A magnesium fluoride resonant cavity for generating high-dimensional quantum entanglement

Abstract

The present invention discloses a magnesium fluoride resonant cavity for generating high-dimensional quantum entanglement. The resonant cavity is made of magnesium fluoride (MgF2) material through precision cutting, grinding and polishing to form a microcavity with a precisely controllable structure. At the same time, a high-dimensional ultra-bright quantum entangled source preparation scheme based on the resonant cavity is provided. The pump light is coupled to the magnesium fluoride resonant cavity through a tapered optical fiber. A nonlinear four-wave mixing process occurs in the resonant cavity, which will generate multiple pairs of discrete signal light and idle light photon pairs. Each pair of signal light and idle light satisfies the frequency entanglement relationship, and a high-dimensional quantum entangled source preparation scheme can be realized. By optimizing the design of the magnesium fluoride resonant cavity structure, the structural dispersion can be optimized, the repetition frequency (FSR) can be controlled, and a resonant cavity with an ultra-high quality factor (Q value) can be obtained, thereby improving the nonlinear conversion efficiency of the four-wave mixing process and generating ultra-bright entangled photon pairs.

Description

Technical Field

[0001] The present invention relates to the fields of quantum communication and quantum entanglement source preparation, and in particular to a magnesium fluoride resonant cavity for generating high-dimensional quantum entanglement. Background Art

[0002] Quantum entanglement describes a correlation property between particles or groups of particles. Quantum entanglement source is an indispensable part of quantum communication system. Based on the resonant cavity structure composed of third-order nonlinearity, the four-wave mixing process occurs in the cavity, which is an effective scheme to generate high-dimensional ultra-bright quantum entanglement source. The four-wave mixing process refers to the pump light (frequency ω) in the third-order nonlinear material. P ) interacts with nonlinear materials to generate signal light (frequency ω S ) and idle light (frequency ω I ) is a nonlinear process.

[0003] The existing resonant cavity structure based on third-order nonlinearity has a low quality factor and a low efficiency in generating signal light and idle light photon pairs, thus affecting the quality of the quantum entanglement source. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a magnesium fluoride resonant cavity for generating high-dimensional quantum entanglement.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: a magnesium fluoride resonant cavity for generating high-dimensional quantum entanglement, comprising a resonant cavity body, the resonant cavity body is a closed cavity, and the resonant cavity body is made of magnesium fluoride material;

[0006] The resonant cavity body is a vertically and horizontally symmetrical structure that is wide in the middle and narrow at both ends, the upper surface and the lower surface are circular planes, and the side walls are upper and lower arc surfaces that are symmetrical in the upper and lower directions, and the upper and lower arc surfaces are smoothly connected by fillets;

[0007] The diameter R of the upper and lower surfaces is 1.5-3 mm, and the distance H between the upper and lower surfaces is 0.8-1.5 mm;

[0008] The included angle θ of the fillet is 50-70 degrees, and the fillet radius of the fillet is 0.02-0.05 mm.

[0009] Preferably, the distance from the fillet vertex to the center point of the resonant cavity body is 2-2.5 mm.

[0010] Preferably, the pump light is input through a tapered optical fiber located at one side of the resonant cavity body and arranged parallel to the upper and lower surfaces, and the pump light satisfying the resonant wavelength condition is coupled into the resonant cavity body.

[0011] Preferably, the distance between the tapered optical fiber and the surface of the resonant cavity body on the same side thereof is less than 6 μm.

[0012] Preferably, the pump light is coupled into the resonant cavity body to meet the following conditions:

[0013] The optical path L around the cavity is equal to an integer multiple of the wavelength, that is, nL = m·λ m , where λ m represents the resonant pump light wavelength, and m represents the mth resonant mode.

[0014] Preferably, the pump light ω P Multiple nonlinear four-wave mixing processes occur simultaneously in the resonant cavity. In each nonlinear four-wave mixing process, two pump light photons generate one signal light photon ω. S and an idle photon ω I .

[0015] Preferably, the four-wave mixing process satisfies the energy conservation condition 2ω P =ω S +ω I and the momentum conservation condition

[0016] Preferably, the repetition frequency FSR in the resonant cavity body satisfies FSR=c / nL, and the repetition frequency refers to the frequency interval between the mth resonance mode and the m-1th resonance mode.

[0017] Beneficial technical effects of the present invention:

[0018] The structural shape of the magnesium fluoride resonant cavity of the present invention changes the structural dispersion of the resonant cavity, controls the repetition frequency, and realizes an ultra-high quality factor; multiple four-wave mixing processes occur in the resonant cavity of the present invention, and multiple pairs of discrete signal light and idle light photon pairs can be generated, each pair of signal light and idle light photon pairs are in an entangled relationship, and high-dimensional quantum entanglement can be prepared; the present invention utilizes the high quality factor of the magnesium fluoride resonant cavity, and the intensity of the generated signal light and idle light photon pairs is high, and high-brightness quantum entanglement with a signal light idle light photon pair generation rate corresponding to each milliwatt (mW) of pump light greater than 1 megahertz (MHz) can be prepared. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the design of the resonant cavity body and the optical fiber used for coupling in one embodiment of the present invention.

[0020] Figure 2 The energy conservation conditions and momentum conservation conditions of the four-wave mixing process in one embodiment of the present invention, as well as multiple pairs of discrete signal light and idle light photon pairs generated by four-wave mixing in the resonant cavity.

[0021] Figure 3 FIG. 4 is a schematic cross-sectional view of a resonant cavity body according to an embodiment of the present invention.

[0022] Figure 4 for Figure 3 A partial enlarged schematic diagram of part A in the middle.

[0023] Figure 5 The dispersion relations (D) corresponding to the 0th order transverse electric (TE0) mode, the 0th order transverse magnetic (TM0) mode and the 1st order transverse electric (TE1) mode of the magnesium fluoride resonant cavity for generating high-dimensional ultrabright quantum entanglement in one embodiment of the present invention are shown in FIG. int ) and electric field distribution. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments, but the scope of protection claimed in the present invention is not limited to the following specific embodiments.

[0025] like Figure 1-5 As shown, a magnesium fluoride resonant cavity for generating high-dimensional quantum entanglement includes a resonant cavity body 1, wherein the resonant cavity body is a closed cavity, and the resonant cavity body is made of magnesium fluoride (MgF 2 ) material, magnesium fluoride (MgF 2 ) The absorption coefficient of crystal materials is low, so the microcavity made of them can have a high Q value, and can efficiently convert pump light into quantum entangled photon pairs through the four-wave mixing process. In addition, crystal materials such as magnesium fluoride and calcium fluoride are insensitive to the humidity of the surrounding environment, can maintain stable physical properties for a long time, and are easy to store.

[0026] Specifically, the specific structure of the resonant cavity body is as follows: the resonant cavity body 1 is a vertically and horizontally symmetrical structure that is wide in the middle and narrow at both ends, the upper surface 11 and the lower surface 12 are circular planes, and the side walls are upper arc surfaces 13 and lower arc surfaces 14 that are symmetrical in the upper and lower directions, and the upper arc surfaces and the lower arc surfaces are smoothly connected by fillets 15;

[0027] The specific dimensions are: the diameter R of the upper and lower surfaces is 1.5-3 mm, the distance H of the upper and lower surfaces is 0.8-1.5 mm, the angle of the fillet is 50-70 degrees, the fillet radius of the fillet is 0.02-0.05 mm, and the distance from the fillet vertex to the center point of the resonant cavity body is 2-2.5 mm.

[0028] Specifically, the pump light is coupled into the resonant cavity through the tapered optical fiber 2 near the magnesium fluoride resonant cavity. The preferred beam waist diameter of the tapered optical fiber 2 is 4-5 μm, and the preferred distance from the magnesium fluoride resonant cavity is less than 6 μm. In this embodiment, the distance is 5 μm. In order to achieve matching between the light field in the tapered optical fiber and the optical mode of the magnesium fluoride resonant cavity, the tapered optical fiber is parallel to the upper and lower surfaces of the resonant cavity.

[0029] Due to the resonance condition of the resonant cavity, the wavelength of the light retained in the cavity must satisfy: the optical path L around the cavity is equal to an integer multiple of the wavelength, that is, nL = m·λ m , where λ m represents the resonant pump light wavelength, and m represents the mth resonant mode.

[0030] As a preferred embodiment, a nonlinear four-wave mixing process occurs in the magnesium fluoride resonant cavity. The four-wave mixing process refers to the pump light (frequency ω) in the third-order nonlinear material. P ) interacts with nonlinear materials to generate signal light (frequency ω S ) and idle light (frequency ω I ) is a nonlinear process. Since two pump light photons generate one signal light photon and one idle light photon in this process, and four photons act at the same time, it is called four-wave mixing. Multiple four-wave mixing processes occur simultaneously in the magnesium fluoride resonant cavity, which can generate multiple pairs of discrete signal light and idle light photon pairs. The four-wave mixing process satisfies the energy conservation condition (2ω P =ω S +ω I ) and the momentum conservation condition The generated signal light and idle light are distributed as follows Figure 2 As shown, they are located on both sides of the pump light. Each pair of signal light (|1> S ,|2> S ,|3> S ...) and idle light (|1> I ,|2> I ,|3> I …) are entangled, and the number of entangled photon pairs is greater than two, thus realizing high-dimensional quantum entanglement.

[0031] As a preferred embodiment, the cross-sectional design structure of the magnesium fluoride resonant cavity is shown as follows: Figure 3 and 4 The preferred geometric parameters are shown in Table 1. By designing the cross-sectional structural geometric parameters, the structural dispersion can be optimized and the repetition frequency can be controlled. The repetition frequency refers to the frequency interval between the mth resonance mode and the m-1th resonance mode (e.g. Figure 2As shown), it satisfies FSR = c / nL. The smaller the repetition frequency, the more signal light idle light photon pairs are generated, and the higher the entanglement dimension is. The dispersion relation (D) corresponding to the 0th order transverse electric (TE0) mode, the 0th order transverse magnetic (TM0) mode and the 1st order transverse electric (TE1) mode of the preferred magnesium fluoride resonator near 1550nm is int ) and the electric field distribution as Figure 5 shown.

[0032] As a preferred embodiment, due to the ultra-high quality factor, the cascaded four-wave mixing process in the magnesium fluoride resonant cavity can efficiently convert pump light into quantum entangled photon pairs, generate high-brightness signal light and idle light photon pairs, and the generated optical high-dimensional quantum entangled photon pairs have a large distribution bandwidth and can provide rich spectrum resources.

[0033] Table 1: Cross-sectional structural geometric parameters of the magnesium fluoride resonant cavity

[0034]

[0035] In Table 1, W1 is the distance from the upper and lower surfaces to the central axis, W2 is the distance from the fillet vertex to the edge of the upper and lower surfaces, R is the directness of the upper and lower surfaces, θ is the fillet angle, r is the fillet radius, and H is the distance between the upper and lower surfaces.

[0036] The structural shape of the magnesium fluoride resonant cavity of the present invention changes the structural dispersion of the resonant cavity, controls the repetition frequency, and realizes an ultra-high quality factor; multiple four-wave mixing processes occur in the resonant cavity of the present invention, and multiple pairs of discrete signal light and idle light photon pairs can be generated, each pair of signal light and idle light photon pairs are in an entangled relationship, and high-dimensional quantum entanglement can be prepared; the present invention utilizes the ultra-high quality factor of the magnesium fluoride resonant cavity, and the intensity of the generated signal light and idle light photon pairs is high, and high-brightness quantum entanglement can be prepared.

[0037] According to the disclosure and teaching of the above description, those skilled in the art to which the present invention belongs may also make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the invention should also fall within the scope of protection of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the invention.

Claims

1. A magnesium fluoride resonant cavity for generating high-dimensional quantum entanglement, characterized in that: It includes a resonant cavity body, the resonant cavity body is a closed cavity, and the resonant cavity body is made of magnesium fluoride; The resonant cavity body is a vertically and horizontally symmetrical structure that is wide in the middle and narrow at both ends, the upper surface and the lower surface are circular planes, and the side walls are upper and lower arc surfaces that are symmetrical in the upper and lower directions, and the upper and lower arc surfaces are smoothly connected by fillets; The diameter R of the upper and lower surfaces is 1.5-3 mm, and the distance H between the upper and lower surfaces is 0.8-1.5 mm; The angle of the fillet is 50-70 degrees, and the fillet radius of the fillet is 0.02-0.05mm; The distance from the fillet vertex to the center point of the resonant cavity body is 2-2.5 mm; The pump light undergoes multiple nonlinear four-wave mixing processes simultaneously in the resonant cavity body. In each nonlinear four-wave mixing process, two pump light photons generate one signal light photon and one idle light photon.

2. A magnesium fluoride resonant cavity for generating high-dimensional quantum entanglement as claimed in claim 1, characterized in that: The pump light is input through a tapered optical fiber located at one side of the resonant cavity body and arranged parallel to the upper and lower surfaces, and the pump light meeting the resonant wavelength condition is coupled into the resonant cavity body.

3. A magnesium fluoride resonant cavity for generating high-dimensional quantum entanglement as claimed in claim 2, characterized in that: The distance between the tapered optical fiber and the surface of the resonant cavity body on the same side thereof is less than 6 μm.

4. A magnesium fluoride resonant cavity for generating high-dimensional quantum entanglement as claimed in claim 1, characterized in that: The pump light is coupled into the resonant cavity body to meet the following conditions: The optical path around the cavity is equal to an integer multiple of the wavelength of the pump light.

5. A magnesium fluoride resonant cavity for generating high-dimensional quantum entanglement as claimed in claim 4, characterized in that: The four-wave mixing process satisfies the energy conservation condition 2ω P＝ ω S +ω I and the momentum conservation condition Where: P is the pump light frequency, ω S is the signal light frequency, ω I is the idle optical frequency.

6. A magnesium fluoride resonant cavity for generating high-dimensional quantum entanglement as claimed in claim 4, characterized in that: The repetition frequency FSR in the resonant cavity body satisfies FSR=c / nL, and the repetition frequency refers to the frequency interval between the mth resonance mode and the m-1th resonance mode.

Images