Reflection type four-photon entanglement source

Abstract

The invention discloses a reflection-type four-photon entanglement source, and the source comprises a light source assembly which generates pump light, focuses the pump light, and emits a first focusing light beam; the conversion assembly comprises a conversion crystal and a concave reflector, and the concave reflector is used for focusing the light beam penetrating through the conversion crystal and reflecting a second focused light beam; the conversion crystal is used for generating two groups of first parametric light beams after receiving the first focused light beam and generating two groups of second parametric light beams after receiving the second focused light beam; each group of first parametric light beams is compensated through one group of compensation components to form a first compensation light beam; each group of second parametric light beams is compensated through a compensation assembly to form a second compensation light beam; one first compensation light beam and one second compensation light beam are combined through the combination assembly to form two combined light beams. According to the invention, two groups of first parameter light beams and two groups of second parameter light beams are generated through the conversion crystal so as to prepare for forming a four-photon entanglement source.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photon entanglement source generation, in particular to a reflection type four-photon entanglement source. BACKGROUND

[0002] Quantum mechanics originated in the 19th century, and quantum entanglement is the most basic property in quantum mechanics, which is an important difference between the quantum world and the classical world. At present, the focus of research of many quantum entanglement research teams is mainly on the preparation and application of multi-photon entangled states. Multi-photon entangled states are formed by overlapping, post-selection and other technologies of beam splitters, so that multiple entangled photon pairs are coherently superimposed.

[0003] There are several methods for generating entangled photon pairs at present, but the most commonly used and the easiest one is spontaneous parametric down-conversion (SPDC). The spontaneous parametric down-conversion process can be divided into type I parametric down-conversion and type II parametric down-conversion according to the phase matching of the crystal. For type I spontaneous parametric down-conversion process, it can be expressed as e→o+o or o→e+e. In which, the pump light undergoes spontaneous parametric down-conversion in the type I nonlinear crystal to pump out two signal lights and idler lights with the same polarization. Type II parametric down-conversion can be expressed as e→e+o or o→e+o, which means that the pump light generates two signal lights and idler lights with different polarizations in the type II parametric down-conversion process. The pump light undergoes the SPDC process on the type II nonlinear crystal to form two conical signal lights and idler lights. The distance between the two conical surfaces depends on the cutting angle of the crystal. When the cutting surfaces of the two cones become two intersecting circles, the photons at the intersection point are a pair of entangled photons.

[0004] In the prior art, when preparing a multi-photon entanglement source, multiple crystals are used in a cascading manner to generate multi-photon entanglement. However, the use of multiple crystals will cause the multi-photon entanglement source device to have a large space, which is not conducive to integration and miniaturization. SUMMARY

[0005] The present application provides a reflection type four-photon entanglement source, which reduces the occupied space of the entanglement source and is easy to integrate. Specifically, it comprises:

[0006] A light source assembly generates pump light and emits a first focused light beam after focusing;

[0007] A conversion assembly includes a conversion crystal and a concave mirror, wherein the concave mirror is used to focus and reflect a second focused light beam through the conversion crystal; the conversion crystal is used to generate two groups of first parametric light beams after receiving the first focused light beam, and generate two groups of second parametric light beams after receiving the second focused light beam;

[0008] a compensation assembly, each group of first parametric light beams is compensated by a compensation assembly to form a first compensation light beam; each group of second parametric light beams is compensated by a compensation assembly to form a second compensation light beam; wherein the compensation includes time compensation and space compensation;

[0009] a joint assembly, wherein a first compensation light beam and a second compensation light beam are combined by the joint assembly to form two combined light beams.

[0010] Further, the light source assembly includes a laser, a first focusing lens, an I-type BBO crystal, a dichroic mirror, a short-wave pass filter, and a second focusing lens, wherein,

[0011] The light emitted by the laser passes through the first focusing lens, the I-type BBO crystal, the dichroic mirror, the short-wave pass filter, and the second focusing lens in sequence to emit a first focused light beam.

[0012] Further, the conversion crystal includes a first 1 / 2 wave plate, a first II-type BBO crystal, and a second II-type BBO crystal, wherein,

[0013] The first II-type BBO crystal and the second II-type BBO crystal are arranged in parallel, and the first 1 / 2 wave plate is arranged between the first II-type BBO crystal and the second II-type BBO crystal.

[0014] Further, the first focused light beam passes through the first II-type BBO crystal, the first 1 / 2 wave plate, and the second II-type BBO crystal in sequence to generate two groups of first parametric light beams.

[0015] Further, the first focused light beam passes through the first II-type BBO crystal, the first 1 / 2 wave plate, and the second II-type BBO crystal in sequence, and the transmitted light beam is focused by a concave mirror to reflect a second focused light beam. The second focused light beam passes through the second II-type BBO crystal, the first 1 / 2 wave plate, and the first II-type BBO crystal in sequence to generate two groups of second parametric light beams.

[0016] Further, the compensation assembly includes a lithium niobate crystal, a collimating lens, and a yttrium vanadate crystal, wherein,

[0017] A group of first parametric light beams passes through the collimating lens, the lithium niobate crystal, and the yttrium vanadate crystal in the corresponding compensation assembly in sequence to be compensated to form a first compensation light beam.

[0018] A group of second parametric light beams passes through the collimating lens, the lithium niobate crystal, and the yttrium vanadate crystal in the compensation assembly in sequence to be compensated to form a second compensation light beam.

[0019] Further, the joint assembly includes a delay line and a polarization beam splitter, wherein,

[0020] The one of the first compensation light beams and the one of the second compensation light beams are combined by a polarization beam splitter to form two combined light beams.

[0021] Further, a polarization detection assembly is further included, and the other first compensation light beam, the other second compensation light beam and the two combined light beams are subjected to polarization detection treatment by the polarization detection assembly to measure the polarization of the photons as a basis for judging the entanglement source quality.

[0022] Further, the polarization detection assembly includes an interference filter and a polarizer, wherein the other first compensation light beam, the other second compensation light beam and the two combined light beams are incident to the interference filter in the corresponding polarization detection assembly, and then are incident to the polarizer in the corresponding polarization detection assembly.

[0023] Further, a right-angle reflection prism is further included, wherein each of the first light beams and each of the second light beams is incident to the collimating lens of the corresponding compensation assembly after passing through the right-angle reflection prism.

[0024] Further, the combination assembly further includes a second 1 / 2 wave plate, wherein the one of the second compensation light beams is incident to the polarization beam splitter after passing through the second 1 / 2 wave plate.

[0025] Further, a detection assembly is further included, wherein the detection assembly includes a collimator and a detector, and the light beam emitted by the polarizer is incident to the detector in the detection assembly after passing through the collimator in the detection assembly.

[0026] Further, a non-true zero-order 1 / 4 wave plate is further included, wherein the one of the combined light beams is incident to the interference filter in the corresponding polarization detection assembly after passing through the non-true zero-order 1 / 4 wave plate.

[0027] The reflective four-photon entanglement source of the present application generates two groups of first light beams through a conversion crystal, and then focuses the light beams transmitted by the first focusing light beams through the conversion crystal and a concave mirror to form two groups of second light beams, thereby preparing for forming a four-photon entanglement source. In addition, the conversion crystal for generating the first light beams is used in the present application to generate the second light beams, and the structure is more compact and convenient to integrate compared with the cascade scheme. BRIEF DESCRIPTION OF DRAWINGS

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0029] Figure 1 This is a top-view structural diagram of a reflective four-photon entangled source according to the present invention;

[0030] Figure 2 This is a schematic diagram of the structure of the conversion crystal of the present invention.

[0031] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and the accompanying drawings. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] It should be noted that all directional indications in the embodiments of the present invention, such as up, down, left, right, front, back, etc., are only used to explain the relative positional relationship and movement of the components in a specific posture as shown in the attached figure. If the specific posture changes, the directional indication will also change accordingly.

[0034] Furthermore, the use of terms such as "first" and "second" in this invention is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0035] like Figure 1 As shown, an embodiment of the present invention provides a reflective four-photon entangled source, comprising the following components:

[0036] Light source component 1 generates pump light, which is then focused to emit a first focused beam;

[0037] The conversion assembly 2 comprises a conversion crystal 21 and a concave mirror 22, wherein the concave mirror 22 is used for focusing and reflecting the light beam transmitted through the conversion crystal 21 to form a second focused light beam; the conversion crystal 21 is used for generating two groups of first parametric light beams after receiving a first focused light beam and generating two groups of second parametric light beams after receiving a second focused light beam;

[0038] The compensation assembly 3 is used for compensating each group of first parametric light beams to form a first compensation light beam and compensating each group of second parametric light beams to form a second compensation light beam; wherein the compensation comprises time compensation and space compensation;

[0039] The joint assembly 4 is used for combining a first compensation light beam and a second compensation light beam to form two joint light beams.

[0040] In some embodiments of the present application, the light source assembly 1 comprises a laser 11, a first focusing lens 12, an I-type BBO crystal 13, a dichroic mirror 14, a short-wave pass filter 15 and a second focusing lens 16.

[0041] In some embodiments of the present application, based on the above-mentioned structure of the light source assembly 1, the laser 11 emits light which, after sequentially passing through the first focusing lens 12, the I-type BBO crystal 13, the dichroic mirror 14, the short-wave pass filter 15 and the second focusing lens 16, emits a first focused light beam. An example is given as follows:

[0042] In the example, the laser 11 is an ultrafast fiber laser which emits laser pulses with a center wavelength of 780 nm. The light source assembly 1 can have the following working process:

[0043] The 780 nm laser pulses emitted by the ultrafast fiber laser are focused on the I-type BBO crystal 13 after passing through the first focusing lens 12, and generate 390 nm wavelength pulses by frequency doubling. The 390 nm wavelength light is reflected after passing through the dichroic mirror 14, and the 780 nm wavelength laser pulses are transmitted and can be collected by a light garbage can. The reflected 390 nm wavelength light is used as pump light which is further filtered by the short-wave pass filter 15 to remove residual 780 nm light, and then is focused by the lens 16 to emit a first focused light beam.

[0044] In some embodiments of the present application, as Figure 2As shown, the conversion crystal 21 in the conversion assembly 1 includes a first 1 / 2 wave plate 211, a first II-type BBO crystal 212, and a second II-type BBO crystal 213, wherein the first II-type BBO crystal 212 and the second II-type BBO crystal 213 are arranged in parallel, and the first 1 / 2 wave plate 211 is arranged between the first II-type BBO crystal 212 and the second II-type BBO crystal 213.

[0045] In some embodiments of the present application, based on the above-mentioned conversion crystal 21 configuration, the first focused light beam generates two groups of first parametric light beams after sequentially passing through the first II-type BBO crystal 212, the first 1 / 2 wave plate 211, and the second II-type BBO crystal 213. An example is given as follows:

[0046] In some embodiments of the present application, the first 1 / 2 wave plate 211 is selected as a 1 / 2 wave plate with a working wavelength of 780 nm, wherein the 1 / 2 wave plate is arranged at an angle of 45°. An example is given as follows:

[0047] After the first focused light beam passes through the entire conversion crystal 21, two groups of first parametric light beams with a wavelength of 780 nm are generated, which are a group of first o light 214 (i.e., one group of first parametric light beams) and a group of first e light 215 (i.e., another group of first parametric light beams). The first o light 214 is ordinary light, which is V-polarized, and the first e light 215 is extraordinary light, which is H-polarized. After passing through the first 1 / 2 wave plate in the conversion crystal 21, the first o light 214 becomes H-polarized, and the first e light 215 becomes V-polarized. Since the working wavelength of the first 1 / 2 wave plate 211 is 780 nm, the polarization of the pump light is not changed, and the first o light 214 passing through the second II-type BBO crystal 213 is V-polarized, and the first e light 215 is H-polarized. The polarization of the pump light is H-polarized.

[0048] In some embodiments of the present application, the concave mirror 22 in the conversion assembly 1 can focus the light beam transmitted through the conversion crystal 21 and reflect the second focused light beam. That is, after the first focused light beam sequentially passes through the first II-type BBO crystal 212, the first 1 / 2 wave plate 211, and the second II-type BBO crystal 213, the transmitted light beam is focused by the concave mirror 22 and reflects the second focused light beam. The second focused light beam sequentially passes through the second II-type BBO crystal 213, the first 1 / 2 wave plate 211, and the first II-type BBO crystal 212 to generate two groups of second parametric light beams. An example is given as follows:

[0049] The second focused light beam passes through the entire conversion crystal 21 to generate two groups of second parametric light beams with a wavelength of 780 nm, that is, one group of second o light 216 (that is, one group of second parametric light beams) and one group of second e light 217 (that is, another group of second parametric light beams). The second o light 216 is ordinary light, which is V-polarized, and the second e light 217 is extraordinary light, which is H-polarized. After passing through the second 1 / 2 wave plate in the conversion crystal 21, the second o light 216 becomes H-polarized, and the second e light 217 becomes V-polarized. Since the first 1 / 2 wave plate 211 has a working wavelength of 780 nm, the polarization of the pump light is not changed, and the second o light 216 passing through the first II-type BBO crystal 213 is V-polarized, and the second e light 217 is H-polarized. The polarization of the pump light is H-polarized.

[0050] In some embodiments of the present application, the compensation assembly 3 includes a lithium niobate crystal 31, a collimating lens 32, and a yttrium vanadate crystal 33. One group of first parametric light beams is compensated after sequentially passing through the collimating lens 32, the lithium niobate crystal 31, and the yttrium vanadate crystal 33 in the corresponding compensation assembly 3 to form a first compensation light beam, and another group of first parametric light beams also corresponds to form another first compensation light beam. One group of second parametric light beams is compensated after sequentially passing through the collimating lens 32, the lithium niobate crystal 31, and the yttrium vanadate crystal 33 in the corresponding compensation assembly 3 to form a second compensation light beam, and another group of second parametric light beams also corresponds to form another second compensation light beam. An example is given below:

[0051] In this example, two groups of first parametric light beams with a wavelength of 780 nm, Figure 1 The left group of first o light 214 includes two beams of first o light 214 Figure 1 (not shown in the middle, only one beam is shown), which are spatially coincident after passing through the corresponding lithium niobate crystal 31, achieving spatial compensation, then incident on the corresponding collimating lens 32, and collimated by the collimating lens 32 to be incident on the yttrium vanadate crystal 33. After passing through the yttrium vanadate crystal 33, they are temporally coincident, achieving temporal compensation, and finally forming one beam of first compensation light. Figure 1 The right group of first e light 215 includes two beams of first e light 215 Figure 1 (not shown in the middle, only one beam is shown), which are spatially coincident after passing through the corresponding lithium niobate crystal 31, achieving spatial compensation, then incident on the corresponding collimating lens 32, and collimated by the collimating lens 32 to be incident on the yttrium vanadate crystal 33. After passing through the yttrium vanadate crystal 33, they are temporally coincident, achieving temporal compensation, and finally forming another beam of first compensation light.

[0052] In this example, two groups of second parametric light beams with a wavelength of 780 nm, Figure 1 The right group of second o light 216 includes two beams of second o light 216Figure 1 The two beams are not shown in the figure, only one beam is shown, which is spatially overlapped after passing through the corresponding lithium niobate crystal 31, achieving spatial compensation, then is incident to the corresponding collimating lens 32, and is collimated by the collimating lens 32 and then is incident to the yttrium vanadate crystal 33, and after passing through the yttrium vanadate crystal 33, is temporally overlapped, achieving temporal compensation, that is, finally forming another second compensation light beam. Figure 1 The left group of second e light 217 contains two first e light beams 217 Figure 1 The two beams are not shown in the figure, only one beam is shown, which is spatially overlapped after passing through the corresponding lithium niobate crystal 31, achieving spatial compensation, then is incident to the corresponding collimating lens 32, and is collimated by the collimating lens 32 and then is incident to the yttrium vanadate crystal 33, and after passing through the yttrium vanadate crystal 33, is temporally overlapped, achieving temporal compensation, that is, finally forming another second compensation light beam.

[0053] In this embodiment, the lithium niobate crystal 31 is used to compensate for the spatial misalignment caused by the two type II BBO crystals 213, and the yttrium vanadate crystal 31 is used to compensate for the temporal misalignment caused by the two crystals. After passing through the lithium niobate crystal and the yttrium vanadate crystal, the parametric light generated by different type II BBO crystals is indistinguishable in space and time, that is, compensation is performed. The collimating lens 32 is used to change the corresponding parametric light into a collimated light beam, which is convenient for subsequent collection.

[0054] In addition, in some embodiments of the present application, the entanglement source further comprises a right-angle reflection prism 8, wherein each group of first parametric light beams and each group of second parametric light beams are incident to the collimating lens 32 of the corresponding compensation assembly 3 after passing through a right-angle reflection prism 8.

[0055] In some embodiments of the present application, since there is a time difference and a spatial difference between one of the first compensation light beams and one of the second compensation light beams, compensation is needed for the two compensation light beams. Therefore, in the present application, the joint assembly 4 comprises a delay line 41, a polarization beam splitter 42 and a second 1 / 2 wave plate 43, wherein the one of the first compensation light beams (i.e. the first compensation light beam after compensation of the first e light 215) is temporally compensated between the delay line 41 and the one of the second compensation light beams, and then the one of the second compensation light beams (i.e. the second compensation light beam after compensation of the second e light 217) and the one of the second compensation light beams after passing through the second 1 / 2 wave plate 43 are spatially overlapped by the polarization beam splitter 42, thereby finally being jointed to form two joint light beams. In this embodiment, the premise of forming the joint light beam is that the polarizations of the two incident compensation light beams are orthogonal. Since the polarizations of the one of the first compensation light beams and the one of the second compensation light beams are the same, a second 1 / 2 wave plate 43 with an angle of 45° is arranged to rotate the polarization of the one of the second compensation light beams by 90°, so that the polarization of the one of the second compensation light beams is orthogonal to the polarization of the one of the first compensation light beams.

[0056] In some embodiments of the present application, the entanglement source further comprises a non-true zero-order 1 / 4 wave plate 7, and one of the two joint beams passes through the non-true zero-order 1 / 4 wave plate 7 and then enters the interference filter 51 in the corresponding polarization component 5, the non-true zero-order 1 / 4 wave plate 7 can compensate the phase difference between the corresponding joint beam and the other joint beam, and the angle of the non-true zero-order 1 / 4 wave plate 7 can be adjusted as needed.

[0057] In some embodiments of the present application, the entanglement source further comprises a polarization component 5, wherein the other first compensation beam, the other second compensation beam and the two joint beams pass through the polarization component 5 for polarization processing, and the polarization of the photons is measured as the basis for judging the quality of the entanglement source.

[0058] In some embodiments of the present application, the polarization component 5 comprises an interference filter 51 and a polarizer 52, wherein the first compensation beam, the second compensation beam and the two joint beams that are not combined all enter the interference filter 51 in the corresponding polarization component 5, and then enter the polarizer 52 in the corresponding polarization component 5, so that the polarization of the photons is measured as the basis for judging the quality of the entanglement source. Figure 1 In the first o light forming a compensation beam, for example, the following is specific:

[0059] The first compensation beam formed by the first o light 214 narrows the spectrum of the first compensation beam after passing through the interference filter 51, for example, 3nm, and improves the interference visibility of the photons, and the first compensation beam after passing through the interference filter passes through the polarizer 52 for state tomography.

[0060] In some embodiments of the present application, the detection component 6 comprises a collimator 61 and a detector 62, wherein the light beam emitted by the polarizer 52 passes through the collimator 61 in the detection component 6 and then enters the detector 62 in the detection component 6, and the parametric light is coupled into a single-mode optical fiber through the collimator 61, and then input into the detector 62, for example, a single-photon detector.

[0061] The above only describes the preferred embodiments of the present application, and does not limit the patent scope of the present application, and any equivalent structural transformation made by using the content of the present application specification and drawings, or direct / indirect application in other related technical fields is included in the patent protection scope of the present application.

Claims

1. A reflective four-photon entangled source, characterized in that, The application relates to a light source assembly (1) for generating pump light and focusing the pump light into a first focused light beam; a conversion assembly (2) for focusing light beams transmitted through a conversion crystal (21) into a second focused light beam by means of a concave mirror (22), wherein the conversion crystal (21) is arranged to generate two groups of first parametric light beams upon receiving the first focused light beam and two groups of second parametric light beams upon receiving the second focused light beam; a compensation assembly (3) for compensating each group of first parametric light beams to form a first compensated light beam and for compensating each group of second parametric light beams to form a second compensated light beam, wherein the compensation comprises time compensation and spatial compensation; and a combination assembly (4) for combining one first compensated light beam and one second compensated light beam to form two combined light beams. The light source assembly (1) comprises a laser (11), a first focusing lens (12), an I-type BBO crystal (13), a dichroic mirror (14), a short-wave-pass filter (15) and a second focusing lens (16), wherein the laser (11) emits light which is sequentially transmitted through the first focusing lens (12), the I-type BBO crystal (13), the dichroic mirror (14), the short-wave-pass filter (15) and the second focusing lens (16) to form the first focused light beam. The conversion crystal (21) comprises a first 1 / 2 wave plate (211), a first II-type BBO crystal (212) and a second II-type BBO crystal (213), wherein the first II-type BBO crystal (212) and the second II-type BBO crystal (213) are arranged in parallel, and the first 1 / 2 wave plate (211) is arranged between the first II-type BBO crystal (212) and the second II-type BBO crystal (213). The first focused light beam is sequentially transmitted through the first II-type BBO crystal (212), the first 1 / 2 wave plate (211) and the second II-type BBO crystal (213) to generate two groups of first parametric light beams. The first focused light beam is sequentially transmitted through the first II-type BBO crystal (212), the first 1 / 2 wave plate (211) and the second II-type BBO crystal (213), and the light beams transmitted through the second II-type BBO crystal (213), the first 1 / 2 wave plate (211) and the first II-type BBO crystal (212) are focused by the concave mirror (22) to form the second focused light beam which is sequentially transmitted through the second II-type BBO crystal (213), the first 1 / 2 wave plate (211) and the first II-type BBO crystal (212) to generate two groups of second parametric light beams.

2. The entanglement source of claim 1, wherein, The compensation assembly (3) comprises a lithium niobate crystal (31), a collimating lens (32) and a yttrium vanadate crystal (33), wherein each group of first parametric light beams is sequentially transmitted through the collimating lens (32), the lithium niobate crystal (31) and the yttrium vanadate crystal (33) in the corresponding compensation assembly (3) to form a first compensated light beam; and each group of second parametric light beams is sequentially transmitted through the collimating lens (32), the lithium niobate crystal (31) and the yttrium vanadate crystal (33) in the corresponding compensation assembly (3) to form a second compensated light beam. ​ 3. The entanglement source of claim 1, wherein, ​ ​ 4. The entanglement source of claim 3, wherein, ​ 5. The entanglement source of claim 3, wherein, ​ 6. The entanglement source of any one of claims 1-5, wherein, ​ ​ A group of second parametric light beams are compensated after passing through a collimating lens (32), a lithium niobate crystal (31) and a yttrium vanadate crystal (33) in a group of compensation assemblies (3) in sequence to form second compensation light beams.

7. The entanglement source of any one of claims 1-5, wherein, The combination assembly (4) comprises a delay line (41) and a polarization beam splitter (42), wherein, One of the first compensation light beams passes through the delay line (41) and is combined with one of the second compensation light beams to form two combined light beams.

8. The entanglement source of any one of claims 1-5, wherein, The detection assembly (5) is further included, and the other first compensation light beam, the other second compensation light beam and the two combined light beams pass through the detection assembly (5) for polarization detection to measure the polarization of the photons as a basis for judging the quality of the entanglement source.

9. The entanglement source of claim 8, wherein, The detection assembly (5) comprises an interference filter (51) and a polarizer (52), wherein the other first compensation light beam, the other second compensation light beam and the two combined light beams are incident to the interference filter (51) in the corresponding detection assembly (5) and then to the polarizer (52) in the corresponding detection assembly (5).

10. The entanglement source of claim 8, wherein, The right-angle reflection prism (8) is further included, wherein each of the first parametric light beams and each of the second parametric light beams passes through the right-angle reflection prism (8) and is incident to the collimating lens (32) of the corresponding compensation assembly (3).

11. The entanglement source of claim 7, wherein, The combination assembly (4) further comprises a second 1 / 2 wave plate (43), wherein one of the second compensation light beams is incident to the polarization beam splitter (42) after passing through the second 1 / 2 wave plate (43).

12. The entanglement source of claim 7, wherein, The detection assembly (6) is further included, wherein the detection assembly (6) comprises a collimator (61) and a detector (62), and the light beam emitted by the polarizer (52) passes through the collimator (61) in the detection assembly (6) and is incident to the detector (62) in the detection assembly (6).

13. The entanglement source of claim 7, wherein, The non-true zero-order 1 / 4 wave plate (7) is further included, wherein one of the combined light beams is incident to the interference filter (51) in the corresponding detection assembly (5) after passing through the non-true zero-order 1 / 4 wave plate (7).

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