Method for co-preparing large and small Josephson junctions based on Manhattan method and application of large and small Josephson junctions

Abstract

The invention discloses a Josephson junction preparation method based on a Manhattan method and application thereof, and the method employs a multi-angle evaporation technology to achieve the synchronous preparation of a small-size Josephson junction and a large-size Josephson junction on a same wafer. The key technical problems that the large Josephson junction and the small Josephson junction cannot be prepared at the same time, and the large Josephson junction is prone to short circuit, low in yield and poor in uniformity in the traditional process are solved. By optimizing the evaporation mode, the Josephson junction structure design and the process parameters, the preparation processes of the large Josephson junction and the small Josephson junction are coordinated and unified, the junction is easy to form, the yield is high, the large Josephson junction can form a high-uniformity Josephson junction chain, and the preparation process is simple. The prepared Josephson junction can be applied to a Fluxium and adjustable resonator-superconducting quantum bit coupling system, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to superconducting quantum computing, specifically to a method for fabricating both large and small Josephson junctions based on the Manhattan method, and to a Fluxonium device and a tunable resonator-superconducting quantum bit coupling system fabricated based on this method. Background Technology

[0002] Josephson junctions are the core components of superconducting qubits (qubits) and are widely used in superconducting quantum processors, tunable resonators, and other superconducting quantum systems. Based on mainstream experimental equipment for fabricating Josephson junctions, the minimum precision for laser direct writing to create junction patterns is typically around 1 μm, which can be used for photolithography to fabricate larger Josephson junctions. However, the scale of Josephson junctions, which provide anharmonicity in superconducting qubits, is typically on the order of hundreds of nanometers, requiring electron beam lithography for fabrication. Therefore, with a Josephson junction area of ​​1 μm × 1 μm = 1 μm... 2 Josephson junctions can be classified into two categories based on their size: small-sized Josephson junctions (area < 1 μm). 2 ) and large-size Josephson junctions (area ≥ 1 μm) 2 ).

[0003] Currently, the mainstream fabrication processes for Josephson junctions are the Dolan bridge method and the Manhattan method, but both have certain drawbacks. The Dolan bridge method uses a suspended photoresist bridge structure, which is highly dependent on the angle accuracy of dual-angle evaporation. Moreover, the photoresist bridge is mechanically unstable and prone to collapse during fabrication, resulting in a low yield. Although the traditional Manhattan method eliminates the suspended structure and has better mechanical stability and critical current uniformity, it is limited by the evaporation angle and cannot simultaneously fabricate small-size and large-size Josephson junctions on the same wafer in the same way. Furthermore, short circuits are prone to occur during junction fabrication, and the step-by-step fabrication of small and large junctions can lead to problems such as process compatibility and cumulative process deviations, further degrading device performance.

[0004] In terms of devices, Fluxonium and tunable resonator-superconducting quantum bit coupling systems place stringent demands on the performance of Josephson junctions: Fluxonium requires both a small junction to provide nonlinear inductance and a large junction chain to form a superinductance; tunable resonators require SQUIDs with large Josephson structures to achieve tunable resonant frequencies, while superconducting quantum bits require SQUIDs with small Josephson structures to achieve tunable transition frequencies. Existing fabrication processes cannot simultaneously meet the fabrication requirements of both large and small Josephson junctions, which limits the integration density, performance stability, tunability, and mass production capabilities of superconducting quantum devices. Summary of the Invention

[0005] The purpose of this invention is to provide a method for co-fabrication of small and large Josephson junctions based on the Manhattan method, as well as a Fluxonium device and a tunable resonator-superconducting quantum bit coupling system fabricated based on this method, so as to solve the technical problems in the existing Josephson junction fabrication that cannot simultaneously achieve small Josephson junctions and large Josephson junctions, resulting in low yield and poor uniformity.

[0006] The technical solution to achieve the objective of this invention is: a method for co-fabrication of small and large Josephson junctions based on the Manhattan method, wherein, based on the Manhattan method, a multi-angle evaporation process is used to simultaneously fabricate small-size and large-size Josephson junctions on the same wafer, wherein:

[0007] The small-sized Josephson junction has a Manhattan structure and an area of ​​less than 1 μm. 2 ;

[0008] The large-size Josephson junction is a Manhattan structure with an area greater than 1 μm. 2 ;

[0009] The multi-angle evaporation process includes bi-angle evaporation or quadri-angle evaporation;

[0010] Both Josephson junctions of different sizes are aluminum-based Josephson junctions, and the evaporation direction and angle of the larger Josephson junction are consistent with those of the smaller Josephson junction.

[0011] Furthermore, the evaporation angle in the multi-angle evaporation process is 30° to 45°.

[0012] Furthermore, the junction area of ​​the small-sized Josephson junction is from 140 nm × 140 nm to 500 nm × 500 nm; the junction area of ​​the large-sized Josephson junction is from 1500 nm × 1500 nm to 3300 nm × 3300 nm.

[0013] Furthermore, the large-size Josephson junctions can be connected in series to form a chain; the smallest structural unit of the chain consists of four large-size Josephson junctions connected in series in a 2 × 2 configuration; the chain and the small-size Josephson junctions are prepared by multi-angle evaporation simultaneously.

[0014] Furthermore, the dual-angle evaporation process includes the following steps:

[0015] (1) First vapor deposition: The first layer of aluminum film is vapor deposited at an oblique angle along the first direction;

[0016] (2) In-situ oxidation: Oxidation in a pure oxygen environment to form an aluminum oxide barrier layer;

[0017] (3) Second vapor deposition: A second aluminum film is deposited at an oblique angle along a second direction perpendicular to the first direction.

[0018] Furthermore, the four-angle evaporation process, based on the two-angle evaporation process, adds the following steps:

[0019] After step (1), a third aluminum film is deposited in the opposite direction of the first direction; after step (3), a fourth aluminum film is deposited in the opposite direction of the second direction; the thickness and deposition rate of the third aluminum film are consistent with those of the first layer; the thickness and deposition rate of the fourth aluminum film are consistent with those of the second layer.

[0020] Furthermore, the evaporation angle is always 45°.

[0021] Furthermore, it also includes the following complete process integrated with multi-angle evaporation technology:

[0022] (1) Coating: Depositing a tantalum superconducting thin film on a sapphire substrate;

[0023] (2) Photolithography and etching: Laser direct writing photolithography and RIE etching processes are used to form the circuit pattern except for the junction region;

[0024] (3) Sample cleaning: including cleaning of organic reagents, cleaning of piranha solution and cleaning with deionized water;

[0025] (4) Electron beam exposure: forming a junction pattern that simultaneously contains small-sized Josephson junctions and large-sized Josephson junctions or junction chains;

[0026] (5) Multi-angle evaporation and oxidation: Select a dual-angle or quadri-angle evaporation process according to the design to complete the aluminum film evaporation and in-situ oxidation in sequence;

[0027] (6) Subsequent processing: including dicing, adhesive removal and organic reagent cleaning to complete device fabrication.

[0028] A Fluxonium device, comprising:

[0029] The small-sized Josephson junction prepared by the method described above is used to provide nonlinear inductance;

[0030] Large-size Josephson junctions prepared using the method described above are used to construct superinductors;

[0031] And read out the resonator and capacitor.

[0032] A tunable resonator-superconducting quantum bit coupling system, comprising:

[0033] The SQUID fabricated using the method described herein comprises a resonator frequency tuning unit composed of a large-size Josephson structure and a superconducting quantum bit junction region composed of a small-size Josephson structure.

[0034] In addition, there is a tunable resonator body, a tunable superconducting quantum bit structure, and a readout resonator.

[0035] Compared with existing technologies, the significant advantages of this invention are: 1) It solves the technical bottleneck that traditional processes cannot simultaneously fabricate small Josephson junctions and large Josephson junctions on the same wafer, significantly shortening the fabrication cycle and improving integration; 2) It improves yield and structural integrity, has strong compatibility, and can be directly applied to the fabrication of superconducting quantum devices such as Fluxonium devices and tunable resonator-superconducting quantum bit coupling systems; 3) It has high process controllability, and the junction area and resistance can be precisely controlled by adjusting the evaporation angle and pattern parameters to meet the design requirements of different quantum devices. Attached Figure Description

[0036] Figure 1 A schematic diagram of an aluminum-based Josephson junction;

[0037] Figure 2 A schematic diagram of Josephson junction preparation by oblique angle evaporation, showing the main process flow and junction formation process;

[0038] Figure 3 Schematic diagrams for preparing Josephson junctions by (a) two-angle and (b) four-angle evaporation;

[0039] Figure 4 Design the layout and junction graphics for Fluxonium;

[0040] Figure 5 Design layout and SQUID pattern for tunable resonator-superconducting quantum bit coupling system;

[0041] Figure 6 The resistance values ​​of the small Josephson junction and the linear fitting curve are shown.

[0042] Figure 7 The resistance values ​​of the large Josephson junction and the linear fitting curve;

[0043] Figure 8 For Fluxonium f 01 With changes in applied voltage;

[0044] Figure 9 The resonant frequency of the adjustable resonator varies with the applied voltage;

[0045] Figure 10 The change in the transition frequency of a superconducting quantum bit with the applied voltage. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0047] This invention provides an improved Manhattan method fabrication process. Based on the traditional Manhattan method, the evaporation process is optimized to multi-angle evaporation (dual-angle or quad-angle). Small Josephson junctions and large Josephson junctions are simultaneously fabricated on the same wafer under the same evaporation angle and direction, improving the structural integrity, resistance uniformity, and quantum performance of the devices. This also saves process steps and achieves strong process compatibility. Specific technical details are as follows:

[0048] (I) Josephson knot structural design

[0049] Small-sized Josephson junctions employ a Manhattan structure, and their junction area is typically less than 1 μm². 2 (For example, 140 nm × 140 nm to 500 nm × 500 nm). Large-size Josephson junctions employ a Manhattan structure, with a junction area greater than or equal to 1 μm. 2 (e.g., 1500 nm × 1500 nm to 3300 nm × 3300 nm). Both Josephson junctions of different sizes are aluminum (101)-alumina (102)-aluminum (103) structures, and the evaporation direction and angle of the large-size Josephson junction are consistent with those of the small-size Josephson junction, thereby avoiding process deviations caused by step-by-step preparation.

[0050] Large-size Josephson junctions can be further connected in series to form a Josephson junction chain. The smallest structural unit of this chain consists of four large-size Josephson junctions arranged in a 2 × 2 series configuration, and a predetermined pattern is formed in one step using electron beam lithography. When using a four-angle evaporation process, if the width of the square structure in the chain pattern is defined as D and the thickness of the photoresist is h, then under the condition that D = 2h, the junction area of ​​the four large-size Josephson junctions in the smallest structural unit is equal to D. 2 This allows for the preparation of highly uniform bond chains.

[0051] (II) Multi-angle evaporation process

[0052] An oblique evaporation method is used, leveraging the height difference between the sidewalls and bottom of the photoresist pattern to ensure that the evaporated aluminum film deposits only on one side of the developed pattern, rather than covering the entire pattern. This allows for controlled fabrication of Josephson junctions by controlling the evaporation direction and angle. Specifically, this can be divided into the following two processes:

[0053] (1) Double-angle evaporation

[0054] Includes the following steps:

[0055] First vapor deposition: Deposit the first layer of aluminum film at a 45° angle along the first direction (e.g., transverse direction);

[0056] In-situ oxidation: Controlled oxidation is carried out in a pure oxygen environment to form an aluminum oxide barrier layer;

[0057] Second vapor deposition: A second aluminum film is vapor deposited at a 45° angle along a second direction (e.g., longitudinal direction) perpendicular to the first direction.

[0058] (2) Four-angle evaporation

[0059] Based on dual-angle evaporation, two reverse evaporation steps are added:

[0060] Before the first vapor deposition, a third aluminum film is vapor deposited in the opposite direction to the first direction;

[0061] After the second vapor deposition, a fourth aluminum film is vapor deposited in the opposite direction of the second direction;

[0062] The thickness and evaporation rate of the third and fourth aluminum films are consistent with those of the first and second layers, respectively, thereby further enhancing the symmetry and uniformity of the junction.

[0063] During evaporation, the baffle can be briefly closed to switch the evaporation angle, and then the baffle can be reopened to continue evaporation.

[0064] (III) Complete process flow

[0065] This invention's fabrication process simultaneously performs electron beam exposure, evaporation, oxidation, and stripping of both small and large Josephson junctions (and their chains), eliminating the need for separate steps and reducing process steps while avoiding the impact of batch variations and inter-wafer process fluctuations. It can be seamlessly integrated with conventional superconducting device fabrication processes, specifically including the following steps:

[0066] (1) Coating: Deposit superconducting thin films (such as 200 nm tantalum films) on substrates such as sapphire.

[0067] (2) Photolithography and etching: Laser direct writing photolithography and reactive ion etching are used to form the circuit pattern except for the junction region;

[0068] (3) Sample cleaning: Organic solvent cleaning, piranha solution cleaning and deionized water cleaning are performed in sequence to ensure surface cleanliness;

[0069] (4) Electron beam exposure: Using double-layer photoresist (such as MMA / PMMA) and conductive adhesive, a pattern containing small-sized Josephson junctions, large-sized Josephson junctions or junction chains is formed in one step by electron beam exposure;

[0070] (5) Multi-angle evaporation and oxidation: Select a dual-angle or quadri-angle evaporation process according to the design to complete the aluminum film evaporation and in-situ oxidation in sequence;

[0071] (6) Subsequent processing: including spin coating of protective adhesive, dicing, adhesive removal and final cleaning, to complete device fabrication.

[0072] To verify the effectiveness of the present invention, the following experimental design was conducted.

[0073] (iv) Expansion and Application

[0074] The present invention also proposes a Fluxonium device, comprising:

[0075] The small-sized Josephson junction prepared by the method described above is used to provide nonlinear inductance;

[0076] Large-size Josephson junctions prepared using the method described above are used to construct superinductors;

[0077] And read out the resonator and capacitor.

[0078] A tunable resonator-superconducting quantum bit coupling system, comprising:

[0079] The SQUID fabricated using the method described herein comprises a resonator frequency tuning unit composed of a large-size Josephson structure and a superconducting quantum bit junction region composed of a small-size Josephson structure.

[0080] In addition, there is a tunable resonator body, a tunable superconducting quantum bit structure, and a readout resonator.

[0081] To verify the effectiveness of the present invention, the following experimental design was conducted.

[0082] Example 1: Resistance Characterization of Big and Small Josephson Junctions

[0083] For the fabrication and measurement of Josephson junctions of different sizes, this embodiment fabricates small-sized Josephson junctions (side length 140 nm ~ 500 nm) and large-sized Josephson junctions (side length 1500 nm ~ 3300 nm) on the same wafer, with four samples in each group. Following the specific implementation method, the layout is set as a junction array consisting of a small junction (501) and a large junction (502). During fabrication, a 200 nm tantalum film is used as the electrode, and Josephson junctions are fabricated through four-angle evaporation (303, 304). After fabrication, eight chip samples are tested separately. A probe station is used to perform four-terminal resistance testing, and the junction resistance is measured multiple times and the average value is taken. For a material with resistivity ρ, cross-sectional area S, and length L, the resistance R = ρL / S. Since the parameter L in the Josephson junction fabricated in the above manner is generally 2 nm, the measured resistance data is linearly fitted using R∝(1 / S), and the results are as follows. Figure 6 , Figure 7 As shown.

[0084] Measurement results show that the average resistance of the small Josephson junction is 2.819 kΩ ~ 82.871 kΩ, and the average resistance of the large Josephson junction is 0.185 kΩ ~ 2.144 kΩ. The resistance of the Josephson junction is inversely proportional to the junction area, and the resistance decreases significantly with increasing junction side length. Regarding uniformity, calculations of the coefficients of variation for the large and small junctions show that the coefficient of variation for the large junction is higher than that for the small junction. This indicates a significant decrease in uniformity for the large junction, while the small junction is generally superior to the large junction. The smaller junction exhibits more precise manufacturing process control, leading to a larger deviation in the fitted curve of the large junction.

[0085] Example 2: Josephson Linkage Uniformity Test

[0086] For the preparation and measurement of large Josephson junctions, this embodiment prepared junctions of 20, 40, 60, 80, and 100 large Josephson structures on the same wafer, with 5 samples in each group, according to... Figure 4 The illustrated junction chain (402) was fabricated. Four-terminal resistance was tested using a probe station, and the junction resistance was measured multiple times and averaged. The results showed that the total resistance of the large Josephson junction chain increased approximately linearly with the number of junctions, with a coefficient of variation ≤ 5% for 40-80 junctions, and the average resistance fluctuation range of a single unit was less than 13%. The average resistance of a single structural unit was stable at 3.220-3.740 kΩ, with a fluctuation range of less than 13%, which is superior to the traditional Manhattan method.

[0087] Example 3: Fluxonium Device Fabrication and Measurement

[0088] This embodiment fabricates a Fluxonium device, in which a small-sized Josephson junction serves as a nonlinear inductor; a large-sized Josephson junction chain constitutes a superinductor; and a readout resonator and capacitor are combined to complete device integration. The specific process is as follows:

[0089] 1. Pretreatment and coating: A sapphire substrate (201) with high lattice matching degree with tantalum was selected, and a 200 nm tantalum film was grown at high temperature by magnetron sputtering.

[0090] 2. Photolithography and etching: Spin-coating positive photoresist S1813, and using laser direct writing technology to transfer the pre-set circuit pattern (except for the junction region) to the tantalum film surface; developing with MF319 developer to remove excess photoresist; performing reactive ion etching to obtain the tantalum film circuit structure.

[0091] 3. Sample cleaning: The sample was ultrasonically cleaned sequentially with N-methylpyrrolidone (NMP), acetone, and isopropanol to remove surface organic matter; a piranha solution with a volume ratio of 7:3 (H2SO4-H2O2) was prepared and the sample was cleaned at 115℃ for 20 min to completely remove residual photoresist; the sample was ultrasonically cleaned three times with deionized water for 5 min each time to remove any residue from the piranha solution.

[0092] 4. Electron beam exposure: MMA photoresist (202) and PMMA A7 photoresist (203) are spin-coated sequentially to form a double-layer photoresist structure, and a layer of conductive adhesive (204) is spin-coated on the surface; the junction pattern is drawn using electron beam exposure (EBL) technology, including the pattern of the small Josephson junction and the unit pattern of the large Josephson junction chain; the conductive adhesive is removed by rinsing with deionized water for 1 min, and after drying with a nitrogen gun, it is developed with a MIBK / IPA = 1:3 mixed solution for 40 s and fixed with isopropanol for 20 s to obtain the junction photoresist pattern.

[0093] 5. Dual-angle evaporation and oxidation: Using a PLASSYS MEB550SL3 system, argon ion milling at 300 V and 21 mA was first performed in the sample injection chamber along the evaporation direction for 1 min 40 s in each direction to remove the oxide layer on the tantalum film surface; then, dual-angle evaporation was performed:

[0094] (1) First evaporation: A 40 nm aluminum film (205) is deposited at a rate of 0.5 nm / s along a transverse angle of 45° (301).

[0095] (2) In-situ oxidation: The sample is sent into the oxidation chamber and oxidized in pure oxygen environment for 5 min to form an aluminum oxide barrier layer (206).

[0096] (3) Second evaporation: 100 nm aluminum film (205) is deposited at a rate of 0.5 nm / s along the longitudinal direction at a 45° angle (302).

[0097] (4) Protective oxidation: Send the sample into the injection chamber and oxidize it for 10 min in a pure oxygen environment.

[0098] 6. Post-processing: Spin-coat a protective adhesive to prevent damage to the junction area during dicing; dic the wafer to obtain individual device samples; heat in an 80℃ N-methylpyrrolidone water bath for 4 h to remove the photoresist and protective adhesive, achieving stripping; clean with acetone and isopropanol in sequence, and dry with a nitrogen gun to complete sample preparation.

[0099] 7. The device was placed in a refrigerator and measured and characterized at an environment of 20 mK;

[0100] Measurement results show that the Fluxonium device fabricated based on this method, according to... Figure 4 The design layout shown and the above-described process flow are used for fabrication, including a small Josephson junction (401) providing inductive nonlinearity, a large Josephson junction chain (402) constituting superinductance, a readout resonator (403), and a capacitor, with a transition frequency f. 01 Test results are as follows Figure 8 The darkest line at the top indicates that Fluxonium prepared in this manner exhibits flux periodicity, f 01 The resonant frequency range is 5.0 ~ 5.4 GHz.

[0101] Example 4: Fabrication and Measurement of a Tunable Resonator-Superconducting Quantum Bit Coupled System

[0102] This embodiment fabricates a tunable resonator-superconducting qubit coupling system based on a Josephson junction SQUID. A large-size Josephson junction SQUID is used to adjust the resonator frequency; a small-size Josephson junction SQUID forms the superconducting qubit junction region. The specific process is as follows:

[0103] 1. Pretreatment and coating: A sapphire substrate (201) with high lattice matching degree with tantalum was selected, and a 200 nm tantalum film was grown at high temperature by magnetron sputtering.

[0104] 2. Photolithography and etching: Spin-coating positive photoresist S1813, and using laser direct writing technology to transfer the pre-set circuit pattern (except for the junction region) to the tantalum film surface; developing with MF319 developer to remove excess photoresist; performing reactive ion etching to obtain the tantalum film circuit structure.

[0105] 3. Sample cleaning: The sample was ultrasonically cleaned sequentially with N-methylpyrrolidone (NMP), acetone, and isopropanol to remove surface organic matter; a piranha solution with a volume ratio of 7:3 (H2SO4-H2O2) was prepared and the sample was cleaned at 115℃ for 20 min to completely remove residual photoresist; the sample was ultrasonically cleaned three times with deionized water for 5 min each time to remove any residue from the piranha solution.

[0106] 4. Electron beam exposure: MMA photoresist (202) and PMMA A7 photoresist (203) are spin-coated sequentially to form a double-layer photoresist structure, and a layer of conductive adhesive (204) is spin-coated on the surface; the junction pattern is drawn using electron beam exposure (EBL) technology, including the small Josephson junction pattern in the tunable superconducting qubit and the large Josephson junction pattern of the tunable resonator; the conductive adhesive is removed by rinsing with deionized water for 1 min, and after drying with a nitrogen gun, the junction pattern is developed with a MIBK / IPA = 1:3 mixed solution for 40 s and fixed with isopropanol for 20 s to obtain the junction photoresist pattern.

[0107] 5. Four-angle evaporation and oxidation: Using a PLASSYS MEB550SL3 system, argon ion milling at 300 V and 21 mA was first performed along the evaporation direction in the sample injection chamber for 1 min 40 s in each direction to remove the oxide layer on the tantalum film surface. Then, four-angle evaporation was performed.

[0108] (1) First vapor deposition: Along the transverse 45° (303), two layers of 40 nm aluminum film (205) are deposited sequentially at a rate of 0.5 nm / s, with the two vapor deposition directions being opposite;

[0109] (2) In-situ oxidation: The sample is sent into the oxidation chamber and oxidized in pure oxygen environment for 5 min to form an aluminum oxide barrier layer (206).

[0110] (3) Second evaporation: Along the longitudinal direction at a 45° angle (303), two 100 nm aluminum films (205) are deposited sequentially at a rate of 0.5 nm / s, with the two evaporation directions being opposite;

[0111] (4) Protective oxidation: Send the sample into the injection chamber and oxidize it for 10 min in a pure oxygen environment.

[0112] 6. Post-processing: Spin-coat a protective adhesive to prevent damage to the junction area during dicing; dic the wafer to obtain individual device samples; heat in an 80℃ N-methylpyrrolidone water bath for 4 h to remove the photoresist and protective adhesive, achieving stripping; clean with acetone and isopropanol in sequence, and dry with a nitrogen gun to complete sample preparation.

[0113] 7. The device was placed in a refrigerator and measured and characterized at an environment of 20 mK;

[0114] Measurement results show that the tunable resonator-superconducting quantum bit coupling system prepared based on this method, according to... Figure 5 The design layout shown and the above process flow were used for fabrication. The resonant frequency tuning results of the SQUID composed of large Josephson junctions (501) are as follows. Figure 9 As shown, the resonant frequency of this resonator exhibits a periodic variation with the tuning voltage, and the adjustable resonant frequency range reaches 40 MHz, covering a frequency range of approximately 4.38–4.42 GHz. The tuning results of the superconducting quantum bit transition frequency of the SQUID composed of a small Josephson junction (502) are as follows. Figure 10 As shown, the transition frequency of the superconducting quantum bit exhibits a periodic change with the tuning voltage, with a tuning range of approximately 50 MHz and a frequency coverage of approximately 6.80 ~ 6.85 GHz.

[0115] The above examples demonstrate that the method of the present invention can stably achieve the simultaneous fabrication of large and small Josephson junctions, and the fabricated junctions and devices exhibit excellent performance.

[0116] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0117] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for co-preparing large and small Josephson junctions based on the Manhattan method, characterized in that, Based on the Manhattan method, a multi-angle evaporation process is used to simultaneously fabricate small-size Josephson junctions and large-size Josephson junctions on the same wafer, wherein: The small-sized Josephson junction has a Manhattan structure and an area of ​​less than 1 μm. 2 ; The large-size Josephson junction is a Manhattan structure with an area greater than 1 μm. 2 ; The multi-angle evaporation process includes bi-angle evaporation or quadri-angle evaporation; Both Josephson junctions of different sizes are aluminum-based Josephson junctions, and the evaporation direction and angle of the larger Josephson junction are consistent with those of the smaller Josephson junction.

2. The method for co-preparing large and small Josephson junctions based on the Manhattan method according to claim 1, characterized in that, The vapor deposition angle in the multi-angle evaporation process is 30° to 45°.

3. The method for co-preparing large and small Josephson junctions based on the Manhattan method according to claim 1, characterized in that, The small-sized Josephson junction has a junction area of ​​140 nm × 140 nm to 500 nm × 500 nm; the large-sized Josephson junction has a junction area of ​​1500 nm × 1500 nm to 3300 nm × 3300 nm.

4. The method for preparing large and small Josephson junctions based on the Manhattan method according to claim 1, characterized in that, The large-size Josephson junctions can be connected in series to form a chain; the smallest structural unit of the chain consists of four large-size Josephson junctions connected in series in a 2 × 2 configuration; the chain and the small-size Josephson junctions are prepared by multi-angle evaporation simultaneously.

5. The method for co-preparing large and small Josephson junctions based on the Manhattan method according to claim 1, characterized in that, The dual-angle evaporation process includes the following steps: (1) First vapor deposition: The first layer of aluminum film is vapor deposited at an oblique angle along the first direction; (2) In-situ oxidation: Oxidation in a pure oxygen environment to form an aluminum oxide barrier layer; (3) Second vapor deposition: A second aluminum film is deposited at an oblique angle along a second direction perpendicular to the first direction.

6. The method for co-preparing large and small Josephson junctions based on the Manhattan method according to claim 5, characterized in that, The four-angle evaporation process adds the following steps to the two-angle evaporation process: After step (1), a third aluminum film is deposited in the opposite direction of the first direction; after step (3), a fourth aluminum film is deposited in the opposite direction of the second direction; the thickness and deposition rate of the third aluminum film are consistent with those of the first layer; the thickness and deposition rate of the fourth aluminum film are consistent with those of the second layer.

7. The method for preparing large and small Josephson junctions based on the Manhattan method according to claim 5 or 6, characterized in that, The evaporation angle is always 45°.

8. The method for preparing large and small Josephson junctions based on the Manhattan method according to any one of claims 1 to 7, characterized in that, It also includes the following complete process integrated with multi-angle evaporation technology: (1) Coating: Depositing a tantalum superconducting thin film on a sapphire substrate; (2) Photolithography and etching: Laser direct writing photolithography and RIE etching processes are used to form the circuit pattern except for the junction region; (3) Sample cleaning: including cleaning of organic reagents, cleaning of piranha solution and cleaning with deionized water; (4) Electron beam exposure: forming a junction pattern that simultaneously contains small-sized Josephson junctions and large-sized Josephson junctions or junction chains; (5) Multi-angle evaporation and oxidation: Select a dual-angle or quadri-angle evaporation process according to the design to complete the aluminum film evaporation and in-situ oxidation in sequence; (6) Subsequent processing: including dicing, adhesive removal and organic reagent cleaning to complete device fabrication.

9. A Fluxonium device, characterized in that, include: A small-sized Josephson junction prepared by the method of any one of claims 1 to 8 is used to provide nonlinear inductance; Large-sized Josephson junctions prepared by the method of any one of claims 1 to 8 are used to construct superinductors; And read out the resonator and capacitor.

10. A tunable resonator-superconducting quantum bit coupling system, characterized in that, include: A Josephson structure SQUID prepared by any one of claims 1 to 8, the SQUID comprising a resonator frequency tuning unit composed of a large-size Josephson structure and a superconducting quantum bit junction region composed of a small-size Josephson structure; In addition, there is a tunable resonator body, a tunable superconducting quantum bit structure, and a readout resonator.

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