Adjustable quantum light source system combined with liquid crystal element

Abstract

The invention discloses an adjustable quantum light source system combined with a liquid crystal element. The adjustable quantum light source system comprises a pumping source, a liquid crystal element, a quarter-wave plate, a nonlinear crystal and a color filter, the pumping source is located on the first side of the liquid crystal element, and the quarter-wave plate, the nonlinear crystal and the color filter are sequentially arranged on the second side of the liquid crystal element; the pumping source is used for emitting pumping laser, and the pumping laser enters the liquid crystal element; an output light beam of the liquid crystal element is transmitted through the quarter-wave plate, the nonlinear crystal and the color filter in sequence, and then light beams in different quantum states are generated and output. The liquid crystal element comprises a geometric phase lens array arranged in an n * n structure. According to the adjustable quantum light source system provided by the invention, the n * n geometric phase lens array in the liquid crystal element is adjusted as required, so that the dynamic control of the output photon state and the output dimension is realized, and the problems that a traditional quantum entangled state preparation system is single in function, and the dynamic control of the output photon state cannot be realized are solved.

Description

Technical Field

[0001] The present invention relates to the field of liquid crystal micro-nano structure manipulation and quantum information technology, and in particular to an adjustable quantum light source system combined with a liquid crystal element. Background Art

[0002] In recent years, quantum information technology has achieved rapid development, and photons are currently one of the important carriers of quantum information. Compared with superconducting systems and atomic systems, photons are an ideal flying bit that does not carry charge and is relatively less likely to interact with the external environment and decoherence; at the same time, light has multiple controllable degrees of freedom, such as phase, wavelength, polarization, spatial mode, orbital angular momentum, etc., 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 now be obtained through nonlinear crystal spontaneous parametric down-conversion technology, spontaneous four-wave mixing technology, and the photoexciton process of quantum dot materials. These high-quality quantum light sources have also been successfully applied to quantum teleportation, key distribution, quantum computing and other fields.

[0003] At present, researchers are also exploring quantum light sources with different entanglement dimensions or multi-photon quantum light sources. Among them, both the entanglement dimension and the number of photons mean the number of controllable quantum bits, and can be used to give full play to the great advantages of quantum parallel computing in quantum information processing. Both are of great significance. However, after the construction of most quantum light sources, their structures, systems, and functions are fixed, and the controllable quantum bits are fixed. It is difficult to dynamically manipulate the optical quantum bits output by the light source, especially for the properties such as the entanglement dimension and the number of photons mentioned above. This often limits the application of quantum light sources in related fields such as quantum information processing. Summary of the invention

[0004] An embodiment of the present invention provides an adjustable quantum light source system combined with a liquid crystal element. The adjustable quantum light source system realizes dynamic control of the output photon state and the output dimension by adjusting the n×n geometric phase lens array in the liquid crystal element as needed, so as to solve the problems that the traditional quantum entangled state preparation system has a single function and cannot realize dynamic control of the output photon state.

[0005] According to one aspect of the present invention, there is provided an adjustable quantum light source system combined with a liquid crystal element, comprising a pump source, a liquid crystal element, a quarter wave plate, a nonlinear crystal and a color filter, wherein the pump source is located on a first side of the liquid crystal element, and 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 used 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 is transmitted through the quarter wave plate, the nonlinear crystal and the color filter in sequence, and then generates light beams of different quantum states and outputs them;

[0008] Wherein, the liquid crystal element comprises a first substrate and a second substrate which are arranged opposite to each other, and a nematic liquid crystal layer arranged between the first substrate and the second substrate;

[0009] A first alignment layer is disposed on a side of the first substrate close to the second substrate, and a second alignment layer is disposed on a side of the second substrate 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 directors of the molecules of the nematic liquid crystal layer to form a geometric phase lens array with an n×n structural arrangement, and the geometric phase lens array includes n×n geometric phase lenses;

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

[0011] Optionally, in the geometric phase lens array, the optical axis arrangement of the nematic liquid crystal in each geometric phase lens is circularly symmetric and arranged in a quadratic function type along the radial direction, and the liquid crystal molecules in the nematic liquid crystal layer are uniformly arranged in parallel along a 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 both include structured n×n transparent electrodes, the transparent electrodes are aligned with the geometric phase lens, and different electric fields are independently applied to each transparent electrode region to independently regulate the phase delay of the geometric phase lens in the corresponding region.

[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 forming a second alignment layer on one side of the second substrate;

[0016] The first substrate and the second substrate are arranged opposite to each other, and a nematic liquid crystal layer is prepared between the first substrate and the second substrate to form a liquid crystal cell;

[0017] Among them, 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 molecular directors of the nematic liquid crystal layer to form a geometric phase lens array with an n×n structural arrangement, and the geometric phase lens array includes n×n geometric phase lenses, where n is an integer greater than or equal to 2.

[0018] Optionally, during the preparation of the liquid crystal element, a stable liquid crystal polymer layer is finally used to align the nematic liquid crystal layer.

[0019] Optionally, the pump laser has a circular polarization state that matches 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.

[0020] Optionally, the diagonal length of the geometric phase lens array of the liquid crystal element is 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.

[0021] Optionally, the operating wavelength of the quarter wave plate matches the wavelength of the pump laser, and the thickness of the quarter wave plate is smaller 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 array of the geometric phase lens array is located inside the nonlinear crystal;

[0023] The color filter is a bandpass filter, and the bandpass filter is used to filter the pump laser.

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

[0025] The adjustable quantum light source system combined with a liquid crystal element provided in an embodiment of the present invention comprises a pump source, a liquid crystal element, a quarter wave plate, a nonlinear crystal and a color filter, wherein the pump source is located on the first side of the liquid crystal element, and the quarter wave plate, the nonlinear crystal and the color filter are sequentially arranged on the second side of the liquid crystal element; the pump source emits a pump laser, and the pump laser is incident on the liquid crystal element; the n×n geometric phase lens array of the liquid crystal element dynamically regulates the pump laser; the output light beam of the liquid crystal element is sequentially transmitted through the quarter wave plate, the nonlinear crystal and the color filter, and generates light beams of different quantum states and outputs them. The adjustable quantum light source system combined with a liquid crystal element provided in an embodiment of the present invention realizes dynamic control of the output photon state and the output dimension by adjusting the n×n geometric phase lens array in the liquid crystal element as needed, so as to solve the problems that the traditional preparation system of quantum entangled state has a single function and cannot realize dynamic control of the output photon state, and improves the flexibility of the quantum light source.

[0026] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 A schematic diagram of the three-dimensional structure of an adjustable quantum light source system based on a liquid crystal element provided in an embodiment of the present invention;

[0029] Figure 2 A schematic diagram of the yz side structure of an adjustable quantum light source system based on a liquid crystal element provided in an embodiment of the present invention;

[0030] Figure 3 A schematic diagram of the structure of a liquid crystal element of an adjustable quantum light source system provided by an embodiment of the present invention;

[0031] Figure 4 A schematic diagram of the spontaneous parametric down-conversion principle of an adjustable quantum light source system combined with a liquid crystal element provided in an embodiment of the present invention;

[0032] Figure 5 A schematic diagram of the control principle of the orientation angle and tilt angle of a liquid crystal element in an adjustable quantum light source system combined with a liquid crystal element provided by an embodiment of the present invention;

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

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

[0035] Figure 8 A schematic diagram of an optical path system when an adjustable quantum light source system combined with a liquid crystal element is used as a four-photon source provided by an embodiment of the present invention;

[0036] Fig. 9 A schematic flow chart of a method for preparing a liquid crystal element provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

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

[0039] Figure 1 A schematic diagram of the three-dimensional structure of an adjustable quantum light source system based on a liquid crystal element provided in an embodiment of the present invention, Figure 2 The yz side structure diagram of the adjustable quantum light source system based on liquid crystal elements provided in the embodiment of the present invention is shown in FIG. Figure 1 and Figure 2 , the tunable quantum light source system includes a pump source ( Figure 1 and Figure 2The liquid crystal element 100 is a liquid crystal element having a first side and a second side and a second side thereof; the pump source is used to emit a pump laser pump, which is incident on 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 to generate light beams of different quantum states and output them.

[0040] Figure 3 A schematic diagram of the structure of a liquid crystal element in an adjustable quantum light source system provided by an embodiment of the present invention, referring to Figure 3 The liquid crystal element includes a first substrate 10 and a second substrate 20 which are arranged opposite to each other, and a nematic liquid crystal layer 30 arranged between the first substrate 10 and the second substrate 20; a first orientation layer 40 is arranged on the side of the first substrate 10 close to the second substrate 20, and a second orientation layer 50 is arranged on the side of the second substrate 20 close to the first substrate 10; the first orientation layer 40 and the second orientation layer 50 have the same orientation direction, and the first orientation layer 40 and the second orientation layer 50 control the molecular directors of the nematic liquid crystal layer to form a geometric phase lens array with an n×n structural arrangement, and the geometric phase lens array includes 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. The first orientation layer 40 and the second orientation layer 50 can be divided into n×n regions corresponding to geometric phase lenses, where n is an integer greater than or equal to 2, for example, n=5 can be selected.

[0042] In this embodiment, taking the liquid crystal element including a 5×5 geometric phase lens array as an example, the nonlinear crystal may be a barium borate BBO crystal.

[0043] Continue to refer Figure 1 and Figure 2The working process of the adjustable quantum light source system is as follows: a pump laser with circular polarization matching 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 circular polarized light into the nonlinear crystal 300 to form a 5×5 beam focus array with a high energy density; the quarter wave plate 200 is close to the rear side of the liquid crystal element 100, and the circular polarized light emitted from the liquid crystal element 100 is converted into linear polarized light; the nonlinear crystal 300 is close to the rear side of the quarter wave plate 200, and a nonlinear spontaneous parametric down conversion process occurs in the nonlinear crystal 300 to generate photon pairs; the color filter 400 is close to the rear side of the nonlinear crystal 300, and filters out the pump laser wavelength component, so that the signal photons and idler photon pair array generated by the down conversion pass through. 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 and Figure 2 The length, width and thickness of a structured liquid crystal 5×5 geometric phase lens array, a quarter wave plate 200 and a nonlinear crystal 300 are only shown by way of example, but are not intended to limit the present invention. In other embodiments, the length, width and thickness can be set according to the detection requirements to ensure that the diagonal length of the structured liquid crystal 5×5 geometric phase lens array 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. The operating wavelength of the quarter wave plate 200 matches the wavelength of the pump laser, the thickness of the quarter wave plate 200 is thin enough and can be set 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 array of the geometric phase lens array is located inside the nonlinear crystal 300, and the color filter 400 is a bandpass filter, which is used to filter the pump laser. At the same time, Figure 2 The specific distribution of the director vectors of the nematic liquid crystal layer molecules controlled by the first and second alignment layers is not shown. A feasible distribution can be referred to Figure 5 and Figure 7 .

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

[0046] For example, Figure 4 A schematic diagram of the principle of spontaneous parametric down-conversion of an adjustable quantum light source system combined with a liquid crystal element provided in an embodiment of the present invention. The nonlinear spontaneous parametric down-conversion process occurs in a nonlinear crystal, and the energy conservation and phase matching conditions (momentum conservation) are satisfied during the process. 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, and the two have mutually orthogonal linear polarization states. The specific phase matching conditions in the spontaneous parametric down-conversion process satisfy: k p =k s +k i At the same time, the cutting angle of the nonlinear crystal meets the requirements of beam-like phase matching, making the phase matching beam-like. The related photon rings generated by the down-conversion will converge into two symmetrical points, and the wave vector direction of the down-converted photons is fixed, which is convenient for the collection and collimation of subsequent photons.

[0047] For example, Figure 5A schematic diagram of the control principle of the orientation angle and inclination angle of a liquid crystal element in an adjustable quantum light source system combined with a liquid crystal element provided in an embodiment of the present invention. The inclination angle θ of the liquid crystal will change under the action of an external electric field. Based on the birefringence characteristics of the molecules in the nematic phase liquid crystal layer, the equivalent phase delay brought by the liquid crystal element will change, so that the phase delay of the nematic phase liquid crystal in each structured electrode area 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 probability of occurrence of the nonlinear spontaneous parametric down-conversion process in the corresponding area, and will also change the relative amplitude of the down-converted photon pairs. The different external electric fields applied independently to each electrode area can also independently control the modulation efficiency of the geometric phase lens in the corresponding area, and dynamically manipulate the amplitude term of the output light 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 set independently, which can change the relative phase of the incident light in different geometric phase lens areas. 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 generated.

[0049] It should be noted that Figure 5 The initial orientation angle distribution of the structured liquid crystal 5×5 geometric phase lens array is only exemplarily shown, and is not intended to limit the embodiments of the present invention. In other embodiments, the initial orientation angle distribution can be selected for the adjustable quantum light source combined with the liquid crystal element according to actual needs.

[0050] For example, Figure 6 A schematic diagram of the specific regulation of the orientation angle and tilt angle of the liquid crystal element on the output light quantum state when an adjustable quantum light source system combined with a liquid crystal element is used as a high-dimensional quantum entanglement source provided by an embodiment of the present invention. When the adjustable quantum light source is used as a high-dimensional entanglement source, 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 adjustable quantum light source combined with the liquid crystal element is a Bell state, expressed as: |ψ>=2 -0.5 (|00>+|11>). After the molecular tilt angle of the nematic liquid crystal layer is regulated and the initial orientation angle arrangement of the structured liquid crystal 5×5 geometric phase lens array is set, the specific quantum state after the amplitude and phase of the light quantum state are regulated is expressed as: |ψ>=a|00>+be iφ |11>, where a 2 +b 2 =1.

[0051] For example, Figure 7 A schematic diagram of the regulation of the number of photons output at the same time by a liquid crystal element when an adjustable quantum light source system combined with a liquid crystal element is used as a multi-photon source provided by an embodiment of the present invention. When the adjustable quantum light source combined with a liquid crystal element is used as a multi-photon source, optionally, each electrode region in the structured liquid crystal 5×5 geometric phase lens array can independently apply a different external electric field to regulate the modulation efficiency of the geometric phase lens to be close to 1 or close to 0. Thus, the switching of each geometric phase lens in the structured liquid crystal 5×5 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 generated simultaneously as a multi-photon source can be changed.

[0052] It should be noted that Figure 7 The above is only an example of a possible way to change the number of photons generated at the same time when the adjustable quantum light source system is used as a multi-photon source, and it is not a limitation of the embodiments of the present invention. In a specific implementation, the number of photons generated at the same time is also limited by the power of the pump laser and other properties, and the switch of each geometric phase lens in the lens array can be designed according to specific needs.

[0053] For example, Figure 8 A schematic diagram of an optical path system when an adjustable quantum light source system combined with a liquid crystal element is used as a four-photon source provided in an embodiment of the present invention. The complete optical path system of the four-photon source includes: an adjustable quantum light source system 1, a lens 2, a prism 3, a polarization beam splitter 4 and a reflector 5. The lens 2 is placed relatively parallel to the light-emitting side of the adjustable quantum light source system 1, and the four down-converted photons generated can be re-collimated by the lens 2; the prism 3 is placed on the light-emitting 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 photon pairs, and the signal photon (s0, s1) is reflected by the polarization beam splitter 4, while the idler photon (i0, i1) with another linear polarization state is transmitted; the reflector 5 is placed at the end of the optical path to reflect and collimate the two idler photons transmitted from the polarization beam splitter 4, and finally obtain four beams of mutually parallel single photons on the light-emitting side of the optical path system.

[0054] The adjustable quantum light source system provided in the embodiment of the present invention can be used as both a high-dimensional entanglement source and a multi-photon source. The nematic phase liquid crystal optical axis in the structured liquid crystal 5×5 geometric phase lens array has a 5×5 structural arrangement along the planes of the first substrate and the second substrate. Under the control of the structured external electric field, the geometric phase lens modulation efficiency of each area in the 5×5 structure can be adjusted, thereby changing the light quantum state output by the quantum light source system. Therefore, the adjustable quantum light source system combined with liquid crystal elements provided in the embodiment of the present invention can adjust the structured liquid crystal 5×5 geometric phase lens array on demand through a structured external electric field, dynamically manipulate the light quantum bits output by the light source, and improve the flexibility of the quantum light source.

[0055] Optional, continue to refer to Figure 3 In the geometric phase lens array, the optical axis arrangement of the nematic liquid crystal in each geometric phase lens presents 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 arranged in parallel along a direction perpendicular to the first substrate 10 and the second substrate 20.

[0056] The nematic phase liquid crystal optical axis is obtained by calculating the phase distribution of the structured geometric phase lens array. The nematic phase liquid crystal molecules in each structure have circular symmetry and have a quadratic function type arrangement along the radial direction. The orientation angle satisfies: α = -π[(r 2 +f 2 ) 0.5 -f] / λ+α0, where r is the radial coordinate, α0 is the initial orientation angle of the nematic liquid crystal molecules, f is the focal length of the geometric phase lens, and λ is the wavelength of the transmitted light.

[0057] Continue to refer Figure 3 Optionally, one side of the first substrate 10 and one side of the second substrate 20 both include a structured n×n transparent electrode 60, the transparent electrode 60 is aligned with the position of the geometric phase lens, and a different electric field is independently applied to each transparent electrode area to independently regulate the phase delay of the geometric phase lens in the corresponding area.

[0058] The transparent electrode 60 can be an ITO electrode. By setting 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, transparent electrodes may not be set, and the liquid crystal element can be directly placed in the electric field set in the partition to achieve phase modulation of the geometric phase lens. The specific implementation can be selected according to the actual situation. When an external electric field is applied, the molecules of the nematic liquid crystal layer will deflect along the direction of the electric field, and the inclination angle of the liquid crystal molecules will change. Based on the birefringence characteristics of the molecules of the nematic liquid crystal layer, the phase delay of the nematic liquid crystal in each structured electrode area can be regulated by an external electric field. Under different phase delay conditions, the geometric phase lens has different polarization conversion efficiencies and different modulation efficiencies, and then the probability of occurrence of the nonlinear spontaneous parametric down-conversion process in the corresponding area also changes, that is, the relative amplitude of the down-converted photon pair changes accordingly. The different external electric fields applied independently to each electrode area can also independently regulate the modulation efficiency of the geometric phase lens in the corresponding area, and dynamically manipulate the amplitude term of the output light quantum state.

[0059] Continue to refer Figure 3 Optionally, the liquid crystal element further includes a sealant 70 disposed between the first substrate 10 and the second substrate 20 , wherein the sealant 70 may be a UV curing sealant to control the total thickness of the nematic liquid crystal layer 30 .

[0060] The adjustable quantum light source system combined with liquid crystal elements provided in the embodiment of the present invention 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] Fig. 9 A schematic diagram of a method for preparing a liquid crystal element provided by an embodiment of the present invention, which is used to prepare a liquid crystal element in an adjustable quantum light source system, with reference to Fig. 9 , the preparation method comprises:

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

[0063] Optionally, after providing the first substrate and the second substrate, the method further includes:

[0064] forming a transparent electrode layer 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 geometric phase lens, and a different electric field is independently applied to each transparent electrode area to independently adjust the phase delay of the geometric phase lens in the corresponding area.

[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 5×5 independent electrode area. After ultrasonic cleaning with a detergent for 30 minutes, drying in a 120°C oven for 40 minutes, and then UV ozone cleaning, the contact effect between the ITO surface and 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] Among them, the process of forming the orientation 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, and after the spin coating is completed, annealing the first substrate to form a first orientation 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, and after the spin coating is completed, annealing the second substrate to form a second orientation layer. Exemplarily, the annealing atmosphere is air, the annealing temperature is 80°C to 120°C, and the annealing time is 8min to 12min. The first SD1 orientation layer and the second SD1 orientation layer are oriented to form the same 5×5 geometric phase lens array target control pattern, and the orientation parameters are set according to the required structure. After orientation, a propylene glycol methyl ether acetate solution with a mass concentration of 25% is spin-coated on the first SD1 orientation layer and the second SD1 orientation layer. The spin coating parameters are a time of about 30 seconds and a rotation speed of about 3600 rpm. After spin coating, it is placed on a hot stage and annealed at 80°C for about 2 minutes to evaporate to form a uniform film, and then placed in a room temperature environment to cool for 1 minute, and then polymerized with an ultraviolet lamp for 7 minutes to 8 minutes to form a more stable first liquid crystal polymer orientation layer and a second liquid crystal polymer orientation layer.

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

[0070] Optionally, the initial orientation angle α0 in the arrangement structure of the liquid crystal molecules in each geometric phase lens region can be set independently.

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

[0072] S130, disposing the first substrate and the second substrate opposite to each other, preparing a nematic liquid crystal layer between the first substrate and the second substrate, and forming a liquid crystal cell.

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

[0074] In a specific implementation, a UV curable adhesive containing spacers can be used to control the distance between the first substrate and the second substrate, and a nematic liquid crystal layer is prepared between the first substrate and the second substrate to form a structured liquid crystal 5×5 geometric phase lens array. Optionally, during the preparation process of the liquid crystal element, a stable liquid crystal polymer layer is finally required to orient the nematic liquid crystal layer to form the desired geometric phase lens array.

[0075] When the first substrate and the second substrate are opposite, the first orientation layer and the second orientation layer are arranged relative to each other. The first structured ITO electrode layer and each structured transparent electrode region of the second structured ITO electrode layer are aligned, and each electrode region can independently apply a different external electric field to independently adjust the phase delay of the geometric phase lens of the corresponding region.

[0076] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An adjustable quantum light source system combined with a liquid crystal element, characterized in that: It comprises a pump source, a liquid crystal element, a quarter wave plate, a nonlinear crystal and a color filter, wherein the pump source is located on a first side of the liquid crystal element, and the quarter wave plate, the nonlinear crystal and the color filter are sequentially arranged on a second side of the liquid crystal element; The pump source is used to emit pump laser, and the pump laser is incident on the liquid crystal element; The output light beam of the liquid crystal element is transmitted through the quarter wave plate, the nonlinear crystal and the color filter in sequence, and then generates light beams of different quantum states and outputs them; Wherein, the liquid crystal element comprises a first substrate and a second substrate which are arranged opposite to each other, and a nematic liquid crystal layer arranged between the first substrate and the second substrate; A first alignment layer is disposed on a side of the first substrate close to the second substrate, and a second alignment layer is disposed on a side of the second substrate 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 directors of the molecules of the nematic liquid crystal layer to form a geometric phase lens array with an n×n structural arrangement, and the geometric phase lens array includes n×n geometric phase lenses; Here, n is an integer greater than or equal to 2.

2. The adjustable quantum light source system according to claim 1, characterized in that: In the geometric phase lens array, the nematic liquid crystal optical axis arrangement in each geometric phase lens presents circular symmetry and is arranged in a quadratic function type along the radial direction. The liquid crystal molecules in the nematic liquid crystal layer are uniformly arranged in parallel along a direction perpendicular to the first substrate and the second substrate.

3. The adjustable quantum light source system according to claim 1, characterized in that: In the liquid crystal element, one side of the first substrate and one side of the second substrate both include structured n×n transparent electrodes, the transparent electrodes are aligned with the geometric phase lenses, and different electric fields are independently applied to each transparent electrode area to independently regulate the phase delay of the geometric phase lens in the corresponding area.

4. The adjustable quantum light source system according to claim 1, characterized in that: The liquid crystal element is prepared by the following steps: providing a first substrate and a second substrate; 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; The first substrate and the second substrate are arranged opposite to each other, and a nematic liquid crystal layer is prepared between the first substrate and the second substrate to form a liquid crystal cell; Among them, 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 molecular directors of the nematic liquid crystal layer to form a geometric phase lens array with an n×n structural arrangement, and the geometric phase lens array includes n×n geometric phase lenses, where n is an integer greater than or equal to 2.

5. The adjustable quantum light source system according to claim 4, characterized in that: During the preparation process of the liquid crystal element, the nematic liquid crystal layer is finally oriented by using the liquid crystal polymer layer.

6. The adjustable quantum light source system according to claim 1, characterized in that: The pump laser has a circular polarization state matching the geometric phase lens array of the liquid crystal element and is vertically incident on the geometric phase lens array. The liquid crystal element, the quarter wave plate, the nonlinear crystal and the color filter are placed parallel to each other.

7. The adjustable quantum light source system according to claim 1, characterized in that: The diagonal length of the geometric phase lens array of the liquid crystal element is 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.

8. The adjustable quantum light source system according to claim 1, characterized in that: The operating wavelength of the quarter wave plate matches the wavelength of the pump laser, and the thickness of the quarter wave plate is smaller than the focal length of the geometric phase lens.

9. The adjustable quantum light source system according to claim 1, characterized in that: 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 array of the geometric phase lens array is located inside the nonlinear crystal; The color filter is a bandpass filter, and the bandpass filter is used to filter the pump laser.

10. The adjustable quantum light source system according to claim 1, characterized in that: The nonlinear crystal includes a barium metaborate crystal.

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