Multiple cryogenic systems separated within a common vacuum space

Abstract

Techniques are provided that facilitate multiple cryogenic systems compartmentalized within a common vacuum space. In one example, a cryostat may include multiple thermal stages and a thermal switch. The multiple thermal stages may be interposed between a 4-Kelvin (K) stage and a cold plate stage. The multiple thermal stages may include a still stage and an intermediate thermal stage that may be mechanically coupled directly to the still stage via a support. A thermal switch may be coupled to the intermediate thermal stage and an adjacent thermal stage. The thermal switch may facilitate altering the thermal profile of the cryostat by providing a switchable thermal path between the intermediate thermal stage and an adjacent thermal stage.

Description

[Technical Field]

[0001] The present disclosure relates to cryogenic environments and, more particularly, to techniques for facilitating multiple compartmentalized cryogenic systems within a common vacuum space. Summary of the Invention

[0002] 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 to define the scope of particular embodiments or 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 are described that facilitate multiple compartmentalized cryogenic systems within a common vacuum space.

[0003] According to one embodiment, the cryostat may include multiple thermal stages and thermal switches. The multiple thermal stages may be interposed between a 4-Kelvin (K) stage and a cold plate stage. The multiple thermal stages may include a still stage and an intermediate thermal stage that may be directly mechanically coupled to the still stage via a support. Thermal switches may be coupled to the intermediate thermal stage and an adjacent thermal stage. The thermal switches may facilitate changing the thermal profile of the cryostat by providing a switchable thermal path between the intermediate thermal stage and the adjacent thermal stage.

[0004] According to another embodiment, the cryostat may include a still stage and a thermal switch. The still stage may be directly mechanically coupled to the intermediate thermal stage via a support. The still stage and the intermediate thermal stage may be included among multiple thermal stages interposed between the 4-K stage and the cold plate stage. The thermal switch may be coupled to the intermediate thermal stage and an adjacent thermal stage. The thermal switch may facilitate changing the thermal profile of the cryostat by providing a switchable thermal path between the intermediate thermal stage and the adjacent thermal stage.

[0005] According to another embodiment, the cryostat may include an enclosed thermal volume and a thermal switch. The enclosed thermal volume may be formed by an intermediate thermal stage coupled to a thermal shield. The intermediate thermal stage may be directly mechanically coupled to the still stage via a support strut. The still stage and intermediate thermal stage may be included among multiple thermal stages interposed between the 4-K stage and the cold plate stage. A thermal switch may be coupled to the intermediate thermal stage and an adjacent thermal stage. The thermal switch may facilitate changing the thermal profile of the cryostat by providing a switchable thermal path between the intermediate thermal stage and the adjacent thermal stage. [Brief explanation of the drawings]

[0006] [Figure 1] 1 illustrates an exemplary, non-limiting cryostat according to one or more embodiments described herein.

[0007] [Figure 2] FIG. 1 shows a circuit schematic of an exemplary, non-limiting cryostat according to one or more embodiments described herein.

[0008] [Figure 3] 1 illustrates an exemplary, non-limiting cryostat with switchable thermal paths facilitating multiple compartmentalized cryogenic systems within a common vacuum space, according to one or more embodiments described herein.

[0009] [Figure 4] 1 illustrates another exemplary, non-limiting cryostat having switchable thermal paths facilitating multiple compartmentalized cryogenic systems within a common vacuum space, according to one or more embodiments described herein.

[0010] [Figure 5] 1 illustrates an exemplary, non-limiting cryostat having multiple switchable thermal paths facilitating multiple compartmentalized cryogenic systems within a common vacuum space, according to one or more embodiments described herein.

[0011] [Figure 6] 1 illustrates an exemplary, non-limiting thermal switch that facilitates switchable thermal paths in a coupled state, according to one or more embodiments described herein.

[0012] [Figure 7] 7 illustrates the exemplary non-limiting thermal switch of FIG. 6 in a separated state.

[0013] [Figure 8] 1 illustrates another exemplary non-limiting thermal switch that facilitates switchable thermal paths according to one or more embodiments described herein. DETAILED DESCRIPTION OF THE INVENTION

[0014] The following detailed description is merely exemplary and is not intended to limit the embodiments and / or the application or uses of the embodiments, nor is it intended to be bound by any express or implied information presented in the preceding Technical Field or Summary sections or in the Detailed Description section.

[0015] One or more embodiments will now be described with reference to the drawings, wherein like reference 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 one or more embodiments. It will be apparent, however, that in various instances, one or more embodiments may be practiced without these specific details.

[0016] FIG. 1 illustrates an exemplary, non-limiting cryostat 100 according to one or more embodiments described herein. As shown in FIG. 1 , the cryostat 100 includes an outer vacuum chamber 110 formed by a sidewall 120 interposed between a top plate 130 and a bottom plate 140. During operation, the outer vacuum chamber 110 can maintain a pressure differential between an ambient environment 150 of the outer vacuum chamber 110 and an interior 160 of the outer vacuum chamber 110. The cryostat 100 further includes multiple thermal stages (or stages) 170 disposed within the interior 160, each mechanically coupled to the top plate 130. The multiple stages 170 include stage 171, stage 173, stage 175, stage 177, and stage 179. Each stage in the multiple stages 170 can be associated with a different temperature. For example, stage 171 may be a 50-Kelvin (50-K) stage associated with a temperature of 50 Kelvin (K), stage 173 may be a 4-Kelvin (4-K) stage associated with a temperature of 4 K, stage 175 may be associated with a temperature of 700 milliKelvin (mK), stage 177 may be associated with a temperature of 100 mK, and stage 179 may be associated with a temperature of 10 mK. Each stage of the plurality of stages 170 is spatially isolated from the other stages of the plurality of stages 170 by a plurality of support posts (e.g., support posts 172 and 174). In one embodiment, stage 175 may be a still stage, stage 177 may be a cold plate stage, and stage 179 may be a mixing chamber stage.

[0017] FIG. 2 shows a circuit schematic of an exemplary, non-limiting cryostat 200 according to one or more embodiments described herein. A cryostat (e.g., cryostat 100 of FIG. 1) can maintain samples or devices disposed on a sample mounting surface located within the cryostat at temperatures near absolute zero, facilitating evaluation of such samples or devices under cryogenic conditions. Cryostats typically provide such low temperatures using five thermal stages mechanically coupled to a cold plate (e.g., top plate 130) of an outer vacuum chamber. The five thermal stages of a cryostat can have a thermal profile in which each subsequent thermal stage has a progressively lower temperature than present in the preceding thermal stage. Evaluating samples or devices under cryogenic conditions typically involves interacting with such samples or devices using one or more devices located at ambient temperatures outside the cryostat. To that end, the cryostat can include input / output (I / O) lines that facilitate the propagation of electrical signals between samples disposed within the cryostat and devices external to the cryostat.

[0018] As an example, a superconducting qubit may be disposed on sample mounting surface 260 of cryostat 200. Four I / O lines couple the superconducting qubit disposed on sample mounting surface 260 to one or more devices external to cryostat 200: drive line 271; flux line 273; pump line 275; and output (or readout) line 277. Those skilled in the art will appreciate that these four I / O lines may contribute to the thermal load placed on cryostat 200 in many ways. One way the four I / O lines may contribute to the thermal load is that each I / O line may provide a thermal path along which heat may be conducted from a hotter thermal stage to a colder thermal stage. For example, in FIG. 2 , drive line 271 is routed from 50-K stage 210 to mixing chamber stage 250 of cryostat 200. Along its routing path through the cryostat 200, the drive line 271 may provide a thermal path through which heat may be conducted from a higher temperature thermal stage to a lower temperature thermal stage, such as from the 50-K stage 210 to the 4-K stage 220.

[0019] Another way in which the four I / O lines may contribute to the thermal load relates to heat (e.g., Joule heating) generated due to dissipation of signals propagating along each given I / O line or through intervening electrical components. For example, a microwave flux signal propagating along magnetic flux line 273 toward a SQUID loop associated with a superconducting qubit disposed on sample mounting surface 260 may introduce heat onto still stage 230 of cryostat 200 via thermal coupling 274. As another example, a microwave pump signal propagating along magnetic flux line 273 for operation of traveling-wave parametric amplifier (TWPA) 281 may introduce heat onto cooling stage 240 via magnetic flux line 273 and attenuator 283 coupled to cooling stage 240.

[0020] Another way in which the four I / O lines may contribute to the heat load involves the radiative load that a hotter thermal stage presents to a cooler thermal stage. For example, a direct current (DC) signal biasing high electron mobility transistor (HEMT) amplifier 285 to facilitate measurements of superconducting qubits disposed on sample mounting surface 260 via output line 277 may introduce heat onto 4-K stage 220. Such heat introduced onto 4-K stage 220 may expose a cooler thermal stage (e.g., still stage 230) to the radiative load that 4-K stage 220 presents to the cooler thermal stage as 4K blackbody radiation.

[0021] As described above, a cryostat can maintain samples or devices placed on a sample mounting surface located within the cryostat at temperatures near absolute zero to facilitate evaluation of such samples or devices under cryogenic conditions. The five thermal stages of a cryostat typically used to provide such cryogenic conditions can have a thermal profile in which each subsequent thermal stage has a progressively lower temperature than exists in the preceding thermal stage. The thermal profile can exist within a common vacuum space defined by the outer vacuum chamber of the cryostat that encloses the five thermal stages.

[0022] In some cases, temperatures near absolute zero may be advantageous for characterizing samples or devices under cryogenic conditions. For example, temperatures near absolute zero may be advantageous for characterizing 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 cases, higher temperatures may be sufficient for characterizing samples or devices under cryogenic conditions. For example, a temperature of about 4 K may be sufficient for characterizing HEMT devices or several niobium (Nb) resonators under cryogenic conditions. As another example, a temperature of about 1 K may be sufficient for characterizing several Josephson junction (JJ) devices (e.g., JJ field-effect transistors) or several Nb resonators under cryogenic conditions. As another example, a temperature of about 300 mK may be sufficient for characterizing qubit devices, microwave components, or several JJ devices. Thus, multiple cryogenic systems compartmentalized within a common vacuum space of a cryostat may facilitate improved efficiency by flexibly altering the cryostat's thermal profile to accommodate different characterization conditions. The embodiments described herein facilitate multiple compartmentalized cryogenic systems within a common vacuum space by providing intermediate thermal stages that provide additional cooling capacity to the cryostat and switchable thermal paths between adjacent thermal stages.

[0023] 3 illustrates an exemplary, non-limiting cryostat 300 having switchable thermal paths that facilitate multiple compartmentalized cryogenic systems within a common vacuum space, according to one or more embodiments described herein. As illustrated by FIG. 3, the cryostat 300 includes a 50-K stage 305 that may be coupled to a cold plate (e.g., top plate 130 of FIG. 1) of an outer vacuum chamber (not shown). The outer vacuum chamber may define a common vacuum space (e.g., interior 160) that encapsulates the various thermal stages of the cryostat 300 at a common pressure.

[0024] Cryostat 300 further comprises multiple thermal stages interposed between 4-K stage 310 and cold plate stage 325. The multiple thermal stages include still stage 320 and intermediate thermal stage 315. Intermediate thermal stage 315 is directly mechanically coupled to 4-K stage 310 via support post 311 and to still stage 320 via support post 316. Intermediate thermal stage 315 is indirectly mechanically coupled to 50-K stage 305 via support post 306, to cold plate stage 325 via support post 321, and to mixing chamber stage 330 via support post 326.

[0025] 3 also shows that the cryostat 300 further comprises an enclosed thermal volume 340, which may be formed by a thermal shield 342 coupled to the intermediate thermal stage 315. The enclosed thermal volume 340 may be thermally isolated from a volume 345 of the cryostat 300 that is external to the enclosed thermal volume 340. In FIG. 3, the thermal shield 342 is shown as being interposed between the intermediate thermal stage 315 and a thermal plate 344, forming the enclosed thermal volume 340. However, in other embodiments, the thermal shield 342 and the thermal plate 344 may be implemented as a single element, such that the single element may be coupled to the intermediate thermal stage 315 to form the enclosed thermal volume 340.

[0026] The intermediate thermal stage 315 may have feedthrough elements 317 interposed in a wiring structure 370 that facilitates propagation of electrical signals between the 4-K stage 310 and the cold plate stage 325. The wiring structure 370 may include I / O lines that couple a sample disposed within the cryostat 300 to one or more devices external to the cryostat 300. For example, the wiring structure 370 may include I / O lines such as the drive lines 271, the magnetic flux lines 273, the pump lines 275, and / or the power (or readout) lines 277 of FIG. 2. In one embodiment, the intermediate thermal stage 315 may comprise copper, gold, silver, brass, platinum, or a combination thereof.

[0027] The intermediate thermal stage 315 may provide additional cooling capacity for the cryostat 300 via a sealed pot 350 coupled to the intermediate thermal stage 315. To that end, the sealed pot 350 facilitates evaporative cooling of the helium medium, i.e., helium-4. A condenser line 352 may couple an outlet port 362 of a pump 360 to the sealed pot 350 via the 4-K stage 310. In one embodiment, the pump 360 may be a vacuum pump for circulating the helium medium through the sealed pot 350. In one embodiment, the pump 360 may be located external to the cryostat 300. In one embodiment, the pump 360 may be located within the cryostat 300. In this embodiment, the pump 360 may be implemented as a sorb pump. The condenser line 352 may provide a return path for the helium medium to the sealed pot 350. A pumping line 354 may couple an inlet port 364 of the pump 360 to the sealed pot 350 via the 4-K stage 310. The 4-K stage 310 may provide a path for the capacitor line 352 and / or the pump line 354 via a feedthrough element, such as the feedthrough element 312 .

[0028] As shown by FIG. 3 , the cryostat 300 further includes a thermal switch 380 coupled to the intermediate thermal stage 315 and an adjacent thermal stage. In the example of FIG. 3 , the adjacent thermal stage is the 4-K stage 310. Exemplary, non-limiting thermal switches suitable for implementing the thermal switch 380 are discussed in more detail below with respect to FIGS. 6-7 . The thermal switch 380 may facilitate changing the thermal profile of the cryostat 300 by providing a switchable thermal path between the intermediate thermal stage 315 and the 4-K stage 310. To that end, the transfer medium of the thermal switch 380 may provide a thermal path that thermally couples (or shorts) the intermediate thermal stage 315 to the 4-K stage 310 when the thermal switch 380 is in a coupled state. When the thermal switch 380 transitions from the coupled state to the decoupled state, the thermal path provided by the transfer medium of the thermal switch 380 may be removed, thereby thermally isolating the intermediate thermal stage 315 from the 4-K stage 310.

[0029] In one embodiment, the propagation medium may include a helium medium. In one embodiment, the propagation medium may include a superconducting material (e.g., aluminum). In this embodiment, the thermal switch 380 may be transitioned to the decoupling state by transitioning the propagation medium from a non-superconducting state to a superconducting state. In one embodiment, the propagation medium may be transitioned from a non-superconducting state to a superconducting state by reducing the temperature of the propagation medium below the critical temperature of the superconducting material. In one embodiment, the superconducting material may be placed in a magnetic field. In one embodiment, the propagation medium may be transitioned from a superconducting state to a non-superconducting state by increasing the strength of the magnetic field above the critical magnetic field of the superconducting material.

[0030] During operation, helium-4 may flow in a gaseous state from outlet port 362 toward sealed pot 350. Feedthrough element 312 may thermally secure capacitor wire 352 to 4-K stage 310. As helium-4 flows out of feedthrough element 312, it may transition from a gaseous state to a liquid state. The liquid helium-4 may accumulate in sealed pot 350. When thermal switch 380 is in the disconnected state, inlet port 364 of pump 360 may be operated to reduce the pressure above the liquefied helium-4 accumulated in sealed pot 350. Helium-4 in a gaseous state may form above the liquefied helium-4 accumulated in sealed pot 350 by evaporation and flow to inlet port 364 of pump 360 via pumping wire 354. Heat carried by the gaseous helium-4 flowing through pumping line 354 may reduce the temperature of the liquefied helium-4 remaining in sealed pot 350. Such evaporative cooling of the liquefied helium-4 within sealed pot 350 may reduce the temperature of intermediate thermal stage 315, which may operate at a temperature of approximately 1 K.

[0031] Operating intermediate thermal stage 315 at a temperature of approximately 1 K may facilitate partitioning cryostat 300 into multiple cryogenic systems (e.g., enclosed thermal volumes 340 and 345) operating at different temperatures within a common vacuum space. For example, cryostat 300 may further include additional thermal switches (not shown), such as a thermal switch interposed between intermediate thermal stage 315 and still stage 320; a thermal switch interposed between still stage 320 and cold plate stage 325; and a thermal switch interposed between cold plate stage 325 and mixing chamber stage 330. In this example, each interposed thermal switch may be transitioned to a coupled state, such that still stage 320, cold plate stage 325, and mixing chamber stage 330 are each thermally isotropic with intermediate thermal stage 315 and may operate at a temperature of approximately 1 K.

[0032] When the thermal switch 380 is in an engaged state, the inlet port 364 of the pump 360 can be operated to maintain the pressure above the liquefied helium-4 accumulated in the sealed pot 350 at the common pressure of the common vacuum space. Maintaining the pressure above the liquefied helium-4 accumulated in the sealed pot 350 at the common pressure can inhibit evaporative cooling of the liquefied helium-4 within the sealed pot 350. Without such evaporative cooling, the intermediate thermal stage 315 can be thermally isotropic with the 4-K stage 310 via the thermal path provided by the thermal switch 380, thereby allowing the intermediate thermal stage 315 to operate at a temperature of approximately 4 K. In one embodiment, the sealed pot 350 can be vacuum-sealed or cryogenically sealed. In one embodiment, the sealed pot 350 can include a sintered material to facilitate optimization of the thermal budget. The sintered material can include silver, gold, copper, platinum, and the like.

[0033] 4 illustrates another exemplary, non-limiting cryostat 400 having switchable thermal paths that facilitate multiple compartmentalized cryogenic systems within a common vacuum space, according to one or more embodiments described herein. As illustrated by FIG. 4, the cryostat 400 includes a 50-K stage 405 that may be coupled to a cold plate (e.g., top plate 130 of FIG. 1) of an outer vacuum chamber (not shown). The outer vacuum chamber may define a common vacuum space (e.g., interior 160) that encapsulates the various thermal stages of the cryostat 400 at a common pressure.

[0034] Cryostat 400 further comprises multiple thermal stages interposed between 4-K stage 410 and cold plate stage 425. The multiple thermal stages include a still stage 415 and an intermediate thermal stage 420. Intermediate thermal stage 420 is directly mechanically coupled to still stage 415 via support posts 416 and to cold plate stage 425 via support posts 421. Intermediate thermal stage 420 is indirectly mechanically coupled to 50-K stage 405 via support posts 406, to 4-K stage 410 via support posts 411, and to mixing chamber stage 430 via support posts 426.

[0035] 4 also shows that the cryostat 400 further comprises an enclosed thermal volume 440, which may be formed by a thermal shield 442 coupled to the intermediate thermal stage 420. The enclosed thermal volume 440 may be thermally isolated from a volume 445 of the cryostat 400 that is external to the enclosed thermal volume 440. In FIG. 4, the thermal shield 442 is shown as being interposed between the intermediate thermal stage 420 and a thermal plate 444, forming the enclosed thermal volume 440. However, in other embodiments, the thermal shield 442 and the thermal plate 444 may be implemented as a single element, such that the single element may be coupled to the intermediate thermal stage 420 to form the enclosed thermal volume 440.

[0036] The intermediate thermal stage 420 may have feedthrough elements 422 interposed in a wiring structure 470 that facilitates propagation of electrical signals between the 4-K stage 410 and the cold plate stage 425. The still stage 415 may also include feedthrough elements 418 interposed in the wiring structure 470. The wiring structure 470 may include I / O lines that couple a sample disposed within the cryostat 400 to one or more devices external to the cryostat 400. For example, the wiring structure 470 may include I / O lines such as the drive lines 271, the magnetic flux lines 273, the pump lines 275, and / or the power (or readout) lines 277 of FIG. 2 . In one embodiment, the intermediate thermal stage 420 may comprise copper, gold, silver, brass, platinum, or a combination thereof.

[0037] The intermediate thermal stage 420 may provide additional cooling capacity for the cryostat 400 via a sealed pot 450 coupled to the intermediate thermal stage 420. To that end, the sealed pot 450 facilitates evaporative cooling of the helium medium, i.e., helium-3. A condenser line 452 may couple an outlet port 462 of a pump 460 to the sealed pot 450 via the 4-K stage 410. In one embodiment, the pump 460 may be a vacuum pump for circulating the helium medium through the sealed pot 450. In one embodiment, the pump 460 may be located external to the cryostat 400. In one embodiment, the pump 460 may be located within the cryostat 400. In this embodiment, the pump 460 may be implemented as an adsorption pump. The condenser line 452 may provide a return path for the helium medium to the sealed pot 450. A pumping line 454 may couple an inlet port 464 of the pump 460 to the sealed pot 450 via the 4-K stage 410. 4-K stage 410 may provide a path for capacitor line 452 and / or pump line 454 via a feedthrough element, such as feedthrough element 412. Still stage 415 may provide a path for capacitor line 452 and / or pump line 454 via a feedthrough element, such as feedthrough element 422.

[0038] As shown by FIG. 4 , the cryostat 400 further includes a thermal switch 480 coupled to the intermediate thermal stage 420 and an adjacent thermal stage. In the example of FIG. 4 , the adjacent thermal stage is the still stage 415. Exemplary, non-limiting thermal switches suitable for implementing the thermal switch 480 are discussed in more detail below with respect to FIGS. 6-7 . The thermal switch 480 may facilitate modifying the thermal profile of the cryostat 400 by providing a switchable thermal path between the intermediate thermal stage 420 and the still stage 415. To that end, the transfer medium of the thermal switch 480 may provide a thermal path that thermally couples (or shorts) the intermediate thermal stage 420 to the still stage 415 when the thermal switch 480 is in a coupled state. When the thermal switch 480 transitions from the coupled state to the decoupled state, the thermal path provided by the transfer medium of the thermal switch 480 may be removed, thereby thermally isolating the intermediate thermal stage 420 from the still stage 415.

[0039] In one embodiment, the propagation medium may include a helium medium. In one embodiment, the propagation medium may include a superconducting material (e.g., aluminum). In this embodiment, the thermal switch 480 may be transitioned to the decoupling state by transitioning the propagation medium from a non-superconducting state to a superconducting state. In one embodiment, the propagation medium may be transitioned from a non-superconducting state to a superconducting state by reducing the temperature of the propagation medium below the critical temperature of the superconducting material. In one embodiment, the superconducting material may be placed in a magnetic field. In one embodiment, the propagation medium may be transitioned from a superconducting state to a non-superconducting state by increasing the strength of the magnetic field above the critical magnetic field of the superconducting material.

[0040] During operation, helium-3 may flow in a gaseous state from outlet port 462 toward sealed pot 450. Feedthrough elements 412 and / or 417 may thermally secure capacitor line 452 to 4-K stage 410 and / or still stage 415, respectively. As helium-3 flows out of feedthrough elements 412 and / or 417, it may transition from a gaseous state to a liquid state. The liquid helium-3 may accumulate in sealed pot 450. When thermal switch 480 is in the disconnected state, inlet port 464 of pump 460 may be operated to reduce the pressure above the liquefied helium-3 accumulated in sealed pot 450. Helium-3 in a gaseous state may form above the liquefied helium-3 accumulated in sealed pot 450 by evaporation and flow to inlet port 464 of pump 460 via pumping line 454. Heat carried by the gaseous helium-3 flowing through pumping line 454 may reduce the temperature of the liquefied helium-3 remaining in sealed pot 450. Such evaporative cooling of the liquefied helium-3 in sealed pot 470 may reduce the temperature of intermediate thermal stage 420, which may operate at a temperature of approximately 300 mK.

[0041] Operating intermediate thermal stage 420 at a temperature of approximately 300 mK may facilitate partitioning cryostat 400 into multiple cryogenic systems (e.g., enclosed thermal volumes 440 and 445) operating at different temperatures within a common vacuum space. For example, cryostat 400 may further include additional thermal switches (not shown), such as a thermal switch interposed between intermediate thermal stage 420 and cold plate stage 425; and a thermal switch interposed between cold plate stage 425 and mixing chamber stage 430. In this example, each interposed thermal switch may be transitioned to a coupled state, such that cold plate stage 425 and mixing chamber stage 430 are thermally isotropic with intermediate thermal stage 420 and may each operate at a temperature of approximately 300 mK.

[0042] When the thermal switch 480 is in an engaged state, the inlet port 464 of the pump 460 can be operated to maintain the pressure above the liquefied helium-3 accumulated in the sealed pot 450 at the common pressure of the common vacuum space. Maintaining the pressure above the liquefied helium-3 accumulated in the sealed pot 450 at the common pressure can inhibit evaporative cooling of the liquefied helium-3 within the sealed pot 450. Without such evaporative cooling, the intermediate thermal stage 420 can be thermally isotropic with the still stage 415 via the thermal path provided by the thermal switch 480, thereby allowing the intermediate thermal stage 420 to operate at a temperature of approximately 700 mK. In one embodiment, the sealed pot 450 can be vacuum-sealed or cryogenically sealed. In one embodiment, the sealed pot 450 can include a sintered material to facilitate optimization of the thermal budget. The sintered material can include silver, gold, copper, platinum, and the like.

[0043] FIG. 5 illustrates an exemplary, non-limiting cryostat 500 having multiple switchable thermal paths facilitating multiple compartmentalized cryogenic systems within a common vacuum space, according to one or more embodiments described herein. As illustrated by FIG. 5 , the cryostat 500 includes a 50-K stage 505 that can be coupled to a cold 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) that encapsulates the various thermal stages of the cryostat 500 at a common pressure. The cryostat 500 further includes multiple thermal stages interposed between a 4-K stage 510 and a cold plate stage 530. The multiple thermal stages include a still stage 520 and multiple intermediate thermal stages (e.g., intermediate thermal stage 515 and intermediate thermal stage 525).

[0044] FIG. 5 also shows that the cryostat 500 further comprises an enclosed thermal volume 540 and an enclosed thermal volume 550 nested within the enclosed thermal volume 540. The enclosed thermal volume 540 may be thermally isolated from the enclosed thermal volume 550 and a volume 545 of the cryostat 500 that is external to the enclosed thermal volume 540. The enclosed thermal volume 540 may be formed by a thermal shield 542 coupled to the intermediate thermal stage 515. In FIG. 5, the thermal shield 542 is shown as being interposed between the intermediate thermal stage 515 and a thermal plate 544 to form the enclosed thermal volume 540. However, in other embodiments, the thermal shield 542 and the thermal plate 544 may be implemented as a single element such that the single element may be coupled to the intermediate thermal stage 515 to form the enclosed thermal volume 540. The enclosed thermal volume 550 may be formed by a heat shield 552 coupled to the intermediate thermal stage 525. In Figure 5, the heat shield 552 is shown as being interposed between the intermediate thermal stage 525 and a heat plate 554 to form the enclosed thermal volume 550. However, in other embodiments, the heat shield 552 and the heat plate 554 may be implemented as a single element such that the single element may be coupled to the intermediate thermal stage 525 to form the enclosed thermal volume 550.

[0045] Intermediate thermal stage 515 is mechanically directly coupled to 4-K stage 510 via support posts 511 and to still stage 520 via support posts 516. Intermediate thermal stage 515 is mechanically indirectly coupled to 50-K stage 505 via support posts 506, to intermediate thermal stage 525 via support posts 521, to cold plate stage 530 via support posts 526, and to mixing chamber stage 535 via support posts 531. Intermediate thermal stage 525 is mechanically directly coupled to still stage 520 via support posts 521 and to cold plate stage 530 via support posts 526. Intermediate thermal stage 525 is mechanically indirectly coupled to 50-K stage 505 via support posts 506, to 4-K stage 510 via support posts 511, to intermediate thermal stage 515 via support posts 516, and to mixing chamber stage 535 via support posts 531. Intermediate thermal stages 515 and 525 are directly mechanically coupled to either side of still stage 520 via supports 516 and 521, respectively.

[0046] The intermediate thermal stages 515 and 525 may have interposed feedthrough elements 518 and 527, respectively, in a wiring structure 580 that facilitates propagation of electrical signals between the 4-K stage 510 and the cold plate stage 530. The still stage 520 may also include interposed feedthrough elements 523 in the wiring structure 580. The wiring structure 580 may include I / O lines that couple a sample disposed within the cryostat 500 to one or more devices external to the cryostat 500. For example, the wiring structure 580 may include I / O lines such as the drive lines 271, the magnetic flux lines 273, the pump lines 275, and / or the power (or readout) lines 277 of FIG. 2 . In one embodiment, the intermediate thermal stages 515 and / or 525 may comprise copper, gold, silver, brass, platinum, or a combination thereof.

[0047] Intermediate thermal stage 515 may 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 the helium medium, i.e., helium-4. Condenser line 562 may couple outlet port 567 of pump 565 to sealed pot 560 via 4-K stage 510. Condenser line 562 may provide a return path for the helium medium to sealed pot 560. Pumping line 564 may couple inlet port 569 of pump 565 to sealed pot 560 via 4-K stage 510. 4-K stage 510 may provide passage for condenser line 562 and / or pumping line 564 via feedthrough elements, such as feedthrough element 512.

[0048] Intermediate thermal stage 525 may provide additional cooling capacity for cryostat 500 via sealed pot 570 coupled to intermediate thermal stage 525. To that end, sealed pot 570 facilitates evaporative cooling of the helium medium, i.e., He-3. Condenser line 572 may couple outlet port 577 of pump 575 to sealed pot 570 via 4-K stage 510. In one embodiment, pumps 565 and / or 575 may be vacuum pumps for circulating the corresponding helium medium through sealed pots 560 and / or 570, respectively. In one embodiment, pumps 565 and / or 575 may be located external to cryostat 500. In one embodiment, pumps 565 and / or 575 may be located within cryostat 500. In this embodiment, pumps 565 and / or 575 may be implemented as adsorption pumps. Condenser line 572 may provide a return path for the helium medium to sealed pot 570. Pumping wires 574 may couple an inlet port 579 of pump 575 to sealed pot 570 via 4-K stage 510. 4-K stage 510 may provide passage for capacitor wires 572 and / or pumping wires 574 via feedthrough elements, such as feedthrough element 513. Intermediate thermal stage 515 may provide passage for capacitor wires 572 and / or pumping wires 574 via feedthrough elements, such as feedthrough element 517. Still stage 520 may provide passage for capacitor wires 572 and / or pumping wires 574 via feedthrough elements, such as feedthrough element 522.

[0049] 5, cryostat 500 further comprises a plurality of thermal switches coupled to various thermal stages of cryostat 500. The plurality of thermal switches includes thermal switch 591 coupled to 4-K stage 510 and intermediate thermal stage 515; thermal switch 593 coupled to intermediate thermal stage 515 and still stage 520; and thermal switch 595 coupled to still stage 520 and intermediate thermal stage 525. Exemplary, non-limiting thermal switches suitable for implementing thermal switches 591, 593, and / or 595 are discussed in more detail below with respect to FIGS. 6-7. Thermal switches 591, 593, and / or 595 may each provide a switchable thermal path between various thermal stages of cryostat 500, thereby facilitating altering the thermal profile of cryostat 500.

[0050] To that end, each thermal switch may have a transfer medium that can provide a thermal path that thermally couples (or shorts) the respective thermal stages when the thermal switch is in a coupled state. For example, thermal switch 591 may have 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 coupled state. When a given thermal switch transitions from a coupled state to a decoupled state, the thermal path provided by the transfer medium of that thermal switch may be removed, thereby thermally isolating the respective thermal stages. Continuing with the above example, the thermal path provided by the transfer medium of thermal switch 591 may be removed when thermal switch 591 transitions to a decoupled state, thereby thermally isolating intermediate thermal stage 515 from 4-K stage 510.

[0051] In one embodiment, the propagation medium may include a helium medium. In one embodiment, the propagation medium may include a superconducting material (e.g., aluminum). In this embodiment, the thermal switch 830 may be transitioned to the decoupling state by transitioning the propagation medium from a non-superconducting state to a superconducting state. In one embodiment, the propagation medium may be transitioned from a non-superconducting state to a superconducting state by reducing the temperature of the propagation medium below the critical temperature of the superconducting material. In one embodiment, the superconducting material may be placed in a magnetic field. In one embodiment, the propagation medium may be transitioned from a superconducting state to a non-superconducting state by increasing the strength of the magnetic field above the critical magnetic field of the superconducting material.

[0052] During operation, helium-4 may flow in a gaseous state from outlet port 567 toward sealed pot 560. Feedthrough element 512 may thermally secure capacitor line 562 to 4-K stage 510. As helium-4 flows out of feedthrough element 512, it may transition from a gaseous state to a liquid state. The liquid helium-4 may accumulate in sealed pot 560. When thermal switch 591 is in the disconnected state, inlet port 567 of pump 565 may be operated to reduce the pressure above the liquefied helium-4 accumulated in sealed pot 560. Helium-4 in a gaseous state may form above the liquefied helium-4 accumulated in sealed pot 560 by evaporation and flow to inlet port 569 of pump 560 via pumping line 564. Heat carried by the gaseous helium-4 flowing through pumping line 564 may reduce the temperature of the liquefied helium-4 remaining in sealed pot 560. Such evaporative cooling of the liquefied helium-4 in sealed pot 540 may reduce the temperature of intermediate thermal stage 515, which may operate at a temperature of approximately 1 K.

[0053] Operating intermediate thermal stage 515 at a temperature of about 1 K may facilitate partitioning cryostat 500 into multiple cryogenic systems (e.g., enclosed thermal volumes 540 and 545) operating at different temperatures within a common vacuum space. For example, cryostat 500 may further include additional thermal switches (not shown), such as a thermal switch interposed between intermediate thermal stage 525 and cold plate stage 530; and a thermal switch interposed between cold plate stage 530 and mixing chamber stage 535. In this example, each thermal switch interposed between intermediate thermal stage 515 and mixing chamber stage 535 (i.e., thermal switches 593 and 595 in addition to the additional thermal switches interposed between intermediate thermal stage 525, cold plate stage 530, and mixing chamber stage 535) may be transitioned to a coupled state. By transitioning their intervening thermal switches to a coupled state, the mixing chamber stage 535 and each thermal stage intervening between the intermediate thermal stage 515 and the mixing chamber stage 535 can be thermally isotropic with the intermediate thermal stage 515 and operate at a temperature of approximately 1K.

[0054] When thermal switch 591 is in an engaged state, inlet port 567 of pump 565 can be operated to maintain the pressure above the liquefied helium-4 accumulated in sealed pot 560 at the common pressure of the common vacuum space. Maintaining the pressure above the liquefied helium-4 accumulated in sealed pot 560 at the common pressure can inhibit evaporative cooling of the liquefied helium-4 within sealed pot 560. In the absence of such evaporative cooling, intermediate thermal stage 515 can be thermally isotropic with 4-K stage 510 via the thermal path provided by thermal switch 591, thereby allowing intermediate thermal stage 515 to operate at a temperature of approximately 4 K.

[0055] During operation, helium-4 may flow in a gaseous state from outlet port 567 toward sealed pot 560. Feedthrough element 512 may thermally secure capacitor line 562 to 4-K stage 510. As helium-4 flows out of feedthrough element 512, it may transition from a gaseous state to a liquid state. The liquid helium-4 may accumulate in sealed pot 560. When thermal switch 591 is in the disconnected state, inlet port 567 of pump 565 may be operated to reduce the pressure above the liquefied helium-4 accumulated in sealed pot 560. Helium-4 in a gaseous state may form above the liquefied helium-4 accumulated in sealed pot 560 by evaporation and flow to inlet port 569 of pump 560 via pumping line 564. Heat carried by the gaseous helium-4 flowing through pumping line 564 may reduce the temperature of the liquefied helium-4 remaining in sealed pot 560. Such evaporative cooling of the liquefied helium-4 in sealed pot 540 may reduce the temperature of intermediate thermal stage 515, which may operate at a temperature of approximately 1 K.

[0056] Operating intermediate thermal stage 515 at a temperature of about 1 K may facilitate partitioning cryostat 500 into multiple cryogenic systems (e.g., enclosed thermal volumes 540 and 545) operating at different temperatures within a common vacuum space. For example, cryostat 500 may further include additional thermal switches (not shown), such as a thermal switch interposed between intermediate thermal stage 525 and cold plate stage 530; and a thermal switch interposed between cold plate stage 530 and mixing chamber stage 535. In this example, each thermal switch interposed between intermediate thermal stage 515 and mixing chamber stage 535 (i.e., thermal switches 593 and 595 in addition to the additional thermal switches interposed between intermediate thermal stage 525, cold plate stage 530, and mixing chamber stage 535) may be transitioned to a coupled state. By transitioning their intervening thermal switches to a coupled state, the mixing chamber stage 535 and each thermal stage intervening between the intermediate thermal stage 515 and the mixing chamber stage 535 can be thermally isotropic with the intermediate thermal stage 515 and operate at a temperature of approximately 1K.

[0057] When thermal switch 591 is in an engaged state, inlet port 567 of pump 565 can be operated to maintain the pressure above the liquefied helium-4 accumulated in sealed pot 560 at the common pressure of the common vacuum space. Maintaining the pressure above the liquefied helium-4 accumulated in sealed pot 560 at the common pressure can inhibit evaporative cooling of the liquefied helium-4 within sealed pot 560. In the absence of such evaporative cooling, intermediate thermal stage 515 can be thermally isotropic with 4-K stage 510 via the thermal path provided by thermal switch 591, thereby allowing intermediate thermal stage 515 to operate at a temperature of approximately 4 K.

[0058] During operation, helium-3 may flow in a gaseous state from outlet port 577 toward sealed pot 570. Feedthrough elements 513, 517, and / or 522 may thermally secure capacitor wire 572 to 4-K stage 510, intermediate thermal stage 515, and / or still stage 520, respectively. As helium-3 flows out of feedthrough elements 513, 517, and / or 522, it may transition from a gaseous state to a liquid state. Helium-3 in the liquid state may accumulate in sealed pot 570. When thermal switches 591, 593, and 595 are each in an isolated state, inlet port 579 of pump 575 may be operated to reduce the pressure above the liquefied helium-3 accumulated in sealed pot 570. Gaseous helium-3 may be formed above the liquefied helium-3 accumulated in sealed pot 570 by evaporation and flow to inlet port 579 of pump 575 via pumping line 574. Heat carried by the gaseous helium-3 flowing through pumping line 574 may lower the temperature of the liquefied helium-3 remaining in sealed pot 570. Such evaporative cooling of the liquefied helium-3 within sealed pot 570 may lower the temperature of intermediate thermal stage 525, which may operate at a temperature of approximately 300 mK.

[0059] Operating intermediate thermal stage 525 at a temperature of approximately 300 mK may also facilitate partitioning cryostat 500 into multiple cryogenic systems (e.g., enclosed thermal volumes 550 and 545) operating at different temperatures within a common vacuum space. For example, cryostat 500 may further include additional thermal switches (not shown), such as a thermal switch interposed between intermediate thermal stage 525 and cold plate stage 530; and a thermal switch interposed between cold plate stage 530 and mixing chamber stage 535. In this example, each thermal switch interposed between intermediate thermal stage 525 and mixing chamber stage 535 may be transitioned to a coupled state. By transitioning the intervening thermal switches to a coupled state, cold plate stage 530 and mixing chamber stage 535 may be thermally isotropic with intermediate thermal stage 525 and operate at a temperature of approximately 300 mK.

[0060] When thermal switches 591, 593, and 595 are each in a coupled state, inlet port 579 of pump 575 can be operated to maintain the pressure above the liquefied helium-3 accumulated in sealed pot 570 at the common pressure of the common vacuum space. Maintaining the pressure above the liquefied helium-3 accumulated in sealed pot 570 at the common pressure can inhibit evaporative cooling of the liquefied helium-3 within sealed pot 570. In the absence of such evaporative cooling, intermediate thermal stage 525 can be thermally isotropic with one or more higher temperature thermal stages of cryostat 500. For example, intermediate thermal stage 525 can be isotropic with 4-K stage 510 via the thermal path provided by thermal switches 591, 593, and 595, such that intermediate thermal stage 515 can operate at a temperature of approximately 4 K. As another example, intermediate thermal stage 525 may be thermally isotropic with intermediate thermal stage 515 via the thermal path provided by thermal switches 593 and 595, thereby allowing intermediate thermal stage 525 to operate at a temperature of approximately 1 K. As another example, intermediate thermal stage 525 may be thermally isotropic with still stage 520 via the thermal path provided by thermal switch 595, thereby allowing intermediate thermal stage 525 to operate at a temperature of approximately 700 mK. In one embodiment, sealed pots 560 and / or 570 may be vacuum sealed or cryogenically sealed. In one embodiment, sealed pots 560 and / or 570 may include a sintered material to facilitate optimization of the thermal budget. The sintered material may include silver, gold, copper, platinum, and the like.

[0061] 6-7 illustrate an exemplary, non-limiting thermal switch 600 facilitating a switchable thermal path according to one or more embodiments described herein. As illustrated by FIGS. 6-7 , the thermal switch 600 includes a housing 610 formed by coupling a top portion 612 to a bottom portion 614 using an attachment mechanism 620 to define an interior volume 630. In FIGS. 6-7 , the attachment mechanism 620 is shown as a bolt. However, in other embodiments, a different attachment mechanism may be used to implement the attachment mechanism 620. For example, the attachment mechanism 620 may be implemented as a welded joint that couples the top portion 612 to the bottom portion 614. The thermal switch 600 further includes a piston 640 disposed within the interior volume 630 and one or more permanent magnets 650 surrounding the piston 640. A Helmholtz coil system may be formed by surrounding the bottom portion 614 using a pair of superconducting wires 660. The Helmholtz coil system may interact with one or more permanent magnets 650 surrounding the piston 640 to facilitate magnetic actuation of the thermal switch 600 .

[0062] During operation, helium medium can be admitted to the internal volume 630 via a capillary tube 672 coupled to an outlet port (not shown) of the pump when the thermal switch 600 is in the coupled state shown in FIG. 6 . While in the coupled state, the helium medium in the internal volume 630 can thermally couple adjacent thermal stages coupled to the thermal switch 600. The thermal switch 600 can transition from the coupled state shown in FIG. 6 to the decoupled state shown in FIG. 7 by applying an electrical signal to a pair of superconducting wires 660 forming a Helmholtz coil system. As shown in FIG. 7 , applying an electrical signal to the pair of superconducting wires 660 forming the Helmholtz coil system can cause the ruby ​​bead 690 to contact the polymer sheet 680. Contacting the ruby ​​bead 690 with the polymer sheet 680 can prevent further ingress of helium medium into the internal volume 630. In one embodiment, the polymer sheet 680 comprises polyamideimide. Because further ingress of helium medium into interior volume 630 is prevented, a pump inlet port (not shown) can remove residual helium medium from interior volume 630 via capillary tube 674, thermally isolating adjacent thermal stages coupled to thermal switch 600. In one embodiment, the helium medium can be helium-4. In this embodiment, thermal switch 600 can be a magnetically actuated superfluidic leak-tight valve. In one embodiment, the helium medium can be helium-3. In this embodiment, thermal switch 600 can be a magnetically actuated superfluidic leak-tight valve.

[0063] 8 illustrates another exemplary, non-limiting thermal switch 800 that facilitates a switchable thermal path according to one or more embodiments described herein. The thermal switch 800 includes a metal object 830 disposed within an interior volume 820 defined by a sealed container 810. In one embodiment, the metal object 830 may include brass. In one embodiment, the sealed container 810 may include stainless steel. As illustrated by FIG. 8 , one or more charcoal pellets 840 and a heating element 850 may be coupled to the metal object 830. In one embodiment, the one or more charcoal pellets 840 and / or the heating element 850 may be coupled to the metal object 830 using epoxy.

[0064] The internal volume 820 of the sealed vessel 810 may contain a helium medium. In one embodiment, the helium medium may be introduced into the internal volume 820 of the sealed vessel 810 at room temperature. In one embodiment, the helium medium may be introduced into the internal volume 820 of the sealed vessel 810 through a valve (not shown) disposed in the wall of the sealed vessel 810. In one embodiment, the helium medium may be introduced into the internal volume 820 of the sealed vessel 810 at a pressure of about 10 millibars (about 1 kilopascal). When the temperature in the internal volume 820 of the sealed vessel 810 falls below 10 K, the charcoal pellets 840 may remove the helium medium from the internal volume 820 by absorbing the helium medium. In one embodiment, where the helium medium is helium-4, the charcoal pellets 840 may efficiently remove the helium medium from the internal volume 820 when the temperature in the internal volume 820 falls below 4.2 K. In one embodiment where the helium medium is helium-3, the charcoal pellet 840 can efficiently remove the helium medium from the internal volume 820 when the temperature within the internal volume 820 is below 3.1 K. Removing the helium medium from the internal volume 820 through absorption by the charcoal pellet 840 transitions the thermal switch 800 to an isolated state. In the isolated state, adjacent thermal stages coupled to the thermal switch 800 are thermally isolated. An electrical signal can be applied to the heating element 850 via the conductive elements 852 and 854. Heat generated by the heating element 850 can be applied to the charcoal pellet 840 via the metal object 830. Applying heat to the charcoal pellet 840 can release the helium medium absorbed by the charcoal pellet 840 into the internal volume 820, thereby transitioning the thermal switch 800 from the isolated state to a coupled state. In the coupled state, adjacent thermal stages coupled to the thermal switch 800 are thermally coupled.

[0065] Embodiments of the present invention may be systems, methods, and / or devices integrated at any possible level of technical detail. What has been described above includes merely examples of systems, methods, and devices. Of course, for purposes of describing the present disclosure, it is not possible to describe every conceivable combination of components or computer-implemented methods, but one skilled in the art will recognize that many further combinations and permutations of the present disclosure are possible. Furthermore, to the extent that terms such as "including," "having," "comprising," and the like are used in the detailed description, claims, appendices, and drawings, such terms are intended to be inclusive in the same manner as the term "comprising" is interpreted when used as a transitional phrase in a claim.

[0066] Additionally, the term "or" is intended to mean an inclusive "or" rather than an exclusive "or." That is, unless otherwise specified or clear from context, "X employs A or B" is intended to mean either of the natural and inclusive permutations. That is, X employs A; X employs B; or, if X employs both A and B, "X employs A or B" is satisfied under any of the foregoing cases. Furthermore, the articles "a" and "an," as used in this specification and the accompanying drawings, should generally be construed to mean "one or more" unless otherwise specified or clear from context that the singular form is intended. As used herein, the terms "example" and / or "exemplary" are used to mean serving as an example, instance, or illustration. For the avoidance of doubt, the subject matter disclosed herein is not limited to such examples. Additionally, any aspect or design described herein as "example" and / or "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects or designs, nor is it intended to exclude equivalent exemplary structures and techniques known to those skilled in the art.

[0067] The description of various embodiments is presented for illustrative purposes and is not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein has been selected to best explain the principles of the embodiments, practical applications of, or technical improvements to, the technology found in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

[0068] While certain exemplary embodiments have been described, these embodiments are presented by way of example only and are not intended to limit the scope of the disclosure herein. Accordingly, the foregoing description is not intended to imply that any particular feature, characteristic, step, module, or block is necessary or essential. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; further, 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 disclosure herein. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the particular disclosure herein.

Claims

1. A cryostat, a plurality of thermal stages interposed between the 4-Kelvin (K) stage and the cold plate stage, the plurality of thermal stages including a still stage and an intermediate thermal stage mechanically coupled directly to the still stage via a support; and a thermal switch coupled to the intermediate thermal stage and an adjacent thermal stage, the thermal switch providing a switchable thermal path between the intermediate thermal stage and the adjacent thermal stage, thereby facilitating changing the thermal profile of the cryostat; Equipped with The thermal switch is a magnetically actuated superfluidic leak-proof valve. Cryostat.

2. A cryostat, a plurality of thermal stages interposed between the 4-Kelvin (K) stage and the cold plate stage, the plurality of thermal stages including a still stage and an intermediate thermal stage mechanically coupled directly to the still stage via a support; and a thermal switch coupled to the intermediate thermal stage and an adjacent thermal stage, the thermal switch providing a switchable thermal path between the intermediate thermal stage and the adjacent thermal stage, thereby facilitating changing the thermal profile of the cryostat; Equipped with The thermal switch comprises a superconducting material disposed within a magnetic field. Cryostat.

3. 3. The cryostat of claim 1, wherein the plurality of thermal stages are enclosed within an outer vacuum chamber defining a common vacuum space.

4. 4. The cryostat of claim 1, wherein the intermediate thermal stage operates at a temperature of about 300 millikelvin (mK) or about 1 Kelvin (K).

5. 5. The cryostat of claim 1, wherein the adjacent thermal stage is the still stage or the 4-K stage.

6. an additional thermal switch coupled to the 4-K stage, the additional thermal switch facilitating changing the thermal profile of the cryostat by providing an additional switchable thermal path between the 4-K stage and the intermediate thermal stage, the additional thermal switch and the additional thermal switch being coupled to opposite sides of the intermediate thermal stage; 6. The cryostat of claim 1, further comprising:

7. 7. A cryostat according to claim 1, wherein the thermal switch comprises a capillary tube containing a helium medium.

8. 8. The cryostat of claim 7, wherein the helium medium is helium-3 or helium-4.

9. 9. A cryostat as claimed in any one of claims 7 to 8, wherein the helium medium thermally shorts the intermediate thermal stage to the adjacent thermal stage.

10. 10. The cryostat of claim 1, wherein the intermediate thermal stage provides access to a pump and a pumping line connecting the sealed pot of an additional intermediate thermal stage to facilitate vaporization of helium-3.

11. A cryostat, a still stage directly mechanically coupled to an intermediate thermal stage via a support, the still stage and the intermediate thermal stage being included among a plurality of thermal stages interposed between a 4-Kelvin (K) stage and a cold plate stage; and a thermal switch coupled to the intermediate thermal stage and an adjacent thermal stage, the thermal switch providing a switchable thermal path between the intermediate thermal stage and the adjacent thermal stage, thereby facilitating changing the thermal profile of the cryostat; Equipped with The thermal switch is a magnetically actuated superfluidic leak-proof valve. Cryostat.

12. A cryostat, a still stage directly mechanically coupled to an intermediate thermal stage via a support, the still stage and the intermediate thermal stage being included among a plurality of thermal stages interposed between a 4-Kelvin (K) stage and a cold plate stage; and a thermal switch coupled to the intermediate thermal stage and an adjacent thermal stage, the thermal switch providing a switchable thermal path between the intermediate thermal stage and the adjacent thermal stage, thereby facilitating changing the thermal profile of the cryostat; Equipped with The thermal switch comprises a superconducting material disposed within a magnetic field. Cryostat.

13. 13. The cryostat of claim 11 or 12, further comprising a thermal shield coupled to the intermediate thermal stage and forming an enclosed thermal volume.

14. 14. The cryostat of claim 13, wherein the still stage is disposed within the enclosed thermal volume.

15. 14. The cryostat of claim 13, wherein the still stage is located outside the enclosed thermal volume.

16. 16. The cryostat of any one of claims 13 to 15, wherein the cold plate stage is disposed within the enclosed thermal volume.

17. an additional enclosed thermal volume nested within the enclosed thermal volume, the additional enclosed thermal volume being formed by an additional intermediate thermal stage coupled to an additional thermal shield, the additional intermediate thermal stage being included among the plurality of thermal stages; 17. The cryostat of claim 13, further comprising:

18. A cryostat, a contained thermal volume formed by an intermediate thermal stage coupled to a thermal shield, the intermediate thermal stage being directly mechanically coupled to a still stage via supports, the still stage and the intermediate thermal stage being included among a plurality of thermal stages interposed between a 4-Kelvin (K) stage and a cold plate stage; and a thermal switch coupled to the intermediate thermal stage and an adjacent thermal stage, the thermal switch providing a switchable thermal path between the intermediate thermal stage and the adjacent thermal stage, thereby facilitating changing the thermal profile of the cryostat; Equipped with The thermal switch is a magnetically actuated superfluidic leak-proof valve. Cryostat.

19. A cryostat, a contained thermal volume formed by an intermediate thermal stage coupled to a thermal shield, the intermediate thermal stage being directly mechanically coupled to a still stage via supports, the still stage and the intermediate thermal stage being included among a plurality of thermal stages interposed between a 4-Kelvin (K) stage and a cold plate stage; and a thermal switch coupled to the intermediate thermal stage and an adjacent thermal stage, the thermal switch providing a switchable thermal path between the intermediate thermal stage and the adjacent thermal stage, thereby facilitating changing the thermal profile of the cryostat; Equipped with The thermal switch comprises a superconducting material disposed within a magnetic field. Cryostat.

20. 20. The cryostat of claim 18 or 19, wherein the enclosed thermal volume is nested within an additional enclosed thermal volume formed by an additional intermediate thermal stage coupled to an additional thermal shield, the additional intermediate thermal stage being included among the plurality of thermal stages.

21. 21. The cryostat of claim 20, wherein the additional enclosed thermal volume is enclosed within a common vacuum space defined by an outer vacuum chamber of the cryostat.

22. 22. The cryostat of any one of claims 18 to 21, wherein the adjacent thermal stage is the still stage or the 4-K stage.

23. 23. The cryostat of any one of claims 18 to 22, wherein a mixing chamber stage of the cryostat is disposed within the enclosed thermal volume.

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