Vibration isolation unit, cryostat and dilution refrigerator

Abstract

The utility model discloses a vibration isolation unit, a cryostat and a dilution refrigerator. The vibration isolation unit comprises a first connecting line, and the first connecting line is connected with the interior of the cryostat and a cable take-up and pay-off device; the spring element is connected with the connecting line I; the second connecting line is connected with the spring element. The cryostat comprises a pulse tube refrigeration unit. The lower part of the pulse tube refrigerator is connected with a cooling disc unit; the dilution refrigerator includes a cryostat. The vibration isolation unit is connected with the quantum chip, so that the quantum chip unit is not in direct contact with the multi-stage cold disc unit, the quantum chip unit is in a suspended state and is only connected with the vibration isolation unit, and mechanical vibration caused by the pulse tube refrigerator and environmental factors can be effectively isolated.

Description

Technical Field

[0001] The present invention relates to the technical field of quantum computers, and in particular to a vibration isolation unit, a cryostat, and a dilution refrigerator. Background Art

[0002] The quantum chips of superconducting quantum computers require extremely low temperatures to operate, typically provided by a dilution refrigerator. These refrigerators primarily consist of a pulse tube cooling system, a mixed helium dilution cooling system, and a cryostat. These systems progressively cool the multiple cold plates within the cryostat until the temperature reaches the millikelvin level. Active components of the pulse tube cooling system, such as the expander and rotary valve, generate mechanical vibrations of a specific frequency, which are transmitted through pipes and cold heads to the cryostat and its internal cold plates, ultimately reaching the quantum chip. These mechanical vibrations can directly or indirectly affect the performance and reliability of superconducting quantum chips by coupling with electrical signals in microwave cables, generating additional noise, or affecting the decoherence time of quantum bits.

[0003] In the related art, as the power and structural size of the dilution refrigerator continue to increase, the mechanical vibration generated by the pulse tube refrigerator will increase, resulting in intensified vibration of the quantum chip, affecting the stable operation of the superconducting quantum computer. In order to reduce the impact of this vibration on the superconducting quantum computer, the related art connects the cold head and the low-temperature thermostat of the pulse tube refrigerator with a welded bellows, and uses a flexible cold chain such as a copper braided structure to transfer heat between the cold head and the cold plates at each level to isolate the vibration transmission. However, the above solution cannot meet the extremely low vibration requirements of large-bit dilution refrigerators, and will still affect the stable operation of superconducting quantum computing. Summary of the Invention

[0004] The object of the present invention is to solve the above problems. The present invention provides a vibration-isolated cryostat, a cryostat and a dilution refrigerator.

[0005] In order to achieve the above-mentioned purpose, the present invention specifically adopts the following technical solutions:

[0006] A vibration isolation unit, comprising:

[0007] A retractable connecting wire 1, wherein the connecting wire 1 is connected to a cold plate unit inside the cryostat;

[0008] a cable retracting device, the cable retracting device being connected to the connecting line 1 and configured to drive the connecting line 1 to be reeled or released;

[0009] a spring element, the spring element being connected to the connecting line 1, and the spring element being extended or contracted when the connecting line 1 is wound or released;

[0010] A second connecting line, wherein the second connecting line is connected to an end of the spring element, and the other end of the second connecting line is connected to the quantum chip unit;

[0011] The connecting wire drives the spring element to stretch, so that the quantum chip unit is not in direct contact with the low-temperature thermostat, thereby achieving vertical vibration isolation and / or lateral vibration isolation of the quantum chip.

[0012] Optionally, it further includes a plurality of connection lines three connected to the bottom cold plate inside the low-temperature thermostat, and the other ends of the connection lines three are all connected to the quantum chip unit.

[0013] Optionally, it also includes multiple flexible cold chains connected to the bottom cold plate inside the low-temperature thermostat, and the other ends of the multiple flexible cold chains are connected to the quantum chip unit. The flexible cold chains are used to transfer cold energy to the quantum chip unit and isolate vibration.

[0014] Optionally, the flexible cold chain is a flat copper strip, and the flat copper strip is in a curved configuration and is heat-treated.

[0015] Optionally, the first connecting wire and the third connecting wire are both Kevlar fiber braided wires, and the second connecting wire is a copper braided wire.

[0016] A low temperature thermostat comprises a cold plate unit, wherein the cold plate unit comprises a plurality of cold plates, and through holes are formed on some of the cold plates;

[0017] The vibration isolation unit described in any one of the above items passes through the through hole and is connected to the quantum chip unit.

[0018] Optionally, at least two cold plates of the cold plate unit are provided with through holes on the same axis.

[0019] A dilution refrigerator comprising the cryostat described in any one of the above;

[0020] A pulse tube cooling unit is provided at the upper end of the cryostat;

[0021] The cryostat is provided with any one of the vibration isolation units described above inside.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1. The present invention provides a vibration isolation unit connected to the quantum chip, so that the quantum chip unit and the multi-stage cold plate unit are not in direct contact, and the quantum chip unit is suspended and only connected to the vibration isolation unit, which can effectively isolate the mechanical vibration caused by the pulse tube refrigerator and environmental factors.

[0024] 2. The present disclosure can effectively isolate the vertical vibration and / or lateral vibration of the quantum chip unit through the spring elements, Kevlar fiber braided wire and copper braided wire in the vibration isolation unit.

[0025] 3. The present disclosure provides a plurality of flat copper belts under the multi-stage cold plate unit, which are connected to the quantum chip unit. The flat copper belts can transfer the cooling capacity of the multi-stage cold plate unit to the quantum chip unit through the flat copper belts.

[0026] 4. The present invention provides multiple Kevlar braided wires connected to the quantum chip unit below the multi-stage cold plate unit, thereby preventing the quantum chip unit from accidentally falling and ensuring the safety of the structure.

[0027] In order to more clearly illustrate the structural features and functions of the present invention, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the internal structure of the cryostat;

[0029] Figure 2 It is a schematic diagram of the composition of the vibration isolation unit;

[0030] Figure 3 It is a schematic diagram of the composition of the vibration isolation unit after the spring element is stretched;

[0031] Figure 4 It is a stereogram of the cryostat;

[0032] Figure 5 It is a three-dimensional diagram of a dilution refrigerator;

[0033] Figure 6 It is a parameter design flow chart of the vibration isolation unit.

[0034] Figure numerals: 1. Pulse tube refrigeration unit; 101. Pulse tube cold head; 102. Bellows; 103. Normal temperature flange; 104. Two-stage cold finger; 105. Flexible copper braid; 2. Cold plate unit; 201. First-stage cold plate; 202. Second-stage cold plate; 203. Third-stage cold plate; 204. Fourth-stage cold plate; 205. Through hole one; 206. Fifth-stage cold plate; 207. Through hole two; 208. Connecting rod; 3. Flexible cold chain; 301. Flat copper strip; 4. Vibration isolation unit; 401. Cable retracting device; 402. Connecting line one; 403. Spring element; 404. Connecting line two; 5. Quantum chip unit; 501. Base; 502. Quantum chip; 503. Flexible cable; 6. Connecting line three; 7. Barrel shell; 8. Interface; 9. Support frame. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0036] like Figure 1-Figure 3 as well as Figure 5 As shown, in one embodiment, a vibration isolation unit is provided inside a cryostat, which is an important component of a dilution refrigerator. A pulse tube cooling unit 1 is provided at the upper end of the cryostat, and a cold plate unit 2 is connected below the pulse tube cooling unit 1. The cold plate unit 2 is connected to a quantum chip unit 5 through multiple flexible cold chains 3 below the cold plate unit 2.

[0037] The vibration isolation unit 4 extends through the through-holes of the cold plate unit 2 and connects to the quantum chip unit 5. Specifically, the cold plate unit includes multiple cold plates, and the vibration isolation unit 4 extends through the through-holes of the last several cold plates in the cold plate unit 2. The vibration isolation unit 4 can be used to isolate vertical and / or lateral vibrations transmitted by the pulse tube cooling unit 1. Specifically, the vibration isolation unit 4 can have a "pendulum" structure. It is understood that a "pendulum" structure refers to a structure in which the upper end of the vibration isolation unit 4 is fixed, while the lower end is not fixed, forming a "pendulum" structure with a movable lower end. The upper end of the vibration isolation unit 4 is connected to the lower end of one of the cold plates in the cold plate unit 2, and the lower end of the vibration isolation unit 4 is connected to the quantum chip unit 5. During vibration isolation, the vibration isolation unit 4 moves upward under the traction of the cable retraction device 17, placing the quantum chip unit 5 in a non-contact relative position with the cold plate unit 2, effectively isolating mechanical vibrations caused by the pulse tube refrigerator and environmental factors. At the same time, the vibration isolation unit 4 itself has a vibration reduction performance, which can further effectively isolate the vertical vibration and / or lateral vibration transmitted by the pulse tube refrigerator.

[0038] Optionally, refer to Figure 1-Figure 2The specific structure of the vibration isolation unit 4 is described below. The vibration isolation unit 4 includes at least a spring element 403. In some embodiments, the spring element 403 can be a stainless steel spring. A second connecting wire 404, i.e., a copper braided wire, is connected to the lower end of the spring element 403. The copper braided wire passes through the second through-hole 207 and connects to the quantum chip unit 5. The upper end of the spring element 403 is connected to a first connecting wire 402. In some embodiments, the first connecting wire 402 can be a Kevlar braided wire. The other end of the first connecting wire 402 is connected to a cable retractor 401. The cable retractor 401 is fixed to the lower end of the cold plate. In some embodiments, the cable retractor 401 can be fixed to the lower end of the third cold plate 203. The cable retractor 401 can be used to reel in or unreel the first connecting wire 402.

[0039] When in the reeled state, the cable reeling device 401 reels the connecting wire 1 402, causing the spring element 403 to move upward and stretch, driving the copper braided wire 404 below and the quantum chip unit 5 to move upward, so that the quantum chip unit 5 is not in direct contact with the cold plate unit 2, so that the weight of the quantum chip unit 5 is completely suspended and supported by the vibration isolation unit 4, which can effectively isolate vibration. Optionally, in addition to its connecting function, the copper braided wire can also lower the temperature of the spring element 403, effectively reducing the impact of the heat radiation of the spring element 403 at room temperature on the cooling capacity of the cold plate unit 2. Optionally, the cable reeling device 401 can be a small motor that drives the wheel to rotate, and the connecting wire 1 402 is connected to the wheel, thereby realizing the reeling and unreeling of the fiber braided wire 1 402.

[0040] Optionally, refer to Figure 1 , discloses a low-temperature thermostat, including a cold plate unit 2, which includes multiple cold plates arranged in sequence from top to bottom. Specifically, the cold plates are a first-level cold plate 201, a second-level cold plate 202, a third-level cold plate 203, a fourth-level cold plate 204 and a fifth-level cold plate 206 from top to bottom. The temperature of the cold plate structure decreases from top to bottom until it reaches the milliK level. Two adjacent cold plates are connected by a connecting rod 208 arranged at the edge.

[0041] Optionally, refer to Figure 2-Figure 3, through holes are opened on multiple cold plates, and the through holes are on the same axis. In some embodiments, through hole one 205 and through hole two 207 are opened on the surface of the fourth-stage cold plate 204 and the fifth-stage cold plate 206 respectively, and the upper end of the vibration isolation unit 4 is installed on the lower end of the third-stage cold plate 203, and passes through through hole one 205 and through hole two 207 in sequence to connect with the vibration isolation unit 4 below. In some embodiments, the vibration isolation unit 4 can also be installed at the lower end of other cold plate structures, such as the second-stage cold plate 202 or the fourth-stage cold plate 204, and is set according to actual needs, which is not limited here. By opening through holes in the cold plate structure, the structure between the structures can be reduced, and vibration can be effectively isolated.

[0042] Optionally, refer to Figure 2 The cold plate unit 2 and the quantum chip unit 5 are connected by multiple flexible cold chains 3. The flexible cold chains 3 include multiple flat copper strips 301. The flat copper strips 301 have a certain flexibility and can reduce the vibration transmission from the cold plate unit 2 to the quantum chip unit 5. Among them, multiple flat copper strips 301 are arranged around the through hole. Due to the decoupling between the quantum chip unit 5 and the cold plate unit 2 (i.e., non-direct contact), this will cause the cold energy to be unable to be transferred from the cold plate to the quantum chip unit 5. By adding multiple flat copper strips 301, the cold energy of the cold plate unit 2 can be transferred to the quantum chip unit 5. In some embodiments, each flat copper strip 301 is connected to the cold plate unit 2 and the quantum chip unit 5 by bolts. In some embodiments, the flat copper strip 301 is heat-treated to reduce the stiffness, and a curved configuration is adopted to further reduce the stiffness and increase the degree of deformability.

[0043] Optionally, the quantum chip unit 5 is connected to the cold plate structure via a plurality of connecting wires 36, and a plurality of fiber braided wires are arranged around the through hole. In some embodiments, the quantum chip unit 5 is connected to the lower end of the five-stage cold plate 206 by four groups of connecting wires 36, and the connecting wires 36 can be made of Kevlar fiber braided wire, which has the characteristics of low stiffness and flexible deformation. Figure 3 When the cable retracting device 401 does not release the connecting wire 1 402, the spring element 403 is not stretched, and there is no interaction between the connecting wire 2 404 and the quantum chip unit 5. The four sets of connecting wires 3 6 are taut. At this time, the quantum chip unit 5 is completely suspended below the connecting wires 3 6. At this time, the vibration isolation unit 4 does not work. This state is used in the early installation and debugging stages. Among them, the connecting wire 3 6 can prevent the quantum chip unit 5 from falling when the vibration isolation unit 4 fails, such as when the spring element 403, the connecting wire 1 402 or the connecting wire 2 404 breaks, thereby ensuring the safety of the structure.

[0044] Optionally, refer to Figure 3The quantum chip unit 5 includes a base 501, on which a quantum chip 502 is mounted. The quantum chip 502 is connected to a flexible cable 503, through which a microwave side hole of the superconducting quantum bit can be accessed. A plurality of openings are provided below the base 501, through which the counterweight can be added or removed to adjust the natural frequency.

[0045] Optionally, refer to Figure 4 The cryostat also includes a barrel housing 7, which is installed from top to bottom, enclosing the multi-layer shielded barrel and cold plate unit 2. It is securely connected to a room-temperature flange 103 via bolts. In some embodiments, a sealing ring is provided at the connection between the barrel housing 7 and the room-temperature flange 103 to meet the vacuum requirements of the cryostat. Various interfaces 8 are also provided on the room-temperature flange 103, such as a port for the mixed helium dilution refrigeration system, a vacuum extraction port, and a microwave cable port.

[0046] refer to Figure 5 In one embodiment, a dilution refrigerator is disclosed, comprising the aforementioned cryostat. A support frame 9 is provided on the exterior of the cryostat. The support frame 9 is primarily composed of an aluminum alloy profile and has a mounting plate attached to the top. The cryostat is hoisted onto the mounting plate and secured with bolts.

[0047] A pulse tube cooling unit 1 is provided at the upper end of the cryostat. The pulse tube cooling unit 1 is a pulse tube cooling system comprising a pulse tube cold head 101, which is connected to a normal temperature flange 103 via a bellows 102. The pulse tube cold head 101 can transfer cooling energy to the cold plate unit 2 below, and the bellows 102 can effectively isolate the vibration transmitted by the pulse tube cold head 101. Optionally, a two-stage cold finger 104 is provided below the pulse tube cold head 101. The two-stage cold finger 104 is connected to the cold plate unit 2 via a flexible copper braid 105, which can effectively cool the cold plate unit 2 and reduce the transmission of vibration.

[0048] The above-mentioned vibration isolation unit 4 is arranged inside the cryostat, and the vibration isolation unit 4 can effectively isolate the vertical vibration and / or lateral vibration to which the quantum chip unit is subjected.

[0049] refer to Figure 6 The present application also discloses a method for processing the vibration isolation unit 4, the specific steps of which include:

[0050] S100. Determine the main mechanical vibration frequency received by the dilution refrigerator and the inherent parameters of the dilution refrigerator. Specifically, the main mechanical vibration frequency refers to the main mechanical vibration frequency f0 received by the dilution refrigerator from the pulse tube refrigeration system. The inherent parameters of the dilution refrigerator include the equivalent mass M composed of the quantum chip unit 5, i.e., the base 501, the quantum chip 502, and the flexible cable 503, and the actual available height H in the vertical direction inside the cryostat max and the designed maximum deformation amount ΔL of the spring element 403 max .

[0051] S200. Calculate the vertical natural frequency and the lateral natural frequency of the vibration isolation unit 4 according to Formula 1. Specifically, Formula 1 is:

[0052]

[0053] where f r is the lateral natural frequency, f v is the longitudinal natural frequency, K is the stiffness of the spring element 403, and g is the universal gravitational constant

[0054] S300. Determine the target of the vibration isolation of the vibration isolation unit 4, and solve the parameters of each component in the vibration isolation unit 4 based on the target joint equations. Specifically, the steps to determine the parameters of each component of the vibration isolation unit include:

[0055] S310. Determine that the vertical natural frequency is less than the main mechanical vibration frequency, i.e., f r < f0. Considering Hooke's law of the spring, the actual deformation amount of the spring should be less than the designed maximum deformation amount, and the actual size of the vibration isolation structure should be less than the actual available space height in the vertical direction inside the cryostat. Adjust the parameters of each component in the vibration isolation unit 4 based on the above constraints and solve them based on Equation Set 1. Specifically, Equation Set 1 is:

[0056]

[0057] S320. Determine that the lateral natural frequency is less than the main mechanical vibration frequency, i.e., f v < f0. Since f v < f r , the designed natural frequencies in the lateral and vertical directions are both less than the low-frequency vibration frequency f0 of the pulse tube refrigeration system. It can be seen that the requirements of the current design target are higher, and vibration isolation in both the lateral and vertical directions can be achieved simultaneously. Considering Hooke's law of the spring, the actual deformation amount of the spring should be less than the designed maximum deformation amount, and the actual size of the vibration isolation structure should be less than the actual available space height in the vertical direction inside the cryostat. Adjust the parameters of each component in the vibration isolation unit 4 based on the above constraints and solve them based on Equation Set 2. Specifically, Equation Set 2 is:

[0058]

[0059] The stiffness K and initial length L of the spring element 403 can be solved by the above equations. S , deformation after increasing load ΔL S , the length L1 of the Kevlar fiber braided wire, and the length L2 of the copper braided wire 404.

[0060] S400 , processing the components in the vibration isolation unit 4 according to the parameters obtained in step S300 .

[0061] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A vibration isolation unit, characterized in that: include: A retractable connecting wire 1, wherein the connecting wire 1 is connected to a cold plate unit inside the cryostat; a cable retracting device, the cable retracting device being connected to the connecting line 1 and configured to drive the connecting line 1 to be reeled or released; a spring element, the spring element being connected to the connecting line 1, and the spring element being extended or contracted when the connecting line 1 is wound or released; A second connecting line, wherein the second connecting line is connected to an end of the spring element, and the other end of the second connecting line is connected to the quantum chip unit; The connecting wire drives the spring element to stretch, so that the quantum chip unit is not in direct contact with the low-temperature thermostat, thereby achieving vertical vibration isolation and / or lateral vibration isolation of the quantum chip.

2. The vibration isolation unit according to claim 1, wherein: It also includes a plurality of connecting wires three connected to the bottom cold plate inside the low-temperature thermostat, and the other ends of the connecting wires three are all connected to the quantum chip unit.

3. The vibration isolation unit according to claim 1, wherein: It also includes multiple flexible cold chains connected to the bottom cold plate inside the low-temperature thermostat, and the other ends of the multiple flexible cold chains are connected to the quantum chip unit. The flexible cold chains are used to transfer cold energy to the quantum chip unit and isolate vibration.

4. The vibration isolation unit according to claim 3, wherein: The flexible cold chain is a flat copper strip, and the flat copper strip is in a bent configuration and is heat-treated.

5. The vibration isolation unit according to claim 2, wherein: The first connecting wire and the third connecting wire are both Kevlar fiber braided wires, and the second connecting wire is a copper braided wire.

6. A cryostat, characterized in that The cold plate unit comprises a plurality of cold plates, and a through hole is opened on some of the cold plates; The vibration isolation unit according to any one of claims 1 to 5 passes through the through hole and is connected to the quantum chip unit.

7. The cryostat according to claim 6, wherein At least two cold plates of the cold plate unit are provided with through holes on the same axis.

8. A dilution refrigerator, characterized in that: A cryostat comprising any one of claims 6 to 7; A pulse tube cooling unit is provided at the upper end of the cryostat; The cryostat is provided with a vibration isolation unit according to any one of claims 1 to 5 inside.

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