Optimization method and device for joint reading signal of quantum bits, and quantum computer

Abstract

The application provides an optimization method for a joint reading signal of a quantum bit, and the optimization method comprises the following steps: determining a parameter initial value of a parameter in a joint reading signal to be optimized based on a quantum bit to be jointly read; generating at least one initial joint reading signal with the parameter initial value; obtaining a first reading fidelity of each quantum bit when the initial joint reading signal acts on the quantum bit to be jointly read; obtaining a loss function value corresponding to the initial joint reading signal, the loss function value being used to represent a difference between the first reading fidelity of all quantum bits and a theoretical value of the first reading fidelity; optimizing the value of the parameter based on the loss function value, and returning to the step of generating the initial joint reading signal until the loss function value converges. The technical scheme of the application can improve the optimization efficiency of the joint reading signal.

Description

Technical Field

[0001] This invention belongs to the field of quantum computing, and in particular relates to an optimization method, apparatus and quantum computer for joint readout of quantum bits. Background Technology

[0002] Quantum bit information refers to the quantum state possessed by a quantum bit. The basic quantum states are the |0> state and the |1> state. After a quantum bit is manipulated, its quantum state changes. On a quantum chip, this is reflected in the change of the quantum state possessed by the quantum bit after the quantum chip is executed, which is the execution result of the quantum chip. This execution result is carried and transmitted by the quantum bit read signal (usually an analog signal).

[0003] The process of rapidly measuring the quantum state of a qubit using its readout signal is crucial for understanding the performance of quantum chips. High fidelity in qubit measurement results has always been a key objective pursued by the quantum computing industry. The parameters of the qubit readout signal significantly impact the fidelity of the measurement results. To achieve high qubit readout fidelity, the parameters of the qubit readout signal need to be optimized to obtain the optimal parameters.

[0004] Current technology is relatively mature in determining the measurement results of a single qubit that is unaffected by other qubits. However, multiple correlated qubits have a more practical and broader application prospect, making the determination of measurement results for multiple correlated qubits running quantum computing tasks particularly important. Joint readout signals can simultaneously read the quantum state information of multiple qubits; however, the readout fidelity of existing joint readout signals still differs to some extent from the readout fidelity of individual qubit readouts, necessitating optimization of the joint readout signals.

[0005] Existing optimization methods for joint readout signals directly use fidelity as the evaluation criterion, resulting in low optimization efficiency. To improve optimization efficiency while achieving ideal readout fidelity, an optimization method for qubit joint readout signals is needed.

[0006] It should be noted that the information disclosed in the background section of this application is intended only to enhance the understanding of the general background of this application, and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0007] The purpose of this invention is to provide an optimization method, apparatus, and quantum computer for joint readout signals of qubits, in order to solve the problem of low optimization efficiency of joint readout signals in the prior art.

[0008] To achieve the above objectives, in a first aspect, the present invention provides an optimization method for joint readout signals of quantum bits, the optimization method comprising:

[0009] The initial values ​​of the parameters in the joint readout signal to be optimized are determined based on the qubits to be jointly read.

[0010] Generate at least one initial joint readout signal having the initial value characteristics of the parameters;

[0011] The first read fidelity of each qubit is obtained when the initial joint read signal is applied to the qubit to be jointly read;

[0012] The loss function values ​​corresponding to the initial joint readout signals are obtained respectively. The loss function values ​​are used to represent the difference between the first readout fidelity of all qubits and the theoretical value of the first readout fidelity.

[0013] The parameter values ​​are optimized based on the loss function value, and the process returns to the step of generating the initial joint readout signal until the loss function value converges.

[0014] Optionally, the parameters include any one or more of the following: power value, frequency value corresponding to the qubit to be jointly read, and amplitude value corresponding to the qubit to be jointly read.

[0015] Optionally, when the number of qubits to be jointly read is N, the number of parameters is 2N+1.

[0016] Optionally, the number of initial joint read signals generated is greater than the number of parameters.

[0017] Optionally, obtaining the loss function value corresponding to the initial joint readout signal includes:

[0018] The loss function value corresponding to the initial joint readout signal is obtained based on the cross-entropy loss function, wherein the cross-entropy loss function is:

[0019]

[0020] Where, p i Let q be the theoretical value of the first read fidelity of the i-th qubit. i Let H be the first read fidelity of the i-th qubit, and let H represent the cross-entropy.

[0021] Optionally, optimizing the parameter value based on the loss function value includes:

[0022] The values ​​of the parameters are updated using a global optimization algorithm based on the initial values ​​of the parameters and their corresponding loss function values.

[0023] Optionally, updating the parameter values ​​using a global optimization algorithm based on the initial values ​​of the parameters and their corresponding loss function values ​​includes:

[0024] The initial values ​​of the parameters and their corresponding loss function values ​​are used as the initial values ​​for the Nelder-Mead algorithm, and the Nelder-Mead algorithm is used to update the values ​​of the parameters.

[0025] Optionally, the loss function value includes the loss function value obtained using the logarithmic loss function.

[0026] Optionally, the theoretical value of the first read fidelity includes the second read fidelity when the qubit to be jointly read is read individually.

[0027] Secondly, this application provides a readable storage medium having a computer program stored thereon, which, when executed, enables the optimization method for the joint readout signal of qubits provided in the first aspect of this application.

[0028] Thirdly, this application provides an optimization device for joint readout signals of quantum bits, the optimization device comprising:

[0029] The initial value acquisition module is configured to determine the initial values ​​of the parameters in the joint readout signal to be optimized based on the qubits to be jointly read.

[0030] A signal generation module is configured to generate at least one initial joint readout signal having the initial value characteristics of the parameters;

[0031] A fidelity acquisition module is configured to obtain the first read fidelity of each qubit when the initial joint read signal is applied to the qubit to be jointly read;

[0032] The loss function value acquisition module is configured to acquire the loss function values ​​corresponding to the initial joint readout signals respectively. The loss function values ​​are used to represent the difference between the first readout fidelity of all qubits and the theoretical value of the first readout fidelity.

[0033] An optimization module is configured to optimize the value of the parameters based on the loss function value and return to the step of generating the initial joint readout signal until the loss function value converges.

[0034] Fourthly, this application provides a quantum computer, including the optimized apparatus for the joint readout signal of the qubits provided in the third aspect of this application.

[0035] Compared with the prior art, the technical solution of this application has the following beneficial effects:

[0036] The proposed optimization method for qubit joint readout signals utilizes loss function values ​​as evaluation criteria. Based on these loss function values, the joint readout signals of the qubits to be jointly read are optimized, thereby improving the optimization efficiency of the joint readout signals. The first readout fidelity obtained through joint readout is converted into a loss function value, and the joint readout signals are optimized based on this value. The smaller the loss function value, the better the optimization effect, which more intuitively reflects the optimization effect of joint readout and helps to improve optimization efficiency.

[0037] The readable storage medium, the optimization device for the joint readout signal of the quantum bits, and the optimization method for the joint readout signal of the quantum computer and the quantum bits proposed in this application belong to the same inventive concept and therefore have the same beneficial effects, which will not be elaborated here. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a flowchart illustrating an optimized method for the joint readout of quantum bits according to an embodiment of this application;

[0040] Figure 2 This is a schematic diagram of the connection structure of an optimized device for jointly reading the quantum bit signal according to an embodiment of this application. Detailed Implementation

[0041] The specific embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. The advantages and features of the present invention will become clearer from the following description and claims. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present invention.

[0042] In the description of this invention, it should be understood that the terms "center", "upper", "lower", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0043] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0044] This application provides an optimized method for joint readout of quantum bits, referring to... Figure 1 As shown, Figure 1 This is a flowchart illustrating the optimization method for the joint readout signal of qubits provided in the embodiments of this application. Figure 1 As can be seen from this, the optimization method includes:

[0045] Step S1: Determine the initial values ​​of the parameters in the joint readout signal to be optimized based on the qubits to be jointly read;

[0046] Step S2: Generate at least one initial joint readout signal having the characteristics of the initial values ​​of the parameters;

[0047] Step S3: Obtain the first readout fidelity of each qubit when the initial joint readout signal is applied to the qubit to be jointly read;

[0048] Step S4: Obtain the loss function value corresponding to the initial joint readout signal respectively. The loss function value is used to represent the difference between the first readout fidelity of all qubits and the theoretical value of the first readout fidelity.

[0049] Step S5: Optimize the value of the parameter based on the loss function value, and return to the step of generating the initial joint readout signal until the loss function value converges.

[0050] The optimization method described in this application uses the loss function value as an evaluation criterion to optimize the joint reading signal of the qubits to be jointly read, thereby improving the optimization efficiency of the joint reading signal. The first reading fidelity obtained by joint reading is converted into a loss function value, and the joint reading signal is optimized based on the loss function value. The smaller the loss function value, the better the optimization effect, which can more intuitively reflect the effect of joint reading optimization and is conducive to improving optimization efficiency.

[0051] In step S1, the qubits to be jointly read are generally integrated on a quantum chip. Other qubits may also be integrated on the quantum chip, but these other qubits do not participate in the joint reading. The quantum chip also generally integrates a readout resonant cavity, a qubit frequency control line, and a qubit state control line, all coupled to each qubit. A readout signal is sent to the readout resonant cavity via a readout signal transmission line, and readout feedback signals reflected or transmitted from the readout resonant cavity are received. By analyzing the readout feedback signals, the quantum state information of the corresponding qubit can be obtained. The qubit frequency control line is used to transmit a bias voltage signal and / or a pulse bias control signal. Both the bias voltage signal and the bias control signal can control the qubit frequency of the corresponding qubit. The qubit state control line is used to transmit a qubit state control signal, which can control the state of the corresponding qubit.

[0052] In step S1, the joint readout signal is used to simultaneously read the quantum state information of the qubits to be jointly read. Specifically, all the qubits to be jointly read are coupled to a readout resonant cavity, and a readout signal transmission line is coupled to the readout resonant cavity to which all the qubits to be jointly read are coupled. The joint readout signal is sent to the readout signal transmission line to obtain a joint readout feedback signal, and the joint readout feedback signal is analyzed to obtain the quantum state information of the qubits to be jointly read.

[0053] The joint readout signal is generated by determining the initial values ​​of its parameters, generating an initial waveform by an AWG waveform generator, and then up-converting it through a mixer.

[0054] Specifically, in step S1, the initial parameter values ​​include any one or more of the following: power value, frequency value corresponding to the qubit to be jointly read, and amplitude value corresponding to the qubit to be jointly read. That is, one or more of these parameters can be optimized according to optimization needs.

[0055] In some embodiments, the number of qubits to be jointly read is N, and the number of parameters is 2N+1, meaning that optimization is performed for all of the parameters.

[0056] In step S2, at least one initial joint readout signal is generated to provide at least one set of first readout fidelities for all the qubits to be jointly read during the joint readout process. This facilitates analysis of the first readout fidelity and optimization based on the initial joint readout signal, resulting in an optimized joint readout signal with a higher first readout fidelity. Correspondingly, when there is more than one initial joint readout signal, a corresponding number of initial values ​​should be assigned to the same parameter in step S1 to generate a corresponding number of initial joint readout signals with different initial values ​​for the same parameter, optimized for that parameter.

[0057] In some embodiments of this application, the number of initial joint read signals generated is greater than the number of parameters, in order to provide more data that can be analyzed, reduce the difficulty of optimization, and improve the efficiency of optimization.

[0058] Step S3 involves applying the initial joint readout signal to the readout signal transmission line to obtain a set of first readout fidelities. Furthermore, when there is more than one initial joint readout signal, each initial joint readout signal needs to be applied to the readout signal transmission line separately to obtain multiple sets of first readout fidelities encompassing all the qubits to be jointly read during the joint readout process. This allows for analysis of multiple sets of first readout fidelities and optimization based on multiple initial joint readout signals.

[0059] In step S4, the reading effect of the initial joint readout signal is evaluated using a loss function value, which is obtained based on the first readout fidelity and its theoretical value obtained in step S3. Furthermore, when there is more than one initial joint readout signal, the loss function value corresponding to each initial joint readout signal needs to be obtained separately.

[0060] In some embodiments, the second read fidelity when the qubit to be jointly read is read individually can be used as the theoretical value of the first read fidelity. That is, the optimal result of the optimization is that the reading effect of the jointly read signal can reach the level of single-bit reading.

[0061] The loss function value can represent the quality of each set of initial joint readout signals. Specifically, the smaller the loss function value, the better the readout effect of the corresponding initial joint readout signal.

[0062] Since each group of first read fidelity includes the first read fidelity of all the qubits to be jointly read during the joint read process, the amount of data is large. In addition, when there are many parameters to be optimized, the number of initial joint read signals to be generated is also larger, and the number of first read fidelities to be obtained is also larger, which is not conducive to observing the quality of the initial joint read signal corresponding to each group of initial parameter values. Therefore, each group of first read fidelity is converted into a loss function value, so that each group of initial joint read signals corresponds to a loss function value. The smaller the loss function value, the better the read effect, which makes it easier to judge the quality of the initial joint read signal under a set of initial parameter values ​​more quickly, thereby improving optimization efficiency.

[0063] Specifically, obtaining the loss function value includes: obtaining the loss function value corresponding to the initial joint readout signal based on the cross-entropy loss function, wherein the cross-entropy loss function is:

[0064]

[0065] Where, p i Let q be the theoretical value of the first read fidelity of the i-th qubit. i Let H be the first read fidelity of the i-th qubit, and let H represent the cross-entropy.

[0066] The cross-entropy loss function can effectively evaluate the difference between the first read fidelity and the theoretical value of the first read fidelity.

[0067] In some embodiments, a logarithmic loss function may also be used to obtain the loss function value of the initial joint readout signal.

[0068] In step S5, the value of the parameter is optimized based on the loss function value, and the process returns to the step of generating multiple initial joint readout signals until the loss function value converges.

[0069] Specifically, it can be set that when the loss function value is less than a first preset value, the initial joint reading signal corresponding to the loss function value at this time is considered to meet the fidelity requirements of the joint reading signal, and the value of the parameter of the initial joint reading signal at this time is used as the value of the optimized parameter.

[0070] In some embodiments, optimizing the parameter value based on the loss function value includes:

[0071] The values ​​of the parameters are updated using a global optimization algorithm based on the initial values ​​of the parameters and their corresponding loss function values.

[0072] Global optimization algorithms generally have a rigorous theoretical basis, rather than relying solely on expert experience. Theoretically, they can find the optimal solution or a near-optimal solution within a certain time.

[0073] Specifically, the initial values ​​of the parameters and their corresponding loss function values ​​are used as the initial values ​​for the Nelder-Mead algorithm, and the Nelder-Mead algorithm is used to update the values ​​of the parameters.

[0074] The Nelder-Mead algorithm is an algorithm for finding local minima of a multivariate function. Its advantage is that it does not require the function to be differentiable and can converge to a local minimum relatively quickly. In this embodiment, the direct relationship between the initial parameter values ​​of the initial joint readout signal and the loss function value is unknown. The relationship between the parameter values ​​and the loss function value is indirectly established through the first readout fidelity. Therefore, the Nelder-Mead algorithm is very suitable for optimizing the initial joint readout signal in this embodiment.

[0075] Based on the same inventive concept, this application also provides an optimized device for joint readout signals of quantum bits, see reference. Figure 2 , Figure 2 This is a schematic diagram of the structure of the optimization device for the quantum bit readout signal provided in the embodiments of this application. The optimization device includes:

[0076] The initial value acquisition module 110 is configured to determine the initial values ​​of the parameters in the joint readout signal to be optimized based on the qubits to be jointly read.

[0077] Signal generation module 120 is configured to generate at least one initial joint readout signal having the initial value characteristics of the parameters;

[0078] The fidelity acquisition module 130 is configured to acquire the first read fidelity of each qubit when the initial joint read signal is applied to the qubit to be jointly read;

[0079] The loss function value acquisition module 140 is configured to acquire the loss function values ​​corresponding to the initial joint readout signals respectively. The loss function values ​​are used to represent the difference between the first readout fidelity of all qubits and the theoretical value of the first readout fidelity.

[0080] The optimization module 150 is configured to optimize the value of the parameter based on the loss function value and return to the step of generating the initial joint readout signal until the loss function value converges.

[0081] Based on the same inventive concept, this application also provides a readable storage medium storing a computer program thereon, which, when executed, can implement the optimized method for the joint readout signal of quantum bits provided in an embodiment of this application.

[0082] Based on the same invention, this application also provides a quantum computer, which includes an optimization device for the joint readout signal of the qubits provided in an embodiment of this application.

[0083] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," or "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0084] The above are merely preferred embodiments of the present invention and do not constitute any limitation on the present invention. Any equivalent substitutions or modifications made by those skilled in the art to the technical solutions and content disclosed in the present invention without departing from the scope of the present invention shall be deemed to have remained within the protection scope of the present invention.

Claims

1. An optimized method for joint readout of quantum bits signals, characterized in that, The optimization method includes: The initial values ​​of the parameters in the joint readout signal to be optimized are determined based on the qubits to be jointly read. An initial waveform is generated based on the initial values ​​of the parameters, and then up-converted by a mixer to generate at least one initial joint readout signal; The first read fidelity of each qubit is obtained when the initial joint read signal is applied to the qubit to be jointly read; The loss function values ​​corresponding to the initial joint readout signals are obtained respectively. The loss function values ​​are used to represent the difference between the first readout fidelity of all qubits and the theoretical value of the first readout fidelity. The parameter values ​​are optimized based on the loss function value, and the process returns to the step of generating the initial joint readout signal until the loss function value converges.

2. The method as described in claim 1, characterized in that, The parameters include any one or more of the following: power value, frequency value corresponding to the qubit to be jointly read, and amplitude value corresponding to the qubit to be jointly read.

3. The method as described in claim 1, characterized in that, When the number of qubits to be jointly read is N, the number of parameters is 2N+1.

4. The method as described in claim 1, characterized in that, The number of initial joint read signals generated is greater than the number of parameters.

5. The method as described in claim 1, characterized in that, The step of obtaining the loss function value corresponding to the initial joint readout signal includes: The loss function value corresponding to the initial joint readout signal is obtained based on the cross-entropy loss function, wherein the cross-entropy loss function is: Where, p i Let q be the theoretical value of the first read fidelity of the i-th qubit. i Let H be the first read fidelity of the i-th qubit, and let H represent the cross-entropy.

6. The method as described in claim 1, characterized in that, The optimization of the parameter values ​​based on the loss function values ​​includes: The values ​​of the parameters are updated using a global optimization algorithm based on the initial values ​​of the parameters and their corresponding loss function values.

7. The method as described in claim 6, characterized in that, The process of updating the parameter values ​​using a global optimization algorithm based on the initial values ​​of the parameters and their corresponding loss function values ​​includes: The initial values ​​of the parameters and their corresponding loss function values ​​are used as the initial values ​​for the Nelder-Mead algorithm, and the Nelder-Mead algorithm is used to update the values ​​of the parameters.

8. The method as described in claim 1, characterized in that, The loss function value includes the loss function value obtained using the logarithmic loss function.

9. The method as described in claim 1, characterized in that, The first theoretical value of read fidelity includes the second read fidelity when the qubit to be read is read individually.

10. A readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed, it can implement the optimized method for the joint readout signal of quantum bits as described in any one of claims 1 to 9.

11. An optimized device for joint readout of quantum bits, characterized in that, The optimization device includes: The initial value acquisition module is configured to determine the initial values ​​of the parameters in the joint readout signal to be optimized based on the qubits to be jointly read. A signal generation module is configured to generate an initial waveform based on the initial value of the parameters, and to generate at least one initial joint readout signal having the characteristics of the initial value of the parameters through up-conversion by a mixer. A fidelity acquisition module is configured to obtain the first read fidelity of each qubit when the initial joint read signal is applied to the qubit to be jointly read; The loss function value acquisition module is configured to acquire the loss function values ​​corresponding to the initial joint readout signals respectively. The loss function values ​​are used to represent the difference between the first readout fidelity of all qubits and the theoretical value of the first readout fidelity. An optimization module is configured to optimize the value of the parameters based on the loss function value and return to the step of generating the initial joint readout signal until the loss function value converges.

12. A quantum computer, characterized in that, The optimized apparatus for joint readout of quantum bits as described in claim 11.

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