Quantum entanglement source device and quantum computing equipment

Abstract

The present application discloses a quantum entanglement source device and a quantum computing device including the quantum entanglement source device. The quantum entanglement source device includes: a pump light source for generating linearly polarized light; a light source adjustment component for adjusting the linearly polarized light to polarized light with a linear polarization state of a predetermined angle; and a BBO crystal component for generating entangled photon pairs based on the polarized light with a linear polarization state of a predetermined angle and a BBO crystal. Entangled photon pairs can be generated using the embodiments of the present application.

Description

Technical Field

[0001] The present application relates to the field of quantum computing technology, and in particular to a quantum entanglement source device and a quantum computing device including the quantum entanglement source device. Background Art

[0002] Quantum entanglement is an important concept in quantum mechanics. As one of the foundations of quantum communication and quantum computing, quantum entanglement has many applications and is also a common subject in quantum information disciplines in colleges and universities. There are many known methods for generating quantum entanglement, such as waveguide-based entanglement sources, ion trap entanglement, superconducting quantum circuit entanglement, etc. It is currently believed that the simplest and most practical way to generate entanglement sources is to use the spontaneous parametric down-conversion process of nonlinear crystals to generate entanglement sources. Spontaneous parametric down-conversion (SPDC) is a typical quantum nonlinear optical process and one of the commonly used technologies for generating entangled photon pairs. It plays an important role in quantum information processing. At present, there are liberation solutions that use the parametric down-conversion process of nonlinear crystals to generate entanglement sources. However, the existing solutions are built using spatial optical devices. The actual construction process is complicated and the overall size of the device is large, which is not conducive to integration. More importantly, the stability of the built device is not good. Quantum optical experiments have high requirements for device precision, and the maintenance cost is difficult to reduce. It cannot meet the practical needs of the quantum field, which seriously affects the normal use of researchers. There is considerable room for optimization in the solution for preparing quantum entangled sources, and further research and optimization is needed. Summary of the invention

[0003] In view of this, an embodiment of the present application provides a quantum entanglement source device and a quantum computing device to solve at least one technical problem.

[0004] On the one hand, an embodiment of the present application provides a quantum entanglement source device, including: a pump light source for generating linearly polarized light; a light source adjustment component for adjusting the linearly polarized light to polarized light with a linear polarization state at a predetermined angle; and a BBO crystal component for generating entangled photon pairs based on the polarized light with a linear polarization state at a predetermined angle and a BBO crystal.

[0005] Optionally, the BBO crystal assembly includes: a first optical fiber collimator, used to focus the polarized light with a linear polarization state at a predetermined angle onto a BBO crystal; and a BBO crystal, used to generate an entangled photon pair based on the polarized light with a linear polarization state at a predetermined angle, the entangled photon pair including a first optical signal and a second optical signal that form a first angle with each other.

[0006] Optionally, the BBO crystal assembly includes: a second optical fiber collimator for transmitting the first optical signal to a predetermined optical signal processing device; and / or a third optical fiber collimator for transmitting the second optical signal to a predetermined optical signal processing device.

[0007] Optionally, the light source adjustment component includes: a first optical fiber polarization beam splitter, used to perform polarization selective filtering on the linear polarized light to output polarized light in a first polarization state or a second polarization state; a first optical fiber polarization controller, used to adjust the polarized light in the first polarization state or the second polarization state to output polarized light in the linear polarization state with a predetermined angle.

[0008] Optionally, the first polarization state includes a horizontal polarization state, the second polarization state includes a vertical polarization state; the polarized light with a linear polarization state of a predetermined angle includes 45° linear polarized light, wherein the range of adjustment error allowed during adjustment of the first optical fiber polarization controller is between -5° and +5°.

[0009] Optionally, the entangled photon pair is generated by a parametric down-conversion process of linearly polarized light in a BBO crystal, wherein the size of the first angle is proportional to the size of a cutting angle of the BBO crystal.

[0010] Optionally, the method further includes: a first optical fiber filter connected to the output end of the second optical fiber collimator, for filtering out photons in the first optical signal that do not conform to the wavelength of the entangled photons; and / or a second optical fiber filter connected to the output end of the third optical fiber collimator, for filtering out photons in the second optical signal that do not conform to the wavelength of the entangled photons.

[0011] Optionally, the method further comprises: at least two precision adjustment seats for carrying at least a second fiber collimator and a third fiber collimator, a lens being further arranged on the precision adjustment seat, and a focal length of the lens being determined according to a distance between the BBO crystal and the fiber collimator.

[0012] Optionally, a maximum straight-line distance of the areas occupied by the first optical fiber collimator, the BBO crystal, the second optical fiber collimator, and the third optical fiber collimator is less than or equal to 22 centimeters.

[0013] Optionally, the method further includes: a testing component for measuring and counting the first optical signal and the second optical signal, and determining the quality of the entangled photon pair based on single-channel counting values ​​and coincidence counting values ​​of the first optical signal and the second optical signal.

[0014] Optionally, the test component includes: a first single-photon detector, used to detect and count the first optical signal, and record the single-channel count value corresponding to the first optical signal; a second single-photon detector, used to detect and count the second optical signal, and record the single-channel count value corresponding to the second optical signal; a coincidence counter, used to receive the electrical signals output by the first single-photon detector and the second single-photon detector and perform time coincidence measurement and counting on the electrical signals to obtain coincidence count values ​​of the first optical signal and the second optical signal; and a quality analysis module, used to determine the quality of the entangled photon pair based on the single-channel count values ​​and coincidence count values ​​of the first optical signal and the second optical signal.

[0015] Optionally, the first optical signal is signal light, and the second optical signal is idler light.

[0016] Optionally, the test component includes: a second optical fiber polarization controller arranged between the first optical fiber filter and the first single-photon detector, for adjusting the polarization state of the first optical signal; and a third optical fiber polarization controller arranged between the second optical fiber filter and the second single-photon detector, for adjusting the polarization state of the second optical signal.

[0017] Optionally, the test component includes: a second optical fiber polarization beam splitter arranged between the second optical fiber polarization controller and the first single-photon detector, for performing polarization filtering on the first optical signal after adjusting the polarization state; a third optical fiber polarization beam splitter arranged between the third optical fiber polarization controller and the second single-photon detector, for performing polarization filtering on the second optical signal after adjusting the polarization state.

[0018] Optionally, one or more devices in the apparatus are connected to upstream and downstream devices via polarization-maintaining optical fibers.

[0019] On the other hand, an embodiment of the present application also provides a quantum computing device, which includes the quantum entanglement source device as described above.

[0020] The quantum entanglement source device of the embodiment of the present application can be used to adjust the polarization state of the linearly polarized light generated by the pump light source, and the adjusted polarized light can generate entangled photon pairs through the BBO crystal component. Compared with the previous entanglement source equipment, the quantum entanglement source device of the embodiment of the present application is easy to maintain and has higher adjustment accuracy, which can meet the practical needs of quantum optical experiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solution of the embodiments of the present application, the following briefly introduces the drawings in the embodiments of the present application.

[0022] Figure 1 The structure of a quantum entanglement source device according to an embodiment of the present application is schematically shown.

[0023] Figure 2 The structure of another quantum entanglement source device according to an embodiment of the present application is schematically shown.

[0024] Figure 3 The micro-assembly diagram of a BBO crystal component according to an embodiment of the present application is schematically shown.

[0025] Figure 4 A schematic diagram of the micro-assembly of a BBO crystal component according to another embodiment of the present application is shown.

[0026] Description of reference numerals:

[0027] 100, quantum entanglement source device; 110, pump light source; 120, light source adjustment component; 130, BBO crystal component; 121, first optical fiber polarization beam splitter; 122, first optical fiber polarization controller; 131, first optical fiber collimator; 132, second optical fiber collimator; 133, third optical fiber collimator; 135, BBO crystal; 1361, 1362, 1363 precision adjustment seat; 1371, 1372, 1373, lens; 1 315, 1325, 1335, five-axis adjustment frame; 61, 62, 63, microlens; 138, first optical fiber filter; 139, second optical fiber filter; 140, test assembly; 141, first single-photon detector; 142, second single-photon detector; 143, coincidence counter; 146, second optical fiber polarization controller; 147, third optical fiber polarization controller; 148, second optical fiber polarization beam splitter; 149, third optical fiber polarization beam splitter. DETAILED DESCRIPTION

[0028] The principles and spirit of the present application will be described below with reference to several exemplary embodiments. The elements and their numbers in the drawings herein are for illustration and not for limitation, and the names in the drawings are for distinction and do not have any limiting meaning.

[0029] The present application embodiment provides a quantum entanglement source device 100, referring to Figure 1 , which includes a pump light source 110, a light source adjustment component 120 and a BBO crystal component 130. The pump light source 110 is used to generate linearly polarized light. The light source adjustment component 120 is used to adjust the linearly polarized light into polarized light with a linear polarization state of a predetermined angle. The BBO crystal component 130 is used to generate entangled photon pairs based on the polarized light with a linear polarization state of a predetermined angle and the BBO crystal.

[0030] The pump light source 110 of the quantum entanglement source device 100 of the embodiment of the present application generates pump light, and the light source adjustment component 120 adjusts the polarization state of the pump light so that the light entering the BBO crystal component 130 has a fixed polarization state. The BBO crystal component 130 generates entangled photon pairs based on polarized light. The optical path for realizing the above-mentioned whole process can use optical fiber devices to transmit optical signals. Compared with the method based on space device construction, the entanglement source device designed in the present application is smaller in size, easier to integrate, and has higher overall stability. It can save the debugging time of the experimenters and reduce the maintenance cost. It can meet the practical needs of the quantum field to a certain extent and provide convenient conditions for further scientific research experiments.

[0031] Optionally, one or more devices in the quantum entanglement source device 100 of the embodiment of the present application are connected to upstream and downstream devices through polarization-maintaining optical fibers. For example, the pump light source 110 can generate continuous linearly polarized light, and the linearly polarized light source is output through the polarization-maintaining optical fiber to maintain the stability of the polarization state; further, optionally, the optical fiber output port can use an 8-degree bevel connector to reduce the light source noise caused by the reflected light.

[0032] In the exemplary embodiment of the present application, the light source adjustment component 120 in the quantum entanglement source device 100 may include a first optical fiber polarization beam splitter 121 and a first optical fiber polarization controller 122 to generate linear polarization light with a certain angle.

[0033] Specifically, the first optical fiber polarization beam splitter 121 can perform polarization selective filtering on linear polarized light, and output polarized light of the first polarization state or the second polarization state. Optionally, the first polarization state and the second polarization state can be horizontal polarization state and vertical polarization state, respectively, to prepare for the subsequent adjustment of the light polarization state. The first optical fiber polarization controller 122 can adjust the polarized light of the first polarization state or the second polarization state, so as to output polarized light of a linear polarization state with a predetermined angle (45° linear polarized light). Among them, the allowable adjustment error when adjusting the first optical fiber polarization controller 122 can be within ±5°, that is, the adjustment error range is between -5° and +5°, and the preferred adjustment error is within ±2° to ±3° (preferably the adjustment error range is between -3° and +3°, and more preferably between -2° and +2°), so as to meet the accuracy requirements of quantum experiments as much as possible. Studies have found that the larger the error, the lower the interference contrast of the entangled source generated, and the lower the degree of violation of the Bell inequality.

[0034] In other words, the optical fiber polarization beam splitter is an optical fiber device that selectively filters the polarization of the optical signal. In the embodiment of the present application, the first optical fiber polarization beam splitter 121 can select the polarization of linear polarization light as horizontal or vertical polarization light. The polarization extinction ratio of the first optical fiber polarization beam splitter 121 can be above 20dB to prevent polarization crosstalk from affecting subsequent adjustments. The polarized light output by the first optical fiber polarization beam splitter 121 is input to the input port of the first optical fiber polarization controller 122. By adjusting the angle of the first optical fiber polarization controller 122, the polarization state of the pump light can be adjusted to a predetermined angle, for example, to 45° linear polarization, so that the output polarization light has equal projections in the horizontal and vertical polarization states. Afterwards, the predetermined angle linear polarization output by the first optical fiber polarization controller 122 enters the BBO crystal assembly 130. Optionally, the pigtails of the first optical fiber polarization beam splitter 121 and the first optical fiber polarization controller 122 (both optical fiber devices) are polarization-maintaining optical fibers, which can make the polarization state in the optical signal transmission channel stable.

[0035] In the exemplary embodiment of the present application, the BBO crystal assembly 130 in the quantum entanglement source device 100 may include a BBO crystal 135 and a first fiber collimator 131 to generate entangled photon pairs.

[0036] Specifically, the first fiber collimator 131 receives the predetermined angle linear polarization light output by the first fiber polarization controller 122, and the first fiber collimator 131 focuses the predetermined angle linear polarization light onto the BBO crystal 135. During operation, if the overall size of the device is not considered, the distance between the BBO crystal 135 and the first fiber collimator 131 can be adjusted according to the focal length of the first fiber collimator 131, so that the light output from the first fiber collimator 131 can just be focused on the BBO crystal 135, and the light beam is incident on the BBO crystal 135, so that the light processing process is optimized as much as possible.

[0037] Next, the BBO crystal 135 can generate an entangled photon pair based on the predetermined angle linear polarized light, and the entangled photon pair includes a first light signal and a second light signal, and the first light signal and the second light signal have different emission directions, thereby forming an angle. Specifically, the entangled photon pair can be generated by the parametric down-conversion process of the linear polarized light in the BBO crystal 135. Among them, the BBO crystal 135 has different separation angles for the entangled photon pairs generated by the parametric down-conversion according to different cutting angles. That is, the size of the angle between the two light signals of the entangled photon pair is determined by the cutting angle of the BBO crystal 135, and specifically, the size of the angle is proportional to the size of the cutting angle of the BBO crystal 135. Then, based on this, the emission angle of the entangled photon pair can be calculated according to the cutting angle of the BBO crystal 135. For example, the entangled photon pair generated by parametric down-conversion in the BBO crystal 135 may include signal light and idler light. The emission angles of the signal light and the idler light can be deduced according to the cutting angle of the BBO crystal 135, thereby facilitating the collection and processing of the entangled photon pair.

[0038] Regarding BBO crystals, it is generally believed that the single BBO product is a high-quality nonlinear frequency doubling crystal with the highest resistance to light damage, good light transmittance, and widest phase matching range in the current field of laser technology. The parametric down-conversion process is that after the pump light enters the BBO crystal, a pair of entangled photons can be generated based on the second-order nonlinear optical effect in the crystal. This process satisfies the conservation of energy and momentum (that is, it satisfies the phase matching condition), that is, the cutting angle of the BBO crystal and the emission angle of the entangled photon pair meet the phase matching condition, which is manifested as the angle of the entangled photon pair being proportional to the cutting angle of the BBO crystal. For example, when the wavelength of the pump light λ=405nm, the BBO crystal cutting angle is 29.2°, the angle of the entangled photon pair is 3°, and when the BBO crystal cutting angle is 30°, the angle of the entangled photon pair is 6.1°. The following schematically shows the conversion relationship between the angle of an entangled photon pair generated by pump light passing through a BBO crystal and the cutting angle of the BBO crystal:

[0039]

[0040] Where θ is the cutting angle of the BBO crystal, n o and n e are the refractive indices of the o-light and e-light decomposed by the pump light in the BBO crystal (related to the wavelength of the pump light), ω p is the frequency of the pump light, α is the angle between the outgoing photon and the optical axis, and the angle between the entangled photon pair is 2α.

[0041] refer to Figure 2Optionally, the BBO crystal assembly 130 may further include a second optical fiber collimator 132, which can transmit the first optical signal of the entangled photon pair to a predetermined optical signal processing device. Optionally, the BBO crystal assembly 130 may further include a third optical fiber collimator 133, which can transmit the second optical signal of the entangled photon pair to a predetermined optical signal processing device. The second optical fiber collimator 132 and the third optical fiber collimator 133 are respectively placed on the outgoing optical paths of the two optical signals of the entangled photon pair, and the entangled photon pair can be collected and transmitted to a downstream device. Optionally, the downstream device includes a test device for the entangled photon pair.

[0042] The above describes the principle and process of generating entangled photon pairs by the quantum entanglement source device 100 of the present application through an exemplary embodiment. Further, the quantum entanglement source device 100 of the present application may also include one or more precision adjustment seats, which can carry two of the first fiber collimator 131, the second fiber collimator 132 and the third fiber collimator 133, and one or more lenses may be arranged on the precision adjustment seat, and the focal length of the lens may be determined according to the distance between the BBO crystal and the fiber collimator.

[0043] refer to Figure 3 Taking the first fiber collimator 131 placed on the precision adjustment seat 1361, the second fiber collimator 132 placed on the precision adjustment seat 1362, and the third fiber collimator 133 placed on the precision adjustment seat 1363 as an example, the lens is arranged as follows: the lens 1371 can be placed at the exit end of the first fiber collimator 131, and the focal length of the lens 1371 can be determined according to the distance between the BBO crystal 135 and the first fiber collimator 131. For example, if the distance between the center of the BBO crystal 135 and the first fiber collimator 131 is 50 mm, a lens with a focal length of 50 mm can be selected as the lens 1371. Similarly, lens 1372 can be placed at the incident end of the second fiber collimator 132, and the focal length of lens 1372 can be determined according to the distance between the BBO crystal 135 and the second fiber collimator 132; lens 1373 can be placed at the incident end of the third fiber collimator 133, and the focal length of lens 1373 can be determined according to the distance between the BBO crystal 135 and the third fiber collimator 133.

[0044] By adjusting the precision adjustment seats 1361, 1362, 1363 and the lenses 1371, 1372, 1373, the polarized light output from the first fiber collimator 131 can be focused and incident on the BBO crystal 135, and the two beams of entangled photon pairs generated by the BBO crystal 135 enter the second fiber collimator 132 and the third fiber collimator 133 respectively.

[0045] As an illustrative embodiment, in the overall design, the distances between the BBO crystal 135 and the first fiber collimator 131, the second fiber collimator 132, and the third fiber collimator 133 can be adjusted as needed according to the spatial size requirements of the entire BBO crystal assembly 130. After the distances are determined, the focal length of the lens required can be determined accordingly, and lenses with suitable focal lengths are selected as lens 1371, lens 1372, and lens 1373. According to the above design, in situations where the integration requirement is high, for example, the smaller the space occupied by the quantum entanglement source device 100 is required, the shorter the focal length lens should be selected, so that the spatial size of the BBO crystal assembly 130 can be compressed as much as possible without affecting the normal operation of the BBO crystal assembly 130.

[0046] The above describes the micro-assembly process design for the BBO crystal component 130 in the present application. Optionally, lenses 1371, 1372 and 1373 can be micro-lenses. Micro-lenses refer to lenses with very small focal lengths and sizes, which can enable the light beam collimated by the first fiber collimator 131 to be focused onto the BBO crystal 135 within a very short distance, so that the generated entangled photon pairs can be quickly collimated into the second fiber collimator 132 and the third fiber collimator 133.

[0047] Based on the above-mentioned micro-assembly process design, the entire coupling distance of the BBO crystal assembly 130 can be very short, especially the straight-line distance of the optical path of the BBO crystal assembly 130 can be greatly compressed. Optionally, the maximum straight-line distance of the area occupied by the BBO crystal 135, the first fiber collimator 131, the second fiber collimator 132 and the third fiber collimator 133 can be reduced to no more than 22 cm, preferably no more than 10 cm. The design according to the embodiment of the present application can effectively reduce the volume of the entire quantum entanglement source device 100, which is convenient for integration.

[0048] In addition, after the positions of the lenses and precision adjustment seats are determined, they can be fixed with glue to enhance the stability of the entire coupling link, thereby improving the stability of the entire entanglement source. Figure 4 Taking the five-axis adjustment frame as an example of a precision adjustment seat, the three fiber collimators 131, 132 and 133 can be installed on the three five-axis adjustment frames 1315, 1325 and 1335 respectively, and the micro lenses 61, 62 and 63 are respectively bonded to the ends of each fiber collimator with epoxy glue, and the knobs of the three five-axis adjustment frames are adjusted (corresponding to the horizontal swing angle, pitch swing angle, tilt swing angle, horizontal translation and vertical translation). After all dimensions are adjusted, they are also fixed with glue. Optionally, the single-channel detector count and coincidence count are maximized. At this time, the positions of the three collimators 131, 132 and 133 are optimal. At this time, all the knobs of the three five-axis adjustment frames are fixed with glue. The purpose is to fix all the changeable dimensions in the entire coupling process to ensure that the orientation will not change due to external forces.

[0049] In the exemplary embodiment of the present application, optionally, after obtaining the entangled photon pair, the light beam of the entangled photon pair can be filtered, and for this purpose, a filtering device can be provided at the output end of the BBO crystal assembly 130, and the filtering device can include a first optical fiber filter 138 and a second optical fiber filter 139. The first optical fiber filter 138 is connected to the output end of the second optical fiber collimator 132, and can filter out the photons in the first optical signal that do not conform to the wavelength of the entangled photons; the second optical fiber filter 139 is connected to the output end of the third optical fiber collimator 133, and can filter out the photons in the second optical signal that do not conform to the wavelength of the entangled photons, and can reduce the noise caused by external environmental noise or pump photons.

[0050] Additionally, after the entangled photon pair is generated using the BBO crystal component 130, the entangled photon pair can also be tested for quality using a dedicated test device. In the illustrative embodiment of the present application, the quantum entangled source device 100 may also include a test component 140 for performing a measurement-based measurement and counting on the first optical signal and the second optical signal, and the quality of the entangled photon pair can be evaluated based on the measurement value and the count value.

[0051] Optionally, the test component 140 may include a first single photon detector 141, a second single photon detector 142, and a coincidence counter 143. Specifically, the first single photon detector 141 may detect and count the first optical signal, the second single photon detector 142 may detect and count the second optical signal, and the coincidence counter 143 may receive the electrical signals output by the first single photon detector 141 and the second single photon detector 142, and perform time coincidence measurement and counting on the electrical signals, and the measured value and the count value may reflect the quality of the entangled photon pair. Generally, a single photon detector (SPD) is an ultra-low noise device that can detect the presence of a single photon and convert it into a measurable electrical signal output, thereby realizing the detection and counting of a single photon, and can be applied in the fields of quantum optics, laser ranging, bio-optics, etc. The basic working principle of a coincidence counter is to identify the output signal of the detector into a digital signal and perform statistical analysis on these digital signals in multiple measurement cycles. In quantum computing or quantum simulation experiments, a coincidence counter can be used to analyze coincidence events measured by a single photon detector (SPD), which can provide key data support for quantum research. For example, the generated entangled photon pairs can be tested for characteristics such as Bell inequality tests and interference contrast. The following will explain the test process and results in detail through specific examples.

[0052] Optionally, the test assembly 140 may further include a second fiber polarization controller 146 and a third fiber polarization controller 147, wherein the second fiber polarization controller 146 is disposed between the first fiber filter 138 and the first single-photon detector 141, and can adjust the polarization state of the first optical signal; the third fiber polarization controller 147 is disposed between the second fiber filter 139 and the second single-photon detector 142, and can adjust the polarization state of the second optical signal. The reason for such an arrangement is that when a single-photon detector and a coincidence counter are used for detection, the polarization state of the light beam can be adjusted, and the second fiber polarization controller 146 and the third fiber polarization controller 147 can be used to make the light beam of the entangled photon pair in different polarization states (for example, but not limited to, 0° polarization state, 90° polarization state, +45° polarization state, -45° polarization state) to complete the detection. The adjustment error of the second fiber polarization controller 146 and the third fiber polarization controller 147 should be controlled within ±2° to ±3°, preferably within ±2° (preferably the adjustment error range is between -3° and +3°, more preferably between -2° and +2°).

[0053] Optionally, the test assembly 140 may further include a second optical fiber polarization beam splitter 148 and a third optical fiber polarization beam splitter 149, wherein the second optical fiber polarization beam splitter 148 is disposed between the second optical fiber polarization controller 146 and the first single-photon detector 141, and may perform polarization filtering on the first optical signal after adjusting the polarization state; the third optical fiber polarization beam splitter 149 is disposed between the third optical fiber polarization controller 147 and the second single-photon detector 142, and may perform polarization filtering on the second optical signal after adjusting the polarization state. The second optical fiber polarization beam splitter 148 and the third optical fiber polarization beam splitter 149 may be used to perform polarization filtering on the light beam that is about to enter the single-photon detector and the coincidence counter, and filter out polarized light that does not meet the requirements, thereby reducing test errors and improving test accuracy.

[0054] Optionally, the pigtails of all optical fiber devices used in the test assembly 140 are polarization-maintaining optical fibers, so as to ensure the stability of the polarization state of the optical signal transmitted in the optical fiber and reduce the test error caused by the polarization change.

[0055] As an illustrative example, the model information of several devices or equipment that can be used is listed below. These model information do not constitute any limitation on the implementation of the embodiments of the present application. In the process of implementing the technical solution of the present application, suitable devices and equipment can be selected according to the needs to execute the complete or partial solution of the embodiments of the present application. A group of model information of devices and equipment that can be selectively used is as follows.

[0056] 1) The pump light source 110 may be a semiconductor laser with a line width of 0.6 nm and a central wavelength of 405 ± 0.1 nm.

[0057] 2) The first optical fiber collimator 131 may be a CFC11A-A type optical fiber collimator.

[0058] 3) The second fiber collimator 132 and the third fiber collimator 133 may be CFC11P-B fiber collimators.

[0059] 4) The BBO crystal 135 may be a BBO crystal that is phase-matched in type I and is formed by bonding two 0.3×0.3×0.5 mm optical axis perpendicular crystals, with a cutting angle of 30°.

[0060] 5) The first optical fiber polarization controller 122 can use a 405 polarization-maintaining pigtail with a two-ring structure, a diameter of 27 mm, and an FC / PC connector.

[0061] 6) The first optical fiber polarization beam splitter 121 may be a PBS-405-P21110 model.

[0062] 7) The second optical fiber polarization controller 146 and the third optical fiber polarization controller 147 can adopt the FPC023 model.

[0063] 8) The first optical fiber filter 138 and the second optical fiber filter 139 can be selected with a central wavelength of 810 nm and a bandwidth of 3 nm, and use polarization-maintaining pigtails.

[0064] 9) The second optical fiber polarization beam splitter 148 and the third optical fiber polarization beam splitter 149 can both adopt the PBS-780-P21110 model.

[0065] The entangled photon pairs generated by the quantum entanglement source device 100 of the present application can be detected, and the detection preparation process and the analysis of the detection results are schematically described below.

[0066] The SPDC process of BBO crystal parametric down-conversion can generate entangled photon pairs (such as signal light and idler light). If the two beams of the entangled photon pair are horizontally polarized light and vertically polarized light, the entangled state generated is The two optical signals that generate entangled photon pairs are connected to two optical fiber filters respectively. The optical signals output by the two optical fiber filters are connected to two optical fiber polarization controllers respectively. The polarization state is adjusted by the optical fiber polarization controller (such as adjusting to 0°, 90° or ±45°, with an error of no more than ±2°, that is, the error is between -2° and +2°). The output optical signals enter two optical fiber polarization beam splitters for polarization filtering. The optical signals output by the optical fiber polarization beam splitters are respectively input into two single photon detectors SPD to obtain two electrical signals, which are both input into the coincidence counter for testing. Several schematic test results are as follows:

[0067] a) Scenario 1:

[0068] If the two output polarization states of the entangled photon pair (such as signal light and idler light) are modulated to the horizontal polarization state (0°) or the vertical polarization state (90°) through the polarization controller, the measurement basis is "HH" or "VV", and the coincidence count value is the largest, which is recorded as C. max .

[0069] b) Case 2:

[0070] If the polarization controller is used to modulate one of the two output polarization states of the entangled photon pair (such as signal light and idler light) to a horizontal polarization state (0°) and the other to a vertical polarization state (90°), the measurement basis is "HV" or "VH", and the minimum coincidence count value is recorded as C. min .

[0071] c) Case 3:

[0072] If the two output polarization states of the entangled photon pair (such as signal light and idler light) are modulated to the +45° polarization state or the -45° polarization state simultaneously through the polarization controller, the measurement basis is "++" or "--", and the coincidence count value is the largest, which is recorded as C. max .

[0073] d) Case 4:

[0074] If the polarization controller is used to modulate one of the two output polarization states of the entangled photon pair (such as signal light and idler light) to a +45° polarization state and the other to a -45° polarization state, the measurement basis is "+-" or "-+", and the coincidence count value is the smallest, which is recorded as C. min .

[0075] Furthermore, based on the above test results, we can also obtain the violation results of Bell inequality, entanglement brightness and entanglement source interference contrast. HH , C VV , C HV , C VH , C ++ , C -- , C +- , C -+ ) and the values ​​of multiple matrices (such as E(0°,-45°), E(0°,45°), E(-90°,-45°), E(-90°,45°)) that can be obtained under other measurement bases, based on which the violation results of Bell's inequality, entanglement brightness, and entanglement source interference contrast can be calculated. The following is a set of schematic examples:

[0076]

[0077] Among them, CHH is the coincidence count value under HH measurement basis per unit time, C VV is the coincidence count value under VV measurement basis per unit time, C HV is the coincidence count value in the HV measurement basis per unit time. For example, if the two polarization controllers are adjusted to the horizontal polarization state during the test, the measurement basis is HH, and the entangled photon pair generated by the BBO crystal is detected, and the coincidence count C is recorded. HH If the two polarization controllers are adjusted to the perpendicular polarization state, the measurement basis is VV, and the entangled photon pairs generated by the BBO crystal are detected, and the coincidence count C is recorded. VV In addition, it is necessary to measure the actual power of the pump light before it reaches the BBO crystal. The brightness of the entangled light can be calculated using the above entanglement brightness calculation formula to evaluate the quality of the entangled photon pair.

[0078] Based on at least one of the above embodiments of the present application, optical signal transmission involved can use optical fiber devices, and the devices used to realize parametric down-conversion are embedded in the optical path in a micro-assembly process. Compared with the BBO entangled source built by the existing space devices, the present application has higher stability, lower maintenance cost, smaller size, and easier integration; in addition, compared with some entangled source preparation devices that use optical fiber devices but require dual-wavelength input and output, the optical fiber devices used in the present application only require single wavelength transmission, no customized devices are required, the cost is lower, and no interferometer is required. There is no strict requirement for the length of the optical fiber, etc., which greatly reduces the construction complexity of such devices in the same field, and releases the intensity of the construction work of the researchers on the quantum entangled source device. On this basis, researchers can construct a quantum computing device including a quantum entangled source device to generate entangled photon pairs and conduct further quantum optical experiments and related quantum computing processing.

[0079] In addition, it should be noted that the present application is not limited to the specific configurations and processes described above and shown in the figures. For the sake of simplicity, a detailed description of some known knowledge is omitted in the text. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present application is not limited to the specific steps described and shown, and those skilled in the art can make various changes, modifications and additions, or change the order between the steps after understanding the spirit of the present application.

[0080] It should be understood that the protection scope of the present application is not limited to this document. Any technician familiar with the technical field can think of some equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should be included in the protection scope of the present application.

Claims

1. A quantum entanglement source device, characterized in that: include: A pump light source, a first optical fiber polarization beam splitter, a first optical fiber polarization controller, a first optical fiber collimator, a BBO crystal, a second optical fiber collimator, a third optical fiber collimator, a second optical fiber polarization controller, a third optical fiber polarization controller, a first single-photon detector, a second single-photon detector, a coincidence counter, a mass analysis module, three precision adjustment seats and three microlenses, wherein the first optical fiber collimator, the second optical fiber collimator, the third optical fiber collimator and the three microlenses are respectively mounted on the three precision adjustment seats, wherein the linear distance of the area occupied by the first optical fiber collimator, the BBO crystal, the second optical fiber collimator and the third optical fiber collimator is not greater than 10 cm; wherein, During the operation of the quantum entanglement source device, the pump light generated by the pump light source outputs vertical or horizontal polarized light through the first optical fiber polarization beam splitter, and the polarized light outputs a predetermined angle polarized light through the first optical fiber polarization controller. After the predetermined angle polarized light enters the BBO crystal, an entangled photon pair is output, and the entangled photon pair includes a first optical signal and a second optical signal, wherein the first optical signal is output to the second optical fiber polarization controller through the second optical fiber collimator and the microlens to adjust the polarization state, and the second optical signal is output to the third optical fiber polarization controller through the third optical fiber collimator and the microlens to adjust the polarization state, and the adjusted first optical signal and the second signal light are in different polarization states, and the single-channel count value of the first optical signal is determined by the first single-photon detector, the single-channel count value of the second optical signal is determined by the second single-photon detector, and then the coincidence count value of the first optical signal and the second optical signal is obtained by the coincidence counter, and the quality analysis module determines the quality of the entangled photon pair according to the single-channel count value of the first optical signal and the second optical signal and the coincidence count value; The adjustment errors of the first optical fiber polarization controller, the second optical fiber polarization controller and the third optical fiber polarization controller are all between -2° and +2°, and all devices except the BBO crystal are connected to the upstream and downstream devices through polarization-maintaining optical fibers.

2. The quantum entanglement source device according to claim 1, characterized in that: The predetermined angle polarized light includes 45° linear polarized light.

3. The quantum entanglement source device according to claim 1, characterized in that: The entangled photon pair is generated by a parametric down-conversion process of linearly polarized light in a BBO crystal, wherein the angle between two optical signals of the entangled photon pair is proportional to the cutting angle of the BBO crystal.

4. The quantum entanglement source device according to claim 1, characterized in that: Also includes: A first optical fiber filter connected to the output end of the second optical fiber collimator, used for filtering out photons in the first optical signal that do not conform to the wavelength of the entangled photons; and / or, The second optical fiber filter is connected to the output end of the third optical fiber collimator and is used to filter out the photons in the second optical signal that do not conform to the wavelength of the entangled photons.

5. The quantum entanglement source device according to claim 1, characterized in that: The first optical signal is signal light, and the second optical signal is idler light.

6. The quantum entanglement source device according to claim 1, characterized in that: Also includes: A second optical fiber polarization beam splitter disposed between the second optical fiber polarization controller and the first single-photon detector, for performing polarization filtering on the first optical signal after adjusting the polarization state; The third optical fiber polarization beam splitter arranged between the third optical fiber polarization controller and the second single-photon detector is used for performing polarization filtering on the second optical signal after the polarization state is adjusted.

7. A quantum computing device, characterized in that include: The quantum entanglement source device according to any one of claims 1 to 6.

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