A quantum teleportation system and method with frequency conversion function

Abstract

The present invention provides a quantum teleportation system with a frequency conversion function, including a Charlie end, an Alice end, and a Bob end. The present invention provides a method of using a single crystal to simultaneously provide a high-quality entanglement source at the Charlie end and perform two nonlinear processes of converting the frequency of a low-frequency single photon to the communication band of 1550 nm, achieving wide frequency conversion, communication band optimization, equipment simplification, and cost reduction, improving the stability of phase matching, and being more conducive to long-distance transmission. The present invention also provides a quantum teleportation method with a frequency conversion function.

Description

Technical Field

[0001] The present invention relates to the technical field of quantum teleportation, and particularly to a quantum teleportation system and method with a frequency conversion function. Background Art

[0002] Large-scale quantum computing and long-distance quantum communication are an inevitable direction in quantum information research. Among them, quantum teleportation is not only a theoretical and experimental manifestation of the particularity and superiority of quantum mechanics, but also the core technology of direct quantum communication, and is an important development direction for the practical application of quantum communication. Quantum teleportation can realize the transmission of quantum states between distant nodes in a quantum network without directly exchanging quantum information, playing a key role in the development of quantum communication, quantum computing, and quantum networks. With the development of quantum communication and quantum network technologies towards long-distance and large-scale directions, in order to further realize long-distance quantum teleportation, it is necessary to prepare high-quality quantum light sources in the communication band, which is also essential for remote quantum key distribution and multi-node quantum networks.

[0003] In quantum communication, an important problem that needs to be urgently solved is to reduce the loss during photon transmission. In the metropolitan fiber optic communication network, the optimal communication wavelength is 1550 nm, at which the fiber transmission loss is the lowest, and it is most suitable for long-distance photon transmission and the establishment of quantum networks. Therefore, in order to realize long-distance quantum teleportation, its wavelength needs to be maintained in the 1550 nm communication band. Currently, in the quantum teleportation technology, the wavelength of the single photon whose quantum state needs to be transmitted at the Alice end needs to be the same as that of the entangled photon, which requires the wavelength of the single photon to be 1550 nm. For single photons with other wavelengths, non-degenerate entangled light sources (one 1550 nm photon at the Bob end and one photon with other wavelengths at the Alice end) can be used for quantum teleportation, but the brightness of such entangled light sources is low, and neither the single photon nor the non-1550 nm photons in the entangled light source can be transmitted over long distances, which limits the application range of quantum teleportation. Summary of the Invention

[0004] The purpose of the present invention is: aiming at the deficiencies in the above background art, to provide a single crystal that simultaneously provides a high-quality entangled source at the Charlie end and two non-linear processes for converting the frequency of low-frequency single photons to the 1550 nm communication band, so as to reduce the complexity of the device, improve the stability of phase matching, and be more conducive to long-distance transmission.

[0005] To achieve the above purpose, the present invention provides a quantum teleportation system with a frequency conversion function, including a Charlie end, an Alice end, and a Bob end;

[0006] The Charlie end is provided with a Sagnac loop, a PPLN crystal, a DPBS, and a DHWP; the PPLN crystal is arranged inside the Sagnac loop; the DPBS is provided with port A and port B; the Charlie end is further provided with a PUMP, an ATT, an HWP, and a QWP; the pump light generated by the PUMP is adjusted in power by the ATT, and then the polarization direction of the pump light is set by the HWP and the QWP, and finally it is injected into port A of the DPBS;

[0007] The DPBS divides the pump light into two beams, the DHWP is arranged on the optical path of one of the beams, the clockwise vertically polarized light is converted into horizontally polarized light by the DHWP, and then enters the PPLN crystal and generates horizontally polarized photon pairs at 1550 nm, and then transmits and exits from port A; the horizontally polarized pump light propagating in the counterclockwise direction passes through the PPLN crystal, generates horizontally polarized photon pairs at 1550 nm, and is then converted into vertically polarized photon pairs by the DHWP, and then is reflected by the DPBS and exits from port A; the two optical paths obtain an entangled state after adjusting the phase compensation of the interference optical path;

[0008] Port B of the DPBS receives single photons and divides them into two beams. The clockwise horizontally polarized light is converted into vertically polarized light by the DHWP, undergoes a process of parametric down-conversion with the horizontally polarized pump light, and is converted into vertically polarized single photons at 1550 nm, and then is reflected by the DPBS and exits from port B; the counterclockwise vertically polarized light passes through the PPLN crystal, is converted into vertically polarized single photons at 1550 nm, and is then converted into horizontally polarized single photons by the DHWP, and then is transmitted by the DPBS and exits from port B; the two optical paths generate a quantum state by modulating the attenuation amplitude and phase;

[0009] A DM and a BS are further arranged between port A of the DPBS and the PUMP. The DM is used to introduce the entangled photon pairs emitted from port A into the BS, and the BS splits them into two beams. One beam of entangled photons is transmitted to the Bob end through a quantum channel, and the other beam of entangled photons is sent to the Alice end for joint Bell state measurement; port B of the DPBS sends the emitted single photons to the Alice end for joint Bell state measurement;

[0010] The Alice end is provided with an SPD, an FBS, an HWP, and a QWP. The HWP and the QWP are used for polarizing single-photon beams. The FBS is used to combine single photons and entangled photons into the SPD for joint Bell state measurement; a classical channel is arranged between the Alice end and the Bob end, and the joint Bell state measurement results are transmitted to the Bob end through the classical channel;

[0011] The Bob side is provided with an SPD, a POL, an HWP, and a QWP; the entangled photons transmitted from the quantum channel are polarized under the action of the HWP, the QWP, and the POL and then received by the SPD. According to the result of the joint Bell state measurement of the classical channel, a corresponding unitary transformation is performed on the entangled photons to obtain the required quantum state.

[0012] Further, both the Alice side and the Bob side are provided with an SMF and an FC. The FC is used to couple the light beam into the SMF, and then it is transmitted through the SMF to the corresponding SPD.

[0013] Further, the combination of the QWP and the HWP is used to adjust the photon polarization to any direction for initial polarization and subsequent adjustment.

[0014] The present invention also provides a quantum teleportation method with a frequency conversion function, which adopts a quantum teleportation system with a frequency conversion function as described above. The power of the pump light entering the system is adjusted by the ATT, and then the polarization direction of the pump light is set through the QWP and the HWP to make the pump light polarized at 45°. The 775 nm pump light is incident from port A and is split into two beams by the PBS and enters the Sagnac loop; the clockwise vertically polarized light is converted into horizontally polarized light by the fixed 45° DHWP, and 1550 nm horizontally polarized photon pairs are generated through the spontaneous parametric down-conversion process in the PPLN crystal: This photon pair is transmitted through the PBS and exits from port A; the horizontally polarized pump light propagating in the counterclockwise direction passes through the PPLN crystal, generates 1550 nm horizontally polarized photon pairs, and is converted into vertically polarized photon pairs through the DHWP: This photon pair is reflected by the PBS and exits from port A; an entangled state is obtained: Where φ0 represents the relative phase between the two-photon pairs. By adjusting the phase compensation of the optical path after interference, φ0 = 0, so as to obtain the required entangled state: |Φ + > 23 = |H>2|H>3 + |V>2|V>3; the entangled state is split into two beams by the BS, one beam is transmitted to the Bob side through the quantum channel, and one beam is sent to the Alice side for joint Bell state measurement;

[0015] The 45° polarized 517 nm single photon is incident from port B, is split into two beams by the PBS and enters the Sagnac loop. The clockwise horizontally polarized single photon is converted into a vertically polarized single photon by the fixed 45° DHWP, and undergoes a parametric down-conversion process with the 775 nm horizontally polarized pump light to be converted into a 1550 nm vertically polarized single photon: The difference-frequency single photon is emitted from port B; the vertically polarized single photon in the counterclockwise direction passes through the PPLN crystal, is converted into a vertically polarized single photon at 1550 nm, and is converted into a horizontally polarized single photon through the DHWP: The difference-frequency single photon is emitted from port B; by modulating the amplitude and phase of the attenuated laser, the quantum state to be transmitted is generated: |φ>1 = α|H>1 + β|V>1;

[0016] At the Alice end, the entangled photon pair overlaps with the frequency-converted input single photon on the FBS, a joint Bell state measurement is performed, and the measurement result is transmitted to the Bob end through the classical channel; at the Bob end, the photon transmitted by the Charlie end is received through the quantum channel, and according to the result of the joint Bell state measurement on the classical channel, a corresponding unitary transformation is made on the photon, so as to obtain the required information to realize quantum teleportation.

[0017] The above scheme of the present invention has the following beneficial effects:

[0018] The quantum teleportation system and method with frequency conversion function provided by the present invention realizes the combination of multiple parametric down-conversion processes in the quantum teleportation process and uses the same nonlinear crystal to realize. Compared with the existing technologies that mostly use a nonlinear crystal to realize a single type of parametric down-conversion, and multiple sets of parametric down-conversion systems are required to generate multiple different types of entangled photons at the same time, this scheme utilizes the properties of the nonlinear crystal, designs and regulates the polarization period and temperature that need to satisfy quasi-phase matching, and realizes the work of multiple types of parametric down-conversion with the same crystal, significantly reducing the experimental complexity and saving costs;

[0019] The present invention realizes the quantum teleportation process with frequency conversion function. According to the calculation and simulation, when the temperature and polarization period of the PPLN crystal are set to appropriate working points, single photons with any wavelength in the 460 nm - 580 nm band can be converted to the communication band to realize long-distance quantum teleportation. For example: when the temperature of the PPLN crystal is set to 128.36 °C and the polarization period is 16.341 μm, the single photon with a wavelength of 517 nm to be transmitted can be frequency down-converted to 1550 nm;

[0020] The entanglement source generated in the present invention can be combined with the communication band with less fiber loss to realize entanglement distribution over a longer distance. Currently, the entangled photon pairs generated in experiments are mostly around 800 nm, and photons at this wavelength have relatively large losses in fiber transmission. This scheme converts the 775 nm pump light into entangled photon pairs at 1550 nm, which can be compatible with the existing mature technologies in the communication band to realize metropolitan-level entangled photon distribution;

[0021] Other beneficial effects of the present invention will be described in detail in the subsequent specific implementation part. Description of the Drawings

[0022] Figure 1 This is a schematic diagram of the system of the present invention. Detailed Embodiments

[0023] The following describes the embodiments of the present disclosure through specific examples. Those skilled in the art can easily understand other advantages and effects of the present disclosure from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all of the embodiments. The present disclosure can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present disclosure. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other. Based on the embodiments in the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present disclosure.

[0024] It should be noted that the following describes various aspects of the embodiments within the scope of the appended claims. It should be obvious that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is illustrative only. Based on the present disclosure, those skilled in the art should understand that one aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects described herein can be used to implement the device and / or practice the method. Additionally, this device and / or this method can be implemented using other structures and / or functionality in addition to one or more of the aspects described herein.

[0025] It should also be noted that the drawings provided in the following embodiments only schematically illustrate the basic concept of the present disclosure. The drawings only show the components related to the present disclosure and are not drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and ratio of each component in its actual implementation can be arbitrarily changed, and the component layout type may also be more complex. Additionally, in the following description, specific details are provided for the purpose of facilitating a thorough understanding of the examples. However, those skilled in the art will understand that the described aspects can be practiced without these specific details.

[0026] As Figure 1 shown, an embodiment of the present invention provides a quantum teleportation system with a frequency conversion function, including a Charlie end, an Alice end, and a Bob end.

[0027] The Charlie side is provided with a Sagnac loop, a PPLN crystal, a DPBS, and a DHWP. The PPLN crystal is arranged inside the Sagnac loop structure. In this embodiment, when the 775-nm pump light and the 517-nm single photon pass through the PPLN crystal with a polarization period of 16.341 μm and a temperature of 128.36 °C from both ends of the DPBS respectively, two nonlinear processes of collinear Type-0 and collinear Type-II can be achieved simultaneously, thereby generating high-quality entangled photon pairs and single photons. (Note: This method is also applicable to non-517-nm single photons. Just adjust the polarization period and temperature of the PPLN crystal to achieve the above functions.)

[0028] Among them, the 775-nm pump light is generated by the Charlie side. The Charlie side is also provided with a PUMP, an ATT, an HWP, and a QWP. The pump light generated by the PUMP is adjusted in power by the ATT, and then the polarization direction of the pump light is set by the HWP and the QWP, making the pump light polarized at 45°, and finally injected into port A of the DPBS.

[0029] The DPBS divides the 775-nm pump light into two beams. The DHWP is arranged on the optical path of one of the beams. The clockwise vertically polarized light is converted into horizontally polarized light by the fixed 45° DHWP, and then enters the PPLN crystal and generates a pair of 1550-nm horizontally polarized photons. This photon pair is injected into the DPBS, transmitted and exits from port A. The horizontally polarized pump light propagating counterclockwise passes through the PPLN crystal, generates a pair of 1550-nm horizontally polarized photons, and is then converted into a pair of vertically polarized photons by the DHWP. This photon pair is reflected by the DPBS and exits from port A. The two optical paths obtain the required entangled state by adjusting the phase compensation of the interference optical path.

[0030] On the other hand, port B of the DPBS receives the 517-nm single photon and divides it into two beams. The clockwise horizontally polarized light is converted into vertically polarized light by the fixed 45° DHWP, and undergoes a spontaneous parametric down-conversion (SPDC) process with the 775-nm horizontally polarized pump light, converting into a 1550-nm vertically polarized single photon. The difference-frequency single photon is reflected by the DPBS and exits from port B. At the same time, the counterclockwise vertically polarized light passes through the PPLN crystal, is converted into a 1550-nm vertically polarized single photon, and is then converted into a horizontally polarized single photon by the DHWP. The difference-frequency single photon is transmitted by the DPBS and exits from port B. The two optical paths generate the quantum state to be transmitted by modulating the attenuation amplitude and phase.

[0031] There is also a DM and a BS between port A of the DPBS and the PUMP. The entangled photon pairs emitted from port A are introduced into the BS through the DM. The BS splits them into two beams. One beam of entangled photons is transmitted to the Bob side through the quantum channel, and the other beam of entangled photons is sent to the Alice side for joint Bell state measurement (BSM). There is also a DM between port B of the DPBS and the Alice side. The single photons emitted from port B are sent to the Alice side through the DM for joint Bell state measurement (BSM).

[0032] In the Alice side, there are an SPD, an FBS, an HWP, and a QWP. The single-photon beam at 517 nm is polarized by the HWP and QWP. At the same time, the quantum state single photons emitted from port B are polarized by the HWP and QWP and then combined with the entangled photons by the FBS and enter the SPD for joint Bell state measurement. There is also a classical channel between the Alice side and the Bob side. The results of the joint Bell state measurement are transmitted to the Bob side through the classical channel.

[0033] In the Bob side, there are an SPD, a POL, an HWP, and a QWP. The entangled photons transmitted from the quantum channel are received by the SPD after being polarized under the action of the HWP, QWP, and POL. According to the results of the joint Bell state measurement in the classical channel, a corresponding unitary transformation is made on the entangled photons, so as to obtain the required quantum state and realize quantum teleportation.

[0034] In addition, both the Alice side and the Bob side are provided with an SMF and an FC. The light beam is coupled into the SMF through the FC and then transmitted to the corresponding SPD through the SMF. In the Charlie side, there is also an M to reflect the optical path so that the optical path proceeds in a preset manner through each device.

[0035] Among them, SMF: single-mode fiber, single-mode fiber; FC: fiber coupling, fiber coupler; POL: Polarizer, polarizer; M: mirror, mirror; QWP: Quarter-wavelength plate, quarter-wave plate; HWP: half-wavelength plate, half-wave plate; ATT: attenuator, attenuator; PUMP: pump lightsource, pump light source; DHWP: dual-wavelength half-wave plate, dual-wavelength half-wave plate; DPBS: dual-polarizing beam splitter, dual-polarizing beam splitter; BS: beam splitter, beam splitter; PPLN: Periodically polarized lithium niobate, periodically poled lithium niobate; DM: dichroic mirror, dichroic mirror.

[0036] In this embodiment, the combination of QWP and HWP can adjust the photon polarization to any direction, which can play the role of initial polarization (POL also has this function) and subsequent adjustment. ATT plays the role of adjusting the output power. The greater the attenuation, the lower the subsequent pump light power. In the system, DHWP is generally set with the fast axis direction at 45° to the optical axis direction. For the pump light at 775 nm and the entangled photon pair at 1550 nm, it can rotate their polarization directions by 90°, that is, change the horizontal polarization to vertical polarization and the vertical polarization to horizontal polarization. DPBS can satisfy the polarization splitting of the pump wavelength 775 nm light and can also complete the polarization splitting of the entangled photon pair, and cooperate with the Sagnac loop to realize the preparation of Bell states. The PPLN crystal is a non-linear crystal whose regional polarity can be artificially modulated, and realizes quasi-phase matching of the designed frequency to increase the efficiency of non-linear effect photon generation.

[0037] Based on the same inventive concept, this embodiment also provides a quantum teleportation method. At the Charlie end, according to the matrix of the non-linear susceptibility tensor, a crystal configuration that cuts along the y direction and propagates in the x direction is selected in the PPLN crystal. Based on the Sagnac loop, type-0 (H→H+H) parametric down-conversion is used to generate entangled photon pairs in the communication band, and type-II (V+H→V) parametric down-conversion is used to realize the frequency conversion of single photons.

[0038] Adjust the pump light power entering the system through ATT, and then set the polarization direction of the pump light through QWP and HWP so that the pump light is polarized at 45°. The 775 nm pump light is incident from port A and is split into two beams by PBS and enters the Sagnac loop. The clockwise vertically polarized light is converted into horizontally polarized light by a fixed 45° DHWP, and horizontally polarized photon pairs at 1550 nm are generated through the SPDC process in the PPLN crystal: The photon pair is transmitted through PBS and exits from port A. At the same time, the horizontally polarized pump light propagating in the counterclockwise direction passes through the PPLN crystal, generates horizontally polarized photon pairs at 1550 nm, and is converted into vertically polarized photon pairs through DHWP: The photon pair is reflected by PBS and exits from port A. Therefore, an entangled state is obtained: where φ0 represents the relative phase between the two-photon pairs. By adjusting the phase compensation of the optical path after interference, φ0 = 0 can be achieved, thus obtaining the required entangled state: |Φ + > 23 = |H>2|H>3 + |V>2|V>3. The entangled state is split into two beams by a BS. One beam is transmitted through the quantum channel to the Bob side, and the other beam is sent to the Alice side for joint Bell state measurement (BSM).

[0039] The 517 nm single photon polarized at 45° to be transmitted is incident from port B, and is also split into two beams by PBS and enters the Sagnac loop structure. The horizontally polarized single photon in the clockwise direction is converted into a vertically polarized single photon by a fixed 45° DHWP, and undergoes the SPDC conversion process with the 775 nm horizontally polarized pump light, and is converted into a 1550 nm vertically polarized single photon: The difference-frequency single photon exits from port B. At the same time, the vertically polarized single photon in the counterclockwise direction passes through the PPLN crystal, is converted into a 1550 nm vertically polarized single photon, and is converted into a horizontally polarized single photon through DHWP: The difference-frequency single photon exits from port B. By modulating the amplitude and phase of the attenuated laser, the quantum state to be transmitted is generated: |φ>1 = α|H>1 + β|V>1.

[0040] In the Alice side, the entangled state photon pairs overlap with the frequency-converted input single photon on the FBS, perform joint Bell state measurement (BSM), and transmit the measurement results to the Bob side through the classical channel. In the Bob side, photons transmitted from the Charlie side are received through the quantum channel. According to the results of the joint Bell state measurement on the classical channel, corresponding unitary transformations are performed on the photons, so as to obtain the required information and realize quantum teleportation.

[0041] In summary, the solution provided in this embodiment realizes the combination of multiple parametric down-conversion processes in the quantum teleportation process and uses the same nonlinear crystal to achieve it. Compared with the existing technologies that mostly use a single nonlinear crystal to achieve a single type of parametric down-conversion and require multiple sets of parametric down-conversion systems to generate multiple different types of entangled photons simultaneously, this solution utilizes the properties of the nonlinear crystal and designs and controls the polarization period and temperature that need to satisfy quasi-phase matching, realizing the work of multiple types of parametric down-conversion with the same crystal, significantly reducing the experimental complexity and saving costs.

[0042] At the same time, this solution realizes the quantum teleportation process with frequency conversion function. According to the calculation and simulation, when the temperature and polarization period of the PPLN crystal are set to the appropriate working points, single photons with any wavelength in the 460nm - 580nm band can be converted to the communication band to achieve long-distance quantum teleportation. For example, when the temperature of the PPLN crystal is set to 128.36 °C and the polarization period is 16.341 μm, the single photon with a wavelength of 517nm to be transmitted can be frequency down-converted to 1550nm.

[0043] In addition, the generated entanglement source can be combined with the communication band with less fiber loss to achieve entanglement distribution over a longer distance. Currently, the entangled photon pairs generated in experiments are mostly around 800nm, and photons at this wavelength have relatively large losses in fiber transmission. This solution can convert the 775nm pump light into 1550nm entangled photon pairs, which can be compatible with the existing mature technologies in the communication band to achieve metropolitan-level entangled photon distribution.

[0044] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0045] The above embodiments only represent several implementation manners of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the application. It should be noted that for those of ordinary skill in the art, without departing from the concept of this application, several deformations and improvements can still be made, and these all belong to the protection scope of this application. Therefore, the protection scope of this application should be subject to the appended claims.

Claims

1. A quantum teleportation system with a frequency conversion function, characterized in that It includes a Charlie side, an Alice side, and a Bob side; The Charlie side is provided with a Sagnac loop, a PPLN crystal, a DPBS, and a DHWP; the PPLN crystal is arranged inside the Sagnac loop; the DPBS is provided with port A and port B; the Charlie side is further provided with a PUMP, an ATT, an HWP, and a QWP; the pump light generated by the PUMP adjusts the power through the ATT, and then sets the polarization direction of the pump light through the HWP and the QWP, and finally enters port A of the DPBS; The DPBS divides the pump light into two beams, the DHWP is arranged on the optical path of one of the beams, the clockwise vertically polarized light is converted into horizontally polarized light by the DHWP, then enters the PPLN crystal and generates horizontally polarized photon pairs at 1550 nm, and then transmits and exits from port A; the horizontally polarized pump light propagating in the counterclockwise direction passes through the PPLN crystal, generates horizontally polarized photon pairs at 1550 nm, and is then converted into vertically polarized photon pairs by the DHWP, and then is reflected by the DPBS and exits from port A; the two optical paths obtain an entangled state after adjusting the phase compensation of the interference optical path; Port B of the DPBS receives single photons and divides them into two beams. The clockwise horizontally polarized light is converted into vertically polarized light by the DHWP, undergoes a parametric down-conversion process with the horizontally polarized pump light, and is converted into vertically polarized single photons at 1550 nm, and then is reflected by the DPBS and exits from port B; the counterclockwise vertically polarized light passes through the PPLN crystal, is converted into vertically polarized single photons at 1550 nm, and is then converted into horizontally polarized single photons by the DHWP, and then is transmitted by the DPBS and exits from port B; the two optical paths generate a quantum state by modulating the attenuation amplitude and phase; A DM and a BS are also arranged between port A of the DPBS and the PUMP. The DM is used to introduce the entangled photon pairs exiting from port A into the BS. The BS divides them into two beams. One beam of entangled photons is transmitted to the Bob side through a quantum channel, and the other beam of entangled photons is sent to the Alice side for a joint Bell state measurement; port B of the DPBS sends the exiting single photons to the Alice side for a joint Bell state measurement; An SPD, an FBS, an HWP, and a QWP are arranged in the Alice side. The HWP and the QWP are used for polarizing the single-photon beam. The FBS is used to combine the single photon and the entangled photon into the SPD for a joint Bell state measurement; a classical channel is arranged between the Alice side and the Bob side, and the joint Bell state measurement result is transmitted to the Bob side through the classical channel; The Bob side is provided with an SPD, a POL, an HWP, and a QWP; the entangled photons transmitted from the quantum channel are received by the SPD after being polarized under the action of the HWP, the QWP, and the POL, and a unitary transformation corresponding thereto is performed on the entangled photons according to the result of the joint Bell state measurement through the classical channel to obtain the required quantum state.

2. A quantum teleportation system with a frequency conversion function according to claim 1, characterized in that, Both the Alice side and the Bob side are provided with an SMF and an FC. The FC is used to couple the light beam into the SMF and then transmit it to the corresponding SPD through the SMF.

3. A quantum teleportation system with a frequency conversion function according to claim 1, characterized in that, The combination of the QWP and the HWP is used to adjust the polarization of the photon to any direction for initial polarization and subsequent adjustment.

4. A quantum teleportation method with a frequency conversion function, which uses a quantum teleportation system with a frequency conversion function as described in any one of claims 1-3, characterized in that Adjust the pump light power entering the system through ATT, and then set the polarization direction of the pump light through QWP and HWP so that the pump light is polarized at 45°; the 775 nm pump light is incident from port A and is split into two beams by PBS and enters the Sagnac loop; the clockwise vertically polarized light is converted into horizontally polarized light by a fixed 45° DHWP, and horizontal polarized photon pairs at 1550 nm are generated through the spontaneous parametric down-conversion (SPDC) process in the PPLN crystal: This photon pair is transmitted through the PBS and exits from port A; the horizontally polarized pump light propagating in the counterclockwise direction passes through the PPLN crystal, generates horizontally polarized photon pairs at 1550 nm, and is converted into vertically polarized photon pairs through the DHWP: This photon pair is reflected by the PBS and exits from port A; an entangled state is obtained: where φ0 represents the relative phase between the two-photon pairs, and by adjusting the phase compensation of the optical path after interference, φ0 = 0, so as to obtain the required entangled state: |Φ + > 23 = |H>2|H>3 + |V>2|V>3; the entangled state is split into two beams by the BS, one beam is transmitted through the quantum channel to the Bob side, and one beam is sent to the Alice side for joint Bell state measurement; Single photons at 517 nm with 45° polarization are incident from port B, and are split into two beams by the PBS and enter the Sagnac loop. The horizontally polarized single photons in the clockwise direction are converted into vertically polarized single photons by a fixed 45° DHWP, and undergo a difference frequency generation (DFG) process with horizontally polarized pump light at 775 nm, and are converted into vertically polarized single photons at 1550 nm: The difference frequency single photons are emitted from port B; the vertically polarized single photons in the counterclockwise direction pass through the PPLN crystal, are converted into vertically polarized single photons at 1550 nm, and are converted into horizontally polarized single photons through the DHWP: The difference frequency single photons are emitted from port B; By modulating the amplitude and phase of the attenuated laser, the quantum state to be transmitted is generated: |φ>1 = α|H>1 + β|B>1; In the Alice side, the entangled state photon pair overlaps with the frequency-converted input single photon on the FBS for joint Bell state measurement, and the measurement result is transmitted to the Bob side through the classical channel; in the Bob side, the photon transmitted from the Charlie side is received through the quantum channel, and a unitary transformation corresponding thereto is performed on the photon according to the result of the joint Bell state measurement through the classical channel, so as to obtain the required information and realize quantum teleportation.

Images