Separated extremely-low-temperature noise thermometer based on superconducting quantum interference device and method

Abstract

The invention discloses a separated extremely-low-temperature noise thermometer based on a superconducting quantum interference device and a method. The separated extremely-low-temperature noise thermometer comprises a metal noise source, a thermal noise pickup coil, a first-stage SQUID chip circuit, a second-stage SQUID chip circuit, a magnetic flux locking electronics part and a noise reading electronics part. The first-stage SQUID chip circuit comprises a first input coil, a bias resistor, a feedback coil and a first-stage SQUID; the second-stage SQUID array chip circuit comprises a second-stage SQUID array and a second input coil; the magnetic flux locking electronics part comprises an amplifier, an integrator and a feedback resistor; the noise readout electronics part comprises a digital-to-analog converter and a signal processing module. The method comprises steps S1 to S5. The thermal noise detection coil and the SQUID loop coil are separated, heat interference caused by SQUID direct current bias is avoided, direct interference between the detection coil and the SQUID feedback coil is effectively weakened, and therefore the temperature measurement accuracy is improved, and the device can be used for mK pole low-temperature measurement.

Description

Technical Field

[0001] This invention relates to the field of superconducting quantum interference device (SQI) technology, and in particular to a split-type ultra-low temperature noise thermometer and method based on a superconducting quantum interference device. Background Technology

[0002] With the rapid development of quantum computing, superconducting electronics, and low-temperature physics, the demand for high-precision temperature measurement in extremely low-temperature environments (millikelvin level) is becoming increasingly urgent. Core components such as qubit chips and superconducting single-photon detectors need to operate in environments close to absolute zero. Tiny temperature fluctuations can cause quantum state decoherence or signal distortion, thus placing extremely high demands on the sensitivity and anti-interference capabilities of temperature monitoring.

[0003] The current international low-temperature scale PLTS-2000 (based on the melting pressure of He, 0.9 mK~1 K) relies on expensive equipment and complex operation, and is limited to a few laboratories. Traditional thermometers such as coulomb blocking thermometers (static, slow), nuclear magnetic resonance thermometers (expensive equipment), and resistance thermometers (significant errors <100 mK) lack sufficient time resolution and noise suppression capabilities, making it difficult to meet the real-time dynamic monitoring requirements of quantum systems.

[0004] Superconducting quantum interference devices (SQUIDs), currently the most sensitive magnetic sensors, can theoretically measure temperature by detecting thermal noise magnetic fields, with an equivalent energy resolution approaching the quantum limit. SQUID-based flux noise thermometers, based on the Nyquist principle, offer primary measurement potential and are suitable for dynamic, multi-physical quantity coupled experiments, making them an ideal candidate method for ultra-low temperature measurement. However, Magnicon's MFFT-1 flux fluctuation thermometer, with a temperature measurement range of 1 mK to 4.2 K, has a SQUID chip directly mounted on a copper noise source. Approximately 100 pW of heat is conducted to the copper noise source. Furthermore, the thermal noise detection coil and the SQUID feedback coil share the same chip, leading to severe crosstalk between coils, significantly increasing system noise and affecting measurement accuracy. Therefore, a novel ultra-low temperature noise thermometer based on SQUID is needed, addressing these issues through structural optimization and innovative noise suppression mechanisms. Summary of the Invention

[0005] To address the aforementioned shortcomings of existing technologies, this invention proposes a separate cryogenic noise thermometer and method based on a superconducting quantum interference device (SQUID). By separating the thermal noise detection coil from the SQUID loop coil, thermal interference caused by the SQUID DC bias is avoided, and the direct interference between the detection coil and the SQUID feedback coil is effectively reduced, thereby improving the accuracy of temperature measurement. This method can be used for mK cryogenic measurements.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A split-type cryogenic noise thermometer based on a superconducting quantum interference device is provided, including at least one cryogenic noise temperature sensing system. The cryogenic noise temperature sensing system includes a metal noise source, a thermal noise pickup coil, a first-stage SQUID chip circuit, a second-stage SQUID array chip circuit, a flux-locked electronics section, and a noise readout electronics section. The thermal noise pickup coil is used to read the magnetic flux noise signal of the metal noise source. The first-stage SQUID chip circuit converts the magnetic flux noise signal into an output voltage signal. This circuit includes a first input coil, a bias resistor, a feedback coil, and a first-stage SQUID. The second-stage SQUID array chip circuit amplifies the output voltage signal from the first-stage SQUID. This circuit includes a second input coil and a second-stage SQUID array. The first-stage SQUID, the second input coil, and the bias resistor are connected in series to form a closed loop. The feedback coil is overlapped or cross-coupled with the first-stage SQUID. The second input coil is overlapped or cross-coupled with the second-stage SQUID array. A thermal noise pickup line is also included. The first input coil and the second superconducting coil are connected by a superconducting wire to form a closed loop. The thermal noise pickup coil is mounted on a metallic noise source. The first input coil and the first-stage SQUID are coupled by overlapping or cross coupling. The flux-locked electronics section includes an amplifier, an integrator, and a feedback resistor. One end of the second-stage superconducting loop is grounded, and the other end is connected to the positive input terminal of the amplifier. The negative input terminal of the amplifier is grounded, and the output terminal of the amplifier is connected to the input terminal of the integrator. The output terminal of the integrator is connected to the feedback resistor and the feedback coil in sequence. The noise readout electronics section includes a digital-to-analog converter and a signal processing module. The input terminal of the integrator is connected to the input terminal of the digital-to-analog converter, and the digital-to-analog converter is electrically connected to the signal processing module.

[0007] Furthermore, the superconducting loop of the first-stage SQUID is a first-order gradient structure or a second-order gradient structure, and the superconducting loop of the second-stage SQUID is a first-order gradient structure or a second-order gradient structure.

[0008] Furthermore, the superconducting wire is either niobium wire or aluminum wire.

[0009] Furthermore, the metallic noise source is made of pure copper.

[0010] Furthermore, the first-stage SQUID and the second-stage SQUID array are low-temperature SQUIDs based on Nb or NbN thin films.

[0011] Furthermore, both the first-stage SQUID and the second-stage SQUID array consist of two Josephson junctions connected in parallel to form a closed superconducting loop. The first-stage SQUID has 1-100 SQUIDs, and the second-stage SQUID array has 2-100 SQUIDs.

[0012] Furthermore, the first-stage SQUID chip circuit and the second-stage SQUID array chip circuit are separate structures. The first-stage SQUID chip circuit is located on the first cold plate of the refrigerator, and the second-stage SQUID array chip circuit is located on the second cold plate or the first cold plate of the refrigerator.

[0013] Furthermore, the first-stage SQUID chip circuit and the second-stage SQUID array chip circuit are integrated into one structure, with the first-stage SQUID and the second-stage SQUID array on the same chip. The first-stage SQUID chip circuit and the second-stage SQUID array chip circuit are located on the first cold plate of the refrigerator.

[0014] Furthermore, it includes two low-temperature noise temperature sensing systems. The digital-to-analog converters of the two low-temperature noise temperature sensing systems are connected through a data processing module. The data processing module performs cross-correlation analysis on the signals output by the two digital-to-analog converters and outputs the temperature signal after the fusion of the two data streams.

[0015] A detection method for the aforementioned split-type cryogenic thermometer based on a superconducting quantum interference device is provided, comprising the following steps: S1: Thermal noise pickup coil (1) collects the magnetic flux noise signal of the metal noise source, and the first-stage SQUID chip circuit converts the magnetic flux noise signal into an output voltage signal; S2: The second-stage SQUID array chip circuit amplifies the output voltage signal output by the first-stage SQUID chip circuit and sends it to the amplifier (7) and integrator (8) for processing to obtain the amplified output signal; S3: The amplified output signal is converted into a temperature signal by the digital-to-analog converter (11). The temperature signals output by the two low-temperature noise temperature sensing systems are: ; in, , These are the combined signals of the two output temperature signals. The magnetic flux noise signal read from the thermal noise pickup coil (1) is the signal obtained from the magnetic flux noise. These are the noise error signals of the two low-temperature noise sensing systems, respectively. S4: Total signal for both output channels , Perform cross-correlation calculations; ; in, Indicates taking the total signal conjugate, Indicates the acquisition of magnetic flux noise signal conjugate, Indicates taking noise error signal Conjugate; S5: Due to magnetic flux noise signal Noise error signal The calculation formulas for the independent and interrelated components are simplified as follows: ; Among them, the simplified This refers to the measured temperature noise spectrum, also known as the temperature noise spectrum. Temperature noise is equal to voltage noise. .

[0016] The beneficial effects of this invention are as follows: The present invention relates to a split-type cryogenic noise thermometer based on a superconducting quantum interference device (SQUID). This thermometer separates the thermal noise pickup coil from the SQUID loop coil, avoiding thermal interference caused by the SQUID DC bias and effectively reducing direct interference between the thermal noise pickup coil and the SQUID feedback coil, thereby improving temperature measurement accuracy. It can be used for mK cryogenic measurement.

[0017] The first-stage SQUID chip circuit and the second-stage SQUID array chip circuit of the present invention can be designed separately or as a whole, which can meet the needs of different application scenarios. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the structural principle of the present invention; Figure 2 This is the second-stage SQUID array chip circuit, which is the first-stage SQUID chip circuit. Figure 3 This is a schematic diagram of the second-stage SQUID array chip circuit. Figure 4 This is a schematic diagram showing the installation positions of the first-stage SQUID chip circuit and the second-stage SQUID array chip circuit on the refrigerator in Example 1. Figure 5 This is a schematic diagram of a two-channel low-temperature noise temperature sensing system.

[0019] The symbols for the main components in the diagram are explained below: 1. Thermal noise pickup coil; 2. First input coil; 3. Bias resistor; 4. Second input coil; 5. First-stage SQUID; 6. Second-stage SQUID array; 7. Amplifier; 8. Integrator; 9. Feedback resistor; 10. Feedback coil; 11. Digital-to-analog converter; 12. Metal noise source. Detailed Implementation

[0020] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0021] Example 1 like Figure 1 As shown, a split-type cryogenic noise thermometer based on a superconducting quantum interference device includes at least one cryogenic noise temperature sensing system. The cryogenic noise temperature sensing system includes a metal noise source 12, a thermal noise pickup coil 1, a first-stage SQUID chip circuit, a second-stage SQUID array chip circuit, a flux-locking electronics section, and a noise readout electronics section. The metal noise source 12 is preferably made of pure copper, and the purity of the metal noise source is greater than 99.999%.

[0022] The thermal noise pickup coil 1 works in conjunction with the first-stage SQUID chip circuit to read the magnetic flux noise signal of the metal noise source 12. The thermal noise pickup coil 1 can not only eliminate the external uniform magnetic field, but also eliminate the external gradient magnetic field, thus resisting external interference.

[0023] like Figure 2 As shown, the first-stage SQUID array chip circuit is used to amplify the output voltage signal of the first-stage SQUID. The first-stage SQUID chip circuit includes a first input coil 2, a bias resistor 3, a feedback coil 10, and a first-stage SQUID 5.

[0024] like Figure 3 As shown, the second-stage SQUID array chip circuit amplifies the output voltage signal of the first-stage SQUID. The second-stage SQUID array chip circuit includes a second input coil 4 and a second-stage SQUID array 6. The feedback coil 10 is overlapped or cross-coupled with the first-stage SQUID 5. The first-stage SQUID 5, the second input coil 4, and the bias resistor 3 are connected in series to form a closed loop. The thermal noise pickup coil 1 and the first input coil 2 are connected via a superconducting wire to form a closed loop. The thermal noise pickup coil 1 and the first input coil 2 are mounted in contact with the metal noise source 12. The first input coil 2 is overlapped or cross-coupled with the first-stage SQUID 5. The second input coil 4 is overlapped or cross-coupled with the second-stage SQUID array 6. A first niobium sleeve is provided outside the first-stage SQUID chip circuit, and the first-stage SQUID chip circuit is fixed to the metal noise source 12 through the first niobium sleeve. The second-stage SQUID array chip circuit is externally provided with a second niobium sleeve, and the second-stage SQUID array chip circuit is fixed to the metal noise source 12 through the second niobium sleeve.

[0025] The flux-locked electronics section is used to operate the SQUID. This section includes an amplifier 7, an integrator 8, and a feedback resistor 9. One end of the second-stage superconducting loop is grounded, and the other end is connected to the positive input terminal of amplifier 7. The negative input terminal of amplifier 7 is grounded, and the output terminal of amplifier 7 is connected to the input terminal of integrator 8. The output terminal of integrator 8 is sequentially connected to feedback resistor 9 and feedback coil 10. The other end of feedback coil 10 is grounded. The feedback coil 10 is either overlapped or cross-coupled with the first-stage SQUID 5.

[0026] The noise readout electronics section is used to convert the voltage signal into a temperature signal. This section includes a digital-to-analog converter (DAC) 11 and a signal processing module. The input terminal of the integrator 8 is connected to the input terminal of the DAC 11, and the DAC 11 is electrically connected to the signal processing module. The DAC 11, in conjunction with the signal processing module equipped with Fourier transform analysis software, and the noise readout circuit, forms the noise readout electronics section.

[0027] Both the first-stage SQUID5 and the second-stage SQUID array 6 consist of two Josephson junctions connected in parallel to form a closed superconducting loop. The superconducting loop of the first-stage SQUID5 is preferably a first-order or second-order gradient structure, and the superconducting loop of the second-stage SQUID6 is also preferably a first-order or second-order gradient structure. Both the first-stage SQUID and the second-stage SQUID array employ low-temperature SQUIDs based on Nb or NbN thin films. The first-stage SQUID5 contains 1-100 SQUIDs; it can be a single SQUID or a series array of SQUIDs, with the number of series-connected SQUIDs ranging from 2 to 100. The second-stage SQUID array 6 also contains 2-100 SQUIDs.

[0028] like Figure 4 As shown, the first-stage SQUID chip circuit and the second-stage SQUID array chip circuit are separate structures. The first-stage SQUID chip circuit and the second-stage SQUID array chip circuit are respectively set on two different metal noise sources 12. The first-stage SQUID chip circuit is set on the first cold plate of the refrigerator, and the second-stage SQUID array chip circuit is set on the second cold plate or the first cold plate of the refrigerator. In this embodiment, the first cold plate is an mK plate with a temperature range of 1mK to 1K, and the second cold plate is a 4K plate with a temperature range of 1K to 6K.

[0029] Example 2 In Embodiment 2, the difference between Embodiment 1 and Embodiment 2 lies in the overall structure of the first-stage SQUID chip circuit and the second-stage SQUID array chip circuit. In this embodiment, the first-stage SQUID chip circuit and the second-stage SQUID array chip circuit are integrated into a single structure; the first-stage SQUID and the second-stage SQUID array are on the same chip; the first-stage SQUID chip circuit and the second-stage SQUID array chip circuit are disposed on the same metallic noise source 12; and the first-stage SQUID chip circuit and the second-stage SQUID array chip circuit are disposed on the first cold plate of the refrigerator.

[0030] The fabrication methods for the first-level SQUID5 and the second-level SQUID array 6 are as follows: A1, Magnetron sputtering of Nb / Al-AlO x / Nb three-layer film preparation, photolithography etching to form patterns; A2. SiO2 thin films are grown by PECVD and patterned by photolithography and etching. A3. Nb line layer is sputtered by magnetron sputtering and patterned by photolithography etching; A4. Electron beam evaporation of PdAu layer, patterned by stripping method.

[0031] Example 3 like Figure 5 As shown, this embodiment includes two low-temperature noise temperature sensing systems. Each low-temperature noise temperature sensing system is the same as that in Embodiments 1 and 2. The digital-to-analog converters 11 of the two low-temperature noise temperature sensing systems are connected through a data processing module. The data processing module performs cross-correlation analysis on the signals output by the two digital-to-analog converters 11 and outputs the temperature signal after the fusion of the two data streams.

[0032] A detection method for a split-type cryogenic thermometer based on a superconducting quantum interference device includes the following steps: S1: Thermal noise pickup coil 1 collects the magnetic flux noise signal of the metal noise source, and the first-stage SQUID chip circuit converts the magnetic flux noise signal into an output voltage signal. S2: The second-stage SQUID array chip circuit amplifies the output voltage signal from the first-stage SQUID chip circuit and sends it to amplifier 7 and integrator 8 for processing to obtain the amplified output signal. S3: The amplified output signal is converted into a temperature signal by the digital-to-analog converter 11. The temperature signals output by the two low-temperature noise temperature sensing systems are: ; in, , These are the combined signals of the two output temperature signals. The magnetic flux noise signal read from thermal noise pickup coil 1. These are the noise error signals of the two low-temperature noise sensing systems, respectively. S4: Total signal for both output channels , Perform cross-correlation calculations; ; in, Indicates taking the total signal conjugate, Indicates the acquisition of magnetic flux noise signal conjugate, Indicates taking noise error signal Conjugate; S5: Due to magnetic flux noise signal Noise error signal The calculation formulas for the independent and interrelated components are simplified as follows: ; Among them, the simplified This refers to the measured temperature noise spectrum, also known as the temperature noise spectrum. Temperature noise is equal to voltage noise. .

[0033] The working process and principle of the split-type ultra-low temperature noise thermometer of the present invention are as follows: the metal noise source 12 converts temperature noise into magnetic flux noise, the copper noise sensor 12 collects the magnetic flux noise of the metal noise source 12, suppresses non-thermal noise sources, the first-stage SQUID chip circuit converts the magnetic flux signal into a voltage signal, and the second-stage SQUID array circuit reads the voltage signal and converts it into temperature, thereby obtaining the temperature value of the metal noise source 12.

[0034] The temperature measurement principle is based on the Nyquist principle, and the specific formula is as follows:

[0035] formula, For voltage noise, For system bandwidth, Boltzmann's constant, The temperature to be measured. It is a resistor.

Claims

1. A split-type ultra-low temperature noise thermometer based on a superconducting quantum interference device, characterized in that, It includes at least one low-temperature noise temperature sensing system, which includes a metal noise source (12), a thermal noise pickup coil (1), a first-level SQUID chip circuit, a second-level SQUID array chip circuit, a flux-locking electronics section and a noise readout electronics section; The thermal noise pickup coil (1) is used to read the magnetic flux noise signal of the metal noise source (12); The first-stage SQUID chip circuit is used to convert the magnetic flux noise signal into an output voltage signal. The first-stage SQUID chip circuit includes a first input coil (2), a bias resistor (3), a feedback coil (10), and a first-stage SQUID (5). The second-stage SQUID array chip circuit is used to amplify the output voltage signal of the first-stage SQUID. The second-stage SQUID array chip circuit includes a second input coil (4) and a second-stage SQUID array (6). The first-stage SQUID (5), the second input coil (4), and the bias resistor (3) are connected in series to form a closed loop. The feedback coil (10) and the first-stage SQUID (5) are coupled in an overlapping or cross-coupled manner. The thermal noise pickup coil (1) and the first input coil (2) are connected by a superconducting wire to form a closed loop. The thermal noise pickup coil (1) is mounted on a metal noise source (12). The first input coil (2) and the first-stage SQUID (5) are coupled in an overlapping or cross-coupled manner. The second input coil (4) and the second-stage SQUID (6) are coupled in an overlapping or cross-coupled manner. The flux-locked electronics section includes an amplifier (7), an integrator (8), and a feedback resistor (9). One end of the second-stage superconducting loop is grounded, and the other end is connected to the positive input terminal of the amplifier (7). The negative input terminal of the amplifier (7) is grounded. The output terminal of the amplifier (7) is connected to the input terminal of the integrator (8). The output terminal of the integrator (8) is connected to the feedback resistor (9) and the feedback coil (10) in sequence. The noise readout electronics section includes a digital-to-analog converter (11) and a signal processing module. The input terminal of the integrator (8) is connected to the input terminal of the digital-to-analog converter (11), and the digital-to-analog converter (11) is electrically connected to the signal processing module.

2. The split-type cryogenic thermometer based on a superconducting quantum interference device according to claim 1, characterized in that, The superconducting loop of the first-stage SQUID (5) is a first-order gradient structure or a second-order gradient structure, and the superconducting loop of the second-stage SQUID (6) is a first-order gradient structure or a second-order gradient structure.

3. The split-type cryogenic thermometer based on a superconducting quantum interference device according to claim 2, characterized in that, The superconducting wire is either niobium wire or aluminum wire.

4. The split-type cryogenic thermometer based on a superconducting quantum interference device according to claim 3, characterized in that, The metal noise source (12) is made of pure copper.

5. The split-type cryogenic thermometer based on a superconducting quantum interference device according to claim 4, characterized in that, The first-stage SQUID (5) and the second-stage SQUID array (6) are low-temperature SQUIDs based on Nb or NbN thin films.

6. The split-type cryogenic thermometer based on a superconducting quantum interference device according to claim 5, characterized in that, The first-stage SQUID (5) and the second-stage SQUID array (6) are both two Josephson junctions connected in parallel to form a closed superconducting loop. The number of SQUIDs in the first-stage SQUID (5) is 1-100, and the number of SQUIDs in the second-stage SQUID array (6) is 2-100.

7. The split-type cryogenic thermometer based on a superconducting quantum interference device according to claim 6, characterized in that, The first-stage SQUID chip circuit and the second-stage SQUID array chip circuit are separate structures. The first-stage SQUID chip circuit is located on the first cold plate of the refrigerator, and the second-stage SQUID array chip circuit is located on the second cold plate or the first cold plate of the refrigerator.

8. The split-type cryogenic thermometer based on a superconducting quantum interference device according to claim 7, characterized in that, The first-stage SQUID chip circuit and the second-stage SQUID array chip circuit are integrated into one structure. The first-stage SQUID and the second-stage SQUID array are on the same chip. The first-stage SQUID chip circuit and the second-stage SQUID array chip circuit are located on the first cold plate of the refrigerator.

9. The split-type cryogenic thermometer based on a superconducting quantum interference device according to claim 8, characterized in that, It includes two low-temperature noise temperature sensing systems. The digital-to-analog converters (11) of the two low-temperature noise temperature sensing systems are connected through a data processing module. The data processing module performs cross-correlation analysis on the signals output by the two digital-to-analog converters (11) and outputs the temperature signal after the fusion of the two data.

10. A detection method for a split-type ultra-low temperature noise thermometer based on a superconducting quantum interference device as described in claim 9, characterized in that, Includes the following steps: S1: Thermal noise pickup coil (1) collects the magnetic flux noise signal of the metal noise source, and the first-stage SQUID chip circuit converts the magnetic flux noise signal into an output voltage signal; S2: The second-stage SQUID array chip circuit amplifies the output voltage signal output by the first-stage SQUID chip circuit and sends it to the amplifier (7) and integrator (8) for processing to obtain the amplified output signal; S3: The amplified output signal is converted into a temperature signal by the digital-to-analog converter (11). The temperature signals output by the two low-temperature noise temperature sensing systems are: ； in, , These are the combined signals of the two output temperature signals. The magnetic flux noise signal read from the thermal noise pickup coil (1) is the signal obtained from the magnetic flux noise. These are the noise error signals of the two low-temperature noise sensing systems, respectively. S4: Total signal for both output channels , Perform cross-correlation calculations; ； in, Indicates taking the total signal conjugate, Indicates the acquisition of magnetic flux noise signal conjugate, Indicates taking noise error signal The conjugate; S5: Due to magnetic flux noise signal Noise error signal The calculation formulas for the independent and interrelated components are simplified as follows: ； Among them, the simplified This refers to the measured temperature noise spectrum, also known as the temperature noise spectrum. Temperature noise is equal to voltage noise. .

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