Four-channel router

Abstract

The invention relates to the field of quantum communication, in particular to a four-channel router which comprises a bus waveguide and two lower waveguides, and the lower waveguides are located on the two sides of the bus waveguide respectively. A first echo wall mode cavity group is arranged between the lower waveguides and the bus waveguide, and the first echo wall mode cavity group is used for coupling photons input by the bus waveguide and outputting the photons to the lower waveguides; a reflector is arranged on the side, away from the photon input end, of the bus waveguide, a second echo wall mode cavity set is arranged between the lower waveguides and the bus waveguide, the reflector is used for reflecting photons and inputting the photons into the second echo wall mode cavity set, and the second echo wall mode cavity set is used for outputting the input photons into the lower waveguides. The directions of photons output by the first echo wall mode cavity group and the second echo wall mode cavity group are opposite. By adopting the technical scheme of the invention, a one-way path of an output channel is effectively converted into four channels, and frequency detuning among the resonant cavities is changed through a resonant cavity rotating technology.

Description

Technical Field

[0001] The present invention relates to the field of quantum communication, and in particular to a four-channel router. Background Art

[0002] As an important building block of quantum information processing, quantum networks are used to effectively transmit quantum signals through channels and connect quantum computers. They have become part of the increasingly prosperous field of quantum physics and information science. Usually, quantum networks are composed of quantum channels and quantum nodes, where quantum channels are provided by one-dimensional optical waveguides, and single photons are transmitted on the waveguide channels as quantum information carriers. As a key component of quantum nodes, quantum routers distribute quantum signals to different quantum channels by controlling the interaction between waveguides and quantum quantum emitters. Many single-photon routing studies have been implemented in waveguide quantum electrodynamics systems, including atomic bits, quantum dots, optomechanical systems, whispering gallery resonators, cavity and circuit quantum electrodynamics systems, and chiral systems.

[0003] Since a quantum network is usually a multi-channel system, a quantum router needs to manipulate the transmission of photons from one channel to another. Therefore, for multi-channel systems, it is quite important to provide a controllable path for users to route the desired frequency to the output channel with a high routing rate. In recent years, several multi-channel quantum routing schemes have been proposed, that is, connecting more quantum emitters to the output ports in the branch waveguide. Among these proposals, single photon routing from the input waveguide to many other output ports is proposed, but its inefficiency will limit potential applications. In order to increase the routing rate, reflectors or phase shifters with high-precision positions need to be connected to the main line waveguide, which leads to the complexity of the system structure. Therefore, it is necessary to design a quantum router with high performance and simple structure. Summary of the invention

[0004] To solve the above problems, the present invention provides a four-channel router, which is composed of three waveguides and four single-mode whispering gallery mode resonators. It can effectively convert the one-way transmission of the output channel into four-channel transmission, and change the frequency detuning between the resonators by rotating the resonator technology.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows: a four-channel router, comprising a main line waveguide and two drop waveguides, wherein the drop waveguides are respectively located on both sides of the main line waveguide;

[0006] A first whispering gallery mode cavity group is provided between the drop waveguide and the main line waveguide, and the first whispering gallery mode cavity group is used to couple the photons input by the main line waveguide and output the photons to each drop waveguide;

[0007] A reflector is provided on the side of the main line waveguide away from the input photon end, and a second whispering gallery mode cavity group is provided between the lower waveguide and the main line waveguide. The reflector is used to reflect photons and input the photons into the second whispering gallery mode cavity group, and the second whispering gallery mode cavity group is used to output the input photons to each lower waveguide. The photons output by the first whispering gallery mode cavity group and the second whispering gallery mode cavity group are in opposite directions.

[0008] Furthermore, the number of whispering gallery mode cavities in the first whispering gallery mode cavity group and the second whispering gallery mode cavity group are both 2.

[0009] The above scheme has the following beneficial effects:

[0010] 1. In this scheme, photons are injected from the input end of the main waveguide, coupled and transported to the two lower waveguides in the first whispering gallery mode cavity group, and the photons have opposite directions. The photons that have not entered the first whispering gallery mode cavity group continue to move to the reflector, and are reflected and input to the second whispering gallery mode cavity group under the action of the reflector, and then coupled and output to the two lower waveguides, and the photons have the same direction. As a result, both ends of the lower waveguide output opposite photons, completing the four-channel routing.

[0011] 2. In this scheme, a reflector is used to reflect photons and redirect them to the second whispering gallery mode cavity group. With this structure, the crosstalk effect between different frequencies can be suppressed, and the frequency detuning between the resonant cavities can be adjusted through the whispering gallery mode cavity technology, so that multiple peak frequencies in the four-channel structure with a high routing efficiency of about 1 can be achieved as needed.

[0012] 3. This scheme is independent of the exact location of the reflector and the resonant cavity, which helps to reduce the complexity of the router.

[0013] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A schematic diagram of an embodiment of a four-channel router of the present invention;

[0015] Figure 2 A schematic diagram of scattered data of a four-channel router embodiment of the present invention;

[0016] Figure 3 It is a schematic diagram of transmission probability data in the incident photon routing spectrum according to the frequency detuning of the four-channel router embodiment of the present invention;

[0017] Figure 4 It is a schematic diagram of the frequency detuning data of the four-channel router embodiment of the present invention and the routing rate data of the four drop ports;

[0018] Figure 5Schematic diagram of the effect of dissipation on the routing rate of coupled waveguides in an embodiment of a four-channel router of the present invention. DETAILED DESCRIPTION

[0019] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the 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", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0021] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0022] The following is further described in detail through specific implementation methods:

[0023] As attached Figure 1-Figure 5 As shown: a four-channel router, comprising a main line waveguide and two drop waveguides, wherein the drop waveguides are respectively located on both sides of the bus waveguide;

[0024] A first whispering gallery mode cavity group is provided between the drop waveguide and the main line waveguide, and the first whispering gallery mode cavity group is used to couple the photons input from the main line waveguide and output the photons to each drop waveguide;

[0025] A reflector is provided on the side of the main line waveguide away from the input photon end. The reflector is a total reflection mirror. A second whispering gallery mode cavity group is provided between the lower waveguide and the main line waveguide. The reflector is used to reflect photons and input them into the second whispering gallery mode cavity group. The second whispering gallery mode cavity group is used to output the input photons to each lower waveguide. The photons output by the first whispering gallery mode cavity group and the second whispering gallery mode cavity group are in opposite directions.

[0026] The number of whispering gallery mode cavities in the first whispering gallery mode cavity group and the second whispering gallery mode cavity group are both 2.

[0027] The specific implementation process is as follows:

[0028] The input photons from the left port of the bus waveguide are directly coupled to the first whispering gallery mode cavity group, and are transmitted to the drop waveguide through the first whispering gallery mode cavity, and are output from the left end of the drop waveguide. The remaining photons in the main line waveguide continue to move forward and are reflected and redirected by the reflector, thereby entering the second whispering gallery mode cavity group. The photons are transmitted into the drop waveguide through the second whispering gallery mode cavity group and are output from the right end of the drop waveguide. This allows both ends of the two drop waveguides to output photons, totaling four output lines.

[0029] Figure 1 The middle and lower waveguides 1 and 2 are located on both sides of the main line waveguide respectively. The first whispering gallery mode cavity group is the resonant cavity R1 and the resonant cavity R2 located at x=0, the second whispering gallery mode cavity group is the resonant cavity R3 and the resonant cavity R4 located at x=d1, and the reflector is located at x=d2.

[0030] The total Hamiltonian of the system in real space can be expressed as To express it, as follows:

[0031]

[0032] in represents the Bosonic operator that produces a right-moving (left-moving) photon at position x in waveguide m, v g is the group velocity of the propagating photon with input frequency ω, δ(x)[δ(x-d1)] means that the resonator-waveguide interaction occurs at x=0(d1), γ n represents the energy dissipated in these resonant cavities.

[0033] Assume that a single photon is incident from the left in the main waveguide with energy E k =ω, then the characteristic state of the Hamiltonian (1) of the above formula is given by H|ψ>=E k |ψ> is defined and can be expressed as:

[0034]

[0035] in This means that these guided wave modes and resonant cavity modes are in a vacuum state with zero photons, and represent the wave functions of the guided modes of these waveguide channels in the left and right directions, and represents the excitation probability amplitude of the photon in the nth resonant cavity.

[0036] The wave function form is:

[0037]

[0038] Here, t a and r a Respectively represent the transmission amplitude and reflection amplitude in the main line waveguide channel. m is the reflection amplitude from the reflector. t1 and t3 are the transmission amplitudes in drop waveguide 1, and t2 and t4 are the transmission amplitudes in drop waveguide 2. θ(x) represents the Heaviside step function, and θ(0) = 1 / 2.

[0039] Using boundary conditions on the mainline waveguide The obtained scattering amplitude is as follows:

[0040]

[0041] in, M1=Δω+iγ1+iΓ b1 , M2=Δω+Δω 12 +iγ2+iΓ cv , M3=Δω+Δω 13 +iγ3+iΓ b3 , M4=Δω+Δω 14 +iγ4+iΓ c4 Δω=ω-ω1 is the frequency detuning between the incident photon frequency and the resonant cavity 1, Δω 1n =ω1-ω n is the frequency detuning between resonant cavity 1 and resonant cavity n.

[0042] The routing characteristics in the system are studied based on the scattering probability in the coupled system and are denoted as T a(1，2，3，4) =|t a(1，2，3，4) | and R a =|r a | 2 First, consider the case where only resonant cavity 1 is coupled to the bus waveguide, at which the resonant cavity-waveguide coupling ratio P = Γ b1 / Γ a1 For simplicity, all parameters are expressed in terms of coupling Γ a1 When a single photon is incident from the left side of the main waveguide, it will pass through the main waveguide and be reflected back by the reflector. It will also be transmitted to the lower waveguide 1 through the resonant cavity, as shown in Figure 2 (a) and Figure 2(b) shows a single transmission peak of T1 at the resonance point Δω = 0 of different resonant cavity-waveguide couplers. Under the conditions of P = 1 and zero dissipation γ1 = 0, the routing rate is the maximum peak, which means that the moving photons along the bus waveguide are completely blocked by the coupled resonant cavity 1 and then completely transmitted to the output port of the drop waveguide 1. This situation is due to the equal resonant cavity-waveguide coupling Γ b1 =Γ a1 The effect of the two symmetrical coupling paths generated by the photon current is the same, through which the entire transmission between the two waveguides can be realized. At the same time, the photon current conservation relation R a +T1=1, when dissipation is ignored, both ports remain unchanged for any frequency.

[0043] When the other three waveguides are coupled to the main waveguide through an additional coupling resonant cavity, all four output channels are effective. The scattering spectra of single photons and Δω at the four output ports are shown in Figure 2 (c) shows that for an appropriate inter-resonant frequency detuning Δω 12 =Δω 23 =Δω 34 = 25, four transmission peaks with the same frequency n will appear at the center frequency of Δω. This means that the system can be used as a one-way quantum router. In addition, the influence of the resonant cavity-waveguide coupler on the four transmission peaks is shown in Figure 2 (d) For simplicity, P = Γ bn / Γ an Take it as the coupling ratio and assume it is the same. As shown in the figure, for these equal resonant cavity-waveguide couplings, the four transmission peaks in these channels appear in four regions, and a straight line with P=1 passes through these peak points. Similar to the case of the single resonant cavity mentioned above, a more symmetrical transmission path is formed between these waveguides and the resonant cavity, so that the input frequency is transmitted more efficiently.

[0044] The effect of frequency detuning between resonators on the routing efficiency of incident photons is manifested in that when more transmission channels appear, crosstalk between different signals is generated due to photon interference, resulting in lower routing efficiency of the input frequency. Figure 3 As shown in (a), T n The minimum peak appears at the resonance site ω1=ω2=ω3=ω4, where the strongest crosstalk is generated. The probability of T1 and T2 overlapping with the minimum route is about 0.44, which is the general resonance peak of a multi-single-mode excited quantum emitter in a multi-channel routing system. T3 and T4 also overlap with the smaller route with a probability of 0.12. Since the transmitted photons of the two channels on the right come from the reflected part and are more disturbed by the reflector. For simplicity, the frequency detuning device Δω between the resonant cavities is 23 =Δω 34 =Δω 12, when the frequency detuning between the resonant cavities is changed to Δω 12 It is obvious that as the detuning value increases, Δω 12 The crosstalk decreases sharply, and the peak value of the scattering spectrum quickly reaches the maximum output value of unity, such as Figure 3 (b) and Figure 3 (c) as shown.

[0045] Figure 3 (d) shows the transmission peak of T1, which increases when the frequency detuning between the resonators increases at the resonance point ω1. 12 =10, the corresponding signal loss C caused by crosstalk from other signals 2(3，4) Reduced to zero.

[0046] To gain a deeper understanding of the effect of inter-cavity frequency detuning on the routing efficiency of the four output ports, Figure 4 (a) The output peak spectra of the four channels with different inter-resonance frequency detuning and their center frequency positions are plotted. and The overlap increases sharply from the minimum routing ratio of 0.44 to the maximum of 1, similar to the resonant cavity frequency detuning Δω 12 When it gets bigger and Varies from 0.12 to 1. Figure 4 (b) also shows that these transmission peaks with maximum values ​​are displayed in four different narrow and straight windows. The transmission peak of T1 is fixed at ω1 and presented vertically, while the center frequencies of the other three channels are tilted and spread with a frequency shift equal to the inter-resonant frequency detuning of each channel signal.

[0047] Experiments have shown that the frequency detuning between resonators can be controlled by rotating the resonator. For a rotating resonator with an angular velocity of Ω, the light circulating in the whispering gallery mode cavity will undergo a Fizeau shift related to the angular velocity, which will cause the transmission to deviate from the resonant frequency of the whispering gallery mode cavity. Therefore, controlling the frequency detuning between resonators can be used as a new way to achieve efficient routing, because the widened frequency interval can effectively suppress the crosstalk from these transmission signals. However, these channel routings are independent of the determined positions of these resonators and reflectors. As shown in Equation (3), since the horizontal propagation and reflection directions of the photons and the rotating mode direction of the resonator meet the mode direction matching conditions, the position-related exponential term is eliminated under the action of the mode square to obtain the routing rate. Compared with the previous scheme that requires a precise phase shift related to the reflector position to obtain a higher transmission probability, this scheme does not require a router with a precise position, which has certain advantages. In the above discussion, dissipation is not considered. In actual experiments, the routing system will inevitably suffer from the loss of the resonator. Figure 5(a) Describes the effect of dissipation on the routing rate of the coupled waveguides. Obviously, compared with the routing spectrum without dissipation, all transmission rates of the four channels decrease with the increase of dissipation. Due to the leakage of photons, even the symmetrical coupling path cannot completely transfer photons, which leads to the displacement of the coupling ratio P corresponding to the maximum transfer peak. Figure 5 As shown in (b), increasing the loss of the resonant cavity reduces the maximum peak and shifts p to higher values, e.g., strong dissipation γ = Γ a This results in a significant shift of about p = 1.5. Here we take the dissipation γ to be equal n =γ0. However, for a high-quality resonant cavity with extremely low losses, a high T n The transmission rate is still usable, such as the expected result of γ0 = 0.05 is about 0.95.

[0048] In the single-photon quantum routing of a coupled four-channel waveguide system with mirrors, the photon scattering amplitudes in these ports are accurately derived using real-space methods. The results show that high routing on these channels is achievable, and the router can route photons to any output channel as needed by adjusting parameters. The scheme of multi-channel routing of single photons can be used to realize other quantum devices such as filters, switches and demultiplexers.

[0049] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A four-channel router, characterized in that: It includes a main line waveguide and two drop waveguides, and the drop waveguides are respectively located on both sides of the main line waveguide; A first whispering gallery mode cavity group is provided between the drop waveguide and the main line waveguide, and the first whispering gallery mode cavity group is used to couple the photons input by the main line waveguide and output the photons to each drop waveguide; A reflector is provided on the side of the main line waveguide away from the input photon end, and a second whispering gallery mode cavity group is provided between the down-waveguide and the main line waveguide. The reflector is used to redirect photons and input them into the second whispering gallery mode cavity group, and the second whispering gallery mode cavity group is used to output the input photons to each down-waveguide. The photons output by the first whispering gallery mode cavity group and the second whispering gallery mode cavity group are in opposite directions.

2. The four-channel router according to claim 1, characterized in that: The number of whispering gallery mode cavities in the first whispering gallery mode cavity group and the second whispering gallery mode cavity group are both 2.

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