A three-stage pre-cooling cryostat for a multi-channel superconducting single photon detector

Abstract

The application discloses a three-stage precooling cryostat of a multi-channel superconducting single-photon detector, which comprises a vacuum cover, a GM refrigerator secondary cylinder, a GM refrigerator primary cylinder, a GM refrigerator cold head, a primary precooling structure, a secondary precooling structure, a tertiary precooling structure, a low-temperature radio frequency coaxial line and a sample table for placing the superconducting single-photon detector; the primary precooling structure, the secondary precooling structure and the tertiary precooling structure are sequentially arranged in the vacuum cover from bottom to top; the three-stage precooling mode can prevent the temperature of the sample table from being increased due to the increase of the number of the radio frequency coaxial lines, and can ensure that the temperature of the sample table is stably kept at the working temperature of the detector, so that the detector can be continuously and stably operated in the best state.

Description

Technical Field

[0001] This invention belongs to the field of cryogenic thermostat technology, specifically a three-stage pre-cooling cryogenic thermostat for a multi-channel superconducting single-photon detector. Background Technology

[0002] Superconducting nanowire single-photon detectors (SNSPDs) can be applied in various fields involving single-photon or high-speed weak light detection, such as quantum communication, single-photon source calibration, long-distance ranging, non-destructive integrated circuit testing, and fiber optic time-domain reflectometers. Typically, the optimal operating temperature of SNSPD detectors is below 2.5K, which places particularly high demands on the temperature stability of the cryostat sample stage. Traditional cryostat sample stages suffer from drawbacks such as high temperatures, poor temperature stability, and difficulties in detector installation, making it impossible to ensure the detector operates at its optimal state.

[0003] With the widespread application of detectors, single detectors can no longer meet the needs of scientific research, thus giving rise to multi-pixel detectors. An increase in the number of pixels means an increase in the number of radio frequency coaxial cables, which in turn raises the temperature of the sample stage. Therefore, developing a stable cryostat suitable for multi-channel superconducting nanowire single-photon detectors is crucial. Summary of the Invention

[0004] Purpose of the invention: To address the problem that as the number of pixels increases, the temperature of the sample stage in the cryostat rises, causing the detector to be unable to maintain a stable state at its optimal level, this invention proposes a three-stage pre-cooling cryostat for a multi-channel superconducting single-photon detector. Through a three-stage pre-cooling method, the sample stage temperature is not affected by the increase in the number of RF coaxial cables, ensuring that the sample stage temperature remains stable at the detector's operating temperature, enabling the detector to continuously and stably operate at its optimal state.

[0005] Technical solution: A three-stage pre-cooling cryogenic thermostat for a multi-channel superconducting single-photon detector, comprising a vacuum chamber, a second-stage cylinder of a GM refrigerator, a cold stage of a GM refrigerator, a first-stage pre-cooling structure, a second-stage pre-cooling structure, a third-stage pre-cooling structure, a cryogenic radio frequency coaxial cable, and a sample stage for placing the superconducting single-photon detector; the first-stage, second-stage, and third-stage pre-cooling structures are arranged sequentially from bottom to top inside the vacuum chamber;

[0006] The first-stage precooling structure includes a first-stage cold stage and several first-stage SMA connectors disposed on the first-stage cold stage; the second-stage precooling structure includes a cylinder block cold stage; the third-stage precooling structure includes a second-stage cold stage, a temperature buffer stage, and several second-stage SMA connectors, with the several second-stage SMA connectors disposed on the upper surface of the sample stage, the temperature buffer stage disposed on the lower surface of the sample stage, and the second-stage cold stage connected to the temperature buffer stage.

[0007] One end of the cryogenic radio frequency coaxial line is connected to the superconducting nanowire detector, and the other end extends downward, connecting to the secondary SMA connector and the primary SMA connector in sequence, and then to the SMA hermetic connector. The external voltage provides the working bias to the superconducting nanowire detector through the SMA hermetic connector. The cryogenic radio frequency coaxial line located at the cylinder cold stage is tightly attached to the cylinder cold stage through the wire clamping plate.

[0008] The secondary cylinder of the GM refrigeration unit is located between the primary and secondary cooling platforms; the cylinder cooling platform is installed on the secondary cylinder of the GM refrigeration unit; the GM refrigeration unit cooling platform is connected to the primary and secondary cooling platforms and is used to provide cooling capacity to the primary and secondary cooling platforms.

[0009] Furthermore, the primary precooling structure also includes a primary cold shield cover, and the secondary and tertiary precooling structures are both housed within the primary cold shield cover, with the bottom of the primary cold shield cover positioned on the primary cold platform.

[0010] Furthermore, it also includes a sample stage shield, the bottom of which is fixed to the sample stage.

[0011] Furthermore, it also includes a vacuum manual valve, which operates inside the vacuum chamber.

[0012] Furthermore, the cylinder cooling platform is installed at 5-50% of the total height of the secondary cylinder of the GM refrigeration unit.

[0013] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0014] (1) This invention greatly reduces the heat conduction and heat leakage of the radio frequency coaxial line by adopting three-stage pre-cooling, and reduces the heat conduction and heat leakage of the low temperature radio frequency coaxial line to the first and second stage cold stages by pressing the wire plate to tightly attach the low temperature radio frequency coaxial line to the cylinder cold stage, thereby indirectly increasing the useful work of the cooling capacity of the second stage cold stage. Ultimately, the sample stage temperature can be increased without increasing the number of radio frequency coaxial lines, and the sample stage temperature can reach the working temperature of the detector, ensuring that the detector can work continuously and stably in the best state.

[0015] (2) By employing multi-level shielding, the present invention can greatly reduce external magnetic field noise and reduce radiative heat leakage within the cavity;

[0016] (3) The present invention uses a vacuum hood in conjunction with a vacuum manual valve to make the vacuum level in the cavity lower than 10Pa, thereby reducing convective heat leakage;

[0017] (4) The present invention adopts a cylinder cold stage with a snap-fit ​​structure, which can form an angle (angle ±160°) with the sample stage, making it easy to adjust the tightness of the low temperature radio frequency coaxial line and prevent interference of the low temperature radio frequency coaxial line with the first-level cold screen shield. Attached Figure Description

[0018] Figure 1 This is a diagram of the overall system.

[0019] Figure 2 For the local internal structure of the system Figure 1 ;

[0020] Figure 3 For the local internal structure of the system Figure 2 . Detailed Implementation

[0021] The technical solution of the present invention will now be further described with reference to the accompanying drawings.

[0022] like Figure 1 and Figure 2 As shown, this embodiment discloses a three-stage pre-cooling cryogenic thermostat suitable for multi-channel superconducting nanowire single-photon detectors. It mainly includes a vacuum chamber 1, a primary cold shield 2, a sample stage shield 3, a secondary SMA connector 4, a sample stage 5, a cryogenic RF coaxial cable 6, a wire clamping plate 7, a cylinder cold stage 8, a primary SMA connector 9, a primary cold stage 10, a KF25 clamp 11, a temperature buffer stage 12, a secondary cold stage 13, a GM refrigerator secondary cylinder 14, a KF25 vacuum manual valve 15, a vacuum baffle 16, an SMA airtight connector 17, an airtight aviation connector 18, a thermostat bracket 19, a GM refrigerator cold stage 20, and a thermometer 21.

[0023] The specific connection relationship is as follows: the primary cold shield 2 and the primary cold stage 10 are set inside the vacuum chamber 1, and the lower end of the primary cold shield 2 is fixed on the primary cold stage 10. A ring of primary SMA connectors 9 is provided on the primary cold stage 10. Inside the primary cold shield 2, from top to bottom, are: sample stage shield 3, sample stage 5, temperature buffer stage 12, secondary cold stage 13, and cylinder cold stage 8. Among them, the sample stage shield 3 is fixed on the sample stage 5. The sample stage 5 is used to fix the superconducting single-photon detector, and a ring of SMA connectors 9 is provided on the sample stage 10. The sample stage 5 is equipped with a secondary SMA connector 4 and a thermometer 21 for measuring the temperature of the sample stage 5. A temperature buffer stage 12 is disposed on the lower surface of the sample stage 5 to reduce temperature fluctuations. This temperature buffer stage 12 is connected to a secondary cold stage 13. A cylinder cold stage 8 is disposed between the primary cold stage 10 and the secondary cold stage 13. Specifically, the cylinder cold stage 8 is installed on the secondary cylinder 14 between the primary cold stage 10 and the secondary cold stage 13 of the GM refrigerator. Specifically, the cylinder cold stage 8 is installed at 5-50% of the total height of the secondary cylinder 14. One end of the low-temperature RF coaxial cable 6 is connected to the superconducting nanowire detector, and the other end is connected from top to bottom to the secondary SMA connector 4, the primary SMA connector 9, and the SMA airtight connector 17. The low-temperature RF coaxial cable 6 is tightly fitted to the cylinder cold stage 8 through several pressure plates 7 to provide heat conduction. The SMA airtight connector 17 is mounted on the vacuum baffle 16. The SMA airtight connector 17 facilitates the provision of a suitable operating bias to the superconducting nanowire detector from the outside, enabling the detector to begin normal operation. The signal line of the thermometer 21 is soldered to the airtight aviation connector 18 and fixed to the cryostat in this embodiment via the KF25 clamp 11, used to acquire the electrical signal from the thermometer inside the cryostat. The KF25 vacuum manual valve 15 is mounted on the cryostat in this embodiment via the KF25 clamp 11, used to isolate the vacuum from the atmospheric pressure environment of the cryostat. The GM refrigeration stage 20 is connected to the compressor to provide cooling capacity for cooling the primary and secondary stages.

[0024] In operation, a GM refrigerator with a minimum temperature of 2.1K on the secondary cold stage is used as the cold source. A mechanical pump connected to a KF25 vacuum manual valve 15 is used to evacuate the vacuum chamber 1. When the internal pressure reaches 10Pa, convective heat loss is reduced. At this point, the GM refrigerator is turned on. When the sample stage 5 temperature reaches 70K, the KF25 vacuum manual valve 15 is closed, and then the mechanical pump is turned off. The GM refrigerator cold stage 20 provides sufficient cooling capacity to cool the primary cold stage 10 and the secondary cold stage 13. The primary cold stage 10 cools the primary cold shield 2 and the primary SMA connector 9 to 40K. The primary SMA connector 9 transfers the temperature to the low-temperature RF coaxial cable 6. The low-temperature RF coaxial cable 6 is fixed to the cylinder cold stage 8 for pre-cooling, reducing heat conduction and heat loss from the low-temperature RF coaxial cable 6 to the secondary cold stage 13. The secondary SMA connector 4 installed on the sample stage 5 pre-cools the low-temperature RF coaxial cable 6, reducing heat conduction and heat loss from the low-temperature RF coaxial cable 6 to the sample stage 5. A temperature buffer stage 12 is installed under the sample stage 5 to reduce temperature fluctuations in the sample stage 5. A secondary cold stage 13 cools the sample stage 5, temperature buffer stage 12, and secondary SMA connector 4 to 2.1K. The final temperature of the superconducting nanowire detector mounted on the sample stage 5 will match that of the sample stage 5, and the superconducting nanowire detector will enter the superconducting state. An appropriate operating bias is provided to the superconducting nanowire detector externally via a hermetically sealed aerospace connector 18, and the superconducting nanowire detector begins normal operation.

[0025] In this embodiment, the cylinder cold stage 8 adopts a snap-fit ​​structure, forming an angle with the sample stage 5. The angle is ±160°, which is used to adjust the tightness of the low-temperature radio frequency coaxial line 6 and prevent the low-temperature radio frequency coaxial line 6 from interfering with the primary cold screen shield.

[0026] In this embodiment, the primary cold shield 2, primary cold stage 10, sample stage 5, sample stage shield 3, cylinder cold stage 8, and pressure plate 7 are made of materials with good thermal conductivity. The surface of these materials is treated with gold plating, silver plating, or nickel plating to reduce the surface reflectivity of the structure and reduce radiative heat leakage inside the cavity.

[0027] In this embodiment, the temperature buffer stage uses a material with a large specific heat capacity at 10K temperature to reduce temperature fluctuations on the sample stage 5.

[0028] This embodiment uses a multi-level shielding design, including a vacuum cover 1, a primary cold shield cover 2, and a sample stage shield cover 3, to reduce external magnetic field noise and reduce radiative heat leakage inside the thermostat.

[0029] The low-temperature radio frequency coaxial cable 6 in this embodiment adopts a segmented connection, which has the advantages of simple structure and convenient installation.

[0030] This embodiment employs a three-stage pre-cooling method to reduce heat conduction and leakage of the RF coaxial cable. Specifically, the low-temperature RF coaxial cable 6 installed on the first-stage cold stage 10 and the second-stage cold stage 13 is fixed to the cylinder cold stage 8 using a wire clamping plate 7, thus constituting a three-stage pre-cooling process. The first-stage cold stage 10 constitutes the first-stage pre-cooling, the cylinder cold stage 8 constitutes the second-stage pre-cooling, and the second-stage cold stage 13 constitutes the third-stage pre-cooling. This reduces the heat conduction and leakage of the low-temperature RF coaxial cable 6 to the first-stage and second-stage cold stages, indirectly increasing the useful work of the cooling capacity of the second-stage cold stage. Ultimately, the sample stage temperature can be kept constant regardless of the increase in the number of low-temperature RF coaxial cables 6, reaching the operating temperature of the superconducting nanowire detector, ensuring that the superconducting nanowire detector can continuously and stably operate in its optimal state.

[0031] This embodiment reduces convective heat leakage within the cavity by using vacuum extraction and a three-stage pre-cooling structure to reduce thermal conduction leakage of the low-temperature radio frequency coaxial line 6, which facilitates the installation of more superconducting nanowire detectors. The thermostat in this embodiment is designed with multi-stage shielding to reduce external magnetic field noise and radiative heat leakage within the cavity.

Claims

1. A three-stage pre-cooling cryostat for a multi-channel superconducting single-photon detector, characterized in that: It includes a vacuum chamber, a GM refrigerator secondary cylinder, a GM refrigerator cold stage, a primary precooling structure, a secondary precooling structure, a tertiary precooling structure, a low-temperature radio frequency coaxial cable, and a sample stage for placing a superconducting single-photon detector; the primary, secondary, and tertiary precooling structures are arranged sequentially from bottom to top inside the vacuum chamber. The primary precooling structure includes a primary cooling stage and several primary SMA connectors disposed on the primary cooling stage. The secondary precooling structure includes a cylinder block cooling platform; The three-stage precooling structure includes a two-stage cold stage, a temperature buffer stage, and several two-stage SMA connectors. The several two-stage SMA connectors are disposed on the upper surface of the sample stage, the temperature buffer stage is disposed on the lower surface of the sample stage, and the two-stage cold stage is connected to the temperature buffer stage. One end of the low-temperature radio frequency coaxial line is connected to the superconducting nanowire detector, and the other end extends downward, connecting in sequence to a secondary SMA connector and a primary SMA connector, and then to an SMA hermetic connector. The external voltage provides the working bias to the superconducting nanowire detector through the SMA hermetic connector. The low-temperature radio frequency coaxial cable located at the cylinder block cold stage is tightly attached to the cylinder block cold stage through a pressure plate; The secondary cylinder of the GM refrigeration unit is located between the primary and secondary cooling platforms; the cylinder cooling platform is installed on the secondary cylinder of the GM refrigeration unit; the GM refrigeration unit cooling platform is connected to the primary and secondary cooling platforms and is used to provide cooling capacity to the primary and secondary cooling platforms. The primary precooling structure also includes a primary cold shield cover. The secondary and tertiary precooling structures are both housed inside the primary cold shield cover, and the bottom of the primary cold shield cover is set on the primary cold platform.

2. The three-stage pre-cooling cryostat for a multi-channel superconducting single-photon detector according to claim 1, characterized in that: It also includes a sample stage shield, the bottom of which is fixed to the sample stage.

3. The three-stage pre-cooling cryostat for a multi-channel superconducting single-photon detector according to claim 1, characterized in that: It also includes a vacuum manual valve, which operates inside the vacuum chamber.

4. The three-stage pre-cooling cryostat for a multi-channel superconducting single-photon detector according to claim 1, characterized in that: The cylinder cooling platform is installed at 5-50% of the total height of the secondary cylinder of the GM refrigeration unit.

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