Josephson junction array microwave coupling cavity

Abstract

The invention provides a Josephson junction array microwave coupling cavity. The Josephson junction array microwave coupling cavity comprises a reflecting spherical surface, a reflecting plane, a matched circuit board and a Josephson junction array chip, a Josephson junction array circuit is arranged on the Josephson junction array chip; a rectangular waveguide tube is arranged above the reflecting spherical surface; the rectangular waveguide tube is connected with the central position of the reflecting spherical surface so as to feed in microwaves; the matched circuit board is arranged on the reflecting plane and is connected with the Josephson junction array chip; a first through hole is formed in the position, corresponding to the center of the reflecting spherical surface, of the matched circuit board, so that a Josephson junction array chip can be placed in the first through hole; the Josephson junction array chip is installed on the reflection plane, and the part, provided with the Josephson junction array circuit, of the Josephson junction array chip and the reflection plane are installed in a separated mode. The influence of a reflection plane on a magnetic field in a near space range can be eliminated, and the critical current of the Josephson junction array is stabilized.

Description

Technical Field

[0001] The present invention relates to the technical field of Josephson junction array microwave coupling, in particular to a Josephson junction array microwave coupling cavity. Background Art

[0002] When a Josephson junction array (a circuit consisting of several Josephson junctions connected in series) is coupled to microwaves, under appropriate conditions, its DC current-voltage characteristic curve exhibits a voltage plateau, meaning that the voltage remains constant within a certain current range. This characteristic can be exploited to generate a standard DC voltage within a certain range. Several main methods for coupling Josephson junction arrays to microwaves include: a) direct current coupling via transmission lines; b) waveguide antenna coupling; and c) Fabry-Perot cavity coupling.

[0003] Each microwave coupling method is applicable to different Josephson junction array schemes. Among them, a) transmission line direct current coupling and b) waveguide antenna coupling are mainly applicable to niobium-based low-temperature superconducting Josephson junction arrays. The two are used for microwave coupling at frequencies of around 20 GHz and 70 GHz, respectively. Both belong to traveling wave coupling. The main advantage is that the microwave coupling has good uniformity and can be used for large-scale junction arrays with more than tens of thousands of junctions. The reason why they are applicable to niobium-based low-temperature superconducting Josephson junctions is that these two microwave driving schemes require the junctions to be connected in series in the central conductor of the coplanar waveguide to form an array, while the niobium-based low-temperature superconducting Josephson junction can be made at any spatial position on the chip and can adapt to the geometric structure of the coplanar waveguide.

[0004] c) Fabry-Perot cavity coupling is primarily applicable to high-temperature superconducting bi-crystal Josephson junction arrays, commonly used for microwave coupling at frequencies around 70 GHz. Within the field of high-temperature superconductors, bi-crystal junctions are a relatively mature fabrication technology and offer relatively consistent junction array parameters. However, this technology requires the spatial arrangement of the junctions to lie along the grain boundaries of the bi-crystal substrate, making it impractical to connect them in series within a coplanar waveguide transmission line. This precludes the use of a) direct current coupling through the transmission line or b) waveguide antenna coupling.

[0005] The existing c) Fabry-Perot cavity coupling method is to place the Josephson junction array chip in the "Fabry-Perot cavity". The installation method is to directly mount the Josephson junction array chip on the reflection plane of the Fabry-Perot cavity using low-temperature adhesive. The disadvantage of this method is that the distance between the reflection plane and the junction array is close, and the presence of the reflection plane will affect the magnetic field in the adjacent space, interfering with the critical current of the Josephson junction array.

[0006] In view of this, a Josephson junction array microwave coupled cavity is needed. Summary of the Invention

[0007] To address the problem in existing technologies where the presence of a reflective plane affects the magnetic field in the adjacent space, interfering with the critical current of a Josephson junction array, the present invention provides a Josephson junction array microwave coupled cavity that eliminates the effect of the reflective plane on the magnetic field in the adjacent space and stabilizes the critical current of the Josephson junction array. The specific technical solution is as follows: A Josephson junction array microwave coupling cavity comprises: a reflecting spherical surface, a reflecting plane, a matching circuit board, and a Josephson junction array chip; the Josephson junction array chip is provided with a Josephson junction array circuit; the reflecting spherical surface is located above the reflecting plane, with an inner cavity facing the reflecting plane; a rectangular waveguide is provided above the reflecting spherical surface, connected to the center of the reflecting spherical surface for feeding microwaves; the matching circuit board is mounted on the reflecting plane and connected to the Josephson junction array chip; a first through hole is provided at a position on the matching circuit board corresponding to the center of the reflecting spherical surface; the size of the first through hole is adapted to that of the Josephson junction array chip, so that the Josephson junction array chip can be placed in the first through hole; the Josephson junction array chip is mounted on the reflecting plane, and the portion of the Josephson junction array chip where the Josephson junction array circuit is provided is mounted separately from the reflecting plane.

[0008] Furthermore, the reflecting plane is provided with a groove at a position corresponding to the Josephson junction array circuit; the size of the groove is larger than the size of the Josephson junction array circuit, so that the Josephson junction array circuit is suspended above the reflecting plane.

[0009] Furthermore, the groove corresponds to the center of the reflective spherical surface.

[0010] Furthermore, the groove is located at the center of the reflection plane.

[0011] Furthermore, after the Josephson junction array chip is mounted on the reflective plane on the groove, the space inside the groove remains connected to the external space.

[0012] Furthermore, the groove is square; the side length of the groove is smaller than the diagonal length of the Josephson junction array chip; the side of the Josephson junction array chip and the side of the groove are mounted at a 45-degree rotation angle.

[0013] Furthermore, the groove is a rectangular groove; the Josephson junction array chip is a square; the length of the long side of the groove is greater than the side length of the Josephson junction array chip, and the length of the short side is less than the side length of the Josephson junction array chip.

[0014] Furthermore, a substrate is provided between the Josephson junction array chip installation and the reflective plane, so that the Josephson junction array chip and the reflective plane are installed separately.

[0015] Furthermore, the Josephson junction array chip, the substrate and the reflection plane are mounted by gluing with low-temperature glue.

[0016] Furthermore, the curvature radius of the reflecting sphere is 40 mm and the aperture is 25 mm; the rectangular waveguide tube adopts the WR-12 standard rectangular waveguide; the diameter of the reflecting plane is 25 mm; the distance between the reflecting plane and the fixed point of the spherical crown of the reflecting sphere is 15 mm; the Josephson junction array chip is a square with a side length of 10 mm; and the thickness of the Josephson junction array chip is 0.5 mm.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. It can eliminate the influence of the reflection plane on the magnetic field in the adjacent space and stabilize the critical current of the Josephson junction array. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly describes the drawings required for the specific embodiments or the description of the prior art. Similar elements or parts are generally identified by similar reference numerals throughout the drawings. Elements or parts in the drawings are not necessarily drawn to scale.

[0019] Figure 1 This is a schematic diagram of the structure of the first Josephson junction array microwave coupled cavity; Figure 2 This is a schematic diagram of the structure of the second type of Josephson junction array microwave coupled cavity; Figure 3 This is a schematic diagram of the structure of the third type of Josephson junction array microwave coupled cavity.

[0020] Reference numerals: waveguide tube 1, reflecting sphere 2, Josephson junction array chip 3, substrate 4, matching circuit board 5, reflecting plane 6, groove 7. DETAILED DESCRIPTION

[0021] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0022] It should be understood that when used in this application, the terms "include" and "comprising" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or collections thereof.

[0023] It should also be understood that the terms used in the present specification are only for the purpose of describing particular embodiments and are not intended to limit the present invention. As used in the present specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms unless the context clearly indicates otherwise.

[0024] It should be further understood that the term "and / or" used in this application refers to and includes any and all possible combinations of one or more of the associated listed items.

[0025] Example 1 like Figure 1 The figure shows a schematic structural diagram of a Josephson junction array microwave coupling cavity, comprising: a reflecting spherical surface 2, a reflecting plane 6, a supporting circuit board 5, and a Josephson junction array chip 3; the Josephson junction array chip 3 is provided with a Josephson junction array circuit; the reflecting spherical surface 2 is located above the reflecting plane 6, with the inner cavity facing the reflecting plane 6; a rectangular waveguide 1 is provided above the reflecting spherical surface 2, connected to the center of the reflecting spherical surface 2 for feeding microwaves; the supporting circuit board 5 is mounted on the reflecting plane 6 and connected to the Josephson junction array chip 3; a first through hole is provided at a position on the supporting circuit board 5 corresponding to the center of the reflecting spherical surface 2; the size of the first through hole is adapted to the size of the Josephson junction array chip 3, so that the Josephson junction array chip 3 can be placed in the first through hole; the Josephson junction array chip 3 is mounted on the reflecting plane 6, and the portion of the Josephson junction array chip 3 provided with the Josephson junction array circuit is mounted separately from the reflecting plane 6.

[0026] Furthermore, the curvature radius of the reflecting sphere 2 is 40 mm and the aperture is 25 mm; the rectangular waveguide tube 1 adopts the WR-12 standard rectangular waveguide; the diameter of the reflecting plane 6 is 25 mm; the distance between the reflecting plane 6 and the spherical crown fixed point of the reflecting sphere 2 is 15 mm; the Josephson junction array chip 3 is a square with a side length of 10 mm; and the thickness of the Josephson junction array chip 3 is 0.5 mm.

[0027] Furthermore, a substrate 4 is provided between the Josephson junction array chip 3 and the reflective plane 6 , and the Josephson junction array chip 3 and the reflective plane 6 are installed separately through the substrate 4 .

[0028] Furthermore, the Josephson junction array chip 3, the substrate 4 and the reflection plane 6 are mounted together using low-temperature glue.

[0029] This solution is a hemispherical Fabry-Perot resonant cavity, consisting of a reflective sphere 2 and a reflective plane 6. This means that the two reflective planes 6 of a conventional Fabry-Perot resonant cavity are replaced by a single reflective sphere 2. A rectangular waveguide 1 is connected to the center of the reflective sphere 2, feeding a microwave drive signal into the hemispherical Fabry-Perot resonant cavity, exciting its resonant mode and thereby coupling with the Josephson junction array chip 3. This solution adheres the Josephson junction array chip 3 to a substrate 4 of a certain thickness using low-temperature adhesive, and then mounts the entire chip on the reflective plane 6 of the Fabry-Perot resonant cavity using low-temperature adhesive. This alters the distance between the Josephson junction array chip 3 and the reflective plane 6 of the Fabry-Perot resonant cavity, eliminating magnetic fields in the adjacent space and stabilizing the critical current of the Josephson junction array. However, it will also make the dielectric environment around the Josephson junction array circuit more complicated, increase the difficulty of calculating the effective dielectric constant, and excessive use of low-temperature glue will also bring more microwave losses and reduce the microwave coupling efficiency between the Fabry-Perot resonant cavity and the Josephson junction array.

[0030] Example 2 like Figure 2 The difference between this solution and the first embodiment is that the structure of the reflection plane 6 of the hemispherical Fabry-Perot resonant cavity is changed, and a groove is formed at the mounting location of the Josephson junction array chip 3, so that the junction array chip can be mounted in the air without using a substrate 4. The specific structure is as follows: A reflective spherical surface 2 and a reflective plane 6 are machined and fabricated, wherein the center of the reflective spherical surface 2 is connected to a rectangular waveguide 1 within a corresponding frequency range. A groove 7 of a certain size is machined on the reflective plane 6 of the Fabry-Perot resonator, at the location for mounting the Josephson junction array chip 3, using milling or other feasible machining methods. The dimensions of the groove 7 and the dimensions of the Josephson junction array chip 3 must satisfy the following requirements: providing the necessary support points for mounting the Josephson junction array chip 3, ensuring that the back of the Josephson junction array circuit is suspended, and maintaining communication between the interior of the groove 7 and the exterior space after the Josephson junction array chip 3 is mounted on the groove 7.

[0031] The reflecting plane 6 is provided with a groove 7 at a position corresponding to the Josephson junction array circuit; the size of the groove 7 is larger than the size of the Josephson junction array circuit, so that the Josephson junction array circuit is suspended above the reflecting plane 6.

[0032] Furthermore, the groove 7 corresponds to the center of the reflective spherical surface 2 , that is, the reflective spherical surface 2 and the reflective plane 6 are installed facing each other at a certain spatial distance, and the groove on the reflective plane 6 is opposite to the center of the reflective spherical surface 2 .

[0033] Furthermore, the groove 7 is located at the center of the reflection plane 6 , that is, the center of the reflection plane 6 corresponds to the center position of the reflection spherical surface 2 .

[0034] Furthermore, after the Josephson junction array chip 3 is mounted on the reflective plane 6 on the groove 7 , the inner space of the groove 7 remains connected with the external space.

[0035] Furthermore, the groove 7 is square, with a depth generally around 1 mm and typically no less than 0.5 mm, which can be selected based on the resonant mode requirements of the Fabry-Perot resonator. The side length of the groove 7 is slightly smaller than the diagonal length of the Josephson junction array chip 3, typically 2 to 5 mm shorter. The edges of the Josephson junction array chip 3 and the edges of the groove 7 are mounted at a 45-degree rotation angle. The Josephson junction array chip 3 is mounted on the reflective plane 6, with the four corners of the Josephson junction array chip 3 positioned on steps outside the four edges of the groove 7. These corners are then securely affixed with low-temperature adhesive (a possible low-temperature adhesive is, for example, low-temperature varnish). This achieves the effect of suspending the Josephson junction array circuit on the Josephson junction array chip 3, adjusting the distance between the Josephson junction array circuit and the reflective plane 6 of the Fabry-Perot resonator, without introducing an additional spacer 4.

[0036] A Josephson junction array chip 3 is mounted on the slot of the reflection plane 6 of the Fabry-Perot resonant cavity, so that the junction array can be suspended above the reflection plane 6; microwaves are then fed through the rectangular waveguide 1 connected to the reflecting sphere 2, and microwave coupling of the Josephson junction array can be achieved using the Fabry-Perot resonant cavity.

[0037] This embodiment improves the structure of the reflecting plane 6 of the hemispherical Fabry-Perot resonant cavity, so that the Josephson junction array circuit in the Josephson junction array chip 3 can be mounted on the reflecting plane 6 in a suspended manner. This not only eliminates the influence of the reflecting plane 6 on the magnetic field in the adjacent space and stabilizes the critical current of the Josephson junction array, but also avoids the complex dielectric environment and higher microwave loss caused by the addition of low-temperature glue and substrate 4.

[0038] Example 3 like Figure 3The manufacturing specifications of the Fabry-Perot resonant cavity and the Josephson junction array chip 3 are the same as those of Example 2. This solution differs from Example 2 in that the groove 7 is a rectangular groove, typically with a depth of 1 mm; the Josephson junction array chip 3 is square; the long side of the groove 7 is longer than the side length of the Josephson junction array chip 3, while the short side is shorter. Specifically, the long side of the groove 7 is 2 mm to 5 mm longer than the side length of the square Josephson junction array chip 3, while the short side of the groove 7 is 2 mm to 5 mm shorter than the side length of the square Josephson junction array chip 3. The Josephson junction array chip 3 is mounted on the reflective plane 6 by placing a pair of parallel sides of the Josephson junction array chip 3 on steps outside the long side of the rectangular groove 7 and securely attaching these parallel sides with low-temperature adhesive. This achieves the effect of suspending the Josephson junction array chip 3 in this solution.

[0039] Any dimensions not specified in this solution can be determined using public methods or data.

[0040] The present application provides a Josephson junction array microwave coupling cavity, comprising: a reflecting sphere 2, a reflecting plane 6, a supporting circuit board 5, and a Josephson junction array chip 3. The Josephson junction array chip 3 is provided with a Josephson junction array circuit. A rectangular waveguide 1 is provided above the reflecting sphere 2 and connected to the center of the reflecting sphere 2 for feeding microwaves. The supporting circuit board 5 is mounted on the reflecting plane 6 and connected to the Josephson junction array chip 3. A first through-hole is provided at a position on the supporting circuit board 5 corresponding to the center of the reflecting sphere 2, allowing the Josephson junction array chip 3 to be placed in the first through-hole. The Josephson junction array chip 3 is mounted on the reflecting plane 6, and the portion of the Josephson junction array chip 3 where the Josephson junction array circuit is provided is mounted separately from the reflecting plane 6. This arrangement can eliminate the influence of the reflecting plane 6 on the magnetic field in the adjacent space and stabilize the critical current of the Josephson junction array.

[0041] Those skilled in the art will appreciate that the units of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition of each example has been generally described in terms of function in the above description. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0042] In the embodiments provided by the present invention, it should be understood that the division of units is merely a logical function division, and there may be other division methods in actual implementation, for example, multiple units can be combined into one unit, one unit can be split into multiple units, or some features can be ignored, etc.

[0043] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0044] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes various media that can store program code, such as a USB flash drive, read-only memory (ROM), random access memory (RAM), a mobile hard drive, a magnetic disk, or an optical disk.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of this application.

Claims

1. A Josephson junction array microwave coupled cavity, characterized in that: include: Reflecting sphere, reflecting plane, matching circuit board and Josephson junction array chip; The Josephson junction array chip is provided with a Josephson junction array circuit; the reflecting spherical surface is located above the reflecting plane, and the inner cavity is opposite to the reflecting plane; a rectangular waveguide is provided above the reflecting spherical surface, and the rectangular waveguide is connected to the center of the reflecting spherical surface for feeding microwaves; the matching circuit board is mounted on the reflecting plane and connected to the Josephson junction array chip; a first through hole is provided at a position of the matching circuit board corresponding to the center of the reflecting spherical surface; the size of the first through hole is adapted to the Josephson junction array chip, so that the Josephson junction array chip can be placed in the first through hole; the Josephson junction array chip is mounted on the reflecting plane, and the portion of the Josephson junction array chip where the Josephson junction array circuit is provided is mounted separately from the reflecting plane.

2. The Josephson junction array microwave coupled cavity according to claim 1, characterized in that: The reflecting plane is provided with a groove at a position corresponding to the Josephson junction array circuit; the size of the groove is larger than the size of the Josephson junction array circuit, so that the Josephson junction array circuit is suspended above the reflecting plane.

3. The Josephson junction array microwave coupled cavity according to claim 2, characterized in that: The groove corresponds to the center of the reflective spherical surface.

4. The Josephson junction array microwave coupled cavity according to claim 3, characterized in that: The groove is located at the center of the reflecting plane.

5. The Josephson junction array microwave coupled cavity according to claim 2, characterized in that: After the Josephson junction array chip is mounted on the reflective plane on the groove, the space inside the groove is kept in communication with the external space.

6. The Josephson junction array microwave coupled cavity according to claim 5, characterized in that: The groove is square; the side length of the groove is smaller than the diagonal length of the Josephson junction array chip; the side of the Josephson junction array chip and the side of the groove form a 45-degree rotation angle for mounting.

7. The Josephson junction array microwave coupled cavity according to claim 5, characterized in that: The groove is a rectangular groove; the Josephson junction array chip is a square; the length of the long side of the groove is greater than the side length of the Josephson junction array chip, and the length of the short side is less than the side length of the Josephson junction array chip.

8. The Josephson junction array microwave coupled cavity according to claim 1, characterized in that: A substrate is provided between the Josephson junction array chip installation and the reflection plane, so that the Josephson junction array chip and the reflection plane are installed separately.

9. The Josephson junction array microwave coupled cavity according to claim 8, characterized in that: The Josephson junction array chip, the substrate and the reflection plane are mounted by gluing with low-temperature glue.

10. The Josephson junction array microwave coupled cavity according to any one of claims 1 to 9, characterized in that: The curvature radius of the reflecting sphere is 40 mm and the aperture is 25 mm; the rectangular waveguide tube adopts the WR-12 standard rectangular waveguide; the diameter of the reflecting plane is 25 mm; the distance between the reflecting plane and the fixed point of the spherical crown of the reflecting sphere is 15 mm; the Josephson junction array chip is a square with a side length of 10 mm; and the thickness of the Josephson junction array chip is 0.5 mm.

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