A single-photon dual-degree-of-freedom entanglement generation and measurement experimental device

Abstract

The present invention relates to the field of quantum information and communication, and specifically to a single-photon dual-degree-of-freedom entanglement generation and measurement experimental device. The device includes a correlation photon source module and an entangled state preparation module arranged in sequence along the optical path direction; the correlation photon source module is used to generate a spin single-photon beam; the entangled state preparation module is used to generate a single-photon beam of spin-orbit angular momentum entangled state from the spin single-photon beam, and the spin-orbit angular momentum entangled state is dual-degree-of-freedom entanglement. The present invention establishes an information carrier through the spin and orbital angular momentum of a single photon, and can construct an infinite-dimensional Hilbert space, rather than being limited to a two-dimensional Hilbert space, so that the spin and orbital angular momentum of a single photon cooperate with each other and can carry infinite bits of information, thereby improving the application field of quantum communication.

Description

Technical Field

[0001] The present invention relates to the field of quantum information and communication, and in particular to a single-photon double-degree-of-freedom entanglement generation and measurement experimental device. Background Art

[0002] As a unique resource in the world of quantum physics, quantum entanglement has changed the way we process information. In the field of quantum communication, the polarization degree of freedom of two photons is usually used as an information carrier to reflect quantum entanglement, but the polarization degree of freedom can only realize the encoding of quantum in two-dimensional Hilbert space, thus limiting the application field of quantum communication. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a single-photon two-degree-of-freedom entanglement generation and measurement experimental device. By introducing the orbital angular momentum of the photon, a single photon can be used as an information carrier, thereby improving the application field of quantum communication.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A single-photon double-degree-of-freedom entanglement generation and measurement experimental device, the device comprises a correlation photon source module and an entangled state preparation module arranged in sequence along the optical path direction;

[0006] The associated photon source module is used to generate a spin single photon beam;

[0007] The entangled state preparation module is used to generate a single photon beam of spin-orbit angular momentum entangled state from a spin single photon beam, and the spin-orbit angular momentum entangled state is double-degree-of-freedom entanglement.

[0008] Further, the entangled state preparation module includes a second modulation unit and an orbital angular momentum unit which are sequentially arranged along the optical path direction of the spin single photon beam generated by the associated photon source module;

[0009] The second modulation unit is used to adjust the phase and light intensity of the spin single photon beam generated by the associated photon source module;

[0010] The orbital angular momentum unit is used to generate a single photon beam in a spin-orbital angular momentum entangled state from the spin single photon beam emitted by the second modulation unit.

[0011] Furthermore, the second modulation unit includes a second quarter-wave plate, a second half-wave plate and a third polarization beam splitter which are sequentially arranged along the optical path direction.

[0012] Furthermore, the device also includes a quantum state tomography module, which includes a third lens, a fourth quarter wave plate, a third half wave plate, a fourth polarization beam splitter, a fourth lens, and a spatial light phase modulator, which are sequentially arranged along the optical path direction of the single photon beam of spin-orbit angular momentum entangled state generated by the entangled state preparation module; the spatial light phase modulator is used to cooperate with the transverse phase diagram of the known orbital angular momentum to obtain the orbital angular momentum of the spin-orbit angular momentum single photon beam prepared by the entangled state preparation module;

[0013] The focal lengths of the third lens and the fourth lens are equal, and the distance between the third lens and the fourth lens along the optical path is twice the focal length; the distance between the third lens and the orbital angular momentum unit along the optical path is one time the focal length; and the distance between the spatial light phase modulator and the fourth lens along the optical path is one time the focal length.

[0014] Further preferably, the quantum state tomography module further includes a fifth lens and a sixth lens; an angle is set between the optical path direction of the spin orbital angular momentum single photon beam prepared by the spatial light phase modulator and the entangled state preparation module, so as to make the reflection direction of the spin orbital angular momentum single photon beam by the spatial light phase modulator deviate from the incident direction, and the fifth lens and the sixth lens are sequentially arranged along the reflection direction;

[0015] The focal length of the fifth lens is equal to the focal length of the sixth lens, and is equal to the focal length of the third lens and the focal length of the fourth lens. The distance between the fifth lens and the sixth lens along the reflection direction is twice the focal length. The distance between the spatial light phase modulator and the fifth lens along the reflection direction is one time the focal length.

[0016] The spin single-photon beam generated by the correlated photon source module includes two groups of spin single-photon beams, and the two groups of spin single-photon beams constitute correlated photon beams, one of which is injected into the entangled state preparation module; the device also includes a photon detection module, and the other group of spin single-photon beams is injected into the photon detection module; the photon detection module is used to obtain correlated photon pairs constituted by the spin single-photon beam emitted by the quantum state tomography module through the sixth lens and the other group of spin single-photon beams generated by the correlated photon source module.

[0017] Furthermore, the associated photon source module includes a laser, a first modulation unit, a first lens, a nonlinear crystal, a second lens, and a second polarization beam splitter arranged in sequence along the optical path direction; a first filter is arranged on a side of the second polarization beam splitter away from the second lens, a second filter is arranged on a side of the second polarization beam splitter adjacent to the first filter, and the optical path direction of the second filter is perpendicular to the optical path direction of the first filter; the first filter and the second filter are respectively used to emit spin single photon beams;

[0018] The first modulation unit is used to adjust the phase and light intensity of the single photon beam emitted by the laser.

[0019] Further preferably, the first modulation unit includes a first quarter wave plate, a first half wave plate and a first polarization beam splitter which are sequentially arranged along the optical path direction.

[0020] Further, the photon detection module includes a first fiber collimator, a first optical fiber, a first single-photon detector, a second fiber collimator, a second optical fiber, a second single-photon detector, and a coincidence counter;

[0021] The spin single photon beam generated by the associated photon source module enters the coincidence counter via the second fiber collimator, the second optical fiber, and the second single photon detector; the spin single photon beam emitted by the quantum state tomography module via the sixth lens enters the coincidence counter via the first fiber collimator, the first optical fiber, and the first single photon detector.

[0022] Further preferably, the first optical fiber collimator is located at the focus of the sixth lens.

[0023] Further preferably, the orbital angular momentum unit is a liquid crystal vortex wave plate, and the q value of the liquid crystal vortex wave plate is 1.

[0024] The beneficial effects of the present invention are as follows:

[0025] (1) The present invention establishes an information carrier through the spin and orbital angular momentum of a single photon, and can construct an infinite-dimensional Hilbert space instead of being limited to a two-dimensional Hilbert space. The spin and orbital angular momentum of a single photon cooperate with each other, realizing the entanglement of multiple degrees of freedom of a single photon, and can carry infinite bits of information, thereby improving the application field of quantum communication.

[0026] (2) The present invention establishes information carriers through the spin and orbital angular momentum of single photons, greatly improving the capacity and spectrum utilization of quantum communication systems. At the same time, the orbital angular momentum modes of different topological charges are orthogonal to each other, reducing mutual interference during transmission. The uncertain relationship between the topological charge of orbital angular momentum and the phase angle makes it have high communication confidentiality.

[0027] (3) The orbital angular momentum unit of the present invention is a liquid crystal vortex wave plate, which can effectively generate and regulate the coupling process of spin and orbital angular momentum, has a simple structure, high conversion efficiency, and can improve the quality of the light beam.

[0028] The correlated photon source module of the present invention prepares correlated photon pairs through nonlinear crystals, and the optical path is simple and convenient, and the correlated photon pair preparation efficiency is high.

[0029] (4) The quantum state tomography module of the present invention reduces the prepared spin orbital angular momentum single photon beam to a spin single photon beam, which forms a correlated photon pair with the sub-spin single photon beam output by the correlated photon source module. The correlated photon pair can also be used as an information carrier. Therefore, the device of the present invention can increase the number of information carriers.

[0030] In addition, the quantum state tomography module and the photon detection module of the present invention cooperate with each other. When the coincidence counter in the photon detection module collects the correlated photon pair, it indicates that the entangled state preparation module has prepared the spin-orbital angular momentum single photon beam. Otherwise, the entangled state preparation module has not prepared the spin-orbital angular momentum single photon beam. Therefore, this experimental device can verify whether the entangled state preparation module has prepared the spin-orbital angular momentum single photon beam.

[0031] (5) The spatial light phase modulator involved in the present invention performs phase deflection modulation on the incident light beam according to the phase of the incident spin-orbit angular momentum entangled single photon beam through a reverse phase diagram loaded on its liquid crystal display by a computer, so that the entangled light beam is restored to a Gaussian light beam before the entangled state preparation module, and the orbital angular momentum of the spin-orbit angular momentum single photon beam prepared by the entangled state preparation module is obtained after being collected by the detection module.

[0032] (6) The present invention uses a combination of a quarter-wave plate, a half-wave plate and a polarization beam splitter to obtain any stable phase of the photon beam and to adjust the intensity of the outgoing light of the photon beam.

[0033] (7) The focal lengths of the fifth lens, the sixth lens, the third lens and the fourth lens of the present invention are all equal, and the distance between the third lens and the fourth lens is twice the focal length, and the distance between the fifth lens and the sixth lens is also twice the focal length. Therefore, the third lens and the fourth lens constitute a 4f imaging system, and the fifth lens and the sixth lens also constitute a 4f imaging system. The dual 4f imaging system accelerates the evolution process of the orbital angular momentum of a single photon and enhances the interaction effect with the spatial light modulator.

[0034] (8) The orbital angular momentum entanglement of the present invention is a multi-dimensional entangled state, which is easier to achieve than the multi-photon entangled state and is of great significance in the field of quantum communication. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is the overall structure diagram of the present invention;

[0036] Figure 2 is a structural diagram of the associated photon source module of the present invention;

[0037] Figure 3 This is a structural diagram of the entangled state preparation module of the present invention;

[0038] Figure 4It is a structural diagram of the quantum state tomography module of the present invention;

[0039] Figure 5 is a structural diagram of the photon detection module of the present invention;

[0040] Figure 6a , 6b , 6c, 6d are transverse phase distribution diagrams of the photon orbital angular momentum of the present invention;

[0041] Figure 7a and 7b It is the experimental data density matrix result diagram of the present invention.

[0042] The meanings of the symbols in the figure are as follows:

[0043] 1-Associated photon source module 111-Laser 112-First quarter wave plate

[0044] 113 - first half-wave plate 114 - first polarization beam splitter 115 - first lens 116 - nonlinear crystal

[0045] 117 - second lens 118 - second polarization beam splitter 119 - first filter 120 - second filter

[0046] 2- entangled state preparation module 21- second quarter wave plate 22- second half wave plate

[0047] 23-third polarization beam splitter 24-orbital angular momentum unit 25-third quarter wave plate

[0048] 3-Quantum state tomography module 31-Third lens 32-Fourth quarter wave plate 33-Third half wave plate

[0049] 34- fourth polarization beam splitter 35- fourth lens 36- spatial light phase modulator 37- fifth lens

[0050] 38-Sixth lens

[0051] 4-photon detection module 41-first optical fiber collimator 42-second optical fiber collimator

[0052] 43-first optical fiber 44-second optical fiber 45-first single photon detector

[0053] 46-Second single photon detector 47-Coincidence counter DETAILED DESCRIPTION

[0054] The following is a clear and complete description of the technical solution of the present invention in combination with the embodiments and the accompanying drawings. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] A single-photon two-degree-of-freedom entanglement generation and measurement experimental device, such as Figure 1 As shown, the device includes a correlation photon source module 1, an entangled state preparation module 2, a quantum state tomography module 3 and a photon detection module 4 which are sequentially arranged along the optical path. The following describes them respectively:

[0056] like Figure 2 As shown, the associated photon source module 1 includes a laser 111, a first quarter wave plate 112, a first half wave plate 113, a first polarization beam splitter 114, a first lens 115, a nonlinear crystal 116, a second lens 117, and a second polarization beam splitter 118, which are sequentially arranged along the optical path direction; a first filter 119 is arranged on the side of the second polarization beam splitter 118 away from the second lens 117, and a second filter 120 is arranged on the side of the second polarization beam splitter 118 adjacent to the first filter 119, and the optical path direction of the second filter 120 is perpendicular to the optical path direction of the first filter 119. The first filter 119 emits a first spin single photon beam, and the second filter 120 emits a second spin single photon beam. Both the first filter 119 and the second filter 120 only allow light with a wavelength of 810 nm to pass through, and can prevent light with a wavelength of 405 nm from passing through, so as to protect the device. The nonlinear crystal 116 is a PPKTP crystal (potassium titanyl phosphate crystal) for generating correlated photon pairs of orthogonal polarizations.

[0057] The laser 111 is a semiconductor continuous laser, which serves as a pump beam to provide an initial beam for the entire device. The central wavelength of the beam is 405 nm, the spectral line width is less than 0.06 nm, and the output power can reach 66 mW.

[0058] The working wavelengths of the first quarter wave plate 112, the first half wave plate 113, and the first polarization beam splitter 114 are all 405nm. The function of the wave plate is mainly to adjust the polarization state of the light beam. The first quarter wave plate 112 and the first half wave plate 113 are combined into a wave plate group, which can modulate the pump light to any phase. The wave plate group cooperates with the first polarization beam splitter 114 to adjust the intensity of the output light beam while maintaining the phase stability of the pump light. After the 405nm pump light passes through the first quarter wave plate 112, the first half wave plate 113, and the first polarization beam splitter 114, the output is a horizontally polarized light with a phase-stable light intensity of 1mw.

[0059] The first lens 115 and the second lens 117 are lenses of the same model, with an operating wavelength of 405 nm and a focal length f of 100 mm. The first lens 115 is used to converge the horizontally polarized light beam to the center of the nonlinear crystal 116, and the second lens 117 is used to collimate the output light of the nonlinear crystal 116.

[0060] The nonlinear crystal 116 uses the spontaneous parametric down-conversion process to convert the 405nm pump light incident on the crystal into 810nm light, and the light emitted by the nonlinear crystal 116 is a mixed beam of 405nm and 810nm. The nonlinear crystal 116 is 15mm long, and the two end faces of the nonlinear crystal 116 in the light propagation direction are coated with anti-reflection films of 405nm and 810nm wavelengths. When the pump light intensity is 1mw, the generation rate of entangled photon pairs is 40000mw-1s-1, which has a high brightness.

[0061] The working center wavelength of the second polarization beam splitter 118 is 810 nm. Its function is to separate the mixed light beam into a horizontally polarized transmission light beam and a vertically polarized reflection light beam when the mixed light beam is vertically incident on its end face.

[0062] The first filter 119 is located at the end of the transmission light path of the second polarization beam splitter 118, and is used to receive and filter the horizontally polarized transmission light beam; the second filter 120 is located at the end of the reflection light path of the second polarization beam splitter 118, and receives the vertically polarized reflection light beam. The first filter 119 and the second filter 120 are the same type of bandpass filters, with a working center wavelength of 800nm ​​and a half-height width of 40nm, which filter out non-single-photon signals in the spatial light beam, complete the filtering function of the optical frequency, and are used to improve the signal-to-noise ratio of the test system.

[0063] like Figure 3 As shown, the entangled state preparation module 2 includes a second quarter wave plate 21, a second half wave plate 22, a third polarization beam splitter 23, an orbital angular momentum unit 24, and a third quarter wave plate 25, which are sequentially arranged along the optical path direction of the spin single photon beam generated by the associated photon source module 1. The orbital angular momentum unit 24 is a liquid crystal vortex wave plate; the q value of the liquid crystal vortex wave plate is 1, and q is the topological charge.

[0064] The second quarter wave plate 21 is located immediately after the first filter 119 and receives the horizontally polarized single photon beam.

[0065] The second quarter wave plate 21, the second half wave plate 22 and the third polarization beam splitter 23 all have an operating wavelength of 810 nm, and they work together to adjust the phase and output light intensity of horizontally polarized single photons.

[0066] The orbital angular momentum unit 24 is also called a liquid crystal vortex wave plate, a half-wave plate whose optical axis changes periodically in a spatial polar coordinate system, and can convert the plane wavefront of circularly polarized light (left or right) into a vortex beam with orbital angular momentum, thereby realizing the coupling of photon spin angular momentum and orbital angular momentum. The topological charge q in the liquid crystal vortex wave plate reflects the speed at which the optical axis changes with the azimuth angle. In this device, the q value of the orbital angular momentum unit 24 is 1, and the size is 9mm×9mm.

[0067] The orbital angular momentum before the incident orbital angular momentum unit 24 is zero, which can be described as follows:

[0068]

[0069] |H>|l=0> indicates that the incident photon is horizontally polarized light |H> and its orbital angular momentum is zero |l=0>. This horizontally polarized light is composed of right-handed circularly polarized light with zero orbital angular momentum |σ + > and left-handed circularly polarized light |σ - >.

[0070] After the light beam passes through the orbital angular momentum unit 24, the orbital angular momentum topological charge q is ±1, which can be described as follows:

[0071]

[0072] |Φ + > represents the entangled state of the photon after passing through the orbital angular momentum unit 24, which can be represented by the right-handed polarized light |σ + > and the orbital angular momentum is -1, i.e. |l=-1>, the left-handed polarized light composition represents |σ _ >.

[0073] The third quarter wave plate 25 has an operating wavelength of 810 nm and is used to change the polarization state characteristics of a single photon to optimize subsequent polarization projection measurement values.

[0074] like Figure 4 As shown, the quantum state tomography module 3 includes a third lens 31, a fourth quarter wave plate 32, a third half wave plate 33, a fourth polarization beam splitter 34, a fourth lens 35, a spatial light phase modulator 36, a fifth lens 37 and a sixth lens 38 arranged in sequence along the optical path. The orbital angular momentum unit 24 is located at 150 mm on the side of the third lens 31 close to the orbital angular momentum unit 24. An angle is set between the spatial light phase modulator 36 and the light emitted by the entangled state preparation module 2.

[0075] The third lens 31, the fourth lens 35, the fifth lens 37 and the sixth lens 38 are lenses of the same model and have the same focal length. The focal length parameter of the lens selected by this device is 150 mm. The third lens 31 and the fourth lens 35 constitute the first 4f imaging system, and the distance between the two is twice the focal length of the lens 300 mm. The orbital angular momentum unit 24 is located at the object point of the first 4f imaging system, that is, the third lens 31 is placed 150 mm behind the orbital angular momentum unit 24, and is used to shape the light beam emitted from the orbital angular momentum unit 24 into parallel light. The spatial light phase modulator 36 is located at the image point of the first 4f imaging system, that is, the spatial light phase modulator 36 is placed 150 mm behind the fourth lens 35, and is used to better project the light beam after the action of the orbital angular momentum unit 24 onto the liquid crystal screen of the spatial light phase modulator 36, thereby enhancing the effect of the spatial light phase modulator 36.

[0076] The fourth quarter-wave plate 32, the third half-wave plate 33 and the fourth polarization beam splitter 34 all have an operating wavelength of 810 nm. The fourth quarter-wave plate 32 and the third half-wave plate 33 form a wave plate group, which obtains arbitrary phase light by rotating the long axis angle. The three work together to perform spin angular momentum phase deflection modulation on single photons.

[0077] The spatial light phase modulator 36 performs small-angle reflection and diffraction processing on the light beam through its liquid crystal display. This device is used to perform orbital angular momentum phase deflection modulation on the incident spin-orbital angular momentum entangled single photon. The principle is to load a conjugate reflective phase mask plate based on the known angular momentum of the vortex light to annihilate the photon spiral phase wavefront to restore the Gaussian beam, thereby determining the orbital angular momentum topological charge value q and realizing the distribution of orbital angular momentum. The reflective phase mask plate can be loaded onto the liquid crystal display of the spatial light phase modulator 36 through a computer-generated hologram, thereby generating a corresponding spiral phase negative.

[0078] The fifth lens 37 and the sixth lens 38 are at a distance of twice the focal length of the lens and form a second 4f imaging system. The spatial light phase modulator 36 is located at the object point of the second 4f imaging system, that is, 150 mm in front of the fifth lens, and is used to transmit the light beam after the action of the spatial light phase modulator 36 to the first fiber collimator 41. The 4f imaging system is constructed to strengthen the evolution process of single photons during spatial propagation, shorten the length of the experimental device, and make the structure of the experimental device simpler and more compact.

[0079] like Figure 5 As shown, the photon detection module 4 includes a first fiber collimator 41, a first optical fiber 43, a first single-photon detector 45, a second fiber collimator 42, a second optical fiber 44, a second single-photon detector 46, and a coincidence counter 47;

[0080] The second spin single-photon beam enters the coincidence counter 47 via the second fiber collimator 42 , the second optical fiber 44 , and the second single-photon detector 46 ; the single-photon beam in the spin-orbit angular momentum entangled state enters the coincidence counter 47 via the first fiber collimator 41 , the first optical fiber 43 , and the first single-photon detector 45 .

[0081] The first fiber collimator 41 and the second fiber collimator 42 are fiber collimators of the same type of FC / PC connectors, with an operating wavelength range of 750nm-1100nm, and are used to couple Gaussian beams into optical fibers. The first optical fiber 43 and the second optical fiber 44 are both single-mode optical fibers with an operating wavelength of 810nm. Single-mode optical fibers can only pass zero mode, so they are used to transmit and filter photons. At the same time, the first single-photon detector 45 and the second single-photon detector 46 are used to receive single photons, and use the principle of photoelectric conversion to detect the information of the photons and transmit them to the coincidence counter 47.

[0082] The coincidence counter 47 is used for coincidence counting. The principle is to use a dual-channel input signal, respectively receive the output signals from the first single-photon detector 45 and the second single-photon detector 46, count each channel separately, set the window time and delay time and other parameters through the main interface of the display screen, detect the arrival of the pulse within the set coincidence time window, and count according to the coincidence measurement result, that is, the number of associated photon pairs.

[0083] Example

[0084] A single-photon dual-degree-of-freedom entanglement generation and measurement experimental device based on the above modules can realize the generation and verification of single-photon spin-orbital angular momentum entanglement. It is described in detail as follows:

[0085] S1, start the laser 111, confirm that the associated photon source module 1 is working properly, thereby outputting a horizontally polarized single photon with zero orbital angular momentum. The long-axis angles of the second quarter-wave plate 21 and the second half-wave plate 22 are rotated together to output a horizontally polarized single photon with stable phase and light intensity. Then the position of the orbital angular momentum unit 24 is precisely positioned so that the light beam is incident normally at the center of the phase plate, and the long-axis angle of the third quarter-wave plate 25 is adjusted to put the photon in the optimal phase state. At this point, the conversion of the single photon from spin angular momentum to orbital angular momentum is completed, and the orbital angular momentum topological charge q is converted from 0 to ±1;

[0086] S2, phase polarization modulation is performed on the single photon entangled with spin-orbit angular momentum. By changing the angle of the long axis of the fourth quarter-wave plate 32 and the third half-wave plate 33, the spin-orbit angular momentum of the single photon entangled with spin-orbit angular momentum can be projected onto the four states of |H>, |V>, |R>, and |D>.

[0087] Among them: |H> and |V> are ground states, |R> and |D> are photon mixed superposition states, which are composed of the superposition of ground states |H> and |V>.

[0088] The relationship is:

[0089] S3, performs orbital angular momentum modulation on the single photon with spin and orbital angular momentum entanglement, and calculates that the spatial optical phase modulator 36 outputs a spiral phase diagram on its liquid crystal display. Figure 6a , 6b , 6c, and 6d represent the orbital angular momentum of entangled single photons, respectively representing |l=1>, |l=-1>, and the mixed states |+> and |r>.

[0090] The relationship between the mixed states |+> and |r> and l is:

[0091] S4, the spin-orbit angular momentum entangled single photon is modulated and restored to Gaussian light. The position and angle of the fiber collimator are adjusted to collect and couple into the single photon detector. At the same time, the vertically polarized photon in the other associated photon source module 1 is also collected as a marker single photon and coupled to another single photon detector. Then the signals generated by the two photons reach the coincidence counter for coincidence measurement and counting.

[0092] S5, records the test data of this experimental example, which is expressed as the following matrix:

[0093]

[0094] The density matrix result is shown in the figure below: Figure 7a and 7b As shown, Figure 7a represents the real part of the result, Figure 7b The representative imaginary part result is compared with the ideal matrix, and it is calculated that the fidelity of this device is 95.57%.

Claims

1. A single-photon double-degree-of-freedom entanglement generation and measurement experimental device, characterized by: The device comprises a correlation photon source module (1) and an entangled state preparation module (2) which are sequentially arranged along the light path direction; The associated photon source module (1) is used to generate a spin single photon beam; The entangled state preparation module (2) is used to generate a single photon beam in a spin-orbit angular momentum entangled state from a spin single photon beam, where the spin-orbit angular momentum entangled state is double-degree-of-freedom entanglement; The entangled state preparation module (2) comprises a second modulation unit and an orbital angular momentum unit (24) which are sequentially arranged along the optical path direction of the spin single photon beam generated by the associated photon source module (1); The second modulation unit is used to adjust the phase and light intensity of the spin single photon beam generated by the associated photon source module (1); The orbital angular momentum unit (24) is used to generate a single photon beam in a spin-orbital angular momentum entangled state from the spin single photon beam emitted by the second modulation unit; The device also includes a quantum state tomography module (3), the quantum state tomography module (3) including a third lens (31), a fourth quarter wave plate (32), a third half wave plate (33), a fourth polarization beam splitter (34), a fourth lens (35), and a spatial light phase modulator (36) which are sequentially arranged along the optical path direction of the single photon beam of the spin orbital angular momentum entangled state generated by the entangled state preparation module (2); the spatial light phase modulator (36) is used to cooperate with the transverse phase diagram of the known orbital angular momentum to obtain the orbital angular momentum of the single photon beam of the spin orbital angular momentum prepared by the entangled state preparation module (2); The focal lengths of the third lens (31) and the fourth lens (35) are equal, and the distance between the third lens (31) and the fourth lens (35) along the optical path is twice the focal length; the distance between the third lens (31) and the orbital angular momentum unit (24) along the optical path is once the focal length; and the distance between the spatial light phase modulator (36) and the fourth lens (35) along the optical path is once the focal length; The quantum state tomography module (3) further comprises a fifth lens (37) and a sixth lens (38); an angle is provided between the spatial light phase modulator (36) and the optical path direction of the spin orbital angular momentum single photon beam prepared by the entangled state preparation module (2), so as to make the reflection direction of the spin orbital angular momentum single photon beam by the spatial light phase modulator (36) deviate from the incident direction, and the fifth lens (37) and the sixth lens (38) are arranged in sequence along the reflection direction; The focal length of the fifth lens (37) is equal to the focal length of the sixth lens (38), and is equal to the focal length of the third lens (31) and the focal length of the fourth lens (35); the distance between the fifth lens (37) and the sixth lens (38) along the reflection direction is twice the focal length; and the distance between the spatial light phase modulator (36) and the fifth lens (37) along the reflection direction is one time the focal length; The spin single photon beam generated by the associated photon source module (1) includes two groups of spin single photon beams, the two groups of spin single photon beams constitute associated photon beams, one group of which is injected into the entangled state preparation module (2); the device also includes a photon detection module (4), the other group of spin single photon beams is injected into the photon detection module (4); the photon detection module (4) is used to obtain associated photon pairs constituted by the spin single photon beam emitted by the quantum state tomography module (3) through the sixth lens (38) and the other group of spin single photon beams generated by the associated photon source module (1); The associated photon source module (1) comprises a laser (111), a first modulation unit, a first lens (115), a nonlinear crystal (116), a second lens (117), and a second polarization beam splitter (118) which are sequentially arranged along the optical path direction; a first filter (119) is arranged on a side of the second polarization beam splitter (118) away from the second lens (117); a second filter (120) is arranged on a side of the second polarization beam splitter (118) adjacent to the first filter (119), and the optical path direction of the second filter (120) is perpendicular to the optical path direction of the first filter (119); the first filter (119) and the second filter (120) are respectively used to emit spin single photon beams; The first modulation unit is used to adjust the phase and light intensity of the single photon beam emitted by the laser (111); The photon detection module (4) comprises a first optical fiber collimator (41), a first optical fiber (43), a first single-photon detector (45), a second optical fiber collimator (42), a second optical fiber (44), a second single-photon detector (46), and a coincidence counter (47); The spin single photon beam generated by the associated photon source module (1) enters the coincidence counter (47) via the second optical fiber collimator (42), the second optical fiber (44), and the second single photon detector (46); the spin single photon beam emitted by the quantum state tomography module (3) via the sixth lens (38) enters the coincidence counter (47) via the first optical fiber collimator (41), the first optical fiber (43), and the first single photon detector (45); The orbital angular momentum unit (24) is a liquid crystal vortex wave plate, and the topological charge q value of the liquid crystal vortex wave plate is 1.

2. The single-photon double-degree-of-freedom entanglement generation and measurement experimental device as claimed in claim 1, characterized in that: The second modulation unit comprises a second quarter-wave plate (21), a second half-wave plate (22) and a third polarization beam splitter (23) which are arranged in sequence along the optical path direction.

3. The single-photon double-degree-of-freedom entanglement generation and measurement experimental device according to claim 1, characterized in that: The first modulation unit comprises a first quarter-wave plate (112), a first half-wave plate (113) and a first polarization beam splitter (114) which are sequentially arranged along the optical path direction.

4. The single-photon double-degree-of-freedom entanglement generation and measurement experimental device as claimed in claim 1, characterized in that: The first optical fiber collimator (41) is located at the focus of the sixth lens (38).

Images