CN108604037B - Method and device for generating polarization entangled photon pair - Google Patents
Method and device for generating polarization entangled photon pair Download PDFInfo
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- CN108604037B CN108604037B CN201680080574.1A CN201680080574A CN108604037B CN 108604037 B CN108604037 B CN 108604037B CN 201680080574 A CN201680080574 A CN 201680080574A CN 108604037 B CN108604037 B CN 108604037B
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- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
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- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
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- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
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- G02F1/225—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference in an optical waveguide structure
Abstract
A method and a device for generating polarization entangled photon pairs belong to the technical field of optical communication. An input beam of photons is divided into two beams of photons with the same energy, the two beams of photons are converted into a TE mode polarized photon pair with the same polarization state, one beam of the TE mode polarized photon pair is converted into a TM mode polarized photon pair, and the TE mode polarized photon pair and the TM mode polarized photon pair are further superposed to obtain a polarization entangled photon pair. The defect that the polarization entangled photon pair is only generated in the conical light beam overlapping area in the prior art is overcome, the generated TE mode and TM mode polarized photon pair are all used for generating the polarization entangled photon pair, the generation efficiency of the polarization entangled photon pair is improved, the energy of the TE mode and TM mode polarized photon pair is the same, and therefore the brightness of the entangled light source is high. In addition, the device has a simple structure, can be solidified in a silicon-based optical waveguide chip, and has relatively stable phase.
Description
Technical Field
The invention relates to the technical field of optical communication, in particular to a method and a device for generating polarization entangled photon pairs.
Background
Quantum entanglement is the most important resource in quantum information processing, and is a special quantum state in a composite system formed by multiple particles. Entanglement sources in quantum entanglement include photons, electrons, ions, and the like. Because of the relatively good coherence of photons, entangled photons become a commonly used quantum entanglement source. Photons have different degrees of freedom, e.g., polarization degrees of freedom, path degrees of freedom, angular momentum degrees of freedom, etc., each of which may be used to encode information. Because the degree of freedom of polarization can be flexibly controlled through the wave plate, the polarization entangled photon pair based on the degree of freedom of polarization is widely applied to quantum information processing.
Currently, an optical waveguide of an SOI (Silicon On Insulator) is mainly used, and based On the third-order nonlinearity of a Silicon material, pump photons generate a spontaneous four-wave mixing process to generate a correlated photon pair. However, in the silicon linear waveguide, because of a large birefringence effect between a TE mode (transverse Electric mode) and a TM mode (transverse Magnetic mode), the generation efficiency of a pair of TE mode polarized photons is greater than that of a pair of TM mode polarized photons, resulting in almost all pairs of TE mode polarized photons generated in the silicon linear waveguide. In order to acquire polarization-entangled photon pairs, improvements in the methods of generating polarization photon pairs are needed.
Fig. 1 illustrates a method for generating polarization-entangled photon pairs based on a spontaneous parametric down-conversion process of a second-order nonlinear crystal. Referring to fig. 1, when a beam of pump photons with a shorter wavelength is incident on the second-order nonlinear crystal, the photons undergo a spontaneous parametric down-conversion process and are split into two photons with lower energy. One of the two photons is a horizontally polarized photon, the other is a vertically polarized photon, the outgoing directions of the two photons are the directions indicated by the two cones in fig. 1, and the photon pairs in the overlapped region of the two cones can be superposed into a polarization-entangled photon pair.
In the process of implementing the invention, the inventor finds that the prior art has at least the following problems:
only the photon pairs in the overlapping region of the two cones can generate polarization-entangled photon pairs, and the photons in other regions cannot be utilized, so that the generation efficiency of the polarization-entangled photon pairs is low, and the brightness of an entangled light source is low. The device has a complex structure, the optical path needs to be finely adjusted by all methods of bulk optics, and the phase is unstable.
Disclosure of Invention
In order to solve the problems in the prior art, embodiments of the present invention provide a method and an apparatus for generating polarization-entangled photon pairs. The technical scheme is as follows:
in a first aspect, there is provided an apparatus for generating polarization-entangled photon pairs, the apparatus comprising: the device comprises a beam splitter, a photon pair generation module, a fundamental mode conversion module and a polarization converter;
the beam splitter comprises an input end, a first output end and a second output end, the beam splitter divides the photon beam input by the input end into a first photon beam and a second photon beam with the same energy, the first photon beam is output through the first output end, and the second photon beam is output through the second output end;
the photon pair generation module comprises a first photon pair generation unit and a second photon pair generation unit, the first photon pair generation unit is connected with the first output end and can trigger the first photon beam to generate a first TE mode polarized photon pair, and the second photon pair generation unit is connected with the second output end and can trigger the second photon beam to generate a second TE mode polarized photon pair;
the fundamental mode conversion module comprises a first fundamental mode conversion unit and a second fundamental mode conversion unit, the first fundamental mode conversion unit is connected with the first photon pair generation unit and can convert the first TE mode polarized photon pair into a first TE fundamental mode polarized photon pair, and the second fundamental mode conversion unit is connected with the second photon pair generation unit and can convert the second TE mode polarized photon pair into a second TE fundamental mode polarized photon pair;
the polarization converter comprises a first polarization conversion unit and a second polarization conversion unit, the first polarization conversion unit is connected with the first base mode conversion unit and can couple the first TE base mode polarization photon pair into the second polarization conversion unit, the second polarization conversion unit is connected with the second base mode conversion unit and can convert the first TE base mode polarization photon pair into a first TM base mode polarization photon pair, and the first TM base mode polarization photon pair and the second TE base mode polarization photon pair are superposed into a polarization entanglement photon pair to output the polarization entanglement photon pair.
The TE mode polarized photon pair and the TM mode polarized photon pair generated in the invention are all used for generating the polarization entangled photon pair, the generation efficiency of the polarization entangled photon pair is higher, the energy of the TE mode polarized photon pair and the energy of the TM mode polarized photon pair are the same, and the brightness is higher when the polarization entangled photon pair obtained by the TE mode polarized photon pair and the TM mode polarized photon pair is used as an entangled light source. Furthermore, the device has a simple structure, and can be solidified in the silicon-based optical waveguide chip, so that the phase of the generated polarization-entangled photon pair is stable.
With reference to the first aspect, in a first possible implementation manner of the first aspect, the beam splitter is a Y-type beam splitter. Not only enriching the form of the beam splitter, but also enabling a beam of processed photons to be accurately split into two beams of photons with the same energy.
With reference to the first aspect, in a second possible implementation manner of the first aspect, the beam splitter is a multi-mode interferometer, and the multi-mode interferometer further includes a multi-mode waveguide region, where the multi-mode waveguide region is connected to the input end, the first output end, and the second output end. Not only enriching the form of the beam splitter, but also enabling a beam of processed photons to be accurately split into two beams of photons with the same energy.
With reference to the first aspect to the second possible implementation manner of the first aspect, in a third possible implementation manner of the first aspect, the beam splitter, the photon pair generation module, the fundamental mode conversion module, and the polarization converter are all composed of a silica cladding layer and a silicon nanowire.
In combination with the third possible implementation manner of the first aspect, in a fourth possible implementation manner of the first aspect, the silicon nanowires in the photon pair generating module are bent and surrounded in the silica cladding, and the structures of the silicon nanowires in the first photon pair generating unit and the second photon pair generating unit are the same, so that photon pairs with the same polarization state can be generated by the first photon pair generating unit and the second photon pair generating unit.
With reference to the fourth possible implementation manner of the first aspect, in a fifth possible implementation manner of the first aspect, the silicon nanowires of the first photon pair generating unit and the silicon nanowires of the second photon pair generating unit are distributed in a spiral shape.
With reference to the third possible implementation manner of the first aspect, in a sixth possible implementation manner of the first aspect, the silicon nanowires in the fundamental mode conversion module are distributed in a tapered shape, so that TE modes in the upper and lower optical waveguides can be converted into different fundamental modes.
With reference to the sixth possible implementation manner of the first aspect, in a seventh possible implementation manner of the first aspect, a width of the silicon nanowire in the first basic mode conversion unit is smaller than a width of the silicon nanowire in the second basic mode conversion unit.
With reference to the first aspect, in an eighth possible implementation manner of the first aspect, the polarization converter is a polarization converter based on an asymmetric directional coupler.
In a second aspect, there is provided a method for generating a polarization-entangled photon pair, the method applying the apparatus for generating a polarization-entangled photon pair according to the first aspect, the method comprising:
the beam splitter divides the photon beam input by the input end into a first photon beam and a second photon beam with the same energy, the first output end transmits the first photon beam to the first photon pair generating unit, the first photon pair generating unit triggers the first photon beam to generate a first TE mode polarized photon pair and transmits the first TE mode polarized photon pair to the first fundamental mode conversion unit, the second output end transmits the second photon beam to the second photon pair generating unit, the second photon pair generating unit triggers the second photon beam to generate a second TE mode polarized photon pair and transmits the second TE mode polarized photon pair to the second fundamental mode conversion unit;
the first base mode conversion unit converts the first TE mode polarization photon pair into a first TE base mode polarization photon pair and transmits the first TE base mode polarization photon pair to the first polarization conversion unit, and the second base mode conversion unit converts the second TE mode polarization photon pair into a second TE base mode polarization photon pair and transmits the second TE base mode polarization photon pair to the second polarization conversion unit;
the first polarization conversion unit couples the first TE basic mode polarization photon pair into the second polarization conversion unit, the second polarization conversion unit converts the first TE basic mode polarization photon pair into a first TM basic mode polarization photon pair, the first TM basic mode polarization photon pair and the second TE basic mode polarization photon pair are superposed into a polarization entangled photon pair, and the polarization entangled photon pair is output.
The technical scheme provided by the embodiment of the invention has the following beneficial effects:
an input beam of photons is divided into two beams of photons with the same energy, the two beams of photons are converted into a TE mode polarized photon pair with the same polarization state, one beam of the TE mode polarized photon pair is converted into a TM mode polarized photon pair, and the TE mode polarized photon pair and the TM mode polarized photon pair are further superposed to obtain a polarization entangled photon pair. The invention breaks through the defect that the polarization entangled photon pair is only generated in the conical light beam overlapping area in the prior art, the generated TE mode and TM mode polarized photon pair are all used for generating the polarization entangled photon pair, the generation efficiency of the polarization entangled photon pair is improved, and the energy of the TE mode and TM mode polarized photon pair is the same, so that the brightness of the entangled light source is higher. In addition, the device has a simple structure, can be solidified in a silicon-based optical waveguide chip, and has relatively stable phase.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a prior art method for generating polarization-entangled photon pairs according to the present invention;
FIG. 2 is a schematic diagram of a polarization-entangled photon pair generation apparatus according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a Y-splitter according to another embodiment of the present invention;
FIG. 4 is a schematic diagram of a multimode interferometer according to another embodiment of the present invention;
FIG. 5 is a schematic diagram of a structure of an optical waveguide according to another embodiment of the present invention;
FIG. 6 is a schematic diagram of a polarization transformer according to another embodiment of the present invention;
FIG. 7 is a flow chart of a method for generating polarization-entangled photon pairs according to another embodiment of the present invention.
Wherein the reference numerals are: 1. a beam splitter; 11. an input end; 12. a first output terminal; 13. a second output terminal; 14. a multimode waveguide region; 2. a photon pair generating module; 21. a first photon pair generation unit; 22. a second photon pair generation unit; 3. a base mode conversion module; 31. a first fundamental mode conversion unit; 32. a second fundamental mode conversion unit; 4. a polarization converter; 41. a first polarization conversion unit; 42. a second polarization conversion unit.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
Referring to fig. 2, an embodiment of the present invention provides a polarization-entangled photon pair generation apparatus, including: the device comprises a beam splitter 1, a photon pair generation module 2, a basic mode conversion module 3 and a polarization converter 4.
The beam splitter 1 divides a photon beam input by the input end 11 into a first photon beam and a second photon beam with the same energy, wherein the first photon beam is output through the first output end 12, and the second photon beam is output through the second output end 13;
the photon pair generating module 2 comprises a first photon pair generating unit 21 and a second photon pair generating unit 22, the first photon pair generating unit 21 is connected with the first output end 12, the first photon pair generating unit 21 can trigger the first photon beam to generate a first TE mode polarized photon pair and transmit the generated first TE mode polarized photon pair; the second photon pair generating unit 22 is connected to the second output end 13, and the second photon pair generating unit 22 can trigger the second photon beam to generate a second TE mode polarized photon pair and transmit the generated second TE mode polarized photon pair, in this embodiment, the first TE mode polarized photon pair and the second TE mode polarized photon pair are associated photon pairs having the same polarization state, and are completely the same, and only the transmission paths are different;
the fundamental mode conversion module 3 includes a first fundamental mode conversion unit 31 and a second fundamental mode conversion unit 32, the first fundamental mode conversion unit 31 is connected to the first photon pair generation unit 21, and is configured to receive the first TE mode polarized photon pair generated by the first photon pair generation unit 21, convert the first TE mode polarized photon pair into a first TE fundamental mode polarized photon pair, and further transmit the first TE fundamental mode polarized photon pair; the second fundamental-mode conversion unit 32 is connected to the second photon pair generation unit 22, and is configured to receive the second TE mode polarized photon pair generated by the second photon pair generation unit 22, convert the second TE mode polarized photon pair into a second TE mode polarized photon pair, and further transmit the second TE fundamental mode polarized photon pair;
the polarization converter 4 comprises a first polarization conversion unit 41 and a second polarization conversion unit 42, wherein the first polarization conversion unit 41 is connected with the first basic mode conversion unit 31 and is used for receiving the first TE basic mode polarization photon pair transmitted by the first basic mode conversion unit 31 and coupling the first TE basic mode polarization photon pair into the second polarization unit; the second polarization conversion unit 42 is connected to the second TE fundamental mode polarized photon pair, and configured to receive the second TE fundamental mode polarized photon pair transmitted by the second fundamental mode polarization conversion unit 32, convert the first TE fundamental mode polarized photon pair into the first TM fundamental mode polarized photon pair under the condition that effective refractive indexes of the first TE fundamental mode polarized photon pair in the first polarization conversion unit 41 and the TM fundamental mode polarized photon pair in the second polarization conversion unit 42 are equal, and superimpose the first TM fundamental mode polarized photon pair and the second TE fundamental mode polarized photon pair into a polarization entangled photon pair, so as to output the polarization entangled photon pair.
In one embodiment of the invention, referring to fig. 3, the beam splitter 1 may be a Y-type beam splitter. When the beam splitter 1 is a Y-type beam splitter, the positional relationship among the input end 11, the first output end 12 and the second output end 13 in the Y-type beam splitter is as shown in fig. 3.
In another embodiment of the invention, referring to fig. 4, the beam splitter 1 may also be a multimode interferometer. When the beam splitter 1 is a multimode interferometer, the multimode interferometer includes an input end 11, a first output end 12, a second output end 13, and a multimode waveguide region 14, and the multimode waveguide region 14 is connected to the input end 11, the first output end 12, and the second output end 13. The width and length of the multimode waveguide region 14 are set as required to ensure that the optical field achieves 50/50 splitting, i.e. the input photon beam can be split into a first photon beam and a second photon beam with the same energy.
In this embodiment, the polarization-entangled photon pair generating device shown in fig. 2 may be an optical waveguide, and the optical waveguide is generally mainly composed of a silica cladding and a silicon nanowire, and therefore, the beam splitter 1, the photon pair generating module 2, the fundamental mode conversion module 3, and the polarization converter 4 shown in fig. 2 are each composed of a silica cladding and a silicon nanowire. Correspondingly, the input end 11, the first output end 12 and the second output end 13 included in the beam splitter 1 are also composed of the silica cladding and the silicon nanowire; the first photon pair generation unit 21 and the second photon pair generation unit 22 included in the photon pair generation module 2 are also composed of a silica clad and a silicon nanowire; the first and second fundamental- mode conversion units 31 and 32 included in the fundamental-mode conversion module 3 are also composed of a silica clad and silicon nanowires; the first polarization conversion unit 41 and the second polarization conversion unit 42 included in the polarization converter 4 are also composed of a silica clad and a silicon nanowire. In general, in an optical waveguide, light beams are mainly transmitted along silicon nanowires, and in order to visually show a transmission path of the light beams in the optical waveguide, fig. 5 shows a distribution of the silicon nanowires constituting each functional module in the device in an optical waveguide chip.
When the polarization-entangled photon pair generating device shown in fig. 2 is an optical waveguide, the silicon nanowire in the photon pair generating module 2 is bent and surrounded in the silica cladding, the structure is compact, and the length meets the design requirement, so that when the photon pair generating module 2 transmits a light beam, a spontaneous four-wave mixing process can be generated by utilizing the third-order nonlinearity of the silicon nanowire waveguide, and a TE mode polarized photon pair is generated. In order to ensure that the polarized photon pairs generated by the first and second photon pair generating units 21 and 22 have the same polarization state, the silicon nanowires in the first and second photon pair generating units 21 and 22 have the same size and are symmetrically distributed. As shown in fig. 5, the silicon nanowires in the first photon pair generating unit 21 and the second photon pair generating unit 22 are symmetrically distributed and have a spiral shape, and of course, the shape of the silicon nanowires in the first photon pair generating unit 21 and the second photon pair generating unit 22 may also be other shapes, which is not limited in this embodiment.
In this embodiment, the silicon nanowires in the base mode conversion module 3 are distributed in a tapered shape, the width of the silicon nanowires in the first base mode conversion unit 31 is gradually reduced, and the width of the silicon nanowires in the second base mode conversion unit 32 is gradually increased, so that the first base mode conversion unit 31 becomes a thin optical waveguide and the second base mode conversion unit 32 becomes a thick optical waveguide, and of course, the width of the silicon nanowires in the first base mode conversion unit 31 may be gradually increased, and the width of the silicon nanowires in the second base mode conversion unit 32 may be gradually reduced, so that the first base mode conversion unit 31 becomes a thick optical waveguide and the second base mode conversion unit 32 becomes a thin optical waveguide. In short, it is only necessary to ensure that the two optical waveguides in the fundamental mode conversion module 3 have different thicknesses. In the present embodiment, the width of the silicon nanowire in the basic mode conversion module 3 is determined by the width of the silicon nanowire in the polarization converter 4, specifically, the width of the silicon nanowire in the first polarization conversion unit 41 determines the width of the silicon nanowire in the first basic mode conversion unit 31, the width of the silicon nanowire in the second polarization conversion unit 42 determines the width of the silicon nanowire in the second basic mode conversion unit 32, and when the width of the silicon nanowire in the polarization converter 4 changes, the width of the silicon nanowire in the basic mode conversion module 3 needs to be redesigned according to the requirement.
When the first photon pair generation unit 21 transmits the generated first TE mode polarized photon pair to the first base mode conversion unit 31, the first base mode conversion unit 31 converts the mode of the first TE mode deflected photon pair into a corresponding base mode according to the width of the silicon nanowire itself, so as to obtain a first TE base mode polarized photon pair. When the second photon pair generating unit 22 transmits the generated second TE mode polarized photon pair to the second fundamental mode converting unit 32, the second fundamental mode converting unit 32 converts the mode of the second TE mode polarized photon pair into a corresponding fundamental mode according to the width of the silicon nanowire itself, so as to obtain a second TE fundamental mode polarized photon pair. Since the optical waveguides corresponding to the first fundamental mode conversion unit 31 and the second fundamental mode conversion unit 32 are different, the first TE fundamental mode polarized photon pair and the second TE fundamental mode polarized photon pair obtained after conversion are different.
In the present embodiment, the polarization converter 4 is a polarization converter of an asymmetric directional coupler, and the lengths and widths of the silicon nanowires in the first polarization converting unit 41 and the second polarization converting unit 42 are also different. In an embodiment of the present invention, the length of the silicon nanowire in the first polarization conversion unit 41 may be smaller than the length of the silicon nanowire in the second polarization conversion unit 42, and the width of the silicon nanowire in the first polarization conversion unit 41 is smaller than the width of the silicon nanowire in the second polarization conversion unit 42, when the first polarization conversion unit 41 does not output the polarization-entangled photon pair, it may serve as a test port, and the second polarization conversion unit 42 serves as an output end to output the polarization-entangled photon pair. In another embodiment of the present invention, the length of the silicon nanowire in the first polarization conversion unit 41 may be greater than the length of the silicon nanowire in the second polarization conversion unit 42, and the width of the silicon nanowire in the first polarization conversion unit 41 is greater than the width of the silicon nanowire in the second polarization conversion unit 42, when the first polarization conversion unit 41 outputs the polarization-entangled photon pair as an output end, and the second polarization conversion unit 42 does not output the polarization-entangled photon pair and may serve as a test port.
In this embodiment, based on the polarization converter of the asymmetric directional coupler, when the widths of the silicon nanowires in the first polarization conversion unit 41 and the second polarization conversion unit 42 satisfy a certain condition, the effective refractive indexes of the first TE fundamental mode polarized photon pair in the optical waveguide corresponding to the first polarization conversion unit 41 and the second TM fundamental mode polarized photon pair in the optical waveguide corresponding to the second polarization conversion unit 42 can be equal, and then according to the coupling mode theory,the TE fundamental mode polarized photon pairs in the thinner optical waveguides can be coupled into the thicker optical waveguides and converted into TM fundamental mode polarized photon pairs in the thicker optical waveguides, and the TE fundamental mode polarized photon pairs in the thicker optical waveguides still propagate in the thicker optical waveguides. The TE fundamental mode can be expressed as TE0Mode, the TM fundamental mode, may be denoted TM0And (5) molding. For example, as shown in FIG. 6 (a), the coupling region has a length of 36.8um when the TE is in a thin optical waveguide0TM in mode and thick optical waveguide0When the effective refractive index of the mode is equal, TE in the thin optical waveguide can be converted0Coupling of mode photon pairs into a coarse optical waveguide, TE in a coarse optical waveguide0The mode photon pairs still propagate in the coarse optical waveguide. Fig. 6 (b) is a cross-sectional view of the polarization converter, in which w1 is the width of the thin optical waveguide, w2 is the width in the thick optical waveguide, g is the distance between the thin waveguide and the thick waveguide, and h is the height of the thick optical waveguide. w1 may be 330nm, w2 may be 600nm, g may be 100nm, h may be 250nm, however, in practical application, the above structural parameters may be specifically designed according to requirements, and are not limited to the above listed data, as long as the TE in the thin optical waveguide is satisfied0TM in mode and thick optical waveguide0The effective refractive indices of the modes are equal and the length of the coupling region is required to ensure TE in the thin optical waveguide0Mode conversion to mostly TM in coarse waveguide0And (5) molding.
In this embodiment, the first photon pair generation unit 21, the first fundamental mode conversion unit 31, and the first polarization conversion unit 41 may constitute an add optical waveguide, and the second photon pair generation unit 22, the second fundamental mode conversion unit 32, and the second polarization conversion unit 42 may constitute a drop optical waveguide. By adding metal electrodes in the upper path of optical waveguide and the lower path of optical waveguide and applying voltage, the relative phase of photons in the upper path of optical waveguide and the lower path of optical waveguide can be adjusted by using the photo-thermal effect, and the polarization entanglement state of | psi ═ a | TE, TE > + be is obtainediθPolarization entangled photon pairs of | TM, TM >. Where ψ is a polarization entangled state, θ is a relative phase, a and b are arbitrary parameters, and a and b satisfy a normalization condition | a | light2+|b|2＝1。
According to the device provided by the embodiment of the invention, an input beam of photons is divided into two beams of photons with the same energy, the two beams of photons are converted into a TE mode polarization photon pair with the same polarization state, one beam of TE mode polarization photon pair is converted into a TM mode polarization photon pair, and the TE mode polarization photon pair and the TM mode polarization photon pair are further superposed to obtain a polarization entangled photon pair. The invention breaks through the defect that the polarization entangled photon pair is only generated in the conical light beam overlapping area in the prior art, the generated TE mode and TM mode polarized photon pair are all used for generating the polarization entangled photon pair, the generation efficiency of the polarization entangled photon pair is improved, and the energy of the TE mode and TM mode polarized photon pair is the same, so that the brightness of the entangled light source is higher. In addition, the device has a simple structure, can be solidified in a silicon-based optical waveguide chip, and has relatively stable phase.
Based on the apparatus for generating polarization-entangled photons shown in fig. 2, an embodiment of the present invention provides a method for generating polarization-entangled photons, and referring to fig. 7, the method provided by the embodiment includes:
701. the beam splitter divides a photon beam input by the input end into a first photon beam and a second photon beam with the same energy, the first photon beam is transmitted to the first photon pair generating unit by the first output end, the first photon pair generating unit triggers the first photon beam to generate a first TE mode polarized photon pair, the first TE mode polarized photon pair is transmitted to the first basic mode conversion unit, the second photon beam is transmitted to the second photon pair generating unit by the second output end, the second photon pair generating unit triggers the second photon beam to generate a second TE mode polarized photon pair, and the second TE mode polarized photon pair is transmitted to the second basic mode conversion unit.
702. The first base mode conversion unit converts the first TE mode polarization photon pair into a first TE base mode polarization photon pair and transmits the first TE base mode polarization photon pair to the first polarization conversion unit, and the second base mode conversion unit converts the second TE mode polarization photon pair into a second TE base mode polarization photon pair and transmits the second TE base mode polarization photon pair to the second polarization conversion unit.
703. The first polarization conversion unit couples the first TE basic mode polarization photon pair into the second polarization conversion unit, the second polarization conversion unit converts the first TE basic mode polarization photon pair into a first TM basic mode polarization photon pair, and the first TM basic mode polarization photon pair and the second TE basic mode polarization photon pair are superposed into a polarization entangled photon pair to output the polarization entangled photon pair.
Taking the generating device of polarization-entangled photon pair as an optical waveguide as an example, the process of generating the polarization-entangled photon pair based on the optical waveguide is as follows:
firstly, pumping photons are input into an SOI optical chip from the outside of the chip, and are divided into two photon beams with the same energy through a beam splitter and transmitted to an upper optical waveguide and a lower optical waveguide.
And secondly, a spontaneous four-wave mixing process is generated by utilizing the third-order nonlinearity of the silicon linear waveguide, and the upper and lower optical waveguides respectively generate TE mode polarized photon pairs with the same polarization state.
Thirdly, the tapered optical waveguide converts the mode of the TE mode polarized photon pair into a fundamental mode TE in the thick and thin optical waveguides0And (5) molding.
Fourthly, using a polarization converter to convert TE in the thin waveguide0Conversion of mode photons to TM in a coarse waveguide0Mode photon to convert TE in a coarse waveguide0Mode photon pairing and converted TM0And superposing the mode photon pairs to obtain polarization-entangled photon pairs, and outputting the polarization-entangled photon pairs.
According to the method provided by the embodiment of the invention, an input beam of photons is divided into two beams of photons with the same energy, the two beams of photons are converted into a TE mode polarization photon pair with the same polarization state, one beam of TE mode polarization photon pair is converted into a TM mode polarization photon pair, and the TE mode polarization photon pair and the TM mode polarization photon pair are further superposed to obtain a polarization entangled photon pair. The invention breaks through the defect that the polarization entangled photon pair is only generated in the conical light beam overlapping area in the prior art, the generated TE mode and TM mode polarized photon pair are all used for generating the polarization entangled photon pair, the generation efficiency of the polarization entangled photon pair is improved, and the energy of the TE mode and TM mode polarized photon pair is the same, so that the brightness of the entangled light source is higher. In addition, the device has a simple structure, can be solidified in a silicon-based optical waveguide chip, and has relatively stable phase.
It should be noted that: in the polarization-entangled photon pair generating device provided in the above embodiment, when generating polarization-entangled photons, only the division of the above functional modules is used as an example, and in practical applications, the above functions may be distributed by different functional modules according to needs, that is, the internal structure of the polarization-entangled photon pair generating device is divided into different functional modules, so as to complete all or part of the above described functions. In addition, the generation apparatus of polarization-entangled photon pairs and the generation method of polarization-entangled photon pairs provided by the above embodiments belong to the same concept, and specific implementation processes thereof are described in the method embodiments and are not described herein again.
It will be understood by those skilled in the art that all or part of the steps for implementing the above embodiments may be implemented by hardware, or may be implemented by a program instructing relevant hardware, where the program may be stored in a computer-readable storage medium, and the above-mentioned storage medium may be a read-only memory, a magnetic disk or an optical disk, etc.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (9)
1. An apparatus for generating polarization-entangled photon pairs, said apparatus comprising: the device comprises a beam splitter, a photon pair generation module, a fundamental mode conversion module and a polarization converter;
the beam splitter comprises an input end, a first output end and a second output end, the beam splitter divides the photon beam input by the input end into a first photon beam and a second photon beam with the same energy, the first photon beam is output through the first output end, and the second photon beam is output through the second output end;
the photon pair generation module comprises a first photon pair generation unit and a second photon pair generation unit, the first photon pair generation unit is connected with the first output end and can trigger the first photon beam to generate a first TE mode polarized photon pair, and the second photon pair generation unit is connected with the second output end and can trigger the second photon beam to generate a second TE mode polarized photon pair;
the fundamental mode conversion module comprises a first fundamental mode conversion unit and a second fundamental mode conversion unit, the first fundamental mode conversion unit is connected with the first photon pair generation unit and can convert the first TE mode polarized photon pair into a first TE fundamental mode polarized photon pair, and the second fundamental mode conversion unit is connected with the second photon pair generation unit and can convert the second TE mode polarized photon pair into a second TE fundamental mode polarized photon pair;
the polarization converter comprises a first polarization conversion unit and a second polarization conversion unit, the first polarization conversion unit is connected with the first basic mode conversion unit and can couple the first TE basic mode polarization photon pair into the second polarization conversion unit, the second polarization conversion unit is connected with the second fundamental mode conversion unit, and can be used for converting the first TE fundamental mode polarized photon pair in the first polarization conversion unit and the TM fundamental mode polarized photon pair in the second deflection conversion unit into the second TE fundamental mode polarized photon pair, converting the first TE fundamental mode polarized photon pair to a first TM fundamental mode polarized photon pair, and superposing the first TM fundamental mode polarized photon pair and the second TE fundamental mode polarized photon pair into a polarization entangled photon pair, and outputting the polarization entangled photon pair, wherein the polarization converter is a polarization converter based on an asymmetric directional coupler.
2. The apparatus of claim 1, wherein the beam splitter is a Y-beam splitter.
3. The apparatus of claim 1, wherein the beam splitter is a multi-mode interferometer further comprising a multi-mode waveguide region connecting the input end, the first output end, and the second output end.
4. The apparatus of any one of claims 1 to 3, wherein the beam splitter, the photon pair generation module, the fundamental mode conversion module and the polarization converter are each comprised of a silica cladding and silicon nanowires.
5. The apparatus of claim 4, wherein the silicon nanowires in the photon pair generating module are bent around within a silica cladding, and the silicon nanowires in the first and second photon pair generating units are identical in structure.
6. The apparatus of claim 5, wherein the silicon nanowires of the first and second photon pair generating units are each distributed in a spiral.
7. The apparatus of claim 4, wherein the silicon nanowires in the fundamental mode conversion module are distributed in a tapered shape.
8. The apparatus of claim 7, wherein the width of the silicon nanowire in the first basic mode conversion unit is smaller than the width of the silicon nanowire in the second basic mode conversion unit.
9. A method for generating polarization-entangled photon pairs, wherein the method employs the apparatus for generating polarization-entangled photon pairs according to any one of the above claims 1 to 8, the method comprising:
the beam splitter divides the photon beam input by the input end into a first photon beam and a second photon beam with the same energy, the first output end transmits the first photon beam to the first photon pair generating unit, the first photon pair generating unit triggers the first photon beam to generate a first TE mode polarized photon pair and transmits the first TE mode polarized photon pair to the first fundamental mode conversion unit, the second output end transmits the second photon beam to the second photon pair generating unit, the second photon pair generating unit triggers the second photon beam to generate a second TE mode polarized photon pair and transmits the second TE mode polarized photon pair to the second fundamental mode conversion unit;
the first base mode conversion unit converts the first TE mode polarization photon pair into a first TE base mode polarization photon pair and transmits the first TE base mode polarization photon pair to the first polarization conversion unit, and the second base mode conversion unit converts the second TE mode polarization photon pair into a second TE base mode polarization photon pair and transmits the second TE base mode polarization photon pair to the second polarization conversion unit;
the first polarization conversion unit couples the first TE fundamental mode polarization photon pair to the second polarization conversion unit, the second polarization conversion unit converts the first TE fundamental mode polarization photon pair into a first TM fundamental mode polarization photon pair under the condition that effective refractive indexes of the first TE fundamental mode polarization photon pair in the first polarization conversion unit and the TM fundamental mode polarization photon pair in the second polarization conversion unit are equal, and superimposes the first TM fundamental mode polarization photon pair and the second TE fundamental mode polarization photon pair into a polarization entangled photon pair, and outputs the polarization entangled photon pair, and the polarization converter is a polarization converter based on an asymmetric directional coupler.
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| PCT/CN2016/085540 WO2017214791A1 (en) | 2016-06-13 | 2016-06-13 | Polarization entangled photon pair generation method and apparatus |
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| JP2005258232A (en) * | 2004-03-15 | 2005-09-22 | Univ Nihon | Polarization entangled photon couple generating device |
| CN101553756A (en) * | 2006-09-22 | 2009-10-07 | 惠普开发有限公司 | Compact, single chip-based, entangled polarization-state photon sources and methods for generating photons in entangled polarization states |
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| JP4098530B2 (en) * | 2002-02-01 | 2008-06-11 | 独立行政法人科学技術振興機構 | Entanglement photon pair generator |
| AT505634B1 (en) * | 2007-10-17 | 2009-03-15 | Arc Austrian Res Centers Gmbh | DEVICE FOR PRODUCING RESTRICTED PHOTONS |
| GB2510916B (en) * | 2013-02-19 | 2015-04-08 | Univ Bristol | Optical source |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2005258232A (en) * | 2004-03-15 | 2005-09-22 | Univ Nihon | Polarization entangled photon couple generating device |
| CN101553756A (en) * | 2006-09-22 | 2009-10-07 | 惠普开发有限公司 | Compact, single chip-based, entangled polarization-state photon sources and methods for generating photons in entangled polarization states |
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| WO2017214791A1 (en) | 2017-12-21 |
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