A microwave power measurement device and method based on cold atoms

Abstract

This invention discloses a microwave power measurement device and method based on cold atoms. The measurement device includes a microwave cavity, a cutoff waveguide, a rectangular waveguide, and a cold atom vacuum cavity. Cold atoms are prepared by introducing cooling light through the upper and lower end faces of the microwave cavity. Then, the cold atoms in the microwave cavity are coherently excited from the ground state to the Rydberg state using coupling light and probe light generated by a laser. The frequencies of the coupling light and probe light are adjusted to generate appropriate detuning and achieve two-photon resonance conditions. Simultaneously, microwaves generated by a microwave source are fed into the rectangular waveguide on the side of the microwave cavity and then coupled into the cavity to interact with the cold atoms, causing the Raman absorption peak of the probe light to split. By fitting the splitting interval of the Raman absorption peak, the microwave power can be calculated. This invention utilizes the electromagnetically induced absorption effect to adiabatically eliminate intermediate states and suppress spontaneous emission, obtaining a Raman absorption spectral signal with sub-natural linewidth, thereby improving the accuracy of microwave power measurement and having significant value in microwave power source tracing.

Description

Technical Field

[0001] This invention relates to the field of quantum precision measurement technology, specifically to a microwave power measurement device and method based on cold atoms. Background Technology

[0002] In recent years, quantum precision measurement of physical quantities has developed rapidly, and this method can be traced back to fundamental physical constants. In 2012, Shaffer's research group at the University of Oklahoma, using the EIT and AT (Autler-Townes) splitting effects in a rubidium-based Rydberg atomic bubble, transformed the measurement of microwave electric field intensity into an optical frequency measurement, thus tracing back to Planck's constant and achieving precise measurement of microwave electric field intensity. The smallest electric field intensity measured was 8 μVcm. -1 Sensitivity is 30 μVcm -1 Hz -1 / 2 This overcomes the shortcomings of traditional dipole antenna measurements.

[0003] In 2018, the National Institute of Standards and Technology (NIST) in the United States completed a source-tracing measurement of microwave power within a rectangular waveguide in a rubidium-Redburgh atomic bubble, utilizing the EIT and AT (Autler-Townes) splitting effects. They fed microwaves into the rectangular waveguide and measured the maximum microwave electric field intensity within the waveguide to trace the source of the microwave power.

[0004] However, current experimental measurements and theoretical analyses indicate that the thermal atom ensemble exhibits a wide EIT linewidth due to the non-uniform Doppler effect, limiting measurement accuracy. Furthermore, most cold atom-based measurement devices are bulky, which restricts measurement in certain situations. Therefore, it is necessary to design a miniaturized device based on a cold atom system to further improve the accuracy of microwave power measurement. Summary of the Invention

[0005] In view of this, in order to solve the above-mentioned problems in the prior art, the present invention proposes a microwave power measurement device and method based on cold atoms. By using cold Rydberg atoms, an electromagnetically induced absorption effect is generated on the probe light to obtain a Raman absorption peak with a sub-natural linewidth, thereby improving the accuracy of microwave power measurement. At the same time, the microwave cavity-cold atom integrated device is used to measure the microwave power of cold atoms.

[0006] The present invention solves the above problems through the following technical means:

[0007] On one hand, the present invention provides a microwave power measurement device based on cold atoms, including a microwave cavity, a first cutoff waveguide, a second cutoff waveguide, a third cutoff waveguide, a fourth cutoff waveguide, a fifth cutoff waveguide, a rectangular waveguide, and a vacuum cold atom cavity;

[0008] The first cutoff waveguide is connected to a small hole on the upper end cover of the microwave cavity for introducing the first cooling light;

[0009] The second cutoff waveguide is connected to a small hole on the lower end cover of the microwave cavity for introducing the second cooling light;

[0010] The rectangular waveguide is connected to one of the small holes on the sidewall of the microwave cavity, and the transmission mode of the rectangular waveguide is TE. 10 Used to excite the TM inside the microwave cavity 01 Mode electromagnetic fields;

[0011] The third cutoff waveguide and the fourth cutoff waveguide are respectively connected to two symmetrical small holes on the side wall of the microwave cavity. The third cutoff waveguide is used to pass in the probe light, and the fourth cutoff waveguide is used to pass in the coupling light.

[0012] The fifth cutoff waveguide connects to the last small hole on the side wall of the microwave cavity, which is used to connect the vacuum cold atom cavity inside the microwave cavity to an external vacuum pumping device.

[0013] On the other hand, the present invention provides a microwave power measurement method based on cold atoms, comprising the following steps:

[0014] The cooling light generated by the first laser is injected into the microwave cavity from the cutoff waveguides at the upper and lower end faces of the microwave cavity to prepare cold atomic clusters.

[0015] The first laser stops generating cooling light, and the second and third lasers generate probe light and coupling light respectively. These light enter the microwave cavity from the cutoff waveguide on the side of the microwave cavity in a phase-to-phase manner, coherently exciting the cold atoms of the vacuum rubidium atom bubble in the microwave cavity from the ground state to the Rydberg state. The frequencies of the probe light and coupling light are set to be detuned, and the conditions for two-photon resonance are achieved.

[0016] Simultaneously, microwaves are fed into the microwave cavity from the rectangular waveguide and interact with the cold Rydberg atoms therein. The absorption signal of the probe light is received by a photodetector, and the Raman absorption peak splitting (EIA-ATS) diagram of the probe light is obtained.

[0017] By fitting the splitting pattern of the Raman absorption peak of the probe light, the splitting interval can be obtained, and the power of the microwave can be calculated based on the splitting interval.

[0018] The formula for calculating the microwave power is as follows:

[0019]

[0020] in, To reduce Planck's constant, Δf is the splitting width of the Raman absorption peak, μ is the transition dipole moment of the Rydberg atom, R is the cross-sectional radius of the microwave cavity, and v 01 It is the first root of the 0th order Bessel function. For v 01 The corresponding first derivative value of the 0th order Bessel function. ω is the value of the microwave cavity TM. 010 The resonant frequency in the mode, where ε is the dielectric constant and β is the time-free phase constant.

[0021] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0022] 1. Based on the characteristic of suppressing spontaneous emission by large detuning of intermediate states, this invention realizes a Raman absorption peak with subnatural linewidth. By measuring the split width of the Raman absorption peak, the accuracy of microwave power measurement is greatly improved, thus providing a new technical basis for the research on precision measurement of microwave electric fields.

[0023] 2. This invention is applicable to cold atom systems, and the method is simple and easy to implement;

[0024] 3. Based on the physical characteristics of Rydberg atomic states, such as long energy level lifetimes and large transition dipole moments between Rydberg states, this invention can generate strong interactions even at relatively weak microwave power, and theoretically, even weaker microwave power can be measured.

[0025] 4. This invention has the advantages of automatic calibration, atomic cooling, microwave power detection integration, high precision, and traceability to basic physical constants. In the current era of miniaturization of measuring devices, it has broad application prospects and value. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a system architecture diagram of the microwave power measurement device of the present invention;

[0028] Figure 2 This is a cross-sectional view of a cold atom microwave power detection device (the coupling light and microwaves have been hidden).

[0029] Figure 3 A schematic diagram of the theoretical simulation of the EIA-ATS peak;

[0030] Figure 4 This is a schematic diagram of the energy level structure of a cold atom.

[0031] Figure 5 This is a flowchart of the microwave power measurement method of the present invention;

[0032] Explanation of reference numerals in the attached figures:

[0033] 1. Microwave cavity; 2. Fifth cutoff waveguide; 3. Rectangular waveguide; 4. Third cutoff waveguide; 5. First cutoff waveguide; 6. Coupled light; 7. First cooling light; 8. Second cooling light; 9. Probe light; 10. Vacuum cold atom cavity; 11. Second cutoff waveguide; 12. Fourth cutoff waveguide; 13. Photodetector. Detailed Implementation

[0034] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0035] Example 1

[0036] like Figure 1 , Figure 2 As shown, the present invention provides a microwave power measurement device based on cold atoms, including a microwave cavity 1, a first cutoff waveguide 5, a second cutoff waveguide 11, a third cutoff waveguide 4, a fourth cutoff waveguide 12, a fifth cutoff waveguide 2, a rectangular waveguide 3, and a vacuum cold atom cavity 10.

[0037] The microwave cavity 1 is a TM capable of diffuse reflection laser cooling of atoms. 010 The cylindrical microwave cavity of the model has a microwave electric field uniformly distributed along the longitudinal direction at the central axis, and is made of oxygen-free copper material.

[0038] The inner surfaces of the upper and lower end faces of the microwave cavity 1 are silver-plated, highly polished mirror surfaces, exhibiting mirror reflection characteristics. Two small holes are evenly spaced 3.5 mm from the center of the circle along the axis of symmetry on the upper end face. These holes connect to the first cutoff waveguide 5, which is used to transmit the first cooling light 7 and simultaneously prevent leakage of the electromagnetic field within the microwave cavity 1. Similarly, two small holes are evenly spaced 3.5 mm from the center of the circle in a direction perpendicular to the line connecting the holes on the upper end face. These holes connect to the second cutoff waveguide 11, which is used to transmit the second cooling light 8 and simultaneously prevent leakage of the electromagnetic field within the microwave cavity 1.

[0039] The microwave cavity 1 has four symmetrical small holes on its sidewall. One of these holes is used for coupling between the transmission-type rectangular waveguide 3 and the microwave cavity 1. External microwave signals are coupled to the antenna between the rectangular waveguide 3 and the external microwave signal via a coaxial cable before being fed into the microwave cavity 1. Two symmetrical small holes on the sidewall of the microwave cavity 1 are connected to the third cutoff waveguide 4 and the fourth cutoff waveguide 12, respectively. The third cutoff waveguide 4 is used to pass in the probe light 9 and prevent leakage of the electromagnetic field within the microwave cavity 1. The fourth cutoff waveguide 12 is used to pass in the coupling light 6 and also prevent leakage of the electromagnetic field within the microwave cavity 1. The last small hole on the sidewall of the microwave cavity 1 is connected to the fifth cutoff waveguide 2, which is used to connect the vacuum cold atom cavity 10 inside the microwave cavity 1 to an external vacuum pumping device. The cold atom is rubidium atom. Both the cutoff waveguide and the rectangular waveguide are coupled to the microwave cavity via small hole coupling.

[0040] The first laser generates cooling light, which enters the microwave cavity through the first and second cutoff waveguides, respectively. The second and third lasers generate probe light and coupling light, respectively, which are directed into the microwave cavity in opposite directions along the horizontal direction.

[0041] The working principle of the microwave power measuring device of this invention is as follows:

[0042] 1) Cold atoms are prepared by injecting cooling light generated by a first laser into a microwave cavity;

[0043] 2) Then the first laser stops shooting cooling light, and the strong coupling light generated by the third laser and the probe light generated by the second laser are sequentially passed into the microwave cavity, so that the frequencies of the two lasers are appropriately detuned and the two-photon resonance condition is achieved.

[0044] 3) When microwaves are fed in through the rectangular waveguide on the sidewall of the microwave cavity, the Raman absorption peak of the probe light is split. Finally, by fitting the split width of the Raman absorption peak, the microwave power can be measured.

[0045] In this embodiment, the vacuum cold atom cavity is a glass vacuum cavity, and the glass vacuum cavity is in a high vacuum. The cold atoms are rubidium atoms (Rb). The probe light generated by the second laser and the coupling light generated by the third laser are used to excite the cold atoms to a Rydberg state using two photons. The microwave electric field generated by the microwave source couples the Rydberg state to a neighboring Rydberg state, forming a four-level system.

[0046] Figure 3 This is a schematic diagram of a theoretical simulation of the intensity of the microwave electric field to be measured. By experimentally selecting a suitable detuning factor Δ, a microwave electric field is applied to cold atoms, causing the Raman absorption peak of the cold atoms to split. By measuring the splitting width of the Raman absorption peak, the magnitude of the microwave power to be measured can be determined. The formula for calculating microwave power is as follows:

[0047]

[0048] in, To reduce Planck's constant, Δf is the splitting width of the Raman absorption peak, μ is the transition dipole moment of the Rydberg atom, R is the cross-sectional radius of the microwave cavity, and v 01 It is the first root of the 0th order Bessel function. For v 01 The corresponding first derivative value of the 0th order Bessel function. ω is the value of the microwave cavity TM. 010 The resonant frequency in the mode, where ε is the dielectric constant and β is the time-free phase constant.

[0049] Figure 4 This is a schematic diagram of the energy level structure of a cold atom. The probe light couples to states 1 and 2, the coupled light couples to states 2 and 3, and the microwave couples to two neighboring Rydberg states 3 and 4. The detuning is Δ.

[0050] The microwave power measurement device of this invention is based on cold Rydberg atom manipulation technology and electromagnetically induced absorption effect. It suppresses spontaneous emission by detecting large detuning and adiabatic elimination of intermediate states in light, thus achieving a sub-natural linewidth absorption peak. After introducing microwaves, the microwave power can be calculated by measuring the splitting width of the Raman absorption peak. This method achieves high-precision measurement of microwave power, providing a new approach for the precise measurement and research of microwave power.

[0051] Example 2

[0052] Figure 5 This is a flowchart of the microwave power measurement method based on cold atoms according to the present invention. The main idea of ​​the microwave power measurement method based on cold atoms in this invention is to transform the measurement of microwave power into the measurement of electric field intensity at a uniform electric field distribution within the microwave cavity, and then into the measurement of the Raman absorption peak splitting interval, including the following steps:

[0053] Step 301: Cooling light is introduced into the cutoff waveguides at the upper and lower end faces of the microwave cavity to prepare cold atoms;

[0054] Step 302: First, introduce coupling light into the side cutoff waveguide of the microwave cavity, then introduce probe light in opposite directions, and simultaneously feed microwaves into the rectangular waveguide to excite the microwave cavity to generate TM. 010 Mode electromagnetic fields;

[0055] Step 303: Obtain the EIA-ATS diagram of the probe light, and use Lorentz fitting to obtain the splitting distance between the two peaks, thereby calculating the microwave power.

[0056] The formula for calculating microwave power is as follows:

[0057]

[0058] in, To reduce Planck's constant, Δf is the splitting width of the Raman absorption peak, μ is the transition dipole moment of the Rydberg atom, R is the cross-sectional radius of the microwave cavity, and v 01 It is the first root of the 0th order Bessel function. For v 01 The corresponding first derivative value of the 0th order Bessel function. ω is the value of the microwave cavity TM. 010 The resonant frequency in the mode, where ε is the dielectric constant and β is the time-free phase constant.

[0059] The microwave power measurement method of this invention is based on the technology of cold Rydberg atom manipulation and electromagnetic induced absorption effect. It eliminates intermediate states through large detuning adiabatic elimination to suppress spontaneous emission and achieves a narrow linewidth Raman absorption peak. Then, it splits the absorption peak by interacting with microwaves. By measuring the split width of the Raman absorption peak, it achieves high-precision measurement of microwave power, thus providing a new approach for the research of precise microwave power measurement.

[0060] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A microwave power measurement device based on cold atoms, characterized in that, It includes a microwave cavity, a first cutoff waveguide, a second cutoff waveguide, a third cutoff waveguide, a fourth cutoff waveguide, a fifth cutoff waveguide, a rectangular waveguide, and a vacuum cold atom cavity; The upper surface of the microwave cavity has two small holes, which are connected to a first cutoff waveguide. The first cutoff waveguide is used to pass in the first cooling light and at the same time prevent the leakage of electromagnetic field inside the microwave cavity. The lower end face of the microwave cavity has two small holes, which are connected to a second cutoff waveguide. The second cutoff waveguide is used to pass in the second cooling light and at the same time prevent the leakage of electromagnetic field inside the microwave cavity. The microwave cavity has four small holes on its sidewall. One of the holes is connected to a rectangular waveguide, which is used to feed microwaves. External microwave signals are coupled to the antenna between the rectangular waveguide and the microwave cavity. Two symmetrical small holes on the sidewall of the microwave cavity are respectively connected to the third cutoff waveguide and the fourth cutoff waveguide. The third cutoff waveguide is used to pass in the probe light and at the same time prevent the leakage of the electromagnetic field in the microwave cavity; the fourth cutoff waveguide is used to pass in the coupling light and at the same time prevent the leakage of the electromagnetic field in the microwave cavity. The last small hole on the sidewall of the microwave cavity is connected to the fifth cutoff waveguide, which is used to connect the vacuum cold atom cavity inside the microwave cavity to the external vacuum pumping equipment. The microwave cavity is a cylindrical microwave cavity made of oxygen-free copper material; the microwave electric field of the microwave cavity is uniformly distributed along the central axis in the longitudinal direction.

2. The microwave power measurement device based on cold atoms according to claim 1, characterized in that, The inner sides of the upper and lower end faces of the microwave cavity are silver-plated, highly polished mirror surfaces, which have mirror reflection characteristics.

3. The microwave power measurement device based on cold atoms according to claim 1, characterized in that, The upper end face of the microwave cavity has two small holes evenly spaced 3.5 mm from the center of the circle on the axis of symmetry, and the lower end face also has two small holes evenly spaced 3.5 mm from the center of the circle in the direction perpendicular to the line connecting the small holes on the upper end face.

4. The microwave power measurement device based on cold atoms according to claim 1, characterized in that, The microwave cavity has four symmetrical small holes on its sidewall.

5. The microwave power measurement device based on cold atoms according to claim 1, characterized in that, The cold atom is a rubidium atom.

6. A microwave power measurement method based on cold atoms, characterized in that, The method is applied to the measuring device as described in claim 1; the method includes the following steps: Cooling light is introduced into the microwave cavity through the cutoff waveguide at the upper and lower end faces of the microwave cavity using a first laser to prepare cold atoms. The first laser stops emitting cooling light, and then the probe light and coupling light generated by the second laser and the third laser respectively are used to coherently excite the cold atoms in the microwave cavity from the ground state to the Rydberg state. The frequency of the coupling light and the probe light is adjusted to produce an appropriate detuning and achieve the two-photon resonance condition. Simultaneously, the microwaves generated by the microwave source are fed into the rectangular waveguide on the sidewall of the microwave cavity, and then coupled into the cavity to excite the TM. 010 The electromagnetic field of the mode is used to obtain the splitting pattern of the Raman absorption peak of the probe light; The power of the microwave source was calculated by fitting the splitting interval of the Raman absorption peak.

7. The microwave power measurement method based on cold atoms according to claim 6, characterized in that, The formula for calculating microwave power is as follows: in, To reduce Planck's constant, Δf is the splitting width of the Raman absorption peak, μ is the transition dipole moment of the Rydberg atom, R is the cross-sectional radius of the microwave cavity, and v 01 It is the first root of the 0th order Bessel function. For v 01 The corresponding first derivative of the 0th order Bessel function, where ω is the value of the microwave cavity TM. 010 The resonant frequency in the mode, where ε is the dielectric constant and β is the time-free phase constant.

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