Two-photon interference system

Abstract

The utility model discloses a two-photon interference system, and the system comprises a light source device which can output a first single-photon signal and a second single-photon signal; the first adjusting branch can adjust the polarization state of the first single-photon signal; the second adjusting branch can adjust the optical path of the second single-photon signal; the coupling device can couple the first single-photon signal and the second single-photon signal and divide the coupled optical signal into two beams to be output; and the detection device can obtain the coincidence counting rate of the two beams of optical signals output by the coupling device. According to the invention, the polarization state of the first single-photon signal can be adjusted through the first adjusting branch, and the optical path of the second single-photon signal can be adjusted through the second adjusting branch, so that the two single-photon signals can interfere with each other in the coupling device, and the detection device can obtain the coincidence counting rate after the interference of the two single-photon signals. The two-photon interference system is simple in structure and convenient to operate.

Description

Technical Field

[0001] The present application relates to the fields of quantum information technology and optical system technology, and more specifically, to a two-photon interference system. Background Art

[0002] Quantum interference technology has important applications in quantum information science. Quantum interference technology is the basis of quantum manipulation technology and an important means to achieve quantum communication. The progress of quantum interference technology can greatly promote the development of quantum information science.

[0003] Multi-photon interference is one of the most common phenomena in quantum interference, and two-photon interference is a special case of multi-photon interference. Two-photon interference can be used to verify Bell's inequality, Bell basis measurement, quantum teleportation, and quantum logic gate operation.

[0004] How to construct a two-photon interference system with a simple structure and easy operation is an urgent problem to be solved in the field of two-photon interference technology. Utility Model Content

[0005] In view of this, the present application provides a technical field of optical systems, and the scheme is as follows:

[0006] A two-photon interference system, comprising:

[0007] A light source device, the light source device is capable of outputting a first single-photon signal and a second single-photon signal;

[0008] A first adjustment branch, the first adjustment branch can adjust the polarization state of the first single-photon signal;

[0009] a second adjustment branch, the second adjustment branch being capable of adjusting the optical path length of the second single-photon signal;

[0010] A coupling device, which can couple the single photon signals output by the two adjustment branches and output the coupled optical signals in two beams;

[0011] The detection device can obtain the coincidence counting rate of the two light signals output by the coupling device.

[0012] Preferably, in the above two-photon interference system, the coupling device comprises a fiber single-mode coupler having two input ends and two output ends;

[0013] The output end of the first adjustment branch is connected to an input end of the optical fiber single-mode coupler through a first output optical fiber; the output end of the second adjustment branch is connected to another input end of the optical fiber single-mode coupler through a second output optical fiber;

[0014] The input end of the first adjustment branch is connected to the output end of the light source device outputting the first single photon signal through the first input optical fiber; the input end of the second adjustment branch is connected to the output end of the light source device outputting the second single photon signal through the second input optical fiber.

[0015] Preferably, in the above two-photon interference system, the first adjustment branch includes a polarization controller, the input end of the polarization controller is connected to the first input optical fiber, and the output end of the polarization controller is connected to the first output optical fiber.

[0016] Preferably, in the above two-photon interference system, the polarization controller is a manual polarization controller having a plurality of optical fiber rings, and is capable of adjusting the polarization state of the single-photon signal based on adjusting the length of the optical fiber jumper.

[0017] Preferably, in the above two-photon interference system, the second adjustment branch includes:

[0018] A first fixed-focus collimator, wherein the input end pigtail of the first fixed-focus collimator is connected to the second input optical fiber;

[0019] A second fixed-focus collimator, wherein the output end pigtail of the second fixed-focus collimator is connected to a second output optical fiber;

[0020] There is a spatial distance between the light outlet of the first fixed-focus collimator and the light entrance of the second fixed-focus collimator.

[0021] Preferably, in the above two-photon interference system, a bandpass filter is provided at the light entrance of the second fixed-focus collimator, and the bandpass filter is used to filter out external stray light.

[0022] Preferably, in the above two-photon interference system, the second fixed-focus collimator is fixed on a moving platform, and the moving platform is used to adjust the position of the second fixed-focus collimator to adjust the spatial distance.

[0023] Preferably, in the above two-photon interference system, the detection device is a dual-channel coincidence counter, and the dual-channel coincidence counter includes:

[0024] Two detectors, the two detectors are respectively connected to an output end of the coupling device through an optical fiber;

[0025] The electronic control board is used to determine the coincidence counting rate of the two light signals output by the coupling device based on the detection results of the detector.

[0026] Preferably, in the above two-photon interference system, the optical path of the first single-photon signal transmitted from the light source device to the coupling device is equal to the optical path of the second single-photon signal transmitted from the light source device to the coupling device.

[0027] Preferably, in the above two-photon interference system, it also includes:

[0028] A host connected to the detection device can draw a two-photon interference curve based on the coincidence count rate.

[0029] It can be known from the above description that the two-photon interference system provided by the technical solution of the present application includes: a light source device, which can output a first single-photon signal and a second single-photon signal; a first adjustment branch, which can adjust the polarization state of the first single-photon signal; a second adjustment branch, which can adjust the optical path of the second single-photon signal; a coupling device, which can couple the first single-photon signal and the second single-photon signal, and output the coupled optical signal in two beams; a detection device, which can obtain the coincidence count rate of the two light signals output by the coupling device. The present application can adjust the polarization state of the first single-photon signal through the first adjustment branch, and adjust the optical path of the second single-photon signal through the second adjustment branch, so that the two single-photon signals can interfere in the coupling device, so that the detection device can obtain the coincidence count rate after the interference of the two single-photon signals. The two-photon interference system has a simple structure and is easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the related technologies, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0031] The structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with this technology. They are not used to limit the conditions under which this application can be implemented, and therefore have no substantive technical significance. Any structural modification, change in proportion or adjustment of size, without affecting the effects and purposes that can be achieved by this application, should still fall within the scope of the technical contents disclosed in this application.

[0032] Figure 1 A schematic diagram of the structure of a two-photon interference system provided in an embodiment of the present application;

[0033] Figure 2 A schematic diagram of the structure of another two-photon interference system provided in an embodiment of the present application;

[0034] Figure 3 A two-photon interference curve diagram provided in an embodiment of the present application. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the embodiments in the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0036] It is obvious to those skilled in the art that various modifications and changes can be made in the present application without departing from the spirit or scope of the present application. Therefore, the present application is intended to cover modifications and changes of the present application that fall within the scope of the corresponding claims (technical solutions for protection) and their equivalents. It should be noted that the implementation methods provided in the embodiments of the present application can be combined with each other without contradiction.

[0037] The two-photon interference system needs to mainly include interference, filtering, single-photon detection and coincidence counting parts. In the conventional two-photon interference system, the two photon pairs need to be collimated by the collimator, then turned by the high-reflectivity reflector, and finally interfered at the beam splitter prism. Each photon will be transmitted or reflected at the beam splitter prism with a certain probability. Finally, the coupler will collect one transmitted photon through the beam splitter prism and another reflected photon through the beam splitter prism. The collected photons are transmitted to the single-photon detector through the optical fiber, and the output electrical signal is processed by electronics, and then the single-path count and coincidence count are uploaded and displayed on the upper computer software. In the conventional two-photon interference system, a half-wave plate is required to rotate the polarization direction of the photon. In addition, a polarization plate is required to detect whether the polarization of the photon is rotated to the best. The conventional two-photon interference system mainly builds a spatial optical path through spatial discrete optical devices, and the position distance of each optical device needs to be controlled. The experimental construction is relatively complicated and the operation is difficult.

[0038] In view of this, an embodiment of the present application provides a two-photon interference system, which adjusts the polarization state of a first single-photon signal through a first adjustment branch, and adjusts the optical path of the second single-photon signal through a second adjustment branch, so that the optical path of the two single-photon signals reaching a coupling device is consistent, and then the two single-photon signals can interfere in the coupling device, so that the detection device can obtain the coincidence count rate of the two single-photon signals after interference. The two-photon interference system has a simple structure and is easy to operate, and can realize two-photon interference simply and quickly.

[0039] Furthermore, in the embodiments of the present application, a two-photon interference system can be built using optical fiber devices to replace the two-photon interference system built using spatially discrete optical devices, which can not only reduce the cost of the two-photon interference experiment, but also reduce the difficulty of system construction and system debugging. Most importantly, the system stability can be improved, the system size is smaller, and it can cooperate with the host computer software to process the two-photon interference experiment data. It has high operability, and the system has strong expandability and practicality.

[0040] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0041] refer to Figure 1 As shown, Figure 1 A schematic diagram of the structure of a two-photon interference system provided in an embodiment of the present application, wherein the two-photon interference system includes:

[0042] A light source device 10, the light source device 10 is capable of outputting a first single-photon signal and a second single-photon signal;

[0043] A first adjustment branch 11, the first adjustment branch 11 can adjust the polarization state of the first single-photon signal;

[0044] A second adjustment branch 12, the second adjustment branch 12 can adjust the optical path of the second single-photon signal;

[0045] A coupling device 13, the coupling device 13 can couple the single photon signals output by the two adjustment branches, and output the coupled optical signals in two beams;

[0046] The detection device 14 can obtain the coincidence count rate of the two light signals output by the coupling device 13.

[0047] The two-photon interference system provided in the embodiment of the present application can adjust the polarization state of the first single-photon signal through the first adjustment branch, and adjust the optical path of the second single-photon signal through the second adjustment branch, so that the two single-photon signals can interfere in the coupling device, so that the detection device can obtain the coincidence count rate after the interference of the two single-photon signals. The two-photon interference system has a simple structure and is easy to operate.

[0048] Wherein, the light source device 10 is an entangled source or other isochronous light source capable of achieving interference, and the light source device 10 can output a first single-photon signal and a second single-photon signal respectively through two optical fibers. Among the two optical fibers, one optical fiber connected to the first adjustment branch 11 is used as the first input optical fiber described below, providing the first single-photon signal for the first adjustment branch 11, and the other optical fiber connected to the second adjustment branch 12 is used as the second input optical fiber described below, providing the second single-photon signal for the second adjustment branch 12. Optionally, the light source device 10 includes a barium borate (BBO) crystal, and can output a single-photon signal through two optical fibers respectively, and the optical fiber connection between the light source device 10 and the two adjustment branches can be realized without a beam splitter.

[0049] The light source device 10 has two optical fibers, which respectively output a first single-photon signal and a second single-photon signal. One of the two optical fibers can be reused as a first input optical fiber, connected to the input end of the first adjustment branch 11, as described below, when the first adjustment branch 11 is a polarization controller, the optical fiber is connected to the input end of the polarization controller; the other of the two optical fibers can be reused as a second input optical fiber, connected to the input end of the second adjustment branch 12, as described below, when the second adjustment branch 12 includes a first fixed-focus collimator 121, the optical fiber is connected to the pigtail at the input end of the first fixed-focus collimator 121.

[0050] refer to Figure 2 As shown, Figure 2 A schematic diagram of the structure of another two-photon interference system provided in an embodiment of the present application, Figure 2 In the illustrated embodiment, the coupling device 13 includes a fiber single-mode coupler having two input ends A and B and two output ends C and D; the fiber single-mode coupler can couple the first single-photon signal and the second single-photon signal, and then output the two beams based on a 50:50 beam splitting ratio, so that the same photon has a 50% probability of being output from the two optical fibers to the respective corresponding detectors. Each input end and output end of the fiber single-mode coupler has a pigtail.

[0051] The output end of the first adjustment branch 11 is connected to an input end A of the optical fiber single-mode coupler through the first output optical fiber; the pigtail of the input end A can be reused as the first output optical fiber, so that the length of the first output optical fiber between the first adjustment branch 11 and the optical fiber single-mode coupler can be reduced. In other ways, it is also possible to set a separate optical fiber connected to the output end of the first adjustment branch 11, and the optical fiber is connected to the pigtail of the input end A of the optical fiber single-mode coupler. In this case, the first output optical fiber includes the output end connection optical fiber of the first adjustment branch 11 and the pigtail of the input end A. In the embodiment of the present application, the pigtail of the multiplexed input end A is used as the first output optical fiber for explanation.

[0052] The output end of the second adjustment branch 12 is connected to the other input end B of the optical fiber single-mode coupler through the second output optical fiber; in the implementation of the present application, the pigtail at the input end B of the multiplexed optical fiber single-mode coupler is used as the second output optical fiber to reduce the length of the second output optical fiber between the second adjustment branch 12 and the optical fiber single-mode coupler. In this way, the output end pigtail of the second fixed-focus collimator 122 and the pigtail at the input end B of the optical fiber single-mode coupler can be connected through a flange. In other ways, the output end pigtail of the second fixed-focus collimator 122 can be connected to the pigtail at the input end B of the optical fiber single-mode coupler through a separate optical fiber, and in this case, the second output optical fiber also includes this optical fiber.

[0053] The input end of the first adjustment branch 11 is connected to the output end of the light source device 10 outputting the first single photon signal through the first input optical fiber; the input end of the second adjustment branch 12 is connected to the output end of the light source device 10 outputting the second single photon signal through the second input optical fiber.

[0054] The detection device 14 is a dual-channel coincidence counter, which includes: two detectors, which are respectively connected to the two output ends of the coupling device through optical fibers; an electronic control board ( Figure 2 The electronic control board is used to determine the coincidence count rate of the two light signals output by the coupling device 13 based on the detection results of the detector. The two detectors are respectively connected to the two output ends of the optical fiber single-mode coupler through optical fibers. In the embodiment of the present application, a dual-channel coincidence counter is used to check the change of the coincidence count rate to characterize the interference phenomenon.

[0055] In the dual-channel coincidence counter, the two detectors are both single-photon detectors, and the two detectors are respectively a first detector 141 and a second detector 142 , which are respectively connected to an output end D and an output end C of the optical fiber single-mode coupler.

[0056] As mentioned above, a dual-channel coincidence counter can be used for coincidence counting. A dual-channel input optical signal can be used. Two built-in detectors are used to receive the optical signal after interference in the optical fiber single-mode coupler. The two detectors count separately and detect the arrival of the optical signal within the set coincidence time window. The electronic control board counts the coincidence measurement results and obtains the coincidence counting rate.

[0057] Compared with the two-photon interference system constructed by conventional spatially discrete optical devices, in the two-photon interference system used in the embodiment of the present application, the optical devices are all optical fiber devices, so that the two adjustment branches and the light source device 10, the coupling device 13 and the two adjustment branches, and the coupling device 13 and the detector can be connected through corresponding optical fibers, which not only reduces the experimental cost of two-photon interference, but also can greatly reduce the difficulty of building and debugging the two-photon interference system, and can also improve the stability of the system. Moreover, the two-photon interference system built by optical fiber devices is smaller in size and more portable.

[0058] At the same time, as described below, the experimental data can also be processed based on the processing software in the host computer. The system has high operability, strong expandability and practicality.

[0059] In the embodiment of the present application, the first adjustment branch 11 includes a polarization controller, the input end of the polarization controller is connected to the first input optical fiber, and the output end of the polarization controller is connected to the first output optical fiber. Optionally, the polarization controller is a manual polarization controller having multiple optical fiber rings, which can adjust the polarization state of the single photon signal based on adjusting the length of the optical fiber jumper.

[0060] like Figure 2 As shown, the second regulating branch 12 includes:

[0061] A first fixed-focus collimator 121, wherein the input end pigtail of the first fixed-focus collimator 121 is connected to the second input optical fiber;

[0062] A second fixed-focus collimator 122, wherein the output end pigtail of the second fixed-focus collimator 122 is connected to the second output optical fiber, and is connected to the input end B of the optical fiber single-mode coupler through the second output optical fiber;

[0063] There is a spatial distance between the light outlet of the first fixed-focus collimator 121 and the light inlet of the second fixed-focus collimator 122. Both fixed-focus collimators are optical fiber fixed-focus collimators.

[0064] In the two-photon interference system, the second adjustment branch 12 includes two optical fiber fixed-focus collimators. The first fixed-focus collimator 121 can collimate the second single-photon signal into a spatially collimated light beam, and the second fixed-focus collimator 122 can couple the spatially collimated light beam to the second output optical fiber to be input to the input end B of the optical fiber single-mode coupler.

[0065] Optionally, the second fixed-focus collimator 122 is fixed on a moving platform 123, and the moving platform 123 is used to adjust the spatial distance. In this way, the position of the second fixed-focus collimator 122 can be adjusted by the moving platform 123 to change the optical path of the second single-photon signal, so that the optical paths of the two single-photon signals reaching the coupling device 13 are the same, thereby generating interference.

[0066] In the two-photon interference system provided in the embodiment of the present application, a bandpass filter ( Figure 2 The bandpass filter is not shown in the figure), and the bandpass filter is used to filter out external stray light to reduce the influence of background noise on the interference phenomenon.

[0067] In order to make the first single-photon signal and the second single-photon signal satisfy the interference condition, the optical path of the first single-photon signal transmitted from the light source device 10 to the coupling device 13 is set to be equal to the optical path of the second single-photon signal transmitted from the light source device 10 to the coupling device 13. As described above, the optical path of the second single-photon signal can be changed by adjusting the position of the second fixed-focus collimator 122, so that the optical path of the first single-photon signal transmitted from the light source device 10 to the coupling device 13 is equal to the optical path of the second single-photon signal transmitted from the light source device 10 to the coupling device 13.

[0068] The first single photon signal adjusted by the first adjustment branch 11 and the second single photon signal adjusted by the second adjustment branch 12 interfere in the coupling device 13. The coupling device 13 divides the interfered optical signal into two beams, and detects the two optical signals through two connected detectors respectively.

[0069] The tail fibers of the two optical fiber fixed-focus collimators are connected to the corresponding optical fibers through flanges. In the embodiment of the present application, after the alignment and coupling debugging of the two optical fiber fixed-focus collimators is completed, the optical fiber optical path is connected to the flange to ensure the reliability of the two-photon interference system.

[0070] The two-photon interference system provided in the embodiment of the present application also includes: a host connected to the detection device 14, and the host can draw a two-photon interference curve based on the coincidence count rate.

[0071] In building Figure 2 The two-photon interferometer system shown also includes:

[0072] Corresponding to the two paths of single-photon signals output by the light source device 10, the first input optical fiber transmitting the first single-photon signal is connected to the polarization controller through a flange. The second input optical fiber outputting the second single-photon signal is connected to the first fixed-focus collimator 121 through a flange;

[0073] There is an initial spatial distance L between the light outlet of the first fixed-focus collimator 121 and the light entrance of the second fixed-focus collimator 122;

[0074] The length of the second input optical fiber + the length of the pigtail of the first fixed-focus collimator 121 + L / 1.5 + the length of the pigtail of the second fixed-focus collimator 122 + the length of the pigtail at the input end B = the length of the first input optical fiber + the length of the optical fiber jumper of the polarization controller + the length of the pigtail at the input end A; wherein, the transmission speed of light in air is 1.5 times that of light in glass, so the transmission speed of light in air is equivalently transformed into light propagation in optical fiber through L / 1.5 transformation;

[0075] The pigtail at the output end C of the optical fiber single-mode coupler is connected to the second detector 142 , and the pigtail at the output end D of the optical fiber single-mode coupler is connected to the first detector 141 .

[0076] for Figure 2 In the two-photon interference system shown, the first single-photon signal output by the light source device 10 can be transmitted to the polarization controller through an optical fiber, and then transmitted to the input end A of the optical fiber single-mode coupler through the polarization controller. The second single-photon signal output by the light source device 10 can be transmitted to the first fixed-focus collimator 121 through another optical fiber, and then transmitted to the air through the first fixed-focus collimator 121. After being transmitted for a distance in the air, it is coupled to the optical fiber by the second fixed-focus collimator 122, and then transmitted to the input end B of the optical fiber single-mode coupler. The pigtail of the second fixed-focus collimator 122 and the pigtail of the input end B of the optical fiber single-mode coupler are connected by a flange. After the optical signals transmitted in the two adjustment branches reach the optical fiber single-mode coupler at the same time, the photons interfere, and after being split 50:50 by the optical fiber single-mode coupler, they enter the two detectors inside the dual-channel coincidence counter respectively, and are converted from optical pulses to electrical pulses. Based on the detection results of the detectors, the single-channel optical signal is subjected to photon technology calculation, and the coincidence counter after the calibration delay is subjected to coincidence counting calculation, and the interference curve is drawn and displayed by the software in the host.

[0077] by Figure 2 When the two-photon interference system realizes two-photon interference, the method includes:

[0078] First, the two-photon interference system shown is constructed based on the technical solution provided in the embodiment of the present application. As mentioned above, the light source device 10 has two optical fibers that output a single-photon signal respectively, and one of the two optical fibers can be connected to the reserved port of the polarization controller through a flange, and the other can be connected to the pigtail of the first fixed-focus collimator 121.

[0079] Then, after the two single-photon signals are coupled in the optical fiber single-mode coupler, they enter the two detector channels of the dual-channel coincidence counter through the output terminals C and D respectively to obtain the coincidence counting rate M at this time.

[0080] Further, the first step value adjusts the mobile platform 123, and records the corresponding coincidence count rate K. Among them, the first step value can be 10μm~30μm, preferably 10μm. When |MK| fluctuates greater than the set threshold, continue scanning with the second step value until the photon coincidence count reaches an extreme value (minimum or maximum), and the current position corresponds to the interference point. At this time, the maximum and minimum values ​​of the coincidence count rate respectively represent that the photon interference is in a state of mutual accumulation and mutual destruction. Among them, the second step value is less than the first step value, and the range of the second step value is 1μm~5μm. Optionally, the threshold is set to be not less than 200, and the interference point can be located more accurately and quickly based on the set threshold.

[0081] Further, the polarization controller is adjusted to find the minimum K1 and maximum K2 of the counting rate. The larger the contrast K2 / K1, the better. At this point, the debugging of the single-photon interference system is completed.

[0082] After the debugging of the single-photon interference system is completed, multiple sets of coincidence counting rates are obtained within the preset distance range of the interference point, that is, within a certain distance range (coherence length) before and after the interference point, and the two-photon interference curve graph is drawn and displayed through the software in the host.

[0083] refer to Figure 3 As shown, Figure 3 A two-photon interference curve diagram provided in an embodiment of the present application, Figure 3 The horizontal axis is the displacement in mm, and the vertical axis is the coincidence count rate in cps. The maximum and minimum coincidence count rates represent the states of photon interference being in the constructive and destructive states, respectively.

[0084] From the above description, it can be seen that the embodiment of the present application builds a two-photon interference system based on an optical fiber single-mode coupler, an optical fiber fixed-focus collimator and a polarization controller. The two-photon interference system can use the optical fiber single-mode coupler for light splitting and beam combining, use the optical fiber fixed-focus collimator with the mobile platform 123 to manually or electrically adjust the optical path, and use the polarization controller to adjust the polarization state of the single-photon signal.

[0085] The two-photon interference system can ensure the consistency of the optical path of the two single-photon signals reaching the optical fiber single-mode coupler by converting the corresponding optical fiber length through the spatial optical path on the basis of ensuring the isochronism of the light source. The optical fiber length between the optical fiber single-mode coupler and the two detectors also needs to be the same or approximately the same to achieve the isochronism of the two optical signal lines output by the optical fiber single-mode coupler reaching the detector.

[0086] The two-photon interference system provided by the embodiment of the present application has at least the following advantages:

[0087] The two-photon interference system uses a fiber fixed-focus collimator with a mobile platform 123 to manually or electrically adjust the optical path of two light paths, and is highly practical, and can demonstrate quantum distance measurement and interference experiments through interference phenomena;

[0088] The two-photon interference system is built on fiber optic devices, using fiber optic devices to replace most of the spatial discrete optical devices. The system optical path is almost all fiber optic, and only the spatial optical coupling is used between the two fiber fixed-focus collimators, making the system more stable. In addition, the polarization controller is used to replace the structure of the polarization beam splitter and the half-wave plate, which reduces the use of devices, saves costs, and makes the optical path debugging more stable and convenient; Obviously, the implementation of the two-photon interference system is not limited to Figure 2 As shown, Figure 2 Each fiber optic device can be replaced by another fiber optic device having the same function. Alternatively, some fiber optic devices can be replaced by non-fiber optic devices.

[0089] The optical path of the two-photon interference system is simple and convenient, the construction is simple, the debugging difficulty is low, the size after implementation is small, the weight is light, and the maneuverability is good. The two-photon interference system has high stability and reliability. Compared with other photon interference experimental devices, it is more convenient to apply to scientific research and is convenient for users to debug experiments.

[0090] The various embodiments in this specification are described in a progressive, parallel, or progressive and parallel manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referenced to each other.

[0091] It should be noted that in the description of the present application, it should be understood that the description of the drawings and embodiments is illustrative rather than restrictive. The same reference numerals throughout the embodiments of the specification identify the same structure. In addition, for the sake of understanding and ease of description, the drawings may exaggerate the thickness of some layers, films, panels, regions, etc. It is also understood that when an element such as a layer, film, region, or substrate is referred to as "on" another element, the element may be directly on the other element or there may be an intermediate element. In addition, "on" refers to positioning an element on or below another element, but does not essentially refer to positioning on the upper side of another element according to the direction of gravity.

[0092] The terms "upper", "lower", "top", "bottom", "inner", "outer", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present application. When a component is considered to be "connected" to another component, it may be directly connected to the other component or there may be a centrally arranged component at the same time.

[0093] It should also be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that an article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such article or device. In the absence of further restrictions, the elements defined by the sentence "comprising a ..." do not exclude the existence of other identical elements in the article or device including the above elements.

[0094] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A two-photon interference system, characterized in that: include: A light source device, wherein the light source device is capable of outputting a first single-photon signal and a second single-photon signal; a first adjustment branch, wherein the first adjustment branch is capable of adjusting a polarization state of the first single-photon signal; a second adjustment branch, wherein the second adjustment branch is capable of adjusting the optical path length of the second single-photon signal; A coupling device, wherein the coupling device is capable of coupling the single photon signals output by the two adjustment branches and outputting the coupled optical signals in two beams; A detection device is capable of acquiring a coincidence count rate of two light signals output by the coupling device.

2. The two-photon interference system according to claim 1, characterized in that: The coupling device comprises a fiber single-mode coupler having two input ends and two output ends; The output end of the first adjustment branch is connected to one input end of the optical fiber single-mode coupler through a first output optical fiber; the output end of the second adjustment branch is connected to the other input end of the optical fiber single-mode coupler through a second output optical fiber; The input end of the first adjustment branch is connected to the output end of the light source device outputting the first single-photon signal through a first input optical fiber; the input end of the second adjustment branch is connected to the output end of the light source device outputting the second single-photon signal through a second input optical fiber.

3. The two-photon interference system according to claim 2, characterized in that: The first adjustment branch includes a polarization controller, an input end of the polarization controller is connected to the first input optical fiber, and an output end of the polarization controller is connected to the first output optical fiber.

4. The two-photon interference system according to claim 3, characterized in that: The polarization controller is a manual polarization controller with multiple optical fiber rings, and can adjust the polarization state of a single photon signal based on adjusting the length of an optical fiber jumper.

5. The two-photon interference system according to claim 2, characterized in that: The second regulating branch comprises: A first fixed-focus collimator, wherein an input end pigtail of the first fixed-focus collimator is connected to the second input optical fiber; A second fixed-focus collimator, wherein the output end pigtail of the second fixed-focus collimator is connected to the second output optical fiber; Wherein, there is a spatial distance between the light outlet of the first fixed-focus collimator and the light entrance of the second fixed-focus collimator.

6. The two-photon interference system according to claim 5, characterized in that: The light entrance of the second fixed-focus collimator is provided with a bandpass filter, and the bandpass filter is used to filter out external stray light.

7. The two-photon interference system according to claim 5, characterized in that: The second fixed-focus collimator is fixed on a moving platform, and the moving platform is used to adjust the position of the second fixed-focus collimator to adjust the spatial distance.

8. The two-photon interference system according to claim 1, characterized in that: The detection device is a dual-channel coincidence counter, and the dual-channel coincidence counter includes: Two detectors, the two detectors are respectively connected to an output end of the coupling device through optical fibers; An electronic control board is used to determine the coincidence count rate of the two light signals output by the coupling device based on the detection result of the detector.

9. The two-photon interference system according to claim 1, characterized in that: The optical path of the first single-photon signal transmitted from the light source device to the coupling device is equal to the optical path of the second single-photon signal transmitted from the light source device to the coupling device.

10. The two-photon interference system according to any one of claims 1 to 9, characterized in that: Also includes: A host connected to the detection device can draw a two-photon interference curve diagram based on the coincidence count rate.

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