Patent Publication Number: US-2022221108-A1

Title: Multiple cryogenic systems sectioned within a common vacuum space

Description:
BACKGROUND 
     The subject disclosure relates to cryogenic environments, and more specifically, to techniques of facilitating multiple cryogenic systems sectioned within a common vacuum space. 
     SUMMARY 
     The following presents a summary to provide a basic understanding of one or more embodiments of the invention. This summary is not intended to identify key or critical elements, or delineate any scope of the particular embodiments or any scope of the claims. Its sole purpose is to present concepts in a simplified form as a prelude to the more detailed description that is presented later. In one or more embodiments described herein, systems, devices, and/or methods that facilitate multiple cryogenic systems sectioned within a common vacuum space are described. 
     According to an embodiment, a cryostat can comprise a plurality of thermal stages and a thermal switch. The plurality of thermal stages can intervene between a 4-Kelvin (K) stage and a Cold Plate stage. The plurality of thermal stages can include a Still stage and an intermediate thermal stage that can be directly coupled mechanically to the Still stage via a support rod. The thermal switch can be coupled to the intermediate thermal stage and an adjacent thermal stage. The thermal switch can facilitate modifying a thermal profile of the cryostat by providing a switchable thermal path between the intermediate thermal stage and the adjacent thermal stage. 
     According to another embodiment, a cryostat can comprise a Still stage and a thermal switch. The Still stage can be directly coupled mechanically to an intermediate thermal stage via a support rod. The Still stage and the intermediate thermal stage can be included among a plurality of thermal stages intervening between a 4-K stage and a Cold Plate stage. The thermal switch can be coupled to the intermediate thermal stage and an adjacent thermal stage. The thermal switch can facilitate modifying a thermal profile of the cryostat by providing a switchable thermal path between the intermediate thermal stage and the adjacent thermal stage. 
     According to another embodiment, a cryostat can comprise an enclosed thermal volume and a thermal switch. The enclosed thermal volume can be formed by an intermediate thermal stage coupled to a thermal shield. The intermediate thermal stage can be directly coupled mechanically to a Still stage via a support rod. The Still stage and the intermediate thermal stage can be included among a plurality of thermal stages intervening between a 4-K stage and a Cold Plate stage. The thermal switch can be coupled to the intermediate thermal stage and an adjacent thermal stage. The thermal switch can facilitate modifying a thermal profile of the cryostat by providing a switchable thermal path between the intermediate thermal stage and the adjacent thermal stage. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example, non-limiting cryostat, in accordance with one or more embodiments described herein. 
         FIG. 2  illustrates a circuit schematic of an example, non-limiting cryostat, in accordance with one or more embodiments described herein. 
         FIG. 3  illustrates an example, non-limiting cryostat with a switchable thermal path that facilitates multiple cryogenic systems sectioned within a common vacuum space, in accordance with one or more embodiments described herein. 
         FIG. 4  illustrates another example, non-limiting cryostat with a switchable thermal path that facilitates multiple cryogenic systems sectioned within a common vacuum space, in accordance with one or more embodiments described herein. 
         FIG. 5  illustrates an example, non-limiting cryostat with multiple switchable thermal paths that facilitate multiple cryogenic systems sectioned within a common vacuum space, in accordance with one or more embodiments described herein. 
         FIG. 6  illustrates an example, non-limiting thermal switch that facilitates a switchable thermal path in a coupling state, in accordance with one or more embodiments described herein. 
         FIG. 7  illustrates the example, non-limiting thermal switch of  FIG. 6  in a decoupling state. 
         FIG. 8  illustrates another example, non-limiting thermal switch that facilitates a switchable thermal path, in accordance with one or more embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely illustrative and is not intended to limit embodiments and/or application or uses of embodiments. Furthermore, there is no intention to be bound by any expressed or implied information presented in the preceding Background or Summary sections, or in the Detailed Description section. 
     One or more embodiments are now described with reference to the drawings, wherein like referenced numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a more thorough understanding of the one or more embodiments. It is evident, however, in various cases, that the one or more embodiments can be practiced without these specific details. 
       FIG. 1  illustrates an example, non-limiting cryostat  100 , in accordance with one or more embodiments described herein. As shown in  FIG. 1 , cryostat  100  comprises an outer vacuum chamber  110  formed by a sidewall  120  intervening between a top plate  130  and a bottom plate  140 . In operation, outer vacuum chamber  110  can maintain a pressure differential between an ambient environment  150  of outer vacuum chamber  110  and an interior  160  of outer vacuum chamber  110 . Cryostat  100  further comprises a plurality of thermal stages (or stages)  170  disposed within interior  160  that are each mechanically coupled to top plate  130 . The plurality of stages  170  includes: stage  171 , stage  173 , stage  175 , stage  177 , and stage  179 . Each stage among the plurality of stages  170  can be associated with a different temperature. For example, stage  171  can be a 50-kelvin (50-K) stage that is associated with a temperature of 50 kelvin (K), stage  173  can be a 4-kelvin (4-K) stage that is associated with a temperature of 4 K, stage  175  can be associated with a temperature of 700 millikelvin (mK), stage  177  can be associated with a temperature of 100 mK, and stage  179  can be associated with a temperature of 10 mK. Each stage among the plurality of stages  170  is spatially isolated from other stages of the plurality of stages  170  by a plurality of support rods (e.g., support rods  172  and  174 ). In an embodiment, stage  175  can be a Still stage, stage  177  can be a Cold Plate stage, and stage  179  can be a Mixing Chamber stage. 
       FIG. 2  illustrates a circuit schematic of an example, non-limiting cryostat  200 , in accordance with one or more embodiments described herein. A cryostat (e.g., cryostat  100  of  FIG. 1 ) can maintain samples or devices positioned on a sample mounting surface located within the cryostat at temperatures approaching absolute zero to facilitate evaluating such samples or devices under cryogenic conditions. Cryostats generally provide such low temperatures utilizing five thermal stages that are mechanically coupled to a room temperature plate (e.g., top plate  130 ) of an outer vacuum chamber. The five thermal stages of a cryostat can comprise a thermal profile in which each subsequent thermal stage has a progressively lower temperature than exists at a preceding thermal stage. Evaluating samples or devices under cryogenic conditions generally involves interacting with such samples or devices using one or more devices that sit at room temperature conditions external to a cryostat. To that end, a cryostat can include input/output (I/O) lines that facilitate propagation of electrical signals between a sample positioned within the cryostat and the devices external to the cryostat. 
     By way of example, superconducting qubits can be positioned on a sample mounting surface  260  of cryostat  200 . Coupling the superconducting qubits positioned on sample mounting surface  260  to one or more devices external to cryostat  200  are four I/O lines: a drive line  271 ; a flux line  273 ; a pump line  275 ; and an output (or readout) line  277 . One skilled in the art will appreciate that these four I/O lines can contribute to a heat load placed on cryostat  200  in a number ways. One way that the four I/O lines can contribute to the heat load is that each I/O line can provide a thermal path along which heat can be conducted from higher temperature thermal stages to lower temperature thermal stages. For example, in  FIG. 2 , drive line  271  is routed from a 50-K stage  210  of cryostat  200  to a Mixing Chamber stage  250 . Along that routing path through cryostat  200 , drive line  271  can provide a thermal path through which heat can be conducted from higher temperature thermal stages to lower temperature thermal stages, such as from 50-K stage  210  to a 4-K stage  220 . 
     Another way that the four I/O lines can contribute to the heat load relates to heat (e.g., Joule heating) generated due to dissipation of signals propagating along a given I/O line or via an intervening electrical component. For example, a microwave flux signal propagating along flux line  273  towards a SQUID loop associated with the superconducting qubits positioned on sample mounting surface  260  can introduce heat on a Still stage  230  of cryostat  200  via a thermal coupling  274 . As another example, a microwave pump signal propagating along flux line  273  for operation of a traveling wave parametric amplifier (TWPA)  281  can introduce heat on a Cold stage  240  via an attenuator  283  coupled to flux line  273  and Cold stage  240 . 
     Another way that the four I/O lines can contribute to the heat load involves a radiative load that higher temperature thermal stages represent to lower temperature thermal stages. For example, direct current (DC) signals biasing a high electron mobility transistor (HEMT) amplifier  285  to facilitate measurement of the superconducting qubits positioned on sample mounting surface  260  via output line  277  can introduce heat on the 4-K stage  220 . Such heat introduced on the 4-K stage  220  can expose lower temperature thermal stages (e.g., Still stage  230 ) to a radiative load that the 4-K stage  220  represents to the lower temperature thermal stages as 4 K blackbody radiation. 
     As discussed above, cryostats can maintain samples or devices positioned on a sample mounting surface located within the cryostat at temperatures approaching absolute zero to facilitate evaluating such samples or devices under cryogenic conditions. The five thermal stages of a cryostat generally used to provide such cryogenic conditions can comprise a thermal profile in which each subsequent thermal stage has a progressively lower temperature than exists at a preceding thermal stage. That thermal profile can exist within a common vacuum space defined by an outer vacuum chamber of the cryostat that encloses the five thermal stages. 
     In some instances, temperatures approaching absolute zero can be advantageous in evaluating samples or devices under cryogenic conditions. For example, temperatures approaching absolute zero can be advantageous in evaluating incoherent noise in superconducting circuits, exotic phase transitions in confined superfluid helium-3, and topological effects of localization and disorder in highly correlated systems. In other instances, higher temperatures can be sufficient to evaluate samples or devices under cryogenic conditions. For example, temperatures of about 4 K can be sufficient to evaluate HEMT devices or some niobium (Nb) resonators under cryogenic conditions. As another example, temperatures of about 1 K can be sufficient to evaluate some Josephson Junction (JJ) devices (e.g., JJ field-effect transistors) or some NB resonators under cryogenic conditions. As another example, temperatures of about 300 mK can be sufficient to evaluate qubit devices, microwave components, or some JJ devices. Therefore, multiple cryogenic systems sectioned within a common vacuum space of a cryostat can facilitate improved efficiency by flexibly modifying a thermal profile of the cryostat to accommodate varying evaluation conditions. Embodiments described herein facilitate multiple cryogenic systems sectioned within a common vacuum space by providing switchable thermal paths between intermediate thermal stages providing additional cooling capacity to a cryostat and adjacent thermal stages. 
       FIG. 3  illustrates an example, non-limiting cryostat  300  with a switchable thermal path that facilitates multiple cryogenic systems sectioned within a common vacuum space, in accordance with one or more embodiments described herein. As shown by  FIG. 3 , cryostat  300  comprises a 50-K stage  305  that can be coupled to a room temperature plate (e.g., top plate  130  of  FIG. 1 ) of an outer vacuum chamber (not shown). The outer vacuum chamber can define a common vacuum space (e.g., interior  160 ) enclosing the various thermal stages of cryostat  300  at a common pressure. 
     Cryostat  300  further comprises a plurality of thermal stages intervening between a 4-K stage  310  and a Cold Plate stage  325 . Those plurality of thermal stages include a Still stage  320  and an intermediate thermal stage  315 . Intermediate thermal stage  315  is directly coupled mechanically to 4-K stage  310  via support rod  311  and Still stage  320  via support rod  316 . Intermediate thermal stage  315  is indirectly coupled mechanically to 50-K stage  305  via support rod  306 , Cold Plate stage  325  via support rod  321 , and Mixing Chamber stage  330  via support rod  326 . 
       FIG. 3  also shows that cryostat  300  further comprises an enclosed thermal volume  340  that can be formed by a thermal shield  342  coupled to intermediate thermal stage  315 . Enclosed thermal volume  340  can be thermally isolated from a volume  345  of cryostat  300  that is external to enclosed thermal volume  340 . In  FIG. 3 , thermal shield  342  is illustrated as intervening between intermediate thermal stage  315  and a thermal plate  344  to form enclosed thermal volume  340 . However, in other embodiments, thermal shield  342  and thermal plate  344  can be implemented as a unitary element such that coupling the unitary element to intermediate thermal stage  315  can form enclosed thermal volume  340 . 
     Intermediate thermal stage  315  can comprise a feedthrough element  317  that intervenes in a wiring structure  370  that facilitates propagation of electrical signals between 4-K stage  310  and Cold Plate stage  325 . Wiring structure  370  can comprise an I/O line coupling a sample positioned within cryostat  300  and one or more devices external to cryostat  300 . For example, wiring structure  370  can comprise an I/O line such as drive line  271 , flux line  273 , pump line  275 , and/or output (or readout) line  277  of  FIG. 2 . In an embodiment, intermediate thermal stage  315  can comprise copper, gold, silver, brass, platinum, or a combination thereof. 
     Intermediate thermal stage  315  can provide additional cooling capacity for cryostat  300  via a sealed pot  350  coupled to intermediate thermal stage  315 . To that end, sealed pot  350  facilitates evaporative cooling of a helium medium-helium-4. A condenser line  352  can couple an outlet port  362  of a pump  360  to sealed pot  350  via 4-K stage  310 . In an embodiment, pump  360  can be a vacuum pump for circulating a helium medium through sealed pot  350 . In an embodiment, pump  360  can be located external to cryostat  300 . In an embodiment, pump  360  can be located within cryostat  300 . In this embodiment, pump  360  can be implemented as a sorb pump. Condenser line  352  can provide a return path for the helium medium to sealed pot  350 . A pumping line  354  can couple an inlet port  364  of pump  360  to sealed pot  350  via 4-K stage  310 . 4-K stage  310  can provide passage for condenser line  352  and/or pumping line  354  via a feedthrough element, such as feedthrough element  312 . 
     As shown by  FIG. 3 , cryostat  300  further comprises a thermal switch  380  coupled to intermediate thermal stage  315  and an adjacent thermal stage. In the example of  FIG. 3 , that adjacent thermal stage is 4-K stage  310 . An example, non-limiting thermal switch that is suitable for implementing thermal switch  380  will be discussed in greater detail below with respect to  FIGS. 6-7 . Thermal switch  380  can facilitate modifying a thermal profile of cryostat  300  by providing a switchable thermal path between intermediate thermal stage  315  and 4-K stage  310 . To that end, a transfer medium of thermal switch  380  can provide a thermal path that thermally couples (or shorts) intermediate thermal stage  315  to 4-K stage  310  when thermal switch  380  is in a coupling state. When thermal switch  380  transitions from the coupling state to a decoupling state, the thermal path provided by the transfer medium of thermal switch  380  can be removed, thereby thermally decoupling intermediate thermal stage  315  from 4-K stage  310 . 
     In an embodiment, the transfer medium can comprise a helium medium. In an embodiment, the transfer medium can comprise a superconducting material (e.g., aluminum). In this embodiment, thermal switch  380  can be transitioned into the decoupling state by transitioning the transfer medium from a non-superconducting state to a superconducting state. In an embodiment, the transfer medium can be transitioned from the non-superconducting state to the superconducting state by decreasing a temperature of the transfer medium below a critical temperature of the superconducting material. In an embodiment, the superconducting material can be positioned within a magnetic field. In an embodiment, the transfer medium can be transitioned from the superconducting state to the non-superconducting state by increasing a strength of a magnetic field above a critical magnetic field of the superconducting material. 
     In operation, helium-4 can flow from outlet port  362  towards sealed pot  350  in a gaseous state. Feedthrough element  312  can thermally anchor condenser line  352  to 4-K stage  310 . As the helium-4 flows past feedthrough element  312 , the helium-4 can transition from the gaseous state to a liquid state. Helium-4 in the liquid state can collect in sealed pot  350 . When thermal switch  380  is in the decoupling state, inlet port  364  of pump  360  can be operated to reduce a pressure above the liquified helium-4 collected in sealed pot  350 . Helium-4 in the gaseous state can form above the liquified helium-4 collected in sealed pot  350  through evaporation and flow to inlet port  364  of pump  360  via pumping line  354 . Heat carried by the helium-4 in the gaseous state flowing through pumping line  354  can reduce a temperature of the liquified helium-4 remaining in sealed pot  350 . Such evaporative cooling of the liquified helium-4 in sealed pot  350  can reduce a temperature of intermediate thermal stage  315  such that intermediate thermal stage  315  can operate at a temperature of about 1 K. 
     Operating intermediate thermal stage  315  at a temperature of about 1 K can facilitate sectioning cryostat  300  into multiple cryogenic systems (e.g., enclosed thermal volume  340  and volume  345 ) operating at different temperatures within a common vacuum space. For example, cryostat  300  can further comprise additional thermal switches (not shown), such as a thermal switch intervening between intermediate thermal stage  315  and Still stage  320 ; a thermal switch intervening between Still stage  320  and Cold Plate stage  325 ; and a thermal switch intervening between Cold Plate stage  325  and Mixing Chamber stage  330 . In this example, each intervening thermal switch can be transitioned to a coupling state such that Still stage  320 , Cold Plate stage  325 , and Mixing Chamber stage  330  can each be thermally equalized with intermediate thermal stage  315  to operate at a temperature of about 1 K. 
     When thermal switch  380  is in the coupling state, inlet port  364  of pump  360  can be operated to maintain a pressure above the liquified helium-4 collected in sealed pot  350  at the common pressure of the common vacuum space. Maintaining the pressure above the liquified helium-4 collected in sealed pot  350  at the common pressure can impede evaporative cooling of the liquified helium-4 in sealed pot  350 . Absent such evaporative cooling, intermediate thermal stage  315  can be thermally equalized with 4-K stage  310  via the thermal path provided by thermal switch  380  such that intermediate thermal stage  315  can operate at a temperature of about 4 K. In an embodiment, sealed pot  350  can be vacuum sealed or cryogenically sealed. In an embodiment, sealed pot  350  can comprise sintered material that facilitates thermal budget optimization. The sintered material can comprise silver, gold, copper, platinum, and the like. 
       FIG. 4  illustrates another example, non-limiting cryostat  400  with a switchable thermal path that facilitates multiple cryogenic systems sectioned within a common vacuum space, in accordance with one or more embodiments described herein. As shown by  FIG. 4 , cryostat  400  comprises a 50-K stage  405  that can be coupled to a room temperature plate (e.g., top plate  130  of  FIG. 1 ) of an outer vacuum chamber (not shown). The outer vacuum chamber can define a common vacuum space (e.g., interior  160 ) enclosing the various thermal stages of cryostat  400  at a common pressure. 
     Cryostat  400  further comprises a plurality of thermal stages intervening between a 4-K stage  410  and a Cold Plate stage  425 . Those plurality of thermal stages include a Still stage  415  and an intermediate thermal stage  420 . Intermediate thermal stage  420  is directly coupled mechanically to Still stage  415  via support rod  416  and Cold Plate stage  425  via support rod  421 . Intermediate thermal stage  420  is indirectly coupled mechanically to 50-K stage  405  via support rod  406 , 4-K stage  410  via support rod  411 , and Mixing Chamber stage  430  via support rod  426 . 
       FIG. 4  also shows that cryostat  400  further comprises an enclosed thermal volume  440  that can be formed by a thermal shield  442  coupled to intermediate thermal stage  420 . Enclosed thermal volume  440  can be thermally isolated from a volume  445  of cryostat  400  that is external to enclosed thermal volume  340 . In  FIG. 4 , thermal shield  442  is illustrated as intervening between intermediate thermal stage  420  and a thermal plate  444  to form enclosed thermal volume  440 . However, in other embodiments, thermal shield  442  and thermal plate  444  can be implemented as a unitary element such that coupling the unitary element to intermediate thermal stage  420  can form enclosed thermal volume  440 . 
     Intermediate thermal stage  420  can comprise a feedthrough element  422  that intervenes in a wiring structure  470  that facilitates propagation of electrical signals between 4-K stage  410  and Cold Plate stage  425 . Still stage  415  can also comprise a feedthrough element  418  that intervenes in wiring structure  470 . Wiring structure  470  can comprise an 110 line coupling a sample positioned within cryostat  400  and one or more devices external to cryostat  400 . For example, wiring structure  470  can comprise an 110 line such as drive line  271 , flux line  273 , pump line  275 , and/or output (or readout) line  277  of  FIG. 2 . In an embodiment, intermediate thermal stage  420  can comprise copper, gold, silver, brass, platinum, or a combination thereof. 
     Intermediate thermal stage  420  can provide additional cooling capacity for cryostat  400  via a sealed pot  450  coupled to intermediate thermal stage  420 . To that end, sealed pot  450  facilitates evaporative cooling of a helium medium-helium-3. A condenser line  452  can couple an outlet port  462  of a pump  460  to sealed pot  450  via 4-K stage  410 . In an embodiment, pump  460  can be a vacuum pump for circulating a helium medium through sealed pot  450 . In an embodiment, pump  460  can be located external to cryostat  400 . In an embodiment, pump  460  can be located within cryostat  400 . In this embodiment, pump  460  can be implemented as a sorb pump. Condenser line  452  can provide a return path for the helium medium to sealed pot  450 . A pumping line  454  can couple an inlet port  464  of pump  460  to sealed pot  450  via 4-K stage  410 . 4-K stage  410  can provide passage for condenser line  452  and/or pumping line  454  via a feedthrough element, such as feedthrough element  412 . Still stage  415  can provide passage for condenser line  452  and/or pumping line  454  via a feedthrough element, such as feedthrough element  422 . 
     As shown by  FIG. 4 , cryostat  400  further comprises a thermal switch  480  coupled to intermediate thermal stage  420  and an adjacent thermal stage. In the example of  FIG. 4 , that adjacent thermal stage is Still stage  415 . An example, non-limiting thermal switch that is suitable for implementing thermal switch  480  will be discussed in greater detail below with respect to  FIGS. 6-7 . Thermal switch  480  can facilitate modifying a thermal profile of cryostat  400  by providing a switchable thermal path between intermediate thermal stage  420  and Still stage  415 . To that end, a transfer medium of thermal switch  480  can provide a thermal path that thermally couples (or shorts) intermediate thermal stage  420  to Still stage  415  when thermal switch  480  is in a coupling state. When thermal switch  480  transitions from the coupling state to a decoupling state, the thermal path provided by the transfer medium of thermal switch  480  can be removed, thereby thermally decoupling intermediate thermal stage  420  from Still stage  415 . 
     In an embodiment, the transfer medium can comprise a helium medium. In an embodiment, the transfer medium can comprise a superconducting material (e.g., aluminum). In this embodiment, thermal switch  480  can be transitioned into the decoupling state by transitioning the transfer medium from a non-superconducting state to a superconducting state. In an embodiment, the transfer medium can be transitioned from the non-superconducting state to the superconducting state by decreasing a temperature of the transfer medium below a critical temperature of the superconducting material. In an embodiment, the superconducting material can be positioned within a magnetic field. In an embodiment, the transfer medium can be transitioned from the superconducting state to the non-superconducting state by increasing a strength of a magnetic field above a critical magnetic field of the superconducting material. 
     In operation, helium-3 can flow from outlet port  462  towards sealed pot  450  in a gaseous state. Feedthrough elements  412  and/or  417  can thermally anchor condenser line  452  to 4-K stage  410  and/or Still stage  415 , respectively. As the helium-3 flows past feedthrough elements  412  and/or  417 , the helium-3 can transition from the gaseous state to a liquid state. Helium-3 in the liquid state can collect in sealed pot  450 . When thermal switch  480  is in the decoupling state, inlet port  464  of pump  460  can be operated to reduce a pressure above the liquified helium-3 collected in sealed pot  450 . Helium-3 in the gaseous state can form above the liquified helium-3 collected in sealed pot  450  through evaporation and flow to inlet port  464  of pump  460  via pumping line  454 . Heat carried by the helium-3 in the gaseous state flowing through pumping line  454  can reduce a temperature of the liquified helium-3 remaining in sealed pot  450 . Such evaporative cooling of the liquified helium-3 in sealed pot  470  can reduce a temperature of intermediate thermal stage  420  such that intermediate thermal stage  420  can operate at a temperature of about 300 mK. 
     Operating intermediate thermal stage  420  at a temperature of about 300 mK can facilitate sectioning cryostat  400  into multiple cryogenic systems (e.g., enclosed thermal volume  440  and volume  445 ) operating at different temperatures within a common vacuum space. For example, cryostat  400  can further comprise additional thermal switches (not shown), such as a thermal switch intervening between intermediate thermal stage  420  and Cold Plate stage  425 ; and a thermal switch intervening between Cold Plate stage  425  and Mixing Chamber stage  430 . In this example, each intervening thermal switch can be transitioned to a coupling state such that Cold Plate stage  425  and Mixing Chamber stage  430  can each be thermally equalized with intermediate thermal stage  420  to operate at a temperature of about 300 mK. 
     When thermal switch  480  is in the coupling state, inlet port  464  of pump  460  can be operated to maintain a pressure above the liquified helium-3 collected in sealed pot  450  at the common pressure of the common vacuum space. Maintaining the pressure above the liquified helium-3 collected in sealed pot  450  at the common pressure can impede evaporative cooling of the liquified helium-3 in sealed pot  450 . Absent such evaporative cooling, intermediate thermal stage  420  can be thermally equalized with Still stage  415  via the thermal path provided by thermal switch  480  such that intermediate thermal stage  420  can operate at a temperature of about 700 mK. In an embodiment, sealed pot  450  can be vacuum sealed or cryogenically sealed. In an embodiment, sealed pot  450  can comprise sintered material that facilitates thermal budget optimization. The sintered material can comprise silver, gold, copper, platinum, and the like. 
       FIG. 5  illustrates an example, non-limiting cryostat  500  with multiple switchable thermal paths that facilitate multiple cryogenic systems sectioned within a common vacuum space, in accordance with one or more embodiments described herein. As shown by  FIG. 5 , cryostat  500  comprises a 50-K stage  505  that can be coupled to a room temperature plate (e.g., top plate  130  of  FIG. 1 ) of an outer vacuum chamber (not shown). The outer vacuum chamber can define a common vacuum space (e.g., interior  160 ) enclosing the various thermal stages of cryostat  500  at a common pressure. Cryostat  500  further comprises a plurality of thermal stages intervening between a 4-K stage  510  and a Cold Plate stage  530 . Those plurality of thermal stages include a Still stage  520  and multiple intermediate thermal stages (e.g., intermediate thermal stage  515  and intermediate thermal stage  525 ). 
       FIG. 5  also shows that cryostat  500  further comprises an enclosed thermal volume  540  and an enclosed thermal volume  550  nested within enclosed thermal volume  540 . Enclosed thermal volume  540  can be thermally isolated from enclosed thermal volume  550  and a volume  545  of cryostat  500  that is external to enclosed thermal volume  540 . Enclosed thermal volume  540  can be formed by a thermal shield  542  coupled to intermediate thermal stage  515 . In  FIG. 5 , thermal shield  542  is illustrated as intervening between intermediate thermal stage  515  and a thermal plate  544  to form enclosed thermal volume  540 . However, in other embodiments, thermal shield  542  and thermal plate  544  can be implemented as a unitary element such that coupling the unitary element to intermediate thermal stage  515  can form enclosed thermal volume  540 . Enclosed thermal volume  550  can be formed by a thermal shield  552  coupled to intermediate thermal stage  525 . In  FIG. 5 , thermal shield  552  is illustrated as intervening between intermediate thermal stage  525  and a thermal plate  554  to form enclosed thermal volume  550 . However, in other embodiments, thermal shield  552  and thermal plate  554  can be implemented as a unitary element such that coupling the unitary element to intermediate thermal stage  525  can form enclosed thermal volume  550 . 
     Intermediate thermal stage  515  is directly coupled mechanically to 4-K stage  510  via support rod  511  and Still stage  520  via support rod  516 . Intermediate thermal stage  515  is indirectly coupled mechanically to 50-K stage  505  via support rod  506 , intermediate thermal stage  525  via support rod  521 , Cold Plate stage  530  via support rod  526 , and Mixing Chamber stage  535  via support rod  531 . Intermediate thermal stage  525  is directly coupled mechanically to Still stage  520  via support rod  521  and Cold Plate stage  530  via support rod  526 . Intermediate thermal stage  525  is indirectly coupled mechanically to 50-K stage  505  via support rod  506 , 4-K stage  510  via support rod  511 , intermediate thermal stage  515  via support rod  516 , and Mixing Chamber stage  535  via support rod  531 . Intermediate thermal stages  515  and  525  are directly coupled mechanically to opposing sides of Still stage  520  via support rods  516  and  521 , respectively. 
     Intermediate thermal stages  515  and  525  can comprise feedthrough elements  518  and  527 , respectively, that intervene in a wiring structure  580  that facilitates propagation of electrical signals between 4-K stage  510  and Cold Plate stage  530 . Still stage  520  can also comprise a feedthrough element  523  that intervenes in wiring structure  580 . Wiring structure  580  can comprise an I/O line coupling a sample positioned within cryostat  500  and one or more devices external to cryostat  500 . For example, wiring structure  580  can comprise an I/O line such as drive line  271 , flux line  273 , pump line  275 , and/or output (or readout) line  277  of  FIG. 2 . In an embodiment, intermediate thermal stages  515  and/or  525  can comprise copper, gold, silver, brass, platinum, or a combination thereof. 
     Intermediate thermal stage  515  can provide additional cooling capacity for cryostat  500  via a sealed pot  560  coupled to intermediate thermal stage  515 . To that end, sealed pot  560  facilitates evaporative cooling of a helium medium-helium-4. A condenser line  562  can couple an outlet port  567  of a pump  565  to sealed pot  560  via 4-K stage  510 . Condenser line  562  can provide a return path for that helium medium to sealed pot  560 . A pumping line  564  can couple an inlet port  569  of pump  565  to sealed pot  560  via 4-K stage  510 . 4-K stage  510  can provide passage for condenser line  562  and/or pumping line  564  via a feedthrough element, such as feedthrough element  512 . 
     Intermediate thermal stage  525  can provide additional cooling capacity for cryostat  500  via a sealed pot  570  coupled to intermediate thermal stage  525 . To that end, sealed pot  570  facilitates evaporative cooling of a helium medium-helium-3. A condenser line  572  can couple an outlet port  577  of a pump  575  to sealed pot  570  via 4-K stage  510 . In an embodiment, pumps  565  and/or  575  can be a vacuum pump for circulating a corresponding helium medium through sealed pots  560  and/or  570 , respectively. In an embodiment, pumps  565  and/or  575  can be located external to cryostat  500 . In an embodiment, pumps  565  and/or  575  can be located within cryostat  500 . In this embodiment, pumps  565  and/or  575  can be implemented as a sorb pump. Condenser line  572  can provide a return path for that helium medium to sealed pot  570 . A pumping line  574  can couple an inlet port  579  of pump  575  to sealed pot  570  via 4-K stage  510 . 4-K stage  510  can provide passage for condenser line  572  and/or pumping line  574  via a feedthrough element, such as feedthrough element  513 . Intermediate thermal stage  515  can provide passage for condenser line  572  and/or pumping line  574  via a feedthrough element, such as feedthrough element  517 . Still stage  520  can provide passage for condenser line  572  and/or pumping line  574  via a feedthrough element, such as feedthrough element  522 . 
     As shown by  FIG. 5 , cryostat  500  further comprises multiple thermal switches coupled to various thermal stages of cryostat  500 . The multiple thermal switches include: a thermal switch  591  coupled to 4-K stage  510  and intermediate thermal stage  515 ; a thermal switch  593  coupled to intermediate thermal stage  515  and Still stage  520 ; and a thermal switch  595  coupled to Still stage  520  and intermediate thermal stage  525 . An example, non-limiting thermal switch that is suitable for implementing thermal switches  591 ,  593 , and/or  595  will be discussed in greater detail below with respect to  FIGS. 6-7 . Thermal switches  591 ,  593 , and/or  595  can each facilitate modifying a thermal profile of cryostat  500  by providing a switchable thermal path between the various thermal stages of cryostat  500 . 
     To that end, each thermal switch can comprise a transfer medium that can provide a thermal path that thermally couples (or shorts) respective thermal stages when that thermal switch is in a coupling state. For example, thermal switch  591  can comprise a transfer medium that can provide a thermal path that thermally couples intermediate thermal stage  515  to 4-K stage  510  when thermal switch  591  is in a coupling state. When a given thermal switch transitions from the coupling state to a decoupling state, the thermal path provided by the transfer medium of that thermal switch can be removed, thereby thermally decoupling the respective thermal stages. Continuing with the example above, the thermal path provided by the transfer medium of thermal switch  591  can be removed when thermal switch  591  transitions to the decoupling state, thereby thermally decoupling intermediate thermal stage  515  from 4-K stage  510 . 
     In an embodiment, the transfer medium can comprise a helium medium. In an embodiment, the transfer medium can comprise a superconducting material (e.g., aluminum). In this embodiment, thermal switch  830  can be transitioned into the decoupling state by transitioning the transfer medium from a non-superconducting state to a superconducting state. In an embodiment, the transfer medium can be transitioned from the non-superconducting state to the superconducting state by decreasing a temperature of the transfer medium below a critical temperature of the superconducting material. In an embodiment, the superconducting material can be positioned within a magnetic field. In an embodiment, the transfer medium can be transitioned from the superconducting state to the non-superconducting state by increasing a strength of a magnetic field above a critical magnetic field of the superconducting material. 
     In operation, helium-4 can flow from outlet port  567  towards sealed pot  560  in a gaseous state. Feedthrough element  512  can thermally anchor condenser line  562  to 4-K stage  510 . As the helium-4 flows past feedthrough element  512 , the helium-4 can transition from the gaseous state to a liquid state. Helium-4 in the liquid state can collect in sealed pot  560 . When thermal switch  591  is in the decoupling state, inlet port  567  of pump  565  can be operated to reduce a pressure above the liquified helium-4 collected in sealed pot  560 . Helium-4 in the gaseous state can form above the liquified helium-4 collected in sealed pot  560  through evaporation and flow to inlet port  569  of pump  560  via pumping line  564 . Heat carried by the helium-4 in the gaseous state flowing through pumping line  564  can reduce a temperature of the liquified helium-4 remaining in sealed pot  560 . Such evaporative cooling of the liquified helium-4 in sealed pot  540  can reduce a temperature of intermediate thermal stage  515  such that intermediate thermal stage  515  can operate at a temperature of about 1 K. 
     Operating intermediate thermal stage  515  at a temperature of about 1 K can facilitate sectioning cryostat  500  into multiple cryogenic systems (e.g., enclosed thermal volume  540  and volume  545 ) operating at different temperatures within a common vacuum space. For example, cryostat  500  can further comprise additional thermal switches (not shown), such as a thermal switch intervening between intermediate thermal stage  525  and Cold Plate stage  530 ; and a thermal switch intervening between Cold Plate stage  530  and Mixing Chamber stage  535 . In this example, each thermal switch intervening between intermedial thermal stage  515  and Mixing Chamber stage  535  (i.e., thermal switches  593  and  595  along with the additional thermal switches intervening between intermediate thermal stage  525 , Cold Plate stage  530 , and Mixing Chamber stage  535 ) can be transitioned to a coupling state. By transitioning those intervening thermal switches to the coupling state, Mixing Chamber stage  535  and each thermal stage intervening between intermediate thermal stage  515  and Mixing Chamber stage  535  can be thermally equalized with intermediate thermal stage  515  to operate at a temperature of about 1 K. 
     When thermal switch  591  is in the coupling state, inlet port  567  of pump  565  can be operated to maintain a pressure above the liquified helium-4 collected in sealed pot  560  at the common pressure of the common vacuum space. Maintaining the pressure above the liquified helium-4 collected in sealed pot  560  at the common pressure can impede evaporative cooling of the liquified helium-4 in sealed pot  560 . Absent such evaporative cooling, intermediate thermal stage  515  can be thermally equalized with 4-K stage  510  via the thermal path provided by thermal switch  591  such that intermediate thermal stage  515  can operate at a temperature of about 4 K. 
     In operation, helium-4 can flow from outlet port  567  towards sealed pot  560  in a gaseous state. Feedthrough element  512  can thermally anchor condenser line  562  to 4-K stage  510 . As the helium-4 flows past feedthrough element  512 , the helium-4 can transition from the gaseous state to a liquid state. Helium-4 in the liquid state can collect in sealed pot  560 . When thermal switch  591  is in the decoupling state, inlet port  567  of pump  565  can be operated to reduce a pressure above the liquified helium-4 collected in sealed pot  560 . Helium-4 in the gaseous state can form above the liquified helium-4 collected in sealed pot  560  through evaporation and flow to inlet port  569  of pump  560  via pumping line  564 . Heat carried by the helium-4 in the gaseous state flowing through pumping line  564  can reduce a temperature of the liquified helium-4 remaining in sealed pot  560 . Such evaporative cooling of the liquified helium-4 in sealed pot  540  can reduce a temperature of intermediate thermal stage  515  such that intermediate thermal stage  515  can operate at a temperature of about 1 K. 
     Operating intermediate thermal stage  515  at a temperature of about 1 K can facilitate sectioning cryostat  500  into multiple cryogenic systems (e.g., enclosed thermal volume  540  and volume  545 ) operating at different temperatures within a common vacuum space. For example, cryostat  500  can further comprise additional thermal switches (not shown), such as a thermal switch intervening between intermediate thermal stage  525  and Cold Plate stage  530 ; and a thermal switch intervening between Cold Plate stage  530  and Mixing Chamber stage  535 . In this example, each thermal switch intervening between intermedial thermal stage  515  and Mixing Chamber stage  535  (i.e., thermal switches  593  and  595  along with the additional thermal switches intervening between intermediate thermal stage  525 , Cold Plate stage  530 , and Mixing Chamber stage  535 ) can be transitioned to a coupling state. By transitioning those intervening thermal switches to the coupling state, Mixing Chamber stage  535  and each thermal stage intervening between intermediate thermal stage  515  and Mixing Chamber stage  535  can be thermally equalized with intermediate thermal stage  515  to operate at a temperature of about 1 K. 
     When thermal switch  591  is in the coupling state, inlet port  567  of pump  565  can be operated to maintain a pressure above the liquified helium-4 collected in sealed pot  560  at the common pressure of the common vacuum space. Maintaining the pressure above the liquified helium-4 collected in sealed pot  560  at the common pressure can impede evaporative cooling of the liquified helium-4 in sealed pot  560 . Absent such evaporative cooling, intermediate thermal stage  515  can be thermally equalized with 4-K stage  510  via the thermal path provided by thermal switch  591  such that intermediate thermal stage  515  can operate at a temperature of about 4 K. 
     In operation, helium-3 can flow from outlet port  577  towards sealed pot  570  in a gaseous state. Feedthrough elements  513 ,  517 , and/or  522  can thermally anchor condenser line  572  to 4-K stage  510 , intermediate thermal stage  515 , and/or Still stage  520 , respectively. As the helium-3 flows past feedthrough elements  513 ,  517 , and/or  522 , the helium-3 can transition from the gaseous state to a liquid state. Helium-3 in the liquid state can collect in sealed pot  570 . When thermal switches  591 ,  593 , and  595  are each in the decoupling state, inlet port  579 , inlet port  579  of pump  575  can be operated to reduce a pressure above the liquified helium-3 collected in sealed pot  570 . Helium-3 in the gaseous state can form above the liquified helium-3 collected in sealed pot  570  through evaporation and flow to inlet port  579  of pump  575  via pumping line  574 . Heat carried by the helium-3 in the gaseous state flowing through pumping line  574  can reduce a temperature of the liquified helium-3 remaining in sealed pot  570 . Such evaporative cooling of the liquified helium-3 in sealed pot  570  can reduce a temperature of intermediate thermal stage  525  such that intermediate thermal stage  525  can operate at a temperature of about 300 mK. 
     Operating intermediate thermal stage  525  at a temperature of about 300 mK can also facilitate sectioning cryostat  500  into multiple cryogenic systems (e.g., enclosed thermal volume  550  and volume  545 ) operating at different temperatures within a common vacuum space. For example, cryostat  500  can further comprise additional thermal switches (not shown), such as a thermal switch intervening between intermediate thermal stage  525  and Cold Plate stage  530 ; and a thermal switch intervening between Cold Plate stage  530  and Mixing Chamber stage  535 . In this example, each thermal switch intervening between intermedial thermal stage  525  and Mixing Chamber stage  535  can be transitioned to a coupling state. By transitioning those intervening thermal switches to the coupling state, Cold Plate stage  530  and Mixing Chamber stage  535  can be thermally equalized with intermediate thermal stage  525  to operate at a temperature of about 300 mK. 
     When thermal switches  591 ,  593 , and  595  are each in the coupling state, inlet port  579  of pump  575  can be operated to maintain a pressure above the liquified helium-3 collected in sealed pot  570  at the common pressure of the common vacuum space. Maintaining the pressure above the liquified helium-3 collected in sealed pot  570  at the common pressure can impede evaporative cooling of the liquified helium-3 in sealed pot  570 . Absent such evaporative cooling, intermediate thermal stage  525  can be thermally equalized with one or more higher temperature thermal stages of cryostat  500 . For example, intermediate thermal stage  525  can be thermally equalized with 4-K stage  510  via the thermal paths provided by thermal switches  591 ,  593 , and  595  such that intermediate thermal stage  515  can operate at a temperature of about 4 K. As another example, intermediate thermal stage  525  can be thermally equalized with intermediate thermal stage  515  via the thermal paths provided by thermal switches  593  and  595  such that intermediate thermal stage  525  can operate at a temperature of about 1 K. As another example, intermediate thermal stage  525  can be thermally equalized with Still stage  520  via the thermal path provided by thermal switch  595  such that intermediate thermal stage  525  can operate at a temperature of about 700 mK. In an embodiment, sealed pots  560  and/or  570  can be vacuum sealed or cryogenically sealed. In an embodiment, sealed pots  560  and/or  570  can comprise sintered material that facilitates thermal budget optimization. The sintered material can comprise silver, gold, copper, platinum, and the like. 
       FIGS. 6-7  illustrate an example, non-limiting thermal switch  600  that facilitates a switchable thermal path, in accordance with one or more embodiments described herein. As shown by  FIGS. 6-7 , thermal switch  600  comprises a housing  610  formed by coupling a top portion  612  with a bottom portion  614  define an interior volume  630  using attachment mechanisms  620 . In  FIGS. 6-7 , attachment mechanisms  620  are illustrated as bolts. However, in other embodiment, different attachment mechanisms can be used to implement attachment mechanisms  620 . For example, attachment mechanisms  620  can be implemented as weld joints that couple top portion  612  to bottom portion  614 . Thermal switch  600  further comprises a piston  640  disposed within interior volume  630  and one or more permanent magnets  650  circumscribing piston  640 . A Helmholtz coil system can be formed by circumscribing bottom portion  614  with a pair of superconducting wires  660 . The Helmholtz coil system can interact with the one or more permanent magnets  650  circumscribing  640  to facilitate magnetic actuation of thermal switch  600 . 
     In operation, a helium medium can be received into interior volume  630  via a capillary  672  coupled to an outlet port of a pump (not shown) when thermal switch  600  is in a coupling state shown by  FIG. 6 . While in the coupling state, helium medium within interior volume  630  can thermally couple adjacent thermal stages coupled to thermal switch  600 . Thermal switch  600  can transition from the coupling state shown by  FIG. 6  to a decoupling state shown by  FIG. 7  by applying an electrical signal to the pair of superconducting wires  660  forming the Helmholtz coil system. As shown by  FIG. 7 , applying the electrical signal to the pair of superconducting wires  660  forming the Helmholtz coil system can bring a ruby bead  690  in contact with a polymer seat  680 . Bringing the ruby bead  690  in contact with polymer seat  680  can prevent further ingress of the helium medium into interior volume  630 . In an embodiment, polymer seat  680  comprises polyamide-imide. As further ingress of the helium medium into interior volume  630  is prevented, an inlet port of the pump (not shown) can remove residual helium medium from interior volume  630  via capillary  674  to thermally decouple the adjacent thermal stages coupled to thermal switch  600 . In an embodiment, the helium medium can be helium-4. In this embodiment, thermal switch  600  can be a magnetically actuated superfluid leak tight valve. In an embodiment, the helium medium can be helium-3. In this embodiment, thermal switch  600  can be a magnetically actuated fluid leak tight valve. 
       FIG. 8  illustrates another example, non-limiting thermal switch  800  that facilitates a switchable thermal path, in accordance with one or more embodiments described herein. Thermal switch  800  comprises a metal object  830  disposed within an interior volume  820  defined by a sealed container  810 . In an embodiment, metal object  830  can comprise brass. In an embodiment, sealed container  810  can comprise stainless steel. As shown by  FIG. 8 , one or more charcoal pellets  840  and a heating element  850  can be coupled to metal object  830 . In an embodiment, the one or more charcoal pellets  840  and/or heating element  850  can be coupled to metal object  830  using an epoxy. 
     Interior volume  820  of sealed container  810  can comprise a helium medium. In an embodiment, the helium medium can be introduced into the interior volume  820  of sealed container  810  at room temperature. In an embodiment, the helium medium can be introduced into the interior volume  820  of sealed container  810  via a valve (not shown) disposed within a wall of sealed container  810 . In an embodiment, the helium medium can be introduced into the interior volume  820  of sealed container  810  at a pressure of about 10 millibar. As a temperature within the interior volume  820  of sealed container  810  falls below 10 K, charcoal pellets  840  can remove the helium medium from the interior volume  820  by absorbing the helium medium. In an embodiment in which the helium medium is helium-4, charcoal pellets  840  can efficiently remove the helium medium from the interior volume  820  when the temperature within interior volume  820  falls below 4.2 K. In an embodiment in which the helium medium is helium-3, charcoal pellets  840  can efficiently remove the helium medium from the interior volume  820  when the temperature within interior volume  820  falls below 3.1 K. Removing the helium medium from the interior volume  820  through absorption by charcoal pellets  840  transitions thermal switch  800  into a decoupling state. In the decoupling state, adjacent thermal stages coupled to thermal switch  800  are thermally decoupled. An electrical signal can be applied to heating element  850  via conducting elements  852  and  854 . Heat generated by heating element  850  can be applied to charcoal pellets  840  via metal object  830 . Application of heat to charcoal pellets  840  can release the helium medium that the charcoal pellets  840  absorbed into interior volume  820 , thereby transitioning thermal switch  800  from the decoupling state to a coupling state. In the coupling state, the adjacent thermal stages coupled to thermal switch  800  are thermally coupled. 
     Embodiments of the present invention may be a system, a method, and/or an apparatus at any possible technical detail level of integration. What has been described above includes mere examples of systems, methods, and apparatus. It is, of course, not possible to describe every conceivable combination of components or computer-implemented methods for purposes of describing this disclosure, but one of ordinary skill in the art can recognize that many further combinations and permutations of this disclosure are possible. Furthermore, to the extent that the terms “includes,” “has,” “possesses,” and the like are used in the detailed description, claims, appendices and drawings such terms are intended to be inclusive in a manner similar to the term “comprising” as “comprising” is interpreted when employed as a transitional word in a claim. 
     In addition, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise, or clear from context, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, if X employs A; X employs B; or X employs both A and B, then “X employs A or B” is satisfied under any of the foregoing instances. Moreover, articles “a” and “an” as used in the subject specification and annexed drawings should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form. As used herein, the terms “example” and/or “exemplary” are utilized to mean serving as an example, instance, or illustration. For the avoidance of doubt, the subject matter disclosed herein is not limited by such examples. In addition, any aspect or design described herein as an “example” and/or “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs, nor is it meant to preclude equivalent exemplary structures and techniques known to those of ordinary skill in the art. 
     The descriptions of the various embodiments have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein. 
     While certain example embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope the disclosures herein. Thus, nothing in the foregoing description is intended to imply that any particular feature, characteristic, step, module, or block is necessary or indispensable. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosures herein. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of certain of the disclosures herein.