Cryogenic cooling system

Abstract

A cryogenic cooling system is provided that includes a cryocooler assembly and two or more connected modules. The cryocooler assembly includes one or more cryocoolers. Each of the connected modules comprises: a housing defining an interior volume of the module, the housing having a plurality of sides; and a plurality of stages disposed within the interior volume of the module, wherein one or more stages of the plurality of stages are thermally coupled to the cryogenic refrigerator assembly. Two or more of the modules are connected to each other on respective sides, and the first stage of a first of the modules is thermally coupled to the first stage of a second of the modules.

Description

Technical Field

[0001] The present invention relates to the field of cryogenic cooling systems. One particularly desirable application of this technology is commercial-scale superconducting quantum computing. Background Art

[0002] The expansion of quantum computing based on superconducting quantum information processing (QIP) devices will require continuous low temperatures of about 10mK to 20mK or lower for QIP device operation. For this reason, it is expected that dilution refrigerators (DR) will be essential. Today's industrial QIP companies use commercially available refrigerant-free ("dry") dilution refrigerators that follow traditional form specifications: a series of vertically spaced copper plates with circular cross-sections are thermally isolated from each other, and a single dilution unit is installed between the lower-level plates. Together with the piping connected to the inlet and outlet of the dilution unit and the pumping hardware, a closed cycle dilution refrigerator is formed. A concentric cylindrical radiation shield surrounds each stage plate of the dilution refrigerator insert to reduce the radiant heat load on the dilution refrigerator stage (up to about 0.8K at the distiller stage and down to less than 10mK at the mixing chamber stage). The entire assembly is encapsulated in a cylindrical vacuum container. The assembly is typically mounted on a frame to enable the removal of the radiation shield and the external vacuum chamber (OVC).

[0003] As described above, Figures 1 and 2 show examples of prior art dilution refrigerators. Figure 1 shows a perspective view of a cylindrical outer vacuum chamber 1 supported by a cryostat support frame 10. The external components of the cryogen-free refrigerator in the form of a helium handling system 2 and a pulse tube refrigerator (PTR) 3 are also visible. Figure 2 is a perspective view of a cross section taken through the outer vacuum chamber 1. For clarity, the PTR and dilution unit are not shown in Figure 2. There is a layered arrangement of thermal stages 5 to 9, each thermal stage is in the form of a circular plate and is cooled to a corresponding temperature in use. The nested assembly of cylindrical radiation shields 4 is also visible, each shield connected to a corresponding thermal stage. The first stage of the PTR 3 is mounted to the PT1 stage 5, and the second stage of the PTR 3 is mounted to the PT2 stage 6. The dilution unit forms part of the dilution refrigerator, the dilution unit comprising a distiller and a mixing chamber connected by a set of heat exchangers. The distiller is mounted to the distiller stage 7, and the mixing chamber is mounted to the mixing chamber stage 9. During operation, a working fluid formed by a helium-3 / helium-4 mixture circulates around the dilution unit. The distiller and mixing chamber cool the system due to phase changes or mixing of the working fluid. Cooling is obtained at the mixing chamber by the mixing enthalpy as the helium-3 is diluted into the helium-4. Therefore, the mixing chamber is operable to obtain the lowest temperature of any part of the dilution refrigerator. The helium-3 boils in the distiller, which takes away energy due to the latent heat of evaporation. The "cold plate" 8 forming the corresponding hot stage is arranged between the distiller stage 7 and the mixing chamber stage 9, and an intermediate temperature is obtained during use. A cylindrical thermal radiation shield is connected to each of the PT1 stage 5, the PT2 stage 6 and the distiller stage 7, and surrounds the lower temperature stage.

[0004] In cryogenic applications such as QIP, various heat sink elements are installed at different stages of the dilution refrigerator to ensure adequate thermalization of the experimental circuit. The heat dissipated by the resistive elements and wires increases the heat load of the dilution refrigerator, which means that more cooling power is required to maintain a given base temperature of the system. Although the above-mentioned formal specifications (described with reference to Figures 1 and 2) work well in academic environments where most dry DR systems are installed, this formal specification begins to become limiting as QIP expands in industrial environments. Large radiation shields are cumbersome to operate. The size of such systems is fixed, which limits the maximum experimental size and the available cooling power for each stage. As a way to provide physical space for scalable experiments, although very large vacuum chambers and cryogenic refrigerators can be designed, the huge capital expenditure makes such systems commercially unattractive for manufacturers and consumers. Therefore, there is a need for a cryogenic cooling system that is more suitable for industrial or commercial environments. For example, it is necessary to compensate for the higher heat load that may result from building a larger quantum computer without causing the above-mentioned problems and facilitating new operating modes. Summary of the invention

[0005] A first aspect of the present invention is a cryogenic cooling system comprising a cryogenic refrigerator assembly including one or more cryogenic refrigerators; and

[0006] Two or more connected modules, each of the connected modules comprising:

[0007] a housing defining an interior volume of the module, the housing having a plurality of sides; and

[0008] a plurality of stages disposed within the interior volume of the module, wherein one or more of the plurality of stages are thermally coupled to the cryogenic refrigerator assembly;

[0009] wherein two or more of the modules are connected to each other at corresponding sides; and

[0010] wherein the first said stage of a first said module is thermally coupled to the first said stage of a second said module.

[0011] Compared to the prior art designs of Figures 1 and 2, the cryogenic cooling system of the present invention is modular. This allows the system to be "scaled up" by connecting the interior of a first module to other similar modules, thereby increasing the shared internal volume and the total cooling power available. Users can gradually increase the size of their cryogenic cooling system by connecting additional modules, which solves the problem of high capital expenditures associated with owning large cryogenic cooling systems. The modular design also makes the system easier to maintain because any shielding can be made smaller and the user may only need to remove part of the housing of a given module to access the relevant experimental space therein. The thermal coupling levels of the different connected modules enable the cooling power of the cryogenic refrigerator to be shared throughout the system. Therefore, users can include additional heat dissipation components in their system (usually on or between different cooling levels) and increase the shared internal volume and total cooling power available by connecting the module to other modules (such as n th Instead of replacing the entire system with a larger module, the heat load can be balanced by using a single module (times). Therefore, new applications such as building a QIP server farm can be realized through this technology.

[0012] The cryogenic refrigerator assembly may include a common cryogenic refrigerator (such as a liquid helium refrigeration device) for the corresponding levels of two or more modules in the cooling system. However, typically, the cryogenic refrigerator assembly is configured so that each of the connected modules includes a cryogenic refrigerator that is thermally coupled to one or more levels of the module. These cryogenic refrigerators can take a variety of forms, including cryocoolers, helium-3 or helium-4 refrigerators, and dilution refrigerators, which will be discussed below. Each of the modules may have a cryogenic refrigerator that is mounted to the level of the module via a high thermal conductivity connection.

[0013] One or each of the modules is preferably configured to operate as an independent cryogenic cooling system in a first configuration. Independent operation generally requires that the internal volume of the module is sealed by a housing, and preferably also evacuated. Therefore, in a first configuration, a removable panel can be assembled to the housing of the module (and preferably assembled to the side) to close the internal volume of the module. Each of the modules is preferably also configured to operate as a component of an integrated cryogenic cooling system in a second configuration, and the integrated cryogenic cooling system includes a plurality of modules interconnected at respective sides to form a shared internal volume of the system, wherein a plurality of stages for each of the connected modules are arranged in the system, wherein in a second configuration, the removable panel is removed from the housing. The user can separate the modules and configure one or each module to the first configuration, so as to, for example, perform different experiments using each module. Alternatively, for example, if the target device in the system requires a greater total cooling power, the user can arrange the module to the second configuration. The housing of each of the modules generally includes a frame supporting a plurality of sides. The removable panel (when set) can be assembled to the frame in the first configuration and removed from the frame in the second configuration.

[0014] As previously described, the side of the module (e.g., the first module) can be connected to the opposite side of another module (e.g., the second module). The housing (e.g., frame) of each module typically includes one or more housing connectors for connecting the first module to the second module. One or more housing connectors are typically arranged so that the outer surface of the housing of the first module is configured to fit to the outer surface of the housing of the second module so as to form an integrated cryogenic cooling system. This facilitates simple connection between different modules. For example, the housing connector on the first side surface of the first module can be connected to the housing connector on the second side surface of the second module, and the second side surface of each module is opposite to the first side surface. This front-to-back geometry enables an unlimited number of modules in the system to be connected together. Alternatively, two modules can be connected together by connecting the housing connector on the first surface of the first module to the housing connector on the similar first surface of the second module. The first module can be connected to two modules (one on each side) by connecting the housing connector on the first surface of the first module to the housing connector on the second surface of the second module, and by connecting the housing connector on the second surface of the first module to the housing connector on the first surface of the third module. One or more housing connectors may include a flange, preferably surrounding the removable panel or disposed around the exterior of the removable panel. The housing connector may also include fasteners, such as preferably in the form of a bolt and hole array surrounding a sealing member (such as an O-ring seal), for coupling flanges of different modules together.

[0015] The modular cryogenic cooling system can have sides that form a plurality of different spliced ​​or non-spliced ​​structures. However, a housing in which each of the modules includes four orthogonal sides provides particular advantages. This design allows the module to easily conform to the geometry of most rooms and allows several such modules to be connected together in a space-saving manner. Before the available floor space is filled, more modules can be connected together to increase the total cooling power of the system. Orthogonal symmetry also means that the connected modules can be arranged closely, for example, without the need for spacers to couple adjacent modules together. Therefore, the side of the first module is preferably directly connected to the side of the second module. By bringing adjacent modules close together, for example, by making the modules directly connected to each other without using extended spacers, the total mass to be cooled is reduced, which allows higher cooling efficiency and lower temperatures to be obtained.

[0016] One, more than one or potentially each thermal stage of the first module can be thermally coupled to the corresponding stage of the second module, and optionally thermally coupled to each of the remaining modules in the system. Typically, the second stage of the first module is thermally coupled to the second stage of the second module. The connected stages are typically arranged to obtain similar operating / base temperatures in use, for example within 1K to 2K. The system preferably also includes one or more extension plates, each of which is arranged to connect adjacent stages of different modules in the system. Therefore, the system can be arranged so that one or more stages of the first module are thermally coupled to the corresponding stages of the second module by one or more extension plates that mechanically connect the thermal coupling stages. Therefore, the extension plate can enhance the thermal conductivity between the stages of adjacent modules. In fact, this expands the thermal stage of the first module, for example, so that experimental services can be shared between different modules. Similarly, the cooling power applied to the stage of the first module can then be transferred to another stage of the adjacent second module to compensate for the higher heat load that may be applied to the second module by the experimental service. This means that a larger heat load can be applied to the thermal stage, for example, by combining cables or components that require more dissipation, which may be desirable in some applications. For example, each of the extension plates may be configured such that at a temperature of 20 K, the effective thermal conductivity between the connected stages is higher than 5000 W / mK.

[0017] The extension plates may also perform a thermal shielding function by blocking direct radiation paths between different temperature stages in adjacent modules. For example, the system may include a plurality of said extension plates, wherein one or more of said extension plates are configured such that at a temperature of 20K, the effective thermal conductivity between connected stages is above 5000 W / mK, and wherein one or more of said extension plates are configured such that at a temperature of 20K, the effective thermal conductivity between connected stages is below 50 W / mK. Lower thermal conductivity plates may be used to increase the structural rigidity of an assembly or thermal shield without providing effective thermal coupling between connected stages. This may open up new modes of operation and experimentation that are difficult to replicate using conventional cryostat designs.

[0018] The connected levels are usually at similar heights on different modules. The multiple levels of each module are usually arranged in a layered manner, for example, the first level extends along a plane parallel to the second level, and is spatially dispersed with the second level along an axis orthogonal to the first and second levels. Each level of the first module is preferably coplanar or approximately coplanar with the corresponding level of the second module. Then, one or more extension plates are usually arranged to mechanically connect one or more levels of the first module to the corresponding coplanar level of the second module. The extension plate is usually planar and can bridge the gap between the coplanar levels of adjacent connected modules, effectively extending these levels to form a common connected level of the system. Depending on the experimental needs, the extension plate can be included between any coplanar level or all coplanar levels of the connected modules.

[0019] One or more of the multiple levels typically include one or more level connectors for connecting extension plates between coplanar or "corresponding" levels of the first and second modules. For example, the level connector may include specific means for connecting to the extension plates, such as fastening members disposed at the periphery of the corresponding level or an array of holes for the fastening members. At least one of the one or more extension plates preferably includes an expandable joint. Such a joint can maintain a mechanical connection between the connected levels during relative movement of the connected levels, such as a mechanical connection created by contraction and expansion of components during thermal cycling. For example, at least one of the one or more extension plates may include a braided joint.

[0020] Each stage is usually formed as a platform, (for example) the components of the cryogenic cooling system or the heat sink elements in the electrical system can be mounted on the platform. Each stage is usually a plate formed by a high thermal conductivity material (such as copper) at low temperature. Each stage is usually arranged to obtain a corresponding base temperature by the operation of a cryogenic refrigerator, and therefore can also be referred to as a "hot stage". The cryogenic refrigerator is usually configured to cool each of the stages to cryogenic temperatures (these temperatures are lower than 100 Kelvin) during use. These stages are usually arranged so that the longitudinal axis is orthogonal to the surface extension of each stage. The cryogenic refrigerator is usually configured to apply a thermal gradient (usually along the longitudinal axis) between the stages. Therefore, these stages are usually arranged so that the base temperature of each stage gradually becomes colder in the direction extending between the multiple stages.

[0021] The system is typically configured so that the multiple stages of each of the modules share a common internal volume defined by the housings of the connected modules. The internal volume of the system is typically sealed from the surrounding environment, and the area containing the stages of each module is typically evacuated. This allows the system to operate without the need for gas handling equipment to exhaust any unwanted gases that may liquefy or solidify at low temperatures.

[0022] Radiation shields can be provided on each module and connected together to form a larger radiation shield assembly surrounding the cryogenic components of the system. Each of the modules typically includes one or more radiation shields, each of which is thermally coupled to a corresponding stage of the module and surrounds one or more remaining stages, and each of which includes one or more shield surfaces. The system may also include one or more shield extensions, each of which connects the coplanar shield surfaces of adjacent connected modules, and the coplanar shield surfaces of these adjacent connected modules are generally maintained at approximately the same temperature during use. For a module housing having four orthogonal sides and connected to another module in the system, each of the radiation shields may include one, two or three orthogonal side surfaces extending perpendicular to the corresponding thermally coupled stage. It should be understood that the multiple stages of each of the modules in the system are typically not completely surrounded by the radiation shield of the module, because space should be left for thermally connecting adjacent stages of different modules and / or running experimental services between modules within the internal volume.

[0023] One or more radiation shields may also include a shield connector for connecting shield extensions between adjacent radiation shields of the first module in the second configuration and the second module in the second configuration. Shield extensions may be required in the event that there is a gap between coplanar side surfaces of portions of the radiation shields forming adjacent modules, the shield extensions being arranged to bridge the gap so that the shields of adjacent connected modules are joined together to enclose the cryogenic components of the system.

[0024] Different cryogenic refrigerators can be used, including "wet" refrigerators and cryogen-free ("dry") cryogenic coolers (also referred to herein as mechanical refrigerators) or a combination of the two. The use of cryogenic coolers (such as pulse tube refrigerators, Stirling refrigerators or Gifford-McMahon refrigerators) is particularly cost-effective in smaller devices (e.g., when the system includes up to three connected modules). For systems with more than three modules, it is generally more effective to cool the stages of one or more modules by thermal contact with a refrigerant such as liquid nitrogen or helium. The refrigerant can be stored in one or each of the modules, such as in a Dewar flask / reservoir. Alternatively, the refrigerant can be stored in an external refrigeration device and transported through the module via a conduit. The cryogenic refrigerator can therefore include a conduit for circulating the refrigerant through the module, the conduit including one or more heat exchangers that thermally couple the conduit to one or more of the multiple stages. Such a conduit can generally be used to obtain a temperature below 4 Kelvin, particularly when the refrigerant is helium. The cryogenic cooling assembly may therefore include a helium refrigeration device, which is preferably arranged outside the housing of each module. In this case, one or more of the modules preferably include a first helium heat exchanger thermally coupled to the module's stage, which is arranged to receive a liquid helium flow from the helium refrigeration device. One or more of the modules preferably also include a second helium heat exchanger thermally coupled to a different stage of the module, the second helium heat exchanger being arranged to receive a gaseous helium flow from the helium refrigeration device at a temperature below 100K, preferably between 40K and 80K, more preferably between 50K and 70K. Additionally or alternatively, the cryogenic cooling assembly may include a nitrogen refrigeration device, which is preferably arranged outside the housing of each module. In this case, one or more of the modules preferably include a nitrogen heat exchanger thermally coupled to the module's stage, which is arranged to receive a liquid nitrogen flow from the nitrogen refrigeration device. It should be understood that the nitrogen heat exchanger will be located on a different thermal stage from the first helium heat exchanger.

[0025] In order to achieve sub-millikelvin cooling, one or more modules of the system preferably include a dilution unit of a dilution refrigerator. As previously mentioned, the dilution unit includes a distiller and a mixing chamber. In a particularly desirable embodiment, the first module includes a first dilution unit, and the second module includes a second dilution unit. For example, the first dilution unit may include a distiller installed to a distiller level in a plurality of levels for the first module, and the second dilution unit may include a distiller installed to a distiller level in a plurality of levels for the second module, wherein the distiller levels of the first module and the second module are mechanically connected by extension plates. The distiller levels are generally coplanar, and the extension plates extend between the distiller levels. Depending on the application, the distiller levels connected by the extension plate thermal coupling may be helpful, in which case the extension plate should have a relatively high thermal conductivity. However, in some applications, it may be desirable to have a low effective thermal conductivity between the connected distiller levels, such as so that the heat load applied to one distiller level will not be conducted to another distiller level. In these cases, at a temperature of 20K, the effective thermal conductivity between the distiller levels of the first module and the second module is preferably less than 50W / mK. This arrangement enables the two stills to operate at different steady state temperatures, which may be desirable for certain applications.

[0026] Similarly, the first dilution unit may include a mixing chamber mounted to a mixing chamber stage for a first of the plurality of stages of the module, and the second dilution unit may include a mixing chamber mounted to a mixing chamber stage for a second of the plurality of stages of the module, wherein the mixing chamber stages of the first and second modules are mechanically connected by an extension plate that generally extends between the coplanar mixing chamber stages. It may be desirable to physically connect the mixing chamber stages of the first and second modules respectively without providing effective thermal coupling, in which case the extension plate connecting the mixing chamber plates may be configured such that the effective thermal conductivity between the mixing chamber stages of the first and second modules respectively is less than 50 W / mK at a temperature of 20 K.

[0027] In a preferred embodiment, the first module comprises two or more dilution units, wherein the first dilution unit is preferably arranged such that the first distiller is on the first stage and the first mixing chamber is on the second stage, wherein the second dilution unit is preferably arranged such that the second distiller is on the first stage and the second mixing chamber is on the third stage, the second stage being arranged between the first and third stages. Thus, each of the first, second and third stages can be provided with an active cooling source (in particular a distiller or a mixing chamber). For example, the second stage is thus not dependent on the cooling power of the adjacent first and third stages to compensate for any heat load applied to the second stage.

[0028] The system can be configured to enable various experimental services to be run between different modules. The system preferably includes a target assembly comprising a circuit (e.g., a cable) extending within the system's internal volume between one or more stages of a first module to one or more stages of a second module. For example, the target assembly may form part of a quantum computer. Thus, each module may form an extensible platform for supporting a quantum information processing device.

[0029] Different cryogenic refrigerators can be arranged in different connected modules. In a particularly desirable embodiment, the first module includes a cryogenic refrigerator in the form of a dilution unit or a helium-4 refrigerator with a 1K pot, and the second module or the third module having a stage thermally coupled to the corresponding stage of the first module includes a cryogenic refrigerator in the form of a cryogenic cooler and / or a liquid refrigerant storage. The storage can take the form of a Dewar flask or any suitable tank / container for containing liquid refrigerants. If the storage and the cryogenic cooler are arranged in one module, the storage can be arranged to collect the refrigerant liquefied by the operation of the cryogenic cooler. The storage can be operated to cool one or more stages of the first module, for example, by the refrigerant flowing along a conduit thermally coupled to one or more stages of the first module. The storage can serve as a fault protection mechanism to maintain the cryogenic temperature within the module in the event of a power failure, otherwise, for example, it may affect the operation of any cryogenic cooler. Typically, in the event of a power failure, the storage passively cools the components of the system by conduction, for example, by fixing to one or more stages of the system. Alternatively, active control can be envisioned. For example, the system may further include a controller configured to operate a reservoir to cool one or more stages of the first module in response to a change in state of the cryogenic refrigerator in the system. The controller is typically an electronic controller that may be powered by a battery. The controller is preferably configured to monitor the operation of one or more cryogenic coolers in the system and to operate the reservoir to cool one or more stages of the first module in response to detecting a failure of the monitored cryogenic cooler. The failure may be an unexpected interruption in the operation of the compressor, such as may be caused by a lack of power or a mechanical component failure.

[0030] Preferably, one, more than one or preferably each of the modules in the system further comprises a thermal switch assembly connected to one or more of the plurality of stages, the thermal switch assembly being operable to selectively thermally couple adjacent stages of the plurality of stages. For example, the thermal switch assembly may comprise one or more air gap thermal switches and / or one or more heat pipes. The thermal switch assembly is operable to control thermal conductivity across the assembly, for example allowing the stages to have high thermal conductivity to each other during initial cooling from room temperature, and thermally isolating the respective stages from each other at temperatures below 4 Kelvin or during steady state operation.

[0031] The QIP system may require high cooling power to be applied to each lowest temperature stage. Thus, in a particularly desirable embodiment, the plurality of stages of a first said module comprises a distiller stage, a cold stage, and a mixing chamber stage, the cold stage being disposed between the distiller stage and the mixing chamber stage, the first said module further comprising three dilution units, each said dilution unit comprising a distiller thermally coupled to the distiller stage of the first said module, wherein the first dilution unit further comprises a mixing chamber thermally coupled to the cold stage, and wherein the second dilution unit and the third dilution unit each comprise a mixing chamber thermally coupled to the mixing chamber stage of the first said module.

[0032] Preferably, one or more modules of the system are configured to allow convenient sample acquisition and exchange by using an auxiliary insert with experimental equipment (usually including samples) to be connected to the module. For example, one or more of the modules may include a main insert and a removable auxiliary insert, the main insert including a plurality of main boards formed by corresponding stages of the module, the auxiliary insert including a plurality of auxiliary boards connected in a self-supporting structure, and the system further includes one or more adjustment members, the one or more adjustment members being configured so that when the auxiliary insert is mounted to the main insert, the adjustment members bring the main boards and the auxiliary boards into thermally conductive contact.

[0033] The system design is particularly suitable for QIP applications and for setting up server farms with 1000+ logical qubit systems and error correction. Such large wiring requirements benefit not only from the increased experimental space obtained by connecting multiple modules, but also from the higher cooling power obtained, for example, by connecting multiple dilution refrigerators within the same cryostat. As mentioned above, the modular design also enables multiple cooling technologies to be implemented, distributed in different modules, and facilitates new operating modes. A second aspect of the invention is a quantum information processing device including a cryogenic cooling system according to the first aspect. The features discussed in conjunction with the first aspect of the invention also apply to the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Embodiments of the present invention will now be discussed with reference to the accompanying drawings, in which:

[0035] FIG1 is an external perspective view of a cryogenic refrigerator according to the prior art;

[0036] FIG2 is a perspective cross-sectional view of a cryogenic refrigerator according to the prior art;

[0037] Figure 3 is a schematic diagram of a first module for forming a part of a system according to a first embodiment;

[0038] Figure 4 is a first perspective view of a first module according to a first embodiment;

[0039] Figure 5 is a second perspective view of the first module according to the first embodiment;

[0040] Figure 6 is a perspective view of a first module and a second module for forming a system according to a first embodiment;

[0041] Figure 7 is a perspective view of a cryogenic cooling system including a first module and a second module according to a first embodiment;

[0042] Figure 8 is a schematic diagram of a first arrangement of a cryogenic cooling system including a first module and a second module according to a first embodiment;

[0043] Fig. 9 is a schematic diagram of a low temperature cooling system according to a second embodiment;

[0044] Fig.10 is an exploded perspective view of a first module forming part of a second embodiment;

[0045] Fig.11 is a perspective view of a portion of a first module according to a second embodiment;

[0046] Fig.12 is a perspective view of a cryogenic cooling system according to a third embodiment;

[0047] Fig.13 is a perspective view of a first portion of a cryogenic cooling system according to a third embodiment;

[0048] Fig.14 is a perspective view of a second portion of the cryogenic cooling system according to the third embodiment.

[0049] Fig.15 is a schematic diagram showing a system according to a fourth embodiment of the present invention;

[0050] Fig.16 is a schematic diagram showing a system according to a fifth embodiment of the present invention;

[0051] Fig.17 is a schematic diagram showing a system according to a sixth embodiment of the present invention; and

[0052] Fig.18 is a schematic diagram showing a system according to a seventh embodiment of the present invention. DETAILED DESCRIPTION

[0053] Now refer to Figures 3 to 5A first module 100 for forming part of a cryogenic cooling system according to a first embodiment of the present invention is discussed. The module 100 comprises a generally cubic housing 110 having six orthogonal faces, in contrast to the conventional cylindrical design shown in FIGS. 1 and 2 . The housing has a frame 21 (see Figure 4 ), the frame 21 supports four orthogonal sides extending between the upper and lower surfaces of the housing 110. The upper surface supports the stacked assembly of cooling stages 105 to 109 and two cryogenic refrigerators. The first cryogenic refrigerator is a mechanical refrigerator in the form of a pulse tube refrigerator (PTR) 103 (also referred to as a "cryogenic refrigerator" /

[0054] "refrigerant-free refrigerator"). Alternative mechanical refrigerators that may be used include Gifford-McMahon (GM) refrigerators and Stirling refrigerators. The second cryogenic refrigerator is a dilution unit comprising a distiller 30 and a mixing chamber 31 connected by a set of heat exchangers. The housing is configured to form a vacuum chamber 101 when fully assembled, the interior of which (containing the cryogenic refrigerator and cooling stages 105 to 109) is evacuated in use.

[0055] The assembly of cooling stages 105 to 109 comprises a PT1 stage 105 and a PT2 stage 106. A first stage of a PTR 103 is mounted to the PT1 stage 105 for cooling the PT1 stage 105 to a base temperature of 50K to 70K. A second stage of the PTR 103 is mounted to the PT2 stage 106 for cooling the PT2 stage 106 to a base temperature of 3K to 5K. The assembly further comprises a distiller stage 107 and a mixing chamber stage 109 thermally coupled to the distiller 30 and the mixing chamber 31, respectively. A working fluid formed by a mixture of helium-3 and helium-4 circulates around the dilution unit via a pumping line during operation. The distiller stage 107 and the mixing chamber stage 109 obtain base temperatures of 0.5K to 2K and 5mK to 20mK, respectively, in use. The “cold plate” 108 forms an additional hot stage (hence also referred to herein as a “cold stage”), which is arranged between the distiller stage 107 and the mixing chamber stage 109 and obtains a temperature between the distiller stage 107 and the mixing chamber stage 109, typically 50mK to 150mK.

[0056] A thermal switch assembly (not shown) comprising a plurality of air gap thermal switches selectively thermally couples each cooling stage 106 to 109 in use. The thermal switch assembly is configured to allow heat exchange between the cooling stages 106 to 109 during an initial cooling procedure and to thermally isolate the different stages at low temperatures. Optionally, one or more heat pipes may also be provided, for example between the PT1 stage 105 and the PT2 stage 106. The heat pipes may operate in conjunction with the PTR 103 and the air gap thermal switches to further accelerate the pre-cooling process. The combination of the air gap thermal switches, heat pipes and low thermal conductivity support rods connected to the housing 110 maintains the stages 105 to 109 in the stacked arrangement shown.

[0057] A nested assembly of thermal radiation shields is disposed within the module 100, each thermal radiation shield being connected to a corresponding thermal stage and surrounding low temperature components. The first thermal radiation shield 41 is connected to the PT1 stage 105, the second thermal radiation shield 42 is connected to the PT2 stage 106, and the third thermal radiation shield 43 is connected to the distiller stage 107, wherein the second thermal radiation shield 42 is arranged between the first thermal radiation shield 41 and the third thermal radiation shield 43. The first thermal shield 41 and the second thermal shield 42 are typically aluminum, while the third thermal shield 43 is typically copper. The thermal radiation shields 41 to 43 are configured to form a closed structure when fully assembled and mounted to the corresponding thermal stage, and will surround components of the system that are configured to be cooled to a lower temperature. The thermal radiation shields 41 to 43 have four orthogonal side surfaces that are configured to fit together. In the present embodiment, as Figure 5 As shown, each side surface of each thermal radiation shield includes two coplanar removable panels for providing external access to the area contained by the thermal radiation shield. A handle is connected to the exterior of the side to facilitate assembly and disassembly.

[0058] Figure 4 An external view of the module 100 is provided in a first configuration, wherein the housing 110 is fully assembled. In the first configuration, the module 100 is configured to operate as a stand-alone cryogenic cooling system to achieve cryogenic temperatures inside the module 100. In this embodiment, each side of the housing 110 has a removable panel that can be removed from the frame 21 to provide access to the interior volume of the module 100 defined by the interior of the housing 110. Figure 5 , the front removable panel 35 is removed from the front side 22 of the module 100 (at Figure 4 ), to expose the front side surface of the first thermal radiation shielding cover 41, and the first thermal radiation shielding cover 41 may be removed if necessary, for example, for maintenance.

[0059] Another example where a removable panel may be removed from a side of module 100 is for connecting module 100 to an adjacent module. Module 100 is also configured to operate in a second configuration as part of an integrated cryogenic cooling system comprising a plurality of such modules connected at respective sides. Figure 6 and Figure 7 An example is shown in which two Figures 3 to 5 Such modules are connected together to form an integrated cryogenic cooling system according to the first embodiment. Figure 6 As shown, the removable panel is removed from the right side of the first module 100, and the removable panel is removed from the left side of the second module 150. Then, the first module 100 and the second module 150 are arranged so that the right side of the first module 100 abuts against the left side of the second module 150. The frame 21 for the first module and the second module includes a housing connector 120, which includes a flange on the outside of the housing 110 and a sealing member arranged around the outside of the area for the removable panel. The flange on the right side of the first module 100 is arranged to cooperate with the flange on the left side of the second module 150 by a fastening member (such as a bolt, etc.) that connects the flanges together.

[0060] Once connected, the first module 100 and the second module 150 form a common cryogenic cooling system, the internal volume of which comprises the sum of the internal volumes of the connected modules. Figure 7 As shown. The housings of modules 100, 150 are joined together so that the sealed internal volume of the system including the stages from each module can be evacuated. The thermal radiation shielding side surfaces on the right side of the first module 100 and the left side of the second module 150 are removed. During system assembly, additional radiation shielding side surfaces and sides of the module housings can be removed to provide access and then reassembled. This arrangement creates a large sample space to run experiments that are much larger than those run in a typical single unit cryostat. This has the advantage of not only more space but also more cooling power because one or more adjacent thermal stages of different modules are thermally coupled together.

[0061] In this embodiment, the first module 100 and the second module 150 are configured such that when the first module 100 is connected to the second module 150 via the housing connector 120, each thermal stage of the first module is coplanar with the corresponding thermal stage of the second module 150. This means that adjacent coplanar thermal stages can be connected together by an extension plate 160 extending between adjacent coplanar thermal stages. The extension plate 160 can provide structural benefits in terms of increasing the rigidity of the assembly and has a thermal insulation effect. The extension plate 160 can also be used for heat transfer purposes, such as coupling cooling power from a cryogenic refrigerator on one module to a thermal stage on another module. In this case, a high thermal conductivity material such as copper can be used to form the extension plate. A stage connector 50 is provided at the periphery of each stage 105 to 109, and the stage connector 50 is in the form of an array of holes and bolts for connecting to the extension plate or any other suitable fastening device. These are in Figure 3 100 , where a stage connector 50 is provided at each end of each thermal stage to enable the stage to extend in either direction for connection to an adjacent module to the left or right of the module 100 .

[0062] As previously described, the radiation shields 41 to 43 surround the cryogenic components of the system and are respectively mounted to a corresponding one of the PT1 stage 105, the PT2 stage 106, and the distiller stage 107. Therefore, the width of the PT2 stage 106 is smaller than the width of the PT1 stage 105, the width of the distiller stage 107 is smaller than the width of the PT2 stage 106, and the widths of the cold plate 108 and the mixing chamber stage 109 are also smaller than the width of the distiller stage 107. Therefore, the lateral spacing between the coplanar thermal stages of two adjacent modules is different for each stage. Therefore, as Figure 8 As shown, extension plates 160 of different sizes are used to bridge the gaps between the stage connectors 50 on corresponding stages.

[0063] In a first embodiment, the first radiation shield, the second radiation shield, and the third radiation shield 41 to 43 are configured to surround the cryogenic components of the system. Figure 3 In the configuration shown, each radiation shield has four orthogonal side surfaces, however, when connected to another module in the system, at least one of these side surfaces is removed. This allows experimental services such as wiring to extend between different modules. Multiple shield extensions 180 in the form of plates are assembled to connect to the coplanar surfaces of the radiation shields of the connected modules. Direct physical contact between adjacent radiation shields is generally not required, however, shield connectors 55 are preferably provided at each end of each radiation shield to enable adjacent shield extensions 180 to interlock and preferably be thermally coupled. The shield connector 55 may include any interlocking features, flexible joints, hole and bolt arrays, or any other suitable fastening means for connecting the shield extensions 180.

[0064] Although only two modules are coupled together in the first embodiment, it will be appreciated that any number of modules may be connected together to increase the size of the system. Furthermore, the system is not limited to a one-dimensional array of connected modules, and a two-dimensional array may also be envisioned. A particular benefit of the cubic module design is that it allows the modules to fit closely together. This makes efficient use of available floor space. It also means that the housings of adjacent modules can be directly connected to one another, eliminating the need for any "spacers" between modules, which would increase the size and mass of the system and thus negatively affect cooling performance.

[0065] exist Figure 8 In a first embodiment, two modules 100, 150 are coupled together, each module having the same cryogenic refrigerator configuration. In particular, each module forms a cryogen-free dilution refrigerator, and the PTR and dilution unit are as described in reference Figure 3 However, a particular advantage provided by the modular design is the flexibility of having different chiller arrangements in different modules of the system. Fig. 9 A second embodiment is shown which is substantially the same as the first embodiment, but the mixing chamber 31' of the second module 250 is mounted on a cold plate 208'. Thus, the cooling power applied to the cold plate 208' is significantly increased compared to the first embodiment. This cooling power is also transferred from the first module 200 to the cold plate by means of a copper stage extension plate which thermally couples the coplanar cold plate. Thus, the cold plates of the first module 200 and the second module 250 are not completely dependent on the cooling power of the adjacent stages, but have a dedicated cooling source. This means that they have a greater ability to withstand thermal loads, such as those which may be applied by components of a QIP system, without significantly increasing the operating temperature of the system.

[0066] Fig.10 and Fig.11A perspective view of the first module 200 of the second embodiment is shown. Similar to the first embodiment, a housing connector 220 is provided on each of two opposite sides for directly connecting the module 200 to an adjacent module. The housing connector 220 includes a sealing member 220 surrounded by a bolt and an array of holes. In this embodiment, the housing connector on the right side of the first module 200 is configured to be connected to a corresponding housing connector on the left side of the second module 250. The removable panel 135 can be assembled to the left and right sides of each housing by bolts to close the internal volume of the module 200 and facilitate the independent operation of the module 200. The removable panel 135 is removed to allow the module 200 to be connected to one or more adjacent modules. The sealing member 220 is capable of forming a vacuum seal between the connected housings. In this embodiment, the sealing member 220 includes an O-ring groove and an O-ring on the right side of the first module 200, configured to engage with an O-ring seal disposed on the left side of the second module 250. However, other types of sealing members, such as blade gasket seals, etc., may also be used.

[0067] The front of the module 200 includes a door 210, which is securely mounted to the housing by hinges and bolts so that a vacuum can be maintained inside the housing. The door 210 can be opened to provide access to the interior of the module 200, for example, when servicing and adjusting any bolts (such as those provided on the sides of the housing or radiation shield).

[0068] Fig.12 A perspective view of a system according to a third embodiment is shown, wherein the door 210 of each module 200, 250 is not shown in order to illustrate the various connections between the two modules 200, 250. The third embodiment is substantially the same as the second embodiment and uses the same general module design. However, in the third embodiment, the extension plate between the cold plates 208, 208' is removed so that the cold plate 208 of the first module 200 is disconnected and thermally decoupled from the cold plate 208' of the second module 250. In an alternative embodiment, by using an extension plate with low thermal conductivity (e.g., formed partially or entirely of a material such as plastic or stainless steel), any thermal stage can be thermally decoupled without destroying their physical connection. As an example, it may be desirable to thermally decouple adjacent coplanar stages so that heat from electrical components on a thermal stage of the first module is not conducted to the second module.

[0069] As each module of the system cools down from room temperature, adjacent thermal stages will contract away from each other and may cool at different rates, depending on the exact configuration of each module. There will also be manufacturing tolerances to accommodate. To overcome these issues, the thermal stages in each module can be "indirectly" connected to each other via flexible joints. Reference will now be made to Fig.13 Let's discuss an example of this connection.

[0070] Fig.13 The connection between the coplanar thermal stages of the first module 200 and the second module 250 from the third embodiment is shown. In particular, Fig.13 A flexible mechanical connection is shown formed between the PT1 stage 205 of the first module 200 and the PT1 stage 205' of the second module 250. Similar connections are made between each of the remaining coplanar stages, except for the unconnected cold plates 208, 208' (as previously described). Stage connectors 251 are provided on the left and right sides of each stage for allowing connection between coplanar stages through one or more intermediate extension plates. In this embodiment, the PT1 stage 205 of the first module 200 is connected to the PT1 stage 205' of the second module 250 through the first extension plate 206a and the second extension plate 206b. The undersides of the first extension plate 206a and the second extension plate 206b are linked together by an expandable joint 266, which includes a high thermal conductivity soft braid, for example, made of copper. The expandable joint 266 allows good thermal conduction between adjacent PT1 stages 205, 205' and relative movement between the stages (such as movement that may occur during thermal cycling).

[0071] A labyrinth structure 265 is provided to assist in radiation shielding in the region between the ends of the two extension plates 260a, 260b. The labyrinth structure 265 is formed by disposing a downwardly directed lip on the end of the first extension plate 260a within an upwardly directed lip on the adjacent end of the second extension plate 260b. Additional light absorbing material may be applied to the interface between the two lips inside the labyrinth structure 265 to further assist in thermal shielding. The labyrinth structure 266 allows relative movement between the first extension plate 206a and the second extension plate 206b, which may cause the lips to contact each other. Other methods for connecting adjacent thermal stages can be envisioned, including by using interlocking or staggered components that expand when the connected stages are contracted, thereby maintaining physical (and preferably also thermal) contact between the stages.

[0072] Similar to Fig.13 The structure shown can be used to connect a thermal radiation shield. Fig.12 As shown, each coplanar heat shield of the first module 200 and the second module 250 is coupled together by two heat shield extensions. For example, the first shield extension 280a is mounted to the third shield 143 of the first module 200 through the shield connector 155, which is connected in the same manner as the shield connector 155. Fig.13 The second shield extension 280b is mounted to the third heat shield 143 of the second module 250 via a similar shield connector 155. Fig.14As shown, the first shield cover extension portion 280a and the second shield cover extension portion 280b are coupled together by a shield cover labyrinth structure 275, which is similar to a combined shield cover labyrinth structure. Fig.13 The maze-like structure 266 discussed above. In this case, the end of the first shield extension 280a forms a lip that is disposed within another lip formed on the end of the second shield extension 280b. This engagement allows for some relative movement between the shield extensions 280a, 280b (such as may occur during thermal cycling) and some misalignment due to manufacturing tolerances. A similar coupling is provided between each adjacent coplanar shield extension.

[0073] In practice, the system provides an extendable cryostat comprising an extendable vacuum chamber and an extendable temperature stage. Figures 7 to 9 As discussed, this extensibility allows multiple independent cryostats (or "modules") to be strongly mechanically and strongly thermally coupled together and operated at the same or similar temperatures at corresponding / adjacent thermal stages of each cryostat. Extensibility also allows multiple modules to be strongly (or weakly) mechanically coupled together and operated as a single entity with different temperatures at corresponding / adjacent thermal stages of each module. Fig.12 An example is shown where the co-planar cold plates 208, 208' are separated and therefore thermally decoupled from each other. Another example will now be discussed.

[0074] Fig.15is a schematic diagram showing a system according to a fourth embodiment of the present invention, the fourth embodiment having non-isothermally connected stages. A first module 300 is connected to a second module 350 to form an integrated cryogenic cooling system. The arrangement is substantially the same as the first embodiment, except that the distiller stage 307, cold stage 308 and mixing chamber stage 309 of the first module are not thermally coupled to the corresponding distiller stage 307', cold stage 308' and mixing chamber stage 309' of the second module 350. As previously described, all other coplanar stages are thermally coupled. The first stage extension plate mechanically connects the distiller stage 307 of the first module 300 to the distiller stage 307' of the second module 350, and the second stage extension plate mechanically connects the mixing chamber stage 309 of the first module 300 to the mixing chamber stage 309' of the second module 350. This improves the structural rigidity and thermal shielding of the system. However, the first stage extension plate and the second stage extension plate are configured to have a low thermal conductivity, preferably less than 50W / mK at a temperature of 20K. This enables the coplanar connected stages to reach different operating temperatures and can be achieved in a variety of ways. For example, the first stage extension plates and the second stage extension plates may be partially or entirely composed of a material having a relatively low thermal conductivity at the corresponding operating temperature, such as plastic, silicon, or stainless steel, etc. In this embodiment, copper stage extension plates are used as previously described, but these copper stage extension plates are connected together by stainless steel expandable joints 366. The cold stage 308 of the first module 300 is separated from the cold stage 308' of the second module 350 by a gap, so that adjacent cold stages 308, 308' are substantially thermally isolated from each other and can have different temperatures in use.

[0075] In this embodiment, the system forms part of a QIP system, wherein the first module 300 includes an "input" line 381 and the second module 350 includes an "output" line 383 (shown schematically). Electrical conductors in the form of input line 381 and output line 383 are thermally coupled to corresponding cooled stages of the first module 300 and the second module 350, respectively. Input line 381 transmits electrical signals from a location external to the system to a QIP device 382 (e.g., a qubit processor), which is typically thermally coupled to the lowest temperature stage of the system. Output line 383 transmits electrical signals from the QIP device 382 to a location external to the system. Since the input line is one of the largest sources of heat generated in a QIP experiment via active and passive heat dissipation at different stages of the refrigerator, it is beneficial to be able to operate the output line at a lower temperature than the input line. This maintains the signal-to-noise ratio of the output signals before they can be amplified. Typically, the operating temperatures of the distiller stage 307, the cold stage 308, and the mixing chamber stage 309 of the first module 300 will exceed the operating temperatures of the distiller stage 307', the cold stage 308', and the mixing chamber stage 309' of the second module 350, respectively. Optionally, an additional cryogenic refrigerator may be thermally coupled to the input line 381 relative to the output line 383 in order to compensate for the higher heat load provided by the input line 381. For example, the Fig.15 The arrangement shown is such that two PTRs and two dilution units are provided in the first module 300 .

[0076] The ability to "decouple" these cooling stages by only weakly thermally coupling them together is also useful for applications where a first cryogenic refrigerator on a cooling stage operating at a temperature that is more efficient in managing a high heat load, but that temperature is detrimental to the proper operation of another cryogenic refrigerator connected to the cooling stage. Fig.16 Discuss the example, Fig.16 is a schematic diagram showing a system according to a fifth embodiment of the present invention. A first module 400 is connected to a second module 450 to form an integrated cryogenic cooling system. The arrangement is similar to the first embodiment, but for clarity, components of the QIP system are not shown. As previously described, the first module 400 has a pulse tube refrigerator and a dilution unit, the dilution unit including a distiller 430 and a mixing chamber 431. However, the only cryogenic refrigerator provided in the second module 450 is a helium-4 refrigerator, referred to in the art as a "1-K pot" 432, which is configured to receive a helium flow from an external location via a pumping line. The 1-K pot 432 is connected to a "1K stage" 407', which is thermally coupled to the distiller stage 407 via one or more stage extension plates as previously described. Another difference is that the distiller 430 is connected to the distiller stage 407 via a weak thermal link 467 (such as a plastic or stainless steel ring).

[0077] The assembly may form part of a QIP system having any number of connected electrical components that may provide a heat source. The relatively high cooling power of the thermally coupled 1-K pot operating at 1K to 1.5K or 1.2K to 2K, the larger heat loads applied to the distiller stage 407 may be managed efficiently. The distiller of the dilution device ideally operates in the range of 750mK to 850mK. Thus, the weak thermal link 467 advantageously allows the dilution unit to operate at a more optimized state, independent of the temperature of the 1-K pot. This reduces the overall base temperature of the mixing chamber 431, which may improve the performance of the QIP measurement.

[0078] Different types of modules for different purposes can be connected together to form part of an integrated cooling system. Fig.17 5 is a schematic diagram showing a system according to a sixth embodiment of the present invention. A first module 500 is connected to a second module 550 to form an integrated cryogenic cooling system. In this embodiment, the first module 500 includes a pulse tube refrigerator 503 having a first cooling stage connected to a PT1 stage 505 and a second cooling stage connected to a PT2 stage 506 (as described above). In this embodiment, the PT1 stage 505 and the PT2 stage 506 are thermally coupled to a first tank 590 and a second tank 592, respectively. The first tank 590 is mounted to the PT1 stage 505, and the second tank 592 is mounted to a radiation shield thermally coupled to the PT2 stage 506. Each tank is configured to store a liquid refrigerant in use. More specifically, the first tank 590 is configured to contain nitrogen, which is introduced into the system along a first conduit 591 and is typically liquefied in thermal contact with the PT1 stage 505. The second tank 592 is configured to contain helium-4 introduced into the system along a second conduit 593. The second conduit 593 is thermally coupled to the PT1 stage 505 and the PT2 stage 506 through a heat exchanger so that the helium can be liquefied during cryogenic operation when in thermal contact with the PT2 stage 506. In addition to allowing these fluids to enter the first module 500 for entry into the respective tanks 590, 592, the conduits 591, 593 also provide a path for the gas to be exhausted in the event that the system requires heating or liquid evaporation.

[0079] The second module 550 includes a PT1 stage 505' and a PT2 stage 506', which are thermally coupled to the PT1 stage 505 and the PT2 stage 506 of the first module 500, respectively. Optionally, the second module 550 may also include a low-temperature cooler to facilitate independent cooling of the second module (particularly the PT1 stage 505' and the PT2 stage 506') without being connected to the first module 500. In addition, the second module 550 includes three low-temperature thermal stages: a distiller stage 507', a cold plate 508' and a mixing chamber stage 509', and three dilution units connected to the low-temperature stages. The first dilution unit includes a first distiller 530 and a first mixing chamber 531, the second dilution unit includes a second distiller 530' and a second mixing chamber 531', and the third dilution unit includes a third distiller 530" and a third mixing chamber 531". The first distiller 530, the second distiller 530' and the third distiller 530" are each thermally coupled to the distiller stage 507'. The second mixing chamber 531' and the third mixing chamber 531" are thermally coupled to the mixing chamber stage 509', while the first mixing chamber 531 is thermally coupled to the cold plate 508. The combination of three dilution units, one of which has a mixing chamber coupled to an intermediate cold plate, ensures that high cooling power is provided to each of the lowest temperature stages 507', 508', 509'. This arrangement of the second module 550 is particularly effective in managing the heat loads typically introduced by the electrical components of the QIP system.

[0080] In this embodiment, the first module 500 provides a particular advantage in that, if necessary, the first module acts as a fail-safe mechanism for cooling the second module 550. In particular, the first tank 590 and the second tank 592 are configured to cool the PT1 stage 505' and the PT2 stage 506' of the second module 550 in the event of a failure of the PTR 503 or any cryocooler in the system, such as may occur due to a power outage or mechanical failure. In this embodiment, the first tank 590 (containing liquid nitrogen) is configured to maintain the temperature of the PT1 stage 505' at about 70K, and the second tank 592 (containing liquid helium) is configured to maintain the temperature of the PT2 stage at about 4K. The fail-safe mechanism operates passively by relying on the thermal coupling between the tanks 590, 592 and the rest of the system. In the absence of any power, the temperature inside the system can gradually increase depending on the rate of insulation and mass of the liquid refrigerant in the tanks 590, 592. Typically, the temperature of the internal components of the system will approach the boiling point of the liquid refrigerant and be fixed at the boiling point, while any external loads are absorbed by the latent heat of the liquid. If different tanks are set up to hold different refrigerants, the temperature can be fixed at the higher boiling point of the refrigerant. Only after the liquid boils will the temperature start to rise further. The expected liquid volume and heat load should take into account a "holding time" of hours or days. Therefore, the above system is able to maintain the cryogenic temperature inside the system below 100K for at least 24 hours without any electricity.

[0081] Alternatively, in some embodiments, the system includes an electronic controller (typically powered by a battery) configured to detect a change in state of any cryocooler in the system, such as a change in state that may occur due to an unexpected power outage or mechanical failure. For example, the controller may monitor the operation of a motor of a compressor in PTR 503. In response to detecting a change in state, the controller may operate one or more pumps (forming part of the controller) to deliver a refrigerant, typically in liquid form, along a conduit to cool one or more thermal stages of the system. The refrigerant may be delivered from a location within the system (such as a Fig.17 The first tank 590 and the second tank 592 are shown) or delivered from an external Dewar flask.

[0082] The 4K cooling power in dry dilution refrigerators has historically been provided by cryocoolers. The need for these systems has arisen precisely because they are a dry technology. This simplifies the support infrastructure and experience required to operate the system, making the system more useful in an academic environment. However, for commercial-scale systems, there are reliability issues associated with relying on multiple cryocoolers. As the scale of experiments grows, the available cooling power of 4K also quickly becomes insufficient. In loose assumptions, cryocoolers can actually provide up to about 8W of 4K cooling power, assuming 4 disconnected units, each providing 2W. This already represents a significant investment and has a relatively short life. The components have strict duty cycles, and if this cycle is ignored, it will cause the performance of the cryocooler to degrade. In an industrial environment, the 4K cooling power provided by a factory-scale 4He recirculation system is ideal (commercial suppliers include Air Liquide and LindeKryotechnik). Such systems are implemented in medical equipment (such as an MRI machine) or large physics and engineering experiments (such as CERN and ITER), where high reliability and large cooling power are essential. A standard commercial liquefier unit can easily liquefy 280 l / hr of 4He, which translates into 200W of available 4K cooling power (the liquefier has a capacity of >3500 l / hr, equivalent to >2.5kW of 4K cooling power). The helium liquid can circulate in heat exchanger pipes inside one or more modules, providing the required thermal contact for the 4K cooling bus of the QIP system. The factory-level 4K cooling mechanism enables multiple dilution refrigerators to operate on the same 4K cooling loop. This can include separate quantum computers that can perform separate calculations but share the same pre-cooling system. These quantum computers can be in the same module, or in different modules connected in the same vacuum chamber. An embodiment in which components of the system are cooled by liquid refrigerant received from an external refrigeration device will now be discussed.

[0083] Fig.18 6 is a schematic diagram of a system 600 according to a seventh embodiment of the present invention. The system 600 includes a first module 610, a second module 620, a third module 630, and a fourth module 640. The modules are arranged in a one-dimensional array, wherein the second module 620 is connected to the first module 610 and the third module 630 on two opposite sides, and the third module 630 is connected to the second module 620 and the fourth module 640 on two opposite sides. The housings of the modules are connected together as described in the previous embodiments.

[0084] The first module 610 has a first conduit 651 for receiving a liquid nitrogen stream from a refrigeration device (not shown) outside the module. Alternatively, the first conduit 651 can receive a cold helium gas stream diverted from a helium refrigeration device before the final liquefaction stage. The first conduit 651 is thermally coupled to the first stage 601 of the first module 610 through a first heat exchanger 653. The first module 610 also has a second conduit 655 for receiving a liquid helium stream from the refrigeration device. The second conduit 655 is thermally coupled to the second stage 602 of the first module 610 through a second heat exchanger 657. In use, the first conduit and the second conduit are configured to cool the first stage 601 and the second stage 602 to about 50K to 70K and 4K, respectively, by passing the corresponding refrigerants through the first heat exchanger 653 and the second heat exchanger 657. This provides an alternative to the use of a cryocooler, which is particularly desirable in large-scale installations with more than three connected modules for the reasons described above.

[0085] A variation of this scheme is that the incoming liquid helium-4 flow is used to maintain a large amount of liquid helium in a storage tank thermally connected to the second stage. If the operation of the liquefier is interrupted for a period of time, the use of an internal helium storage will allow the system to continue to operate. It should be noted that if the cooling power required for the second stage is only on the order of a few watts, a helium liquefaction system using a cryocooler (such as Fig.17 ) can be used in the same manner. In this case, when the cryocooler liquefier is replaced with a spare unit, the use of internal storage will allow the system to continue to operate, thereby alleviating concerns about the reliability of the cryocooler. For systems with low cooling power requirements, where the cryocooler can be used to replace a plant-scale helium-4 recycling system, there are known methods in the art that can be used to alleviate the reliability issues of the cryocooler in addition to the cryocooler-based liquefier. However, the number of cryocoolers installed on the system will generally exceed the number strictly required for operation, so the system is able to operate with one or more cryocoolers out of service.

[0086] Returning to the seventh embodiment, the first stage 601 and the second stage 602 of the first module are thermally coupled to the corresponding coplanar stages of the second module 620, the third module 630 and the fourth module 640 through the stage extension plate (as described above) to form a common isothermal stage across the system. Optionally, the aforementioned first conduit 651 and the second conduit 655 can be connected to the corresponding isothermal stage plate on each module in a repeated manner through corresponding heat exchangers, as shown by the dotted lines at the ends of the first conduit 651 and the second conduit 655. Appropriate ports can be provided on the top surface of each module to facilitate the flow of fluid into and between the modules.

[0087] The second module 620 includes a helium-4 refrigerator 632 (also referred to as a "1-K pot") configured to cool the third stage 603 to approximately 1 K. The third stage 603 is thermally coupled to a corresponding coplanar stage of the third module 630, however the third stage is separated from the coplanar third stage 603' of the fourth module 640 by a gap. This enables the third stage 603' of the fourth module 640 to operate at a different temperature than the third stages 603 of the second module 620 and the third module 630. This may be desirable in certain circumstances, as discussed previously with reference to the fourth embodiment.

[0088] The third module 630 has a fourth stage 604 and a fifth stage, the fourth stage 604 being thermally coupled to the corresponding thermal stage of the fourth module 640, the fifth stage forming the lowest temperature stage and not connected to any corresponding stage of the connected modules. The third module 630 also includes a first dilution unit having a first distiller 635 mounted to the third stage 603 by a weak thermal link 667 (such as in combination with Fig.16 605) and a first mixing chamber 636 mounted and thermally coupled to the fifth stage 605. The fourth module 640 includes a second dilution unit having a second distiller 635' mounted to the third stage 603' of the fourth module 640 and a second mixing chamber 636' mounted to the fourth stage 604. This arrangement ensures that each thermal stage is thermally coupled to a respective cryogenic refrigerator, which is particularly advantageous in compensating for heat loads, such as may be applied by any connected electrical equipment.

[0089] Optional QIP system components are available in Fig.18 Schematically shown in FIG. Input line 681 is sequentially connected to each of the first stage 601, the second stage 602, and the third stage 603 within the second module 620. Input line 681 then extends from the third stage 603 within the second module 620 to the third module 630. Input line 681 is then connected to each of the fourth stage 604 and the fifth stage 605 within the third module 630, and to the QIP device within the third module 630, which is thermally coupled to the fifth stage 605. Input line 681 is thereby cooled by each connected thermal stage and is arranged to transmit an electrical signal from a location external to system 600 to QIP device 682. Output line 683 is arranged to transmit an electrical signal from QIP device 682 to another location external to system 600. The output line 683 extends from the QIP device 682 into the fourth module 640 and is then sequentially connected to each of the fifth stage 605 , the fourth stage 604 , the third stage 603 ′, the second stage 602 , and the first stage 601 within the fourth module 640 .

[0090] The seventh embodiment illustrates how the common internal volume of the system 600 created by the connected modules can be used for different parts of the QIP system. The seventh embodiment also shows how the cooling components from the different modules can be used to compensate for the heat loads imposed by the connected electrical equipment (e.g., the heat load caused by the operation of the RF attenuator forming part of the input line 681). In the present case, the relatively large heat load provided by the input line 681 at the third stage 603 is mitigated by the cooling power of the dedicated 1-K pot 632 rather than the distiller of the dilution unit which may have less cooling power. The first distiller 635 is thermally isolated from the input line 681 and the 1-K pot 632 by using a low thermal conductivity link 667. At the fourth stage 604, the heat load from the input line 681 is absorbed by the second mixing chamber 636' which forms part of a dedicated "cold stage dilution refrigerator". This allows the first dilution unit in the third module 630 to be "unloaded" in an otherwise manner, so that the first mixing chamber 636 can operate optimally to reduce the temperature of the QIP equipment 682 and reduce the overall base temperature of the system 600. In use, the fourth stage 604 typically achieves a base temperature of about 100 mK to 200 mK, and the fifth stage 605 typically achieves a base temperature of about 10 mK to 20 mK, or possibly lower, depending on the heat load imposed by any connected electrical equipment.

[0091] It should be understood that the modular approach described herein provides the user with the flexibility of combining different modules with corresponding refrigeration arrangements according to experimental needs. For example, the operation of multiple closed-loop (or open-loop) refrigerators (including dilution refrigerators, helium-3 refrigerators or helium-4 refrigerators) in a cryostat allows the cooling power of several cooling systems to be combined by isothermally mechanically strongly coupling and thermally strongly coupling the cooling stages of these refrigerators. This can be achieved by linking the mixing chambers of multiple dilution units together using high thermal conductivity materials at the cold stage. Alternatively, the cooling power of several cooling systems can be separated by mechanically strongly (or weakly) coupling but weakly thermally coupled mode, and their cooling stages are coupled together so that these cooling stages are non-isothermal. This can be achieved by operating a mixing chamber of a dilution unit at one temperature, and another mixing chamber of another dilution unit at different temperatures. In addition, the cooling at the PT2 level (usually having an operating temperature of about 4K) can also be provided by any one (or any combination) of a cryocooler, a dry mechanical contact portion with the cold part of the helium recondensation system, or a connection portion with a liquid helium pool.

[0092] The levels of modules in the system can be considered to form a main insert that can be connected to an auxiliary insert that contains a target device. The target device can be conveniently loaded into the system and exchanged by connecting the auxiliary insert to the main insert, further increasing the customizability of the system. The auxiliary insert may include a plurality of auxiliary boards connected in a self-supporting structure, each auxiliary board being generally connectable to a corresponding level of the main board forming the main insert. One or more adjustment members may be configured so that when the auxiliary insert is mounted to the main insert, the adjustment member brings the main board and the auxiliary board into thermal contact. For example, the adjustment member may change the spacing between the main board and the auxiliary board, or the adjustment member may include a deformable member that forms part of the corresponding main board or auxiliary board (as described in WO 2021 / 170,976A1). Multiple auxiliary inserts may be connected to the main insert, for example two or more auxiliary inserts may be connected on each side of two opposite sides of the module (depending on the size and configuration of the module). For example, as Fig.10 As shown, the auxiliary insert can be easily accessed through a door on the side of the housing.

[0093] Each module can be considered to form a "unit cell" of an expandable system. These modules can be configured to operate independently or be coupled to adjacent modules to expand the cooling power and internal physical space of the system, so that these modules are operated as a single larger system as the complexity of the experiment grows. The modules connected in the system can provide different functions and can have different sizes, shapes or occupied spaces from other modules in the system, as long as the housing allows interconnection as described above. The expandable temperature level is convenient for combining a larger number of cryogenic cooling systems into a common temperature level, for example to compensate for higher heat loads. The option of the corresponding temperature level of weak thermal coupling allows these levels to be subdivided into different temperature regions, so as to allow, for example, the optimal operation of the connected equipment. Further preferred features and advantages are as described above. In a word, the system described herein provides an expandable cryogenic system that can operate at millikelvin temperatures.

Claims

1. A low temperature cooling system, comprising: a cryogenic refrigerator assembly, the cryogenic refrigerator assembly comprising one or more cryogenic refrigerators; as well as Two or more connected modules, each of the connected modules comprising: a housing defining an interior volume of the module, the housing having a plurality of sides; and a plurality of stages disposed within the interior volume of the module, wherein one or more of the plurality of stages are thermally coupled to the cryogenic refrigerator assembly; wherein two or more of the modules are connected to each other at corresponding sides; and wherein the first said stage of a first said module is thermally coupled to the first said stage of a second said module.

2. The cryogenic cooling system according to claim 1, wherein: The cryogenic refrigerator assembly is configured such that each of the connected modules includes a cryogenic refrigerator thermally coupled to one or more stages of the module.

3. The cryogenic cooling system according to claim 1 or 2, wherein: Each of the modules is configured to operate as an independent cryogenic cooling system in a first configuration, whereby in the first configuration a removable panel is mounted to the housing of the module to enclose the interior volume of the module.

4. The cryogenic cooling system according to claim 3, wherein: Each of the modules is also configured to operate as a component of an integrated cryogenic cooling system in a second configuration, the integrated cryogenic cooling system comprising a plurality of the modules connected to each other on respective sides to form a shared internal volume of the system, wherein the plurality of stages of each of the connected modules are arranged in the system, wherein, in the second configuration, the removable panel is removed from the housing.

5. A cryogenic cooling system according to any one of the preceding claims, wherein: Each of the connected modules comprises four orthogonal sides.

6. A cryogenic cooling system according to any one of the preceding claims, wherein: A side of the first said module is directly connected to a side of the second said module.

7. A cryogenic cooling system according to any one of the preceding claims, wherein: The second said stage of a first said module is thermally coupled to the second said stage of a second said module.

8. A cryogenic cooling system according to any one of the preceding claims, wherein: One or more stages of a first said module are connected to corresponding stages of a second said module by one or more extension plates.

9. The cryogenic cooling system according to claim 8, wherein: Each of the extension plates is configured such that at a temperature of 20 K, the effective thermal conductivity between the connected stages is higher than 5000 W / mK.

10. The cryogenic cooling system according to claim 8, further comprising a plurality of the extension plates, wherein one or more of the extension plates are configured such that the effective thermal conductivity between the connected stages is higher than 5000 W / mK at a temperature of 20 K, and one or more of the extension plates are configured such that the effective thermal conductivity between the connected stages is lower than 50 W / mK at a temperature of 20 K.

11. The cryogenic cooling system according to any one of claims 8 to 10, wherein: The connected levels are approximately coplanar.

12. The cryogenic cooling system according to any one of claims 8 to 11, wherein: At least one of the one or more extension plates comprises an expandable joint, the expandable joint preferably being configured to maintain a mechanical connection between the connected stages during relative movement of the connected stages.

13. A cryogenic cooling system according to any one of the preceding claims, wherein: The plurality of stages of each of the modules share a common interior volume defined by the housings of the connected modules, wherein the interior volume of the system is sealed from an ambient environment.

14. A cryogenic cooling system according to any one of the preceding claims, wherein: each said module comprising one or more radiation shields, each said radiation shield being thermally coupled to a respective stage of said module and surrounding one or more remaining stages, each said radiation shield comprising one or more shield surfaces; The system also includes one or more shield extensions, each shield extension connecting coplanar shield surfaces of adjacent connected modules.

15. A cryogenic cooling system according to any one of the preceding claims, wherein: The first of said modules comprises a first dilution unit, and wherein the second of said modules comprises a second dilution unit.

16. The cryogenic cooling system according to claim 15, wherein: The first dilution unit comprises a distiller mounted to a distiller stage among the plurality of stages of a first said module, and wherein the second dilution unit comprises a distiller mounted to a distiller stage among the plurality of stages of a second said module, wherein the respective distiller stages of the first module and the second module are mechanically connected by an extension plate.

17. The cryogenic cooling system according to claim 16, wherein: At a temperature of 20 K, the effective thermal conductivity between the respective distiller stages of the first module and the second module is lower than 50 W / mK.

18. The cryogenic cooling system according to any one of claims 15 to 17, wherein: The first dilution unit comprises a mixing chamber mounted to a mixing chamber stage among the plurality of stages of a first said module, and wherein the second dilution unit comprises a mixing chamber mounted to a mixing chamber stage among the plurality of stages of a second said module, wherein the respective mixing chamber stages of the first module and the second module are mechanically connected by an extension plate.

19. The cryogenic cooling system according to any one of claims 15 to 18, wherein: The effective thermal conductivity between the mixing chamber stages of each of the first module and the second module is lower than 50 W / mK at a temperature of 20 K.

20. A cryogenic cooling system according to any one of the preceding claims, wherein: The system also includes a target assembly including circuitry extending within the interior volume of the system and between stages of two or more of the connected modules.

21. A cryogenic cooling system according to any one of the preceding claims, wherein: The first module comprises a cryogenic refrigerator in the form of a dilution unit or a 1-K pot, and wherein the second module or a third module having a stage thermally coupled to a corresponding stage of the first module comprises a cryogenic refrigerator in the form of a cryogenic cooler and / or a reservoir for a liquid refrigerant.

22. The cryogenic cooling system according to claim 21, wherein: The reservoir is arranged to collect refrigerant liquefied by operation of the cryocooler.

23. The cryogenic cooling system according to claim 21 or 22, wherein: Said reservoir is operable to cool one or more stages of a first said module.

24. A cryogenic cooling system according to any one of the preceding claims, wherein: The cryogenic cooling assembly comprises a helium refrigeration device, which is preferably arranged outside the housing of each of the modules.

25. The cryogenic cooling system according to claim 24, wherein: One or more of the modules comprises a first helium heat exchanger thermally coupled to the stage of the module, the first helium heat exchanger being arranged to receive a flow of liquid helium from the helium refrigeration plant.

26. The cryogenic cooling system according to claim 25, wherein: One or more of the modules comprises a second helium heat exchanger thermally coupled to the stage of the module, the second helium heat exchanger being arranged to receive a gaseous helium flow having a temperature below 100K, preferably between 40K and 80K, more preferably between 50K and 70K from the helium refrigeration device.

27. A cryogenic cooling system according to any one of the preceding claims, wherein: The cryogenic cooling assembly comprises a nitrogen refrigeration device, which is preferably arranged outside the housing of each of the modules.

28. The cryogenic cooling system according to claim 27, wherein: One or more of the modules comprises a nitrogen heat exchanger thermally coupled to the stage of the module, the nitrogen heat exchanger being arranged to receive a flow of liquid nitrogen from the nitrogen refrigeration plant.

29. A cryogenic cooling system according to any one of the preceding claims, wherein: The plurality of stages of the first module include a distiller stage, a cold stage and a mixing chamber stage, the cold stage being arranged between the distiller stage and the mixing chamber stage, the first module further including three dilution units, each of the dilution units including a distiller thermally coupled to the distiller stage of the first module, wherein the first dilution unit also includes a mixing chamber thermally coupled to the cold stage, and wherein the second dilution unit and the third dilution unit each include a mixing chamber thermally coupled to the mixing chamber stage of the first module.

30. A quantum information processing device comprising a cryogenic cooling system according to any one of the preceding claims.

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