Microwave standard field irradiation system based on open resonant cavity and superconducting test method

Abstract

The invention discloses a microwave standard field irradiation system based on an open resonant cavity and a superconducting test method. The microwave standard field irradiation system comprises a microwave source which is provided with a sending port and a receiving port; the resonant cavity is provided with a first port coupled with the transmitting port and a second port coupled with the receiving port, so that an electromagnetic field is generated on a transmission path of a microwave signal; the sample table is located in the resonant cavity, and a sample placed on the sample table is located on a transmission path of the microwave signal; and the shell is used for accommodating the resonant cavity and keeping a low-temperature environment in a testing process. The microwave standard field irradiation system utilizes standing wave characteristics on a transmission path of a microwave signal to enhance the electric field intensity of a sample position so as to improve the signal-to-noise ratio of a quantum measurement signal, thereby improving the measurement accuracy. In addition, the calculation of the standard irradiation electric field can be simplified.

Description

Technical Field

[0001] The present invention relates to quantum measurement technology, and more specifically, to a microwave standard field irradiation system based on an open resonant cavity and a superconducting test method. Background Art

[0002] The superconducting Josephson junction is a superconducting junction device composed of a superconductor-insulator-superconductor. When a thin insulating layer passes between two superconductors, superconducting electron pairs (Cooper pairs) can tunnel through the insulating layer to form a superconducting current. The superconducting Josephson junction can generate a very stable voltage, so it can be used as a very accurate voltage reference. The parallel connection of multiple superconducting Josephson junctions can generate a high-precision voltage reference. The superconducting Josephson junction can generate a high-frequency AC superconducting current under the action of an applied voltage, so it can be used to develop millimeter-wave and terahertz radiation sources. Using multiple superconducting Josephson junctions arranged in an array can achieve coherent superposition of power, thereby enhancing the radiation intensity. The superconducting Josephson junction has the advantages of fast reaction rate, high quantum limit sensitivity, and low noise. The superconducting Josephson junction also provides an effective way to realize and manipulate quantum states on a macroscopic scale, so it is used as a core device in quantum computers.

[0003] The characterization of quantum properties of superconducting Josephson junctions is the basis for the design and development of superconducting devices. How to provide a standard microwave irradiation field condition for superconducting Josephson junctions is crucial for accurately measuring parameters such as the Shapiro steps used to characterize their quantum properties.

[0004] A traditional superconducting test method is to place a sample prepared with a Josephson junction directly into a waveguide, and measure the relationship between the alternating voltage and the average value of the superconducting current under the action of the microwave irradiation field to obtain the Shapiro steps. However, due to the uneven distribution of the electromagnetic field in the waveguide and the lack of concentrated energy, the coupling between the microwave electromagnetic field and the Josephson junction is poor, making it difficult to measure high-quality Shapiro steps. In addition, there is also a method of using a bare coaxial cable directly near the Josephson junction for microwave irradiation testing. This method usually generates a relatively weak microwave electromagnetic field, has a poor signal-to-noise ratio, and is easily interfered, making it impossible to obtain a satisfactory microwave irradiation environment.

[0005] Therefore, it is expected to optimize the coupling between the electromagnetic field and the Josephson junction in microwave irradiation testing to improve the measurement accuracy and simplify the parameter characterization. Summary of the invention

[0006] In view of the above problems, an object of the present invention is to provide a microwave standard field irradiation system and a superconducting testing method based on an open resonant cavity, wherein the standing wave characteristics on the transmission path of the microwave signal are utilized to enhance the electric field strength at the sample position.

[0007] According to one aspect of the present invention, there is provided a microwave standard field irradiation system, comprising: a microwave source, the microwave source having a transmitting port and a receiving port; a resonant cavity, the resonant cavity having a first port coupled to the transmitting port, and a second port coupled to the receiving port, so as to generate an electromagnetic field on the transmission path of the microwave signal; a sample stage, located in the resonant cavity, a sample placed on the sample stage is located on the transmission path of the microwave signal; and a shell, used to accommodate the resonant cavity and maintain a low-temperature environment during testing.

[0008] Optionally, it further includes: an adjusting screw extending from the outside to the inside of the shell and engaging with a screw hole on the sample stage to move the sample stage.

[0009] Optionally, the resonant cavity includes: a first concave reflecting mirror and a second concave reflecting mirror, which are arranged opposite to each other and have the first port and the second port respectively, wherein the sample stage is located between the first concave reflecting mirror and the second concave reflecting mirror.

[0010] Optionally, the length of the resonant cavity corresponds to the distance between the first concave reflecting mirror and the second concave reflecting mirror, and the resonant cavity has a constant length.

[0011] Optionally, the electromagnetic field in the resonant cavity has a stable Gaussian standing wave distribution, and the vertical position of the sample is located at the position of the electromagnetic wave beam waist.

[0012] Optionally, it also includes: a vector network analyzer, wherein the microwave source is built in the vector network analyzer.

[0013] Optionally, when the resonant cavity is in a state without a sample, the vector network analyzer measures a frequency response curve of a transmission coefficient to obtain a plurality of initial resonant frequencies of the resonant cavity.

[0014] Optionally, when there is a sample in the resonant cavity, the vector network analyzer measures the current resonant frequency and resonant quality factor of the resonant cavity, and, by adjusting the vertical position of the sample, the current resonant frequency of the resonant cavity is minimized relative to a selected resonant frequency among the multiple initial resonant frequencies.

[0015] Optionally, according to the calculation model of the electric field strength at the center of the quasi-optical resonant cavity, the standard irradiation electric field of the current resonant frequency is calculated. :

[0016] (1)

[0017] in, is the current resonant frequency; is the resonance quality factor; P is the microwave feeding power of the resonant cavity; is the dielectric constant of vacuum; is the electromagnetic wave beam waist radius at the sample position, ; R0 is the radius of curvature of the concave reflector, L is the length of the resonant cavity, is the wave number of the electromagnetic wave.

[0018] Optionally, it also includes: a first waveguide, wherein the first end of the first waveguide is coupled to the first port of the resonant cavity, and the second end is coupled to the transmitting port of the microwave source to feed in the microwave signal; and a second waveguide, wherein the first end of the second waveguide is coupled to the second port of the resonant cavity, and the second end is coupled to the receiving port of the microwave source to feed out the microwave signal.

[0019] Optionally, it also includes: a directional coupler coupled to the first waveguide to obtain a sampling signal of the microwave signal; and a power meter connected to the directional coupler to obtain the measured power of the sampling signal, wherein the feeding power of the resonant cavity is calculated based on the output power of the microwave source, the isolation of the directional coupler, and the measured power.

[0020] According to another aspect of the present invention, there is provided a superconducting testing method, comprising: setting a resonant cavity on a transmission path of a microwave signal, the resonant cavity having a first port for feeding in the microwave signal, and a second port for feeding out the microwave signal; placing a superconducting sample at an electric field focusing position in the resonant cavity; and measuring the quantum properties of the superconducting sample.

[0021] Optionally, the resonant cavity includes: a first concave reflecting mirror and a second concave reflecting mirror, which are arranged opposite to each other and respectively have the first port and the second port, wherein a sample stage for placing the superconducting sample is arranged between the first concave reflecting mirror and the second concave reflecting mirror.

[0022] Optionally, the length of the resonant cavity corresponds to the distance between the first concave reflecting mirror and the second concave reflecting mirror, and the resonant cavity has a constant length.

[0023] Optionally, the electromagnetic field in the resonant cavity has a stable Gaussian standing wave distribution, and the vertical position of the superconducting sample is located at the position of the electromagnetic wave beam waist.

[0024] Optionally, placing a superconducting sample at an electric field focusing position in the resonant cavity includes: measuring a transmission coefficient frequency response curve when there is no superconducting sample in the resonant cavity to obtain a plurality of initial resonant frequencies of the resonant cavity.

[0025] Optionally, placing a superconducting sample at the electric field focusing position in the resonant cavity also includes: measuring the current resonant frequency and resonance quality factor of the resonant cavity when the superconducting sample is in the resonant cavity; and minimizing the deviation of the current resonant frequency of the resonant cavity relative to a selected resonant frequency among the multiple initial resonant frequencies by adjusting the vertical position of the superconducting sample.

[0026] Optionally, according to the calculation model of the electric field strength at the center of the quasi-optical resonant cavity, the standard irradiation electric field of the current resonant frequency is calculated. :

[0027] (1)

[0028] in, is the current resonant frequency; is the resonance quality factor; P is the microwave feeding power of the resonant cavity; is the dielectric constant of vacuum; is the electromagnetic wave waist radius at the superconducting sample position, ; R0 is the radius of curvature of the concave reflector, L is the length of the resonant cavity, is the wave number of the electromagnetic wave.

[0029] Optionally, it also includes: using a directional coupler to collect the microwave signal of the first port of the resonant cavity; and using a power meter to obtain the measured power of the microwave signal, wherein the feed power of the resonant cavity is calculated based on the output power of the microwave source, the isolation of the directional coupler, and the measured power.

[0030] Optionally, the superconducting sample is a Josephson junction sample, and measuring the quantum characteristics of the superconducting sample includes: measuring the relationship between a standard irradiation electric field and a superconducting current of the Josephson junction sample.

[0031] According to the microwave standard field irradiation system of the embodiment of the present invention, the standing wave characteristics on the transmission path of the microwave signal are used to enhance the electric field strength at the sample position. Unlike the existing reflective resonant cavity, the resonant cavity operates in the TEM00q fundamental mode on the transmission path of the microwave signal. The electromagnetic field distribution in the resonant cavity has two important characteristics: first, the electromagnetic field is a stable Gaussian standing wave distribution, and the electromagnetic field energy is fully concentrated at the position of the electromagnetic wave waist to generate a sufficiently strong linear polarization electric field; second, the electromagnetic field in the near-axial region of the cavity is approximately a transverse electromagnetic wave, similar to a plane wave in free space. A standard Gaussian distribution electric field is generated in the resonant cavity to act on the sample surface, and the coherent superposition of the transmitted electromagnetic wave and the reflected power wave generates a high electric field intensity, which can improve the microwave coupling efficiency of the superconducting Josephson junction, thereby improving the signal-to-noise ratio of the quantum measurement signal, and then improving the measurement accuracy. In addition, the output power requirements for the microwave source can also be reduced.

[0032] In a preferred embodiment, the resonant cavity can generate multiple resonant fundamental modes within a waveguide frequency band, corresponding to microwave irradiation conditions at multiple operating frequencies. Multiple resonant frequencies can be obtained by testing the transmission coefficient frequency response curve of the resonant cavity. Compared with the irradiation field of a single operating frequency, the present invention uses a single microwave source and utilizes the Gaussian standing wave characteristic to generate irradiation fields of multiple operating frequencies, thereby measuring the quantum characteristics of the Josephson junction sample at multiple operating frequencies, thereby improving the test efficiency.

[0033] In a preferred embodiment, the movement of the sample stage is controlled according to the frequency offset relative to the selected resonant frequency, and the Gaussian standing wave characteristic is used to move the sample to the electromagnetic energy gathering position of the selected resonant frequency. In the existing reflective resonant cavity, resonant cavities of different lengths need to be designed for different resonant frequencies. Unlike the existing reflective resonant cavity, the resonant cavity of the present invention adopts a fixed length and reaches the electromagnetic energy gathering position of different resonant frequencies by moving the vertical position of the sample. Compared with the existing reflective resonant cavity, the present invention adopts a single resonant cavity and measures the quantum characteristics of the Josephson junction sample at multiple operating frequencies by moving the vertical position of the sample, thereby improving the test efficiency.

[0034] Furthermore, the electric field intensity at the sample position can be directly calculated based on the microwave feed power of the resonant cavity, the quality factor of the resonant cavity, the beam waist radius, and the cavity length. The above intermediate parameters can be accurately obtained based on theoretical calculations or actual measurement results. This electric field intensity calculation method not only simplifies the calculation process of the standard irradiation electric field, but also improves the quantization accuracy of the standard irradiation electric field, thereby improving the measurement accuracy of quantum properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0036] Figure 1 A schematic diagram showing the structure of a microwave standard field irradiation system according to the prior art is shown;

[0037] Figure 2 A schematic structural diagram showing a microwave standard field irradiation system according to a first embodiment of the present invention; and

[0038] Figure 3 A flow chart of a superconducting testing method according to a second embodiment of the present invention is shown. DETAILED DESCRIPTION

[0039] The present invention will be described in more detail below with reference to the accompanying drawings. In each of the accompanying drawings, the same elements are represented by similar reference numerals. For the sake of clarity, the various parts in the accompanying drawings are not drawn to scale. In addition, some well-known parts may not be shown.

[0040] Many specific details of the present invention are described below, such as device structure, materials, dimensions, processing technology and techniques, so as to more clearly understand the present invention. However, as those skilled in the art will appreciate, the present invention may be implemented without following these specific details.

[0041] Figure 1 The schematic diagram of the structure of the microwave standard field irradiation system according to the prior art is shown. The microwave standard field irradiation system 100 has a single concave reflector structure.

[0042] The microwave standard field irradiation system 100 includes a housing 11 and a sample stage 1 located inside the housing 11. The housing 11 is made of, for example, stainless steel and has a heat-insulating interlayer to maintain a low-temperature environment during the test. The sample stage 1 is made of, for example, stainless steel and has a central opening.

[0043] The Josephson junction sample 2 is located above the central opening of the sample stage 1, so that the center position of the Josephson junction sample 2 is in an air medium or a vacuum environment. Since the electromagnetic field directly passes through the central opening of the sample stage 1, it is not only beneficial to improve the electromagnetic field strength at the sample position, but also there is no need to consider the interference caused by the sample stage 1 when calculating the electromagnetic field at the sample position, and the electric field strength calculation can be simplified.

[0044] The adjusting screw 3 extends from the outside to the inside of the housing 11, and engages with a screw hole on the sample stage 1. By rotating the adjusting screw 3 outside the housing 11, the sample stage can be moved in the vertical direction.

[0045] The microwave standard field irradiation system 100 further includes a concave reflector 12 , a waveguide 13 , a waveguide-coaxial converter 14 , a coaxial cable 15 , and a microwave source 21 .

[0046] The concave reflector 12 is made of oxygen-free copper, for example, and the surface is polished. In this embodiment, the concave reflector 12 is a spherical mirror. After the curvature radius and the aperture diameter of the spherical surface are optimized, the concave reflector 12 works in the Ka band (26 GHz to 40 GHz). The concave reflector 12 has a central port in the shape of a circular hole. The aperture and thickness of the port need to be optimized so that the modulus of the port reflection coefficient remains below -15 dB in the entire Ka band.

[0047] The waveguide 13 extends from the outside to the inside of the housing 11 and is coupled to the central port of the concave reflector 12. The waveguide 13 operates in the Ka band, for example. The microwave source 21 generates a microwave signal, which is coupled to the waveguide 13 via a coaxial cable 15 and a waveguide-coaxial converter 14. The microwave source 21 feeds the microwave signal to the concave reflector 12 to generate an electromagnetic field inside the housing 11.

[0048] The microwave standard field irradiation system 100 further includes a directional coupler 16 and a power meter 17. The directional coupler 16 is coupled to the waveguide 13 and is used to couple a portion of the microwave signal transmitted on the waveguide 13 to the measurement loop to obtain a sampling signal. The power meter 17 is connected to the directional coupler 16 and is used to measure the power of the sampling signal. According to the output power of the microwave source 21, the coupling degree of the directional coupler 16, and the measured power of the power meter 17, the feeding power of the concave reflector 12 can be calculated.

[0049] According to the microwave standard field irradiation system 100 of the prior art, a concave reflector 12 is used to radiate electromagnetic waves in free space, and a Josephson junction sample 2 is placed on the radiation path of the microwave signal, and the electric field strength at the sample position is estimated based on the feed power of the central port of the concave reflector 12. Since the radiation energy of the microwave signal is small, the electric field strength generated at the sample position is low, so it is difficult to improve the microwave coupling efficiency of the superconducting Josephson junction, resulting in a low signal-to-noise ratio of the quantum measurement signal, and thus low measurement accuracy. Even if the output power of the microwave source is increased, it is still difficult to obtain an ideal electric field strength at the sample position.

[0050] In a further improved microwave standard field irradiation system, the concave reflector 12 is coupled to the transmission port of the microwave source 21, the concave reflector 12 is used to radiate electromagnetic waves in free space, the plane reflector is used to reflect the electromagnetic waves, and the Josephson junction sample 2 is placed between the concave reflector 12 and the plane reflector. Since the concave reflector 12 and the plane reflector form a resonant cavity, the standing wave characteristic can be used to enhance the electric field intensity at the sample position. On the reflection path of the microwave signal, the resonant cavity operates in the TEM00q fundamental mode. However, the electric field intensity generated by the coherent superposition of the radiated electromagnetic wave and the reflected power wave is still too low, especially at high-order resonant frequencies, the electric field intensity is difficult to meet the requirements of superconducting Josephson junction measurement. Even with the existing reflective resonant cavity, it is difficult to measure the quantum characteristics of the Josephson junction sample at multiple resonant frequencies.

[0051] Figure 2 The schematic diagram of the structure of the microwave standard field irradiation system according to the first embodiment of the present invention is shown. The microwave standard field irradiation system 200 has a resonant cavity with a double concave reflector structure.

[0052] The microwave standard field irradiation system 100 includes a housing 11 and a sample stage 1 located inside the housing 11. The housing 11 is made of, for example, stainless steel and has a heat-insulating interlayer to maintain a low-temperature environment during the test. The sample stage 1 is made of, for example, stainless steel and has a central opening. However, the present invention is not limited thereto. The present invention can use any material suitable for microwave penetration to make the sample stage 1, such as quartz, ceramics, plastics, etc. In this case, there is no need to form a central opening on the sample stage.

[0053] The Josephson junction sample 2 is located above the central opening of the sample stage 1, so that the center position of the Josephson junction sample 2 is in an air medium or a vacuum environment. Since the electromagnetic field directly passes through the central opening of the sample stage 1, it is not only beneficial to improve the electromagnetic field strength at the sample position, but also there is no need to consider the interference caused by the sample stage 1 when calculating the electromagnetic field at the sample position, and the electric field strength calculation can be simplified.

[0054] The adjusting screw 3 extends from the outside to the inside of the housing 11 and engages with a screw hole on the sample stage 1. By rotating the adjusting screw 3 outside the housing 11, the sample stage can be moved in the vertical direction. However, the present invention is not limited to this. The present invention can use any actuator that moves the sample stage in the vertical direction. For example, a linear motor that drives the sample stage to move vertically inside the housing 11 can achieve the same function as the adjusting screw 3.

[0055] The microwave standard field irradiation system 200 further includes concave reflectors 12 and 22 , waveguides 13 and 23 , waveguide-coaxial converters 14 and 24 , coaxial cables 15 and 25 , and a vector network analyzer 31 .

[0056] The concave reflectors 12 and 22 are made of oxygen-free copper, for example, and the surface is polished. In the present embodiment, the concave reflectors 12 and 22 are spherical mirrors, respectively. After the optimization design of the curvature radius and the aperture diameter of the spherical surface, the concave reflectors 12 and 22, for example, work in the Ka band (26 GHz to 40 GHz). The concave reflectors 12 and 22 have central ports in the shape of circular holes, respectively. The aperture and thickness dimensions of the ports need to be optimized so that the modulus of the port reflection coefficient remains below -15 dB in the entire Ka band.

[0057] The concave reflectors 12 and 22 are arranged opposite to each other and keep a constant distance, and the sample stage 1 is located between the concave reflectors 12 and 22. A resonant cavity is formed between the concave reflectors 12 and 22, and the length L of the resonant cavity is the distance between the concave reflectors 12 and 22. The electromagnetic field in the resonant cavity has a stable Gaussian standing wave distribution, and the vertical position of the Josephson junction sample 2 is located at the position of the electromagnetic wave beam waist.

[0058] The waveguide 13 extends from the outside to the inside of the housing 11 and is coupled to the central port of the concave reflector 12. The waveguide 13 operates in the Ka band, for example. The waveguide 23 extends from the outside to the inside of the housing 11 and is coupled to the central port of the concave reflector 22. The waveguide 23 operates in the Ka band, for example. The built-in microwave source of the vector network analyzer 31 generates a microwave signal, which is coupled to the waveguide 13 via the coaxial cable 15 and the waveguide-coaxial converter 14, and is coupled to the waveguide 23 via the coaxial cable 25 and the waveguide-coaxial converter 24. The vector network analyzer 31 feeds the microwave signal to the concave reflectors 12 and 22, thereby generating an electromagnetic field inside the housing 11.

[0059] The microwave standard field irradiation system 200 also includes a directional coupler 16 and a power meter 17. The directional coupler 16 is coupled to the waveguide 13 and is used to couple a portion of the microwave signal transmitted on the waveguide 13 to the measurement loop to obtain a sampled signal. The power meter 17 is connected to the directional coupler 16 and is used to measure the power of the sampled signal. According to the output power of the vector network analyzer 31, the coupling degree of the directional coupler 16, and the measured power of the power meter 17, the feed power of the resonant cavity can be calculated.

[0060] In the above-mentioned embodiment, a microwave standard field irradiation system 200 operating in the Ka band is used as an example for explanation. However, the present invention is not limited thereto, and the design and development scheme of the microwave standard field irradiation system 200 is not limited to the Ka band in this case, but can be extended to other microwave or millimeter wave waveguide frequency bands.

[0061] According to the microwave standard field irradiation system 200 of this embodiment, based on the Fabry-Perot quasi-optical resonant cavity principle, the first concave reflector and the second concave reflector are arranged relative to each other to form a resonant cavity. The microwave standard field irradiation system 200 utilizes the standing wave characteristics on the transmission path of the microwave signal to enhance the electric field strength at the sample position. Unlike the existing reflective resonant cavity, the resonant cavity operates in the TEM00q fundamental mode on the transmission path of the microwave signal. The electromagnetic field distribution in the resonant cavity has two important characteristics: first, the electromagnetic field is a stable Gaussian standing wave distribution, and at the position of the electromagnetic wave waist, the electromagnetic field energy is fully concentrated to generate a sufficiently strong linear polarization electric field; second, the electromagnetic field in the near-axial region of the cavity is approximately a transverse electromagnetic wave, similar to a plane wave in free space. A standard Gaussian distribution electric field is generated in the resonant cavity to act on the sample surface, and the coherent superposition of the transmitted electromagnetic wave and the reflected power wave generates a high electric field strength, which can improve the microwave coupling efficiency of the superconducting Josephson junction, thereby improving the signal-to-noise ratio of the quantum measurement signal, and then improving the measurement accuracy. In addition, the output power requirements of the microwave source can also be reduced.

[0062] In a preferred embodiment, the resonant cavity can generate multiple resonant fundamental modes within a waveguide frequency band, corresponding to microwave irradiation conditions at multiple operating frequencies. Multiple resonant frequencies can be obtained by testing the transmission coefficient frequency response curve of the resonant cavity. Compared with the irradiation field of a single operating frequency, the present invention uses a single microwave source and utilizes the Gaussian standing wave characteristic to generate irradiation fields of multiple operating frequencies, thereby measuring the quantum characteristics of the Josephson junction sample at multiple operating frequencies, thereby improving the test efficiency.

[0063] Figure 3 A flow chart of a superconducting test method according to a second embodiment of the present invention is shown. The superconducting test method is used to Figure 2 The microwave standard field irradiation system 200 is shown.

[0064] In step S01 , a resonant cavity is arranged on a transmission path of a microwave signal, wherein the resonant cavity has a first port for feeding in the microwave signal and a second port for feeding out the microwave signal.

[0065] See also Figure 2 In the microwave standard field irradiation system 200, a resonant cavity is formed between the concave reflectors 12 and 22, wherein the resonant cavity length L is the distance between the concave reflectors 12 and 22. The microwave source built into the vector network analyzer 31 feeds microwave signals to the concave reflectors 12 and 22, forming an electromagnetic field in the resonant cavity. The electromagnetic field has a stable Gaussian standing wave distribution. The electric field intensity reaches a maximum value at the position of the electromagnetic wave beam waist.

[0066] In step S02, a sample is placed at the electric field focusing position in the resonant cavity.

[0067] When the resonant cavity has no sample, a vector network analyzer 31 is used to measure the transmission coefficient frequency response curve to obtain a plurality of initial resonant frequencies of the resonant cavity.

[0068] The sample is placed at an initial position in the resonant cavity, which may be, for example, the middle position of the concave reflecting mirrors 12 and 22 .

[0069] When the resonant cavity has no sample, the vector network analyzer 31 is used to measure the current resonant frequency and the resonant quality factor of the resonant cavity.

[0070] See also Figure 2 The adjusting screw 2 extends from the outside to the inside of the housing 11 and engages with the screw hole on the sample stage 1 to move the sample stage 1. The vertical position of the sample is adjusted by moving the sample stage 1 so that the current resonant frequency of the resonant cavity is offset minimally relative to the selected resonant frequency among the multiple initial resonant frequencies. At this time, the vertical position of the sample is at the electric field energy gathering position at the current resonant frequency.

[0071] In step S03, the quantum properties of the sample are measured.

[0072] The sample used in this embodiment is, for example, a Josephson junction sample, and measuring the quantum characteristics of the sample includes: measuring the relationship between the standard irradiation electric field and the superconducting current of the Josephson junction sample.

[0073] See also Figure 2 The microwave signal of the feeding port of the resonant cavity is collected by using a directional coupler 4, and the measured power of the microwave signal is obtained by using a power meter 5. The feeding power P of the resonant cavity is calculated according to the output power of the microwave source, the isolation of the directional coupler, and the measured power.

[0074] Further, according to the calculation model of the electric field strength at the center of the quasi-optical resonant cavity, the standard irradiation electric field of the current resonant frequency is calculated. :

[0075] (1)

[0076] in, is the current resonant frequency; is the resonance quality factor; P is the microwave feeding power of the resonant cavity; is the dielectric constant of vacuum; is the electromagnetic wave beam waist radius at the sample position, ; R0 is the radius of curvature of the concave reflector, L is the length of the resonant cavity, is the wave number of the electromagnetic wave.

[0077] According to the superconducting test method of the present embodiment, based on the Fabry-Perot quasi-optical resonant cavity principle, the first concave reflector and the second concave reflector are arranged relative to each other to form a resonant cavity. According to the frequency offset relative to the selected resonant frequency, the movement of the sample stage is controlled, and the Gaussian standing wave characteristic is used to move the sample to the electromagnetic energy gathering position of the selected resonant frequency. In the existing reflective resonant cavity, resonant cavities of different lengths need to be designed for different resonant frequencies. Unlike the existing reflective resonant cavity, the resonant cavity of the present invention adopts a fixed length and reaches the electromagnetic energy gathering position of different resonant frequencies by moving the vertical position of the sample. Compared with the existing reflective resonant cavity, the present invention adopts a single resonant cavity, and measures the quantum characteristics of the Josephson junction sample at multiple operating frequencies by moving the vertical position of the sample, thereby improving the test efficiency.

[0078] Furthermore, the electric field intensity at the sample position can be directly calculated based on the microwave feed power of the resonant cavity, the quality factor of the resonant cavity, the beam waist radius, and the cavity length. The above intermediate parameters can be accurately obtained based on theoretical calculations or actual measurement results. This electric field intensity calculation method not only simplifies the calculation process of the standard irradiation electric field, but also improves the quantization accuracy of the standard irradiation electric field, thereby improving the measurement accuracy of quantum properties.

[0079] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

[0080] According to the embodiments of the present invention as described above, these embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and changes can be made based on the above description. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can make good use of the present invention and the modified use based on the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A microwave standard field irradiation system, comprising: A microwave source, wherein the microwave source has a transmitting port and a receiving port; a resonant cavity having a first port coupled to the transmitting port and a second port coupled to the receiving port, so as to generate an electromagnetic field on a transmission path of the microwave signal; A sample stage, located in the resonant cavity, wherein the sample placed on the sample stage is located on the transmission path of the microwave signal; as well as The housing is used to accommodate the resonant cavity and maintain a low temperature environment during the test.

2. The microwave standard field irradiation system according to claim 1, further comprising: An adjusting screw extends from the outside to the inside of the housing and is engaged with a screw hole on the sample stage for moving the sample stage.

3. The microwave standard field irradiation system according to claim 1, wherein: The resonant cavity comprises: The first concave reflecting mirror and the second concave reflecting mirror are arranged opposite to each other and respectively have the first port and the second port, Wherein, the sample stage is located between the first concave reflecting mirror and the second concave reflecting mirror.

4. The microwave standard field irradiation system according to claim 3, wherein: The length of the resonant cavity corresponds to the distance between the first concave reflecting mirror and the second concave reflecting mirror, and the resonant cavity has a constant length.

5. The microwave standard field irradiation system according to claim 3, wherein: The electromagnetic field in the resonant cavity has a stable Gaussian standing wave distribution, and the vertical position of the sample is located at the position of the electromagnetic wave beam waist.

6. The microwave standard field irradiation system according to claim 3, further comprising: A vector network analyzer having the microwave source built therein.

7. The microwave standard field irradiation system according to claim 6, wherein: When the resonant cavity has no sample, the vector network analyzer measures a transmission coefficient frequency response curve to obtain a plurality of initial resonant frequencies of the resonant cavity.

8. The microwave standard field irradiation system according to claim 7, wherein: When the resonant cavity has a sample, the vector network analyzer measures the current resonant frequency and the resonant quality factor of the resonant cavity, and, by adjusting the vertical position of the sample, minimizes the deviation of the current resonant frequency of the resonant cavity relative to the selected resonant frequency among the multiple initial resonant frequencies.

9. The microwave standard field irradiation system according to claim 8, wherein: According to the calculation model of the electric field intensity at the center of the quasi-optical resonant cavity, the standard irradiation electric field of the current resonant frequency is calculated. : （1） in, is the current resonant frequency; is the resonance quality factor; P is the microwave feeding power of the resonant cavity; is the dielectric constant of vacuum; is the electromagnetic wave beam waist radius at the sample position, ; R0 is the radius of curvature of the concave reflector, L is the length of the resonant cavity, is the wave number of the electromagnetic wave.

10. The microwave standard field irradiation system according to claim 1, further comprising: a first waveguide, wherein a first end of the first waveguide is coupled to the first port of the resonant cavity, and a second end of the first waveguide is coupled to the transmission port of the microwave source to feed a microwave signal; A second waveguide, wherein a first end of the second waveguide is coupled to the second port of the resonant cavity, and a second end of the second waveguide is coupled to the receiving port of the microwave source to feed out a microwave signal.

11. The microwave standard field irradiation system according to claim 10, further comprising: a directional coupler coupled to the first waveguide to obtain a sampling signal of the microwave signal; as well as a power meter connected to the directional coupler to obtain a measured power of the sampled signal, The feeding power of the resonant cavity is calculated according to the output power of the microwave source, the isolation of the directional coupler, and the measured power.

12. A superconducting testing method, comprising: A resonant cavity is arranged on a transmission path of the microwave signal, wherein the resonant cavity has a first port for feeding in the microwave signal and a second port for feeding out the microwave signal; Placing a superconducting sample at an electric field focusing position in the resonant cavity; as well as The quantum properties of the superconducting sample are measured.

13. The superconducting test method according to claim 12, wherein: The resonant cavity comprises: The first concave reflecting mirror and the second concave reflecting mirror are arranged opposite to each other and respectively have the first port and the second port, Wherein, a sample stage for placing the superconducting sample is arranged between the first concave reflecting mirror and the second concave reflecting mirror.

14. The superconducting testing method according to claim 13, wherein: The length of the resonant cavity corresponds to the distance between the first concave reflecting mirror and the second concave reflecting mirror, and the resonant cavity has a constant length.

15. The superconducting testing method according to claim 13, wherein: The electromagnetic field in the resonant cavity has a stable Gaussian standing wave distribution, and the vertical position of the superconducting sample is located at the position of the electromagnetic wave beam waist.

16. The superconducting test method according to claim 12, wherein: Placing a superconducting sample at an electric field focusing position in the resonant cavity comprises: When the resonant cavity does not have a superconducting sample, a transmission coefficient frequency response curve is measured to obtain a plurality of initial resonant frequencies of the resonant cavity.

17. The superconducting test method according to claim 16, wherein: Placing a superconducting sample at the electric field focusing position in the resonant cavity further comprises: When the resonant cavity has a superconducting sample, measuring the current resonant frequency and resonant quality factor of the resonant cavity; and By adjusting the vertical position of the superconducting sample, the current resonance frequency of the resonance cavity is minimized relative to the selected resonance frequency among the multiple initial resonance frequencies.

18. The superconducting test method according to claim 17, wherein: According to the calculation model of the electric field intensity at the center of the quasi-optical resonant cavity, the standard irradiation electric field of the current resonant frequency is calculated. : （1） in, is the current resonant frequency; is the resonance quality factor; P is the microwave feeding power of the resonant cavity; is the dielectric constant of vacuum; is the electromagnetic wave waist radius at the superconducting sample position, ; R0 is the radius of curvature of the concave reflector, L is the length of the resonant cavity, is the wave number of the electromagnetic wave.

19. The superconducting testing method according to claim 12, further comprising: Using a directional coupler to collect a microwave signal from the first port of the resonant cavity; as well as A power meter is used to obtain the measured power of the microwave signal. The feeding power of the resonant cavity is calculated according to the output power of the microwave source, the isolation of the directional coupler, and the measured power.

20. The superconducting test method according to claim 12, wherein: The superconducting sample is a Josephson junction sample, and measuring the quantum characteristics of the superconducting sample includes: measuring the relationship between the standard irradiation electric field and the superconducting current of the Josephson junction sample.

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