040] in, For Josephson's sake, For effective Josephson energy;

[0041] Step S33: Obtain The value, if Adjust the mutual inductance imbalance until the junction asymmetry parameters are equal. ,Will Substitute the values ​​into the compensation formula to calculate the target mutual inductance imbalance, and then adjust the grounding point to bring the mutual inductance imbalance to the calculated value.

[0042] Preferably, in step S31, The calculation formula is:

[0043] ;

[0044] ;

[0045] ;

[0046] ;

[0047] in, This is the longitudinal transmission coefficient. For the impedance of the quantum bit, For effective Josephson inductance, It is a shunt capacitor.

[0048] Preferably, in step S32, the formula for the longitudinal coupling coefficient is defined as follows:

[0049] ;

[0050] in, For transmission line impedance, For the junction asymmetry parameter, For the sum of mutual inductance, For Josephson's sake, For effective Josephson energy.

[0051] Therefore, this invention proposes a decoherence time enhancement method based on mutual inductance adjustment and junction asymmetry compensation, the beneficial effects of which are as follows:

[0052] (1) This invention breaks through the traditional balance assumption and for the first time explicitly considers the mutual inductance imbalance between the magnetic flux line and the SQUID loop. It achieves active optimization of mutual inductance by adjusting the grounding point position, thus solving the problem of neglecting actual coupling deviation in the prior art.

[0053] (2) This invention utilizes the interaction between mutual inductance imbalance and junction asymmetry to retain the inhibitory effect of junction asymmetry on pure dephase and compensate for the relaxation caused by junction asymmetry through mutual inductance adjustment, thus achieving dual optimization of suppressing dephase and canceling relaxation.

[0054] (3) The present invention can address process errors through parameter matching during the layout design stage without relying on subsequent chip correction, significantly improving the yield and performance consistency of quantum chips and enhancing design fault tolerance.

[0055] (4) This invention can effectively extend the decoherence time of superconducting qubits through this method, thereby improving the quantum gate fidelity, providing key technical support for NISQ circuits to break through the quantum volume limit and fault-tolerant quantum circuits to reduce physical resource consumption, and significantly improving core performance. Attached Figure Description

[0056] Figure 1 This is a flowchart illustrating a decoherence time enhancement method based on mutual inductance adjustment and junction asymmetry compensation.

[0057] Figure 2 This is a schematic diagram of the core circuit structure of a superconducting quantum bit.

[0058] Figure 3 The diagram shows the compensation relationship curve between mutual inductance imbalance and structural asymmetry parameters, where (a) is... hour and The compensation relationship curve, (b) is hour and The compensation relationship curve. Detailed Implementation

[0059] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0060] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0061] Example 1

[0062] like Figure 1 As shown, this invention provides a method for improving decoherence time based on mutual inductance adjustment and junction asymmetry compensation, comprising the following steps:

[0063] Step S1: Construct a theoretical model of a superconducting quantum bit that includes non-equilibrium mutual inductance and an asymmetric Josephson junction. The model is based on the double-junction Transmon quantum bit architecture. The core circuit structure of the superconducting quantum bit is as follows: Figure 2 As shown, it includes a SQUID loop, a flux bias line, and a shunt capacitor, and includes the following steps:

[0064] Step S11: Establish the circuit Lagrangian quantities including unbalanced mutual inductance and asymmetric Josephson junctions. Derive the system Hamiltonian based on the Lagrangian quantities. The formula is:

[0065] ;

[0066] ;

[0067] ;

[0068] ;

[0069] in, For circuit Lagrange quantities, For the Josephson potential operator under interaction, The magnetic flux generated by the current in the branch at node 1. The magnetic flux generated by the current in the branch at node 2. For the flux of the left arm of the SQUID loop, For the flux of the right arm of the SQUID loop, Angular frequency, For distributed inductance, For the system Hamiltonian, For capacitor The charge on it, It is a shunt capacitor. For annihilation operators, To reduce Planck's constant, and These are the mutual inductions of the left and right arms, respectively. and For Josephson knot energy;

[0070] According to the above formula, we can obtain:

[0071] ;

[0072] in, The sum of Josephson's energies. For the flux drop of the first Josephson junction, The flux drop of the second Josephson junction.

[0073] Previous studies have neglected the effect of the latter term in the above formula, but this invention takes into account the effect of the latter term.

[0074] Step S12: Decompose the Josephson junction potential energy into symmetric and antisymmetric potential energy, corresponding to the energy contributions from the symmetry and asymmetry of the junction parameters, respectively. The formula is as follows:

[0075] ;

[0076] ;

[0077] ;

[0078] in, For the Josephson potential operator under interaction, For the flux operator passing through the left arm of the SQUID ring under the interaction, For the flux operator passing through the right arm of the SQUID ring under the interaction, For symmetrical potential energy, To counterbalance potential energy, For the core node magnetic flux, The sum of magnetic flux. This is the difference in magnetic flux;

[0079] in, , Consider the positive direction. This actually represents the total magnetic flux generated by the flux lines in the Squid loop, if This is defined as balanced coupling.

[0080] Step S13: Decompose the sum and difference of magnetic flux into classical and quantum components, using the following formula:

[0081] ;

[0082] ;

[0083] in, This is the classical component of the sum of the magnetic flux of the two arms of the Squid ring. The classical component of the difference in magnetic flux passing through the SQUID ring. Let be the quantum component of the sum of the magnetic flux of the two arms of the SQUID ring. The quantum component is the difference in magnetic flux passing through the SQUID ring.

[0084] If let Based on the above formula, we can derive the following:

[0085] ;

[0086] ;

[0087] use To represent classic ingredients, Representing the quantum components, we obtain the following relationship:

[0088] ;

[0089] ;

[0090] ;

[0091] ;

[0092] in, and It can be represented as:

[0093] ;

[0094] ;

[0095] Substituting into the formula, we get:

[0096] ;

[0097] Define the following parameters:

[0098] Longitudinal coupling coefficient:

[0099] ;

[0100] Longitudinal transmission coefficient:

[0101] ;

[0102] in, This is the ground state of a quantum bit;

[0103] Excited-state wave coefficient:

[0104] ;

[0105] Ground state fluctuation coefficient:

[0106] ;

[0107] ;

[0108] Lateral transmission coefficient:

[0109] ;

[0110] Step S2: Clarify the mutual inductance of the left arm of the SQUID loop Mutual sensation with the right arm And the Josephson junction energy of the left and right arms of the SQUID loop, adjusting the position of the magnetic flux line grounding, changing the numerical relationship of the mutual inductance of the left and right arms until the two mutual inductances meet the conditions. Eliminating relaxation caused by mutual inductance imbalance includes the following steps:

[0111] Step S21: Based on the double-junction Transmon architecture, define the mutual inductance between the flux lines and the left arm of the SQUID loop. Mutual sensation with the right arm The physical coupling location is determined, and a theoretical model incorporating non-equilibrium mutual inductance is constructed. Based on the circuit Lagrangian and Hamiltonian, the physical coupling location is clearly defined. , The logical connection with relaxation;

[0112] Step S22: Locate the grounding point adjustment area and set the grounding point to... and On the coupling path between them, the physical position of the grounding point is shifted step by step, and the position of the GND node is finely adjusted along the coupling direction of the magnetic flux line and the SQUID loop, with the initial position as the reference.

[0113] Step S23: Real-time monitoring and The numerical change was measured by synchronously collecting mutual inductance data of the two arms at different grounding point locations using testing equipment, until it reached... The equilibrium coupling condition.

[0114] The premise here is that the Josephson knot is symmetrical; next, we will consider the case where the knot is asymmetrical.

[0115] While junction asymmetry alone can suppress pure dephase, it exacerbates relaxation. However, the interaction between fluxline coupling imbalance and junction asymmetry suggests that, in certain circumstances, the relaxations induced by each can compensate for each other. We can utilize junction asymmetry to suppress pure dephase while simultaneously using coupling imbalance to compensate for the relaxation introduced by junction asymmetry. An asymmetric mutual inductance coupling structure exists between the fluxline bias line and the SQUID loop, and the imbalance of the mutual inductance is configured to cancel the longitudinal noise coupling caused by the SQUID Josephson junction asymmetry.

[0116] Step S3: Define the junction asymmetry parameter and mutual inductance imbalance, adjust the relationship between mutual inductance imbalance and junction asymmetry parameter, derive the relaxation compensation condition, so that the relaxation caused by mutual inductance imbalance and the relaxation caused by junction asymmetry cancel each other out, thereby improving the decoherence time of the superconducting quantum bit. The compensation relationship satisfies the following formula:

[0117] ;

[0118] ;

[0119] in, For mutual inductance imbalance, For the junction asymmetry parameter, For magnetic flux bias, For a unit magnetic flux quantum, For the Josephson knot energy of the left arm of the SQUID loop, For the Josephson knot energy of the right arm of the SQUID loop, It is Planck's constant. This refers to the amount of charge per unit.

[0120] Step S3 includes the following steps:

[0121] Step S31: Define the junction asymmetry parameters and mutual inductance imbalance. Based on the established circuit model including unbalanced mutual inductance and an asymmetric Josephson junction, and the double-junction Transmon architecture, clarify the circuit Lagrangian and Hamiltonian quantities, incorporate the coupling relationship between the symmetric and antisymmetric potential energies of the Josephson junction, and derive the relaxation rate formula, which is:

[0122] ;

[0123] ;

[0124] Under these conditions, the circuit Lagrange is:

[0125] ;

[0126] ;

[0127] ;

[0128] ;

[0129] ;

[0130] ;

[0131] ;

[0132] ;

[0133] in, For the transmission line in position The magnetic flux, Transmission line space eigenmode functions Position The derivative of For location, For the speed of wave propagation, For distributed inductance, Distributed capacitance;

[0134] Under these conditions, the Hamiltonian is:

[0135] ;

[0136] ;

[0137] It is Planck's constant. To reduce Planck's constant;

[0138] The relaxation rate is defined and calculated using the following formula:

[0139] ;

[0140] in, The relaxation rate, The product's vertical coupling coefficient. For the frequency of qubits, , To charge energy, For effective Josephson energy;

[0141] The calculation formula is:

[0142] ;

[0143] ;

[0144] ;

[0145] ;

[0146] in, This is the longitudinal transmission coefficient. , To reduce Planck's constant, For the impedance of the quantum bit, , For effective Josephson inductance, , It is a shunt capacitor.

[0147] Step S32: Determine the core condition for relaxation cancellation as the longitudinal coupling coefficient. The compensation relationship is derived, and the formula is:

[0148] ;

[0149] in, For Josephson's sake, For effective Josephson energy;

[0150] The formula is obtained as follows:

[0151] ;

[0152] ;

[0153] If we want to make the relaxation rate It is 0, because If it is not 0, then we must make =0, , Therefore, we can conclude that .

[0154] The formula for the longitudinal coupling coefficient is defined as follows:

[0155] ;

[0156] Require After rearranging, we get:

[0157] ;

[0158] Substituting all known conditions and formulas, we get:

[0159] ;

[0160] Step S33: Obtain The value, if Adjust the mutual inductance imbalance until the junction asymmetry parameters are equal. ,Will Substitute the values ​​into the compensation formula to calculate the target mutual inductance imbalance, and then adjust the grounding point to bring the mutual inductance imbalance to the calculated value.

[0161] Therefore, assuming a relaxation rate of 0, we obtain the relationship between the mutual inductance imbalance degree and the asymmetric parameters of the junction, where, let Pi WB is the unit magnetic flux quantum. For unit charge, except All others are constants.

[0162] The results are as follows Figure 3 As shown, in Under the conditions, The desired purpose can be achieved in time, such as Figure 3 As shown in (a); if made Under these conditions, we take a value to let The result at this time is as follows Figure 3 As shown in (b).

[0163] It is worth noting that all contents not described in detail in this invention are existing technologies and are well known to those skilled in the art.

[0164] Therefore, this invention proposes a decoherence time improvement method based on mutual inductance adjustment and junction asymmetry compensation. By constructing a theoretical model of unbalanced mutual inductance and asymmetric junctions, it breaks through the balance assumption of traditional designs and utilizes the interaction between mutual inductance imbalance and junction asymmetry to achieve relaxation cancellation, significantly improving the decoherence time and gate fidelity of qubits. This invention establishes a quantitative relationship between mutual inductance adjustment and junction asymmetry compensation, providing an active fault-tolerant technical means for the layout design of quantum chips, which is of great significance for promoting the practical application of superconducting quantum computing technology.

[0165] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for improving decoherence time based on mutual inductance regulation and junction asymmetry compensation, characterized in that, Includes the following steps: Step S1: Construct a theoretical model of a superconducting quantum bit that includes unbalanced mutual inductance and an asymmetric Josephson junction. The model is based on the double-junction Transmon quantum bit architecture and includes a SQUID loop, a magnetic flux bias line, and a shunt capacitor. Step S2: Determine the mutual inductance of the left arm of the SQUID loop in the superconducting quantum interference device. Mutual sensation with the right arm And the Josephson junction energy of the left and right arms of the SQUID loop, adjusting the position of the magnetic flux line grounding, changing the numerical relationship of the mutual inductance of the left and right arms until the two mutual inductances meet the conditions. Eliminate relaxation caused by mutual inductance imbalance; Step S3: Define the junction asymmetry parameter and mutual inductance imbalance, adjust the relationship between mutual inductance imbalance and junction asymmetry parameter, derive the relaxation compensation condition, so that the relaxation caused by mutual inductance imbalance and the relaxation caused by junction asymmetry cancel each other out, thereby improving the decoherence time of the superconducting quantum bit. The compensation relationship satisfies the following formula: ； ； in, For mutual inductance imbalance, For the junction asymmetry parameter, For magnetic flux bias, For a unit magnetic flux quantum, For the Josephson knot energy of the left arm of the SQUID loop, For the Josephson knot energy of the right arm of the SQUID loop, It is Planck's constant. For unit charge, and These are the mutual inductions of the left and right arms, respectively. and This is the energy of the Josephson knot.

2. The decoherence time enhancement method based on mutual inductance adjustment and junction asymmetry compensation according to claim 1, characterized in that: Step S1 includes the following steps: Step S11: Establish the circuit Lagrangian quantities including unbalanced mutual inductance and asymmetric Josephson junctions. Derive the system Hamiltonian based on the Lagrangian quantities. The formula is: ； ； ； ； in, For circuit Lagrange quantities, For the Josephson potential operator under interaction, The magnetic flux generated by the current in the branch at node 1. The magnetic flux generated by the current in the branch at node 2. For the flux of the left arm of the SQUID loop, For the flux of the right arm of the SQUID loop, Angular frequency, For distributed inductance, For the system Hamiltonian, For capacitor The charge on it, It is a shunt capacitor. For annihilation operators, To reduce Planck's constant; Step S12: Decompose the Josephson junction potential energy into symmetric and antisymmetric potential energy, corresponding to the energy contributions from the symmetry and asymmetry of the junction parameters, respectively. The formula is as follows: ； ； ； in, For the Josephson potential operator under interaction, For the flux operator passing through the left arm of the SQUID ring under the interaction, For the flux operator passing through the right arm of the SQUID ring under the interaction, For symmetrical potential energy, To counterbalance potential energy, For the sum of Josephson's energies, For the core node magnetic flux, The sum of magnetic flux. This is the difference in magnetic flux; Step S13: Decompose the sum and difference of magnetic flux into classical and quantum components, using the following formula: ； ； in, This is the classical component of the sum of the magnetic flux of the two arms of the Squid ring. The classical component of the difference in magnetic flux passing through the SQUID ring. Let be the quantum component of the sum of the magnetic flux of the two arms of the SQUID ring. The quantum component is the difference in magnetic flux passing through the SQUID ring.

3. The decoherence time enhancement method based on mutual inductance adjustment and junction asymmetry compensation according to claim 1, characterized in that: Step S2 includes the following steps: Step S21: Based on the double-junction Transmon architecture, define the mutual inductance between the flux lines and the left arm of the SQUID loop. Mutual sensation with the right arm The physical coupling location is determined, and a theoretical model incorporating non-equilibrium mutual inductance is constructed. Based on the circuit Lagrangian and Hamiltonian, the physical coupling location is clearly defined. , The logical connection with relaxation; Step S22: Locate the grounding point adjustment area and set the grounding point to... and On the coupling path between them, the physical position of the grounding point is shifted step by step, and the position of the GND node is finely adjusted along the coupling direction of the magnetic flux line and the SQUID loop, with the initial position as the reference. Step S23: Real-time monitoring and The numerical change was measured by synchronously collecting mutual inductance data of the two arms at different grounding point locations using testing equipment, until it reached... The equilibrium coupling condition.

4. The decoherence time enhancement method based on mutual inductance adjustment and junction asymmetry compensation according to claim 1, characterized in that: Step S3 includes the following steps: Step S31: Define the junction asymmetry parameters and mutual inductance imbalance. Based on the established circuit model including unbalanced mutual inductance and an asymmetric Josephson junction, and the double-junction Transmon architecture, clarify the circuit Lagrangian and Hamiltonian quantities, incorporate the coupling relationship between the symmetric and antisymmetric potential energies of the Josephson junction, and derive the relaxation rate formula, which is: ； ； ； in, The relaxation rate, The product's vertical coupling coefficient. The frequency of a quantum bit; Step S32: Determine the core condition for relaxation cancellation as the longitudinal coupling coefficient. The compensation relationship is derived, and the formula is: ； in, For Josephson's sake, For effective Josephson energy; Step S33: Obtain The value, if Adjust the mutual inductance imbalance until the junction asymmetry parameters are equal. ,Will Substitute the values ​​into the compensation formula to calculate the target mutual inductance imbalance, and then adjust the grounding point to bring the mutual inductance imbalance to the calculated value.

5. The decoherence time enhancement method based on mutual inductance adjustment and junction asymmetry compensation according to claim 4, characterized in that: In step S31, The calculation formula is: ； ； ； ； in, This is the longitudinal transmission coefficient. For the impedance of the quantum bit, For effective Josephson inductance, It is a shunt capacitor.

6. The decoherence time enhancement method based on mutual inductance adjustment and junction asymmetry compensation according to claim 4, characterized in that: In step S32, the formula for the longitudinal coupling coefficient is defined as follows: ； in, For transmission line impedance, For the junction asymmetry parameter, For the sum of mutual inductance, For Josephson's sake, For effective Josephson energy.

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