Single-channel multi-entangled photon pair generation method, device, equipment and medium

Abstract

The present application relates to a kind of single channel multi-entangled photon pair generation method, device, equipment and medium, belong to nonlinear optics technical field.The method improves the method for generating entangled light in existing nonlinear crystal spontaneous parametric down-conversion, by the quasi-phase matching period of nonlinear crystal is designed specifically, based on spontaneous parametric down-conversion process, simultaneously realize the generation of high-dimensional polarization entangled photon pair of two wavelengths, reduce conversion channel, compared with the existing spontaneous parametric down-conversion generation method, the generated entangled photon pair doubles, and compared with the existing non-spontaneous parametric down-conversion generation method, then no complex optical system, reduce the multi-source of experimental error, so comprehensive compared with the existing entangled light generation method has simple, efficient, reliable and flexible design characteristics, greatly reduce the difficulty of preparation high-dimensional entangled source, can better promote quantum entangled source and the development of quantum information technology.

Description

Technical Field

[0001] The present invention relates to the field of nonlinear optical technology, and in particular to a method, device, equipment and medium for generating single-channel multiple entangled photon pairs. Background Art

[0002] Quantum entanglement sources play a crucial role in quantum information technology. Their significance lies not only in improving communication security, accelerating computing processes, enhancing sensing accuracy, and expanding simulation capabilities, but also in promoting basic scientific research and technological innovation. With the continuous development of quantum technology, quantum entanglement sources are playing a role in a wide range of fields, driving the innovation and development of a series of related technologies, including quantum communication protocols, quantum computing algorithms, quantum sensing technologies, and quantum simulation methods. Furthermore, quantum entanglement, as one of the most non-classical features of quantum mechanics, is of great significance for understanding the basic principles and properties of quantum mechanics. By studying quantum entanglement sources, scientists can further uncover the mysteries of the quantum world and promote the development of basic science.

[0003] Currently, the main methods for generating quantum entangled photon pairs include spontaneous parametric down-conversion (SPDC) in nonlinear crystals, atomic cascade radiation, four-wave mixing (FWM), and quantum dots. SPDC-based nonlinear crystals are relatively simple to implement, exploiting the nonlinear effects of light to split a single photon into two entangled photons of lower energy and longer wavelength. This approach has applications in quantum communication, but current development of nonlinear crystals has limited its scope to generating two-photon entangled sources. Existing methods based on spontaneous parametric down-conversion can only generate a single photon pair, resulting in a small number of photon pairs and low efficiency. Other methods for generating quantum entangled photon pairs, such as four-wave mixing (FWM), are more challenging to implement. This method, for example, generates entangled photon pairs by mixing four optical signals (typically with different frequencies) within a nonlinear element (such as a silicon optical waveguide). While this method can simultaneously generate multiple entangled photon pairs, achieving high-dimensional entangled photon states, and can control the properties of the entangled photons to a certain extent, it is challenging to implement due to the demanding experimental conditions and the high-precision control and optimization required.

[0004] In other words, current methods for generating quantum entangled photon pairs are either difficult or inefficient. Therefore, a simple and efficient method for generating high-dimensional entangled light is urgently needed. Summary of the Invention

[0005] In view of this, the embodiments of the present invention provide a single-channel multi-entangled photon pair generation method, device, equipment and medium to solve the current technical problem that it is difficult to simply and efficiently achieve high-dimensional entangled light generation.

[0006] In a first aspect, a method for generating multiple entangled photon pairs in a single channel is provided, the method comprising:

[0007] According to the quasi-phase matching conditions that the nonlinear crystal must meet during optical parametric down-conversion, determine the first polarization period and the second polarization period of the nonlinear crystal with respect to the wavelength and the refractive index during the type II quasi-phase matching process, wherein the first polarization period represents the polarization period when the signal light is vertically polarized and the idle light is horizontally polarized, and the second polarization period represents the polarization period when the signal light is horizontally polarized and the idle light is vertically polarized;

[0008] Under the constraints that the length of the first polarization period is equal to the length of the second polarization period, and that the wavelength of the signal light is not equal to the wavelength of the idle light, determining the wavelength of the target signal light and the wavelength of the target idle light corresponding to the target pump light of known wavelength, as well as the refractive index corresponding to the target pump light, the refractive index corresponding to the target signal light, and the refractive index corresponding to the target idle light;

[0009] The target polarization period length is determined according to the wavelength of the target signal light, the wavelength of the target idle light, the corresponding refractive index of the target pump light, the corresponding refractive index of the target signal light, and the corresponding refractive index of the target idle light. The target pump light is injected into the periodically polarized crystal under the target polarization period length to complete the generation of single-channel multiple entangled photon pairs.

[0010] In a second aspect, a single-channel multi-entangled photon pair generation device is provided, the device comprising:

[0011] a polarization period determination module, configured to determine, based on a quasi-phase matching condition that the nonlinear crystal must satisfy during optical parametric down-conversion, a first polarization period and a second polarization period of the nonlinear crystal with respect to wavelength and refractive index during a type II quasi-phase matching process, wherein the first polarization period represents a polarization period when the signal light is vertically polarized and the idle light is horizontally polarized, and the second polarization period represents a polarization period when the signal light is horizontally polarized and the idle light is vertically polarized;

[0012] a wavelength and refractive index determination module, configured to determine the wavelength of target signal light and target idle light corresponding to target pump light of known wavelength, as well as the refractive index corresponding to the target pump light, the refractive index corresponding to the target signal light, and the refractive index corresponding to the target idle light, based on the constraints that the length of the first polarization period is equal to the length of the second polarization period and the constraints that the wavelength of the signal light is not equal to the wavelength of the idle light;

[0013] An entangled light generation module is used to determine a target polarization period length based on the wavelength of the target signal light, the wavelength of the target idle light, the corresponding refractive index of the target pump light, the corresponding refractive index of the target signal light, and the corresponding refractive index of the target idle light, and to inject the target pump light into a periodically polarized crystal with the target polarization period length to complete the generation of single-channel multiple entangled photon pairs.

[0014] In a third aspect, an embodiment of the present invention provides a computer device, comprising a processor, a memory, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the method for generating single-channel multiple entangled photon pairs as described in the first aspect is implemented.

[0015] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the single-channel multi-entangled photon pair generation method as described in the first aspect is implemented.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] The single-channel multi-entangled photon pair generation method of the present invention improves the existing method of generating entangled light by spontaneous parametric down-conversion in nonlinear crystals. By targeted design of the quasi-phase matching period of the nonlinear crystal, based on the spontaneous parametric down-conversion process, it simultaneously realizes the generation of high-dimensional polarization entangled photon pairs of two wavelengths, reduces the conversion channels, and doubles the entangled photon pairs compared to the existing spontaneous parametric down-conversion generation method. Compared with the existing non-spontaneous parametric down-conversion generation method, it does not require a complex optical system and reduces the multi-source of experimental errors. Therefore, in general, compared with the existing generation method, it has the characteristics of simplicity, efficiency, reliability and flexible design, which greatly reduces the difficulty of preparing high-dimensional entangled sources and can better promote the development of quantum entangled sources and quantum information technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 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 embodiments or the description of the prior art. 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 paying any creative work.

[0019] Figure 1 This is a schematic diagram of an application environment for a method for generating multiple entangled photon pairs in a single channel provided in the first embodiment of the present invention;

[0020] Figure 2This is a flow chart of a method for generating multiple entangled photon pairs in a single channel provided in Example 1 of the present invention;

[0021] Figure 3 This is a schematic diagram of the principle of generating four-photon entanglement provided by the first embodiment of the present invention;

[0022] Figure 4 This is a schematic diagram of an optical path for generating multiple entangled photon pairs in a single channel provided by one embodiment of the present invention;

[0023] Figure 5 This is a schematic diagram of a periodically poled potassium titanyl phosphate crystal prepared with a target poling period according to one embodiment of the present invention;

[0024] Figure 6 An embodiment of the present invention provides a method based on Figure 5 Schematic diagram of the entangled photon counting results generated by periodically poled potassium titanyl phosphate crystal;

[0025] Figure 7 This is a schematic structural diagram of a single-channel multi-entangled photon pair generation device provided in Example 2 of the present invention;

[0026] Figure 8 This is a structural diagram of a computer device provided in Example 3 of the present invention. DETAILED DESCRIPTION

[0027] In the following description, specific details such as particular system structures and techniques are provided for purposes of illustration, not limitation, to facilitate a thorough understanding of the embodiments of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.

[0028] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0029] It will also be understood that the term "and / or" used in the present description and appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0030] As used in the present specification and the appended claims, the term "if" may be interpreted as "when" or "upon" or "in response to determining" or "in response to detecting," depending on the context. Similarly, the phrase "if it is determined" or "if [described condition or event] is detected" may be interpreted as meaning "upon determination" or "in response to determining" or "upon detection of [described condition or event]" or "in response to detecting [described condition or event]," depending on the context.

[0031] In addition, in the description of the present specification and the appended claims, the terms "first", "second", "third", etc. are only used to distinguish the descriptions and cannot be understood as indicating or implying relative importance.

[0032] References to "one embodiment" or "some embodiments" in the present specification mean that a particular feature, structure, or characteristic described in conjunction with that embodiment is included in one or more embodiments of the present invention. Thus, phrases such as "in one embodiment," "in some embodiments," "in other embodiments," and "in yet other embodiments" appearing in various places in this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "including," "comprising," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0033] Embodiments of the present invention can acquire and process relevant data based on artificial intelligence technology. Artificial Intelligence (AI) refers to the theories, methods, techniques, and application systems that use digital computers or machines controlled by digital computers to simulate, extend, and expand human intelligence, perceive the environment, acquire knowledge, and use that knowledge to achieve optimal results.

[0034] Fundamental AI technologies generally include sensors, dedicated AI chips, cloud computing, distributed storage, big data processing, operating / interaction systems, and mechatronics. AI software technologies primarily encompass computer vision, robotics, biometrics, speech processing, natural language processing, and machine learning / deep learning.

[0035] It should be understood that the order of execution of the steps in the following embodiments does not necessarily mean the order in which they are executed. The order in which each process is executed should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0036] In order to illustrate the technical solution of the present invention, specific embodiments are provided below.

[0037] The method for generating multiple entangled photon pairs in a single channel provided by the first embodiment of the present invention can be applied in the following aspects: Figure 1 in an application environment, wherein the client communicates with the server. The client includes but is not limited to PDAs, desktop computers, laptops, ultra-mobile personal computers (UMPCs), netbooks, cloud terminal devices, personal digital assistants (PDAs) and other terminal devices. The server can be implemented with an independent server or a server cluster consisting of multiple servers. The above-mentioned single-channel multi-entangled photon pair generation method can be applied to the server in Figure 1, and the computer device corresponding to the server is connected to the corresponding database, rule base, etc. to obtain the corresponding data in the database. The above-mentioned computer device can also be connected to the client to collect data and control instructions sent by the client user. The above-mentioned single-channel multi-entangled photon pair generation method can also be applied to Figure 1 The client in the example connects to the target database via a pre-defined application programming interface (API). When the target database is driven to execute a task, a corresponding task log is generated, which can be collected through the API.

[0038] See also Figure 2 , is a flow chart of a method for generating multiple entangled photon pairs in a single channel provided by the first embodiment of the present invention, such as Figure 2 As shown, the single-channel multi-entangled photon pair generation method may include the following steps:

[0039] S101, based on the quasi-phase matching conditions that the nonlinear crystal must meet during optical parametric down-conversion, determine a first polarization period and a second polarization period of the nonlinear crystal with respect to wavelength and refractive index during type II quasi-phase matching, wherein the first polarization period represents the polarization period when the signal light is vertically polarized and the idle light is horizontally polarized, and the second polarization period represents the polarization period when the signal light is horizontally polarized and the idle light is vertically polarized.

[0040] The current methods of generating quantum entangled photon pairs, such as atomic cascade radiation, four-wave mixing, and quantum dots, have implementation principles that determine that their implementation difficulty is difficult to significantly reduce. Therefore, the present invention chooses to improve the efficiency of this method of generating quantum entangled photon pairs based on spontaneous parametric down-conversion in nonlinear crystals. Based on the existing single-channel method that can only generate one entangled photon pair, it is improved to a single-channel method that can generate two entangled photon pairs, thereby increasing the types of entangled light generated from two to four, thereby obtaining a method for simply and efficiently generating high-dimensional entangled light.

[0041] To achieve the above objectives, this embodiment provides a single-channel high-dimensional four-photon entanglement generation scheme, which mainly calculates the period of quasi-phase matching (QPM) of the nonlinear crystal used to generate the quantum entanglement source, and uses a polarization period to simultaneously generate two wavelengths and four different states of polarization entangled photons while ensuring spontaneous parametric down-conversion (SPDC).

[0042] For nonlinear crystals, such as the commonly used potassium titanyl phosphate (KTP), the periodically poled potassium titanyl phosphate (PPKTP) crystal obtained by periodically poling it, and the periodically poled crystal obtained by periodically poling other nonlinear crystals, three types of quasi-phase matching processes can occur:

[0043] 1. When vertically polarized (S-biased) pump light undergoes optical parametric down-conversion to generate vertically polarized signal light and idle light, the process is a type 0 quasi-phase matching process.

[0044] 2. When the vertically polarized (S-polarized) pump light undergoes optical parametric down-conversion to generate horizontally polarized signal light and idle light, the process is a type I quasi-phase matching process;

[0045] 3. When the horizontally polarized (P-biased) pump light undergoes optical parametric down-conversion to generate vertically polarized signal light and horizontally polarized idle light, the process is a type II quasi-phase matching process.

[0046] Since the field usually refers to the process of generating entangled light when the number of photon types generated is greater than 2 as the generation of high-dimensional entangled light, where the specific photon types are determined by the differences in degrees of freedom such as wavelength, frequency, polarization, and spin, it can be seen from the above optical parametric down-conversion (SPDC) process that the photons generated by Type 0 and Type I may only differ in a single degree of freedom, namely wavelength. The difference in a single degree of freedom can only produce two types of photons at most. The photons generated by Type II can be different in both polarization direction and wavelength. The difference in the two degrees of freedom can produce up to four photons, thereby generating high-dimensional entangled light.

[0047] Therefore, we need to use the type II quasi-phase matching process of KTP crystal to achieve high-dimensional entanglement generation, that is, Figure 3 As shown in the principle diagram of four-photon entanglement generation, two photon pairs are generated, specifically, two wavelengths of entangled light are generated, and each wavelength has photons in two states of horizontal polarization and vertical polarization, and then Figure 4 As shown in the optical path diagram of the single-channel multi-entangled photon pair generation, the two entangled lights of different wavelengths generated are separated into wavelengths by a laser beam splitter. Shorter signal light, and wavelength The longer idle light, and since the horizontal polarization and vertical polarization photons exist in the signal light and idle light respectively, four available entangled lights are finally obtained.

[0048] Specifically, the spontaneous parametric down conversion (SPDC) process of the pump light in the nonlinear crystal needs to satisfy quasi-phase matching conditions, one of which is to satisfy energy conservation, and the other is to satisfy momentum conservation, based on the quasi-phase matching conditions, the relationship between the polarization period and the wavelengths of the signal light and the idle light in the quasi-phase matching process can be determined, and the relationship between the polarization period and the refractive index of the pump light, the signal light and the idle light in each direction in the crystal can be determined.

[0049] For the type II quasi-phase matching process, the polarization direction of the signal light and the idle light is mainly YZY propagation, and the propagation directions of the signal light and the idle light in the type II quasi-phase matching process are perpendicular to each other, so if the four-photon entanglement as shown in Figure 3 is to be realized, it can be assumed that one group of the four photons is vertical polarization signal light and horizontal polarization idle light , and the other group is horizontal polarization signal light and vertical polarization idle light .

[0050] Among them, it is assumed that the polarization period corresponding to one group of signal light and idle light is the first polarization period, and the polarization period corresponding to the other group of signal light and idle light is the second polarization period, since the polarization directions of the signal light and the idle light generated by the two groups are different, different relationships between the wavelengths of the signal light and the idle light and the wavelengths of the pump light, the signal light and the idle light in each direction in the crystal, and the refractive index of the pump light, the signal light and the idle light in each direction in the crystal can be obtained.

[0051] S102, with the constraint that the length of the first polarization period is equal to the length of the second polarization period, and the constraint that the wavelength of the signal light is not equal to the wavelength of the idle light, the wavelength of the target signal light corresponding to the target pump light with known wavelength and the wavelength of the target idle light are determined, and the refractive index corresponding to the target pump light, the refractive index corresponding to the target signal light and the refractive index corresponding to the target idle light.

[0052] Since the present application is to realize the generation of high-dimensional entangled light with multiple entangled photons in a single polarization period, i.e. in a single channel, it is expected that the first polarization period and the second polarization period in the above step S101 are equal in length, so as to realize the generation of two groups of signal light and idle light with one polarization period. At the same time, since the generation of four entangled lights is to be realized, it is necessary to ensure that the wavelengths of the signal light and the idle light in the two groups are different, otherwise it will lead to the situation that the signal light of one group The essence is the same, but in the end only two entangled lights are actually produced.

[0053] In summary, this embodiment first selects the wavelength of the pump light input to the crystal, that is, the pump light used to stimulate the generation of signal light and idle light, and records it as the target pump light with a known wavelength. Then, based on the target pump light, the target signal light wavelength and target idle light wavelength corresponding to the target pump light are determined, subject to the constraints that the length of the first polarization period is equal to the length of the second polarization period, and that the signal light wavelength is not equal to the idle light wavelength.

[0054] Among them, regarding the determination of the target signal light wavelength and the target idle light wavelength, one method is to first experimentally measure the refractive indices corresponding to different wavelengths and different propagation directions to obtain a refractive index data table, then substitute the target pump light of known wavelength into the refractive index data table to determine the refractive index of the pump light, and then sequentially select wavelengths of different lengths from the refractive index data table as the signal light wavelength and determine the idle light wavelength corresponding to each selected signal light, as well as the refractive indices of the idle light and signal light. Thus, through repeated attempts, the signal light and idle light that satisfy the aforementioned constraints of the first polarization period length being equal to the second polarization period length and the signal light wavelength being unequal to the idle light wavelength are determined and used as the target signal light and target idle light. Another method is to directly derive and calculate the target signal light and target idle light corresponding to the target pump light, as well as the refractive indices corresponding to the target signal light and target idle light, based on the existing refractive index equation.

[0055] S103, determining a target polarization period length based on the wavelength of the target signal light, the wavelength of the target idle light, the refractive index corresponding to the target signal light, and the refractive index corresponding to the target idle light, injecting the target pump light into a periodically polarized crystal with the target polarization period length to complete the generation of single-channel multiple entangled photon pairs.

[0056] Since the polarization period is related to the wavelength and the refractive index, once the wavelength of the target signal light and the corresponding refractive index of the target signal light, as well as the wavelength of the target idle light and the corresponding refractive index of the target idle light, are known, the aforementioned first polarization period or second polarization period can be calculated. Moreover, since the target signal light and the target idle light are obtained under the constraint that the length of the first polarization period is equal to the length of the second polarization period, the first polarization period is equal to the second polarization period, and both are polarization periods that can successfully generate four entangled photons, that is, the required target polarization period.

[0057] After determining the target poling period, a periodically poled crystal under the target poling period can be selected, or a nonlinear crystal can be periodically poled to obtain a periodically poled crystal under the target poling period.

[0058] Taking potassium titanyl phosphate (KTP) as an example, the periodic poling preparation process involves preparing a mask, using Wiener processing to form periodic electrodes, performing periodic poling via an applied electric field to produce a periodically poled potassium titanyl phosphate (PPKTP) crystal with a target poling period, and then polishing and optically coating the crystal. Of course, in other embodiments, any feasible type of nonlinear crystal can be used, and a periodically poled crystal of that type can be selected or prepared.

[0059] After selecting or preparing a periodically poled crystal under the target polarization period, place the periodically poled crystal under the target polarization period in a Figure 4 The single-channel multi-entangled photon pair shown in the figure generates the crystal position in the optical path, and then uses the laser to generate the target pump light and input it into the periodically polarized crystal under the target polarization period. Figure 3 As shown, four entangled photons with different wavelengths and polarization directions are generated, realizing the generation of single-channel high-dimensional entangled light, that is, realizing the generation of single-channel multiple entangled photon pairs.

[0060] The single-channel multi-entangled photon pair generation method of the present invention breaks the restrictive correlation between polarization and wavelength of photons generated during type II quasi-phase matching in the spontaneous parametric down-conversion process by designing the quasi-phase matching period of the nonlinear crystal, thereby achieving the generation of high-dimensional polarization entangled photon pairs of two wavelengths, reducing the conversion channels, and eliminating the need for complex optical systems to achieve this goal, thereby reducing the multi-source of experimental errors. Therefore, it has the characteristics of simplicity, efficiency, reliability and flexible design, greatly reducing the difficulty of preparing high-dimensional entangled sources, and can better promote the development of quantum entangled sources and quantum information technology.

[0061] In one embodiment, the specific contents of the quasi-phase matching conditions that the nonlinear crystal needs to satisfy during the optical parametric down-conversion process in the above step S101 are given.

[0062] As described in the above embodiment, the quasi-phase matching conditions that the nonlinear crystal needs to meet during the optical parametric down-conversion process include two aspects: one is to satisfy the conservation of energy, and the other is to satisfy the conservation of momentum, as follows:

[0063] Conservation of Energy:

[0064]

[0065] in, represents the frequency of the pump light, represents the frequency of the generated signal light, represents the frequency of the idle light produced;

[0066] Conservation of momentum:

[0067]

[0068]

[0069]

[0070] in, represents the wave vector of the pump light, represents the wave vector of the signal light, represents the wave vector of the idle light, represents the periodic polarization vector, represents the order of quasi-phase matching, which is an integer. The value of determines the effective nonlinear conversion efficiency of the optical parameter conversion process. The larger the value, the lower the nonlinear conversion efficiency, and the corresponding experimentally prepared compressed states and entangled states become lower. represents the wave vector, Express Take the absolute value, It represents the refractive index of the light beam when it propagates in the crystal. The value direction is consistent with the polarization direction of the wave vector. For the type II quasi-phase matching process, the polarization direction is mainly YZY propagation. represents the wavelength of the light beam, represents the polarization period.

[0071] In another embodiment, a specific method for calculating the first polarization period and the second polarization period in the above step S101 is provided.

[0072] In the process of pump light inputting into the nonlinear crystal to stimulate the generation of signal light and idle light, that is, In the process of , based on the specific content of the quasi-phase matching conditions that the nonlinear crystal needs to meet during the optical parametric down-conversion process given in the above embodiment, it can be deduced that:

[0073] Will Substitution We can get: ,thereby ;

[0074] Also because , so we have:

[0075] ,or

[0076] Further deduction yields:

[0077] ,or ,in represents the wavelength of the pump light, represents the wavelength of the signal light, represents the wavelength of idle light;

[0078] Continued by , we can get , thus we can get:

[0079] ,or .

[0080] Since we want to take the type II SPDC process, the polarization direction is mainly YZY propagation, that is, the refractive index of the pump light is Take the Y propagation direction, expressed as ; Refractive index of signal light Take the Z propagation direction, expressed as Idle light refractive index Take the Y propagation direction, expressed as . Therefore, we can get:

[0081] ,or .

[0082] In order to make and To achieve four-photon entanglement with a single-channel cycle, it is necessary to use , at this time for The wavelength produced by the process is The photon is the signal light, the refractive index is in the Z direction, and the wavelength is The photon is idler light, and the refractive index is in the Y direction; The wavelength produced by the process is The photon is idler light, and the refractive index is in the Y direction. The wavelength generated is The photon is the signal light, and the refractive index is in the Z direction. Therefore, a single channel with multiple entangled photon pairs is achieved. and The vertical and horizontal polarization states exist simultaneously, so the first polarization period and the second polarization period can be determined respectively:

[0083] The first polarization period is:

[0084]

[0085] in, represents the first polarization period, represents the wavelength of the signal light, represents the wavelength of idle light, Indicates that the pump light in the nonlinear crystal The refractive index of the direction, Indicates that the signal light in the nonlinear crystal The refractive index of the direction, Indicates that idle light in the nonlinear crystal The refractive index of the direction, Indicates the order of quasi-phase matching.

[0086] The second polarization period is:

[0087]

[0088] in, represents the second polarization period, Indicates that the signal light in the nonlinear crystal The refractive index of the direction, Indicates that idle light in the nonlinear crystal The refractive index of the direction.

[0089] This embodiment provides a specific derivation process of the first polarization period and the second polarization period, and clarifies the basis for deriving the first and second polarization periods and their feasibility.

[0090] In one embodiment, a specific method is provided for implementing the constraints of the length of the first polarization period being equal to the length of the second polarization period and the wavelength of the signal light being unequal to the wavelength of the idle light in step S102.

[0091] In order to make and In order to have both vertical and horizontal polarization states and to achieve four-photon entanglement with a single-channel cycle, it is necessary to , there are two cases:

[0092] when hour:

[0093]

[0094] Due to the nonlinear crystal Monotonically increasing and less than 0, so only when Only when At this time, four entangled lights with different wavelengths and polarization states cannot be formed, so the high-dimensional entangled state does not exist.

[0095] when hour:

[0096]

[0097] There is a unique solution at this time, and , which can form four entangled lights with different wavelengths and polarization states, meeting the requirements of high-dimensional entangled states.

[0098] Therefore, by limiting the ratio of the target signal light wavelength to the target idle light wavelength, the above The proportional formula when , can realize the constraint that the length of the first polarization period is equal to the length of the second polarization period, and the constraint that the wavelength of the signal light is not equal to the wavelength of the idle light, to ensure the establishment of the high-dimensional entangled state.

[0099] In one embodiment, a specific method is provided for determining the wavelength of the target signal light and the wavelength of the target idle light corresponding to the target pump light of known wavelength, as well as the refractive index corresponding to the target pump light, the refractive index corresponding to the target signal light, and the refractive index corresponding to the target idle light in step S102.

[0100] The Sellmeier dispersion formula is an empirical equation that describes the relationship between the refractive index and wavelength in a specific transparent medium. This equation is used to determine the dispersion of light in the medium. Based on this empirical formula, the optimal dispersion relation equation for nonlinear crystals can be determined by least squares fitting:

[0101]

[0102] in, represents the refractive index, represents the wavelength, as well as are the Sellmeier coefficients obtained by the least squares fitting process.

[0103] The four Sellmeier coefficients in the optimal dispersion relation equation have different optimal values ​​for different crystal types and when light propagates in different directions. Their values ​​need to be determined based on actual data through least squares fitting. This embodiment takes the nonlinear crystal as a potassium titanyl phosphate (KTP) crystal as an example, and considering that the implementation process of the present invention selects a type II quasi-phase matching process to achieve single-channel high-dimensional entangled light generation. The polarization direction of the type II quasi-phase matching process is mainly YZY propagation. Therefore, it is only necessary to fit and determine the specific values ​​of the four Sellmeier coefficients in the optimal dispersion relation equation when the potassium titanyl phosphate (KTP) crystal is in the y-direction and the z-direction:

[0104]

[0105]

[0106] in, represents the refractive index of light in the y direction of potassium titanyl phosphate crystal, 、 、 as well as represents the Sellmeier coefficient corresponding to light propagating in the y direction of potassium titanyl phosphate crystal, represents the refractive index of light in the z direction of potassium titanyl phosphate crystal, , , and represent the corresponding Sellmeier coefficients when light propagates in the z direction of potassium titanyl phosphate crystal.

[0107] The embodiment is fitted to obtain, , , , , and , , , .

[0108] Based on the optimal dispersion relation equation, and the target pump light with known wavelength, the refractive index corresponding to the target pump light can be determined first, assuming that the wavelength of the selected target pump light is , then there is .

[0109] Since , then , the relationship between and is substituted into the optimal dispersion relation equation, so that:

[0110]

[0111]

[0112]

[0113]

[0114] Continue to combine the constraint formula obtained by taking the length of the first polarization period equal to the length of the second polarization period as a constraint, and the signal light wavelength and the idler light wavelength are not equal as a constraint , the target signal light wavelength , and the target idler light wavelength can be obtained.

[0115] Since the above solving process is obtained by taking the length of the first polarization period equal to the length of the second polarization period as a constraint, according to the wavelength of the target signal light, the wavelength of the target idler light, the refractive index corresponding to the target pump light, the refractive index corresponding to the target signal light and the refractive index corresponding to the target idler light, the first polarization period or the second polarization period is calculated, and the length of the first polarization period or the length of the second polarization period calculated is taken as the length of the target polarization period.

[0116] At the same time, due to the order of quasi-phase matching The larger the value, the lower the nonlinear conversion efficiency, and the corresponding experimentally prepared compressed states and entangled states become lower. Therefore, in this embodiment, it is preferred that m be 1. At this time:

[0117]

[0118] Correspondingly, the calculation formula of the first polarization period at this time can be obtained when the target pump light wavelength is When the target polarization period length is 64.5µm, the corresponding selection or preparation is as follows Figure 5 As shown, the periodically poled potassium titanyl phosphate (PPKTP) crystal with the target poling period is After the target pump light is injected into the obtained periodically poled potassium titanyl phosphate (PPKTP) crystal, the following can be obtained: Figure 6 Entangled photon counting results shown.

[0119] Depend on Figure 5 and Figure 6 It can be seen that through precise calculations and high-quality preparation of PPKTP crystals, it is possible to successfully generate four-photon entangled photon pairs in a single channel without the need for complex experimental setups or complicated processes such as micro-ring silicon optical waveguide fabrication. This avoids the complexity and efficiency losses that may come with multi-channel systems and allows for more effective control of experimental conditions, such as laser pump intensity and optical component precision, thereby enhancing system stability. By increasing the number of optical components and experimental parameters, entangled states with a larger number of photons can be achieved, promoting the development of fields such as quantum computing and quantum communications.

[0120] Corresponding to the method of the above embodiment, Figure 7 This figure shows a block diagram of a single-channel device for generating multiple entangled photon pairs, according to a second embodiment of the present invention. This device is applied to a computer device, which is connected to a target database via a pre-defined application programming interface (API). When the target database is driven to execute a task, a corresponding task log is generated, which can be collected via the API. For ease of illustration, only the portions relevant to this embodiment of the present invention are shown.

[0121] See also Figure 7 , the entangled light generating device comprises:

[0122] a polarization period determination module 21 for determining, based on a quasi-phase matching condition that the nonlinear crystal must satisfy during optical parametric down-conversion, a first polarization period and a second polarization period with respect to wavelength and refractive index of the nonlinear crystal during a type II quasi-phase matching process, wherein the first polarization period represents a polarization period when the signal light is vertically polarized and the idle light is horizontally polarized, and the second polarization period represents a polarization period when the signal light is horizontally polarized and the idle light is vertically polarized;

[0123] a wavelength and refractive index determination module 22 for determining, based on a constraint that the length of the first polarization period is equal to the length of the second polarization period, and a constraint that the wavelength of the signal light is not equal to the wavelength of the idle light, a wavelength of a target signal light and a wavelength of a target idle light corresponding to a target pump light of known wavelength, as well as a refractive index corresponding to the target pump light, a refractive index corresponding to the target signal light, and a refractive index corresponding to the target idle light;

[0124] The entangled light generating module 23 is used to determine the target polarization period length according to the wavelength of the target signal light, the wavelength of the target idle light, the corresponding refractive index of the target pump light, the corresponding refractive index of the target signal light, and the corresponding refractive index of the target idle light, and inject the target pump light into the periodically polarized crystal under the target polarization period length to complete the generation of single-channel multiple entangled photon pairs.

[0125] Optionally, the polarization period determining module 21 includes:

[0126] The quasi-phase matching condition limiting unit is configured to limit the quasi-phase matching condition to include:

[0127] Conservation of Energy:

[0128]

[0129] in, represents the frequency of the pump light, represents the frequency of the generated signal light, represents the frequency of the idle light produced;

[0130] Conservation of momentum:

[0131]

[0132]

[0133]

[0134] in, represents the wave vector of the pump light, represents the wave vector of the signal light, represents the wave vector of the idle light, represents the periodic polarization vector, represents the order of quasi-phase matching, represents the wave vector, Express Take the absolute value, represents the refractive index of the light beam when it propagates in the crystal, represents the wavelength of the light beam, represents the polarization period.

[0135] Optionally, the polarization period determining module 21 further includes:

[0136] The polarization period limiting unit is used to limit the first polarization period and the second polarization period with respect to the wavelength and the refractive index to be:

[0137] The first polarization period is:

[0138]

[0139] in, represents the first polarization period, represents the wavelength of the signal light, represents the wavelength of idle light, Indicates that the pump light in the nonlinear crystal The refractive index of the direction, Indicates that the signal light in the nonlinear crystal The refractive index of the direction, Indicates that idle light in the nonlinear crystal The refractive index of the direction, represents the order of quasi-phase matching;

[0140] The second polarization period is:

[0141]

[0142] in, represents the second polarization period, Indicates that the signal light in the nonlinear crystal The refractive index of the direction, Indicates that idle light in the nonlinear crystal The refractive index of the direction.

[0143] Optionally, the wavelength and refractive index determination module 22 includes:

[0144] The constraint construction unit is configured to implement the constraint that the length of the first polarization period is equal to the length of the second polarization period, and the signal light wavelength is not equal to the idle light wavelength. The method is:

[0145] limited Then, based on the expression of the first polarization period and the expression of the second polarization period, the following constraint formula is derived:

[0146]

[0147] The ratio of the target signal light wavelength and the target idler light wavelength satisfies the constraint formula, so as to realize the constraint that the length of the first polarization period is equal to the length of the second polarization period, and the constraint that the signal light wavelength is not equal to the idler light wavelength.

[0148] Optionally, the wavelength and refractive index determination module 22 further comprises:

[0149] A wavelength and refractive index calculation unit is configured to determine, based on a Sellmeier dispersion formula, an optimal dispersion relationship equation representing the wavelength and the refractive index in the nonlinear crystal:

[0150]

[0151] wherein, n represents the refractive index, λ represents the wavelength, and are Sellmeier coefficients obtained through a least square fitting process;

[0152] The corresponding refractive index of the target pump light is determined according to the optimal dispersion relationship equation, and the corresponding refractive index of the target pump light, the corresponding refractive index of the target signal light, and the corresponding refractive index of the target idler light are determined in combination with the energy conservation condition. The wavelength of the target signal light and the wavelength of the target idler light are further determined in combination with the constraint formula.

[0153] Optionally, the entangled light generation module 23 comprises:

[0154] A target polarization period length determination unit is configured to calculate the first polarization period or the second polarization period according to the wavelength of the target signal light, the wavelength of the target idler light, the corresponding refractive index of the target pump light, the corresponding refractive index of the target signal light, and the corresponding refractive index of the target idler light, so as to calculate the length of the first polarization period or the length of the second polarization period as the length of the target polarization period.

[0155] Optionally, the apparatus further comprises:

[0156] A crystal type determination module is configured to determine that the nonlinear crystal is a potassium titanyl phosphate crystal, and the periodically poled crystal is a periodically poled potassium titanyl phosphate crystal.

[0157] It should be noted that the information interaction, execution process and other contents between the above modules are based on the same concept as the embodiment of the method of the present invention. Their specific functions and technical effects can be found in the method embodiment part and will not be repeated here.

[0158] Figure 8 This is a schematic diagram of the structure of a computer device provided in the third embodiment of the present invention. Figure 8 As shown, the computer device of this embodiment includes: at least one processor ( Figure 8 Only one is shown), a memory, and a computer program stored in the memory and executable on at least one processor, wherein when the processor executes the computer program, the steps of any of the above-mentioned health prediction method embodiments are implemented.

[0159] The computer device may include, but is not limited to, a processor and a memory. It will be understood by those skilled in the art that Figure 8 The above is merely an example of a computer device and does not constitute a limitation on the computer device. The computer device may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, it may also include a network interface, a display screen, and an input device.

[0160] The processor may be a CPU, other general-purpose processors, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0161] Memory includes readable storage media, internal memory, and the like. Internal memory can be the internal memory of a computer device, providing an environment for the operation of the operating system and computer-readable instructions stored in the readable storage medium. The readable storage medium can be the computer device's hard drive. In other embodiments, it can also be an external storage device, such as a plug-in hard drive, a Smart Media Card (SMC), a Secure Digital (SD) card, or a flash memory card. Furthermore, memory can include both the computer device's internal storage unit and external storage devices. Memory is used to store the operating system, application programs, boot loaders, data, and other programs, such as the program code of computer programs. Memory can also be used to temporarily store data that has been output or is about to be output.

[0162] Those skilled in the art can clearly understand that, for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In actual applications, the above-mentioned functions can be distributed and completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiment can be integrated into a processing unit, or each unit can exist physically alone, or two or more units can be integrated into one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of a software functional unit. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other and are not used to limit the scope of protection of the present invention. The specific working process of the units and modules in the above-mentioned device can refer to the corresponding process in the aforementioned method embodiment, which will not be repeated here. If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention can implement all or part of the process steps in the above-mentioned method embodiments by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When executed by a processor, the computer program can implement the steps of the above-mentioned method embodiments. The computer program includes computer program code, which can be in source code form, object code form, executable file, or some intermediate form. Computer-readable media can include at least: any entity or device capable of carrying computer program code, recording media, computer memory, read-only memory (ROM), random access memory (RAM), electric carrier signals, telecommunications signals, and software distribution media. Examples include USB flash drives, removable hard drives, magnetic disks, or optical disks. In some jurisdictions, based on legislation and patent practice, computer-readable media cannot be electric carrier signals or telecommunications signals.

[0163] The present invention may implement all or part of the processes in the above-mentioned method embodiments, and may also be completed through a computer program product. When the computer program product runs on a computer device, the computer device can implement the steps in the above-mentioned method embodiments when executing the computer program product.

[0164] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant description of other embodiments.

[0165] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present invention.

[0166] In the embodiments provided by the present invention, it should be understood that the disclosed apparatus / computer equipment and methods can be implemented in other ways. For example, the apparatus / computer equipment embodiments described above are merely illustrative. For example, the division of modules or units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0167] Units described as separate components may or may not be physically separate, and components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0168] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention, and should all be included in the scope of protection of the present invention.

Claims

1. A method for generating multiple entangled photon pairs in a single channel, characterized in that: The method comprises: According to the quasi-phase matching conditions that the nonlinear crystal must meet during optical parametric down-conversion, determine the first polarization period and the second polarization period of the nonlinear crystal with respect to the wavelength and the refractive index during the type II quasi-phase matching process, wherein the first polarization period represents the polarization period when the signal light is vertically polarized and the idle light is horizontally polarized, and the second polarization period represents the polarization period when the signal light is horizontally polarized and the idle light is vertically polarized; Under the constraints that the length of the first polarization period is equal to the length of the second polarization period, and that the wavelength of the signal light is not equal to the wavelength of the idle light, determining the wavelength of the target signal light and the wavelength of the target idle light corresponding to the target pump light of known wavelength, as well as the refractive index corresponding to the target pump light, the refractive index corresponding to the target signal light, and the refractive index corresponding to the target idle light; The target polarization period length is determined according to the wavelength of the target signal light, the wavelength of the target idle light, the corresponding refractive index of the target pump light, the corresponding refractive index of the target signal light, and the corresponding refractive index of the target idle light. The target pump light is injected into the periodically polarized crystal under the target polarization period length to complete the generation of single-channel multiple entangled photon pairs.

2. The method for generating multiple entangled photon pairs in a single channel according to claim 1, characterized in that: The quasi-phase matching conditions include: Conservation of Energy: ， in, represents the frequency of the pump light, represents the frequency of the generated signal light, represents the frequency of the idle light produced; Conservation of momentum: ， ， ， in, represents the wave vector of the pump light, represents the wave vector of the signal light, represents the wave vector of the idle light, represents the periodic polarization vector, represents the order of quasi-phase matching, represents the wave vector, Express Take the absolute value, represents the refractive index of the light beam when it propagates in the crystal, represents the wavelength of the light beam, represents the polarization period.

3. The method for generating multiple entangled photon pairs in a single channel according to claim 2, characterized in that: The first polarization period and the second polarization period with respect to wavelength and refractive index are respectively: The first polarization period is: ， in, represents the first polarization period, represents the wavelength of the signal light, represents the wavelength of idle light, Indicates that the pump light in the nonlinear crystal The refractive index of the direction, Indicates that the signal light in the nonlinear crystal The refractive index of the direction, Indicates that idle light in the nonlinear crystal The refractive index of the direction, represents the order of quasi-phase matching; The second polarization period is: ， in, represents the second polarization period, Indicates that the signal light in the nonlinear crystal The refractive index of the direction, Indicates that idle light in the nonlinear crystal The refractive index of the direction.

4. The method for generating multiple entangled photon pairs in a single channel according to claim 3, characterized in that: The method for implementing the constraint that the length of the first polarization period is equal to the length of the second polarization period, and the constraint that the signal light wavelength is not equal to the idle light wavelength is: limited , and then based on the expression of the first polarization period and the expression of the second polarization period, the following constraint formula is derived: ， The ratio of the target signal light wavelength to the target idle light wavelength is limited to satisfy the constraint formula, so as to realize the constraint that the length of the first polarization period is equal to the length of the second polarization period, and the constraint that the signal light wavelength is not equal to the idle light wavelength.

5. The method for generating multiple entangled photon pairs in a single channel according to claim 4, characterized in that: The determining of the wavelength of the target signal light and the wavelength of the target idle light corresponding to the target pump light with a known wavelength, as well as the refractive index corresponding to the target pump light, the refractive index corresponding to the target signal light, and the refractive index corresponding to the target idle light includes: The optimal dispersion relation equation for characterizing wavelength and refractive index in the nonlinear crystal is determined based on the Sellmeier dispersion formula: ， in, represents the refractive index, represents the wavelength, as well as These are the Sellmeier coefficients obtained by the least squares fitting process; The refractive index corresponding to the target pump light is determined according to the optimal dispersion relation equation, and the refractive index corresponding to the target pump light, the refractive index corresponding to the target signal light, and the refractive index corresponding to the target idle light are further determined in combination with the energy conservation condition. The wavelength of the target signal light and the wavelength of the target idle light are further determined in combination with the constraint formula.

6. The method for generating multiple entangled photon pairs in a single channel according to claim 5, characterized in that: The determining of the target polarization period length according to the wavelength of the target signal light, the wavelength of the target idle light, the corresponding refractive index of the target pump light, the corresponding refractive index of the target signal light, and the corresponding refractive index of the target idle light includes: The first polarization period or the second polarization period is calculated according to the wavelength of the target signal light, the wavelength of the target idle light, the corresponding refractive index of the target pump light, the corresponding refractive index of the target signal light, and the corresponding refractive index of the target idle light, so as to use the calculated length of the first polarization period or the calculated length of the second polarization period as the length of the target polarization period.

7. The method for generating multiple entangled photon pairs in a single channel according to any one of claims 1 to 6, characterized in that: The nonlinear crystal is a potassium titanyl phosphate crystal, and the periodically poled crystal is a periodically poled potassium titanyl phosphate crystal.

8. A single-channel multi-entangled photon pair generation device, characterized in that: The device comprises: a polarization period determination module, configured to determine, based on a quasi-phase matching condition that the nonlinear crystal must satisfy during optical parametric down-conversion, a first polarization period and a second polarization period of the nonlinear crystal with respect to wavelength and refractive index during a type II quasi-phase matching process, wherein the first polarization period represents a polarization period when the signal light is vertically polarized and the idle light is horizontally polarized, and the second polarization period represents a polarization period when the signal light is horizontally polarized and the idle light is vertically polarized; a wavelength and refractive index determination module, configured to determine the wavelength of target signal light and target idle light corresponding to target pump light of known wavelength, as well as the refractive index corresponding to the target pump light, the refractive index corresponding to the target signal light, and the refractive index corresponding to the target idle light, based on the constraints that the length of the first polarization period is equal to the length of the second polarization period and the constraints that the wavelength of the signal light is not equal to the wavelength of the idle light; An entangled light generation module is used to determine a target polarization period length based on the wavelength of the target signal light, the wavelength of the target idle light, the corresponding refractive index of the target pump light, the corresponding refractive index of the target signal light, and the corresponding refractive index of the target idle light, and to inject the target pump light into a periodically polarized crystal with the target polarization period length to complete the generation of single-channel multiple entangled photon pairs.

9. A computer device, characterized in that: The computer device includes a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the single-channel multi-entangled photon pair generation method according to any one of claims 1 to 7 is implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the single-channel multi-entangled photon pair generation method according to any one of claims 1 to 7 is implemented.

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