Partially coherent light beam cloning method based on rubidium atom gas

Abstract

The invention provides a partially coherent light beam cloning method based on hot rubidium atom gas. A Gaussian beam and a partially coherent beam act on hot rubidium atom gas at the same time, the Gaussian beam serves as detection light, the partially coherent beam serves as pump light, and precise cloning of the spatial correlation characteristics of the detection light is achieved by combining cooperative regulation and control of microwaves and a magnetic field. In the cloning process, rubidium atoms in the atom pool transfer the anti-bunching coherent characteristic of the pump light to the probe light under the control of microwave parameters, and the spatial correlation structure of a cloned light beam can be observed through CCD detection and computer reconstruction. According to the method, whether the detection light carries the spatial correlation characteristic or not is dynamically regulated and controlled through microwaves, the optical switch and information relay function is achieved, the advantages of being high in fidelity, low in noise and adjustable in parameter are achieved, and a new technical approach is provided for an optical communication network and a quantum information processing system.

Description

Technical Field

[0001] The present invention provides a method for cloning partially coherent beams based on atomic gases, which realizes the high-fidelity and low-noise controllable transfer of the spatial correlation characteristics of the beams by regulating microwave parameters. It belongs to the field of optical information processing and is applicable to optical communication and quantum information processing tasks. Background Art

[0002] Partially coherent beams are random beams with a spatial coherence degree between that of lasers and thermal light. The spatial correlation of partially coherent light is manifested in that the phase distribution and amplitude distribution of the beam have partial randomness. This randomness endows the two-point correlation function of partially coherent light with rich structural characteristics, which can generate various novel physical phenomena such as spatial antibunching, twisted phase, and coherent vortices. The two-point correlation function of partially coherent light can safely store information. Compared with laser beams, the advantage of partially coherent beams in optical communication is that the low coherence of the two-point correlation function enables the information multiplexing and demultiplexing processes to avoid crosstalk. Even in an extremely noisy environment, multiplexing with partially coherent light can achieve high-fidelity information transmission and retrieval.

[0003] The interaction between light and matter is an effective method for realizing the transfer of information between different media. Atomic gases are commonly used media in optical communication and quantum information processing. The Electromagnetic Induced Transparency (EIT) is an atomic control technology based on the quantum interference effect. In EIT, a strong coupling light can make an originally opaque atomic medium transparent to a probe light. However, the EIT effect can only control the amplitude of the probe light and cannot transfer information from the coupling light to the probe light at the phase level.

[0004] The literature [Verma O N, Kant N. All-optical generation of structured light beams via microwave-field-controlled electromagnetically induced transparency [J]. Physical Review A, 2024, 110(1): 013701] reported a method for generating fully coherent vortex light using rubidium atoms. This method utilizes the interaction between microwaves and atoms to transfer the vortex phase of the pump beam to the probe beam, enabling the probe beam to carry the hollow amplitude and helical phase of the pump light when exiting the atomic medium. Although this scheme realizes the cloning of the vortex phase from the coupling light to the probe light, however, this cloning effect is limited to fully coherent beams. Partially coherent beams are random beams, and during the coupling process in the atomic medium, randomness will destroy the quantum interference effect. For partially coherent beams, whether this scheme can be applied and used for the cloning of the two-point correlation function (i.e., spatial correlation) is still an unknown problem.

[0005] The literature [Shao-wen Yu, Yang Zhang, Gang-kun Fu, et al. Spatial anti-bunching correlation in random light fields [J], Optics Express 32(27), 49106 - 49120(2024)] reported a method for generating spatial correlation in random beams. The beams generated by this method not only have anti-bunching characteristics but also have a controllable two-point correlation function, and the spatial correlation of this anti-bunching partially coherent beam will not be destroyed by randomness. However, how to achieve the transfer of this spatial correlation with anti-bunching characteristics during the interaction between light and matter and use it for information cloning is an important problem that the existing technology needs to solve. Summary of the Invention

[0006] The present invention aims to solve the deficiencies of the existing technology and provides a method for cloning partially coherent beams based on rubidium atomic gas. In the present invention, two beams of light interact with hot rubidium atomic gas simultaneously, one of which is a Gaussian beam and the other is an anti-bunching partially coherent beam. The Gaussian beam is used as the probe light and irradiates the inside of the atomic cell, and the probe light will be cloned into an anti-bunching partially coherent beam. Under the action of the microwave field, the probe beam realizes the functions of an optical switch and information relay by whether it carries a spatial correlation structure. The present invention provides a new idea with high fidelity, low noise, and controllability for the application of partially coherent beams in optical switches and information relays.

[0007] The technical solution for realizing the present invention includes the following steps:

[0008] (1) Select three energy levels in the rubidium atomic energy levels to form a Λ - type atomic system. This system consists of a ground state |0>, an intermediate state |1>, and an excited state |2>, which are respectively denoted as |0>, |1>, and |2>. The atom has the longest lifetime in the ground state, the shortest lifetime in the excited state, and the intermediate state has a lifetime between the ground state and the excited state. The ground state |0>, the intermediate state |1>, and the excited state |2> are coupled by three electromagnetic fields to produce a controllable electromagnetically induced transparency (EIT) phenomenon. The three electromagnetic fields are respectively the pump light E c , the probe light E p , and the microwave E r . The probe light E p couples the ground state |0> to the intermediate state |2>, the pump light E c couples the intermediate state |1> to the excited state |2>, and the microwave E r couples the ground state |0> to the intermediate state |1>. In the above process, the detuning of the probe light E p from the corresponding atomic energy level is Δ p , and the detuning of the pump light E c from the corresponding atomic energy level is Δ c . The microwave E r is resonant with the corresponding atomic energy level; Δ p and Δ c are less than the natural linewidth Γ of the excited state |2>, that is, Δ p , Δ c < Γ. The pump light E c is an antibunched partially coherent beam, the probe light E p is a Gaussian beam, and the microwave E r is a plane wave. The intensity of the pump light is 10 times higher than that of the probe light. The rubidium atoms are a hot atomic gas with a temperature between 60 °C and 65 °C;

[0009] (2) The electric field expression of the pump light E c is as follows: The pump light E c is generated by the superposition of several sub - beams with complex amplitudes u m at the central perturbation points in (a m ); φ l m ​is a random phase, whose value ranges between 0 and 2π; the number of superimposed sub-beams is N, satisfying N > 200, where m is the number of the sub-beam, and the central perturbation points of all sub-beams are randomly distributed within a circular region with a radius of C on the beam cross-section. The smaller the area of this circular region, the better the spatial coherence of the pump light. When the radius C is reduced to zero, the pump light changes from anti-bunched partially coherent light to fully coherent light; when the coordinate (0, 0) is the center of the sub-beam, the complex amplitude u l (x, y) can be set as any function;

[0010] (3) The laser generates linearly polarized light with a frequency resonant with the atomic energy level transition |0>→|2>, and its spatial mode is a Gaussian beam. This Gaussian beam passes through the first half-wave plate (HWP) and then through a polarization beam splitter, where it is decomposed into two beams, a transmitted beam and a reflected beam. The power ratio of the transmitted light to the reflected light can be controlled by adjusting the first HWP. After passing through the second HWP, the polarization plane of the transmitted light from the polarization beam splitter is modulated into a linearly polarized mode that matches the spatial light modulator (SLM), and then it is incident on the SLM. The SLM is loaded with a special dynamic hologram sequence and played at a frame rate of 20 ms / frame to generate an anti-bunched partially coherent beam. The first-order diffraction light in the reflected light from the SLM is the anti-bunched partially coherent light. The anti-bunched partially coherent beam is controlled by the first quarter-wave plate (QWP) so that its polarization state changes to right-handed circular polarization. The beam emerging from the first QWP is the pump beam for the atoms. This pump beam enters the atomic cell through the reflected light path of the beam splitter. The reflected light from the polarization beam splitter enters the second QWP through a mirror, and its polarization state changes to left-handed circular polarization. The beam emerging from the second QWP is the probe beam, which also enters the atomic cell. The probe beam and the pump beam overlap in the cross-section of the optical axis, and their optical axes are parallel to each other. The two beams simultaneously interact with the hot rubidium atomic gas in the atomic cell. Before entering the atomic cell, the pump beam and the probe beam are respectively modulated into circularly polarized lights with opposite rotation directions. The atomic cell is placed in a magnetic shielding cavity, where the geomagnetic field and the noise magnetic field are shielded. The atomic cell is placed in a microwave cavity, which can emit microwaves. The atomic cell is irradiated by microwaves. Inside the microwave cavity, there are also two pairs of vertically placed Helmholtz coils for generating a transverse magnetic field. The direction of the magnetic field is perpendicular to the optical axis of the pump light and parallel to the cross-section of the optical axis. Under the action of the magnetic field, the rubidium atoms undergo Zeeman splitting, and the degenerate ground state splits into two energy levels, the ground state |0> and the intermediate state |1>. Under the combined action of the pump beam and the probe beam, the pump light couples the intermediate state |1> and the excited state |2>, and the probe light couples the ground state |0> and the excited state |2>, causing the atoms to exhibit the electromagnetically induced transparency (EIT) effect. After the EIT occurs, the atoms are transparent to the probe beam, and the fluorescence signal of the atomic cluster is the strongest. When the microwave is turned on, the microwave causes the coupling between the intermediate state |1> and the ground state |0>. The probe beam and the pump light interact through the coupling between |1> and |0>. The pump light is generated by the superposition of multiple sub-beams. The partially coherent spatial structure of the pump light is transmitted to the probe light through the amplitude structure and phase structure of the sub-beams, thereby realizing the cloning of the partially coherent beam. The CCD detects the probe beam modulated into a partially coherent light and measures its spatial correlation structure.

[0011] The beneficial effects of the present invention are as follows:

[0012] 1. The present invention proposes a device for controlling the cloning of partially coherent light by EIT in a hot atomic cell using a microwave field.

[0013] 2. The present invention clones complex partially coherent light into another beam based on an atomic system. The correlation intensity and correlation phase of the partially coherent light beam have the characteristics of high fidelity, low noise, and controllability during the cloning process. Description of the Drawings

[0014] Figure 1 It is a schematic structural diagram of a method for cloning a partially coherent light beam based on rubidium atomic gas provided in an embodiment of the present invention.

[0015] Figure 2 It is a schematic diagram of the interaction between light and atoms of a method for cloning a partially coherent light beam based on rubidium atomic gas provided in an embodiment of the present invention. Detailed Embodiments

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and all of them should be covered within the scope of the claims of the present invention.

[0017] As Figure 1 shown, it is a schematic structural diagram of a device for a method for cloning a partially coherent light beam based on rubidium atomic gas provided in this embodiment: It includes a laser 1; a first half-wave plate 2; a polarization beam splitter 3; a second half-wave plate 4; a spatial light modulator 5; a first computer 6; a small hole aperture 7; a first quarter-wave plate 8; a beam splitter 9; an atomic cell 10; a magnetic shielding cavity 11; a microwave cavity 12; a Helmholtz coil 13; a second quarter-wave plate 14; a reflector 15; a CCD 16; a second computer 17.

[0018] In this embodiment, the ground state |0>, the intermediate state |1>, and the excited state |2> are respectively three Zeeman sublevels of the D1 line of rubidium-87 atoms: 5S 1 / 2 , F = 2, m F = -1 energy level, 5S 1 / 2 , F = 2, m F = 1 energy level, and 5P 1 / 2 , F′ = 1, m F ′ = 0 energy level; the 795 nm laser generated by the laser resonates with the D1 line (5S 1 / 2 → 5P 1 / 2 ) of rubidium-87 atoms and outputs a power of 5 mW.

[0019] In this embodiment, a dynamic hologram for generating an anti-bunched partially coherent beam is prepared in the first computer 6; the first computer 6 is connected to the spatial light modulator 5; the dynamic hologram for generating an anti-bunched partially coherent beam is loaded into the spatial light modulator 5; the laser 1 is turned on to generate linearly polarized light at 795 nm that resonates with the D1 line (5S 1 / 2 →5P 1 / 2 ) of rubidium 87 atoms, and the spatial mode is a Gaussian beam; this Gaussian beam passes through the first half-wave plate 2 and then through the polarization beam splitter 3, and is decomposed into two transmitted and reflected light beams. The power ratio of the transmitted light and the reflected light can be controlled by adjusting the first half-wave plate 2; the transmitted light beam passes through the second half-wave plate 4; its polarization plane is modulated into a linearly polarized mode matching the spatial light modulator 5, and then enters the liquid crystal screen of the spatial light modulator 5; the spatial light modulator 5 modulates the laser beam into an anti-bunched partially coherent beam and reflects it; the first-order diffracted light in the reflected beam of the spatial light modulator 5 is selected using the small-aperture diaphragm 7; the first-order diffracted light is incident on the first quarter-wave plate 8, so that the polarization state of the beam changes to right-handed circular polarization; this right-handed circularly polarized beam is the pump beam E c of the atoms, which is reflected by the beam splitter 9 and enters the atomic cell 10; the beam emerging from the first half-wave plate 2 is reflected by the polarization beam splitter 3 and then enters the second quarter-wave plate 14 through the mirror 15, and the polarization state changes to left-handed circular polarization; this left-handed circularly polarized beam is the probe beam E p ; the probe beam E p enters the atomic cell 10 and overlaps with the pump beam E c in a cross-sectional area parallel to the optical axis; the probe beam E p and the pump beam E c simultaneously interact with the hot rubidium atomic gas in the atomic cell 10; the atomic cell 10 is placed in the magnetic shielding cavity 11, and the magnetic shielding cavity 11 is used to shield the geomagnetic field and external noise magnetic fields; the atomic cell 10 is placed in the microwave cavity 12; the microwave cavity 12 can emit microwave E r , so that the atomic cell 10 is irradiated by the microwave E r ; two pairs of vertically placed Helmholtz coils 13 are also arranged inside the microwave cavity 12, which are used to generate a transverse magnetic field to split the ground state energy level of the atoms; under the action of the magnetic field, the rubidium atoms undergo Zeeman splitting, and the degenerate ground state splits into two energy levels, the ground state |0> and the intermediate state |1>; under the combined action of the pump beam E c and the probe beam E p , the atoms undergo the EIT effect; after the EIT effect occurs, the atoms are transparent to the probe beam, and the fluorescence signal of the atomic cluster is the strongest; the microwave cavity 11 is turned on to generate microwave E r , and the microwave couples the intermediate state |1> and the ground state |0> of the atoms, and the pump beam E c and the probe beam E pInteract through the coupling between |1> and |0>; the probe light obtains the amplitude structure and phase structure of the coherence function of the pump light; the pump light is antibunched partially coherent light generated by the superposition of multiple sub-beams, and the partially coherent spatial structure of the pump light is transmitted to the probe light through the amplitude structure and phase structure of the sub-beams, thereby realizing the cloning of the partially coherent beam; the cloned probe beam is transmitted through the beam splitter 9 and imaged on the CCD 16; the CCD 16 takes high-frequency pictures of the probe beam and transmits the images to the second computer 17; the second computer 17 calculates the normalized second-order coherence degree function of the probe beam to obtain its spatial correlation structure.

Claims

1. A technical solution for achieving the object of the present invention is to provide a method for cloning a partially coherent beam based on rubidium atomic gas, comprising the following steps: (1) Select three energy levels in the rubidium atomic energy levels to form an L-type atomic system. This system consists of a ground state |0>, an intermediate state |1>, and an excited state |2>, which are respectively denoted as |0>, |1>, and |2>; the atom has the longest lifetime in the ground state, the shortest lifetime in the excited state, and the intermediate state lifetime is between the ground state and the excited state; the ground state |0>, the intermediate state |1>, and the excited state |2> are coupled by three electromagnetic fields to generate a controllable electromagnetically induced transparency (EIT) phenomenon; the three electromagnetic fields are respectively a pump light E c , a probe light E p , and a microwave E r ; the probe light E p couples the ground state |0> to the intermediate state |2>, the pump light E c couples the intermediate state |1> to the excited state |2>, and the microwave E r couples the ground state |0> to the intermediate state |1>; in the above process, the detuning of the probe light E p from the corresponding atomic energy level is Δ p , and the detuning of the pump light E c from the corresponding atomic energy level is Δ c ; the microwave E r is resonant with the corresponding atomic energy level; Δ p and Δ c are less than the natural linewidth Γ of the excited state |2>, that is, Δ p , Δ c < Γ; the pump light E c is an anti-bunched partially coherent light beam, the probe light E p is a Gaussian light beam, and the microwave E r is a plane wave; the intensity of the pump light is 10 times higher than that of the probe light; the rubidium atoms are a hot atomic gas with a temperature between 60°C and 65°C; (2) Pumping light E c The electric field expression is as follows: The pump light E c is generated by the superposition of a number of sub-beams with central perturbation points having a complex amplitude of u m at (a m , b l ); φ m is a random phase with a value between 0 and 2π; the number of superposed sub-beams is N, where N > 200, and m is the number of the sub-beam. The central perturbation points of all sub-beams are randomly distributed within a circular region with a radius of C on the beam cross-section. The smaller the area of this circular region, the better the spatial coherence of the pump light. When the radius C is reduced to zero, the pump light changes from antibunched partially coherent light to fully coherent light; when the coordinate (0, 0) is the center of the sub-beam, the complex amplitude u l (x, y) of the sub-beam can be set as any function; (3) A laser generates a linearly polarized light resonant with the atomic energy level |0> → |2>, and the spatial mode is a Gaussian beam; this Gaussian beam passes through a first half-wave plate (HWP) and then through a polarization beam splitter, and is decomposed into two transmitted and reflected light beams. The power ratio of the transmitted light and the reflected light can be controlled by adjusting the first HWP; after the transmitted light of the polarization beam splitter passes through the second HWP, its polarization plane is modulated into a linearly polarized mode matching the spatial light modulator (SLM), and then enters the SLM; the SLM is loaded with a special dynamic hologram sequence and played at a frame rate of 20 ms / frame to generate an antibunched partially coherent beam; the first-order diffraction in the SLM reflected light is selected as the antibunched partially coherent light; the antibunched partially coherent beam is regulated by a first quarter-wave plate (QWP) so that the polarization state of the beam changes to right-handed circular polarization; the beam emerging from the first QWP is the pump beam of the atoms; the pump beam enters the atomic cell through the reflected light path of the beam splitter; the reflected light of the polarization beam splitter enters the second QWP through a mirror, and the polarization state changes to left-handed circular polarization; the beam emerging from the second QWP is the probe beam, and this beam also enters the atomic cell; the probe beam and the pump beam overlap in the optical axis cross-section, the optical axes are parallel to each other, and the two beams simultaneously interact with the hot rubidium atomic gas in the atomic cell; the pump beam and the probe beam are respectively modulated into circularly polarized lights with opposite rotation directions before entering the atomic cell; the atomic cell is placed in a magnetic shielding cavity, and the geomagnetic field and the noise magnetic field are shielded; the atomic cell is placed in a microwave cavity, the microwave cavity can emit microwaves, the atomic cell is irradiated by microwaves, and two pairs of vertically placed Helmholtz coils are also arranged inside the microwave cavity to generate a transverse magnetic field; the magnetic field direction is perpendicular to the pump light optical axis and parallel to the optical axis cross-section; under the action of the magnetic field, rubidium atoms undergo Zeeman splitting, and the degenerate ground state splits into two energy levels, the ground state |0> and the intermediate state |1>; under the combined action of the pump beam and the probe beam, the pump light couples the intermediate |1> and the excited state |2>, and the probe light couples the ground state |0> and the excited state |2>, so that the atoms undergo the EIT effect; after the EIT occurs, the atoms are transparent to the probe beam, and the atomic cluster fluorescence signal is the strongest; turn on the microwave, and the microwave couples the intermediate state |1> and the ground state |0>, and the probe beam and the pump light interact through the coupling between |1> and |0>; the pump light is generated by the superposition of multiple sub-beams, and the partially coherent spatial structure of the pump light is transmitted to the probe light through the amplitude structure and the phase structure of the sub-beams, thereby realizing the cloning of the partially coherent beam; the CCD detects the probe beam modulated into a partially coherent light and measures its spatial correlation structure.

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