Method and apparatus for determining quantum bit relaxation time

Abstract

The application discloses a quantum bit relaxation time determination method and device, and relates to the field of quantum computers, wherein the determination method comprises the following steps: acquiring a data set of Ramsey experiment data; determining the period of the experiment data in the data set and the size of a sliding window according to the period; fitting sub-experiment data in each sliding window in the data set by using a trigonometric periodic function model to obtain the first standard deviation of each sub-experiment data; extracting all sub-experiment data with the first standard deviation less than or equal to a first preset value to obtain a training set; fitting the training set by using a periodic decay function model to obtain the quantum bit relaxation time; the method uses the trigonometric periodic function model to fit the experiment data in the unit of the sliding window, finally obtains an accurate training set, trains the periodic decay function model through the training set, and finally obtains the high-precision quantum bit relaxation time through the high-precision periodic decay function model.

Description

Technical Field

[0001] This invention relates to the field of quantum computing, and in particular to a method and apparatus for determining the relaxation time of a quantum bit. Background Technology

[0002] The relaxation time of a qubit is an important performance indicator. In the testing of quantum chips, the relaxation time of a qubit is generally measured by the Ramsey experiment. The existing measurement scheme directly fits the experimental data by fitting a fitting function. This scheme uses a fixed sampling period as the unit fitting point, which is prone to missing the optimal point within the period. Moreover, the existing fitting scheme is a one-time fitting, which cannot accurately determine the fitting parameters of the fitting function model, resulting in poor fitting accuracy and inability to accurately measure the relaxation time of the qubit. Summary of the Invention

[0003] The purpose of this invention is to provide a high-precision quantum bit relaxation time measurement scheme.

[0004] To achieve the above objectives, the present invention provides a method for determining the relaxation time of a quantum bit, comprising:

[0005] Obtain the dataset of Ramsey's experiments;

[0006] Determine the period of the experimental data in the dataset and determine the size of the sliding window based on the period;

[0007] The first standard deviation of each sub-experiment data is obtained by fitting the sub-experiment data within each sliding window of the dataset using a trigonometric periodic function model.

[0008] The training set is obtained by extracting all sub-experimental data whose first standard deviation is less than or equal to the first preset value.

[0009] The relaxation time of a qubit is obtained by fitting a periodic decay function model to the training set, wherein the relaxation time of the qubit is related to the decay period of the periodic decay function model.

[0010] Optionally, determining the period of the experimental data in the dataset and determining the size of the sliding window based on the period includes:

[0011] Obtain the x-coordinate and y-coordinate values ​​of each experimental data point in the dataset;

[0012] Determine the trend of experimental data based on the ordinate values ​​of adjacent experimental data;

[0013] The period of the experimental data is determined based on the trend of the experimental data.

[0014] The size of the sliding window is determined based on the cycle.

[0015] Optionally: The first preset value is less than or equal to 0.5.

[0016] Optionally: the size of the sliding window is greater than or equal to the maximum period of the experimental data.

[0017] Optionally, the relaxation time of the qubit is obtained by fitting a periodic decay function model to the training set, including:

[0018] The experimental data in the training set is used as input data to train the periodic decay function model;

[0019] The second standard deviation of each experimental data point is obtained by fitting the experimental data within each period using the trained periodic decay function model.

[0020] The training status of the periodic decay function model is determined based on the magnitude of the second standard deviation and the second preset value.

[0021] The relaxation time of a qubit is determined using a trained periodic decay function model.

[0022] Optionally, the second preset value is less than or equal to 0.5.

[0023] Optionally, the trigonometric periodic function model is a sine trigonometric function or a cosine trigonometric function.

[0024] Optionally, the cosine trigonometric function model is as follows:

[0025] y1=A2 cos(ωx+φ)+B2

[0026] In the formula, A2 and B2 are fitting parameters, ω is the oscillation angular frequency, φ is the phase, x is the abscissa value of the experimental data, and y is the ordinate value of the experimental data.

[0027] Optionally, the periodic decay function model is a periodic exponential decay function.

[0028] Optionally, the periodic exponential decay function is:

[0029]

[0030] or

[0031]

[0032] In the formula, A1, A2, B1, and B2 are fitting parameters, T2 is the relaxation time, ω is the oscillation angular frequency, φ is the phase, x and x1 are the abscissas of two adjacent coordinate points of the experimental data in the training set, and y is the ordinate of one coordinate point among two adjacent coordinate points of the experimental data in the training set.

[0033] Based on the same inventive concept, the present invention also provides a device for determining the relaxation time of a quantum bit, comprising:

[0034] The acquisition unit is used to acquire datasets of Ramsey experimental data.

[0035] A determining unit is used to determine the period of experimental data in the dataset and determine the size of the sliding window based on the period;

[0036] The first fitting unit uses a trigonometric periodic function model to fit the sub-experimental data within each sliding window of the dataset to obtain the first standard deviation of each sub-experimental data.

[0037] The extraction unit is used to extract all sub-experimental data whose first standard deviation is less than or equal to a first preset value to obtain a training set.

[0038] The second fitting unit is used to fit the training set with a periodic decay function model to obtain the qubit relaxation time, wherein the qubit relaxation time is related to the decay period of the periodic decay function model.

[0039] Based on the same inventive concept, the present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of a method for determining the relaxation time of a quantum bit as described in any of the above technical solutions.

[0040] The advantages of this invention over the prior art are as follows: This scheme uses a sliding window to fit the experimental data using a triangular periodic function model, which can accurately find the fitting point in each period, extract the experimental data that meets the requirements, and finally obtain an accurate training set. Then, the periodic decay function model is trained using the training set to obtain a high-precision periodic decay function model. Finally, the high-precision periodic decay function model can be used to obtain the high-precision quantum bit relaxation time. Attached Figure Description

[0041] Figure 1 This is a flowchart of a method for determining the relaxation time of a quantum bit according to an embodiment of the present invention;

[0042] Figure 2 This is a flowchart illustrating the determination of a sliding window in one embodiment of the present invention;

[0043] Figure 3 This is an experimental result diagram provided by an embodiment of the present invention, which uses a trigonometric periodic function model to fit the sub-experimental data in each sliding window of the dataset;

[0044] Figure 4 This is a flowchart of the training process for a periodic decay function model provided in an embodiment of the present invention;

[0045] Figure 5 This is a fitting result diagram of the envelope of a trained periodic decay function model provided by an embodiment of the present invention;

[0046] Figure 6 This is a structural diagram of a device for determining the relaxation time of a quantum bit according to an embodiment of the present invention. Detailed Implementation

[0047] The specific embodiments of the present invention will now be described in more detail 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.

[0048] 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.

[0049] 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.

[0050] Reference Figure 1 This embodiment provides a method for determining the relaxation time of a quantum bit, including the following steps:

[0051] Step S100: Obtain the dataset of Ramsey's experimental data.

[0052] The Ramsey experiment is an experimental scheme for measuring the frequency and relaxation time of a qubit. The Ramsey experiment can obtain multiple sets of times and arrays of probabilities of the qubit being excited to the |1> state. By fitting the arrays, the relaxation time of the qubit can be obtained.

[0053] In this embodiment, after obtaining the experimental data from the Ramsey experiment, one or more data packets can be organized into a dataset to facilitate subsequent data processing.

[0054] In some embodiments, after obtaining the Ramsey experimental data, abnormal data can be removed by manual or machine screening, which can improve the accuracy of subsequent data processing.

[0055] Step S200: Determine the period of the experimental data in the dataset and determine the size of the sliding window based on the period.

[0056] The size of the sliding window is determined based on the period of the experimental data, ensuring that the sliding window contains experimental data for at least one period. This ensures that the maximum point of each period can be accurately found during the subsequent fitting process, without missing key data, thus improving the fitting accuracy.

[0057] Reference Figure 2 The specific process for determining the sliding window is as follows:

[0058] Step S201: Obtain the x-coordinate and y-coordinate values ​​of each experimental data in the dataset.

[0059] It should be understood that, since the experimental data of the Ramsey experiment is an array of multiple sets of time and the probability of the qubit being excited to the |1> state, the horizontal axis in this embodiment represents time, and the vertical axis represents the probability of the qubit being excited to the inverted |1> state.

[0060] Step S202: Determine the trend of experimental data based on the ordinate values ​​of adjacent experimental data.

[0061] The trend of experimental data can be determined by the magnitude of the ordinate values ​​of two adjacent experimental data points. For example, if the ordinate value of the next time step is greater than the ordinate value of the current time step, it indicates that the data is in an upward trend; if the ordinate value of the next time step is less than the ordinate value of the current time step, it indicates that the data is in a downward trend.

[0062] Step S203: Determine the period of the experimental data based on the trend of the experimental data.

[0063] When two maxima or two minima are found, the entire cycle can be considered to have ended. The difference between the x-coordinates of the two maxima or two minima is the size of the current cycle.

[0064] Step S204: Determine the size of the sliding window based on the period.

[0065] In this embodiment, in order to ensure that the sliding window can contain experimental data for one period, the sliding window is greater than or equal to the maximum period of the experimental data.

[0066] In other embodiments, in order to reduce the computational cost of each sliding window, the size of the sliding window can also be changed with the period, as long as the sliding window contains at least one period of experimental data.

[0067] Step S300: Use a trigonometric periodic function model to fit the sub-experimental data within each sliding window of the dataset to obtain the first standard deviation of each sub-experimental data.

[0068] It should be understood that the trigonometric periodic function model can be either a sine trigonometric function or a cosine trigonometric function. In this embodiment, a cosine trigonometric function model is used, as detailed below:

[0069] y1=A2 cos(ωx+φ)+B2

[0070] In the formula, A2 and B2 are fitting parameters, ω is the oscillation angular frequency, φ is the phase, x is the abscissa value of the experimental data, and y is the ordinate value of the experimental data.

[0071] It should be understood that the sine trigonometric function can be a transformation of the cosine trigonometric function described above.

[0072] The above trigonometric functions are used to fit each experimental data point within each sliding window, and the first standard deviation of each sub-experimental data point is calculated.

[0073] The standard deviation reflects the fitting accuracy of the trigonometric periodic function model. The accuracy of the fit can be determined by calculating the standard deviation between the fitted data and the experimental data, thereby finding suitable sub-experimental data to be used as the training set.

[0074] It should be noted that the specific calculation method and formula for standard deviation are common knowledge in this field, and therefore will not be elaborated here.

[0075] Reference Figure 3 , Figure 3 The figure provided in this embodiment shows the experimental results after fitting the sub-experimental data in each sliding window of the dataset using a triangular periodic function model. The horizontal axis of the figure represents time in nanoseconds, and the vertical axis represents the probability of the quantum bit being excited into the inverted |1> state. As can be seen from the figure, the fitting curve corresponds roughly to the experimental data when the period is relatively large, but the correspondence is generally poor when the period is reduced. This problem can be solved by adaptively changing the size of the sliding window, which will not be described in detail in this embodiment.

[0076] Step S400: Extract all sub-experimental data whose first standard deviation is less than or equal to the first preset value to obtain the training set.

[0077] In this embodiment, all sub-experimental data with a standard deviation less than or equal to a first preset value are selected as the training set, wherein the first preset value is 0.5.

[0078] It should be noted that the closer the standard deviation is to 0, the higher the fitting accuracy. In some other embodiments, in order to improve the subsequent fitting accuracy, the first preset value can be reduced, for example, to 0.3, 0.2, 0.1, etc.

[0079] Step S500: The relaxation time of the qubit is obtained by fitting the training set with a periodic decay function model, wherein the relaxation time of the qubit is related to the decay period of the periodic decay function model.

[0080] In this embodiment, the periodic decay function model adopts a periodic exponential decay function, as detailed below:

[0081]

[0082] In the formula, A1, A2, B1, and B2 are fitting parameters, T2 is the relaxation time, ω is the oscillation angular frequency, φ is the phase, x and x1 are the abscissas of two adjacent coordinate points of the experimental data in the training set, and y is the ordinate of one coordinate point among two adjacent coordinate points of the experimental data in the training set.

[0083] In other embodiments, the periodic decay function model can adopt a periodic exponential decay function or the following formula:

[0084]

[0085] The meanings of the symbols in the formula are the same as in the previous embodiments, so they will not be repeated here.

[0086] As can be seen from the above periodic exponential decay function, as long as the accurate fitting parameters can be obtained, the relaxation time T2 of the qubit can be accurately fitted. Therefore, in this embodiment, the periodic decay function model is trained using the accurate training set selected from the triangular periodic function model to obtain a fitting model that conforms to the real data, such as... Figure 4 As shown, the specific training process is as follows:

[0087] Step S501: Use the experimental data in the training set as input data to train the periodic decay function model.

[0088] Step S502: Use the trained periodic decay function model to fit the experimental data in each period to obtain the second standard deviation of each experimental data.

[0089] Step S503: Determine whether the periodic decay function model has completed training based on the magnitude of the second standard deviation and the second preset value.

[0090] In this embodiment, the training status of the periodic decay function model is determined by comparing the second standard deviation with a second preset value. Specifically, if the second standard deviation is less than the second preset value, the periodic decay function model has completed training; otherwise, further training is not required. In this embodiment, the second preset value is 0.5.

[0091] It should be noted that the closer the standard deviation is to 0, the better the training effect. In some other embodiments, in order to improve the subsequent fitting accuracy, the second preset value can be reduced, for example, to 0.3, 0.2, 0.1, etc.

[0092] Step S504: Determine the relaxation time of the qubit using the trained periodic decay function model.

[0093] Once the periodic decay function model is trained, it can be fitted to the entire experimental data to obtain the relaxation time T2 of the qubit.

[0094] Reference Figure 5 , Figure 5 The figure shows the fitting results of the envelope of the trained periodic decay function model. The horizontal axis represents time in nanoseconds, and the vertical axis represents the probability of the qubit being excited to the inverted state. As can be seen from the figure, the fitting curve of the trained periodic decay function model basically corresponds to the experimental data. Therefore, the measured relaxation time T2 of the qubit is very accurate.

[0095] The method for determining the relaxation time of a qubit described in this embodiment uses a sliding window to fit the experimental data using a triangular periodic function model. This allows for precise identification of the fitting point within each period. Then, the experimental data that meets the requirements is extracted to obtain an accurate training set. The periodic decay function model is then trained using the training set to obtain a high-precision periodic decay function model. Finally, the high-precision periodic decay function model can be used to obtain the high-precision qubit relaxation time.

[0096] Reference Figure 6 This embodiment also provides a device 100 for determining the relaxation time of a quantum bit, comprising:

[0097] The acquisition unit 1001 is used to acquire the dataset of Ramsey experimental data. It should be noted that the specific acquisition method and process have been described in detail in step S100 of the method for determining the relaxation time of a quantum bit in the above embodiment, so they will not be repeated here.

[0098] The determining unit 1002 is used to determine the period of the experimental data in the dataset and determine the size of the sliding window according to the period. It should be noted that since the specific determination method and process have been described in detail in step S200 of the method for determining the relaxation time of a quantum bit in the above embodiment, they will not be repeated here.

[0099] The first fitting unit 1003 uses a trigonometric periodic function model to fit the sub-experimental data within each sliding window of the dataset to obtain the first standard deviation of each sub-experimental data. It should be noted that since the specific fitting method and process have been described in detail in step S300 of the method for determining the relaxation time of a quantum bit in the above embodiment, they will not be repeated here.

[0100] Extraction unit 1004 is used to extract all sub-experimental data whose first standard deviation is less than or equal to a first preset value to obtain a training set. It should be noted that since the specific extraction method and process have been described in detail in step S400 of the method for determining the relaxation time of a quantum bit in the above embodiment, they will not be repeated here.

[0101] The second fitting unit 1005 is used to fit the training set using a periodic decay function model to obtain the qubit relaxation time, wherein the qubit relaxation time is related to the decay period of the periodic decay function model. It should be noted that since the specific fitting method and process have been described in detail in step S500 of the method for determining the qubit relaxation time described in the above embodiment, they will not be repeated here.

[0102] In addition, embodiments of the present invention also provide a computer-readable storage medium, wherein the computer-readable storage medium may store a program, which, when executed, includes some or all of the steps of any of the methods for determining the relaxation time of a quantum bit described in the above method embodiments.

[0103] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage device (CMD). Based on this understanding, the technical solution of this invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a memory and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned memory includes various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0104] Those skilled in the art will understand that all or part of the steps in the various methods of the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, which may include: flash drive, read-only memory (ROM), random access memory (RAM), disk or optical disk, etc.

[0105] 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.

[0106] 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. A method for determining the relaxation time of a quantum bit, characterized in that, include: Obtain the dataset of Ramsey's experiments; Determine the period of the experimental data in the dataset and determine the size of the sliding window based on the period; The first standard deviation of each sub-experiment data is obtained by fitting the sub-experiment data within each sliding window of the dataset using a trigonometric periodic function model. The training set is obtained by extracting all sub-experimental data whose first standard deviation is less than or equal to the first preset value. The relaxation time of a qubit is obtained by fitting a periodic decay function model to the training set, wherein the relaxation time of the qubit is related to the decay period of the periodic decay function model.

2. The determination method according to claim 1, characterized in that, Determining the period of the experimental data in the dataset and determining the size of the sliding window based on the period includes: Obtain the x-coordinate and y-coordinate values ​​of each experimental data point in the dataset; Determine the trend of experimental data based on the ordinate values ​​of adjacent experimental data; The period of the experimental data is determined based on the trend of the experimental data. The size of the sliding window is determined based on the cycle.

3. The determination method according to claim 1, characterized in that: The first preset value is less than or equal to 0.

5.

4. The determination method according to claim 1, characterized in that: The size of the sliding window is greater than or equal to the maximum period of the experimental data.

5. The determination method according to claim 1, characterized in that, The relaxation time of a qubit is obtained by fitting a periodic decay function model to the training set, including: The experimental data in the training set is used as input data to train the periodic decay function model; The second standard deviation of each experimental data point is obtained by fitting the experimental data within each period using the trained periodic decay function model. The training status of the periodic decay function model is determined based on the magnitude of the second standard deviation and the second preset value. The relaxation time of a qubit is determined using a trained periodic decay function model.

6. The determination method according to claim 5, characterized in that, The second preset value is less than or equal to 0.

5.

7. The determination method according to claim 1, characterized in that, The trigonometric periodic function model is: sine trigonometric function or cosine trigonometric function.

8. The determination method according to claim 7, characterized in that, The cosine trigonometric function model is as follows: y1=A2cos(ωx+φ)+B2 In the formula, A2 and B2 are fitting parameters, ω is the oscillation angular frequency, φ is the phase, x is the abscissa value of the experimental data, and y1 is the ordinate value of the experimental data.

9. The determining method according to claim 1 or 7, characterized in that, The periodic decay function model is a periodic exponential decay function.

10. The determination method according to claim 9, characterized in that, The periodic exponential decay function is: or In the formula, A1, A2, B1, and B2 are fitting parameters, T2 is the relaxation time, ω is the oscillation angular frequency, φ is the phase, x and x1 are the abscissas of two adjacent coordinate points of the experimental data in the training set, and y is the ordinate of one coordinate point among two adjacent coordinate points of the experimental data in the training set.

11. A device for determining the relaxation time of a quantum bit, characterized in that, include: The acquisition unit is used to acquire datasets of Ramsey experimental data. A determining unit is used to determine the period of experimental data in the dataset and determine the size of the sliding window based on the period; The first fitting unit uses a trigonometric periodic function model to fit the sub-experimental data within each sliding window of the dataset to obtain the first standard deviation of each sub-experimental data. The extraction unit is used to extract all sub-experimental data whose first standard deviation is less than or equal to a first preset value to obtain a training set. The second fitting unit is used to fit the training set with a periodic decay function model to obtain the qubit relaxation time, wherein the qubit relaxation time is related to the decay period of the periodic decay function model.

12. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of a method for determining the relaxation time of a quantum bit as described in any one of claims 1 to 10.

Images