A quantum controlled not gate

Abstract

The application discloses a quantum controlled NOT gate, which comprises a first input transverse mode converter, a second input transverse mode converter, a first beam splitter, a second beam splitter, a third beam splitter, a fourth beam splitter, a fifth beam splitter, a first output transverse mode converter and a second output transverse mode converter. The controlled NOT gate operation is realized by arranging four transverse waveguide mode converters and five beam splitters, and the structure is simple and compact, the optical path is stable, and the entanglement efficiency between two-bit quantum inputs in the structure is high. When the controlled NOT gate operation is realized, the wavelength of incident light is not limited, the whole structure has wideband effectiveness, and the structure can also use wavelength encoding while using multiple transverse waveguide encoding, so that the waveguide mode encoding and wavelength encoding light can be multiplexed and demultiplexed in the same channel, and therefore the dimension of the controlled NOT gate calculation and communication can be expanded.

Description

Technical Field

[0001] The present application belongs to the field of quantum information technology, and specifically relates to a quantum controlled NOT gate. Background Art

[0002] The quantum controlled NOT gate is an essential core component for building a universal quantum computer. Its function is to change the response of the target bit according to the state of the control bit. Combined with the single-bit quantum gate operation, it can be expanded to a very large scale to realize an arbitrary function quantum information processing system. In theory, the combination of multiple two-bit quantum controlled NOT gates and any single-bit quantum gate can complete all quantum computing tasks. For a schematic diagram of the working principle of the two-bit quantum controlled NOT gate, see Figure 1 , where the upper line represents the control qubit, the lower line represents the target qubit, the solid black dot represents the control bit, and the cross circle represents the target bit. It works as follows: if the control qubit is 0, the target qubit remains unchanged; if the control qubit is 1, the target qubit flips.

[0003] Many schemes for fabricating quantum controlled NOT gates using linear optical elements and photonic systems have been proposed, but the main encoding methods currently focus on dimensions such as polarization encoding and phase encoding. Transverse waveguide mode encoding is an emerging quantum state encoding method. For example, patent number CN100454128C discloses a system for achieving multi-photon field waveguide mode entanglement. Through a quantum controlled NOT gate composed of nonlinear devices such as waveguide mode couplers, Mach-Zehnder interferometers, and semiconductor optical amplifiers, the entanglement of waveguide modes between two light fields is achieved. However, the Kerr medium or semiconductor amplifier used in this technical solution is a nonlinear device, so the efficiency of successful interaction between the two light fields is low.

[0004] On-chip quantum transverse waveguide mode encoding can propagate in multimode waveguides and multimode optical fibers. Light can propagate in a waveguide in multiple waveguide modes, so waveguide modes can be used for high-dimensional encoding processes, which will greatly expand the information capacity of single-bit communication and computing. Therefore, this application proposes a quantum controlled NOT gate using transverse waveguide mode encoding. Summary of the Invention

[0005] Based on the above, this application provides a quantum controlled NOT gate that implements controlled NOT operation by using a transverse waveguide mode converter and a beam splitter. It has a simple and compact structure and high optical path stability. The specific scheme is as follows:

[0006] The present application discloses a quantum controlled NOT gate, comprising a first input transverse mode converter, a second input transverse mode converter, a first beam splitter, a second beam splitter, a third beam splitter, a fourth beam splitter, a fifth beam splitter, a first output transverse mode converter, and a second output transverse mode converter;

[0007] The first input transverse mode converter and the second input transverse mode converter each include an input end, an output upper end, and an output lower end; the first output transverse mode converter and the second output transverse mode converter each include an input upper end, an input lower end, and an output end; the input lower port of the second beam splitter is connected to the output upper end of the first input transverse mode conversion; the output lower port of the second beam splitter is connected to the input upper end of the first output transverse mode conversion; the four ports of the third beam splitter are respectively connected to the output lower end of the first input transverse mode conversion, the output upper port of the first beam splitter, the input lower end of the first output transverse mode conversion, and the input upper port of the fifth beam splitter; the four ports of the first beam splitter are respectively connected to the output upper end of the second input transverse mode conversion, the output lower end of the second input transverse mode conversion, the input lower port of the third beam splitter, and the input upper port of the fourth beam splitter; the four ports of the fifth beam splitter are respectively connected to the output lower port of the third beam splitter, the output upper port of the fourth beam splitter, the input upper end of the second output transverse mode conversion, and the input lower end of the second output transverse mode conversion;

[0008] The first input transverse mode converter is used to transmit the received TE0 mode photons to the input lower port of the second beam splitter or convert the received TE1 mode photons into TE0 mode photons and transmit the converted TE0 mode photons to the input upper port of the third beam splitter;

[0009] The second input transverse mode converter is used to transmit the received TE0 mode photons to the input upper port of the first beam splitter or convert the received TE1 mode photons into TE0 mode photons and transmit the converted TE0 mode photons to the input lower port of the first beam splitter;

[0010] The first output transverse mode converter is used to directly output the TE0 mode photons output from the output lower port of the second beam splitter or convert the TE0 mode photons output from the output upper port of the third beam splitter into TE1 mode photons and output the converted TE1 mode photons;

[0011] The second output transverse mode converter is used to directly output the TE0 mode photons output from the output upper port of the fifth beam splitter or convert the TE0 mode photons output from the output lower port of the fifth beam splitter into TE1 mode photons and output the converted TE1 mode photons;

[0012] The first beam splitter, the second beam splitter, the third beam splitter, the fourth beam splitter and the fifth beam splitter are used to perform path allocation on the input TE0 mode photons. The path allocation ratio of the first beam splitter and the fifth beam splitter is 1:1, and the path allocation ratio of the second beam splitter, the third beam splitter and the fourth beam splitter is 1:2, where the path allocation ratio is the probability of a photon being output from the output end on the same side of the beam splitter input end / the probability of a photon being output from the output end on the opposite side of the beam splitter input end.

[0013] Preferably, the first input transverse mode converter, the second input transverse mode converter, the first beam splitter, the second beam splitter, the third beam splitter, the fourth beam splitter, the fifth beam splitter, the first output transverse mode converter and the second output transverse mode converter are integrated on a substrate through a monolithic integration process.

[0014] Furthermore, the first input transverse mode converter, the second input transverse mode converter, the first output transverse mode converter, and the second output transverse mode converter all include a main straight waveguide and a coupling region optical waveguide, a bending optical waveguide, and a transmission straight waveguide connected in sequence, and the coupling region optical waveguide and the main straight waveguide form an evanescent coupling region; the main straight waveguide of the first input transverse mode converter is connected to the input lower port of the second beam splitter, and the transmission straight waveguide of the first input transverse mode converter is connected to the input upper port of the third beam splitter; the main straight waveguide of the second input transverse mode converter is connected to the input upper port of the first beam splitter, and the transmission straight waveguide of the second input transverse mode converter is connected to the input lower port of the first beam splitter; the main straight waveguide of the first output transverse mode converter is connected to the output lower port of the second beam splitter, and the transmission straight waveguide of the first output transverse mode converter is connected to the output upper port of the third beam splitter; the main straight waveguide of the second output transverse mode converter is connected to the output upper port of the fifth beam splitter, and the transmission straight waveguide of the second output transverse mode converter is connected to the output lower port of the fifth beam splitter.

[0015] In general, the above technical solutions conceived by this application can achieve the following beneficial effects compared with the existing technology:

[0016] This application implements a controlled NOT gate operation by providing four transverse waveguide mode converters and five beam splitters. This structure is simple and compact, with high optical path stability and high entanglement efficiency between the two-bit quantum inputs. When implementing the controlled NOT gate operation, there is no restriction on the wavelength of the incident light, and the entire structure has broadband efficiency. Furthermore, while this structure employs multiple transverse waveguide encoding, it can also employ wavelength encoding, enabling the multiplexing and demultiplexing of waveguide mode-encoded and wavelength-encoded light in the same channel. This expands the computational and communication dimensions of the controlled NOT gate. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in this embodiment or the prior art, the following briefly introduces the drawings required for use in the embodiment or the prior art description. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 Schematic diagram of the principle of a two-bit quantum controlled NOT gate;

[0019] Figure 2 A schematic diagram of the structure of a quantum controlled NOT gate provided in an embodiment of the present application;

[0020] Figure 3 Schematic diagram of the structure of the first input transverse mode converter and the second input transverse mode converter in this application;

[0021] Figure 4 This is a schematic structural diagram of the first output transverse mode converter and the second output transverse mode converter in this application;

[0022] Figure 5 Schematic diagram of the structure of the beam splitter in this application;

[0023] Figure 6 The four paths of the quantum controlled NOT gate of this application are labeled and a transmission path diagram of the photon evolution in one embodiment;

[0024] Figure 7 This is a structural diagram corresponding to an extended embodiment of the quantum controlled NOT gate of this application. DETAILED DESCRIPTION

[0025] To make the above-mentioned purposes, features, and advantages of the present application more clearly understood, the following is a further detailed description of the embodiments of the present application in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0026] In the following description, many specific details are set forth to facilitate a full understanding of the present application. However, the present application may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0027] In order to facilitate understanding and explanation of the technical solutions provided by the embodiments of the present application, the background technology of the present application will be described below.

[0028] Transverse waveguide mode encoding is an emerging quantum state encoding method. For example, patent number CN100454128C discloses a system for achieving waveguide mode entanglement in multiple photon fields. This system achieves entanglement of the waveguide modes between two optical fields by using a quantum controlled NOT gate composed of nonlinear devices such as a waveguide mode coupler, a Mach-Zehnder interferometer, and a semiconductor optical amplifier. However, the Kerr medium or semiconductor amplifier used in this technical solution is a nonlinear device, resulting in low efficiency in the successful interaction between the two optical fields.

[0029] Based on this, the present application provides a quantum controlled NOT gate, such as Figure 2 As shown, it includes a first input transverse mode converter, a second input transverse mode converter, a first beam splitter, a second beam splitter, a third beam splitter, a fourth beam splitter, a fifth beam splitter, a first output transverse mode converter and a second output transverse mode converter.

[0030] In the present application, the first input transverse mode converter, the second input transverse mode converter, the first beam splitter, the second beam splitter, the third beam splitter, the fourth beam splitter, the fifth beam splitter, the first output transverse mode converter and the second output transverse mode converter are integrated on a substrate through a monolithic integration process, that is, the quantum controlled NOT gate is an on-chip structure, the layout of the components is compact, and the optical path stability is high.

[0031] The first input transverse mode converter and the second input transverse mode converter each include an input end, an output upper end, and an output lower end. The input lower end of the second beam splitter is connected to the output upper end of the first input transverse mode converter, and the output lower end of the second beam splitter is connected to the input upper end of the first output transverse mode converter.

[0032] The four ports of the third beam splitter are respectively connected to the output lower end of the first input transverse mode conversion, the output upper port of the first beam splitter, the input lower end of the first output transverse mode conversion, and the input upper port of the fifth beam splitter. Specifically, the input upper port of the third beam splitter is connected to the output lower end of the first input transverse mode conversion, the input lower port of the third beam splitter is connected to the output upper port of the first beam splitter, the output upper port of the third beam splitter is connected to the input lower end of the first output transverse mode conversion, and the output lower port of the third beam splitter is connected to the input upper port of the fifth beam splitter.

[0033] The four ports of the first beam splitter are respectively connected to the output upper end of the second input transverse mode conversion, the output lower end of the second input transverse mode conversion, the input lower port of the third beam splitter, and the input upper port of the fourth beam splitter. Specifically, the input upper port of the first beam splitter is connected to the output upper end of the second input transverse mode conversion, the input lower port of the first beam splitter is connected to the output lower end of the second input transverse mode conversion, the output upper port of the first beam splitter is connected to the input lower port of the third beam splitter, and the output lower port of the first beam splitter is connected to the input upper port of the fourth beam splitter.

[0034] The four ports of the fifth beam splitter are respectively connected to the output lower port of the third beam splitter, the output upper port of the fourth beam splitter, the input upper end of the second output transverse mode conversion, and the input lower end of the second output transverse mode conversion. Specifically, the input upper port of the fifth beam splitter is connected to the output upper end of the second input transverse mode conversion, the input lower port of the first beam splitter is connected to the output lower end of the second input transverse mode conversion, the output upper port of the first beam splitter is connected to the input lower port of the third beam splitter, and the output lower port of the first beam splitter is connected to the input upper port of the fourth beam splitter.

[0035] The first input transverse mode converter and the second input transverse mode converter receive TE0 mode photons or TE1 mode photons generated by an external light source. In the present application, the external light source can be an on-chip single-photon source or an off-chip single-photon source. The on-chip single-photon source is usually composed of devices such as spiral waveguides or microring resonators that can produce on-chip four-wave mixing. The use of an on-chip single-photon source can improve the integration and stability of the chip and reduce the volume of the entire system, but there is a disadvantage of low single-photon emission efficiency. When an off-chip single-photon source is used, the photons it generates can be input to the first input transverse mode converter and the second input transverse mode converter through an edge coupler or a grating coupler.

[0036] The first input transverse mode converter transmits the received TE0 mode photons to the input lower port of the second beam splitter or converts the received TE1 mode photons into TE0 mode photons and transmits the converted TE0 mode photons to the input upper port of the third beam splitter.

[0037] The second input transverse mode converter transmits the received TE0 mode photons to the input upper port of the first beam splitter or converts the received TE1 mode photons into TE0 mode photons and transmits the converted TE0 mode photons to the input lower port of the first beam splitter.

[0038] The first output transverse mode converter directly outputs the TE0 mode photons output from the output lower port of the second beam splitter or converts the TE0 mode photons output from the output upper port of the third beam splitter into TE1 mode photons and outputs the converted TE1 mode photons.

[0039] The second output transverse mode converter is used to directly output the TE0 mode photons output from the output upper port of the fifth beam splitter or convert the TE0 mode photons output from the output lower port of the fifth beam splitter into TE1 mode photons and output the converted TE1 mode photons.

[0040] The first beam splitter, the second beam splitter, the third beam splitter, the fourth beam splitter and the fifth beam splitter are used to perform path allocation for the input TE0 mode photons. The path allocation ratio of the first beam splitter and the fifth beam splitter is 1:1, and the path allocation ratio of the second beam splitter, the third beam splitter and the fourth beam splitter is 1:2, where the path allocation ratio is the probability of a photon being output from the output end on the same side of the beam splitter input end / the probability of a photon being output from the output end on the opposite side of the beam splitter input end.

[0041] Specifically, taking the third beam splitter as an example, the TE0 mode photon input from the upper input port of the third beam splitter, after passing through the path distribution effect of the third beam splitter, the probability of the TE0 mode photon being output from the upper output port of the third beam splitter / the probability of being output from the lower output port of the third beam splitter is 1:2; the TE0 mode photon input from the lower input port of the third beam splitter, after passing through the path distribution effect of the third beam splitter, the probability of the TE0 mode photon being output from the lower output port of the third beam splitter / the probability of being output from the upper output port of the third beam splitter is 1:2.

[0042] In the present application, the first input transverse mode converter, the second input transverse mode converter, the first output transverse mode converter, and the second output transverse mode converter all include a main line straight waveguide and a coupling region optical waveguide, a bending optical waveguide, and a transmission straight waveguide connected in sequence. The coupling region optical waveguide and the main line straight waveguide form an evanescent coupling region. By setting the length and spacing of the evanescent coupling region and the width of the coupling region optical waveguide and the width of the main line straight waveguide, the purpose of mode conversion is achieved. The structures of the first input transverse mode converter and the second input transverse mode converter are as follows: Figure 3 As shown in FIG, by setting the length and spacing of the evanescent coupling region and the width of the optical waveguide in the coupling region and the width of the main line straight waveguide, TE1 mode photons are converted into TE0 mode photons. The structures of the first output transverse mode converter and the second output transverse mode converter are shown in FIG. Figure 4As shown, by adjusting the length and spacing of the evanescent coupling region, as well as the width of the optical waveguide in the coupling region and the width of the main straight waveguide, TE0 mode photons are converted into TE1 mode photons. Furthermore, the main straight waveguide of the first input transverse mode converter is connected to the input lower port of the second beam splitter, and the transmission straight waveguide of the first input transverse mode converter is connected to the input upper port of the third beam splitter; the main straight waveguide of the second input transverse mode converter is connected to the input upper port of the first beam splitter, and the transmission straight waveguide of the second input transverse mode converter is connected to the input lower port of the first beam splitter; the main straight waveguide of the first output transverse mode converter is connected to the output lower port of the second beam splitter, and the transmission straight waveguide of the first output transverse mode converter is connected to the output upper port of the third beam splitter; the main straight waveguide of the second output transverse mode converter is connected to the output upper port of the fifth beam splitter, and the transmission straight waveguide of the second output transverse mode converter is connected to the output lower port of the fifth beam splitter.

[0043] Specifically, when the first input transverse mode converter receives TE0 mode photons, the TE0 mode photons are directly transmitted to the lower input port of the second beam splitter through the main straight waveguide of the first input transverse mode converter. When the first input transverse mode converter receives TE1 mode photons, the TE1 mode photons are transmitted through the main straight waveguide of the first input transverse mode converter to the evanescent coupling region, where they are converted into TE0 mode photons. The TE0 mode photons then pass through the bent optical waveguide and the transmission straight waveguide of the first input transverse mode converter in sequence and are input to the upper input port of the third beam splitter.

[0044] Similarly, when the first output transverse mode converter receives TE0 mode photons output from the lower output port of the second beam splitter, the TE0 mode photons are directly output through the main straight waveguide of the first output transverse mode converter. When the first output transverse mode converter receives TE0 mode photons output from the upper output port of the third beam splitter, the TE0 mode photons are transmitted to the evanescent coupling region through the transmission straight waveguide and the bent optical waveguide of the first output transverse mode converter, where they are converted into TE1 mode photons, which are then output through the main straight waveguide of the first output transverse mode converter.

[0045] The working principle of the second input transverse mode converter is the same as that of the first input transverse mode converter, and the working principle of the second output transverse mode converter is the same as that of the first output transverse mode converter, which will not be repeated here.

[0046] For ease of understanding and description, the upper half of the beam splitter is named the upper branch, and the lower half is named the lower branch, such as Figure 5 The quantum controlled NOT gate of this application includes four paths, namely C0 path, C1 path, T0 path and T1 path, see Figure 6 . The C0 path and the C1 path form the C path, which is the control path. The T0 path and the T1 path form the T path, which is the target path. The C0 path includes the main straight waveguide of the first input transverse mode converter, the lower branch of the second beam splitter, and the main straight waveguide of the first output transverse mode converter. The C1 path includes the coupling area optical waveguide, the bent optical waveguide, and the transmission straight waveguide of the first input transverse mode converter, the upper branch of the third beam splitter, and the transmission straight waveguide, the bent optical waveguide, and the coupling area optical waveguide of the first output transverse mode converter. The T0 path includes the main straight waveguide of the second input transverse mode converter, the upper branch of the first beam splitter, the lower branch of the third beam splitter, the upper branch of the fifth beam splitter, and the main straight waveguide of the second output transverse mode converter. The T1 path includes the coupling area optical waveguide, the bent optical waveguide, and the transmission straight waveguide of the second input transverse mode converter, the upper branch of the fourth beam splitter, the lower branch of the fifth beam splitter, and the transmission straight waveguide, the bent optical waveguide, and the coupling area optical waveguide of the second output transverse mode converter.

[0047] The following diagrams will explain the evolution and transmission process of photons in detail.

[0048] Assume that the first input transverse mode converter receives TE0 mode photons generated by an external light source, and the second input transverse mode converter receives TE1 mode photons generated by an external light source, such as Figure 6 To facilitate the demonstration of the photon evolution process and transmission path, the photons received by the first input transverse mode converter and the second input transverse mode converter are represented by circles with different filling elements. The solid circles represent the photons received by the first input transverse mode converter and their photon evolution, while the filled circles represent the photons received by the second input transverse mode converter and their photon evolution.

[0049] The TE0 mode photons received by the first input transverse mode converter are directly input to the second beam splitter for path distribution, and may be output from the upper output port of the second beam splitter (invalid output), or may be output from the lower output port of the second beam splitter to the main line straight waveguide of the first output transverse mode converter, and then directly output. The TE1 mode photons received by the second input transverse mode converter are converted into TE0 mode photons. The TE0 mode photons obtained after conversion are input into the first beam splitter for path allocation. They may be input into the third beam splitter from the upper output port of the first beam splitter, or may be input into the fourth beam splitter from the lower output port of the first beam splitter. Assuming that they are input into the fourth beam splitter from the lower output port of the first beam splitter, then under the path allocation of the fourth beam splitter, they may be input into the fifth beam splitter from the upper output port of the fourth beam splitter, or may be output from the lower output port of the fourth beam splitter (invalid output). Assuming that they are input into the fifth beam splitter from the upper output port of the fourth beam splitter for path allocation, the TE0 mode photons obtained after conversion may be input into the main straight waveguide of the second output transverse mode converter from the upper output port of the fifth beam splitter, or may be input into the transmission straight waveguide of the second output transverse mode converter from the lower output port of the fifth beam splitter. Then, they pass through the curved waveguide and the evanescent coupling region in sequence. In the evanescent coupling region, the TE0 mode photons are converted into TE1 mode photons and output through the main straight waveguide of the second output transverse mode converter. Assuming that the TE0 mode photons obtained after conversion are output from the output lower port of the fifth beam splitter, the entire transmission path of the TE0 mode photons obtained after conversion through the second input transverse mode converter is referenced to Figure 6 , which corresponds to the T1 path. It should be noted that, from the above content, the transmission process of the TE0 mode photons obtained after conversion has multiple path options. Figure 6 Only one transmission path is shown, and the others are not listed one by one.

[0050] In order to make this application clearer, Figure 2 and Figure 6 The working principle of the quantum controlled NOT gate is explained in detail.

[0051] For the convenience of representation, the TE0 mode photon is recorded as a mode photon, the TE1 mode photon is recorded as b mode photon, and the photon input to the first input transverse mode converter is recorded as the control quantum bit C in , the photon input to the second input transverse mode converter is denoted as the target quantum bit T in , see Figure 2 and Figure 6 As shown in , the quantum states input to the first input transverse mode converter and the second input transverse mode converter can be expressed as:

[0052]

[0053] Among them, αc represents the probability amplitude of the input photon inputting into the first input transverse mode converter in TE0 mode, β c represents the probability amplitude of the input photon inputting into the first input transverse mode converter in TE1 mode, α T represents the probability amplitude of the input photon inputting the second input transverse mode converter in TE0 mode, β T represents the probability amplitude of the input photon inputting the second input transverse mode converter in TE1 mode.

[0054] The quantum state of the input photon after passing through the first input transverse mode converter and the second input transverse mode converter, that is, the quantum state of the photon before reaching the first beam splitter, is expressed as:

[0055]

[0056] in, The generation operators corresponding to the C0 path (the upper output end of the first input lateral mode converter), the C1 path (the lower output end of the first input lateral mode converter), the T0 path (the upper output end of the second input lateral mode converter), and the T1 path (the upper output end of the second input lateral mode converter) respectively.

[0057] Based on the path allocation ratio of the first beam splitter and the fifth beam splitter being 1:1, after the photon is input from the upper input port of the first beam splitter or the upper input port of the fifth beam splitter, the evolution of the generation operator is:

[0058]

[0059] Among them, the left a generation operator representing the input upper port of the first beam splitter or the input upper port of the fifth beam splitter; in represents the generation operator of the output upper port of the first beam splitter or the output upper port of the fifth beam splitter, represents the generator of the output lower port of the first beam splitter or the output lower port of the fifth beam splitter. The meanings of the various terms in the following generator evolution formula are similar to those explained above, but are specific to different beam splitters. Therefore, the meanings of the various terms will not be described one by one in the following.

[0060] After the photon is input from the lower input port of the first beam splitter or the lower input port of the fifth beam splitter, the evolution of the generation operator is:

[0061]

[0062] Based on the path allocation ratio of the second beam splitter, the third beam splitter, and the fourth beam splitter being 1:2, after the photon is input from its upper input port, the evolution of the generation operator is:

[0063]

[0064] After inputting from its input port, the evolution of the generation operator is:

[0065]

[0066] Based on the evolution process of the above generation operator, the input photon passes through the first input transverse mode converter and the second input transverse mode converter respectively, and then passes through the first beam splitter, and the quantum state evolves into:

[0067]

[0068] After passing through the second beam splitter, In this evolution formula represents the generation operator of the output port of the second beam splitter. After passing through the fourth beam splitter, In this evolution formula represents the generation operator of the output lower port of the fourth beam splitter. After passing through the third beam splitter,

[0069] In summary, after passing through the second beam splitter, the third beam splitter, and the fourth beam splitter, the quantum state is expressed as:

[0070]

[0071] After the fifth beam splitter, the generation operator evolves to:

[0072]

[0073]

[0074]

[0075] After passing through the fifth beam splitter and before reaching the first output transverse mode converter and the second output transverse mode converter, the quantum state evolves into:

[0076]

[0077] Because the output from the upper output port of the second beam splitter and the output from the lower output port of the fourth beam splitter are invalid outputs, the output ports containing The quantum state is expressed as:

[0078]

[0079] The terms in which two photons are output simultaneously from the C path and the T path are classified into |ψ'>, and only the terms in which one photon is output from the C path and one from the T path are retained. The C path consists of the C0 path and the C1 path, and the T path consists of the T0 path and the T1 path. The quantum state is expressed as:

[0080]

[0081] After expansion and merging, the quantum state is represented as:

[0082]

[0083] When the first input transverse mode converter inputs TE1 mode photons (b mode photons), α c If is 0, then after passing through the fifth beam splitter and before reaching the first output transverse mode converter and the second output transverse mode converter, the quantum state is:

[0084]

[0085] The quantum state before reaching the first beam splitter is:

[0086]

[0087] Comparing the quantum states of these two processes, we can see that and The probability amplitude does not flip, that is, the target quantum bit T in Do not flip.

[0088] When the first input transverse mode converter inputs TE0 mode photons (a mode photons), β C If is 0, then after passing through the fifth beam splitter and before reaching the first output transverse mode converter and the second output transverse mode converter, the quantum state is:

[0089]

[0090] The quantum state before reaching the first beam splitter is:

[0091]

[0092] Comparing the quantum states of these two processes, we can see that and The probability amplitude flips, that is, the target quantum bit T in The optical path of this application achieves a quantum controlled NOT gate output in a transverse waveguide mode with a probability of 1 / 9. Since the two-photon input state in the application is also a quantum superposition state encoded in the transverse waveguide mode, this application achieves an on-chip quantum controlled NOT gate function with both input and output in the transverse waveguide mode.

[0093] In addition, the quantum controlled NOT gate in this application does not use nonlinear media and nonlinear devices, so the entanglement efficiency between the input two-bit quantum is high.

[0094] The quantum controlled NOT gate in this application is composed only of a transverse waveguide mode converter and a beam splitter, so there is no restriction on the wavelength of the input photons. Therefore, this structure can also use wavelength encoding while using multiple transverse waveguide encodings, realizing the multiplexing and demultiplexing of waveguide mode-encoded and wavelength-encoded light in the same channel, expanding the computing and communication dimensions of the controlled NOT gate. Based on this, this application provides an embodiment of the extended application of the quantum controlled NOT gate, such as Figure 7 As shown, the input end of the first input transverse mode converter and the input end of the second input transverse mode converter are each connected to an optical multiplexer, and the output end of the first output transverse mode converter and the output end of the second output transverse mode converter are each connected to an optical demultiplexer. The optical multiplexer is used to receive multiple photons of different wavelengths output by an external light source and combine the multiple photons into one path, which is then input to the first input transverse mode converter or the second input transverse mode converter accordingly. The optical demultiplexer is used to receive photons output from the first output transverse mode converter or the second output transverse mode converter and output photons of different wavelengths from different output ports, thereby achieving multiplexing and demultiplexing of waveguide mode-coded and wavelength-coded light within the same channel.

[0095] The various embodiments in this specification are described in a progressive, parallel, or progressive and parallel manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referenced to each other.

[0096] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, so that an article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such article or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the article or device comprising the aforementioned elements.

[0097] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present application. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A quantum controlled NOT gate, characterized in that: comprising a first input transverse mode converter, a second input transverse mode converter, a first beam splitter, a second beam splitter, a third beam splitter, a fourth beam splitter, a fifth beam splitter, a first output transverse mode converter, and a second output transverse mode converter; The first input transverse mode converter and the second input transverse mode converter each include an input end, an output upper end, and an output lower end; the first output transverse mode converter and the second output transverse mode converter each include an input upper end, an input lower end, and an output end; the input lower port of the second beam splitter is connected to the output upper end of the first input transverse mode conversion; the output lower port of the second beam splitter is connected to the input upper end of the first output transverse mode conversion; the four ports of the third beam splitter are respectively connected to the output lower end of the first input transverse mode conversion, the output upper port of the first beam splitter, the input lower end of the first output transverse mode conversion, and the input upper port of the fifth beam splitter; the four ports of the first beam splitter are respectively connected to the output upper end of the second input transverse mode conversion, the output lower end of the second input transverse mode conversion, the input lower port of the third beam splitter, and the input upper port of the fourth beam splitter; the four ports of the fifth beam splitter are respectively connected to the output lower port of the third beam splitter, the output upper port of the fourth beam splitter, the input upper end of the second output transverse mode conversion, and the input lower end of the second output transverse mode conversion; The first input transverse mode converter is used to transmit the received TE0 mode photons to the input lower port of the second beam splitter or convert the received TE1 mode photons into TE0 mode photons and transmit the converted TE0 mode photons to the input upper port of the third beam splitter; The second input transverse mode converter is used to transmit the received TE0 mode photons to the input upper port of the first beam splitter or convert the received TE1 mode photons into TE0 mode photons and transmit the converted TE0 mode photons to the input lower port of the first beam splitter; The first output transverse mode converter is used to directly output the TE0 mode photons output from the output lower port of the second beam splitter or convert the TE0 mode photons output from the output upper port of the third beam splitter into TE1 mode photons and output the converted TE1 mode photons; The second output transverse mode converter is used to directly output the TE0 mode photons output from the output upper port of the fifth beam splitter or convert the TE0 mode photons output from the output lower port of the fifth beam splitter into TE1 mode photons and output the converted TE1 mode photons; The first beam splitter, the second beam splitter, the third beam splitter, the fourth beam splitter and the fifth beam splitter are used to perform path allocation on the input TE0 mode photons. The path allocation ratio of the first beam splitter and the fifth beam splitter is 1:1, and the path allocation ratio of the second beam splitter, the third beam splitter and the fourth beam splitter is 1:2, where the path allocation ratio is the probability of a photon being output from the output end on the same side of the beam splitter input end / the probability of a photon being output from the output end on the opposite side of the beam splitter input end.

2. A quantum controlled NOT gate according to claim 1, characterized in that: The first input transverse mode converter, the second input transverse mode converter, the first beam splitter, the second beam splitter, the third beam splitter, the fourth beam splitter, the fifth beam splitter, the first output transverse mode converter and the second output transverse mode converter are integrated on a substrate through a monolithic integration process.

3. The quantum controlled NOT gate according to claim 1, characterized in that: The first input transverse mode converter, the second input transverse mode converter, the first output transverse mode converter, and the second output transverse mode converter all include a main straight waveguide and a coupling region optical waveguide, a bending optical waveguide, and a transmission straight waveguide connected in sequence. The coupling region optical waveguide and the main straight waveguide form an evanescent coupling region; the main straight waveguide of the first input transverse mode converter is connected to the input lower port of the second beam splitter, and the transmission straight waveguide of the first input transverse mode converter is connected to the input upper port of the third beam splitter; the main straight waveguide of the second input transverse mode converter is connected to the input upper port of the first beam splitter, and the transmission straight waveguide of the second input transverse mode converter is connected to the input lower port of the first beam splitter; the main straight waveguide of the first output transverse mode converter is connected to the output lower port of the second beam splitter, and the transmission straight waveguide of the first output transverse mode converter is connected to the output upper port of the third beam splitter; the main straight waveguide of the second output transverse mode converter is connected to the output upper port of the fifth beam splitter, and the transmission straight waveguide of the second output transverse mode converter is connected to the output lower port of the fifth beam splitter.

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