A quantum CNOT gate optical path structure

Abstract

The present application discloses a quantum CNOT gate optical path structure, including an input port array, a first beam splitter array, a first wavelength converter array, an on-chip wavelength division multiplexer, a transmission optical fiber, an on-chip wavelength division multiplexer, a second wavelength converter array, a second beam splitter array, and an output port array. The input port array is used to input control bit photons and target bit photons, the first beam splitter array and the second beam splitter array are used to operate the quantum CNOT gate operation, and the first wavelength converter array, the transmission optical fiber, the on-chip wavelength division / demultiplexer, and the second wavelength converter array are used for re-encoding, transmission, and decoding of quantum states. By splitting the quantum CNOT gate optical path structure for operation and re-encoding / decoding, multi-chip collaborative quantum computing is realized, the scale of optical quantum computing chips is expanded, and computing power is improved. In addition, the optical path operation is stable and easy to modulate, and has good scalability.

Description

Technical Field

[0001] The present application belongs to the field of quantum information technology, and specifically relates to a quantum CNOT gate optical path structure. Background Art

[0002] Quantum computing, as a crucial branch of quantum information science, represents a revolutionary leap in the field of information technology. It uses the principles of quantum mechanics, such as superposition and quantum entanglement, to perform computing tasks, which is fundamentally different from traditional classical computing methods. In quantum computing, quantum bits (qubits) are the basic units of information. They can not only represent 0 or 1, but also multiple combinations of states at the same time. This feature enables quantum computers to theoretically demonstrate performance far superior to traditional computers when dealing with certain types of problems, such as large integer factorization, search algorithms, and simulation of quantum systems.

[0003] The optical quantum computing chip is an integrated circuit based on the principles of quantum mechanics that uses photons for information processing, transmission and calculation. It has the advantages of high integration, high control accuracy, and long coherence time. It integrates multiple optical quantum devices on a single chip through micro-nano processing technology to achieve efficient quantum computing.

[0004] At present, the scale of photonic quantum computing chips (i.e., the area and circuit size of photonic quantum computing chips) is limited by the upper limit of the mask size in the chip process production line, and it is impossible to produce larger photonic quantum computing chips in a single exposure. The size of optical devices in photonic quantum chips cannot be reduced to less than 100 nanometers due to the wavelength of light, which means that the integration of photonic quantum chips is limited. Therefore, at the current process node of optoelectronic integrated circuits, the scale of the optical path in quantum computing chips has encountered a bottleneck, and it is difficult to reach the scale required to reflect the superiority of quantum computing.

[0005] The quantum CNOT gate (Controlled-NOT gate) is a very important logic gate in quantum computing. It operates on two quantum bits, one of which is a control bit and the other is a target bit. In electronic chips, CMOS and PMOS transistors are the basic components of various logic gates; in quantum chips, quantum CNOT gates are the basic units of all complex quantum logic gates. The implementation of quantum CNOT gates in chips requires the combined connection of multiple optical devices (such as on-chip MZ interferometers and microring resonators). When the chip needs to run a large number of quantum logic gates during the calculation process, a large number of quantum CNOT gate optical path structures are required. Due to the limitation of the area of ​​a single chip, the scale of quantum CNOT gates that can be integrated on the chip is limited, which limits the further improvement of quantum computing efficiency.

[0006] The present invention proposes a multi-chip collaborative processing method, and realizes the conversion and transmission of quantum states by converting quantum state path encoding into quantum state wavelength encoding method. It can realize the function of multiple chips collaboratively completing the quantum CNOT gate (quantum controlled NOT gate), breaking through the bottleneck that the current optical quantum computing chip is limited in scale and the quantum computing efficiency cannot reflect the superiority of quantum computing. Summary of the invention

[0007] In order to solve the scale bottleneck problem of the above-mentioned optical quantum computing chip, this application provides a quantum CNOT gate optical path structure, and its specific solution is as follows:

[0008] The present application discloses a quantum CNOT gate optical path structure, including an input port array, a first beam splitter array, a first wavelength converter array, an on-chip wavelength division multiplexer, a transmission optical fiber, an on-chip wavelength division multiplexer, a second wavelength converter array, a second beam splitter array, and an output port array;

[0009] The input port array includes a first input port and a second input port for inputting control bit photons in the quantum CNOT gate, and the input port array also includes a third input port and a fourth input port for inputting target bit photons in the quantum CNOT gate;

[0010] The first beam splitter array includes a plurality of beam splitters for receiving control bit photons and target bit photons and performing initial quantum CNOT gate operations;

[0011] The first wavelength converter array includes at least three coherent wavelength converters, which are used to convert the wavelengths of the photons output by the first beam splitter array to obtain photons with four different wavelengths, and output them to the on-chip wavelength division multiplexer;

[0012] The on-chip wavelength division multiplexer is used to combine photons of four different wavelengths into one path and couple it to a transmission optical fiber. The transmission optical fiber is used to transmit the photons of four different wavelengths to the on-chip wavelength division multiplexer. The on-chip wavelength division multiplexer is used to separate the photons of four different wavelengths into four different intermediate paths and connect them to a second wavelength converter array.

[0013] The second wavelength converter array includes at least three coherent wavelength inverse converters, which are used to perform wavelength inverse conversion on photons of four different wavelengths to obtain photons of the same wavelength, and output them through four output paths respectively;

[0014] The second beam splitter array includes a plurality of beam splitters, which are used to receive the photons outputted from the four output paths of the second wavelength converter array and perform a final quantum CNOT gate operation;

[0015] The output port array includes a first output port and a second output port for outputting target bit photons. The output port array also includes a third output port and a fourth output port for outputting control bit photons.

[0016] Further, the first beam splitter array includes a first beam splitter, a second beam splitter, a third beam splitter, and a fourth beam splitter, each of which includes an input upper end, an input lower end, an output upper end, and an output lower end; the input upper end and the input lower end of the first beam splitter are respectively connected to the third input port and the fourth input port, the output upper end thereof is connected to the input lower end of the third beam splitter, and the output lower end thereof is connected to the input upper end of the fourth beam splitter; the input lower end of the second beam splitter is connected to the first input port; the input upper end of the third beam splitter is connected to the second input port; the output lower end of the second beam splitter, the output upper end of the third beam splitter, the output lower end of the third beam splitter, and the output upper end of the fourth beam splitter are respectively connected to the first wavelength converter array;

[0017] The second beam splitter array includes a fifth beam splitter, the input upper end of the fifth beam splitter is connected to one of the output paths of the second wavelength converter array, and receives photons output from the lower output end of the third beam splitter and undergoing wavelength conversion and inverse conversion. The input lower end of the fifth beam splitter is connected to another output path of the second wavelength converter array, and receives photons output from the upper output end of the fourth beam splitter and undergoing wavelength conversion and inverse conversion.

[0018] Among them, the splitting ratios of the first beam splitter and the fifth beam splitter are both 1:1, and the splitting ratios of the second beam splitter, the third beam splitter, and the fourth beam splitter are respectively 1:2, where the splitting 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.

[0019] Furthermore, the first wavelength converter array includes four coherent wavelength converters for converting the photons output by the first beam splitter array into photons of four different wavelengths different from the wavelength of the incident photons.

[0020] Furthermore, the first beam splitter, the second beam splitter, the third beam splitter, the fourth beam splitter, and the fifth beam splitter are all on-chip directional couplers or on-chip MZ interferometers with fixed splitting ratios.

[0021] Furthermore, the coherent wavelength converter and the coherent wavelength inverse converter are both coherent wavelength converters based on on-chip aluminum nitride microrings, one section of the aluminum nitride microring is covered with a metal electrode, and the gap between the metal electrode and the on-chip aluminum nitride microring is a SiO2 cladding.

[0022] Furthermore, both the on-chip wavelength division multiplexer and the on-chip wavelength division multiplexer are composed of on-chip arrayed waveguide gratings; or both the on-chip wavelength division multiplexer and the on-chip wavelength division multiplexer are composed of cascaded on-chip MZ interferometers.

[0023] Preferably, the quantum CNOT gate optical path structure also includes a first on-chip spot converter and a second on-chip spot converter, the on-chip wavelength division multiplexer is coupled to the transmission optical fiber through the first on-chip spot converter; the on-chip wavelength division multiplexer is coupled to the transmission optical fiber through the second on-chip spot converter.

[0024] Preferably, a filter is connected between each coherent wavelength converter and the on-chip wavelength division multiplexer, and a filter is connected between the on-chip wavelength demultiplexer and each coherent wavelength inverse converter, and the filter is used to filter out noise photons of other wavelengths generated during the wavelength conversion process.

[0025] Preferably, the quantum CNOT gate optical path structure further comprises a control signal end, and the metal electrodes of the coherent wavelength converter and the coherent wavelength inverse converter are connected to the same control signal end.

[0026] In general, the above technical solutions conceived by the present application can achieve the following beneficial effects compared with the prior art:

[0027] The present application provides a quantum CNOT gate optical path structure, including an input port array, a first beam splitter array, a first wavelength converter array, an on-chip wavelength division multiplexer, a transmission optical fiber, an on-chip wavelength division multiplexer, a second wavelength converter array, a second beam splitter array, and an output port array. The input port array includes a first input port and a second input port for inputting control bit photons in the quantum CNOT gate, and the input port array also includes a third input port and a fourth input port for inputting target bit photons in the quantum CNOT gate; the first beam splitter array includes a plurality of beam splitters for receiving control bit photons and target bit photons and performing initial quantum CNOT gate operations; the first wavelength converter array includes at least three coherent wavelength converters for performing wavelength conversion on the photons output by the first beam splitter array to obtain four photons with different wavelengths, and output them to the on-chip wavelength division multiplexer; the on-chip wavelength division multiplexer is used to combine the photons of four different wavelengths into one path and couple them to the transmission optical fiber, and the transmission optical fiber is used to convert the light of four different wavelengths into one path. The photons are transmitted to an on-chip wavelength division multiplexer, which is used to separate the photons of four different wavelengths into four different intermediate paths and connect them to a second wavelength converter array; the second wavelength converter array includes at least three coherent wavelength inverse converters, which are used to perform wavelength inverse conversion on the photons of four different wavelengths to obtain photons of the same wavelength, and output them respectively through four output paths; the second beam splitter array includes a plurality of beam splitters, which are used to receive the photons output by the four output paths of the second wavelength converter array and perform a final quantum CNOT gate operation; the output port array includes a first output port and a second output port, which are used to output target bit photons, and the output port array also includes a third output port and a fourth output port, which are used to output control bit photons.

[0028] Based on the above scheme, it can be known that the present application disassembles the quantum CNOT gate into two parts, encodes the intermediate quantum state generated in the first half by wavelength conversion and transmits it to the other part through optical fiber, then decodes the quantum state, and continues to run and complete the quantum CNOT gate operation through the second half of the quantum CNOT gate. Through this process, the two optical quantum computing chips collaborate to complete the quantum CNOT gate operation and the optical path scale expansion of the optical quantum computing chip, thereby realizing the improvement of the computational efficiency of optical quantum computing. The quantum CNOT gate is disassembled into two parts, and the two optical quantum computing chips each complete a part of the quantum computing process, thereby realizing multi-point collaborative computing, which can realize distributed quantum computing of multiple chips in different locations or chips at different nodes in the network, eliminating the communication steps after quantum computing between different locations or different nodes, and improving the security of quantum computing result transmission. In addition, the present scheme adopts a method of converting path coding into wavelength coding, which can avoid the quantum state instability and complex modulation scheme problems caused by polarization coding or time slice coding used in quantum state transmission in the prior art. The conversion and transmission process of quantum state coding in this scheme is stable and not easily interfered with, and does not require a complex and high-cost modulation process; and because the quantum CNOT gate is the basic unit of most quantum logic gates, the multi-chip collaborative quantum computing mode provided by this application also has good scalability for other types of quantum computing optical path matrices or methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in this embodiment or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 paying creative work.

[0030] Figure 1 A schematic diagram of a quantum CNOT gate optical path structure provided in an embodiment of the present application;

[0031] Figure 2 A schematic diagram of another quantum CNOT gate optical path structure provided in an embodiment of the present application;

[0032] Figure 3 A schematic diagram of a first beam splitter array composed of an MZ interferometer;

[0033] Figure 4 This is a schematic diagram of the structure of the MZ interferometer on this chip;

[0034] Figure 5 is a schematic diagram of the structure of a coherent wavelength converter;

[0035] Figure 6 is a cross-sectional schematic diagram of a coherent wavelength converter;

[0036] Figure 7 A schematic diagram of an on-chip wavelength division multiplexer composed of cascaded on-chip MZ interferometers;

[0037] Figure 8 A schematic diagram of an on-chip wavelength division multiplexer composed of cascaded on-chip MZ interferometers;

[0038] Fig. 9 A schematic diagram of the coupling connection mode of the on-chip wavelength division multiplexer, the on-chip wavelength demultiplexer and the transmission optical fiber;

[0039] Fig.10 A schematic diagram of another quantum CNOT gate optical path structure provided in an embodiment of the present application;

[0040] Fig.11 A schematic diagram of the optical path structure of the inverse quantum CNOT gate provided in an embodiment of the present application. DETAILED DESCRIPTION

[0041] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the embodiments of the present application are further described in detail below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0042] In the following description, many specific details are set forth to facilitate a full understanding of the present application, but the present application may also be implemented in other ways different from those described herein, and 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.

[0043] In order to facilitate the 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.

[0044] At present, the maximum exposure area supported by advanced step-scanning lithography machines is 26mm×33mm. The size of the mask in the silicon-based chip process production line is limited by this. The scale of the photonic quantum computing chip (that is, the area and circuit scale of the photonic quantum computing chip) is also limited by the upper limit of the mask size in the silicon-based process production line. It is impossible to produce a larger photonic quantum computing chip in a single exposure. The size of the optical device in the photonic quantum chip cannot be reduced to less than 100 nanometers due to the wavelength of light, that is, the integration of the photonic quantum chip is limited. Therefore, at the current process node of optoelectronic integrated circuits, the scale of the optical path in the quantum computing chip has encountered a bottleneck, and it is difficult to reach the scale required to reflect the superiority of quantum computing. In addition, the quantum computing process of the current photonic quantum computing system is based on the same core optical path or chip. It is impossible to deploy multiple optical paths or multiple chips to complete a quantum computing task at the same time, so the quantum computing efficiency is limited to the computing power range of a core optical path or chip and cannot be further expanded.

[0045] The present invention proposes a multi-chip collaborative processing method, and realizes the conversion and transmission of quantum states by converting quantum state path coding into quantum state wavelength coding method, which can realize the function of multiple chips collaboratively completing the quantum CNOT gate.

[0046] First, let's introduce the principle of the quantum CNOT gate. The common quantum CNOT gate (also known as the quantum controlled NOT gate) includes a control bit and a target bit. If the control qubit is 0, the target qubit remains unchanged. If the control qubit is 1, the target qubit flips.

[0047] Its ground state truth table is as follows:

[0048] |00> → |00>

[0049] |01> → |01>

[0050] |10> → |11>

[0051] |11> → |10>

[0052] The quantum CNOT gate implemented in the present application is described in detail below in conjunction with specific embodiments.

[0053] Specifically, Figure 1 As shown, the present application provides a quantum CNOT gate optical path structure, including an input port array, a first beam splitter array, a first wavelength converter array, an on-chip wavelength division multiplexer, a transmission optical fiber, an on-chip wavelength division multiplexer, a second wavelength converter array, a second beam splitter array, and an output port array.

[0054] The input port array has four ports, namely the first input port, the second input port, the third input port, and the fourth input port. The first input port and the second input port are used to input the control bit photon in the quantum CNOT gate, and the third input port and the fourth input port are used to input the target bit photon in the quantum CNOT gate. The number of control bit photons is 1, and the photon is input from one of the first input port and the second input port. Specifically, the photon is The probability radiation is input from the first input port, The probability radiation is input from the second input port. Similarly, the number of target bit photons is 1, and the photon is The probability radiation is input from the first input port, The probability radiation is input from the second input port. When the control bit photon and the target bit photon are input from the input port array, the quantum state can be expressed as:

[0055] ;

[0056] The quantum state of the control bit photon is: Cin→ ;

[0057] The quantum state of the target bit photon is: Tin→ .

[0058] Among them, the quantum state of the control bit photon when it is input from the first input port is expressed as , the quantum state of the control bit photon when it is input from the second input port is expressed as ; The quantum state of the target bit photon when it is input from the third input port is expressed as , the quantum state of the target bit photon when it is input from the fourth input port is expressed as .

[0059] The input port array and the target bit photons input from the input port array enter the first beam splitter array. The first beam splitter array includes several beam splitters for receiving control bit photons and target bit photons and performing initial quantum CNOT gate operations. The first beam splitter array is actually the front part after the quantum CNOT gate is disassembled, and the second beam splitter array is the rear part of the CNOT gate. Here, taking the first beam splitter array including four beam splitters as an example, the first part is introduced first. The first beam splitter array includes a first beam splitter, a second beam splitter, a third beam splitter, and a fourth beam splitter. Each beam splitter is a 2x2 beam splitter, and includes an input upper end, an input lower end, an output upper end, and an output lower end. The connection relationship of the four beam splitters is as follows:

[0060] The input upper end and input lower end of the first beam splitter are connected to the third input port and the fourth input port respectively, the output upper end thereof is connected to the input lower end of the third beam splitter, and the output lower end thereof is connected to the input upper end of the fourth beam splitter; the input lower end of the second beam splitter is connected to the first input port; the input upper end of the third beam splitter is connected to the second input port; the output lower end of the second beam splitter, the output upper end of the third beam splitter, the output lower end of the third beam splitter, and the output upper end of the fourth beam splitter are respectively connected to the first wavelength converter array.

[0061] Among them, the splitting ratios of the first beam splitter and the fifth beam splitter are both 1:1, and the splitting ratios of the second beam splitter, the third beam splitter, and the fourth beam splitter are 1:2 respectively, where the splitting 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. A fixed splitting ratio is one of the necessary conditions for realizing a quantum CNOT gate. The splitting ratio is expressed as a light intensity ratio in a macroscopic sense, and in quantum optics, the splitting ratio is expressed as a probability ratio of a photon being output from two ports. Figure 1 Directional couplers are used to achieve photon distribution with a specific splitting ratio. A fixed splitting ratio can be achieved through specific parameter design, such as the optical waveguide width, spacing, and length of the evanescent coupling region of the directional coupler. In addition to directional couplers, MZ interferometers or multimode interferometers can also be used to achieve photon distribution with a fixed splitting ratio.

[0062] After passing through the first beam splitter array, the control bit photons and the target bit photons enter the first wavelength converter array from the four ports of the output lower end of the second beam splitter, the output upper end of the third beam splitter, the output lower end of the third beam splitter, and the output upper end of the fourth beam splitter.

[0063] The first wavelength converter array includes at least three coherent wavelength converters, which are used to convert the photons output by the first beam splitter array into photons of four different wavelengths and output them to the on-chip wavelength division multiplexer. Here, we first take the example of the first wavelength converter array including four coherent wavelength converters. The four coherent wavelength converters are respectively connected to the above four ports. The wavelengths of the control bit photons and the target bit photons are both set to λ0, and the four coherent wavelength converters convert the photons with a wavelength of λ0 into λ1, λ2, λ3, and λ4 respectively. Then the photons of four different wavelengths enter the on-chip wavelength division multiplexer.

[0064] The on-chip wavelength division multiplexer is used to combine photons of four different wavelengths into one path and couple it to the transmission optical fiber. The transmission optical fiber is used to transmit the photons of four different wavelengths to the on-chip wavelength demultiplexer. The on-chip wavelength demultiplexer is used to separate the photons of four different wavelengths into four different paths and connect them to the second wavelength converter array.

[0065] The second wavelength converter array includes at least three coherent wavelength inverse converters, which are used to inversely convert photons of four different wavelengths into photons of the same wavelength, and output them through four output paths respectively. Here, the second wavelength converter array including four coherent wavelength inverse converters is first introduced as an example. The four coherent wavelength inverse converters are respectively connected to the four output paths of the on-chip wavelength division multiplexer. The four coherent wavelength inverse converters convert photons with wavelengths of λ1, λ2, λ3, and λ4 into photons of λ0 respectively, and output them to the second beam splitter array through four output paths.

[0066] The second beam splitter array includes a plurality of beam splitters for receiving photons output from the four output paths of the second wavelength converter array and performing the final quantum CNOT gate operation. Here, the second beam splitter array includes only one beam splitter as an example. The second beam splitter array includes only one beam splitter, namely the fifth beam splitter. The upper input end of the fifth beam splitter is connected to an output path, which receives photons output from the lower output end of the third beam splitter and undergoes wavelength conversion and inverse conversion, namely, the photons transmitted in the transmission optical fiber at λ3; the lower input end of the fifth beam splitter is connected to another output path, which receives photons output from the upper output end of the fourth beam splitter and undergoes wavelength conversion and inverse conversion, namely, the photons transmitted in the transmission optical fiber at λ4.

[0067] The output port array includes a first output port, a second output port, a third output port, and a fourth output port. The third output port and the fourth output port are connected to the output upper end and the output lower end of the fifth beam splitter, and are used to output target bit photons; the first output port and the second output port are directly connected to the other two output paths of the four output paths, namely, the two paths transmitted at wavelengths of λ1 and λ2, and are used to output control bit photons.

[0068] The above is the path and transformation process of a pair of photons consisting of a control bit photon and a target bit photon in the quantum CNOT gate optical path structure provided in this application. Among them, each pair of photons input into the optical path structure will be probabilistically output from two of the output ports. By inputting a photon pair consisting of a control bit photon and a target bit photon multiple times, and performing single photon detection at four output ports, and counting the counts of each port, the quantum CNOT gate function and quantum computing process are finally realized. The specific quantum principles and quantum state evolution process will be described in detail in the subsequent embodiments.

[0069] In the above embodiments, the first wavelength converter array includes four coherent wavelength converters and the second wavelength converter array includes four coherent wavelength inverse converters. In practice, only three coherent wavelength converters and three coherent wavelength inverse converters are needed to realize the quantum CNOT gate function described in this application. Figure 2As shown, in another embodiment, the first wavelength converter array includes three coherent wavelength converters, and the second wavelength converter array includes three coherent wavelength inverse converters. Among them, the lower end of the output of the second beam splitter is directly connected to the on-chip wavelength division multiplexer, and the λ0 photons passing through this path are not converted by wavelength, but are directly input into the on-chip wavelength division multiplexer, and are transmitted to the on-chip wavelength division multiplexer through the transmission optical fiber, and then directly output from the first output port of the output port array. That is, λ0 is not converted throughout the entire process. The photons transmitted on the four paths are still different and do not interfere with each other, so the quantum CNOT gate function can still be realized normally. In terms of physical structure, two coherent wavelength converters are omitted, the space is more compact, and more devices can be set in the same chip. For example, the input port array, the first beam splitter array, the first wavelength converter array, and the on-chip wavelength division multiplexer are used as a CNOT gate sub-unit, and the on-chip wavelength division multiplexer, the second wavelength converter array, the second beam splitter array, and the output port array are also used as a CNOT gate sub-unit. Multiple CNOT gate sub-units are set on a chip. When the number of devices in the first wavelength converter array and the second wavelength converter array is reduced and the occupied area is reduced, more CNOT gate sub-units can be integrated on a chip.

[0070] In other embodiments of the present application, each beam splitter in the first beam splitter array and the second beam splitter array may be an MZ interferometer. Figure 3 The first beam splitter array composed of MZ interferometers has ports without photon input or output left floating. Photons will not enter the first beam splitter array from the floating ports, and photons output from the floating ports will dissipate to the outside world and will not re-enter the first beam splitter array or other subsequent devices. The specific structure of the on-chip MZ interferometer is shown in Figure 1. Figure 4 As shown, it consists of a first 50:50 beam splitter, a second 50:50 beam splitter, an interference upper arm, an interference lower arm, and a phase modulator located in the interference upper arm.

[0071] The two ends of the interference upper arm are respectively connected to the output upper port of the first 50:50 beam splitter and the input upper port of the second 50:50 beam splitter, the two ends of the interference lower arm are respectively connected to the output lower port of the first 50:50 beam splitter and the input lower port of the second 50:50 beam splitter, and the phase modulator is arranged in the interference upper arm (in other embodiments, the phase modulator can also be arranged in the interference lower arm). The phase modulator is used to adjust the phase difference between the interference upper arm and the interference lower arm. By adjusting the phase modulator to change the phase difference between the interference upper arm and the interference lower arm, it can be achieved that the input photons are output from any output port with different probabilities (0% to 100%), that is, any splitting ratio is achieved. In the quantum CNOT gate optical path structure provided in the present application, the phase modulator can be used to achieve that the splitting ratios of the first beam splitter and the fifth beam splitter are both 1:1, and the splitting ratios of the second beam splitter, the third beam splitter, and the fourth beam splitter are respectively 1:2.

[0072] The structure of the coherent wavelength converter (coherent wavelength inverse converter) in this application is as follows Figure 5 and Figure 6 shown. Figure 6 yes Figure 5 Schematic diagram of the cross section of the O-O' axis. Take the conversion of λ0 to λ1 as an example. The coherent wavelength converter consists of a straight waveguide, an aluminum nitride microring and a metal electrode. One section of the aluminum nitride microring is covered with a metal electrode. Two metal electrodes are distributed above and below the aluminum nitride microring respectively. The gap between the metal electrode and the aluminum nitride microring on the chip is a SiO2 cladding. The λ0 photon is input by the straight waveguide. In the evanescent coupling region formed by the straight waveguide and the aluminum nitride microring, the λ0 photon is coupled into the aluminum nitride microring. The metal electrode applies an electric field to the aluminum nitride microring part covered by it, resulting in a nonlinear effect. The energy of the λ0 photon is absorbed and converted into a λ1 photon. The λ1 photon is transmitted to the evanescent coupling region and coupled to the straight waveguide and output from the straight waveguide. The coherent wavelength converters corresponding to other wavelength conversions have the same structure. The difference is that the width of the aluminum nitride microring and the electric field between the metal electrodes are different, so that the conversion of different wavelengths can be achieved.

[0073] In the present application, the on-chip wavelength division multiplexer and on-chip wavelength demultiplexer may adopt an on-chip array waveguide grating or a cascaded on-chip MZ interferometer group. The on-chip array waveguide grating realizes the separation of different wavelengths through different waveguide lengths. It has a simple structure and can achieve stable separation and multiplexing for specific wavelengths. The cascaded on-chip MZ interferometer group adjusts the photon path through each on-chip MZ interferometer, so that photons of different wavelengths are gathered into the same path or photons of different wavelengths in the same path are distributed to different paths. The cascaded on-chip MZ interferometer group is as follows: Figure 7 , Figure 8 As shown. Figure 7 The on-chip wavelength division multiplexer is composed of cascaded on-chip MZ interferometers. Figure 8 It is an on-chip wavelength division multiplexer. The on-chip MZ interferometer can control the output of photons of different wavelengths from one of the output ports through the phase modulator on its interference arm. The combination of multiple on-chip MZ interferometers can realize the distribution function of photons of different wavelengths. The use of on-chip MZ interferometers to build a wavelength division multiplexer is conducive to the precise control of the splitting ratio and can cope with input photons of different wavelengths. For example, the control bit photons and target bit photons at the input end use photons of different wavelengths due to different quantum computing requirements. The use of on-chip MZ interferometers to build a wavelength division multiplexer can be dealt with by adjusting the phase modulator, so that the entire system can cope with a variety of quantum computing scenarios or requirements.

[0074] In the present application, the coupling connection between the on-chip wavelength division multiplexer, the on-chip wavelength division multiplexer and the transmission optical fiber is performed by using an on-chip spot converter. Fig. 9 As shown, the quantum CNOT gate optical path structure also includes a first on-chip spot converter and a second on-chip spot converter. In the area close to the edge of the chip, the waveguide width of the spot converter becomes narrower and tapered, and the spot of light becomes larger and matches the end face of the optical fiber, thereby completing the coupling between the chip waveguide and the end face of the optical fiber.

[0075] In another embodiment of the present application, a filter is connected between each coherent wavelength converter and the on-chip wavelength division multiplexer, and a filter is connected to the output end of each coherent wavelength inverse converter, such as Fig.10 The filter is used to filter out noise photons of other wavelengths generated during the wavelength conversion process.

[0076] In other embodiments of the present application, a control signal terminal is also included, and the metal electrodes of the coherent wavelength converter and the coherent wavelength inverse converter are connected to the same control signal terminal. Fig.10 As shown in the figure, the dotted line connecting all metal electrodes represents the control signal line. When the quantum CNOT gate optical path structure is working, the control signal end sends a control signal, and each coherent wavelength converter converts the photons of the input wavelength according to its own characteristics. The control signal is a turn-on signal or an enable signal, and the specific converted wavelength is also related to the design parameters of the coherent wavelength converter itself.

[0077] In the present application, the input port array, the first beam splitter array, the first wavelength converter array, and the on-chip wavelength division multiplexer can be integrated on the substrate through a monolithic integration process; the on-chip wavelength division multiplexer, the second wavelength converter array, the second beam splitter array, and the output port array can be integrated on the substrate through a monolithic integration process. That is, the input port array, the first beam splitter array, the first wavelength converter array, and the on-chip wavelength division multiplexer can be integrated in the same chip, and the input port array, the first beam splitter array, the first wavelength converter array, and the on-chip wavelength division multiplexer can be integrated in the same chip, combined with the optical path structure composed of the transmission optical fiber, the quantum CNOT gate function of multi-chip collaboration can be completed.

[0078] Combine the following Figure 1 The working principle and quantum state evolution process of the quantum CNOT gate optical path structure provided in this application are explained in detail.

[0079] As mentioned above, when the control bit photon and the target bit photon are input from the input port array, the quantum state can be expressed as:

[0080] ;

[0081] Among them, the quantum state of the control bit photon when it is input from the first input port is expressed as , the quantum state of the control bit photon when it is input from the second input port is expressed as ; The quantum state of the target bit photon when it is input from the third input port is expressed as , the quantum state of the target bit photon when it is input from the fourth input port is expressed as .

[0082] The quantum state evolution of the target bit photon after passing through the first beam splitter (splitting ratio is 1:1) can be expressed as:

[0083] ;

[0084] After passing through the first beam splitter, It means that after the photon passes through the first beam splitter, it is output from its upper output end; It means that after the photon passes through the first beam splitter, it is output from its lower output end.

[0085] The quantum state evolution of the control bit photon after passing through the second beam splitter (splitting ratio is 1:2) can be expressed as:

[0086] ;

[0087] After passing through the second beam splitter, It means that the photon is input from the lower input end of the second beam splitter and output from the lower output end thereof; It means that the photon is input from the lower input end of the second beam splitter and output from the upper output end. The photon output from the upper output end will dissipate to the outside world and will not re-enter the first beam splitter array or other subsequent devices.

[0088] The quantum state evolution of the target bit photon after passing through the fourth beam splitter (splitting ratio is 1:2) can be expressed as:

[0089] ;

[0090] After passing through the fourth beam splitter, It means that the photon is input from the upper input end of the fourth beam splitter and output from its upper output end. It means that the photon is input from the upper input end of the fourth beam splitter and output from the lower output end thereof. The photon output from the lower output end of the fourth beam splitter will dissipate to the outside, will not re-enter the first beam splitter array, and will not enter other subsequent devices.

[0091] The quantum state evolution of the photon after passing through the third beam splitter (splitting ratio is 1:2) can be expressed as:

[0092] ;

[0093] After passing through the third beam splitter, represents the quantum state of the photon output from the upper output end of the third beam splitter, The quantum state of the photon output from the lower end of the third beam splitter output.

[0094] In summary, the quantum state evolution of the first beam splitter, the second beam splitter, the third beam splitter, and the fourth beam splitter, and the quantum state evolution result of the entire system can be expressed as:

[0095] ;

[0096] This is the intermediate quantum state of the quantum CNOT gate provided in this application, that is, the quantum state of the first half of the quantum CNOT gate.

[0097] Then, photons of various wavelengths pass through the first wavelength converter array. After the wavelength is converted, the quantum state can be expressed as:

[0098] ;

[0099] The quantum state after wavelength conversion passes through the on-chip wavelength division multiplexer, transmission fiber, on-chip wavelength division multiplexer, and then passes through the second wavelength converter array. The quantum state can be expressed as:

[0100] ;

[0101] During the evolution and transmission process, each quantum state is transmitted stably without interfering with each other, and the quantum state will not fluctuate due to environmental factors of the transmission optical fiber.

[0102] Then, the photon enters the second beam splitter array, which contains only one beam splitter, namely the fifth beam splitter. The quantum state evolution of the photon after passing through the fifth beam splitter (splitting ratio is 1:1) can be expressed as:

[0103] ;

[0104] After passing through the fifth beam splitter, Corresponding to the λ1 photon path, correspond λ2 Photon path, The path corresponding to the upper end of the fifth beam splitter output and the path corresponding to the lower end of the fifth beam splitter output.

[0105] The quantum state evolution result of the entire system can be expressed as:

[0106] ;

[0107] because and is the photon dissipation term, so it is removed from the terminal quantum state, and then the quantum state is expanded:

[0108] ;

[0109] The items that are outputted by both the C path (control bit, i.e., the first output port and the second output port) and the T path (target bit, i.e., the third output port and the fourth output port) are classified into , only keep the terms with one photon each on the C and T paths (i.e., terms with both subscripts C and T):

[0110] ;

[0111] The term can be eliminated by post-selection, retaining only the front part, that is, the final quantum state is:

[0112] ;

[0113] When controlling the bit photon from Input, that is, input from the first input port, the quantum state is expressed as:

[0114] ;

[0115] Compared to the input quantum state of the target bit " ", the output quantum state of the target bit" "middle and Probability amplitude swap, also known as probability amplitude flip, is the flipping of the target bit;

[0116] When controlling the bit photon from Input, that is, input from the second input port, the quantum state is expressed as:

[0117] ;

[0118] Compared to the input quantum state of the target bit " ", the output quantum state of the target bit" "middle and The probability amplitude remains unchanged, that is, the target bit does not flip.

[0119] Thus, the operation of the quantum CNOT gate is completed.

[0120] Fig.11A reverse multi-chip collaborative quantum CNOT gate is provided, and its optical path structure is exactly the same as that of the aforementioned embodiment. The difference is that the control bit photon and the target bit photon are inputted in reverse from the original output port array and outputted in reverse from the original input port. During the operation of the reverse quantum CNOT gate, the second wavelength converter array is controlled to convert the photon of λ0 into λ5λ6λ7λ8. After reverse transmission through the transmission optical fiber, the first wavelength converter array converts the photon of λ0 into the photon of λ5λ6λ7λ8. After passing through the original first beam splitter array, the photon is outputted from the original input port array. Since the coherent wavelength converter can realize the conversion between different wavelengths by controlling the electrical signal on its metal electrode, the reversibility of wavelength conversion is realized. In addition, due to the established physical structure of the on-chip wavelength division multiplexer and the on-chip wavelength demultiplexer, photons of corresponding wavelengths can propagate forward or backward in it, that is, the multiplexing and demultiplexing of wavelengths are also reversible. The quantum CNOT gate composed of the first beam splitter array and the second beam splitter array in this application is also a bilaterally symmetrical structure. Taking the above factors into consideration, when the control bit photons and the target bit photons are input in reverse from the original output port array and output in reverse from the original input port, the multi-chip collaborative quantum CNOT gate operation can also be completed. That is, the quantum CNOT gate optical path structure provided in this application is essentially a reversible remote quantum CNOT gate. The initiator of quantum computing can be any chip end, and both or multiple parties can freely use the optical path structure to perform quantum CNOT gate operations and quantum computing. All parties can share the same optical path structure to perform quantum computing and realize resource sharing of quantum computing.

[0121] 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.

[0122] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that an article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such article or device. In the absence of further restrictions, the elements defined by the sentence "comprising a ..." do not exclude the existence of other identical elements in the article or device including the above elements.

[0123] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those 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 will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A quantum CNOT gate optical path structure, characterized in that: comprising an input port array, a first beam splitter array, a first wavelength converter array, an on-chip wavelength division multiplexer, a transmission optical fiber, an on-chip wavelength division multiplexer, a second wavelength converter array, a second beam splitter array, and an output port array; The input port array includes a first input port and a second input port for inputting control bit photons in the quantum CNOT gate, and the input port array also includes a third input port and a fourth input port for inputting target bit photons in the quantum CNOT gate; The first beam splitter array includes a plurality of beam splitters for receiving control bit photons and target bit photons and performing initial quantum CNOT gate operations; The first wavelength converter array includes at least three coherent wavelength converters, which are used to convert the wavelengths of the photons output by the first beam splitter array to obtain photons with four different wavelengths, and output them to the on-chip wavelength division multiplexer; The on-chip wavelength division multiplexer is used to combine photons of four different wavelengths into one path and couple it to a transmission optical fiber. The transmission optical fiber is used to transmit the photons of four different wavelengths to the on-chip wavelength division multiplexer. The on-chip wavelength division multiplexer is used to separate the photons of four different wavelengths into four different intermediate paths and connect them to a second wavelength converter array. The second wavelength converter array includes at least three coherent wavelength inverse converters, which are used to perform wavelength inverse conversion on photons of four different wavelengths to obtain photons of the same wavelength, and output them through four output paths respectively; The second beam splitter array includes a plurality of beam splitters, which are used to receive the photons outputted from the four output paths of the second wavelength converter array and perform a final quantum CNOT gate operation; The output port array includes a first output port and a second output port for outputting target bit photons. The output port array also includes a third output port and a fourth output port for outputting control bit photons.

2. A quantum CNOT gate optical path structure according to claim 1, characterized in that: The first beam splitter array includes a first beam splitter, a second beam splitter, a third beam splitter, and a fourth beam splitter, each of which includes an input upper end, an input lower end, an output upper end, and an output lower end; the input upper end and the input lower end of the first beam splitter are respectively connected to the third input port and the fourth input port, the output upper end thereof is connected to the input lower end of the third beam splitter, and the output lower end thereof is connected to the input upper end of the fourth beam splitter; the input lower end of the second beam splitter is connected to the first input port; the input upper end of the third beam splitter is connected to the second input port; the output lower end of the second beam splitter, the output upper end of the third beam splitter, the output lower end of the third beam splitter, and the output upper end of the fourth beam splitter are respectively connected to the first wavelength converter array; The second beam splitter array includes a fifth beam splitter, the input upper end of the fifth beam splitter is connected to one of the output paths of the second wavelength converter array, and receives the photons output from the output lower end of the third beam splitter and undergoing wavelength conversion and inverse conversion, and the input lower end of the fifth beam splitter is connected to another output path of the second wavelength converter array, and receives the photons output from the output upper end of the fourth beam splitter and undergoing wavelength conversion and inverse conversion; Among them, the splitting ratios of the first beam splitter and the fifth beam splitter are both 1:1, and the splitting ratios of the second beam splitter, the third beam splitter, and the fourth beam splitter are respectively 1:2, where the splitting 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.

3. A quantum CNOT gate optical path structure according to claim 1, characterized in that: The first wavelength converter array includes four coherent wavelength converters for converting the photons output by the first beam splitter array into photons of four different wavelengths different from the wavelength of the incident photons.

4. A quantum CNOT gate optical path structure according to claim 2, characterized in that: The first beam splitter, the second beam splitter, the third beam splitter, the fourth beam splitter and the fifth beam splitter are all on-chip directional couplers or on-chip MZ interferometers with fixed splitting ratios.

5. The quantum CNOT gate optical path structure according to claim 1, characterized in that: The coherent wavelength converter and the coherent wavelength inverse converter are both coherent wavelength converters based on on-chip aluminum nitride microrings, one section of the aluminum nitride microring is covered with a metal electrode, and the gap between the metal electrode and the on-chip aluminum nitride microring is a SiO2 cladding.

6. The quantum CNOT gate optical path structure according to claim 1, characterized in that: The on-chip wavelength division multiplexer and the on-chip wavelength demultiplexer are both composed of on-chip arrayed waveguide gratings.

7. The quantum CNOT gate optical path structure according to claim 1, characterized in that: The on-chip wavelength division multiplexer and the on-chip wavelength demultiplexer are both composed of cascaded on-chip MZ interferometers.

8. The quantum CNOT gate optical path structure according to claim 1, characterized in that: It also includes a first on-chip spot converter and a second on-chip spot converter. The on-chip wavelength division multiplexer is coupled to the transmission optical fiber through the first on-chip spot converter; the on-chip wavelength division multiplexer is coupled to the transmission optical fiber through the second on-chip spot converter.

9. The quantum CNOT gate optical path structure according to claim 1, characterized in that: A filter is connected between each coherent wavelength converter and the on-chip wavelength division multiplexer, and a filter is connected to the output end of each coherent wavelength inverse converter, and the filter is used to filter out noise photons of other wavelengths generated during the wavelength conversion process.

10. The quantum CNOT gate optical path structure according to claim 5, characterized in that: It also includes a control signal terminal, and the metal electrodes of the coherent wavelength converter and the coherent wavelength inverse converter are connected to the same control signal terminal.

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