Two-photon interference method

Abstract

The invention discloses a two-photon interference method. A built two-photon interference system comprises a light source device, a first adjusting branch, a second adjusting branch, a coupling device and a detection device. The light source device is capable of outputting a first single-photon signal and a second single-photon signal. Based on the established two-photon interference system, the optical path of a second single-photon signal can be adjusted through a second adjusting branch, and the polarization state of a first single-photon signal can be adjusted through a first adjusting branch, so that the two single-photon signals meet interference conditions, and the coincidence counting rate of two beams of optical signals output by a coupling device can be obtained through a detection device. And two-photon interference can be simply and quickly realized.

Description

Technical Field

[0001] This application relates to the technical fields of quantum information technology and optical system technology. More specifically, it relates to a two-photon interference method. 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 operations, etc.

[0004] How to simply and conveniently achieve two-photon interference is an urgent problem to be solved in the field of two-photon interference technology. Summary of the Invention

[0005] In view of this, this application provides a two-photon interference method, and the solution is as follows:

[0006] A two-photon interference method includes:

[0007] Build a two-photon interference system, which includes: a light source device, a first adjustment branch, a second adjustment branch, a coupling device, and a detection device; the light source device can output a first single-photon signal and a second single-photon signal;

[0008] Adjust the optical path of the second single-photon signal through the second adjustment branch, and adjust the polarization state of the first single-photon signal through the first adjustment branch, so that the first single-photon signal and the second single-photon signal meet the interference conditions;

[0009] When the interference conditions are met, after the first single-photon signal and the second single-photon signal interfere in the coupling device, the interference optical signal is output in two beams through the coupling device;

[0010] Obtain the coincidence counting rate of the two optical signals output by the coupling device through the detection device.

[0011] Preferably, in the above two-photon interference method, the second adjustment branch can adjust the optical path of the second single-photon signal by adjusting the spatial distance between two fiber fixed-focus collimators;

[0012] Making the first single-photon signal and the second single-photon signal meet the interference conditions includes:

[0013] At the initial spatial distance, reduce the spatial distance between the two fiber optic fixed-focus collimators until an interference point is determined, such that the coincidence count rate reaches an extreme value;

[0014] Based on the determined interference point, adjust the polarization state of the first single-photon signal through the first adjustment branch to find the minimum and maximum values of the coincidence count rate.

[0015] Preferably, in the above two-photon interference method, it further includes:

[0016] Obtain multiple groups of coincidence count rates within a preset distance range of the interference point;

[0017] Based on the multiple groups of coincidence count rates and the corresponding displacement amounts, plot a two-photon interference curve graph.

[0018] Preferably, in the above two-photon interference method, the method for building a two-photon interference system includes:

[0019] Use an optical fiber single-mode coupler as the coupling device, and the optical fiber single-mode coupler has two input ends and two output ends;

[0020] Connect the output end of the light source device that outputs the first single-photon signal to the input end of the first adjustment branch through the first input optical fiber, and connect the output end of the first adjustment branch to one input end of the optical fiber single-mode coupler through the first output optical fiber;

[0021] Connect the output end of the light source device that outputs the second single-photon signal to the input end of the second adjustment branch through the second input optical fiber, and connect the output end of the second adjustment branch to the other input end of the optical fiber single-mode coupler through the second output optical fiber.

[0022] Preferably, in the above two-photon interference method, the two fiber optic fixed-focus collimators in the second adjustment branch are respectively a first fixed-focus collimator and a second fixed-focus collimator; the input end pigtail of the first fixed-focus collimator is connected to the second input optical fiber; the output end pigtail of the second fixed-focus collimator is connected to the second output optical fiber; there is a spatial distance between the light output port of the first fixed-focus collimator and the light input port of the second fixed-focus collimator;

[0023] The method for adjusting the spatial distance includes:

[0024] Fix the first fixed-focus collimator, and at the initial spatial distance, adjust the position of the second fixed-focus collimator to reduce the spatial distance until an interference point is determined, such that the coincidence count rate reaches an extreme value.

[0025] Preferably, in the above two-photon interference method, the method for adjusting the position of the second fixed-focus collimator includes:

[0026] Obtain the coincidence count rate at the initial spatial distance through a detection device;

[0027] Adjust the position of the second fixed-focus collimator with the first step value, and record the coincidence counting rate at different positions;

[0028] When the absolute value of the difference between the current coincidence counting rate and the coincidence counting rate at the initial spatial distance fluctuates greater than the set threshold, adjust the position of the second fixed-focus collimator with the second step value until the coincidence counting rate reaches an extreme value;

[0029] Wherein, the second step value is less than the first step value.

[0030] Preferably, in the above two-photon interference method, the first adjustment branch includes a polarization controller, and the method for adjusting the polarization state of the first single-photon signal includes:

[0031] At the determined interference point, adjust the polarization controller to determine the minimum and maximum values of the coincidence counting rate.

[0032] Preferably, in the above two-photon interference method, the polarization controller is a manual polarization controller with multiple fiber loops;

[0033] The method for adjusting the polarization controller includes:

[0034] Adjust the polarization state of the single-photon signal by adjusting the length of the fiber optic jumper.

[0035] Preferably, in the above two-photon interference method, the range of the first step value is 10μm to 30μm;

[0036] The range of the second step value is 1μm to 5μm.

[0037] Preferably, in the above two-photon interference method, the set threshold is not less than 200.

[0038] As can be seen from the above description, in the two-photon interference method provided by the technical solution of the present application, the built two-photon interference system includes: a light source device, a first adjustment branch, a second adjustment branch, a coupling device, and a detection device; the light source device can output a first single-photon signal and a second single-photon signal. Based on the built two-photon interference system, the optical path of the second single-photon signal can be adjusted through the second adjustment branch, and the polarization state of the first single-photon signal can be adjusted through the first adjustment branch, so that the two single-photon signals meet the interference conditions, so as to obtain the coincidence counting rate of the two optical signals output by the coupling device through the detection device, and the two-photon interference can be realized simply and quickly. Description of the Drawings

[0039] To more clearly illustrate the technical solutions in the embodiments of the present application or the related art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0040] The structures, proportions, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the conditions for the implementation of the present application. Therefore, they do not have technical essential significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size, without affecting the effects that the present application can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present application.

[0041] Figure 1 It is a flowchart of a two - photon interference method provided by an embodiment of the present application;

[0042] Figure 2 It is a schematic structural diagram of a two - photon interference system provided by an embodiment of the present application;

[0043] Figure 3 It is a flowchart of a method for making the first single - photon signal and the second single - photon signal satisfy the interference condition provided by an embodiment of the present application;

[0044] Figure 4 It is a schematic flowchart of another two - photon interference method provided by an embodiment of the present application;

[0045] Figure 5 It is a schematic structural diagram of another two - photon interference system provided by an embodiment of the present application;

[0046] Figure 6 It is a two - photon interference curve graph provided by an embodiment of the present application. Detailed implementation manners

[0047] The following will clearly and completely describe the embodiments in the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope protected by the present application.

[0048] Without departing from the spirit or scope of the present application, various modifications and variations can be made in the present application, which are obvious to those skilled in the art. Therefore, the present application is intended to cover the modifications and variations of the present application that fall within the scope of the corresponding claims (the claimed technical solutions) and their equivalents. It should be noted that the embodiments provided in the present application can be combined with each other without contradiction.

[0049] The two-photon interference system mainly includes interference, filtering, single-photon detection, and coincidence counting parts. In a conventional two-photon interference system, two pairs of photons need to be collimated by collimators respectively, then turned by high-reflectivity mirrors, and finally interfere at a beam splitter prism. Each path of photons will transmit or reflect at the beam splitter prism with a certain probability. Finally, the coupler will collect one path of transmitted photons and the other path of reflected photons that have passed through the beam splitter prism. The collected photons are transmitted through an optical fiber to a single-photon detector, the output electrical signal is processed electronically, and then the single-channel counting and coincidence counting are uploaded and displayed on the host computer software. In a conventional two-photon interference system, a half-wave plate is required to rotate the polarization direction of the photons. In addition, a polarization plate is needed to detect whether the polarization of the photons has rotated to the optimal state. The conventional two-photon interference system mainly builds a spatial optical path through spatially discrete optical devices, and the positions and distances of each optical device need to be controlled, so the experimental setup is relatively complex and the operation is difficult.

[0050] In view of this, the embodiment of the present application provides a two-photon interference method. This two-photon interference method adjusts the polarization state of the first single-photon signal through the first adjustment branch, and adjusts the optical path of the second single-photon signal through the second adjustment branch, so that the optical paths of the two single-photon signals reaching the coupling device are the same. Furthermore, the two single-photon signals can interfere at the coupling device, so that the detection device can obtain the coincidence counting rate after the interference of the two single-photon signals. This two-photon interference system has a simple structure and is easy to operate, and can achieve two-photon interference simply and quickly.

[0051] Furthermore, in the embodiment of the present application, a two-photon interference system can be built through optical fiber devices to replace the two-photon interference system constructed by spatially discrete optical devices. This can not only reduce the cost of the two-photon interference experiment, but also reduce the difficulty of system setup and system debugging. Most importantly, it can improve the system stability, the system volume is smaller, it can cooperate with the host computer software to process the two-photon interference experiment data, has high operability, and strong system expandability and practicability.

[0052] To make the above objects, features, and advantages of the present application more obvious and understandable, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0053] Refer to Figure 1 as shown Figure 1The flowchart of a two-photon interference method provided by an embodiment of this application. The two-photon interference method includes:

[0054] Step S11: Set up a two-photon interference system.

[0055] Reference Figure 2 as shown Figure 2 is the structural schematic diagram of a two-photon interference system provided by an embodiment of this application. The two-photon interference system includes: a light source device 10, a first adjustment branch 11, a second adjustment branch 12, a coupling device 13, and a detection device 14.

[0056] In Figure 2 the two-photon interference system shown, the light source device 10 can output a first single-photon signal and a second single-photon signal; the first adjustment branch 11 can adjust the polarization state of the first single-photon signal; the second adjustment branch 12 can adjust the optical path of the second single-photon signal; the two single-photon signals reach the coupling device simultaneously to generate interference; the coupling device 13 can couple the first single-photon signal and the second single-photon signal, and output the coupled optical signal in two beams; the detection device 14 can obtain the coincidence counting rate of the two optical signals output by the coupling device 13.

[0057] Step S12: Adjust the optical path of the second single-photon signal through the second adjustment branch, and adjust the polarization state of the first single-photon signal through the first adjustment branch, so that the first single-photon signal and the second single-photon signal meet the interference conditions.

[0058] Step S13: When the interference conditions are met, after the first single-photon signal and the second single-photon signal generate interference at the coupling device, the coupled optical signal is output in two beams through the coupling device;

[0059] Step S14: Obtain the coincidence counting rate of the two optical signals output by the coupling device through the detection device.

[0060] Among them, the light source device 10 is an entanglement source or other isochronous light sources that can achieve interference. The light source device 10 can output a first single-photon signal and a second single-photon signal through two optical fibers respectively. Among the two optical fibers, one optical fiber connected to the first adjustment branch 11 is used as the following first input optical fiber to provide 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 following second input optical fiber to provide the second single-photon signal for the second adjustment branch 12. Optionally, the light source device 10 includes a barium metaborate (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.

[0061] 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 multiplexed as the first input optical fiber and connected to the input end of the first adjustment branch 11. As described below, when the first adjustment branch 11 is a polarization controller, this optical fiber is connected to the input end of the polarization controller; the other of the two optical fibers is multiplexed as the second input optical fiber and 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, this optical fiber is connected to the pigtail of the input end of the first fixed-focus collimator 121.

[0062] The second adjustment branch 12 can adjust the optical path of the second single-photon signal by adjusting the spatial distance between the two fiber fixed-focus collimators. At this time, the method for making the first single-photon signal and the second single-photon signal satisfy the interference condition can be as Figure 3 shown.

[0063] Refer to Figure 3 shown, Figure 3 which is a flowchart of a method for making the first single-photon signal and the second single-photon signal satisfy the interference condition provided by an embodiment of the present application. The method includes:

[0064] Step S21: At the initial spatial distance, reduce the spatial distance between the two fiber fixed-focus collimators until the interference point is determined, so that the coincidence counting rate reaches an extreme value.

[0065] Step S22: Based on the determined interference point, adjust the polarization state of the first single-photon signal through the first adjustment branch 11 to find the minimum and maximum values of the coincidence counting rate.

[0066] Refer to Figure 4 shown, Figure 4 which is a schematic flowchart of another two-photon interference method provided by an embodiment of the present application. On the basis of the method shown in Figure 3 the method shown in Figure 4 also includes:

[0067] Step S23: Obtain multiple groups of coincidence counting rates within a preset distance range of the interference point;

[0068] Step S24: Draw a two-photon interference curve graph based on multiple groups of coincidence counting rates and the corresponding displacement amounts.

[0069] The two-photon interference system provided by the embodiment of the present application further includes: a host connected to the detection device 14, and the host can draw a two-photon interference curve graph based on the coincidence counting rate. Data processing can be performed through the software in the host, and an interference curve graph and image display can be drawn based on the data processing results, so as to more intuitively display two-photon interference.

[0070] Refer to Figure 5 shown,Figure 5 This is a schematic structural diagram of another two - photon interference system provided by an embodiment of the present application. Figure 5 In the shown manner, the two fiber fixed - focus collimators in the second adjustment branch 12 are respectively the first fixed - focus collimator 121 and the second fixed - focus collimator 122. The second adjustment branch 12 can adjust the optical path of the second single - photon signal by adjusting the spatial distance between the light - output port of the first fixed - focus collimator 121 and the light - input port of the second fixed - focus collimator 122.

[0071] In the above step S11, as Figure 5 shown, the method for building a two - photon interference system includes: using an optical - fiber single - mode coupler as the coupling device 13. The optical - fiber single - mode coupler has two input ends A, B and two output ends C, D; connecting the output end of the light - source device 10 that outputs the first single - photon signal to the input end of the first adjustment branch 11 through the first input optical fiber, and connecting the output end of the first adjustment branch 11 to one input end of the optical - fiber single - mode coupler through the first output optical fiber; connecting the output end of the light - source device 10 that outputs the second single - photon signal to the input end of the second adjustment branch 12 through the second input optical fiber, and connecting the output end of the second adjustment branch 12 to the other input end of the optical - fiber single - mode coupler through the second output optical fiber.

[0072] In Figure 5 the shown two - photon interference system, the optical - fiber single - mode coupler can couple the first single - photon signal and the second single - photon signal and then output them in two beams based on a 50:50 beam - splitting ratio, so that each photon has a 50% probability of being output from the two optical fibers to their respective corresponding detectors. Among them, each input end and output end of the optical - fiber single - mode coupler has a pigtail.

[0073] 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, a separate optical fiber can also be set to be connected to the output end of the first adjustment branch 11, and this optical fiber is connected to the pigtail of the input end A of the optical - fiber single - mode coupler. At this time, the first output optical fiber includes the optical fiber connected to the output end 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 input end A is reused as the first output optical fiber as an example for illustration. 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;

[0074] As Figure 5As shown, the input end pigtail of the first fixed-focus collimator 121 is connected to the second input optical fiber; the output end pigtail of the second fixed-focus collimator 122 is connected to the second output optical fiber; there is a spatial distance between the light output port of the first fixed-focus collimator 121 and the light input port of the second fixed-focus collimator 122.

[0075] In the two-photon interference system, the second adjustment branch 12 includes two 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 into the second output optical fiber to be input into the input end B of the fiber single-mode coupler. In the implementation of this application, the pigtail of the input end B of the multiplexed 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 fiber single-mode coupler. In this way, the output end pigtail of the second fixed-focus collimator 122 and the pigtail of the input end B of the fiber single-mode coupler can be connected through a flange. In other ways, a separate optical fiber can be set to connect the output end pigtail of the second fixed-focus collimator 122 and the pigtail of the input end B of the fiber single-mode coupler. At this time, the second output optical fiber also includes this optical fiber.

[0076] Based on Figure 5 As shown in the second adjustment branch 12, the method for adjusting the spatial distance between the light output port of the first fixed-focus collimator 121 and the light input port of the second fixed-focus collimator 122 includes: fixing the first fixed-focus collimator 121, and at the initial spatial distance, adjusting the position of the second fixed-focus collimator 122 to reduce the spatial distance until the interference point is determined so that the coincidence counting rate reaches an extreme value.

[0077] Optionally, the second fixed-focus collimator 122 is fixed on the 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 through the moving platform 123, and then the spatial distance between the light output port of the first fixed-focus collimator 121 and the light input port of the second fixed-focus collimator 122 can be adjusted 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, and then an interference phenomenon is generated.

[0078] In the two-photon interference system provided by the embodiment of this application, a band-pass filter is provided at the light input port of the second fixed-focus collimator 122 ( Figure 5 The band-pass filter is not shown in the figure), and the band-pass filter is used to filter out external stray light to reduce the influence of background noise on the interference phenomenon.

[0079] The detection device 14 is a dual-channel coincidence counter, and the dual-channel coincidence counter includes: two detectors, and the two detectors are respectively connected to the two output ends of the coupling device through optical fibers; the electronics control board ( Figure 5(not shown in the figure), the electronics control board is used to determine the coincidence count rate of the two optical signals output by the coupling device 13 based on the detection results of the detectors. The two detectors are respectively connected to the two output ends of the fiber optic single-mode coupler through optical fibers. In the embodiments of the present application, a dual-channel coincidence counter is used to view the change of the coincidence count rate to characterize the interference phenomenon.

[0080] In the dual-channel coincidence counter, both of the two detectors are single-photon detectors. The two detectors are respectively a first detector 141 and a second detector 142, which are respectively connected to the output end D and the output end C of the fiber optic single-mode coupler.

[0081] As described above, the dual-channel coincidence counter can be used for coincidence counting. It can receive optical signals through dual channels, and the two detectors receive the optical signals after interference in the fiber optic single-mode coupler. The two detectors respectively perform counting, detect the arrival of the optical signals within a set coincidence time window, and the electronics control board performs counting on the coincidence measurement results to obtain the coincidence count rate.

[0082] Compared with the two-photon interference system constructed by conventional spatially discrete optical devices, in the two-photon interference system used in the embodiments of the present application, the optical devices are all fiber optic 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 detectors can all be connected through corresponding optical fibers. This not only reduces the experimental cost of two-photon interference, but also greatly reduces the difficulty of building and debugging the two-photon interference system, improves the stability of the system, and the two-photon interference system built by fiber optic devices is smaller in volume and more portable. At the same time, the experimental data can be processed based on the processing software in the host, and the system has high operability, strong expandability and practicability.

[0083] In the embodiments 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 with multiple fiber loops, which can adjust the polarization state of the single-photon signal based on adjusting the length of the fiber optic jumper.

[0084] In order to make the first single-photon signal and the second single-photon signal satisfy the interference conditions, it is set 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. As described above, the position of the second fixed-focus collimator 122 can be adjusted to change the optical path of the second single-photon signal, 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.

[0085] 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 with each other in the coupling device 13. The coupling device 13 divides the interfered optical signal into two beams, and the two detectors connected respectively detect the two beams of optical signals.

[0086] Among them, the pigtails of the two fiber optic fixed-focus collimators are respectively connected to the corresponding optical fibers through flanges. In the embodiment of the present application, after the alignment and coupling debugging of the two fiber optic fixed-focus collimators are completed, the connection between the fiber optic optical path and the flange is carried out to facilitate ensuring the reliability of the two-photon interference system.

[0087] When building the two-photon interference system as Figure 5 shown, it also includes:

[0088] Corresponding to the two-way single-photon signals output by the light source device 10, the first input optical fiber for transmitting the first single-photon signal is connected to the polarization controller through a flange. The second input optical fiber for outputting the second single-photon signal is connected to the first fixed-focus collimator 121 through a flange;

[0089] There is an initial spatial distance L between the light output port of the first fixed-focus collimator 121 and the light input port of the second fixed-focus collimator 122;

[0090] 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 of the input end B = the length of the first input optical fiber + the length of the fiber optic jumper of the polarization controller + the length of the pigtail of the input end A; among them, the speed of light in air is 1.5 times the speed of light in glass, so the propagation in air is equivalently transformed into the propagation of light in the optical fiber through the transformation of L / 1.5;

[0091] The pigtail of the output end C of the fiber optic single-mode coupler is connected to the second detector 142, and the pigtail of the output end D of the fiber optic single-mode coupler is connected to the first detector 141.

[0092] For Figure 5In 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 to the input end A of the 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, transmitted to the air through the first fixed-focus collimator 121, coupled into the optical fiber by the second fixed-focus collimator 122 after traveling a certain distance in the air, and then transmitted to the input end B of the fiber single-mode coupler. The pigtail of the second fixed-focus collimator 122 and the pigtail of the input end B of the fiber single-mode coupler are connected by a flange. After the optical signals transmitted in the two adjustment branches reach the fiber single-mode coupler simultaneously, photons interfere. After being split 50:50 by the fiber single-mode coupler, they enter the two detectors inside the dual-channel coincidence counter respectively, are converted from optical pulses to electrical pulses. Based on the detection results of the detectors, photon technology calculations are performed on the single-channel optical signals, and coincidence counting calculations are performed by the coincidence counter after calibration delay. The interference curve graph is plotted and displayed by the software in the host computer.

[0093] In Figure 5 When implementing two-photon interference with the two-photon interference system shown, the method includes:

[0094] First, build the two-photon interference system shown based on the technical solution provided in the embodiment of the present application. As described above, the light source device 10 has two optical fibers that respectively output a single-photon signal. 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.

[0095] Then, after the two single-photon signals are coupled in the fiber single-mode coupler, they enter the two detector channels of the dual-channel coincidence counter through the output ends C and D respectively to obtain the coincidence counting rate M at this time.

[0096] Further, adjust the position of the second fixed-focus collimator 122 to determine the interference point.

[0097] Among them, the method for adjusting the second fixed-focus collimator 122 includes: adjusting the mobile platform 123 with a first step value, and recording the coincidence count rate K at different positions, the first step value can be 10μm~30μm, preferably 10μm; when the absolute value of the difference between the current coincidence count rate and the coincidence count rate at the initial spatial distance fluctuates by more than a set threshold, adjusting the position of the second fixed-focus collimator with a second step value until the coincidence count rate reaches an extreme value (minimum or maximum), that is, when |MK| fluctuates by more than a set threshold, continue scanning with the second step value until the photon coincidence count reaches an extreme value, the current position corresponds to the interference point, and 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. The second step value is less than the first step value, and the range of the second step value is 1μm~5μm.

[0098] Optionally, a threshold value is set to be no less than 200, based on which the interference point can be located more accurately and quickly.

[0099] Furthermore, the polarization state of the first single-photon signal is adjusted by a polarization controller. In this step, the method of adjusting the polarization state of the first single-photon signal by a polarization controller includes: adjusting the polarization controller at a determined interference point to determine the maximum and minimum values ​​of the counting rate. In this step, by adjusting the polarization controller, the minimum K1 and maximum K2 of the counting rate are found, and the larger the contrast K2 / K1, the better. At this point, the debugging of the single-photon interference system is completed. The polarization controller is a manual polarization controller with multiple optical fiber rings, and the method of adjusting the polarization controller includes: adjusting the polarization state of the single-photon signal by adjusting the length of the optical fiber jumper.

[0100] 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.

[0101] refer to Figure 6 As shown, Figure 6 A two-photon interference curve diagram provided in an embodiment of the present application, Figure 6 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.

[0102] 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.

[0103] On the basis of ensuring the isochronism of the light source, the two-photon interference system can convert the corresponding optical fiber length through the spatial optical path to ensure the consistency of the optical path lengths of the two single-photon signals reaching the single-mode optical fiber coupler. The optical fiber lengths between the single-mode optical fiber coupler and the two detectors also need to be the same or approximately the same to achieve the isochronism of the two optical signal lines output by the single-mode optical fiber coupler reaching the detectors.

[0104] Carrying out two-photon interference based on the two-photon interference system provided by the embodiments of the present application has at least the following advantages:

[0105] The two-photon interference system uses a fiber fixed-focus collimator and a moving platform 123 to manually or electrically adjust the optical paths of the two beams of light, which has strong practicability. Quantum ranging and the demonstration of interference experiments can be carried out through the interference phenomenon;

[0106] The two-photon interference system is built based on fiber devices, using fiber devices to replace most of the spatially discrete optical devices. Almost all the optical paths of the system are optical fibers, and only spatial optical coupling is used between the two fiber fixed-focus collimators, making the system more stable. Moreover, a polarization controller is used to replace the structure of a polarization beam splitter and a half-wave plate, reducing the number of devices used, saving costs and making the optical path debugging more stable and convenient; Obviously, the implementation method of the two-photon interference system is not limited to Figure 5 as shown Figure 5 each of the optical fiber devices in can be replaced by other optical fiber devices with the same function. Or, some of the optical fiber devices can be replaced by non-optical fiber devices.

[0107] The optical path of the two-photon interference system is simple and convenient, easy to build, with low debugging difficulty, small volume, light weight, and good mobility after implementation. The two-photon interference system has high stability and reliability, and is more convenient for scientific research compared with other photon interference experimental devices, facilitating users to carry out experimental debugging.

[0108] The various embodiments in this specification are described in a progressive, or parallel, or a combination of progressive and parallel manners. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referred to each other.

[0109] It should be noted that in the description of the present application, it is to be understood that the descriptions of the drawings and embodiments are illustrative rather than restrictive. The same reference numerals throughout the embodiments of the specification identify the same structures. Additionally, for the sake of understanding and ease of description, some layers, films, panels, regions, etc. may be exaggerated in thickness in the drawings. At the same time, it can be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, the element can be directly on the other element or there can be intervening elements. Further, "on" means positioning the element on or under another element, but does not inherently mean positioning on the upper side of another element according to the direction of gravity.

[0110] The orientation or positional relationship indicated by terms such as "upper", "lower", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is 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 thus should not be construed as a limitation on the present application. When a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be intervening components present simultaneously.

[0111] It should also be noted that in this text, relational terms such as first and second 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 term "comprising", "including" or any other variation thereof is intended to cover non-exclusive inclusion, such that an article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such article or device. Without further limitation, an element defined by the statement "comprising a..." does not exclude the presence of additional identical elements in the article or device comprising the above elements.

[0112] 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 readily apparent to those skilled in the art, and the general principles defined herein can 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 these embodiments shown herein, but rather is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A two-photon interference method, characterized in that Including: Construct a two-photon interference system, where the two-photon interference system includes: a light source device, a first adjustment branch, a second adjustment branch, a coupling device, and a detection device; the light source device can output a first single-photon signal and a second single-photon signal; Adjust the optical path of the second single-photon signal through the second adjustment branch, and adjust the polarization state of the first single-photon signal through the first adjustment branch, so that the first single-photon signal and the second single-photon signal meet the interference conditions; When the interference conditions are met, after the first single-photon signal and the second single-photon signal interfere in the coupling device, the interference optical signal is output in two beams through the coupling device; Obtain the coincidence counting rate of the two optical signals output by the coupling device through the detection device.

2. The two-photon interference method according to claim 1, wherein The second adjustment branch can adjust the optical path of the second single-photon signal by adjusting the spatial distance between two fiber fixed-focus collimators; Making the first single-photon signal and the second single-photon signal meet the interference conditions includes: At the initial spatial distance, reduce the spatial distance between the two fiber fixed-focus collimators until the interference point is determined, so that the coincidence counting rate reaches an extreme value; Based on the determined interference point, adjust the polarization state of the first single-photon signal through the first adjustment branch to find the minimum and maximum values of the coincidence counting rate.

3. The two-photon interference method according to claim 2, wherein Also including: Obtain multiple groups of coincidence counting rates within a preset distance range of the interference point; Based on multiple groups of the coincidence counting rates and the corresponding displacement amounts, draw a two-photon interference curve graph.

4. The two-photon interference method according to claim 2, wherein The method for constructing the two-photon interference system includes: Use a fiber single-mode coupler as the coupling device, and the fiber single-mode coupler has two input ends and two output ends; Connect the output end of the first single-photon signal output by the light source device to the input end of the first adjustment branch through a first input fiber, and connect the output end of the first adjustment branch to one input end of the fiber single-mode coupler through a first output fiber; Connect the output end of the second single-photon signal output by the light source device to the input end of the second adjustment branch through a second input fiber, and connect the output end of the second adjustment branch to the other input end of the fiber single-mode coupler through a second output fiber.

5. The two-photon interference method according to claim 4, wherein The two fiber fixed-focus collimators in the second adjustment branch are respectively a first fixed-focus collimator and a second fixed-focus collimator; the input end pigtail of the first fixed-focus collimator is connected to the second input fiber; the output end pigtail of the second fixed-focus collimator is connected to the second output fiber; There is a spatial distance between the light output port of the first fixed-focus collimator and the light input port of the second fixed-focus collimator; The method for adjusting the spatial distance includes: Fix the first fixed-focus collimator, and at the initial spatial distance, adjust the position of the second fixed-focus collimator to reduce the spatial distance until the interference point is determined, so that the coincidence counting rate reaches an extreme value.

6. The two-photon interference method according to claim 5, characterized in that, The method for adjusting the position of the second fixed-focus collimator includes: Obtain the coincidence counting rate at the initial spatial distance through the detection device; Adjust the position of the second focusing collimator with a first step value, and record the coincidence counting rate at different positions; When the absolute value of the difference between the current coincidence counting rate and the coincidence counting rate at the initial spatial distance fluctuates greater than the set threshold, adjust the position of the second focusing collimator with a second step value until the coincidence counting rate reaches an extreme value; Wherein, the second step value is less than the first step value.

7. The two-photon interference method according to claim 6, characterized in that The first adjustment branch includes a polarization controller. The method for adjusting the polarization state of the first single-photon signal includes: At the determined interference point, adjust the polarization controller to determine the minimum and maximum values of the coincidence counting rate.

8. The two-photon interference method according to claim 7, characterized in that, The polarization controller is a manual polarization controller with multiple fiber loops; The method for adjusting the polarization controller includes: Adjust the polarization state of the single-photon signal by adjusting the length of the fiber jumper.

9. The two-photon interference method according to claim 6, characterized in that, The range of the first step value is 10μm - 30μm; The range of the second step value is 1μm - 5μm.

10. The two-photon interference method according to claim 6, characterized in that, The set threshold is not less than 200.

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