CN117015224B - Electromagnetic shielding device and system for keeping superconducting state of Josephson junction - Google Patents
Electromagnetic shielding device and system for keeping superconducting state of Josephson junction Download PDFInfo
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Abstract
The invention relates to an electromagnetic shielding device and a system for keeping a superconductive state of a Josephson junction, wherein the device comprises at least two magnetic shielding units sleeved concentrically, each magnetic shielding unit comprises a cylinder with one end closed and a detachable cover body tightly matched with the other end of the cylinder; the inner wall surface and/or the outer wall surface of the cylinder are/is provided with a non-magnetic isolation layer, and at least one non-magnetic isolation layer is arranged between the adjacent magnetic shielding units; the dimensions of the magnetic shielding elements and the thickness of the non-magnetic isolating layer are determined according to the magnetic field strength of the surrounding environment of the josephson junction and the target shielding effectiveness of the electromagnetic shielding device, and the inside of each magnetic shielding element is set to vacuum so as to maintain the superconducting state of the josephson junction. The electromagnetic shielding device and the electromagnetic shielding system provided by the invention have the advantages of simple structure and strong designability, and can stably and effectively realize electromagnetic shielding of the Josephson junction chip.
Description
Technical Field
The invention belongs to the technical field of electromagnetic shielding, and particularly relates to an electromagnetic shielding device and system for keeping a superconducting state of a Josephson junction.
Background
The presence of a magnetic field in an area is caused by a magnetic flux source, which may be the earth, a motor, a transformer, a power line, etc., the strength of the magnetic field at a location depends on the magnetic field source and the distance of the location from the magnetic field source. In quantum voltage systems, proper electromagnetic shielding is critical to isolate the josephson junction chip from these electromagnetic fields. Increasing the distance from the magnetic field radiation source reduces the strength of the shielded magnetic field, so it is best to isolate the chip from the known electromagnetic field source to remove the chip from the electromagnetic field, which is not generally possible. There are a number of shielding materials that can be used to further reduce the incoming electromagnetic field. In order to develop and design an effective magnetic shielding, it is necessary to first measure the magnetic field strength around the area to be shielded and estimate the source of electromagnetic noise. In the josephson voltage standard system, it is crucial to electromagnetically shield the josephson junction array chip and keep the magnetic noise level very low in the vicinity. In a liquid free helium quantum voltage system, a Closed Cycle Refrigeration (CCR) based cooling system uses a two-stage 4.2K gifford-mcmahon (GM) cryocooler and a vacuum pump to achieve operating temperatures; the disadvantage of using these systems is that they are a major source of electromechanical noise and are very close to the josephson chip, since noise sources cannot be eliminated nor separation distance cannot be increased significantly, magnetic shielding must be carefully designed around the chip to obtain a very low magnetic field area. As in patent CN101059556a, a superconducting qubit measurement system is provided, in which a josephson junction to be measured is placed in a metal sample box, and in particular, the sample box is made of a superconducting metal aluminum material, the josephson junction to be measured and the sample box are in a mk-magnitude temperature environment during measurement, and aluminum is converted into a superconductor after the temperature is reduced to 1.14k, so that the superconducting shielding layer on the periphery of the josephson junction to be measured is formed, and interference of external environmental noise on the sample can be further reduced.
Therefore, how to provide an electromagnetic shielding device which has simple structure, low energy consumption, good electromagnetic shielding effect and wide application scene and can stably and effectively maintain the superconducting state of the Josephson junction is a technical problem to be solved in the field.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides an electromagnetic shielding device and an electromagnetic shielding system for keeping the superconducting state of a Josephson junction, which can realize electromagnetic shielding of a Josephson junction chip.
The invention provides an electromagnetic shielding device for maintaining the superconductive state of a Josephson junction, the device comprising at least two concentrically spaced apart magnetic shielding units, wherein,
each magnetic shielding unit comprises a cylinder with one end closed and a detachable cover body tightly matched with the other end of the cylinder;
the inner wall surface and/or the outer wall surface of the cylinder are/is provided with a non-magnetic isolation layer, and at least one non-magnetic isolation layer is arranged between the adjacent magnetic shielding units;
the dimensions of the magnetic shielding elements and the thickness of the non-magnetic isolating layer are determined according to the magnetic field strength of the surrounding environment of the josephson junction and the target shielding effectiveness of the electromagnetic shielding device, and the inside of each magnetic shielding element is set to vacuum so as to maintain the superconducting state of the josephson junction.
Further, the magnetic shield unit is a cylinder, and is vertically disposed. The influence of the geomagnetic field on the electromagnetic shielding device can be avoided, and the magnetic shielding effect is destroyed.
Further, the diameter of the inner cavity of the magnetic shielding unit with the smallest inner diameter is 15-20 cm, namely the diameter of the inner cavity of the magnetic shielding unit positioned at the innermost side is 15-20 cm.
Further, wherein the outer diameter of each magnetic shield unit is determined, specifically comprising:
，
wherein B is the magnetic flux density of the magnetic shield unit, D is the outer diameter of the magnetic shield unit, H 0 Is the magnetic field strength of the surroundings of the magnetic shielding unit in oersted, d "is the thickness of the magnetic shielding unit, and α is the magnetic flux density coefficient.
Preferably, α is 1.25, i.e. the size of each magnetic shielding element satisfies the following relationship:
。
furthermore, the magnetic shielding unit is made of high magnetic conduction alloy, particularly a MuMetal material, and the non-magnetic isolation layer comprises oxygen-free copper (OFHC copper).
Further, the non-magnetic isolation layers are arranged on the inner wall surface and/or the outer wall surface of the magnetic shielding unit, the thickness of each non-magnetic isolation layer is the same, and the thickness of each magnetic shielding unit is the same;
the determination of the thickness of the non-magnetic spacer layer includes:
obtaining the target shielding effectiveness of the electromagnetic shielding device according to the magnetic field intensity of the surrounding environment of the electromagnetic shielding device and the critical magnetic field of the Josephson junction;
obtaining the outer diameter or the inner diameter of a nonmagnetic isolating layer arranged on each magnetic shielding unit according to the inner diameter and the outer diameter of each magnetic shielding unit;
obtaining shielding effectiveness of each magnetic shielding unit and each nonmagnetic isolating layer according to the inner diameter, the outer diameter and the magnetic permeability of each magnetic shielding unit and the outer diameter, the inner diameter, the relative magnetic permeability and the electric conductivity of each nonmagnetic isolating layer;
obtaining the thickness of each nonmagnetic isolating layer according to the corresponding relation between the thickness of each magnetic shielding unit and the inner diameter and the outer diameter, the corresponding relation between the thickness of each nonmagnetic isolating layer and the inner diameter and the outer diameter, the target shielding effectiveness of the electromagnetic shielding device and the shielding effectiveness of each magnetic shielding unit and each nonmagnetic isolating layer;
further, the thickness of each nonmagnetic spacer layer satisfies the following relationship:
，
wherein d 'is the thickness of each nonmagnetic spacer layer, r' In addition, i Is the outer diameter of the ith nonmagnetic isolating layer, r' Inner, i The inner diameter of the ith nonmagnetic isolation layer, n is the number of layers of the nonmagnetic isolation layer, mu 0 Is vacuum permeability, mu 1 Is the relative permeability of the nonmagnetic isolation layer, ω is the magnetic field angular frequency,is the conductivity of the nonmagnetic spacer layer, y is the imaginary part, d 'is the thickness of each magnetic shielding unit, r', outside, j For the outer diameter of the jth magnetic shielding unit, r' Inner, j The inner diameter of the jth magnetic shielding unit is that m is the number of the magnetic shielding units, and m is less than or equal to n and mu 2 Is the magnetic permeability of the magnetic shielding unit, a ', b', a ', b' are all constant, H is electricityMagnetic field strength of surrounding of magnetic shielding device, B c Is the critical magnetic field.
Further, the non-magnetic isolation layer is formed by magnetron sputtering;
the magnetic shielding unit comprises a magnetic shielding unit, a non-magnetic isolation layer, a magnetic shielding layer and a magnetic shielding layer, wherein the direct current power supply action time, the high-power pulse power supply action time and the ion source action time are taken as one period, and the non-magnetic isolation layer with a preset thickness is formed on the inner wall surface and/or the outer wall surface of the magnetic shielding unit through a plurality of periods.
Further, the direct current power supply action time, the high power pulse power supply action time and the ion source action time in each period are respectively 20-40 min, 200-300 min and 6-8 min.
In a second aspect, there is also provided a josephson voltage system, the system comprising:
the electromagnetic shielding device for keeping the superconducting state of the Josephson junction;
a josephson junction chip located inside the electromagnetic shielding means and having josephson junctions, the josephson junction chip being located at least in the geometric centre of the two concentrically spaced magnetic shielding units.
Further, a temperature sensor and a magnetic field sensor are disposed within the electromagnetic shielding device, and the temperature sensor and the magnetic field sensor are disposed proximate to the josephson junction chip.
Further, the Josephson voltage system also comprises a controller for adjusting the ambient temperature around the magnetic shielding unit and a connector arranged on the magnetic shielding unit with the largest inner diameter, wherein the connector is disconnected with the temperature sensor and the magnetic field sensor respectively.
Further, the system includes: the connector is communicated with the controller when the temperature result detected by the temperature sensor is not greater than the critical temperature of the Josephson junction chip, the controller adjusts the temperature of the surrounding environment of the magnetic shielding unit according to the temperature result detected by the temperature sensor, and the connector is disconnected with the controller when the temperature result detected by the temperature sensor is greater than the critical temperature of the Josephson junction chip.
Further, the controller adjusts the temperature of the surrounding environment of the magnetic shielding unit according to the temperature result detected by the temperature sensor, and further comprises:
acquiring a current temperature result detected by a temperature sensor and a temperature result in a preset time period;
obtaining a temperature change rate according to a temperature result detected by the temperature sensor;
obtaining a temperature change state in the magnetic shielding unit according to the temperature change rate;
and adjusting the ambient temperature of the magnetic shielding unit to a preset value according to the temperature change state, the current temperature result and the temperature threshold value.
Wherein the temperature change state comprises a heating state, a constant temperature state and a cooling state;
according to the temperature change state, the current temperature result and the temperature threshold value, adjusting the ambient temperature of the magnetic shielding unit to a preset value, including:
when the temperature change state is a temperature rise state and the current temperature result is smaller than a temperature threshold value, and when the temperature change state is a temperature reduction state and the current temperature result is larger than the temperature threshold value, the ambient temperature of the magnetic shielding unit is regulated to be unchanged;
when the temperature change state is a temperature rise state and the current temperature result is not less than the temperature threshold value, and when the temperature change state is a constant temperature state and the current temperature result is greater than the temperature threshold value, the ambient temperature of the magnetic shielding unit is reduced;
when the temperature change state is a constant temperature or a temperature reduction state and the current temperature result is not greater than the temperature threshold value, adjusting the ambient temperature of the magnetic shielding unit to a preset temperature; preferably, the predetermined temperature is 4K.
The invention provides an electromagnetic shielding device and a system for keeping a superconductive state of a Josephson junction, which at least comprise the following beneficial effects:
the present invention can realize continuous shielding by providing at least two magnetic shield units, as compared with a single magnetic shield unit. The multiplication effect by the continuous shielding provides significant magnetic field attenuation and prevents saturation of the shielding. And by arranging a non-magnetic isolation layer matched with the magnetic shielding unit, the magnetic shielding of the Josephson junction chip can be realized jointly. The shielding of the low-frequency magnetic field and the high-frequency magnetic field in the surrounding environment is respectively realized through the magnetic shielding unit and the nonmagnetic isolation layer, so that the application scene of the electromagnetic shielding device is improved, and the magnetic shielding effect on the Josephson junction chip can be improved.
By arranging the josephson junction chip in the geometrical centre of the magnetic shielding unit, the magnetic field around the josephson junction chip can be made uniform and symmetrical and the influence of the magnetic field on the josephson junction chip is minimized.
By selecting proper magnetic shielding units and non-magnetic isolating layers, the vacuum degree, temperature and magnetic shielding of the inner side can be ensured to meet the preset requirements on the basis of reducing the cost.
Drawings
Fig. 1 shows a schematic diagram of an electromagnetic shielding device for maintaining a superconducting state of a josephson junction according to an embodiment of the present invention;
fig. 2 shows a schematic diagram of a josephson voltage system according to an embodiment of the invention.
Reference numerals illustrate: 10-electromagnetic shielding device, 11-magnetic shielding unit, 2-Josephson junction chip, 3-magnetic field sensor, 4-temperature sensor, 5-connector, 6-controller.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the following detailed description of alternative embodiments of the present invention is provided with reference to the accompanying drawings.
In josephson junctions, the binding energy of the cooper to electrons is small and very sensitive to any external excitation source. The presence of an external magnetic field will exert a torque on the electron spins, which will tend to destroy these pairs, and as the pairs separate into individual electrons, the josephson junction will become a normal conductor or "non-superconductor". The cooper pair breaks when the magnetic field is above a specific value associated with the superconductor material; this magnetic field value is called the critical magnetic field and depends on the materials involved.
The superconducting state cannot exist in a magnetic field greater than the critical magnetic field, even at absolute zero degrees. This critical magnetic fieldThe critical temperature of the superconductor is closely related to the bandgap. The critical temperature and critical field are parameters that represent the energy that can be supplied to the material in a manner that begins to interfere with the superconducting mechanism. According to the Miesner effect, the superconductor is essentially a repulsive magnetic field, but this is only true if the applied magnetic field does not exceed its critical magnetic field. The critical magnetic field value is typically established at 0K, and gradually decreases as the temperature increases until zero is reached at the superconducting critical temperature. A critical magnetic field (B) at any temperature (T) below the critical temperature c ) The following relation is given:
，
wherein B is c (0) Is a magnetic field required for suppressing superconductivity at 0K, T c Is the critical temperature of the material. Josephson junctions are highly sensitive to any magnetic field and are susceptible to magnetic fields as low as a few gauss.
Referring to fig. 1, the invention provides an electromagnetic shielding device 10 for maintaining the superconducting state of a josephson junction for magnetic shielding of a josephson junction chip 2, said device comprising at least two concentrically spaced magnetic shielding units 11, wherein,
each magnetic shield unit 11 includes a cylinder closed at one end and a detachable cover body tightly fitted with the other end of the cylinder;
a non-magnetic isolation layer is arranged on the inner wall surface and/or the outer wall surface of the cylinder, and at least one non-magnetic isolation layer is arranged between the adjacent magnetic shielding units 11;
the dimensions of the magnetic shielding elements 11 and the thickness of the non-magnetic isolating layer are determined according to the magnetic field strength of the surrounding environment of the josephson junction and the target shielding effectiveness of the electromagnetic shielding device 10, and the inside of each magnetic shielding element 11 is set to vacuum to maintain the superconducting state of the josephson junction.
The number and the size of the magnetic shielding units 11 in the electromagnetic shielding device 10 can be correspondingly selected according to environmental parameters of practical application scenes, for example, when the magnetic field intensity of the surrounding environment of the electromagnetic shielding device 10 is high, a large number of the magnetic shielding units 11 can be arranged, and a hierarchical structure formed by the magnetic shielding units 11 with a certain thickness and the nonmagnetic isolation layers can be selected, so that electromagnetic shielding in the current environment is realized. The non-magnetic isolation layer comprises OFHC copper material (oxygen-free copper), so that the isolation effect on magnetism can be further improved. In order to improve the shielding effect, it is desirable that the inner cavity diameter of the magnetic shielding unit 11 is as small as possible, because the attenuation is inversely proportional to the diameter, and the size of the magnetic shielding is calculated based on the approximation of the ambient field and the desired level of flux density. Preferably, the diameters of the inner cavities of the two magnetic shielding units 11 are 15-20 cm, so that the electromagnetic shielding device 10 has more excellent magnetic shielding effect by selecting a proper diameter range on the basis of shielding based on specific materials. Specifically, the invention can ensure that the vacuum degree, the temperature and the magnetic shielding of the inner side meet the preset requirements on the basis of reducing the cost by selecting the proper size of the magnetic shielding unit 11. For example, when the inner cavity diameter of the inner magnetic shield unit 11 is larger than 20cm, although a good shielding effect can be obtained, the cost of the magnetic shield unit 11 is increased due to its larger diameter, and a problem of difficulty in installation is also liable to occur. When the inner cavity diameter of the inner magnetic shield unit 11 is smaller than 15cm, it has a convenient installation and requires a low cost, but the smaller size of the magnetic shield unit 11 cannot achieve a predetermined effect of the vacuum degree, temperature and magnetic shield of the inner environment.
The magnetic shield unit 11 is made of a material having a high magnetic permeability alloy. Since the magnetic field cannot be generated nor removed, the purpose of the magnetic shielding unit 11 is to redistribute the magnetic field in such a way that a region of zero or very low magnetic field is generated around the josephson junction chip 2 to be shielded. The high permeability material shields the region of the josephson junction chip 2 by pulling the magnetic field towards itself and away from the josephson junction chip 2 to be shielded. When the electromagnetic shielding is realized through the magnetic shielding unit 11, the material of the magnetic shielding unit 11 is selected, so that the electromagnetic shielding unit has a good shielding effect. Preferably, the magnetic shield unit 11 of the present invention is made of a MuMetal material. The ability of the mu metal shield to absorb magnetic energy and to produce very high attenuation by concentrating the magnetic field within the mu metal shield itself makes these shield alloys the preferred material for reducing low frequency electromagnetic interference (EMI). Since the operating environment of the josephson junction chip 2 is more demanding, the magnetic shielding effect needs to meet the predetermined requirements, and therefore, by making two concentrically spaced magnetic shielding elements 11 out of high permeability metal, a housing for the josephson junction chip 2 is made in an extremely low magnetic field region. Because the magnetic field source is very strong and close to the josephson junction chip 2, the multiplication effect of the continuous shielding provides significantly greater magnetic field attenuation and prevents saturation of the shielding compared to a single magnetic shielding of equal wall thickness.
For electromagnetic shielding of the josephson junction chip 2 in different scenarios, the electromagnetic shielding of the josephson junction chip 2 can be accomplished by analyzing its set-up environment, thereby selecting the optimally sized magnetic shielding unit 11. Specifically, the size of each magnetic shielding unit 11 is calculated based on the approximate value of the ambient field and the desired level of flux density, and the size determination of the magnetic shielding unit 11 may specifically include:
，
where B is the flux density of the magnetic shielding unit, D is the diameter of the magnetic shielding unit, H 0 Is the ambient field in oersted and d "is the thickness of the magnetic shielding element.
The non-magnetic isolation layers are arranged on the inner wall surface and/or the outer wall surface of the magnetic shielding unit, the thickness of each non-magnetic isolation layer is the same, and the thickness of each magnetic shielding unit is the same;
the determining of the thickness of each of the nonmagnetic spacer layers includes:
obtaining a target shielding effectiveness of the electromagnetic shielding device 10 according to the magnetic field intensity of the surrounding environment of the electromagnetic shielding device 10 and the critical magnetic field of the Josephson junction;
obtaining the outer diameter or the inner diameter of a nonmagnetic isolating layer arranged on each magnetic shielding unit according to the inner diameter and the outer diameter of each magnetic shielding unit;
obtaining shielding effectiveness of each magnetic shielding unit and each nonmagnetic isolating layer according to the inner diameter, the outer diameter and the magnetic permeability of each magnetic shielding unit and the outer diameter, the inner diameter, the relative magnetic permeability and the electric conductivity of each nonmagnetic isolating layer;
obtaining the thickness of each nonmagnetic spacer layer according to the corresponding relation between the thickness of each magnetic shielding unit and the inner diameter and the outer diameter, the corresponding relation between the thickness of each nonmagnetic spacer layer and the inner diameter and the outer diameter, the target shielding effectiveness of the electromagnetic shielding device 10, and the shielding effectiveness of each magnetic shielding unit and each nonmagnetic spacer layer;
wherein, the thickness of each non-magnetic isolation layer satisfies the following relationship:
，
wherein d 'is the thickness of each nonmagnetic spacer layer, r' In addition, i Is the outer diameter of the ith nonmagnetic isolating layer, r' Inner, i The inner diameter of the ith nonmagnetic isolation layer, n is the number of layers of the nonmagnetic isolation layer, mu 0 Is vacuum permeability, mu 1 The relative magnetic permeability of the non-magnetic isolation layer is the ratio of the magnetic permeability of the non-magnetic isolation layer to the vacuum magnetic permeability, omega is the angular frequency of the magnetic field,is the conductivity of the nonmagnetic spacer layer, y is the imaginary part, d 'is the thickness of each magnetic shielding unit, r', outside, j For the outer diameter of the jth magnetic shielding unit, r' Inner, j For the inner diameter of the jth magnetic shield unit, m is the number of magnetic shield units, m.ltoreq.n, i=1, 2,3,.. 2 Is the magnetic permeability of the magnetic shielding unit, a ', B', a ", B" are all constant, H is the magnetic field strength of the surrounding environment of the electromagnetic shielding device 10, B c Is the critical magnetic field. The invention limits the thickness of each magnetic shielding unit and each non-magnetic isolating layer, so that the structure design can be reduced as much as possible on the basis of meeting the electromagnetic shielding of the current application environmentThe excessive use of the separation layer can reduce the cost of the electromagnetic shielding device 10 of the invention, and has higher economic effect.
The non-magnetic isolation layer in the embodiment of the invention is formed by magnetron sputtering; the magnetic shielding unit comprises a magnetic shielding unit, a non-magnetic isolation layer, a magnetic shielding layer and a magnetic shielding layer, wherein the direct current power supply action time, the high-power pulse power supply action time and the ion source action time are taken as one period, and the non-magnetic isolation layer with a preset thickness is formed on the inner wall surface and/or the outer wall surface of the magnetic shielding unit through a plurality of periods. Further, the direct current power supply action time, the high power pulse power supply action time and the ion source action time in each period are respectively 20-40 min, 200-300 min and 6-8 min.
Referring to fig. 2, the invention also provides a josephson voltage system, the system comprising:
the electromagnetic shielding device 10 described above that maintains the superconducting state of the josephson junction;
a josephson junction chip 2, located inside the electromagnetic shielding device 10, and having josephson junctions.
By arranging the josephson junction chip 2 inside the electromagnetic shielding device 10, electromagnetic shielding of the josephson junction chip 2 can be achieved by the electromagnetic shielding device 10. And by arranging the materials, the sizes and the structures of the electromagnetic shielding device 10, the electromagnetic shielding effect on the Josephson junction chip 2 is improved.
In order to improve the shielding effect on the josephson junction chip 2, the josephson junction chip 2 of the present invention may be arranged in the geometric center of two concentrically spaced magnetic shielding units 11. The magnetic field around the josephson junction chip 2 can be made uniform and symmetrical and the influence of the magnetic field on the josephson junction chip 2 is minimized.
The magnetic shield unit 11 is very effective in preventing any type of low-frequency magnetic noise from entering the magnetic shield case. The low magnetic field enclosure is created by the physical boundaries of the magnetic shield separating and isolating the interior volume, but should ensure that there is no magnetic field source within the chamber. In operating josephson junction array systems there is a potential source of magnetic field (located outside the magnetic shielding unit) in the vicinity of the josephson junction chip 2. In addition, for monitoring the operating conditions of the josephson junction chip 2, a temperature sensor 4 and a magnetic field sensor 3 may also be arranged in the electromagnetic shielding device 10, and the temperature sensor 4 and the magnetic field sensor 3 are arranged close to the josephson junction chip 2. The shielding effect judgment of the electromagnetic shielding device 10 can be completed through the monitored temperature and the magnetic field, so that the working device of the Josephson junction chip 2 in the electromagnetic shielding device is ensured. Further, the josephson voltage system further comprises a controller 6 for regulating the ambient temperature around the magnetic shielding unit, and a connector 5 provided on the magnetic shielding unit with the largest inner diameter, the connector 5 being for disconnectably connecting the temperature sensor 4, the magnetic field sensor 3, respectively, to the controller 6. The connector 5 has different connection effects at different temperatures, specifically, when the temperature result detected by the temperature sensor 4 is not greater than the critical temperature of the josephson junction chip 2, the connector 5 is communicated with the controller 6, the controller 6 adjusts the temperature of the surrounding environment of the magnetic shielding unit according to the temperature result detected by the temperature sensor 4, and when the temperature result detected by the temperature sensor 4 is greater than the critical temperature of the josephson junction chip 2, the connector 5 is disconnected with the controller 6.
Wherein the controller adjusts the temperature of the surrounding environment of the magnetic shielding unit according to the temperature result detected by the temperature sensor 4, further comprising:
acquiring a current temperature result detected by the temperature sensor 4 and a temperature result in a preset time period;
obtaining a temperature change rate according to the temperature result detected by the temperature sensor 4;
obtaining a temperature change state in the magnetic shielding unit according to the temperature change rate;
and adjusting the ambient temperature of the magnetic shielding unit to a preset value according to the temperature change state, the current temperature result and the temperature threshold value.
The temperature change state comprises a heating state, a constant temperature state and a cooling state;
according to the temperature change state, the current temperature result and the temperature threshold value, adjusting the ambient temperature of the magnetic shielding unit to a preset value, including:
when the temperature change state is a temperature rise state and the current temperature result is smaller than a temperature threshold value, and when the temperature change state is a temperature reduction state and the current temperature result is larger than the temperature threshold value, the ambient temperature of the magnetic shielding unit is regulated to be unchanged;
when the temperature change state is a temperature rise state and the current temperature result is not less than the temperature threshold value, and when the temperature change state is a constant temperature state and the current temperature result is greater than the temperature threshold value, the ambient temperature of the magnetic shielding unit is reduced;
when the temperature change state is a constant temperature or a temperature reduction state and the current temperature result is not greater than the temperature threshold value, adjusting the ambient temperature of the magnetic shielding unit to a preset temperature; preferably, the predetermined temperature is 4K.
The disclosed embodiments provide an electromagnetic shielding device 10 that maintains the superconducting state of a josephson junction, the system comprising a processor, a memory, the processor implementing the functions of the above embodiments by executing computer instructions in the memory.
It should be noted that the computer readable medium described in the present disclosure may be a computer readable signal medium or a computer readable storage medium, or any combination of the two. The computer readable storage medium can be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or a combination of any of the foregoing. More specific examples of the computer-readable storage medium may include, but are not limited to: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this disclosure, a computer-readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. In the present disclosure, however, the computer-readable signal medium may include a data signal propagated in baseband or as part of a carrier wave, with the computer-readable program code embodied therein. Such a propagated data signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination of the foregoing. A computer readable signal medium may also be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to: electrical wires, fiber optic cables, RF (radio frequency), and the like, or any suitable combination of the foregoing.
The computer readable medium may be contained in the electronic device; or may exist alone without being incorporated into the electronic device. Computer program code for carrying out operations of the present disclosure may be written in one or more programming languages, including an object oriented programming language such as Java, smalltalk, C ++ and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server; in the case of a remote computer, the remote computer may be connected to the user computer through any kind of network, including a local Area Network (AN) or a Wide Area Network (WAN), or may be connected to AN external computer (e.g., connected through the internet using AN internet service provider).
The flowcharts and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.
The units involved in the embodiments of the present disclosure may be implemented by means of software, or may be implemented by means of hardware. Wherein the names of the units do not constitute a limitation of the units themselves in some cases.
The foregoing description of the preferred embodiments of the present invention has been presented for purposes of clarity and understanding, and is not intended to limit the invention to the particular embodiments disclosed, but is intended to cover all modifications, alternatives, and improvements within the spirit and scope of the invention as outlined by the appended claims.
Claims (9)
1. An electromagnetic shielding device for maintaining the superconductive state of a Josephson junction, characterized in that the device comprises at least two magnetic shielding units arranged concentrically and spaced apart, wherein,
each magnetic shielding unit comprises a cylinder with one end closed and a detachable cover body tightly matched with the other end of the cylinder; the inner wall surface and/or the outer wall surface of the cylinder are/is provided with a non-magnetic isolation layer, and at least one non-magnetic isolation layer is arranged between the adjacent magnetic shielding units;
determining the size of a magnetic shielding unit and the thickness of a non-magnetic isolating layer according to the magnetic field intensity of the surrounding environment of the Josephson junction and the target shielding effectiveness of an electromagnetic shielding device, and setting each magnetic shielding unit to be vacuum so as to keep the superconducting state of the Josephson junction; the diameter of the inner cavity of the magnetic shielding unit with the smallest inner diameter is 15-20 cm; the thickness of each magnetic shielding unit is the same, and the outer diameter of each magnetic shielding unit is determined, including:
；
wherein B is the magnetic flux density of the magnetic shield unit, D is the outer diameter of the magnetic shield unit, H 0 The magnetic field strength of the surrounding environment of the magnetic shielding unit taking oersted as a unit, d' is the thickness of the magnetic shielding unit, and alpha is the magnetic flux density coefficient;
the thickness of each non-magnetic isolation layer is the same, and the determination of the thickness of the non-magnetic isolation layer comprises the following steps:
obtaining the target shielding effectiveness of the electromagnetic shielding device according to the magnetic field intensity of the surrounding environment of the electromagnetic shielding device and the critical magnetic field of the Josephson junction; obtaining the outer diameter or the inner diameter of a nonmagnetic isolating layer arranged on each magnetic shielding unit according to the inner diameter and the outer diameter of each magnetic shielding unit; and according to the corresponding relation between the thickness of each magnetic shielding unit and the inner diameter and the outer diameter, the corresponding relation between the thickness of each non-magnetic isolating layer and the inner diameter and the outer diameter, the inner diameter, the outer diameter, the relative magnetic conductivity and the electric conductivity of each non-magnetic isolating layer and the target shielding effectiveness of the electromagnetic shielding device, obtaining the thickness of each non-magnetic isolating layer.
2. The electromagnetic shielding device for maintaining the superconducting state of the josephson junction according to claim 1, wherein the magnetic shielding unit is made of a high magnetic alloy, and the non-magnetic isolation layer comprises oxygen-free copper.
3. The electromagnetic shielding device of claim 1, wherein the thickness of each nonmagnetic spacer layer satisfies the following relationship:
；
wherein d 'is the thickness of each nonmagnetic spacer layer, r' In addition, i Is the outer diameter of the ith nonmagnetic isolating layer, r' Inner, i The inner diameter of the ith nonmagnetic isolation layer, n is the number of layers of the nonmagnetic isolation layer, mu 0 Is vacuum permeability, mu 1 Is the relative permeability of the nonmagnetic isolation layer, ω is the magnetic field angular frequency,is the conductivity of the nonmagnetic spacer layer, y is the imaginary part, d 'is the thickness of each magnetic shielding unit, r', outside, j For the outer diameter of the jth magnetic shielding unit, r' Inner, j The inner diameter of the jth magnetic shielding unit, m is the number of the magnetic shielding units, mu 2 Is the magnetic permeability of the magnetic shielding unit, a ', B', a 'and B' are constants, H is the magnetic field intensity of the surrounding environment of the electromagnetic shielding device, and B c Is the critical magnetic field.
4. The electromagnetic shielding device for maintaining a superconducting state of a josephson junction according to claim 1, wherein the non-magnetic isolation layer is formed by magnetron sputtering;
the magnetic shielding unit comprises a magnetic shielding unit, a non-magnetic isolation layer, a magnetic shielding layer and a magnetic shielding layer, wherein the direct current power supply action time, the high-power pulse power supply action time and the ion source action time are taken as one period, and the non-magnetic isolation layer with a preset thickness is formed on the inner wall surface and/or the outer wall surface of the magnetic shielding unit through a plurality of periods.
5. The electromagnetic shielding device for keeping the superconducting state of the josephson junction according to claim 4, wherein the direct current power supply operation time, the high power pulse power supply operation time and the ion source operation time in each period are respectively 20-40 min, 200-300 min and 6-8 min.
6. A josephson voltage system, the system comprising:
the electromagnetic shielding device of any one of claims 1-5 that maintains a superconducting state of a josephson junction;
a josephson junction chip located inside the electromagnetic shielding means and having josephson junctions, the josephson junction chip being located in the geometric centre of at least two concentrically spaced magnetic shielding units.
7. The josephson voltage system of claim 6, wherein a temperature sensor and a magnetic field sensor are disposed within the electromagnetic shield, and wherein the temperature sensor and the magnetic field sensor are disposed proximate to the josephson junction chip.
8. The josephson voltage system of claim 7, further comprising a controller for regulating the temperature of the environment surrounding the magnetic shield unit, and a connector provided on the magnetic shield unit having the largest inside diameter, the connector disconnectably connecting the temperature sensor and the magnetic field sensor, respectively, to the controller.
9. The josephson voltage system of claim 8, wherein the connector is in communication with the controller when the temperature result detected by the temperature sensor is not greater than the critical temperature of the josephson junction chip, the controller adjusting the temperature of the environment surrounding the magnetic shield unit based on the temperature result detected by the temperature sensor, and wherein the connector is disconnected from the controller when the temperature result detected by the temperature sensor is greater than the critical temperature of the josephson junction chip.
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