Patent Publication Number: US-2021166149-A1

Title: Quantum noise process analysis method and apparatus, device, and storage medium

Description:
RELATED APPLICATION 
     This application is a continuation of and claims priority to the PCT International Application No. PCT/CN2020/084897, filed with the National Intellectual Property Administration, PRC on Apr. 15, 2020, which claims priority to Chinese Patent Application No. 201910390722.5, filed with the National Intellectual Property Administration, PRC on May 10, 2019, both entitled “QUANTUM NOISE PROCESS ANALYSIS METHOD AND APPARATUS, DEVICE, AND STORAGE MEDIUM”, which are incorporated herein by reference in their entireties. 
    
    
     FIELD OF THE TECHNOLOGY 
     Embodiments of this application relate to the field of quantum technologies, and in particular, to a quantum noise process analysis technology. 
     BACKGROUND OF THE DISCLOSURE 
     A quantum noise process is a quantum information pollution process caused by the interaction between a quantum system or quantum device with a bath or by the imperfection in quantum control. 
     In the related art, information about a dynamical map of a quantum noise process is extracted through quantum process tomography (QPT). The QPT is a mathematical description of inputting a group of standard quantum states to a noise channel and reconstructing a quantum noise process through a series of measurement processes. 
     The limited information about the quantum noise process obtained through pure QPT is insufficient to accurately and comprehensively analyze the quantum noise process. 
     SUMMARY 
     Embodiments of this application provide a quantum noise process analysis method and apparatus, a device, and a storage medium, to resolve the foregoing technical problem in the related art. The technical solutions are as follows: 
     According to an aspect, an embodiment of this application provides a quantum noise process analysis method, including: 
     performing quantum process tomography (QPT) on a quantum noise process of a target quantum system, to obtain dynamical maps of the quantum noise process; 
     extracting transfer tensor maps (TTMs) of the quantum noise process from the dynamical maps, the TTMs being used for representing a dynamical evolution of the quantum noise process; and 
     analyzing the quantum noise process according to the TTMs. 
     According to another aspect, an embodiment of this application provides a quantum noise process analysis apparatus, including: 
     an obtaining module, configured to perform quantum process tomography (QPT) on a quantum noise process of a target quantum system, to obtain dynamical maps of the quantum noise process; 
     an extraction module, configured to extract TTMs of the quantum noise process from the dynamical maps, the TTMs being used for representing a dynamical evolution of the quantum noise process; and 
     an analysis module, configured to analyze the quantum noise process according to the TTMs. 
     According to still another aspect, an embodiment of this application provides a computer device, including a processor and a memory, the memory storing at least one instruction, at least one program, a code set or an instruction set, the at least one instruction, the at least one program, the code set or the instruction set being loaded and executed by the processor to implement the foregoing quantum noise process analysis method. 
     According to yet another aspect, an embodiment of this application provides a computer-readable storage medium, storing at least one instruction, at least one program, a code set or an instruction set, the at least one instruction, the at least one program, the code set or the instruction set being loaded and executed by a processor to implement the foregoing quantum noise process analysis method. 
     According to still yet another aspect, an embodiment of this application provides a computer program product, when executed, the computer program product being configured to perform the foregoing quantum noise process analysis method. 
     The technical solutions provided in the embodiments of this application may include at least the following beneficial effects: 
     In the technical solutions provided in this application, QPT is performed on a quantum noise process, to obtain dynamical maps of the quantum noise process, and a TTM of the quantum noise process is further extracted from the dynamical maps of the quantum noise process. The TTM is used for representing a dynamical evolution of the quantum noise process, that is, reflecting the law of evolution of the dynamical maps of the quantum noise process over time. Compared with pure QPT, this application can obtain richer and more comprehensive information about the quantum noise process. Therefore, when the quantum noise process is analyzed based on the TTM of the quantum noise process, a more accurate and comprehensive analysis of the quantum noise process can be achieved based on the richer and more comprehensive information. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To describe the technical solutions of the embodiments of this application more clearly, the following briefly describes the accompanying drawings for illustrating the embodiments. The accompanying drawings in the following description are merely examples, and a person of ordinary skill in the art may still derive other accompanying drawings according to these accompanying drawings without creative efforts. 
         FIG. 1  is an overall flowchart of a technical solution of this disclosure. 
         FIG. 2  is a flowchart of a quantum noise process analysis method according to an embodiment of this disclosure. 
         FIG. 3  to  FIG. 8  exemplarily show schematic diagrams of several groups of experimental results in a simulated bath. 
         FIG. 9  to  FIG. 14  exemplarily show schematic diagrams of several groups of experimental results in a real bath. 
         FIG. 15  is a block diagram of a quantum noise process analysis apparatus according to an embodiment of this disclosure. 
         FIG. 16  is a block diagram of a quantum noise process analysis apparatus according to another embodiment of this disclosure. 
         FIG. 17  is a schematic structural diagram of a computer device according to an embodiment of this disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     To make the objectives, technical solutions, and advantages of this disclosure clearer, the following further describes implementations of this disclosure in detail with reference to the accompanying drawings. 
     Before the embodiments of this disclosure are described, some terms involved in this disclosure are explained first. 
     1. Quantum system: It is part of the entire universe, and its motion law follows the quantum mechanics. 
     2. Quantum state: All information of the quantum system is represented by a quantum state ρ. ρ is a d×d complex matrix, where d is the quantity of dimensions of the quantum system. 
     3. Quantum noise process: It is a quantum information pollution process caused by interaction between the quantum system or quantum device with the bath or by imperfection in quantum control. Mathematically, this process is a channel represented by using a super-operator, and if the process is expanded to a higher dimensionality, the process may be represented by using a matrix. 
     4. Memory kernel: It is an operator acting on the quantum state, and includes all information about system decoherence triggered by the bath. 
     5. Second-order memory kernel: It is a second-order series expansion of the memory kernel in the coupling strength between the quantum system and the bath. 
     6. Second-order correlation function of noise: It is a correlation function of a system noise between two different time points, and is used for calculating a frequency spectrum of the noise. 
     7. Transfer tensor map (TTM): It is a map recursively extracted from dynamical maps of the quantum noise process, and this map encodes the memory kernel of the quantum system, and can be used for predicting a dynamical evolution of the quantum system and determining properties of the noise. 
     8. Quantum process tomography (QPT): It is a mathematical description of inputting a group of standard quantum states to a noise channel and reconstructing a quantum noise process through a series of measurement processes. 
     In quantum information processing, all information of the quantum system is represented by an evolution ρ(t) of a quantum state over time t. ρ(t) is a d×d complex matrix. Any quantum process, either a quantum information processing process or a quantum noise process, may be represented by using a dynamical map when the system and the bath are in a separable state initially: 
       ε(ρ)=Σ k   A   k   ρA   k   † ,
 
     where A k  is also a d×d matrix and meets Σ i A i   † A≤I, and represents a k th  component of the influence of the bath on the quantum system, and I is an identity matrix. A k   †  represents a Hermitian conjugate, that is, a complex conjugate transpose, of A k  . Because of completeness of a finite-dimensional complex matrix space, an orthogonal basis matrix set {E i } in a d×d matrix space is defined, and then the following may be obtained: 
         A   i =Σ m   a   im   E   m ,
 
     where a im ∈ ,   represents a complex set, E m  is an element in {E i }, and both i and m are positive integers. 
     In this way, the following may be obtained: 
     
       
         
           
             
               
                 ɛ 
                  
                 
                   ( 
                   ρ 
                   ) 
                 
               
               = 
               
                 
                   ∑ 
                   
                     m 
                     , 
                     n 
                   
                 
                  
                 
                   
                     χ 
                     
                       m 
                       , 
                       n 
                     
                   
                    
                   
                     E 
                     m 
                   
                    
                   ρ 
                    
                   
                     E 
                     n 
                     † 
                   
                 
               
             
             , 
             
               
 
             
              
             
               
                 where 
                  
                 
                     
                 
                  
                 
                   χ 
                   
                     m 
                     , 
                     n 
                   
                 
               
               = 
               
                 
                   ∑ 
                   i 
                 
                  
                 
                   
                     a 
                     
                       m 
                        
                       i 
                     
                   
                    
                   
                     a 
                     
                       n 
                        
                       i 
                     
                     * 
                   
                 
               
             
             , 
           
         
       
     
     and is an element of a complex transformation matrix χ whose index is m, n, E n   †  represents a Hermitian conjugate of E n , E n  is an element in {E i }, and ρ represents an input state. 
     In the related art, a quantum noise process analysis method based on QPT is provided. d 2 ×d 2  linearly independent input states ρ j  are used, and each input state ρ j  is transferred to a quantum noise process to obtain an output state ε(ρ j ). Because of completeness of the input states, the output state may be represented as a linear combination of the input states: 
       ε(ρ j )=Σ k   c   jk ρ k , where  c   jk ∈ .
 
     where ε(ρ j ) is an output quantum state obtained after a dynamical map of the quantum state ρ j . In this way, by inputting the same quantum state ρ j  a plurality of times and performing quantum state tomography on an output state, a summation coefficient C jk  may be experimentally solved. A specific process is as follows: 
         E   m ρ j   E   n   † =Σ k   B   m,n,j,k ρ k ,
 
     where B m,n,j,k  is a complex number, B m,n,j,k  is considered as a complex matrix formed by indexes {m, n} and {j, k}, and each of m, n, j, and k is a positive integer. Then, 
       Σ k   c   jk ρ k =ε(ρ j )=Σ m,n,k χ m,n   B   m,n,j,k ρ k .
 
     Because {ρ i } is linearly independent, the following may be obtained: 
         c   jk =Σ m,n χ m,n   B   m,n,j,k .
 
     By transposing B m,n,j,k  , the following may be obtained: 
       χ m,n =Σ j,k   B   m,n,j,k   −1   c   jk .
 
     χ m,n  includes all information about dynamical maps of the quantum noise process. Therefore, once χ m,n  is obtained through QPT, all the information about the dynamical maps of the quantum noise process is obtained. 
     However, the limited information about the quantum noise process obtained through pure QPT is insufficient to accurately and comprehensively analyze the quantum noise process. For example, whether the quantum noise process is a Markov process or a non-Markov process is not determined, a frequency spectrum of the quantum noise process is not obtained, and a correlated noise between different quantum devices in the quantum system is not analyzed. 
     To resolve the foregoing technical problems, an embodiment of this disclosure provides a quantum noise process analysis method.  FIG. 1  is an overall flowchart of a technical solution of this disclosure. In the technical solution provided in this disclosure, QPT is performed on a quantum noise process, to obtain dynamical maps of the quantum noise process, a TTM of the quantum noise process is further extracted from the dynamical maps of the quantum noise process, and then the quantum noise process is analyzed according to the TTM. The TTM is used for representing a dynamical evolution of the quantum noise process, that is, reflecting the law of evolution of the dynamical maps of the quantum noise process over time. Therefore, richer and more comprehensive information about the quantum noise process can be obtained by analyzing the quantum noise process based on the TTM of the quantum noise process than by pure QPT, thereby achieving a more accurate and more comprehensive analysis of the quantum noise process. 
     The technical solution provided in this disclosure is applicable to analysis of a quantum noise process of any quantum system such as a quantum computer, secure quantum communication, the quantum Internet or another quantum system. The interference to the quantum system by quantum noise severely affects the performance of the quantum system, which is the primary barrier hindering the practical application of the quantum system. Therefore, analyzing the quantum noise process and understanding the properties of the noise are crucial for the development of practical quantum systems. In the technical solution provided in this disclosure, analyzing the quantum noise process based on the TTM of the quantum noise process may include, for example, the following analysis content as shown in  FIG. 1 : (1) Markov process determination, e.g., whether the quantum noise process is a Markov process or a non-Markov process can be determined, and whether a special noise suppression solution may be designed for a non-Markov noise, where the solution is, for example, suppressing the occurrence of noise through dynamical decoupling; (2) state evolution prediction, e.g., a state evolution of the quantum noise process may be predicted; (3) extraction of correlation function and frequency spectrum, e.g., a correlation function and a frequency spectrum of the quantum noise process may be obtained, facilitating the integration of a filter of a corresponding frequency band in the process of quantum device manufacturing; and (4) correlated noise analysis, e.g., a correlated noise between different quantum devices in the quantum system may be analyzed, to learn the source of the correlated noise and accordingly design a corresponding solution to suppress the correlated noise. Therefore, the technical solution provided in this disclosure can obtain richer and more comprehensive information about the quantum noise process, thereby providing more information to support the improvement in the performance of the quantum system. 
       FIG. 2  is a flowchart of an example quantum noise process analysis method according to an embodiment of this disclosure. The method is applicable to a computer device, and the computer device may be any electronic device having data processing and storage capabilities, such as a personal computer (PC), a server, or a computing host. The method may include the following steps (step  201  to step  203 ): 
     Step  201 . Perform quantum process tomography (QPT) on a quantum noise process of a target quantum system, to obtain dynamical maps of the quantum noise process. 
     The performing quantum process tomography (QPT) on a quantum noise process to obtain dynamical maps of the quantum noise process has been described above, so the details are not described herein again. 
     Optionally, in this embodiment, QPT may be performed on the quantum noise process at discrete time points. For example, if QPT is performed at K different time points, dynamical maps of the quantum noise process at the K time points may be obtained, K being an integer greater than or equal to 1. Optionally, among the K time points, intervals between neighboring time points may be equal. Alternatively, intervals between neighboring time points may also be not equal, which is not limited in this embodiment. 
     Step  202 . Extract TTMs of the quantum noise process from the dynamical maps. 
     In this embodiment of this disclosure, the TTM of the quantum noise process is used for representing a dynamical evolution of the quantum noise process to reflect the law of evolution of the dynamical maps of the quantum noise process over time. 
     Optionally, if dynamical maps of the quantum noise process at the K time points are obtained in step  201 , a possible implementation of step  201  may include calculating the TTMs of the quantum noise process at the K time points according to the dynamical maps of the quantum noise process at the K time points. In an exemplary embodiment, the TTMs at the K time points are extracted recursively. For example, a TTM T n  of the quantum noise process at an n th  time point is calculated according to the following formula: 
     
       
         
           
             
               
                 T 
                 n 
               
               ≡ 
               
                 
                   ɛ 
                   n 
                 
                 - 
                 
                   
                     ∑ 
                     
                       m 
                       = 
                       1 
                     
                     
                       n 
                       - 
                       1 
                     
                   
                    
                   
                     
                       T 
                       
                         n 
                         - 
                         m 
                       
                     
                      
                     
                       ɛ 
                       m 
                     
                   
                 
               
             
             , 
           
         
       
     
     where T 1 =ε 1 , ε n  represents a dynamical map of the quantum noise process at the n th  time point, ε m  represents a dynamical map of the quantum noise process at an m th  time point, and T n−m  represents a TTM of the quantum noise process at an (n−m) th  time point, both n and m being positive integers. 
     Step  203 . Analyze the quantum noise process according to the TTMs. 
     After the TTMs of the quantum noise process at the K time points are extracted, the quantum noise process may be analyzed accordingly. 
     In an exemplary embodiment, after T n  is determined, the quantum noise process may be considered as a Markov process if the value of |T n | is negligibly small for n&gt;1 according to the definition. Otherwise, the quantum noise process may be considered as a non-Markov process. That is, it may be determined that the quantum noise process is a Markov process when each of moduli of TTMs of the quantum noise process at first time points is less than a preset threshold, the first time points being time points other than the foremost time point of the K time points. It may otherwise be determined that the quantum noise process is a non-Markov process when a modulus of a TTM of the quantum noise process at a second time point is greater than the preset threshold, the second time point being at least one time point other than the foremost time point of the K time points. 
     By means of the above method, based on the TTMs of the quantum noise process, whether the quantum noise process is a Markov process or a non-Markov process can be determined, and a special noise suppression solution may be designed for a non-Markov noise, where the solution include, for example, suppressing the occurrence of noise through dynamical decoupling. 
     Additionally, compared with the dynamical map, a universal equation for describing the evolution of the quantum system in an open bath is a non-temporal localized quantum master equation, and can better reveal the mathematical structure of the quantum noise process. This equation is a differential-integral equation: 
     
       
         
           
             
               
                 
                   d 
                    
                   
                     ρ 
                      
                     
                       ( 
                       t 
                       ) 
                     
                   
                 
                 
                   d 
                    
                   t 
                 
               
               = 
               
                 
                   
                     L 
                     s 
                   
                    
                   
                     ρ 
                      
                     
                       ( 
                       t 
                       ) 
                     
                   
                 
                 + 
                 
                   
                     ∫ 
                     0 
                     t 
                   
                    
                   
                     ds 
                      
                     
                         
                     
                      
                     
                       κ 
                        
                       
                         ( 
                         
                           t 
                           - 
                           s 
                         
                         ) 
                       
                     
                      
                     
                       ρ 
                        
                       
                         ( 
                         s 
                         ) 
                       
                     
                   
                 
               
             
             , 
           
         
       
     
     where ρ(t) represents a quantum state of the quantum system at time t and is represented by using a d×d complex matrix; L s  is a Liouville operator and represents a coherent part in the evolution process of the quantum system; s is an integral parameter; and κ(t) is a memory kernel including all information about system decoherence triggered by the bath. If L s  and κ(t) of the quantum noise process are obtained, the noise mechanism may be completely understood. The basic idea of the technical solution of this disclosure is to calculate a TTM through an experiment and QPT, thereby extracting information about L s  and κ(t). 
     In addition, a joint evolution of the quantum system and the bath is determined by a joint Hamiltonian. The joint Hamiltonian may be represented as: 
     
       
         
           
             
               
                 
                   
                     H 
                      
                     
                       ( 
                       t 
                       ) 
                     
                   
                   = 
                     
                    
                   
                     
                       H 
                       s 
                     
                     + 
                     
                       
                         H 
                         
                           s 
                            
                           b 
                         
                       
                        
                       
                         ( 
                         t 
                         ) 
                       
                     
                   
                 
               
             
             
               
                 
                   
                     = 
                       
                      
                     
                       
                         H 
                         s 
                       
                       + 
                       
                         
                           ∑ 
                           
                             i 
                             , 
                             α 
                           
                         
                          
                         
                           
                             g 
                             i 
                           
                            
                           
                             
                               B 
                               i 
                               α 
                             
                              
                             
                               ( 
                               t 
                               ) 
                             
                           
                            
                           
                             σ 
                             i 
                             α 
                           
                         
                       
                     
                   
                   , 
                 
               
             
           
         
       
     
     where H s  is a Hamiltonian of the quantum system; H sb  is an interactive Hamiltonian of coupling between the quantum system and the bath; σ i   α  is an α th  type of Pauli operator acting on an i th  qubit of the system, both i and α being positive integer indexes; B i   α (t) is an α th  type of bath operator coupled to the i th  qubit; α=x, y, z represents three temporal-spatial directions; and g i  is a coupling strength between the system and the bath. 
     The evolution of a state function of the quantum system follows: 
     
       
         
           
             
               
                 
                   
                     
                       ρ 
                        
                       
                         ( 
                         t 
                         ) 
                       
                     
                     = 
                       
                      
                     
                       
                         Tr 
                         B 
                       
                        
                       
                         [ 
                         
                           
                             
                               exp 
                               + 
                             
                              
                             
                               ( 
                               
                                 
                                   - 
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                                  
                                 
                                   
                                     ∫ 
                                     0 
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                                    
                                   
                                     d 
                                      
                                     s 
                                      
                                     
                                       H 
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                                         ( 
                                         s 
                                         ) 
                                       
                                     
                                   
                                 
                               
                               ) 
                             
                           
                            
                           
                             
                               ρ 
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                                 ( 
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                             ⊗ 
                             
                               ρ 
                               B 
                             
                           
                            
                           
                             
                               exp 
                               - 
                             
                              
                             
                               ( 
                               
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                                     ∫ 
                                     0 
                                     t 
                                   
                                    
                                   
                                     d 
                                      
                                     s 
                                      
                                     
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                                        
                                       
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                         ] 
                       
                     
                   
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                   = 
                     
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                        
                       
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                        
                       
                         ( 
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     where ρ(t) represents a quantum state of the quantum system at time t, ρ(0) represents an initial quantum state of the quantum system, ρ B  is a quantum state of the bath, Tr B  represents calculation of a partial trace of the degree of freedom of the bath, exp + , exp −  are clockwise and counterclockwise time-ordered exponential operators respectively, ε(t) represents a dynamical evolution of the quantum system at the time t, i is a unit pure imaginary number, and s is an integral parameter. 
     If time is discretized by t k+1 −t k =δt (k is a positive integer), a group of dynamical maps {ε k ≡ε(t k )} evolving over time may be defined. Experimentally, the dynamical maps may be obtained by performing QPT at different time points. 
     With reference to the foregoing definition about the formula of the TTM, by using T n  to express ε n  and substituting the expression into the formula of the foregoing state function, the following may be obtained: 
     
       
         
           
             
               
                 ρ 
                  
                 
                   ( 
                   
                     t 
                     n 
                   
                   ) 
                 
               
               = 
               
                 
                   ∑ 
                   
                     m 
                     = 
                     1 
                   
                   
                     n 
                     - 
                     1 
                   
                 
                  
                 
                   
                     T 
                     m 
                   
                    
                   
                     ρ 
                      
                     
                       ( 
                       
                         t 
                         
                           n 
                           - 
                           m 
                         
                       
                       ) 
                     
                   
                 
               
             
             , 
           
         
       
     
     where ρ(t  n ) represents a quantum state at an n th  time point t n , ρ(t n−m ) represents a quantum state at an (n−m) th  time point t n−m , and T m  represents a TTM at an m th  time point. This formula clearly indicates that in the presence of a noise, the state evolution of the quantum system depends on the historical evolution the quantum system. Generally, the dependence of the dynamical evolution on history does not exceed a certain time span. This means that the influence of the noise on the state may be precisely estimated by truncating a convolution of the foregoing formula and keeping K (where K is a positive integer) time points, that is, all items for which t&gt;t K  are discarded. In this way, through QPT on a dynamical map in a short period of time, a TTM in this period of time may be obtained. Then, an evolution of an open system in a long time may be predicted by using the TTM in this short period of time. The quantum state ρ(t n ) at the n th  time point t n  may be calculated through the foregoing formula. In addition, the predicted quantum state may be directly compared with an experiment to verify the effectiveness of dynamics of the open system described through the TTM. In other words, this provides a preliminary basis for determining the effectiveness of the technical solution of this disclosure. 
     To sum up, in the technical solutions provided in this disclosure, QPT is performed on a quantum noise process, to obtain dynamical maps of the quantum noise process, and a TTM of the quantum noise process is further extracted from the dynamical maps of the quantum noise process. The TTM is used for representing a dynamical evolution of the quantum noise process to reflect the law of evolution of the dynamical maps of the quantum noise process over time. Compared with pure QPT, this disclosure can obtain richer and more comprehensive information about the quantum noise process. Therefore, when the quantum noise process is analyzed based on the TTM of the quantum noise process, a more accurate and comprehensive analysis of the quantum noise process can be achieved based on the richer and more comprehensive information. 
     Additionally, in the technical solution provided in this disclosure, the determination of whether the quantum noise process is a Markov process or a non-Markov process according to the TTM of the quantum noise process is further implemented; and the prediction, according to a TTM of the quantum noise process within a period of time, of a state evolution of the quantum noise process within a subsequent time is further implemented. 
     In an exemplary embodiment, after the TTM of the quantum noise process is extracted, a correlation function and a frequency spectrum of the quantum noise process may be further obtained accordingly. The process may include the following steps. 
     1. Extract a second-order memory kernel of the quantum noise process according to the TTMs of the quantum noise process when the quantum noise process is a steady noise. 
     For a steady noise (for example, Gaussian steady noise), the properties of the noise are determined by a correlation function of the noise process. The correlation function of the noise process may be calculated according to a second-order memory kernel of the noise process. 
     In this embodiment of this disclosure, for a quantum noise process, a second-order memory kernel of the quantum noise process is extracted according to the TTMs of the quantum noise process when the quantum noise process is a steady noise. 
     Considering that the time has been discretized and approximated to the second order of a time step δt, an approximation of the TTM may be obtained: 
         T   n =(1 +L   s   δt )δ n,1 +κ( t   n )δ t   2 ,
 
     where δt is the time step, δ n,1  is a Kronecker function having a value of 1 when n=1 and a value of 0 in other cases, n being a positive integer; and κ(t n ) is a value of the memory kernel at time t n . 
     Moreover, according to the open system theory, a precise expression of a dynamical memory kernel κ is: 
       κ( t,t′ )= PL ( t )exp + [∫ t′   t   dsQL ( s )] QL ( t′ ) P,  
 
     where P=Tr B {ρ SB }⊗ρ B  is a map operator, and Q ρ     SB   =ρ SB −P ρ     SB   ; L is a joint Liouville operator acting on the system and the bath, ρ SB  is a joint state of the system and the bath, and Q=I−P is a difference between P and an identity operator I. 
     Because a noise is preliminarily controlled through engineering in an ordinary quantum system, the coupling strength between the quantum system and the bath is relatively weak. When a target quantum system and the bath are in a weak coupling relationship, a second-order perturbation approximation may be established, and therefore the following may be obtained: 
       κ 2 ( t )(⋅)≈&lt; L   sb ( t ) L   sb (0)&gt;(⋅)=Σ αα′ [σ α   , C   αα′ ( t )σ ′′(   t )(⋅)− C*   αα′ ( t )(⋅)σ α′ ( t )],
 
     where κ 2 (t) is a value of a second-order memory kernel at the time t, and C* αα′ (t) is a complex conjugate of C αα′ (t). The foregoing expression is under the Schrödinger representation, and at the same time, it is assumed that a Hamiltonian of a joint system is time-invariant. The second-order correlation function C αα′ (t) is defined as: 
         C   αα′ ( t )= g   2     {circumflex over (B)}   α ( t ) {circumflex over (B)}   α′ (0) . 
     C αα′ (t) is a bath correlation function. Based on the second-order perturbation, a dynamical map may be extracted from an experiment, and a TTM is obtained through QPT, thereby obtaining a memory kernel κ exp  through approximation. That is, κ exp  may be an approximate second-order memory kernel obtained through an experiment. 
     When the target quantum system and the bath are in a strong coupling relationship, the second-order perturbation is no longer a desirable approximation, and a better approximation can be obtained only when there are more high-order items, but a second-order memory kernel can still be extracted by extracting a TTM from experimental data. Specific steps are as follows: selecting N different parameters, performing an experiment on the quantum noise process, and extracting memory kernels respectively corresponding to the N different parameters from the experiment; and performing calculation according to the memory kernels respectively corresponding to the N different parameters, to obtain the second-order memory kernel of the quantum noise process. 
     First, an N-order truncated approximate memory kernel is defined: 
       κ( N,t )=Σ n=1   N κ 2n ( t ),
 
     It is assumed that a memory kernel of a system can be approximated by this approximate memory kernel. Then it is assumed that there is a parameter-adjustable system, parameters of the system may be adjusted in each experiment, and a Hamiltonian of the system is: 
       H s =ω s,i σ z ,
 
     where i represents an experiment performed by selecting an i th  parameter, and σ z  is a Pauli z operator ( 0   1   −1   0 ). For the selected parameter ω s,i  (where ω s,i  belongs to an interval that the experiment can reach), the Hamiltonian is normalized, and the following may be obtained: 
         {tilde over (H)}=σ   z   +g{tilde over (H)}   sb ( t ) 
     where {tilde over (H)} is the normalized Hamiltonian, and g∝1/ω s,i . By performing an experiment on N different ω s,i , a group of memory kernels without physical units may be constructed, with the relationship being as follows: 
       {tilde over (κ)} 2n,i ( t )=γ i   2n {tilde over (κ)} 2n,0 ( t ),
 
     where γ i =ω s,0 /ω s,i  is a normalized parameter, and {tilde over (κ)} 2n,i  represents a 2n-order memory kernel in the case of ω s,i . In this way, the following matrix may be defined: 
     
       
         
           
             A 
             = 
             
               
                 [ 
                 
                   
                     
                       1 
                     
                     
                       1 
                     
                     
                       … 
                     
                     
                       1 
                     
                   
                   
                     
                       
                         γ 
                         1 
                         2 
                       
                     
                     
                       
                         γ 
                         1 
                         2 
                       
                     
                     
                       … 
                     
                     
                       
                         γ 
                         1 
                         
                           2 
                            
                           N 
                         
                       
                     
                   
                   
                     
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                       … 
                     
                     
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                         γ 
                         
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                         γ 
                         
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                            
                           1 
                         
                         4 
                       
                     
                     
                       
                         ... 
                       
                     
                     
                       
                         γ 
                         
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                           - 
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                            
                           N 
                         
                       
                     
                   
                 
                 ] 
               
               . 
             
           
         
       
     
     In addition, the following equation is satisfied: 
         A [{tilde over (κ)} 2,0  . . . {tilde over (κ)} 2N,0 ] T =[{tilde over (κ)}(1) . . . {tilde over (κ)}( N )] T ,
 
     where A is an N-order normalized parameter matrix, and a memory kernel on the right side of the equation may be directly extracted from an experiment through QPT and data processing. Because A is a full-rank matrix, a second-order memory kernel is naturally obtained by solving the linear equation to obtain 2-order to N-order memory kernels without physical units. 
     2. Calculate a correlation function of the quantum noise process according to the second-order memory kernel of the quantum noise process. 
     Optionally, the correlation function C αα′  of the quantum noise process may be numerically extracted according to the following formula: 
     
       
         
           
             
               
                 argmin 
                 
                   
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                       ′ 
                     
                   
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     where κ 2  represents the second-order memory kernel of the quantum noise process, t n  represents the n th  time point, C αα′ (t n ) is a second-order correlation function at the n th  time point t n , κ exp  represents an approximate second-order memory kernel obtained through an experiment, δ t     n     ,t     0    is a Kronecker function (having a value of 1 when n=0 and a value of 0 in other cases), λ n  is an adjustable parameter, and C αα′ (t n−1 ) is a second-order correlation function at an (n−1) th  time point t n−1 . λ n  is used for ensuring that after the target function is minimized, the correlation function can still be continuous. λ n  may be determined by first selecting an initial value and observing the value of the target function followed by iterative adjustments, so as to render the selection of the value of λ n  robust. 
     Optionally, for a non-Gaussian steady noise, only a correlation function higher than 2-order can fully represent statistical properties of the noise. Obtaining of a second-order correlation function of a noise by solving this linear equation A[{tilde over (κ)} 2,0  . . . {tilde over (κ)} 2N,0 ] T =[{tilde over (κ)}(1) . . . {tilde over (κ)}(N)] T  has been described above. If a non-Gaussian steady noise is processed, it may be assumed that a memory kernel of the noise is written as: 
       κ( N,t )=Σ n=2   N κ n ( t ) .
 
     Based on this more generalized memory kernel, the following may be obtained according to the solution described above: 
         A [{tilde over (κ)} 2,0  . . . {tilde over (κ)} N,0 ] T =[{tilde over (κ)}(1) . . . {tilde over (κ)}( N )] T .
 
     By solving this linear equation, second-order and higher-order correlation functions may be obtained. 
     3. Perform a Fourier transform on the correlation function of the quantum noise process, to obtain a frequency spectrum of the quantum noise process. 
     Once the correlation function of the quantum noise process is obtained, a Fourier transform may be performed on the correlation function, to obtain a frequency spectrum J αα′ (ω) of the quantum noise process: 
         J   αα′ (ω)=1/2∫ −∞   ∞   dte   iωt [ C   αα′ ( t )− C*   αα′ ( t )].
 
     This method of obtaining the frequency spectrum of the quantum noise process is not limited by whether the noise is a quantum noise (the system has a feedback to the noise source) or a classical noise, and is not limited by a particular noise type. 
     To sum up, in the technical solution provided in this disclosure, after the TTM of the quantum noise process is extracted, the correlation function and the frequency spectrum of the quantum noise process may be further obtained accordingly, facilitating the integration of a filter of a corresponding frequency band in the process of quantum device manufacturing. 
     In an exemplary embodiment, after the TTM of the quantum noise process is extracted, a correlated noise between different quantum devices in the target quantum system may be further analyzed accordingly to learn the source of the correlated noise. The process may include the following steps. 
     1. Calculate, for s quantum devices included in the target quantum system, a correlated TTM among the s quantum devices according to TTMs respectively corresponding to the s quantum devices, s being an integer greater than 1. 
     2. Analyze a source of a correlated noise among the s quantum devices according to the correlated TTM. 
     A quantum system may include a plurality of quantum devices. A qubit is the simplest quantum device, including only two quantum states. By using TTMs, a noise correlation between the plurality of quantum devices in the same quantum system can be completed. The following mainly describes an example scenario where there are two quantum devices, and the same applies to other scenarios. For example, according to the method provided in this embodiment of this disclosure, a noise correlation between any two quantum devices, or a noise correlation between any three or more quantum devices can also be determined. 
     Dynamical maps of any two quantum systems (or quantum devices) may be decomposed as follows: 
     
       
         
           
             
               
                 
                   
                     
                       ɛ 
                       n 
                     
                     ≡ 
                     
                       
                         
                           ɛ 
                           
                             n 
                             , 
                             1 
                           
                         
                         ⊗ 
                         
                           ɛ 
                           
                             n 
                             , 
                             2 
                           
                         
                       
                       + 
                       
                         δɛ 
                         n 
                       
                     
                   
                 
               
               
                 
                   
                     = 
                     
                       
                         
                           ɛ 
                           _ 
                         
                         n 
                       
                       + 
                       
                         δɛ 
                         
                           
                               
                           
                           n 
                         
                       
                     
                   
                 
               
             
             , 
           
         
       
     
     where ε n,1  represents a dynamical map of a first quantum device, ε n,2  represents a dynamical map of a second quantum device, and δε n  is an unseparated part representing the influence of a correlated noise. In the foregoing decomposition of dynamical maps, a dynamical map ε n →χ n  may be expressed in the form of Choi matrix, that is, χ n  is a Choi matrix being an equivalent representation of the dynamical map, and a trace of the Choi matrix is calculated as follows: 
         Tr   īχn =χ n,i , ( i,ī )=(1, 2), or ( i, ī )=(2, 1).
 
     Then, a Choi matrix χ n,i  of a single quantum device is expressed back as a dynamical map ε n,i . Dynamical maps ε n  of two quantum devices may both be obtained by performing joint QPT on the two quantum devices. δε n  may be used for analyzing the correlated noise. In the case of second-order perturbation, a modulus of δε n  is usually much less than that of  ε   n . In a non-perturbative area, modulus values of δε n  and  ε   n  may be equivalent, or even |δε n | is much greater than Therefore, pure QPT can provide a preliminary determination on the strength of the correlated noise. However, it is rather difficult analyze the source of the correlated noise because all data is mixed together. Usually, sources of the correlated noise between two quantum devices include: (1) a correlated noise generated from direct coupling between the two quantum devices; (2) a correlated noise induced by a shared bath of the two quantum devices; or (3) a combination thereof. 
     An embodiment of this disclosure provides a correlated noise analysis method based on a TTM. By this method, more information about a correlated noise may be obtained. First, a separable TTM is calculated according to  ε   n : 
     
       
         
           
             
               
                 
                   T 
                   _ 
                 
                 n 
               
               = 
               
                 
                   
                     ɛ 
                     _ 
                   
                   n 
                 
                 - 
                 
                   
                     ∑ 
                     
                       m 
                       = 
                       1 
                     
                     
                       n 
                       - 
                       1 
                     
                   
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                         T 
                         _ 
                       
                       
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     and 
         T   n   = T     n   +δT   n , 
     where  T   1 = ε   1 , and δT n  is a noise correlation in transfer tensor map. Similarly, δT n  may be decomposed into: 
       δ T   n   =δLδtδ   n,1 +δκ n   δt   2 ,
 
     where the Liouville super-operator δL reveals whether there is a correlated noise generated from direct coupling between two quantum devices, and δκ n  represents a correlated noise induced by a shared bath. It can be found that a coupling increment caused by δL is in a linear relationship with δt, and a coupling increment caused by δκ n  is in a linear relationship with δt 2 . By selecting two different time steps δt and δt′, two different dynamical maps ε 1  and ε′ 1  may be generated, and then the source of the correlated noise is determined. Considering that the correlated noise has significant influence on fault-tolerant quantum computing, the technical solution of this disclosure can provide a better understanding of the correlated noise and provide guidance on how to perform control, so as to design different noise suppression solutions. 
     For example, through QPT, a joint dynamical map ε n  of two quantum devices in the target quantum system may be obtained, a TTM T n  is further obtained, then ε n,1  and ε n,2  may be obtained by calculating traces for the two quantum devices according to ε n  respectively, and  ε   n =ε n,1 ⊗ε n,2  . Then,  T   n  is obtained through 
     
       
         
           
             
               
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             = 
             
               
                 
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                         _ 
                       
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                     . 
                   
                 
               
             
           
         
       
     
     Finally, δT n =T n − T   n =δLδtδ n,1 +δκ n δt 2 . 
     Then, considering two different time steps δt and δt′: 
     
       
         
           
             { 
             
               
                 
                   
                     
                       
                         δ 
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     δL and δκ n  are calculated respectively. 
     To sum up, in the technical solution provided in this disclosure, after the TTM of the quantum noise process is extracted, a correlated noise between different quantum devices in the target quantum system may be further analyzed accordingly, to learn the source of the correlated noise and design a corresponding solution to suppress the correlated noise. 
     To further verify the effectiveness of the technical solution of this disclosure, numerical analysis is performed for a typical model. After this, on IBM Quantum Experience (which is a quantum computing cloud platform provided by IBM), an attempt is made to perform an experiment and observation on a real superconducting qubit and extract information about a noise process from the real superconducting qubit by using the technical solution of this disclosure. 
     Results of numerical analysis for the typical model are as follows: 
     Case 1: numerical simulation of a single qubit under pure phase decoherence 
     Letting H s =0.1σ z , H sb =B z ((t)σ z ,C zz (0)=λ=4,δt=0.2, TTM results of a free evolution of a single qubit are as shown in  FIG. 3 . Part (a) in  FIG. 3  shows the variation of a Frobenius norm of the TTM over time. It may be seen from the figure that the TTM within a range t 1 →t 6  makes a non-trivial contribution, that is, non-Markov properties are demonstrated in the noise process. A line  31  in part (b) in  FIG. 3  represents an evolution of a real part of a non-diagonal element of a density matrix corresponding to an initial state (|0 +|1 )/√{square root over (2)} over time. A line  32 , a line  33  and a line  34  respectively present prediction effects for the density matrix at different TTM lengths (that is, when K is 1, 3, and 5 respectively). It may be seen that when K is 5, an evolution obtained through the TTM well coincides with an exact solution, and a long-term experimental evolution can be perfectly predicted. 
     Additionally,  FIG. 4  shows the variation of a Bloch volume over time, and the increase in the Bloch volume V(t) within a period of time (t 4 , t 5 , t 6 )demonstrates non-Markov properties of the dynamical process, which proves the conclusion in  FIG. 3  from another perspective. 
     Case 2: extraction of a noise correlation function of a single qubit under pure phase decoherence 
     Letting H s =0.02σ z ,C zz  (0)= B z (t)B z (0) =0.01, δt=0.04, and a frequency spectrum of a quantum noise process (equivalent to a bath noise spectrum) is obtained through a TTM method for a free evolution of a single qubit. Part (a) in  FIG. 5  shows the variation of a noise correlation function C zz  (t) over time in the case of weak coupling between the quantum system and the bath. A line  51  presents an accurate theoretical result of the noise correlation function, and each circle presents a numerical result obtained from a memory kernel under an assumption of K(t)≈K 2 (t) . It can be learned that in the case of weak coupling, an approximate second-order memory kernel obtained from TTM can well depict the quantum noise process. 
     In part (b) in  FIG. 5 , let H s =0.02σ z ,C zz (0)∈(0, 2.56), δt=0.04. In the case of strong coupling between the quantum system and the bath, a noise correlation function at a special time point C zz (t=15δt) changes with a coupling strength C zz (0)λ between the noise and the system. Line  52  represents an accurate theoretical result. Line  53  presents a first numerical result: that is, directly assuming K(t)≈K 2 (t), it can be learned that in the case of strong coupling, there is a big difference between the first numerical result and a real noise spectrum. line  54  presents a second numerical result: that is, directly assuming K(t)≈K 2 (t)+K 4 (t), even in the case of strong coupling under research, a memory kernel obtained from TTM can well reflect the real noise spectrum even for higher order. 
     Case 3: extraction of a correlation function of a single qubit in a bit flip noise 
     Letting H s =0.02δ z ,C xx (0)=0.01, δt=0.04, a frequency spectrum of a quantum noise process (equivalent to a bath noise spectrum) is obtained through a TTM method for a free evolution of a single qubit. In this case, the noise is no longer a pure phase decoherence noise. As shown in  FIG. 6 , a correlation function C xx (t)= B x (t)B x (0)  presented by a circle which is obtained from a memory kernel of a TTM well coincides with a real noise spectrum presented by line  61 . This group of simulation indicates that when the influence of the bath noise exceeds that of pure dephasing, for example, B x (t), B y (t), the method of deducing a noise spectrum from a memory kernel of a TTM is still applicable. 
     Case 4: TTM results of free evolutions of two qubits in two double-qubit pure dephasing models 
     Part (a) in  FIG. 7  shows TTM results of free evolutions of two qubits coupled to each other in a direction z when the two qubits are located in respective independent bath noises. 
     A system Hamiltonian is: H s =ω 1 σ 1   z +ω 2 σ 2   z +ω 12 σ 1   z σ 2   z ,ω 2 =0.1,ω 12 =0.05. 
     A bath Hamiltonian is: H=B 1   z (t)σ 1   z +B 2   z (t)σ 2   z , 
     A correlation function is: C zz (0)= B 1   z (t)B 1   z (0) = B 2   z (t)B 2   z (0) =1, B 1   z (t)B 2   z (t′) =0,δt=0.2. 
     Line  71 , line  72  and line  73  represent a full TTM T n , a separable TTM  T   n  and a correlated TTM δT n , respectively. As shown in the figure, only the first item, that is, δT 1 , in the correlated TTM is non-trivial. The result indicates that in an independent noise bath, a correlated part of a TTM is almost Markovian. Further, it can be learned through analysis that an entanglement of two qubits generated by δL s  leads to a correlated decoherence effect even if noise sources are separated or independent of each other in sapce. 
     Part (b) in  FIG. 7  shows TTM results of free evolutions of two qubits not directly coupled to each other when the two qubits are located in correlated bath noises. 
     A system Hamiltonian is: H s =ω 1 σ 1   z +ω 2 σ 2   z ω 1 =ω 2 =0.1 
     A bath Hamiltonian is: H sb =B 1   z (t)σ 1   z +B 2   z (t)σ 2   z ,C zz (0)= B 1   z (t)B 1   z (0) = B 2   z (t)B 2   z (0) = B 1   z (t)B 2   z (t′) =1,δt=0.2. 
     Line  74 , line  75  and line  76  represent a full TTM T n , a separable TTM  T   n  and a correlated TTM δT n , respectively. In this case, a plurality of δT n  are non-trivial. It may be found through analysis that δK(t 1 ) is the main contributing factor of δT 1 . Therefore, relative importance of different physical mechanisms that cause collective decoherence can be estimated directly according to the norm distribution of TTMs over time. 
     Case 5: prediction effectiveness of dynamics of an open system of double-qubit TTMs. 
     To investigate the importance of δT n ,  FIG. 8  presents a dynamical evolution of non-diagonal matrix elements of a density matrix of two qubits. Prediction results of TTMs whose lengths are (that is, K is) 1, 8, and 16 in a physical state are compared with a real dynamical simulation result. Parts (a) and (b) in  FIG. 8  respectively present prediction results for |ψ(0) =(|00 +|10 )/√{square root over (2)} based on a full TTM and a separable TTM in a first model. Parts (c) and (d) in  FIG. 8  respectively present prediction results for |ψ(0) =(|01 +|10 )/√{square root over (2)} based on a full TTM and a separable TTM in a second model. In both the two cases, the effect of collective decoherence cannot be described by using  T   n  alone. In  FIG. 7 , δT n  is very small, and has little influence. However, as can be seen from  FIG. 8 , δT n  still plays an important role in the prediction of the physical state. This further proves the complex characteristics of a highly non-Markovian system. 
     Additionally, to verify the practicability of the technical solution of this disclosure, tests have been conducted on IBM Quantum Experience. IBM Quantum Experience is a superconducting quantum computing cloud platform provided by IBM, and all computations are run on a real superconducting quantum computer. For a superconducting qubit, because the time for operating a quantum gate is too long (about 100 ns) relative to the correlation time of the bath and the noise process is not pure phase decoherence, the method of extracting a frequency spectrum based on dynamical decoupling of CPMG is inapplicable. 
       FIG. 9  shows research on TTMs of a free evolution of a single qubit on an IBM quantum computing cloud platform “IBM 16 Melbourne”, where δt=2.2 μs. Part (a) in  FIG. 9  shows the norm distribution of TTMs over time. Part (b) in  FIG. 9  shows a dynamical evolution of a state |1 , and line  91  is an experimental result. Line  92 , line  93  and line  94  are respective prediction results for an evolution of |1  when (1, 3, and 5) TTMs are taken respectively. It may be seen that the time scale of the memory kernel is in the order of magnitude of μs, which is not short compared with the quantum gate time of 100 ns. 
       FIG. 10  shows the distribution of a Bloch volume V(t) of a single qubit over time. A transient increase demonstrates the non-Markov characteristics of the quantum system. 
       FIG. 11  shows a dynamic decoupling (DD) evolution of a single qubit on an IBM quantum computing cloud platform “IBM 16 Melbourne”, where δt=2.64 μs. Measurement results of four initial states (a) |ψ(0) =|0 , (b) |ψ(0) =|1 , (c) |ψ(0) =(|0 +|1 )/√{square root over (2)} and (d) |ψ(0) =(|0 +i|1 )/√{square root over (2)} in three spinning directions under the XY4DD protocol are shown. Extension of quantum coherence may be observed. 
       FIG. 12  shows a dynamic decoupling (DD) evolution of a single qubit on an IBM quantum computing cloud platform “IBM 16 Melbourne”, where δt=2. 64 μs. The norm distribution of TTMs over time under the XY4DD protocol is shown. An internal mechanism of extension of quantum coherence may be reflected by this TTM: an effective noise under the XY4DD protocol is more Markovian than a result of a free evolution. 
       FIG. 13  shows research on a TTM of a free evolution of two qubits on an IBM quantum computing cloud platform “IBM 16 Melbourne”, where δt=2. 2 μs. The norm distribution of a full TTM |T n |, a separable TTM | T   n |, and a correlated TTM |δT n | over time is shown. It may be seen that in this group of experiments, the TTMs are all non-trivial in a relatively long time scale, and have relatively strong non-Markov properties. With reference to the result of numerical simulation, it may be preliminarily considered that there are inter-bit coupling and a bath noise correlation between two neighboring bits on the IBM quantum cloud platform. 
       FIG. 14  shows research on TTMs of free evolutions of two qubits on an IBM quantum computing cloud platform “IBM 16 Melbourne”, where δt=2.2 μs. The black line with black dots is an experimental result of an evolution of a density matrix, and three lines represented with circles, triangles and squares are respectively results of predicting an evolution of a density matrix by selecting (1, 2, and 4) TTMs respectively. Parts (a) and (b) in  FIG. 14  respectively present prediction results based on a full TTM and a separable TTM when the initial state is a non-entangled state |ψ(0) =(|11 +|10 )/√{square root over (2)}. Parts (c) and (d) in  FIG. 14  respectively present prediction results based on a full TTM and a separable TTM when an initial state is an entangled state |ψ(0) =(|00 +|11 )/√{square root over (2)}. It can be learned that if no correlated TTM is included, the evolution cannot be accurately predicted either in the entangled state or in the non-entangled state. Through a further analysis of δT 1 , it may be seen that δL s  makes an important contribution, indicating that the two qubits are coupled to each other. 
     The following is an apparatus embodiment of this disclosure, which can be used to execute the method embodiments of this disclosure. For details that are not disclosed in the apparatus embodiments of this disclosure, refer to the method embodiments of this disclosure. 
       FIG. 15  is a block diagram of a quantum noise process analysis apparatus according to an embodiment of this disclosure. The apparatus has functions of implementing the foregoing method embodiments. The functions may be implemented by hardware, or may be implemented by hardware executing corresponding software. The apparatus may be a computer device, or may be disposed in a computer device. The apparatus  1500  may include: an obtaining module  1510 , an extraction module  1520 , and an analysis module  1530 . 
     The obtaining module  1510  is configured to perform quantum process tomography (QPT) on a quantum noise process of a target quantum system, to obtain dynamical maps of the quantum noise process. 
     The extraction module  1520  is configured to extract TTMs of the quantum noise process from the dynamical maps, the TTMs being used for representing a dynamical evolution of the quantum noise process. 
     The analysis module  1530  is configured to analyze the quantum noise process according to the TTMs. 
     To sum up, in the technical solutions provided in this disclosure, QPT is performed on a quantum noise process, to obtain dynamical maps of the quantum noise process, and a TTM of the quantum noise process is further extracted from the dynamical maps of the quantum noise process. The TTM is used for representing a dynamical evolution of the quantum noise process, that is, reflecting the law of evolution of the dynamical maps of the quantum noise process over time. Compared with pure QPT, this disclosure can obtain richer and more comprehensive information about the quantum noise process. Therefore, when the quantum noise process is analyzed based on the TTM of the quantum noise process, a more accurate and comprehensive analysis of the quantum noise process can be achieved based on the richer and more comprehensive information. 
     In some possible designs, the dynamical maps include dynamical maps of the quantum noise process at K time points, K being a positive integer; and the extraction module  1520  is configured to calculate TTMs of the quantum noise process at the K time points according to the dynamical maps of the quantum noise process at the K time points. 
     In some possible designs, the extraction module  1520  is configured to calculate a TTM T n  of the quantum noise process at an n th  time point according to the following formula: 
     
       
         
           
             
               
                 T 
                 n 
               
               ≡ 
               
                 
                   ɛ 
                   n 
                 
                 - 
                 
                   
                     ∑ 
                     
                       m 
                       = 
                       1 
                     
                     
                       n 
                       - 
                       1 
                     
                   
                    
                   
                     
                       T 
                       
                         n 
                         - 
                         m 
                       
                     
                      
                     
                       ɛ 
                       m 
                     
                   
                 
               
             
             , 
           
         
       
     
     where T 1 =ε 1 , ε n  represents a dynamical map of the quantum noise process at the n th  time point, ε m  represents a dynamical map of the quantum noise process at an m th  time point, and T n−m  represents a TTM of the quantum noise process at an (n−m) th  time point, both n and m being positive integers. 
     In some possible designs, as shown in  FIG. 16 , the analysis module  1530  includes a Markov determination sub-module  1531 . 
     The Markov determination sub-module  1531  is configured to: 
     determine that the quantum noise process is a Markov process when each of moduli of TTMs of the quantum noise process at first time points is less than a preset threshold, the first time points being time points other than the foremost time point of the K time points; and 
     determine that the quantum noise process is a non-Markov process when a modulus of a TTM of the quantum noise process at a second time point is greater than the preset threshold, the second time point being at least one time point other than the foremost time point of the K time points. 
     In some possible designs, as shown in  FIG. 16 , the analysis module  1530  includes a state evolution prediction sub-module  1532 . 
     The state evolution prediction sub-module  1532  is configured to predict a state evolution of the quantum noise process within a subsequent time according to the TTMs at the K time points. 
     In some possible designs, the state evolution prediction sub-module  1532  is configured to calculate a quantum state ρ(t n ) of the quantum noise process at an n th  time point t n  according to the following formula: 
     
       
         
           
             
               
                 ρ 
                  
                 
                   ( 
                   
                     t 
                     n 
                   
                   ) 
                 
               
               = 
               
                 
                   ∑ 
                   
                     m 
                     = 
                     1 
                   
                   
                     n 
                     - 
                     1 
                   
                 
                  
                 
                   
                     T 
                     m 
                   
                    
                   
                     ρ 
                      
                     
                       ( 
                       
                         t 
                         
                           n 
                           - 
                           m 
                         
                       
                       ) 
                     
                   
                 
               
             
             , 
           
         
       
     
     where T m  represents a TTM at an m th  time point, and ρ(t n−m ) represents a quantum state at an (n−m) th  time point t n−m , both n and m being positive integers. 
     In some possible designs, as shown in  FIG. 16 , the analysis module  1530  includes: 
     a memory kernel extraction sub-module  1533 , configured to extract a second-order memory kernel of the quantum noise process according to the TTMs when the quantum noise process is a steady noise; 
     a correlation function calculation sub-module  1534 , configured to calculate a correlation function of the quantum noise process according to the second-order memory kernel of the quantum noise process; and 
     a frequency spectrum obtaining sub-module  1535 , configured to perform a Fourier transform on the correlation function of the quantum noise process, to obtain a frequency spectrum of the quantum noise process. 
     In some possible designs, the memory kernel extraction sub-module  1533  is configured to: select N different parameters, perform an experiment on the quantum noise process, and extract memory kernels respectively corresponding to the N different parameters from the experiment; and perform calculation according to the memory kernels respectively corresponding to the N different parameters, to obtain the second-order memory kernel of the quantum noise process. 
     In some possible designs, the correlation function calculation sub-module  1534  is configured to numerically extract the correlation function of the quantum noise process according to the following formula: 
     
       
         
           
             
               
                 argmin 
                 
                   
                     C 
                     
                       αα 
                       ′ 
                     
                   
                    
                   
                     ( 
                     
                       t 
                       n 
                     
                     ) 
                   
                 
               
                
               
                 { 
                 
                   
                      
                     
                       
                         
                           κ 
                           2 
                         
                          
                         
                           ( 
                           
                             
                               t 
                               n 
                             
                             ; 
                             
                               
                                 C 
                                 
                                   αα 
                                   ′ 
                                 
                               
                                
                               
                                 ( 
                                 
                                   t 
                                   n 
                                 
                                 ) 
                               
                             
                           
                           ) 
                         
                       
                       - 
                       
                         
                           κ 
                           exp 
                         
                          
                         
                           ( 
                           
                             t 
                             n 
                           
                           ) 
                         
                       
                     
                      
                   
                   + 
                   
                     
                       ( 
                       
                         1 
                         - 
                         
                           δ 
                           
                             
                               t 
                               n 
                             
                             , 
                             
                               t 
                               0 
                             
                           
                         
                       
                       ) 
                     
                      
                     
                       λ 
                       n 
                     
                      
                     
                       
                         ∑ 
                         
                           α 
                           , 
                           
                             α 
                             ′ 
                           
                         
                       
                        
                       
                          
                         
                           
                             
                               C 
                               
                                 αα 
                                 ′ 
                               
                             
                              
                             
                               ( 
                               
                                 t 
                                 n 
                               
                               ) 
                             
                           
                           - 
                           
                             
                               C 
                               
                                 αα 
                                 ′ 
                               
                             
                              
                             
                               ( 
                               
                                 t 
                                 
                                   n 
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                               ) 
                             
                           
                         
                          
                       
                     
                   
                 
                 } 
               
             
             , 
           
         
       
     
     where κ 2  represents the second-order memory kernel of the quantum noise process, t n  represents the n th  time point, κ exp  is a second-order correlation function at the n th  time point, κ exp  represents an approximate second-order memory kernel obtained through an experiment, δ t     n     ,t     0    represents an interval between the n th  time point and an initial moment, λ n  is an adjustable parameter, and C αα′ (t n−1 ) is a second-order correlation function at an (n−1) th  time point t n−1 . 
     In some possible designs, as shown in  FIG. 16 , the analysis module  1530  includes a correlated noise analysis sub-module  1536 . 
     The correlated noise analysis sub-module  1536  is configured to calculate, for s quantum devices included in the target quantum system, a correlated TTM among the s quantum devices according to TTMs respectively corresponding to the s quantum devices, s being an integer greater than 1; and analyze a source of a correlated noise among the s quantum devices according to the correlated TTM. 
     When the apparatus provided in the foregoing embodiments implements its functions, a description is given only by using the foregoing division of function modules as an example. In actual applications, the functions may be allocated to and implemented by different function modules according to the requirements, that is, the internal structure of the device may be divided into different function modules, to implement all or some of the functions described above. In addition, the apparatus and method embodiments provided in the foregoing embodiments follow similar underlying principles. For the specific implementation process, refer to the method embodiments, so the details are not described herein again. 
       FIG. 17  is a schematic structural diagram of a computer device according to an embodiment of this disclosure. The computer device is configured to implement the quantum noise process analysis method provided in the foregoing embodiments. Specifically: 
     The computer device  1700  includes a central processing unit (CPU)  1701 , a system memory  1704  including a random access memory (RAM)  1702  and a read-only memory (ROM)  1703 , and a system bus  1705  connecting the system memory  1704  and the CPU  1701 . The computer device  1700  further includes a basic input/output system (I/O system)  1706  configured to transmit information between components in the computer, and a mass storage device  1707  configured to store an operating system  1713 , an application program  1714 , and other program module  1715 . 
     The basic I/O system  1706  includes a display  1708  configured to display information and an input device  1709  configured for a user to input information, such as a mouse or a keyboard. The display  1708  and the input device  1709  are both connected to the CPU  1701  by an input/output controller  1710  connected to the system bus  1705 . The basic I/O system  1706  may further include the input/output controller  1710 , to receive and process inputs from multiple other devices, such as a keyboard, a mouse, or an electronic stylus. Similarly, the input/output controller  1710  further provides an output to a display screen, a printer, or other type of output device. 
     The mass storage device  1707  is connected to the CPU  1701  by a mass storage controller (not shown) connected to the system bus  1705 . The mass storage device  1707  and an associated computer-readable medium provide non-volatile storage for the computer device  1700 . That is, the mass storage device  1707  may include a computer-readable medium (not shown), such as a hard disk or a CD-ROM drive. 
     Without loss of generality, the computer-readable medium may include a computer storage medium and a communication medium. The computer storage medium includes volatile and non-volatile, removable and non-removable media implemented by using any method or technology for storing information such as computer-readable instructions, data structures, program modules, or other data. The computer storage medium includes a RAM, a ROM, an EPROM, an EEPROM, a flash memory, or other solid-state storage technique, a CD-ROM, a DVD, or other optical storage, a magnetic cassette, a magnetic tape, a magnetic disk storage, or other magnetic storage device. Certainly, it is known to a person skilled in the art that the computer storage medium is not limited to the foregoing types. The system memory  1704  and the mass storage device  1707  may be collectively referred to as a memory. 
     According to the embodiments of this disclosure, the computer device  1700  may further be connected, through a network such as the Internet, to a remote computer on the network. That is, the computer device  1700  may be connected to a network  1712  by a network interface unit  1711  connected to the system bus  1705 , or may be connected to another type of network or remote computer system (not shown) by a network interface unit  1711 . 
     The memory stores at least one instruction, at least one section of program, a code set or an instruction set, and the at least one instruction, the at least one section of program, the code set or the instruction set is configured to be executed by one or more processors to implement the quantum noise process analysis method provided in the foregoing embodiments. 
     In an exemplary embodiment, a computer-readable storage medium is further provided, the storage medium storing at least one instruction, at least one program, a code set or an instruction set, the at least one instruction, the at least one program, the code set or the instruction set being executed by a processor of a computer device to implement the quantum noise process analysis method provided in the foregoing embodiments. In an exemplary embodiment, the computer-readable storage medium may be a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, or an optical data storage device 
     In an exemplary embodiment, a computer program product is provided. When executed, the computer program product is configured to implement the quantum noise process analysis method provided in the foregoing embodiments. 
     It is to be understood that “plurality of” mentioned in this specification means two or more. “And/or” describes an association relationship between associated objects and means that three relationships may exist. For example, A and/or B may represent the following three cases: Only A exists, both A and B exist, and only B exists. The character “/” in this specification generally indicates an “or” relationship between the associated objects. In addition, the step numbers described in this specification merely exemplarily show a possible execution order of the steps. In some other embodiments, the steps may not be performed according to the order of the numbers. For example, two steps denoted by different numbers may be performed simultaneously, or two steps denoted by different numbers may be performed in an order that is reverse to that shown in the figure, which is not limited in the embodiments of this disclosure. 
     The foregoing descriptions are merely examples of the embodiments of this disclosure, but are not intended to limit this disclosure. Any modification, equivalent replacement, or improvement made without departing from the spirit and principle of this disclosure shall fall within the protection scope of this application.