Low-frequency electric field measurement method and three-photon Rydberg system

Abstract

The invention relates to the field of electric field quantum measurement, in particular to a low-frequency electric field measurement method and a three-photon Rydberg system. The low-frequency electric field measurement method comprises the following steps: moving an atom gas chamber containing cesium atoms to a low-frequency electric field to be measured; cesium atoms are driven by probe light to transition from a ground state 6S1 / 2 to an excited state 6P1 / 2; driving cesium atoms to jump from an excited state 6P1 / 2 to an excited state 9S1 / 2 through decoration light; driving the cesium atoms to transition from an excited state 9S1 / 2 to a higher Rydberg state nP3 / 2 through coupled light to obtain Rydberg atoms; a photoelectric detector is adopted to detect the absorption condition of the detection light; based on the absorption condition, an oscilloscope is adopted to observe EIT spectrum change; based on the EIT spectrum change, obtaining a spectrum frequency shift amount; and the electric field intensity of the low-frequency electric field to be measured is calculated through the spectral frequency shift amount and the polarizability of the Rydberg atoms, so that the shielding problem of the atomic air chamber to the low-frequency electric field can be reduced, the spectral line width is narrower, and the electric field measurement resolution is greatly improved.

Description

Technical Field

[0001] The present application relates to the field of electric field quantum measurement, and in particular to a low-frequency electric field measurement method and a three-photon Rydberg system. Background Art

[0002] With the development of laser technology and the maturity of quantum state manipulation technology, in order to improve the sensitivity and stability of electric field measurement, electric field measurement based on the electromagnetic induced transparency (EIT) effect of Rydberg atoms has attracted more and more attention. Rydberg atoms show unparalleled advantages in electric field measurement due to their unique physical properties. However, they face severe challenges when measuring low-frequency electric fields at kHz and below. The conventional two-photon three-level measurement scheme shows a significant shielding effect on low-frequency electric fields. The reason is that the laser causes the atoms in the gas chamber to undergo photoionization and Penning ionization, and the free electrons are pulled by the low-frequency electric field and accumulated on the inner surface of the gas chamber, shielding the external electric field. Especially when the frequency is as low as kHz, the external electric field is completely shielded and cannot affect the atoms.

[0003] There are currently two main solutions that can reduce or eliminate the shielding effect: one is to use an atomic gas chamber made of sapphire material with a very large surface resistivity (>1012Ω / sq). When the measurement system composed of an atomic gas chamber made of sapphire material is used for low-frequency electric field measurement at kHz frequency, its measurement sensitivity can reach 0.34mV / m·Hz1 / 2, but for electric fields within tens of Hz, its measurement sensitivity is much worse. Because the EIT spectrum changes periodically with the frequency of the electric field, the maximum Stark frequency shift of the spectrum is difficult to accurately identify, and the shielding effect of the atomic gas chamber made of sapphire material on the electric field of tens of Hz is also more obvious. The other is to use an atomic gas chamber with a built-in electrode plate, place the electrode plate inside the gas chamber through micro-nano processing technology, and apply voltage to the electrode plate to generate the electric field to be measured, thereby eliminating the shielding of the gas chamber to the external electric field, but this method is only suitable for laboratory research and is not suitable for spatial electric field measurement in actual application scenarios. Summary of the invention

[0004] In order to reduce the shielding problem of the atomic gas chamber on the low-frequency electric field, the present application provides a low-frequency electric field measurement method and a three-photon Rydberg system.

[0005] In a first aspect, the present application provides a low-frequency electric field measurement method, the low-frequency electric field measurement method comprising:

[0006] Move the atomic gas cell containing cesium atoms to the low-frequency electric field to be measured;

[0007] By driving the cesium atoms from the ground state 6S 1 / 2 Transition to excited state 6P1 / 2 ; Then, the cesium atoms are driven from the excited state 6P by the decoration light 1 / 2 Transition to excited state 9S 1 / 2 ; Then, the cesium atom is driven from the excited state 9S by coupling light 1 / 2 Transition to a higher Rydberg state nP 3 / 2 , to obtain Rydberg atoms;

[0008] Using a photodetector to detect the absorption of the detection light; based on the absorption, using an oscilloscope to observe the EIT spectrum change; based on the EIT spectrum change, obtaining the spectrum frequency shift;

[0009] The electric field intensity of the low-frequency electric field to be measured is calculated based on the spectral frequency shift and the polarizability of the Rydberg atoms.

[0010] Optionally, the wavelengths of the detection light, the decoration light and the coupling light are 895 nm, 636 nm and 2245 nm respectively.

[0011] Optionally, the detection light, the decoration light and the coupling light are all output through a single-mode polarization-maintaining optical fiber.

[0012] In a second aspect, the present application provides a three-photon Rydberg system, which is applied to the low-frequency electric field measurement method described in the first aspect, comprising:

[0013] An atomic gas chamber, a photodetector, an oscilloscope, three single-mode polarization-maintaining optical fibers and three optical fiber lasers; the atomic gas chamber contains cesium atoms, the oscilloscope, the photodetector and the atomic gas chamber are connected in sequence, the optical fiber laser is connected to the atomic gas chamber through the single-mode polarization-maintaining optical fiber, the three optical fiber lasers are respectively used to emit detection light, decoration light and coupling light to the atomic gas chamber, and the oscilloscope is used to display the ETI spectrum detected by the photodetector.

[0014] Optionally, a self-focusing lens is arranged between the single-mode polarization-maintaining optical fiber and the atomic gas chamber.

[0015] In summary, this application at least includes the following beneficial technical effects:

[0016] 1. By using three long-wavelength laser beams, the ionization of atoms can be effectively reduced, thereby reducing the shielding problem of the atomic gas chamber against the low-frequency electric field.

[0017] 2. The present application does not require special processing technology to manufacture the built-in atomic gas chamber and sapphire atomic gas chamber of the electrode plate, and the optical fiber integrated measurement system has higher practicality and field applicability, and can realize the direct measurement of the low-frequency electric field in space. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A flowchart of a low-frequency electric field measurement method in an embodiment of the present application;

[0019] Figure 2 This is an EIT spectrum diagram under the action of a low-frequency electric field in an embodiment of the present application;

[0020] Figure 3 A schematic diagram of a three-photon Rydberg system and a three-photon energy level structure in an embodiment of the present application;

[0021] Explanation of the accompanying drawings: 1. Atomic gas chamber; 2. Photodetector; 3. Oscilloscope; 4. Single-mode polarization-maintaining optical fiber; 5. Optical fiber laser; 6. Lens. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0023] The terms used in the following embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to be used as limitations to the present application. As used in the specification and the appended claims of the present application, the singular expressions "one", "a kind of", "said", "above", "the" and "this" are intended to also include plural expressions, unless there is a clear contrary indication in its context. It should also be understood that the term "and / or" used in the present application refers to and includes any or all possible combinations of one or more listed items. The term "exemplary" means "used as an example, embodiment or illustrative", and any embodiment described as "exemplary" here does not need to be interpreted as being superior to or better than other embodiments. The terms "first" and "second" are only used for descriptive purposes, and cannot be understood as implying or implying relative importance or implicitly indicating the number of indicated technical features. Thus, the features defined as "first" and "second" can expressly or implicitly include one or more of these features, and in the description of the embodiments of the present application, unless otherwise specified, the meaning of "multiple" is two or more.

[0024] An embodiment of the present application provides a low-frequency electric field measurement method.

[0025] refer to Figure 1 , a low-frequency electric field measurement method, comprising the following steps:

[0026] S102: Move the atomic gas cell containing cesium atoms to the low-frequency electric field to be measured.

[0027] The measurement personnel move the atomic gas cell 1 containing cesium atoms to the low-frequency electric field to be measured, so as to measure the electric field strength of the low-frequency electric field to be measured, and avoid moving the atomic gas cell 1 again in the subsequent measurement process.

[0028] S104: Driving cesium atoms from the ground state 6S by probe light 1 / 2 Transition to excited state 6P 1 / 2 ; Then, the cesium atoms are driven from the excited state 6P by the decoration light 1 / 2 Transition to excited state 9S 1 / 2 ; Then, the cesium atom is driven from the excited state 9S by coupling light 1 / 2 Transition to a higher Rydberg state nP 3 / 2 , to obtain Rydberg atoms.

[0029] First, a GRIN lens 6 (self-focusing lens 6) is fixed at each end of the atomic gas chamber 1, and then three fiber lasers 5 are connected to three single-mode polarization-maintaining fibers 4, and then the single-mode polarization-maintaining fibers 4 are fixed to the GRIN lens 6. The three fiber lasers 5 are then set to emit detection light, decoration light, and coupling light, respectively, and the wavelengths of the detection light, decoration light, and coupling light are 895 nm, 636 nm, and 2245 nm, respectively.

[0030] Afterwards, the Rydberg atoms used to measure the electric field are obtained by applying a coherent laser field to the ground state atoms. In the three-photon system, the probe light, the decorative light, and the coupling light cause the atoms to transition to a highly excited state, forming Rydberg atoms. Specifically, a highly excited atom is an atom whose valence electrons are excited to a high quantum state (with a large principal quantum number n), also known as a Rydberg atom. Figure 1 and Figure 3 , 895nm probe light (Rabi frequency Ωp) drives the atom from the ground state |1>(6S 1 / 2 , F=3) to the excited state (6P 1 / 2 , F'=4), the detuning amount is Δp. 636nm decoration light (Rabi frequency Ωd) couples two excited states: |2>(6P 1 / 2 , F'=4) and (9S 1 / 2 ), the detuning amount is Δd. The 2245nm coupling light (Rabi frequency Ωc) will |3>(9S 1 / 2 ) atoms are excited to a higher Rydberg state |4>(nP 3 / 2 ), the detuning amount is Δc.

[0031] In the above process, the stronger coupled light will induce destructive interference in the medium to offset the absorption of the detection light by the atomic medium, making the originally opaque medium transparent, which is called the electromagnetic induced transparency effect.

[0032] S106: using a photodetector to detect the absorption of the detection light; based on the absorption, using an oscilloscope to observe the EIT spectrum change; based on the EIT spectrum change, obtaining the spectrum frequency shift amount.

[0033] The photodetector 2 detects the absorption change of the detection light, that is, the absorption condition. Then the oscilloscope 3 can observe the EIT spectrum change according to the absorption condition, and then obtain the spectrum frequency shift Δ according to the EIT spectrum change. Stark , as follows:

[0034] Under steady-state conditions, the EIT spectrum expression T is derived from the density matrix equation of the interaction between atoms and the laser field, and the complex polarization rate χ of the detection light is as follows:

[0035]

[0036] In formula (1): N is the atomic density, μ 12 is the transition dipole matrix element of the |1> and |2> energy levels driven by the probe light, ε0 is the vacuum dielectric constant, h is the reduced Planck constant, γ ij =(Γ i +Γ j ) / 2 is the decay rate of the atom from the |i> state to the |j> state, Γ1=0, Γ2=2π×4.56MHz, Γ3=2π×1.8MHz, Γ4=2π×1.3kHz, i and j are both used to represent the state of the atom.

[0037] The EIT transmission spectrum after passing through the atomic gas cell 1 is expressed as:

[0038]

[0039] In formula (2), T0 is the incident light intensity of the detection light, k p To detect the light wave vector, L is the length of the atomic gas cell 1 and Im[χ] is the imaginary part of χ.

[0040] S108: The electric field strength of the low-frequency electric field to be measured is calculated through the spectral frequency shift and the polarizability of the Rydberg atoms.

[0041] After further analyzing the variation of the EIT spectrum under the action of an external low-frequency electric field, according to the Stark theory, it can be seen that the response of the EIT spectrum to the external field is manifested as a frequency shift of the spectral signal. The frequency shift ΔStark depends on the field intensity amplitude and the Rydberg state of the atom, which is given by the following formula:

[0042]

[0043] In formula (3), E is the electric field strength, and α is the polarizability of the Rydberg atom.

[0044] Based on the above formula (3), it can be known that the electric field strength of the low-frequency electric field to be measured can be calculated by the spectral frequency shift and the polarizability of the Rydberg atom. By using three beams of long-wavelength laser, the ionization of atoms can be effectively reduced, thereby reducing the shielding problem caused by the atomic gas chamber 1 to the low-frequency electric field. At the same time, since the built-in atomic gas chamber 1 and the sapphire atomic gas chamber 1 of the electrode plate do not require special processing technology, and the optical fiber integrated measurement system has higher practicality and field applicability, it can realize the direct measurement of the low-frequency electric field in space.

[0045] Furthermore, assuming that the amplitude of the low-frequency sinusoidal electric field is A and the frequency is f, that is, E(t) = A·sin(2πft), the variation law of the EIT spectrum under the action of the external field is given by the following formula:

[0046]

[0047] The three-photon excitation scheme cannot completely solve the shielding problem. The electric field actually entering the atomic gas chamber 1 is E act (t), E act (t) = σE(t). Experimental studies have found that the shielding coefficient σ is related to the frequency f of the sinusoidal electric field. Therefore, the actual electric field needs to be corrected by the shielding coefficient σ:

[0048]

[0049] The simulation results were then verified. The low-frequency electric field measurement method can reduce the impact of the shielding effect during low-frequency field measurement and achieve a narrower line width and higher sensitivity. Taking 5kHz and a field strength of 0 to 50V / m as an example, the curve change trend of the EIT spectrum in this range was plotted. The atoms were excited step by step to 53S 1 / 2 The corresponding atomic polarizability α is 79.98MHz·cm 2 / V 2 . refer to Figure 2 , the parameters set in the simulation are: Ω c =2π×3MHz,Ω d =2π×10MHz, N=4×10 7 cm -3 , μ 12 =1.9ea0. When no electric field is applied, the EIT spectrum is a Lorentz peak symmetrical about the center, with a line width of about 1MHz. The EIT peak of the binary subsystem is generally greater than 3.5MHz, so. The three-photon system can not only reduce the shielding effect of the low-frequency field, but also has a narrower line width, which greatly improves the resolution of low-frequency electric field measurement. Under the action of the external field, the EIT spectrum has a frequency shift. Therefore, by measuring the spectral frequency shift ΔStark, combined with formula (3) and the shielding coefficient σ corresponding to the electric field frequency, the size of the electric field to be measured can be obtained.

[0050] This embodiment also provides a three-photon Rydberg system.

[0051] refer to Figure 3 A three-photon Rydberg system includes an atomic gas chamber 1, a photodetector 2, an oscilloscope 3, three single-mode polarization-maintaining optical fibers 4, and three fiber lasers 5; the atomic gas chamber 1 contains cesium atoms, the oscilloscope 3, the photodetector 2, and the atomic gas chamber 1 are connected in sequence, the fiber laser 5 is connected to the atomic gas chamber 1 through the single-mode polarization-maintaining optical fiber 4, and a GRIN lens 6 is arranged between the single-mode polarization-maintaining optical fiber 4 and the atomic gas chamber 1. The three fiber lasers 5 are respectively used to emit detection light, decoration light, and coupling light to the atomic gas chamber 1, and the oscilloscope 3 is used to display the spectrum detected by the photodetector 2.

[0052] Among them, the GRIN lens 6 has a radial refractive index gradient distribution. On the one hand, it can be used as a focusable optical element to achieve precise alignment of three laser beams. On the other hand, it can eliminate reflections between the optical fiber and the glass chamber to ensure maximum light transmission efficiency and minimum coupling loss.

[0053] The various variations and specific examples of the methods provided in the above embodiments are also applicable to the three-photon Rydberg system of the present embodiment. Through the above detailed description of the low-frequency electric field measurement method, those skilled in the art can clearly know the implementation method of the three-photon Rydberg system in the present embodiment. For the sake of brevity of the specification, it will not be described in detail here.

[0054] As described above, the above embodiments are only used to introduce the technical solution of the present application in detail, but the description of the above embodiments is only used to help understand the method and core idea of ​​the present application and should not be understood as limiting the present application. Any changes or substitutions that can be easily thought of by technicians in this technical field within the technical scope disclosed in the present application should be included in the protection scope of the present application.

Claims

1. A low-frequency electric field measurement method, characterized in that: include: Moving an atomic gas chamber (1) containing cesium atoms to a low-frequency electric field to be measured; By driving the cesium atoms from the ground state 6S 1 / 2 Transition to excited state 6P 1 / 2 ; Then, the cesium atoms are driven from the excited state 6P by the decoration light 1 / 2 Transition to excited state 9S 1 / 2 ; Then, the cesium atom is driven from the excited state 9S by coupling light 1 / 2 Transition to a higher Rydberg state nP 3 / 2 , to obtain Rydberg atoms; A photoelectric detector (2) is used to detect the absorption of the detection light; based on the absorption, an oscilloscope (3) is used to observe the EIT spectrum change; based on the EIT spectrum change, a spectrum frequency shift amount is obtained; The electric field intensity of the low-frequency electric field to be measured is calculated based on the spectral frequency shift and the polarizability of the Rydberg atoms.

2. The low-frequency electric field measurement method according to claim 1, characterized in that: The wavelengths of the probe light, the decoration light and the coupling light are 895 nm, 636 nm and 2245 nm respectively.

3. The low-frequency electric field measurement method according to claim 1, characterized in that: The detection light, the decoration light and the coupling light are all output through a single-mode polarization-maintaining optical fiber (4).

4. A three-photon Rydberg system, applied to the low-frequency electric field measurement method according to any one of claims 1 to 3, characterized in that: The three-photon Rydberg system comprises: An atomic gas chamber (1), a photodetector (2), an oscilloscope (3), three single-mode polarization-maintaining optical fibers (4) and three optical fiber lasers (5); the atomic gas chamber (1) contains cesium atoms; the oscilloscope (3), the photodetector (2) and the atomic gas chamber (1) are connected in sequence; the optical fiber laser (5) is connected to the atomic gas chamber (1) via the single-mode polarization-maintaining optical fiber (4); the three optical fiber lasers (5) are respectively used to emit detection light, decoration light and coupling light to the atomic gas chamber (1); and the oscilloscope (3) is used to display the EIT spectrum detected by the photodetector (2).

5. The three-photon Rydberg system according to claim 4, characterized in that: A self-focusing lens (6) is arranged between the single-mode polarization-maintaining optical fiber and the atomic gas chamber.

Images