A single-photon quantum routing method

Abstract

The present invention discloses a single-photon quantum router, comprising parallel quantum channels A and B. Quantum channel A is a single-sided finite waveguide, while quantum channel B is a planar straight waveguide. Two resonant cavities are located between quantum channel A and quantum channel B. Two two-level atoms are embedded within the resonant cavities as optical quantum path nodes, interacting with the resonant cavities. The router first designs a structural scheme for single-photon quantum routing within a broadband frequency range. The single-photon routing process is quantized in real space, and the probability amplitude of a single photon being detected at each output port of the router is calculated. Parameters are then adjusted to simulate the quantum routing process, achieving efficient single-photon quantum routing within the broadband frequency range.

Description

Technical Field

[0001] The present invention relates to the field of quantum technology, and in particular to a single-photon quantum router and a routing method thereof. Background Art

[0002] In recent years, controlling the propagation of photons in waveguides has received increasing attention. Experiments have demonstrated that photons in waveguides can couple with resonant cavities based on their propagation direction and radiate them directionally into the waveguide, achieving chiral coupling between the photon and the resonant cavity. Real-space quantum optical waveguide theory can intuitively describe the transmission and reflection of single photons after photon-resonant cavity coupling in a waveguide, providing a powerful theoretical tool for studying photon-resonant cavity chiral coupling in waveguides and efficiently controlling the directional propagation of photons. By designing chiral coupling between photons and resonants in waveguides, efficient control of photon propagation in waveguide structures can be achieved, laying the foundation for the development of solid-state chiral quantum devices and the construction of chiral optical quantum routing and networks.

[0003] Quantum networks are the foundation for large-scale quantum communication and quantum computing. Research on the propagation and control of photons in waveguide network structures is of great significance. Quantum routers, as the fundamental building blocks of quantum networks, enable photons to enter through a single path, exit from multiple ports, and ultimately transmit the photons to each output port of the quantum network. The single frequency of photons is a bottleneck in current research and development of optical quantum routing, limiting the networking efficiency and information transmission and processing capabilities of optical quantum networks. Therefore, it is necessary to design high-efficiency, solid-state optical quantum routers with a wide spectrum to meet the networking requirements of quantum networks. Summary of the Invention

[0004] To address the shortcoming of existing single-photon quantum routers that they only correspond to a single photon frequency, this paper proposes a high-efficiency broadband frequency single-photon quantum routing method based on chiral quantum optical waveguide theory. The method first designs a structural scheme for single-photon quantum routing within a broadband frequency range, then quantizes the single-photon routing process in real space, calculates the probability amplitude of a single photon being detected at each output port of the router, and adjusts parameters to complete the quantum routing process simulation, achieving high-efficiency single-photon quantum routing within a broadband frequency range.

[0005] In order to solve the above technical problems, the technical solution of the present invention is:

[0006] A single-photon quantum router includes a quantum channel a and a quantum channel b arranged in parallel. The quantum channel a is a unilateral finite waveguide, and the quantum channel b is a planar straight waveguide. Two resonant cavities are provided between the quantum channel a and the quantum channel b. Two two-level atoms are embedded in the resonant cavities as optical quantum path nodes, and the two-level atoms interact with the resonant cavities.

[0007] Among them, quantum channel a and quantum channel b are both planar waveguides.

[0008] Preferably, the unilateral finite waveguide is an incident waveguide, one end of the unilateral finite waveguide is a closed end, and the closed end is a reflection end.

[0009] Preferably, the planar straight waveguide is a non-incident waveguide.

[0010] Preferably, two coupling points are provided in the middle positions of the quantum channel a and the quantum channel b, respectively denoted as coupling point x1 and coupling point x2, wherein one of the two-level atoms is located between the coupling point x1 on the quantum channel a and the quantum channel b, and the other two-level atom is located between the coupling point x2 on the quantum channel a and the quantum channel b.

[0011] The present invention also provides a single-photon quantum routing method, comprising the following steps:

[0012] S1. Design a single-photon quantum router with two quantum routing channels and two quantum routing nodes placed in the middle with a certain distance between the nodes.

[0013] S2. Apply the single-photon quantum router designed in step S1 to perform real-space quantized routing;

[0014] S2-1. Using the real-space chiral quantum optical waveguide theory, give the real-space Hamiltonian corresponding to the propagation of photons in a unilateral finite waveguide and a planar straight waveguide;

[0015] S2-2. Give the real-space Hamiltonian for the chiral coupling of photons at positions x1 and x2 in the two waveguides with the routing nodes.

[0016] S2-3. Give the Hamiltonian of the coupling between the atom and the resonant cavity; express the Hamiltonian of the atom and the resonant cavity themselves;

[0017] S2-4. Give the Hamiltonian acting on the photon at the cutoff waveguide boundary x3=0;

[0018] S2-5. Add the four Hamiltonians obtained in steps S2-1 to S2-4 to form an effective Hamiltonian H corresponding to the optical quantum routing process;

[0019] S2-6. Construct the real-space, single-excitation, and time-independent wave function corresponding to the real-space quantized Hamiltonian, specifically expressed as:

[0020]

[0021] φ a R(x)=e iqx [θ(x1-x)+t a12θ(x - x1)θ(x2 - x) + t a23 θ(x - x2)θ(x3 - x)]

[0022] φ a L(x) = e -iqx [r2θ(x1 - x) + r a12 θ(x - x1 ) θ(x2 - x) + r a23 θ(x - x2)θ(x3 - x)]

[0023] φ b R(x) = e iqx [t bR2 θ(x - x2) + t b12 θ(x - x1)θ(x2 - x)]

[0024] φ b L(x) = e -iqx [t bL2 θ(x1 - x) + r b12 θ(x - x1)θ(x2 - x)]

[0025] φ a，b R(x) / φ a，b L(x) is the probability amplitude of a photon propagating in the waveguide, where t a12 and t a23 are the transfer amplitudes of the photon in the two regions (x1, x2) and (x2, x3) of waveguide a, respectively. r2, r a12 and r a23 represent the reflection amplitudes of the photon in these regions: (x < x1), (x1, x2), and (x2, x). t bR2 / t bL2 and t b12 / r b12 are the transfer amplitudes in waveguide - b; represents the creation operator for the transmitted photon; e c1 / e c2 and e a1 / e a2 represent the excitation amplitudes of the cavity and the atom, respectively; and represent the boson creation / annihilation operator of the cavity and the raising / lowering operator of the atom, respectively.

[0026] S3. Calculation and regulation simulation;

[0027] S3 - 1. Using the Hamiltonian of S2 - 5 and the wave function of S2 - 6 to construct the corresponding Schrödinger equation, which is:

[0028] H|Ψ(x)〉 = E|Ψ(x)〉

[0029] S3-2. According to the coefficients corresponding to the single excited photon state, the resonant cavity and the quantum state of the atom in the process of solving the Schrödinger equation, a coefficient equation system is established, specifically:

[0030]

[0031] S3-3. Use the matrix solving method of linear equations in mathematical scientific computing software to solve the coefficient equations shown in S3-2, and obtain the probability amplitude expression of being detected at the three ports during the single photon routing process;

[0032] S3-4. Arbitrarily select the resonant frequency of the two resonant cavities, the chiral coupling strength, the detuning between the atom and the resonant cavity, the coupling strength between the atom and the resonant cavity, the spacing between the two resonant cavities, and the boundary distance between the resonant cavity and the unilateral finite waveguide. Use MATLAB software to simulate optical quantum routing by incident single photons in a swept frequency manner. Obtain the corresponding single photon reflection probability curves at the incident port and the probability curves of leftward and rightward propagation in the non-incident waveguide within the frequency range of the sum of the resonant frequency and the detuning;

[0033] S3-5. Adjust the frequency range, chiral coupling strength, and atom-resonant cavity coupling strength in the parameters described in S3-4, simulate light quantum routing through the software system, and perform multiple debugging measurements based on the obtained routing probability curve to reduce the reflection probability of single photons and increase the probability of single photon routing propagating to the left and right in the non-incident waveguide.

[0034] The present invention has the following characteristics and beneficial effects:

[0035] The present invention proposes a scheme for regulating single-photon routing within a broadband frequency range. By utilizing a unilateral finite waveguide as an incident waveguide, the present invention significantly increases the coupling frequency between single photons and routing nodes (resonant cavities), improving the utilization rate of incident single photons and routing efficiency, enabling single photons to route through non-incident waveguides with a near-100% probability. The present invention utilizes atoms coupled to resonant cavities to increase the number of routing peaks, adding routing nodes to achieve superposition between routing peaks. This increases the photon frequency range corresponding to single-photon routing, reduces dependence on photon frequency, relaxes the frequency conditions corresponding to high-efficiency single-photon quantum routing, and further enhances the robustness of single-photon routers. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0037] Figure 1 This is a structural block diagram of the single-photon quantum router of the present invention. DETAILED DESCRIPTION

[0038] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0039] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0040] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0041] This embodiment provides a single-photon quantum router, such as Figure 1 As shown, a unilateral finite waveguide is used as the incident waveguide for optical quantum routing, and another planar straight waveguide is used as the non-incident waveguide, so that single photons have only three output ports during the routing process. At the same time, the unilateral finite waveguide can reflect photons, increase the coupling frequency between single photons and routing nodes, and improve the probability of single photons being routed to the non-incident waveguide; two resonant cavities embedded with two-level atoms are used as optical quantum routing nodes, and are placed at the x1 and x2 positions between the two waveguides respectively, so that single photons are chirally coupled with the routing nodes at these two locations, and a controllable single photon geometric phase is generated due to the different positions between the two.

[0042] This embodiment also provides a single-photon quantum router method, which specifically includes the following steps:

[0043] S1. Design the above-mentioned single-photon quantum router;

[0044] S2. Apply the single-photon quantum router designed in step S1 to realize real-space quantized routing.

[0045] The real-space quantized routing process is as follows:

[0046] S2-1. Using the real-space chiral quantum optical waveguide theory, the real-space Hamiltonian corresponding to the propagation of photons in a unilateral finite waveguide and a planar straight waveguide is given. Specifically:

[0047]

[0048] S2-2. The real-space Hamiltonian for the chiral coupling of photons at positions x1 and x2 in the two waveguides with the routing nodes is given as follows:

[0049]

[0050] S2-3. Give the Hamiltonian of the coupling between the atom and the resonant cavity. The Hamiltonian corresponding to the atom and the resonant cavity itself is expressed as follows:

[0051]

[0052] S2-4. The Hamiltonian acting on photons at the cutoff waveguide boundary x3=0 is given as follows:

[0053]

[0054] S2-5. Add the four Hamiltonians obtained in steps S2-1 to S2-4 to form an effective Hamiltonian h corresponding to the optical quantum routing process;

[0055] S2-6. Construct the real-space, single-excitation, and time-independent wave function corresponding to the real-space quantized Hamiltonian, specifically expressed as:

[0056]

[0057] φ a R(x)=e iqx [θ(x1-x)+t a12 θ(x-x1)θ(x2-x)+t a23 θ(x-x2)θ(x3-x)]

[0058] φ a L(x)=e -iqx [r2θ(x1-x)+r a12 θ(x-x1)θ(x2-x)+r a23 θ(x-x2)θ(x3-x)]

[0059] φ b R(x) = e iqx [t R2θ (x - x2) + t b12 θ(x - x1)θ(x2 - x)]

[0060] φ b L(x) = e -iqx [t bL2 θ(x1 - x) + r b12 θ(x - x1)θ(x2 - x)]

[0061] In steps S2-1 to S2-6, represents the ground state of the system; ω c1 / ω c2 and ω e1 / ω e2 respectively represent the resonance frequency of the cavity mode and the atomic-level frequency of the excited-state atom; and respectively represent the cavity dissipation rate and the atomic dissipation rate. Since the cavity is of high quality, the influence of the cavity dissipation on the routing ability is very small. For simplicity, we can ignore the intrinsic dissipation of the cavity; v a / v b represents the group velocity of photon propagation in the waveguide; g1 / g2 represents the coupling strength between the cavity and the atom; V 1(2)R(L) represents the interaction strength between the cavity and the two waveguides in the left-right direction; φ a，b R(x) / φ a，b (x) is the probability amplitude of photon propagation in the waveguide, where t a12 and t<00000​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​

[0063] S3-1. Use the Hamiltonian of S2-5 and the wave function of S2-6 to construct the corresponding Schrödinger equation, which is:

[0064] H|Ψ(x)〉=E|Ψ(x)〉

[0065] S3-2. According to the coefficients corresponding to the single excited photon state, the resonant cavity and the quantum state of the atom in the process of solving the Schrödinger equation, a coefficient equation system is established, specifically:

[0066]

[0067] S3-3. Use the matrix solving method of linear equations in mathematical scientific computing software to solve the coefficient equations shown in S3-2, and obtain the probability amplitude expression of being detected at the three ports during the single-photon routing process, specifically:

[0068]

[0069] Among them, Δ 1 / 2 =E-ω c1 / c2 and Δ E1 / E2 =E-ω e1 / e2 They represent the detuning between the photon and the cavity and the detuning between the photon and the atom, respectively. For simplicity, the two values ​​are made equal in subsequent simulations. represents the effective coupling strength between the photon and the nth atom along the left and right directions; θ1 = qx1, θ2 = qx2 represent the phase shift of the routing photon.

[0070] Using R2=|r2| 2 , T bR2 =|t bR2 | 2 , T bL2 =|t bL2 | 2 Further probability expression is obtained, and the routing probability always satisfies R2+T bR2 +T bL2 =1, that is, under ideal circumstances, the detection probabilities of the three ports meet the normalization requirement.

[0071] S3-4. Arbitrarily select the resonant frequency of the two resonant cavities, the chiral coupling strength, the detuning between the atom and the resonant cavity, the coupling strength between the atom and the resonant cavity, the spacing between the two resonant cavities, and the boundary distance between the resonant cavity and the unilateral finite waveguide. Use MATLAB software to simulate optical quantum routing by incident single photons in a swept frequency manner. Obtain the corresponding single photon reflection probability curves at the incident port and the probability curves of leftward and rightward propagation in the non-incident waveguide within the frequency range of the sum of the resonant frequency and the detuning;

[0072] S3-5. Adjust the frequency range, chiral coupling strength, and atom-resonant cavity coupling strength in the parameters described in S3-4, simulate light quantum routing through the software system, and perform multiple debugging measurements based on the obtained routing probability curve to reduce the reflection probability of single photons and increase the probability of single photon routing propagating to the left and right in the non-incident waveguide.

[0073] As described above, this invention utilizes theoretical simulations of chiral quantum optical waveguides to implement a method for highly efficient single-photon routing within a wide frequency range. This method robustly routes photons to non-incident ports, increasing the efficiency and frequency of optical quantum routers and significantly improving the efficiency of quantum signal transmission and processing.

[0074] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the described embodiments. It will be apparent to those skilled in the art that various changes, modifications, substitutions, and variations of these embodiments, including components, without departing from the principles and spirit of the present invention are still within the scope of protection of the present invention.

Claims

1. A single-photon quantum routing method, characterized in that: The steps include: S1. Design a single-photon quantum router, which includes parallel quantum channels a and b. Quantum channel a is a unilateral finite waveguide, and quantum channel b is a planar straight waveguide. A resonant cavity is located between quantum channels a and b. Two two-level atoms are embedded in the resonant cavity as optical quantum routing nodes. Two coupling points are provided in the middle of quantum channels a and b, respectively denoted as coupling point x1 and coupling point x2. One of the two-level atoms is located between coupling point x1 on quantum channels a and b, and the other two-level atom is located between coupling point x2 on quantum channels a and b. S2. Apply the single-photon quantum router designed in step S1 to perform real-space quantized routing; S2-1. Using the real-space chiral quantum optical waveguide theory, the real-space Hamiltonian corresponding to the propagation of photons in a unilateral finite waveguide and a planar straight waveguide is given. Specifically: S2-2. The real-space Hamiltonian for the chiral coupling of photons at positions x1 and x2 in the two waveguides with the routing nodes is given as follows: S2-3. Give the Hamiltonian of the coupling between the atom and the resonant cavity. The Hamiltonian corresponding to the atom and the resonant cavity itself is expressed as follows: S2-4. The Hamiltonian acting on photons at the cutoff waveguide boundary x3=0 is given as follows: S2-5. Add the four Hamiltonians obtained in steps S2-1 to S2-4 to form an effective Hamiltonian H corresponding to the optical quantum routing process; S2-6. Construct the real-space, single-excitation, and time-independent wave function corresponding to the real-space quantized Hamiltonian, specifically expressed as: f a R(x)=e iqx [θ(x1-x)+t a12 θ(x-x1)θ(x2-x)+t a23 θ(x-x2)θ(x3-x)] f a L(x)=e -iqx [r2θ(x1-x)+r a12 θ(x-x1)θ(x2-x)+r a23 θ(x-x2)θ(x3-x)] f b R(x)=e iqx [t bR2 θ(x-x2)+t b12 θ(x-x1)θ(x2-x)] f b L(x)=e -iqx [t bL2 θ(x1-x)+r b12 θ(x-x1)θ(x2-x)] where, φ a，b R(x) / φ a，b L(x) is the probability amplitude of a photon propagating in the waveguide, where, t a12 and t a23 are the transfer amplitudes of the photon in the two regions (x1, x2) and (x2, x3) of waveguide a respectively; r2, r a12 and r a23 represent the reflection amplitudes of the photon in these regions: (x < x1), (x1, x2) and (x2, x3); t bR2 / t bL2 and t b12 / r b12 are the transfer amplitudes in waveguide - b; represents the creation operator of the transmitted photon; e c1 / e c2 and e a1 / e a2 represent the excitation amplitudes of the cavity and the atom respectively; and represent the boson creation and annihilation operators of the cavity and the raising and lowering operators of the atom respectively; Among them, in steps S2-1 to S2-6, represents the system ground state; ω c1 / ω c2 and ω e1 / ω e2 respectively represent the resonance frequency of the cavity mode and the atomic-level frequency of the excited-state atom; and respectively represent the cavity dissipation rate and the atomic dissipation rate; v a / v b represents the group velocity of photon propagation in the waveguide; g1 / g2 represents the coupling strength between the cavity and the atom; V 1(2)R(L) represents the interaction strength between the cavity and the two waveguides in the left-right direction; φ a，b R(x) / φ a，b L(x) is the probability amplitude of photon propagation in the waveguide, where t a12 and t a23 are the transfer amplitudes of the photon in the two regions (x1, x2) and (x2, x3) in waveguide a respectively; r2, r a12 and r a23 respectively represent the reflection amplitudes of the photon in these regions: (x < x1), (x1, x2) and (x2, x3); t bR2 / t bL2 and t b12 / r b12 are the transfer amplitudes in waveguide -b; represents the creation operator of the transmitted photon; e c1 / e c2 and e a1 / e a2 respectively represent the excitation amplitudes of the empty cavity and the atom; and respectively represent the boson creation and annihilation operators of the cavity and the raising and lowering operators of the atom; S3. Calculation and control simulation: S3-1, using the effective Hamiltonian of S2-5 and the wave function of S2-6 to construct the corresponding Schrödinger equation, which is: H|Ψ(x)>=E|Ψ(x)> S3-2. According to the coefficients corresponding to the single excited photon state, the resonant cavity and the quantum state of the atom in the process of solving the Schrödinger equation, a coefficient equation system is established, specifically: S3-3. Use the matrix solving method of linear equations in mathematical scientific computing software to solve the coefficient equations shown in S3-2, and obtain the probability amplitude expression of being detected at the three ports during the single photon routing process; S3-4. Arbitrarily select the resonant frequency of the two resonant cavities, the chiral coupling strength, the detuning between the atom and the resonant cavity, the coupling strength between the atom and the resonant cavity, the spacing between the two resonant cavities, and the boundary distance between the resonant cavity and the unilateral finite waveguide. Use MATLAB software to simulate optical quantum routing by incident single photons in a swept frequency manner. Obtain the corresponding single photon reflection probability curves at the incident port and the probability curves of leftward and rightward propagation in the non-incident waveguide within the frequency range of the sum of the resonant frequency and the detuning; S3-5. Adjust the frequency range, chiral coupling strength, and atom-resonant cavity coupling strength in the parameters described in S3-4, simulate light quantum routing through the software system, and perform multiple debugging measurements based on the obtained routing probability curve to reduce the reflection probability of single photons and increase the probability of single photon routing propagating to the left and right in the non-incident waveguide.

2. The single-photon quantum routing method according to claim 1, characterized in that: The unilateral finite waveguide is an incident waveguide, one end of the unilateral finite waveguide is a closed end, and the closed end is a reflection end.

3. The single-photon quantum routing method according to claim 1, characterized in that: The planar straight waveguide is a non-incident waveguide.

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