An adjustable quantum light source system incorporating a liquid crystal element

Abstract

The application discloses a kind of adjustable quantum light source systems combined with liquid crystal element.The adjustable quantum light source system includes pump source, liquid crystal element, quarter-wave plate, nonlinear crystal and color filter, pump source is located in the first side of liquid crystal element, quarter-wave plate, nonlinear crystal and color filter are sequentially arranged in the second side of liquid crystal element;Pump source is used to emit pump laser, and pump laser is incident to liquid crystal element;The output beam of liquid crystal element, after being transmitted by quarter-wave plate, nonlinear crystal and color filter in turn, generates different quantum state light beams and outputs.The liquid crystal element includes the geometric phase lens array with n*n structure arrangement.The adjustable quantum light source system provided by the application realizes the dynamic control of output photon state and output dimension by adjusting n*n geometric phase lens array in liquid crystal element as needed, solves the problems, such as single function of traditional quantum entangled state preparation system and inability to realize dynamic control of output photon state.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of liquid crystal micro-nano structure manipulation and quantum information technology, and particularly relates to a tunable quantum light source system combined with a liquid crystal element. BACKGROUND

[0002] In recent years, quantum information technology has developed rapidly, and photons are one of the important carriers of quantum information. Compared with superconducting systems and atomic systems, photons are ideal flying bits, not carrying electric charge, and are relatively difficult to interact with the external environment and decohere. At the same time, light has multiple controllable degrees of freedom, such as phase, wavelength, polarization, spatial mode, and orbital angular momentum, which can be used for information encoding and processing analysis. Therefore, high-quality quantum light sources are an important resource in the field of quantum information. Quantum light sources can be obtained through nonlinear crystal spontaneous parametric down-conversion technology, spontaneous four-wave mixing technology, and light exciton processes of quantum dot materials. These high-quality quantum light sources have been successfully applied in the fields of quantum teleportation, key distribution, and quantum computing.

[0003] At present, researchers are also exploring quantum light sources with different entanglement dimensions or multi-photon quantum light sources. Both the entanglement dimension and the number of photons mean the number of controllable quantum bits, which can be used to take advantage of quantum parallel operation in quantum information processing. Both have important significance. However, most quantum light sources are fixed in structure, system, and function after being built, and the number of controllable quantum bits is fixed. It is difficult to dynamically manipulate the light quantum bits output by the light source, especially for the entanglement dimension and the number of photons mentioned above. This limits the application of quantum light sources in the field of quantum information processing and other related fields in many cases. SUMMARY

[0004] Embodiments of the present application provide a tunable quantum light source system combined with a liquid crystal element. The tunable quantum light source system adjusts the n x n geometric phase lens array in the liquid crystal element on demand to dynamically manipulate the output photon state and the output dimension, thereby solving the problems of single function of a traditional quantum entangled state preparation system and inability to dynamically control the output photon state.

[0005] According to an aspect of the present application, a tunable quantum light source system combined with a liquid crystal element is provided, which includes a pump source, a liquid crystal element, a quarter-wave plate, a nonlinear crystal, and a color filter. The pump source is located on a first side of the liquid crystal element. The quarter-wave plate, the nonlinear crystal, and the color filter are sequentially arranged on a second side of the liquid crystal element.

[0006] The pump source is configured to emit pump laser, and the pump laser is incident on the liquid crystal element.

[0007] The output light beam of the liquid crystal element generates light beams of different quantum states and outputs after being transmitted through the quarter-wave plate, the nonlinear crystal and the color filter in turn;

[0008] The liquid crystal element comprises a first substrate, a second substrate and a nematic liquid crystal layer arranged between the first substrate and the second substrate.

[0009] The first substrate is provided with a first alignment layer on the side close to the second substrate, and the second substrate is provided with a second alignment layer on the side close to the first substrate; the first alignment layer and the second alignment layer have the same alignment direction, and the first alignment layer and the second alignment layer control the director of the nematic liquid crystal layer to form a geometric phase lens array with n×n structure arrangement, the geometric phase lens array comprising n×n geometric phase lenses.

[0010] Wherein, n is an integer greater than or equal to 2.

[0011] Optionally, in the geometric phase lens array, the nematic liquid crystal optical axis in each geometric phase lens is arranged in circular symmetry, and is arranged in a quadratic function type along the radial direction, and the liquid crystal molecules in the nematic liquid crystal layer are uniformly and parallelly arranged along the direction perpendicular to the first substrate and the second substrate.

[0012] Optionally, in the liquid crystal element, one side of the first substrate and one side of the second substrate each comprise a structured n×n transparent electrode, the transparent electrode is aligned with the position of the geometric phase lens, and each transparent electrode region independently applies different electric fields to independently control the phase retardation of the corresponding region of the geometric phase lens.

[0013] Optionally, the liquid crystal element is prepared by the following steps:

[0014] Providing a first substrate and a second substrate;

[0015] Forming a first alignment layer on one side of the first substrate and a second alignment layer on one side of the second substrate;

[0016] Arranging the first substrate and the second substrate oppositely, and preparing a nematic liquid crystal layer between the first substrate and the second substrate to form a liquid crystal cell;

[0017] The first alignment layer is located on the side of the first substrate close to the nematic liquid crystal layer, the second alignment layer is located on the side of the second substrate close to the first substrate, the first alignment layer and the second alignment layer have the same alignment direction, the first alignment layer and the second alignment layer control the director of the nematic liquid crystal layer to form a geometric phase lens array with n*n structure arrangement, and the geometric phase lens array includes n*n geometric phase lenses, and n is an integer greater than or equal to 2.

[0018] Optionally, in the preparation process of the liquid crystal element, the nematic liquid crystal layer is finally oriented by using a stable liquid crystal polymer layer.

[0019] Optionally, the pump laser has a circular polarization state matched with the geometric phase lens array of the liquid crystal element, and is vertically incident on the geometric phase lens array, and the liquid crystal element, the quarter-wave plate, the nonlinear crystal and the color filter are placed in parallel with each other.

[0020] Optionally, the diagonal line length of the geometric phase lens array of the liquid crystal element is less than the coherence length of the pump laser, the size and focal length of each geometric phase lens in the geometric phase lens array are the same, and the initial phase of each geometric phase lens depends on the arrangement structure of the liquid crystal molecules.

[0021] Optionally, the working wavelength of the quarter-wave plate matches the wavelength of the pump laser, and the thickness of the quarter-wave plate is less than the focal length of the geometric phase lens.

[0022] Optionally, the thickness of the nonlinear crystal is equal to twice the focal length of the geometric phase lens array of the liquid crystal element, and the focal point array of the geometric phase lens array is located in the interior of the nonlinear crystal.

[0023] The color filter is a band-pass color filter, and the band-pass color filter is used for filtering the pump laser.

[0024] Optionally, the nonlinear crystal includes a barium metaborate crystal.

[0025] The adjustable quantum light source system combined with the liquid crystal element provided by the embodiment of the present application comprises a pump source, a liquid crystal element, a quarter-wave plate, a nonlinear crystal and a color filter, the pump source is located at a first side of the liquid crystal element, and the quarter-wave plate, the nonlinear crystal and the color filter are sequentially arranged at a second side of the liquid crystal element; the pump laser is emitted by the pump source, and the pump laser is incident to the liquid crystal element; the n*n geometric phase lens array of the liquid crystal element dynamically regulates the pump laser; and the output light beam of the liquid crystal element is sequentially transmitted through the quarter-wave plate, the nonlinear crystal and the color filter, thereby generating light beams of different quantum states and outputting the light beams. The adjustable quantum light source system combined with the liquid crystal element provided by the embodiment of the present application can dynamically control the output photon state and the output dimension by adjusting the n*n geometric phase lens array in the liquid crystal element as required, so as to solve the problems of the single function of the traditional quantum entangled state preparation system and the inability to dynamically control the output photon state, and improve the flexibility of the quantum light source.

[0026] It should be understood that the content described in this part is not intended to identify the key or important features of the embodiments of the present application, nor is it used to limit the scope of the present application. Other features of the present application will become apparent from the following description. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0028] Figure 1 A three-dimensional structural schematic diagram of the adjustable quantum light source system based on the liquid crystal element provided by the embodiment of the present application is shown in the figure.

[0029] Figure 2 A y-z side structural schematic diagram of the adjustable quantum light source system based on the liquid crystal element provided by the embodiment of the present application is shown in the figure.

[0030] Figure 3 A structural schematic diagram of the adjustable quantum light source system in the liquid crystal element provided by the embodiment of the present application is shown in the figure.

[0031] Figure 4 A spontaneous parametric down-conversion principle schematic diagram of the adjustable quantum light source system combined with the liquid crystal element provided by the embodiment of the present application is shown in the figure.

[0032] Figure 5 A control principle schematic diagram of the orientation angle and the tilt angle of the liquid crystal element in the adjustable quantum light source system combined with the liquid crystal element provided by the embodiment of the present application is shown in the figure.

[0033] Figure 6 A specific regulation diagram of the orientation angle and the tilt angle of the liquid crystal element on the output light quantum state when the adjustable quantum light source system combined with the liquid crystal element is used as a high-dimensional quantum entanglement source is provided for the embodiment of the present application.

[0034] Figure 7 A regulation diagram of the liquid crystal element on the number of output photons at the same time when the adjustable quantum light source system combined with the liquid crystal element is used as a multi-photon source is provided for the embodiment of the present application.

[0035] Figure 8 A light path system diagram when the adjustable quantum light source system combined with the liquid crystal element is used as a four-photon source is provided for the embodiment of the present application.

[0036] Figure 9 A flow diagram of the preparation method of the liquid crystal element is provided for the embodiment of the present application. DETAILED DESCRIPTION

[0037] In order to make the person skilled in the art better understand the present application scheme, the technical scheme in the embodiment of the present application will be described clearly and completely below in combination with the drawings in the embodiment of the present application. Obviously, the described embodiment is only a part of the embodiment of the present application, not all. Based on the embodiment in the present application, all other embodiments obtained by the person skilled in the art without creative labor should belong to the protection scope of the present application.

[0038] It should be noted that the terms "first", "second" and the like in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not necessarily limit to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0039] Figure 1 A three-dimensional structure diagram of the adjustable quantum light source system based on the liquid crystal element is provided for the embodiment of the present application, Figure 2 A y-z side structure diagram of the adjustable quantum light source system based on the liquid crystal element is provided for the embodiment of the present application, referring to Figure 1 and Figure 2 The adjustable quantum light source system includes a pump source Figure 1 and Figure 2The liquid crystal element 100, the quarter-wave plate 200, the nonlinear crystal 300 and the color filter 400 are sequentially arranged on the second side of the liquid crystal element 100; the pump source is used for emitting a pump laser pump, and the pump laser pump is incident to the liquid crystal element 100; the output light beam of the liquid crystal element 100 is sequentially transmitted through the quarter-wave plate 200, the nonlinear crystal 300 and the color filter 400, thereby generating light beams of different quantum states and outputting the light beams.

[0040] Figure 3 A structure diagram of a liquid crystal element in an adjustable quantum light source system provided by an embodiment of the present application is shown in FIG. 1. Figure 3 The liquid crystal element includes a first substrate 10, a second substrate 20 and a nematic liquid crystal layer 30 arranged between the first substrate 10 and the second substrate 20; the first substrate 10 is provided with a first alignment layer 40 on the side close to the second substrate 20, and the second substrate 20 is provided with a second alignment layer 50 on the side close to the first substrate 10; the first alignment layer 40 and the second alignment layer 50 have the same alignment direction, and the first alignment layer 40 and the second alignment layer 50 control the director of the molecules of the nematic liquid crystal layer to form a geometric phase lens array with an n×n structure arrangement, the geometric phase lens array including n×n geometric phase lenses; wherein n is an integer greater than or equal to 2.

[0041] The first substrate 10 and the second substrate 20 can be rigid substrates, such as glass substrates, which can be designed according to actual conditions in specific implementation. The first alignment layer 40 and the second alignment layer 50 can be divided into n×n regions corresponding to the geometric phase lenses, wherein n is an integer greater than or equal to 2, for example, n can be selected as 5.

[0042] In this embodiment, the liquid crystal element includes a 5×5 geometric phase lens array, and the nonlinear crystal can be a barium borate BBO crystal.

[0043] Referring to FIG. 1, Figure 1 and Figure 2The working process of the adjustable quantum light source system is as follows: the pump laser with circular polarization matched with the geometric phase lens array of the liquid crystal element 100 is vertically incident on the liquid crystal element 100 with the structured liquid crystal 5*5 geometric phase lens array; each geometric phase lens in the structured 5*5 array converges the incident circularly polarized light into the nonlinear crystal 300 to form a 5*5 beam focus array with high energy density; the quarter-wave plate 200 is closely attached to the rear side of the liquid crystal element 100, and converts the circularly polarized light emitted from the liquid crystal element 100 into linearly polarized light; the nonlinear crystal 300 is closely attached to the rear side of the quarter-wave plate 200, and the nonlinear spontaneous parametric down-conversion process occurs in the nonlinear crystal 300 to generate photon pairs; the color filter 400 is closely attached to the rear side of the nonlinear crystal 300, and filters out the pump laser wavelength component, so that the signal photons generated by the down-conversion and the idler photon pairs array are transmitted. The liquid crystal element 100, the quarter-wave plate 200, the nonlinear crystal 300 and the color filter 400 are all placed parallel to each other.

[0044] It should be noted that, Figure 1 With Figure 2 The length, width and thickness of the structured liquid crystal 5*5 geometric phase lens array, the quarter-wave plate 200 and the nonlinear crystal 300 are only exemplarily shown in the figure, but are not limited to the present application. In other embodiments, the length, width and thickness can be set according to the detection requirements, and the diagonal length of the structured liquid crystal 5*5 geometric phase lens array is ensured to be smaller than the coherence length of the pump laser. The size and focal length of each geometric phase lens in the geometric phase lens array are the same, and the initial phase of each geometric phase lens depends on the arrangement structure of the liquid crystal molecules. The working wavelength of the quarter-wave plate 200 matches the pump laser wavelength, and the thickness of the quarter-wave plate 200 is thin enough, which can be set to be much smaller than the focal length of the geometric phase lens. The thickness of the nonlinear crystal 300 is equal to twice the focal length of the geometric phase lens, the focal point array of the geometric phase lens array is located inside the nonlinear crystal 300, and the color filter 400 is a band-pass color filter for filtering the pump laser. At the same time, Figure 2 The specific distribution of the director of the nematic liquid crystal layer controlled by the first alignment layer and the second alignment layer is not shown in the figure, and a feasible distribution can be referred to Figure 5 and Figure 7 .

[0045] Wherein, when used as a high-dimensional entangled source, although each of the 25 structural regions has a certain probability of generating a pair of down-converted photons, generally only one pair of down-converted photons is generated in the 25 structural regions at the same time, and the final output quantum state can be regarded as an interference superposition of the down-converted photon states generated by each region having different path information, and thus can be regarded as a high-dimensional path entangled state. By encoding the path of the photon pair generated by each geometric phase lens, the output entangled state can be written as: | ψ > = a1| 1, 1 > + a2| 2, 2 > + … + a 25 |25,25>, wherein | a1| 2 + | a2| 2 + … + | a 25 | 2 = 1. When used as a multi-photon source, a pump laser with high power is generally required, and at this time the probability of generating multiple pairs of single photons at the same time is also high. By collecting the photon pairs generated by different geometric phase lens regions, a multi-photon source can be obtained.

[0046] An exemplary, Figure 4 A schematic diagram of the spontaneous parametric down-conversion principle of the adjustable quantum light source system combined with the liquid crystal element is provided for the embodiments of the present application. The nonlinear spontaneous parametric down-conversion process occurs in a nonlinear crystal, and in the process, the energy conservation and phase matching conditions (momentum conservation) are satisfied. The pump laser is extraordinary light (e light), and one of the down-converted photons is ordinary light (o light), and the other is extraordinary light. They have mutually orthogonal linear polarization states. The specific phase matching condition in the spontaneous parametric down-conversion process satisfies: k p = k s + k i . At the same time, the cutting angle of the nonlinear crystal satisfies the requirement of beam-like phase matching, so that the phase matching is of the beam-like type, and the related photon ring generated by the down-conversion is condensed into two symmetric points, and the wave vector direction of the down-converted photons is fixed, facilitating the subsequent collection and collimation of the photons.

[0047] An exemplary, Figure 5A schematic diagram of a control principle of an orientation angle and a tilt angle of a liquid crystal element in a tunable quantum light source system combined with the liquid crystal element is provided for an embodiment of the present application. The tilt angle θ of the liquid crystal will change under the action of an applied electric field. Based on the birefringence characteristics of the molecules of the nematic liquid crystal layer, the equivalent phase delay caused by the liquid crystal element will change, so that the phase delay of the nematic liquid crystal in each structured electrode region can be controlled by the electric field. Under different phase delay conditions, the geometric phase lens has different polarization conversion efficiencies and different modulation efficiencies, which will change the occurrence probability of the nonlinear spontaneous parametric down-conversion process in the corresponding region, and will change the relative amplitude of the down-converted photon pairs. The independent application of different external electric fields to each electrode region can independently control the modulation efficiency of the geometric phase lens in the corresponding region, and dynamically manipulate the amplitude term of the output optical quantum state.

[0048] Optionally, the initial phase of each geometric phase lens depends on the initial orientation angle α0 in the arrangement structure of the liquid crystal molecules, and the initial orientation angle of each geometric phase lens structure can be independently set to change the relative phase of the incident light in different geometric phase lens regions. In the subsequent nonlinear spontaneous parametric down-conversion, the initial phase of the geometric phase lens will change the overall phase of each pair of down-converted signal photons and idler photons produced.

[0049] It should be noted that, Figure 5 Only the initial orientation angle distribution of the structured liquid crystal 5×5 geometric phase lens array is exemplarily shown, which is not a limitation of the embodiment of the present application. In other embodiments, the initial orientation angle distribution can be selected according to actual needs for the tunable quantum light source combined with the liquid crystal element.

[0050] Exemplarily, Figure 6 A specific control schematic diagram of the orientation angle and the tilt angle of the liquid crystal element on the output optical quantum state when the tunable quantum light source system combined with the liquid crystal element is used as a high-dimensional quantum entanglement source is provided for an embodiment of the present application. Taking the output of 2 quantum bits as an example, when the modulation efficiency of the geometric phase lens is close to 1 and no additional initial phase is introduced, the quantum entangled state output by the tunable quantum light source combined with the liquid crystal element is a Bell state, which is represented as: |ψ>=2 -0.5 (|00>+|11>)· After the tilt angle of the molecules of the nematic liquid crystal layer is controlled and the initial orientation angle distribution of the structured liquid crystal 5×5 geometric phase lens array is set, the specific quantum state after the control of the amplitude and the phase of the light quantum state is represented as: |ψ>=a|00>+be iφ |11>, where a 2 +b 2 =1.

[0051] Exemplary, Figure 7 A schematic diagram of the regulation of the number of photons output at the same time by the liquid crystal element when the tunable quantum light source system combined with the liquid crystal element is used as a multi-photon source. When the tunable quantum light source system combined with the liquid crystal element is used as a multi-photon source, each electrode region in the structured liquid crystal 5x5 geometric phase lens array can be independently applied with a different external electric field, and the modulation efficiency of the geometric phase lens can be regulated to be close to 1 or close to 0. Thus, the switching of each geometric phase lens in the structured liquid crystal 5x5 geometric phase lens array can be realized, and the output dimension of the quantum light source can be dynamically regulated, that is, the number of photons simultaneously generated as a multi-photon source can be changed.

[0052] It should be noted that, Figure 7 Only one possible way of changing the number of photons generated at the same time as a multi-photon source when the tunable quantum light source system is used as a multi-photon source is exemplarily shown, which is not a limitation on the embodiments of the present application. In the specific embodiment, the number of photons generated at the same time is also limited by the power and other properties of the pump laser, and meanwhile, the switching of each geometric phase lens in the lens array can be designed according to specific requirements.

[0053] Exemplary, Figure 8 A schematic diagram of the optical path system when the tunable quantum light source system combined with the liquid crystal element is used as a four-photon source. The complete optical path system of the four-photon source includes: a tunable quantum light source system 1, a lens 2, a prism 3, a polarization beam splitter 4, and a mirror 5. The lens 2 is placed in parallel relative to the tunable quantum light source system 1 on the light output side, and the four generated down-converted photons can be recollimated by using the lens 2; the prism 3 is placed on the light output side of the lens 2 to separate the two pairs of down-converted photon pairs generated by the two geometric phase lenses; the polarization beam splitter 4 is placed on the propagation path of each pair of down-converted photons, and the signal photons (s0, s1) are reflected by the polarization beam splitter 4, while the idler photons (i0, i1) having another linear polarization state are transmitted; the mirror 5 is placed at the end of the optical path to reflect and collimate the two paths of idler photons transmitted from the polarization beam splitter 4, and finally four beams of parallel single photons are obtained on the light output side of the optical path system.

[0054] The adjustable quantum light source system provided by the embodiment of the present application can be used as a high-dimensional entanglement source and a multi-photon source. The nematic liquid crystal optical axis in the structured liquid crystal 5x5 geometric phase lens array is arranged in a 5x5 structure along the plane of the first substrate and the second substrate, and the geometric phase lens modulation efficiency of each region in the 5x5 structure can be controlled under the control of a structured external electric field, thereby changing the optical quantum state output by the quantum light source system. Therefore, the adjustable quantum light source system combined with the liquid crystal element provided by the embodiment of the present application can dynamically control the optical quantum bits output by the light source by adjusting the structured liquid crystal 5x5 geometric phase lens array on demand through a structured external electric field, thereby improving the flexibility of the quantum light source.

[0055] Optionally, with reference to Figure 3 , the nematic liquid crystal optical axis in each geometric phase lens is arranged in a circular symmetry, and is arranged in a quadratic function type along the radial direction. The liquid crystal molecules in the nematic liquid crystal layer 30 are uniformly and parallelly arranged along the direction perpendicular to the first substrate 10 and the second substrate 20.

[0056] wherein the nematic liquid crystal optical axis is obtained by calculating the phase distribution of the structured geometric phase lens array, the orientation of the nematic liquid crystal molecules in each structure has a circular symmetry, and is arranged in a quadratic function type along the radial direction. The orientation angle satisfies: alpha = -pi[(r 2 +f 2 ) 0.5 -f] / lambda + alpha0, wherein r is the radial coordinate, alpha0 is the initial orientation angle of the nematic liquid crystal molecules, f is the focal length of the geometric phase lens, and lambda is the wavelength of the transmitted light.

[0057] With reference to Figure 3 , optionally, one side of the first substrate 10 and one side of the second substrate 20 each include a structured n*n transparent electrode 60, the transparent electrode 60 is aligned with the position of the geometric phase lens, and each transparent electrode region independently applies a different electric field to independently control the phase delay of the geometric phase lens in the corresponding region.

[0058] The transparent electrode 60 can be an ITO electrode. By arranging the transparent electrode 60, different electric fields can be applied to each geometric phase lens to achieve phase modulation of the geometric phase lens. It can be understood that, in other embodiments, the transparent electrode can also not be arranged, and the liquid crystal element can be directly placed in the electric field arranged in the partition to achieve phase modulation of the geometric phase lens. In actual implementation, the actual situation can be selected. When an external electric field is applied, the molecules of the nematic liquid crystal layer will be deflected along the direction of the electric field, and the tilt angle of the liquid crystal molecules will change. Based on the birefringence characteristics of the molecules of the nematic liquid crystal layer, the phase retardation of the nematic liquid crystal in each structured electrode region can be controlled by the external electric field. Under different phase retardation conditions, the geometric phase lens has different polarization conversion efficiencies and different modulation efficiencies, and the occurrence probability of the nonlinear spontaneous parametric down-conversion process in the corresponding region also changes, that is, the relative amplitude of the down-converted photon pairs also changes. The independent application of different external electric fields to each electrode region can independently control the modulation efficiency of the geometric phase lens in the corresponding region, and dynamically manipulate the amplitude term of the output optical quantum state.

[0059] With reference to the foregoing Figure 3 Optionally, the liquid crystal element further includes a frame glue 70 arranged between the first substrate 10 and the second substrate 20, where the frame glue 70 can be ultraviolet curing glue, to control the total thickness of the nematic liquid crystal layer 30.

[0060] The adjustable quantum light source system combined with the liquid crystal element provided in the embodiments of the present application will exhibit different functions under different pump lasers and application scenarios, and can be used as a high-dimensional entangled quantum light source and a multi-photon quantum light source, respectively.

[0061] Figure 9 A flowchart of a preparation method of a liquid crystal element provided in the embodiments of the present application is used to prepare the liquid crystal element in the adjustable quantum light source system, with reference to Figure 9 The preparation method includes the following steps.

[0062] S110, providing a first substrate and a second substrate.

[0063] Optionally, after the first substrate and the second substrate are provided, the method further includes the following steps.

[0064] A transparent electrode layer is formed on one side of the first substrate and one side of the second substrate.

[0065] The transparent electrode layer includes a structured n*n transparent electrode, the transparent electrode is aligned with the position of the geometric phase lens, and different electric fields are independently applied to each transparent electrode region to independently control the phase retardation of the geometric phase lens in the corresponding region.

[0066] Specifically, the formation of the transparent electrode layer and the subsequent surface treatment process can be: forming a first structured ITO electrode layer on one side of the first substrate, forming a second structured ITO electrode layer on one side of the second substrate, and the first structured ITO electrode layer and the second structured ITO electrode layer both have the same 5x5 independent electrode area. After ultrasonic cleaning with a cleaning solution for 30 minutes, drying in an oven at 120°C for 40 minutes, and then ultraviolet ozone cleaning, the contact effect of the ITO surface with the SD1 is enhanced.

[0067] S120, forming a first alignment layer on one side of the first substrate and forming a second alignment layer on one side of the second substrate.

[0068] The process of forming the alignment layer can be: spin coating a dimethylformamide solution containing azo dye SD1 with a mass concentration of 0.35% on one side of the first structured ITO electrode layer, after spin coating, annealing the first substrate to form the first alignment layer; spin coating a dimethylformamide solution containing azo dye SD1 with a mass concentration of 0.35% on one side of the second structured ITO electrode layer, after spin coating, annealing the second substrate to form the second alignment layer. Exemplarily, the annealing atmosphere is air, the annealing temperature is 80°C-120°C, and the annealing time is 8min-12min. The first SD1 alignment layer and the second SD1 alignment layer are oriented to form the same 5x5 geometric phase lens array target control pattern, and the orientation parameters are set according to the required structure. After orientation, spin coating a propylene glycol methyl ether acetate solution with a mass concentration of 25% on the first SD1 alignment layer and the second SD1 alignment layer, the spin coating parameters are time about 30s and rotation speed about 3600r / min; after spin coating, annealing on a hot stage at 80°C for about 2min to evaporate and form a uniform film, then placing in a room temperature environment for cooling for 1min, and then polymerizing with a ultraviolet lamp for 7min-8min to form more stable first liquid crystal polymer alignment layer and second liquid crystal polymer alignment layer.

[0069] The 5x5 independent electrode areas of the first structured ITO electrode layer and the second structured ITO electrode layer and the 5x5 geometric phase lens array target control pattern completely coincide.

[0070] Optionally, the initial orientation angle a0 in the arrangement structure of the liquid crystal molecules in each geometric phase lens area can be independently set.

[0071] It should be noted that the spin coating solution composition, spin coating parameters, and annealing parameters described above are only exemplary descriptions, and in other embodiments, they can be adjusted according to actual needs.

[0072] S130, oppositely arranging the first substrate and the second substrate, preparing a nematic liquid crystal layer between the first substrate and the second substrate to form a liquid crystal cell.

[0073] The first alignment layer is located on the side of the first substrate close to the nematic liquid crystal layer, and the second alignment layer is located on the side of the second substrate close to the first substrate. The first alignment layer and the second alignment layer have the same alignment direction. The first alignment layer and the second alignment layer control the director of the nematic liquid crystal layer to form a geometric phase lens array with n x n structure arrangement. The geometric phase lens array includes n x n geometric phase lenses, and n is an integer greater than or equal to 2.

[0074] In the specific implementation, the ultraviolet curing glue containing spacers can be used to control the distance between the first substrate and the second substrate, and the nematic liquid crystal layer is prepared between the first substrate and the second substrate to form a structured liquid crystal 5 x 5 geometric phase lens array. Optionally, in the preparation process of the liquid crystal element, a stable liquid crystal polymer layer is finally used to align the nematic liquid crystal layer to form the required geometric phase lens array.

[0075] When the first substrate and the second substrate are opposite, the first alignment layer and the second alignment layer are arranged opposite to each other. The positions of each structured transparent electrode region of the first structured ITO electrode layer and the second structured ITO electrode layer are aligned. Different external electric fields can be independently applied to each electrode region to independently control the phase delay of the geometric phase lens in the corresponding region.

[0076] The above specific implementation does not constitute a limitation on the protection scope of the present application. Those skilled in the art should understand that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A tunable quantum light source system incorporating a liquid crystal element, characterized by, The pump source is used for emitting pump laser, the pump laser is incident to the liquid crystal element; The output light beam of the liquid crystal element, after transmitting through the quarter-wave plate, the nonlinear crystal and the color filter in turn, generates light beams of different quantum states and outputs; The first substrate and the second substrate are arranged oppositely, and a nematic liquid crystal layer is prepared between the first substrate and the second substrate to form a liquid crystal cell. The first substrate is provided with a first alignment layer on the side close to the second substrate, and the second substrate is provided with a second alignment layer on the side close to the first substrate; the first alignment layer and the second alignment layer have the same alignment direction, and control the director of the nematic liquid crystal layer to form a geometric phase lens array with an n*n structure arrangement, the geometric phase lens array comprising n*n geometric phase lenses. The nematic liquid crystal optical axis in each geometric phase lens in the geometric phase lens array presents circular symmetry and a quadratic function type arrangement along the radial direction, and the liquid crystal molecules in the nematic liquid crystal layer are uniformly and parallelly arranged along the direction perpendicular to the first substrate and the second substrate. The first substrate and the second substrate are arranged oppositely, and a nematic liquid crystal layer is prepared between the first substrate and the second substrate to form a liquid crystal cell.

2. The tunable quantum light source system of claim 1, wherein, The first substrate is provided with a first alignment layer on the side close to the second substrate, and the second substrate is provided with a second alignment layer on the side close to the first substrate; the first alignment layer and the second alignment layer have the same alignment direction, and control the director of the nematic liquid crystal layer to form a geometric phase lens array with an n*n structure arrangement, the geometric phase lens array comprising n*n geometric phase lenses.

3. The tunable quantum light source system of claim 1, wherein, The nematic liquid crystal optical axis in each geometric phase lens in the geometric phase lens array presents circular symmetry and a quadratic function type arrangement along the radial direction, and the liquid crystal molecules in the nematic liquid crystal layer are uniformly and parallelly arranged along the direction perpendicular to the first substrate and the second substrate.

4. The tunable quantum light source system of claim 1, wherein, The first substrate and the second substrate are arranged oppositely, and a nematic liquid crystal layer is prepared between the first substrate and the second substrate to form a liquid crystal cell. The first substrate is provided with a first alignment layer on the side close to the second substrate, and the second substrate is provided with a second alignment layer on the side close to the first substrate; the first alignment layer and the second alignment layer have the same alignment direction, and control the director of the nematic liquid crystal layer to form a geometric phase lens array with an n*n structure arrangement, the geometric phase lens array comprising n*n geometric phase lenses. The nematic liquid crystal optical axis in each geometric phase lens in the geometric phase lens array presents circular symmetry and a quadratic function type arrangement along the radial direction, and the liquid crystal molecules in the nematic liquid crystal layer are uniformly and parallelly arranged along the direction perpendicular to the first substrate and the second substrate. The pump laser has a circular polarization state matched with the geometric phase lens array of the liquid crystal element, and is vertically incident on the geometric phase lens array, and the liquid crystal element, the quarter-wave plate, the nonlinear crystal and the color filter are placed parallel to each other. ​ 5. The tunable quantum light source system of claim 4, wherein, ​ 6. The tunable quantum light source system of claim 1, wherein, ​ 7. The tunable quantum light source system of claim 1, wherein, A diagonal length of a geometric phase lens array of the liquid crystal element is less than a coherence length of the pump laser, a size and a focal length of each geometric phase lens in the geometric phase lens array are the same, and an initial phase of each geometric phase lens depends on an arrangement structure of liquid crystal molecules.

8. The tunable quantum light source system of claim 1, wherein, A working wavelength of the quarter-wave plate matches the pump laser wavelength, and a thickness of the quarter-wave plate is less than a focal length of the geometric phase lens.

9. The tunable quantum light source system of claim 1, wherein, A thickness of the nonlinear crystal is equal to twice a focal length of a geometric phase lens array of the liquid crystal element, and a focal point array of the geometric phase lens array is located inside the nonlinear crystal. The color filter is a band-pass color filter, and the band-pass color filter is used to filter the pump laser.

10. The tunable quantum light source system of claim 1, wherein, The nonlinear crystal includes a barium metaborate crystal.

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