Orbital angular momentum beam detection method based on quantum weak measurement technology

Abstract

The application discloses an orbital angular momentum beam detection method based on quantum weak measurement technology, and the method comprises the following steps: setting a suitable polarization state preparer and a polarization state selector, preparing a virtual weak value, and using a differential distribution of the orbital angular momentum beam obtained by quantum weak measurement differential effect to realize detection of the orbital angular momentum beam and measurement of angular momentum quantum number. The application realizes measurement of the orbital angular momentum beam in a natural state by using optical differential based on quantum weak measurement technology, and reduces energy consumption to a certain extent, thereby providing a simple and low-energy consumption orbital angular momentum detection method for engineering and laboratory related fields, and having important application value in multiple technical fields such as optical communication, transmission and manipulation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of quantum optics, and relates to an orbital angular momentum beam measurement method based on quantum weak measurement, which utilizes quantum weak measurement differential technology to realize orbital angular momentum beam detection and angular quantum number measurement according to a differential distribution of an outgoing light field. BACKGROUND

[0002] Since Allen and his colleagues published the pioneering paper, vortex beams carrying orbital angular momentum (OAM) have shown impressive performance in many fields such as optical communication, transmission and manipulation. OAM provides higher degrees of freedom to enhance the ability of optical communication. Vortex beams show stronger anti-disturbance ability when propagating in free space compared with traditional Gaussian beams. Vortex beams with the above characteristics show good information propagation ability. However, the OAM state is still disturbed during transmission, which makes it difficult to detect OAM at the receiving end. In order to utilize OAM probe beams, researchers have proposed many methods to measure OAM. Based on experimental data evaluation, indirect detection induced by vortex beams and beam recovery using holographic technology are three main methods for OAM detection. Among the three types of representative detection works, Wang et al. proposed a convolutional neural network named RoamN-CNN to identify the OAM of two orthogonal polarization vortex beams from speckle patterns. Genevet et al. proposed a method based on holographic principle, which realized the detection of OAM of light using plasmonic photodiodes. Zhao et al. proposed a multi-point interferometer (IMI) to detect vortex beams and proved that the far-field interference pattern using this method can be used to measure vortex beams with high topological charge. These works have made great contributions in this field. However, the main aspects that need to be improved are large amount of calculation, large amount of simulation and lack of recovery of beams in disturbed space.

[0003] Considering the special phase distribution of vortex beams and the OAM corresponding to the phase jump, optical differentiation is used to detect the phase change of vortex beams. The spatial displacement of vortex beams is generated by constructing virtual weak values through a weak measurement system using a birefringent crystal (BC), and the phase differentiation of vortex beams is realized. The orbital angular momentum of different orders is detected, which reflects the superiority of the detection method in the field of OAM detection. SUMMARY

[0004] The present application aims to provide an orbital angular momentum beam detection method based on quantum weak measurement technology and an orbital angular momentum beam angular quantum number method.

[0005] The application provides an orbital angular momentum beam detection method based on quantum weak measurement technology.

[0006] The polarization state preparer is used for constructing a suitable pre-selection quantum state, and the 1 / 4 wave plate and the polarization state selector are used for jointly constructing a suitable post-selection quantum state and making the post-selection quantum state close to orthogonal to the pre-selection quantum state.

[0007] The polarization state preparer is used for constructing a suitable pre-selection quantum state, and the 1 / 4 wave plate and the polarization state selector are used for jointly constructing a suitable post-selection quantum state and making the post-selection quantum state close to orthogonal to the pre-selection quantum state.

[0008] The birefringent crystal is used for introducing a slight shift between o light and e light, and constructing a weak interaction.

[0009] The polarization state preparer, the birefringent crystal, the 1 / 4 wave plate and the polarization state selector jointly constitute an optical field phase differential system.

[0010] The pre-selection state and the post-selection state are used to introduce imaginary weak values, and phase differential of the orbital angular momentum beam is realized.

[0011] The application further provides a method for detecting an orbital angular momentum beam based on quantum weak measurement technology, and the method comprises the following steps:

[0012] (1)Adjust the experimental setup of the orbital angular momentum beam of the quantum weak measurement technology, so that the polarization angle of the polarization state preparer is parallel to the optical axis of the horizontally placed birefringent crystal, and the polarization state selector is close to orthogonal to the polarization state preparer at a very small angle. After the beam passes through the polarization state preparer, it is vertically incident into the birefringent crystal, and under the action of the birefringent crystal, the o light and e light have a slight displacement along the x axis direction, realizing the weak coupling of the instrument and the detection system. The polarization state selector and the 1 / 4 wave plate constitute the post-selection part in the weak measurement system, and the subsequent detection is completed by adjusting the angle of the polarization state selector in the post-selection. Finally, the light beam is detected in the form of light intensity on the CCD.

[0013] (2) The pre-selection state prepared by the polarization state preparer is obtained according to the following formula:

[0014]

[0015] Where |H> and |V> represent horizontal and vertical polarization states respectively.

[0016] (3) The polarization state obtained by the birefringent crystal is obtained according to the following formula:

[0017]

[0018] Where δ is the slight displacement introduced by the birefringent crystal to the o light and e light. x,y is the wave vector in the x or y direction. Here is the observable operator.

[0019] (4) The post-selection state set by the 1 / 4 wave plate and the polarization state selector is obtained according to the following formula:

[0020]

[0021] Where σ is the post-selection angle. Where ± indicates two symmetrical post-selection states relative to the polarization direction orthogonal to the pre-selection.

[0022] (5) The wave function of the incident light field can be described as φ(q) = A(q)e iP(q) , A(q) and P(q) represent the amplitude distribution and the phase distribution respectively, and the distribution obtained by subtracting the symmetrical post-selection state is:

[0023]

[0024] (6) The Laguerre-Gaussian beam of order l can be expressed as φ(r, θ, z) = L |l| (r, z)e i(lθ+ξ) .Here L(r, z) is the amplitude term, which is independent of the phase term. l is an angular quantum number, p is a radial quantum number, is a Rayleigh length, R=z+f 2 The distribution of the amplitude I LG ∝|L |l| (r,z)| 2 , is a constant at a certain order. The above optical differential operation is carried out in the range. The distribution of the phase function along an arbitrary direction q can be expressed as b(q)=lθ(q)+ξ.

[0025]

[0026] wherein a 2 (q) represents the amplitude I LG distribution. The phase full differential distribution is:

[0027]

[0028] The above formula shows that the differential result of the phase distribution function of the orbital angular momentum beam is directly obtained, so that the corresponding angular momentum of the orbital angular momentum beam is obtained.

[0029] Compared with the prior art, the present application has the following beneficial effects:

[0030] (1) The present application is based on the weak measurement differential scheme, realizes the detection of the orbital angular momentum, and reduces the energy consumption to a certain extent, and provides a simple and low-energy consumption orbital angular momentum detection method for the related fields of engineering and laboratory;

[0031] (2) The present application simplifies the orbital angular momentum detection system to a certain extent, and has very good anti-interference effect by virtue of the ability of the weak measurement detection system to eliminate background noise, so that the detection result of the angular momentum can be obtained more clearly;

[0032] (3) The orbital angular momentum detection system based on the weak measurement technology of the present application avoids introducing reference light for interference, simplifies the experimental device, and can realize the measurement of the quantum number of the angular momentum. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a structure diagram of the orbital angular momentum beam detection method based on the quantum weak measurement technology of the present application; 1, focusing lens, 2, polarization state preparer, 3, birefringent crystal, 4, 1 / 4 wave plate, 5, polarization state selector, 6, collimating lens, 7, photodetector.

[0034] Figure 2 is the test of the orbital angular momentum beam of different angular momentum quantum beams based on the orbital angular momentum beam detection method based on the quantum weak measurement technology, and the phase differential diagram of the orbital angular momentum beam in x and y directions of m=5 and m=8 orbital angular momentum beams. is the test of the orbital angular momentum beam of different angular momentum quantum beams based on the orbital angular momentum beam detection method based on the quantum weak measurement technology, and the phase differential diagram of the orbital angular momentum beam in x and y directions of m=5 and m=8 orbital angular momentum beams.

[0035] Figure 2 Figures (a) and (b) are phase differential maps of the m = 5 orbital angular momentum beam in the x and y directions, respectively; Figure 2 Figures (d) and (e) are phase differential maps of the l = 8 orbital angular momentum beam in the x and y directions, respectively; Figure 2 Figures (c) and (f) are full differential maps of the l = 5 and l = 8 orbital angular momentum beams, respectively. DETAILED DESCRIPTION

[0036] The embodiments of the present application will be described below with reference to the drawings, and the technical solutions of the present application will be further clarified through the embodiments. Obviously, the embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the content of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0037] Embodiment 1

[0038] The orbital angular momentum beam detection method based on quantum weak measurement provided in the embodiment has the structure as shown in Figure 1 The orbital angular momentum beam detection device includes a focusing lens 1, a polarization state preparer 2, a birefringent crystal 3, a 1 / 4 wave plate 4, a polarization state selector 5, a collimating lens 6, and a photoelectric detector 7. The focusing lens 1 and the collimating lens 6 are used to form a 4F system, and the photoelectric detector is a charge-coupled device (CCD) for detecting weak light intensity signals.

[0039] The orbital angular momentum beam detection method based on quantum weak measurement described above: the orbital angular momentum beam is focused by the focusing lens 1 with a focal length f = 250 mm; the beam is prepared as 45° linearly polarized light by the polarization state preparer 2, and a small positional shift in the q direction is introduced between the horizontal polarized light (o light) and the vertical polarized light (e light) by the birefringent crystal 3; the beam is post-selected by the 1 / 4 wave plate 4 and the polarization state selector 5, wherein the optical axis of the 1 / 4 wave plate is along the -45° direction, and the polarization direction of the polarization selector is -45° ± σ, and σ = 0.5° is the post-selection angle; then the beam is collimated by the collimating lens 6 with a focal length f = 250 mm, and finally the light field distribution is received and output by the photoelectric detector 7. The polarization state of the beam of the polarization state preparer and the polarization state set by the 1 / 4 wave plate and the polarization state selector form a quantum weak measurement light path part.

[0040] The method for measuring the orbital angular momentum beam with an order l = 5 or l = 8 based on quantum weak measurement technology in the embodiment is as follows:

[0041] (S1) Adjusting the light path balance to make the uniform Gaussian light incident to the weak measurement system, adjusting the polarizer to make the output light field present as a circular ring, indicating that the output is the differential distribution of Gaussian light, and adjusting the weak measurement differential system to the working point;

[0042] (S2) Experimentally detecting the orbital angular momentum beam with order l=5 (or l=8), rotating the birefringent crystal direction, introducing a position offset in the horizontal direction (x), and obtaining the phase differential distribution of the orbital angular momentum beam in the x direction on the detector; rotating the birefringent crystal direction, introducing a position offset in the vertical direction (y), and obtaining the phase differential distribution of the orbital angular momentum beam in the y direction on the detector.

[0043] (S3) Merging the two differential distributions obtained by using the following formula to obtain the phase full differential distribution of the incident light beam:

[0044]

[0045] Figure 2 In the formula (a) and (b) are the phase differential diagrams of the orbital angular momentum beam with order l=5 in the x and y directions; Figure 2 In the formula (d) and (e) are the phase differential diagrams of the orbital angular momentum beam with order l=8 in the x and y directions. The number of angular momentum of the orbital angular momentum beam corresponds to the number of lobes of the full differential light field distribution. As shown in Figure 2 As shown in the formula (c) and (f), the orbital angular momentum beam with order l=5 shows a five-lobed distribution, and the orbital angular momentum beam with order l=8 shows an eight-lobed distribution.

[0046] The present application is based on quantum weak measurement technology, uses the special phase distribution of the vortex beam and the OAM corresponding to the phase jump, adopts optical differentiation and constructs virtual weak values to detect the phase change of the vortex beam. Compared with the traditional orbital angular momentum beam detection, the present application can realize the detection of the orbital angular momentum beam and the measurement of the angular momentum quantum number without introducing reference light through a simple experimental device, and has good noise suppression effect.

Claims

1. A method for detecting orbital angular momentum (OAM) beams based on quantum weak measurement technology, characterized in that: The method uses a quantum weak measurement technology orbital angular momentum beam experimental device, which comprises a focusing lens (1), a polarization state preparer (2), a birefringent crystal (3), a 1 / 4 wave plate (4), a polarization state selector (5), a collimating lens (6) and a photodetector (7); the orbital angular momentum beam is focused by the focusing lens (1), enters the polarization state preparer (2) to prepare linearly polarized light as a pre-selection state in the weak measurement model, then the birefringent crystal (3) introduces a position offset in the horizontal and vertical polarization directions as a weak interaction, the 1 / 4 wave plate (4) and the polarization state selector (5) jointly prepare elliptical light slightly deviating from the linearly polarized light direction as a post-selection state, the collimating lens (6) collimates the light beam, and the photodetector (7) receives the light field distribution of the signal light; The method comprises the following steps: (1) Adjusting the experimental device of the orbital angular momentum beam of the quantum weak measurement technology, so that the polarization angle of the polarization state preparer (2) is located at The birefringent crystal (3) is horizontally placed, the polarization state selector (5) is close to being orthogonal to the polarization state preparer (2) at a very small angle, after the beam passes through the polarization state preparer (2), the beam is vertically incident into the birefringent crystal (3), under the action of the birefringent crystal (3), the o light and the e light having a slight displacement along the x-axis direction, the weak coupling of the instrument and the detection system is realized, the polarization state selector (5) and the 1 / 4 wave plate (4) constitute the post-selection part in the weak measurement system, the subsequent detection is completed by adjusting the angle of the polarization state selector (5) in the post-selection, finally the beam is detected in the form of light intensity on the CCD. (2) The pre-selection state prepared by the polarization state preparer (2) is obtained according to the following formula: wherein and and horizontal and vertical polarization states; (3) The polarization state obtained by the birefringent crystal (3) is obtained according to the following formula: wherein, is a small displacement introduced by the birefringent crystal (3) for o light and e light, is a wave vector in the x or y direction, is an observable operator; (4) The post-selection state set by the 1 / 4 wave plate (4) and the polarization state selector (5) is obtained according to the following formula: wherein is the rear selection angle, wherein cot , indicates two symmetric rear selection states generated with respect to a polarization direction orthogonal to the front selection. (5) The wave function of the incident light field can be numerically described as , and denote the amplitude distribution and the phase distribution, respectively. The difference between the distributions obtained after the symmetrization of the selected states gives: (6) The Laguerre-Gaussian beam of order p can be expressed as where is the amplitude term, and is independent of the phase term = , is the angular quantum number, p is the radial quantum number, is the Rayleigh length, , the distribution of the amplitude is a constant at a certain order, and the distribution of the phase function along an arbitrary direction q can be expressed as , wherein denotes the amplitude distribution, the full partial distribution of the phase is: The above formula shows that the differential result of the phase distribution function of the orbital angular momentum beam is directly obtained, so that the corresponding angular momentum of the orbital angular momentum beam is obtained.

2. The method of claim 1, wherein the method is based on quantum weak measurement technique. The phase differential of the orbital angular momentum beam is realized by using the weak measurement to construct the imaginary weak value, and the detection of the orbital angular momentum beams of different orders can be realized through the differential pattern.

3. The method for detecting orbital angular momentum beams based on quantum weak measurement technology according to claim 1, characterized in that: The polarization state preparer (2) is configured to select a quantum state before, the 1 / 4 wave plate (4) and the polarization state selector (5) are configured to select a quantum state after; the optical axis of the 1 / 4 wave plate (4) is the same as the polarization direction of the polarization state preparer (2), and the included angle between the polarization state selector (5) and the polarization state preparer (2) is , not more than , the front and rear selection state configuration imaginary weak value.

4. The method of claim 1, wherein the method is based on quantum weak measurement technique. By using the weak measurement differential scheme, the exit field obtained is the phase differential distribution of the orbital angular momentum beam in the x and y directions; according to the phase differential distribution in the x and y directions, the full differential light field distribution can be synthesized, and the differential light field of the orbital angular momentum beam is in the form of petal distribution; according to the pattern, the detection of the orbital angular momentum beam is realized, and the measurement of the angular momentum quantum number is obtained from the number of petals.

5. The method of claim 1, wherein the method is based on quantum weak measurement technique. The weak measurement differential technology has good anti-noise effect, and can obtain the differential distribution of the orbital angular momentum beam after environmental disturbance, so as to realize the detection of the orbital angular momentum beams of different orders.

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