Quantum bit calibration method and apparatus, quantum control system, and quantum computer

Abstract

The application discloses a quantum bit calibration method and device, a quantum control system and a quantum computer. Whether the working point of a to-be-tested quantum bit drifts is determined, the working point including a working voltage and a quantum bit frequency corresponding to the working voltage. If the drift occurs, a gradient optimization algorithm and a Ramsey experiment are used to obtain the drift amount of a degenerate point of the to-be-tested quantum bit. All working points of the to-be-tested quantum bit are calibrated based on the drift amount of the degenerate point of the to-be-tested quantum bit. The scheme of the application uses the gradient optimization algorithm and the Ramsey experiment to obtain the drift amount of the degenerate point of the to-be-tested quantum bit, can effectively realize the calibration of the working point of the quantum bit, and only needs to test the drift amount of the degenerate point, thereby effectively improving the calibration efficiency of the quantum bit.

Description

Technical Field

[0001] This invention relates to the field of quantum computing technology, and in particular to a method, apparatus, quantum control system, and quantum computer for calibrating qubits. Background Technology

[0002] Quantum computing and quantum information is an interdisciplinary field that uses the principles of quantum mechanics to perform computational and information processing tasks. It is closely related to quantum physics, computer science, and informatics. It has experienced rapid development in the last two decades. Quantum algorithms based on quantum computers, such as factorization and unstructured search, have demonstrated performance far exceeding that of existing classical computer-based algorithms, leading to expectations that this field can surpass current computing capabilities. Generally, each qubit can include one or more Josephson junctions, with a capacitor connected in parallel to the junctions to shunt current. The qubit is capacitively coupled to a 2D or 3D microwave cavity, and the electromagnetic energy associated with the qubit is stored in the Josephson junctions and the capacitors and inductors forming the qubit. To enable qubit operation, a flux modulation line is coupled to the qubit. Typically, the flux modulation signal provided by the flux modulation line modulates the electromagnetic energy associated with the qubit, thereby controlling its performance.

[0003] Quantum computing holds the potential to far surpass the performance of classical computers in solving specific problems. However, realizing a quantum computer requires a quantum chip containing a sufficient number and quality of qubits, capable of performing highly fidelity qubit logic gate operations and readouts. The frequency parameters of qubits fluctuate with environmental changes; ignoring these fluctuations leads to a decrease in the fidelity of qubit logic gate operations and affects readout efficiency. Therefore, the parameters of the quantum chip, especially the qubit frequency parameters, need to be calibrated regularly to ensure long-term stable performance and optimal execution of quantum algorithms. Since qubits exhibit random and probabilistic frequency drift, and existing qubit frequency calibration techniques rely heavily on manpower and time, they are not practical for large-scale quantum chip applications.

[0004] Therefore, how to achieve automatic calibration of qubits has become a technical problem that urgently needs to be solved in this field.

[0005] 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

[0006] The purpose of this invention is to provide a method, apparatus, quantum control system, and quantum computer for calibrating qubits, in order to solve the problem that existing qubit frequency calibration techniques rely on a large amount of manpower and time, and are not practical for large-scale quantum chip applications.

[0007] To address the above technical problems, this invention proposes a method for calibrating qubits, comprising:

[0008] Determine whether the operating point of the quantum bit to be measured has drifted, wherein the operating point includes the operating voltage and the quantum bit frequency corresponding to the operating voltage;

[0009] If a drift occurs, the drift amount of the degeneracy point of the sub-bit to be measured is obtained using gradient optimization algorithm and Ramsey experiment;

[0010] All operating points of the sub-bit to be measured are calibrated based on the drift of the degeneracy point of the sub-bit to be measured.

[0011] Optionally, determining whether the operating point of the sub-bit to be measured has drifted includes:

[0012] Ramsey experiments were performed on the sub-bit to be measured at the first operating point and the second operating point, respectively, wherein the first operating point and the second operating point are two operating points symmetrical about the degeneracy point before the drift occurred;

[0013] Based on the results of two Ramsey experiments, it was determined whether the operating point of the sub-bit to be measured had drifted.

[0014] Optionally, determining whether the operating point of the sub-bit to be measured has drifted based on the results of two Ramsey experiments includes:

[0015] Two oscillation frequencies were obtained through two Ramsey experiments;

[0016] The difference between the two oscillation frequencies is used to determine whether the operating point of the sub-bit to be measured has drifted.

[0017] Optionally, determining whether the operating point of the sub-bit to be measured has drifted based on the difference between the two oscillation frequencies includes:

[0018] Determine whether the difference between the two oscillation frequencies is greater than a preset threshold;

[0019] If so, it is determined that the operating point of the sub-bit to be measured has drifted;

[0020] If not, it is determined that the operating point of the sub-bit to be measured has not drifted.

[0021] Optionally, determining whether the operating point of the sub-bit to be measured has drifted includes:

[0022] The actual frequency of the sub-bit to be measured at the first operating point and the second operating point is obtained respectively, wherein the first operating point and the second operating point are two operating points symmetrical about the degeneracy point before the drift occurs;

[0023] Based on the two actual frequencies obtained, it is determined whether the operating point of the sub-bit to be measured has drifted.

[0024] Optionally, obtaining the drift of the degeneracy point of the sub-bit to be measured using gradient optimization algorithms and Ramsey experiments includes:

[0025] Ramsey experiments were performed on the sub-bit to be measured at the first operating point and the second operating point, respectively, wherein the first operating point and the second operating point are two operating points symmetrical about the degeneracy point before the drift occurred;

[0026] The working voltage value of the first working point is adjusted using a gradient optimization algorithm so that the difference between the value of the first oscillation frequency and the value of the second oscillation frequency is within a first preset range, and the working voltage value corresponding to the first working point at this time is obtained as the calibrated voltage. Here, the first oscillation frequency is the result of the Ramsey experiment performed on the sub-bit to be measured at the first working point, and the second oscillation frequency is the result of the Ramsey experiment performed on the sub-bit to be measured at the second working point.

[0027] The drift of the degeneracy point of the sub-bit to be measured is obtained based on the calibrated voltage and the second voltage, wherein the second voltage is the operating voltage corresponding to the second operating point.

[0028] Optionally, obtaining the drift of the degeneracy point of the sub-bit to be measured based on the calibrated voltage and the first voltage includes:

[0029] The calibrated degeneracy point of the sub-bit to be measured is obtained based on the calibrated voltage and the second voltage;

[0030] The drift of the degeneracy point of the sub-bit to be measured is obtained based on the calibrated degeneracy point.

[0031] Optionally, adjusting the operating voltage value of the first operating point using a gradient optimization algorithm includes:

[0032] Get the number of times n has been used to update the operating voltage of the first operating point;

[0033] If the number of times n is less than a first preset value, then a first guess value is obtained based on the first voltage, where the first voltage is the initial operating voltage of the first operating point before adjustment, and the value of the operating voltage of the first operating point is adjusted to the first guess value according to the first voltage and the preset adjustment range.

[0034] Optionally, adjusting the operating voltage value of the first operating point using a gradient optimization algorithm further includes:

[0035] If the number of times n is greater than or equal to the first preset value, then obtain the first voltage V0 and the current guessed value V1, as well as the initial oscillation frequency f0 corresponding to the first voltage and the oscillation frequency f1 corresponding to the current guessed value;

[0036] Based on the first voltage and the current guessed value V1, and the initial oscillation frequency f0 and the oscillation frequency f1 corresponding to the current guessed value, adjust the value of the first voltage to the second guessed value V2:

[0037] Where f is the second oscillation frequency.

[0038] Optionally, adjusting the operating voltage value of the first operating point using a gradient optimization algorithm further includes:

[0039] Obtain the oscillation frequency f2 corresponding to the second guessed value V2;

[0040] Determine whether |f2-f| is less than |f1-f|;

[0041] If so, then update the first voltage V0 to the second guessed value V2 and the initial oscillation frequency f0 to f2.

[0042] Based on the same inventive concept, the present invention also proposes a calibration device for qubits, comprising:

[0043] The judgment unit is used to determine whether the operating point of the quantum bit to be measured has drifted, wherein the operating point includes the operating voltage and the quantum bit frequency corresponding to the operating voltage;

[0044] An optimization unit is used to obtain the drift amount of the degeneracy point of the sub-bit to be measured by using a gradient optimization algorithm and Ramsey experiments when drift occurs.

[0045] A calibration unit is used to calibrate all operating points of the sub-bit to be measured based on the drift of the degeneracy point of the sub-bit to be measured.

[0046] Based on the same inventive concept, the present invention also proposes a quantum control system that calibrates a quantum chip using the calibration method of the qubit described in any one of the above-described features, or includes a calibration device for the qubit described in the above-described features.

[0047] Based on the same inventive concept, the present invention also proposes a quantum computer, including the quantum control system described in the above feature description.

[0048] Based on the same inventive concept, the present invention also proposes a readable storage medium storing a computer program thereon, which, when executed by a processor, can implement the calibration method for the qubits described in any of the above features.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] The proposed quantum bit calibration method determines whether the operating point of the quantum bit to be measured has drifted. The operating point includes the operating voltage and the quantum bit frequency corresponding to the operating voltage. If drift occurs, the drift amount of the degeneracy point of the quantum bit to be measured is obtained using a gradient optimization algorithm and a Ramsey experiment. All operating points of the quantum bit to be measured are calibrated based on the drift amount of the degeneracy point. This application's scheme utilizes a gradient optimization algorithm and a Ramsey experiment to obtain the drift amount of the degeneracy point of the quantum bit to be measured, which can effectively calibrate the operating point of the quantum bit, and only requires testing the drift amount of the degeneracy point, effectively improving the calibration efficiency of the quantum bit.

[0051] The quantum bit calibration device, quantum control system, quantum computer, and readable storage medium proposed in this invention belong to the same inventive concept as the quantum bit calibration method, and therefore have the same beneficial effects, which will not be elaborated here. Attached Figure Description

[0052] Figure 1 This is a schematic flowchart of the quantum bit calibration method proposed in an embodiment of the present invention;

[0053] Figure 2 This is a schematic diagram of the processed modulation spectrum of a sub-bit to be measured;

[0054] Figure 3 This is a schematic diagram of a qubit calibration device proposed in another embodiment of the present invention. Detailed Implementation

[0055] 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.

[0056] 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.

[0057] 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.

[0058] To better understand the technical solution of this application, the inventive concept and related technologies involved in this application will be briefly described below:

[0059] The Ramsey experiment involves applying two π / 2 quantum logic gate operations to a qubit, with a time interval τ between the two operations. A readout pulse is then applied to the qubit after the second π / 2 quantum logic gate operation to obtain the excited state distribution P1(τ). The process of changing the time interval τ to obtain P1(τ) is repeated. A typical Ramsey experiment shows that P1(τ) decays exponentially with time interval τ, as shown in the following mathematical model:

[0060]

[0061] In Equation 1, A and B are fitting coefficients, T0 is the decoherence time of the qubit, and f d Let f0 be the carrier frequency of the microwave pulse signal corresponding to the π / 2 quantum logic gate operation, and f0 be the oscillation frequency of the qubit. Furthermore, f0 is related to the actual frequency f0 of the qubit. q The carrier frequency of π / 2 quantum logic gate operations satisfies:

[0062] f0(f d )=|f q -f d |(2)

[0063] In summary and in conjunction with Formula 2, we can obtain the results of the Ramsey experiment, namely, that the oscillation frequency of the curve is equal to the difference between the carrier frequency of the quantum logic gate operation and the true frequency of the qubit. Therefore, in addition to obtaining the decoherence time of the qubit, the Ramsey experiment can also accurately obtain the true frequency of the qubit at the same time.

[0064] In the Bloch Sphere, if the applied microwave pulse frequency and the superconducting quantum bit frequency are the same, it can be considered that there is no phase accumulation in between, resulting in pure exponential oscillations. If the microwave frequency and the superconducting quantum bit frequency are not the same, sine oscillations will occur. Please refer to [reference needed]. Figure 3 Adding a phase with an oscillation frequency of fringe to the second π / 2, if the microwave pulse and the bit frequency are the same, the resulting oscillation frequency is fringe; if they are not the same, the resulting oscillation frequency is fringe ± frequency difference. Therefore, the actual oscillation frequency is: f_osc = fringe ± frequency difference. Assuming the superconducting quantum bit frequency at its operating point is fq, and the microwave pulse frequency is fp (fixed), then the frequency difference Δf = fq – fp, and the formula for calculating the oscillation frequency is:

[0065] f_osc=fringe+Δf (3)

[0066] That is, f_osc = fringe + (fq – fp); when the superconducting quantum bit does not drift, fp equals fq, the theoretical value of the frequency difference Δf = 0, and the value of the oscillation frequency f_osc equals fringe;

[0067] When the superconducting bit frequency drifts, the frequency difference Δf = fq_offset – fq, at which point Δf is no longer equal to zero. This condition can be used to determine that the bit frequency has drifted, and the oscillation frequency after the drift is: f_osc_offset = fringef + (fq_offset – fq).

[0068] Since the previously measured parameters of the fq-v function have changed, we cannot determine the voltage v_offset corresponding to fq_offset. Therefore, we need to modify the voltage value and experiment. For example, we can increase V_dc to V_dc1 (if Δf < 0, the voltage value needs to be reduced). At the voltage value V_dc1, f_osc1 can be measured through the Ramsey interferometry experiment, which is obtained from the previous oscillation frequency calculation formula.

[0069] f_osc1=fringe + (fq1–fq) (4)

[0070] Although the value of fq1 was not obtained, subtracting formula 4 from formula 3 yields the result:

[0071] f_osc–f_osc1 = fq–fq1 (5)

[0072] Please refer to Figure 1 This invention proposes a method for calibrating qubits, comprising:

[0073] S100: Determine whether the operating point of the quantum bit to be measured has drifted, wherein the operating point includes the operating voltage and the quantum bit frequency corresponding to the operating voltage;

[0074] S200: If a drift occurs, the drift amount of the degeneracy point of the sub-bit to be measured is obtained using the gradient optimization algorithm and the Ramsey experiment;

[0075] S300: Calibrate all operating points of the sub-bit to be measured based on the drift of the degeneracy point of the sub-bit to be measured.

[0076] Unlike existing technologies, the qubit calibration method proposed in this invention determines whether the operating point of the qubit to be measured has drifted. The operating point includes the operating voltage and the qubit frequency corresponding to the operating voltage. If drift occurs, the drift amount of the degeneracy point of the qubit to be measured is obtained using a gradient optimization algorithm and a Ramsey experiment. All operating points of the qubit to be measured are calibrated based on the drift amount of the degeneracy point. The solution of this application utilizes a gradient optimization algorithm and a Ramsey experiment to obtain the drift amount of the degeneracy point of the qubit to be measured, which can effectively calibrate the operating point of the qubit, and only requires testing the drift amount of the degeneracy point, effectively improving the calibration efficiency of the qubit.

[0077] For a quantum bit, the voltage V of the frequency control signal it senses qubit It actually consists of two parts: one is the degeneracy point voltage V. sweet_point The other is the offset voltage V. idle_point The offset voltage can be positive or negative, i.e., V qubit =V sweet_point +V idle_point Those skilled in the art will understand that the degeneracy point mentioned in this embodiment refers to the operating point corresponding to the point where the qubit is insensitive to magnetic flux modulation, and the voltage corresponding to the degeneracy point is the degeneracy point voltage, which can generally be considered as the extreme point of the modulation spectrum of the qubit. Therefore, when the offset voltage V idle_point When the value is 0, it indicates that the qubit is at a degenerate point.

[0078] Please refer to Figure 2 , Figure 2 This is a schematic diagram of the processed modulation spectrum of a quantum bit to be measured. The horizontal axis can be considered as the operating voltage, and the vertical axis is the frequency of the quantum bit. Figure 2 One curve represents the modulation spectrum before the operating point of the measured sub-qubit drifts, and the other curve represents the modulation spectrum after the operating point of the measured sub-qubit drifts. It is important to note that for a single qubit, its modulation spectrum is symmetrical about the degeneracy point. For ease of understanding, Figure 2 By performing simple processing on the modulation spectrum, setting the horizontal coordinate of the degeneracy point before drift to the baseline, i.e., 0, the modulation spectrum after drift is shifted to the right as a whole. Figure 2 Points A and B are two operating points symmetrical about the degeneracy point of the drift leading edge of the sub-bit to be measured. Based on the previous analysis, the offset voltage V at points A and B is... idle_point The absolute values ​​are equal. When the sub-bit to be measured drifts, the working point corresponding to the working voltage at point B becomes point D. If we still use the working voltage corresponding to point A before the drift, then the frequency we measure will definitely be the value at working point E. At this time, the working point symmetrical to working point D in the modulation spectrum after the drift is point C. Since points C and D are symmetrical about the degeneracy point after the drift, as long as we obtain points C and D, we can determine the degeneracy point after the drift. The working voltage and frequency of point D can be obtained directly. What we need to obtain is the working voltage of point C, which has the same frequency as point D.

[0079] To obtain the operating voltage at point C, the applicant proposed using a gradient optimization algorithm. Specifically, we assume that (V_q, fq) represents the operating point C after the drift of the sub-bit to be measured, and fq_0 represents the frequency value corresponding to the voltage after the drift (before calibration) of the sub-bit to be measured (i.e., the frequency corresponding to the operating point E). Since the specific parameters of the curve function after drift are unknown, V_q cannot be obtained even when fq is known; therefore, the problem needs to be transformed.

[0080] Assuming the slope of the tangent line at the working point C is k_q, then the working point C must lie on the line with slope k_q. According to the mathematical principles of the derivative, the derivative of the function f(x) at the point x0 can be defined as: when the variable x in the domain approaches x0, The limit, that is:

[0081]

[0082] Therefore, the problem to be solved is transformed into: finding a point (V2, f_b) on the drifted curve. When (V2, f_b) is close enough to (V_q, fq), the slope at this point is infinitely close to k_q. Therefore, this point can be considered as the working point C of the sub-bit to be measured.

[0083] Those skilled in the art will understand that the tangent slope requires at least two sets of coordinates to calculate. If we shift the voltage by a very small increment to obtain a guessed voltage V1, then the tangent slope at that point is approximately equivalent to:

[0084] k=(fq_step–fq_0) / (V1–V0) (7)

[0085] V0 is the initial operating voltage at point E. As mentioned above, the specific parameters of the function after drift are unknown. Therefore, fq_step and fq_0 cannot be known. This is understandable to those skilled in the art. However, it can be derived from Equation 5:

[0086] f1–f0=fq_step–fq_0 (8)

[0087] k=(f1–f0) / (V1–V0) (9)

[0088] Wherein, the oscillation frequency f1 is obtained by Ramsey experiment after setting the sub-bit to be measured to the guessed voltage V1; f0 is the initial oscillation frequency obtained by Ramsey experiment using the initial value V0; therefore, the approximate slope can be calculated simply by measuring the oscillation frequency through Ramsey experiment. The frequency f at the operating point D can be used as a reference, and the difference between f_osc and f can be compared in each iteration. When the absolute value of the difference is less than or equal to 0.01MHz, we consider that the operating point C of the sub-bit to be measured has been found. It is understood that in this embodiment, the convergence condition can be set as: the absolute value of the difference between the current oscillation frequency and the first frequency f is less than or equal to 0.01MHz. In other embodiments, the convergence condition can also be other cases. For example, in some application scenarios with high requirements for quantum bit frequency, the convergence condition can be set as follows: the absolute value of the difference between the current oscillation frequency and the oscillation frequency at the operating point D is less than or equal to 0.001MHz; while in some application scenarios with low requirements for quantum bit frequency, the convergence condition can be set as follows: the absolute value of the difference between the current oscillation frequency and the oscillation frequency at the operating point D is less than or equal to 0.02MHz; there are many other cases of convergence condition, which will not be elaborated here. The specific choice can be made according to actual needs or actual application scenarios.

[0089] Specifically, in this embodiment, determining whether the operating point of the sub-bit to be measured has drifted includes:

[0090] Ramsey experiments were performed on the sub-bit to be measured at the first operating point and the second operating point, respectively, wherein the first operating point and the second operating point are two operating points symmetrical about the degeneracy point before the drift occurred;

[0091] Based on the results of two Ramsey experiments, it was determined whether the operating point of the sub-bit to be measured had drifted.

[0092] Please refer to Figure 2 Let's assume the first operating point is point A and the second operating point is point B. When the quantum bit to be measured drifts, the operating point corresponding to the original operating voltage at point B becomes point D. If we still use the operating voltage corresponding to point A before the drift, then the frequency we measure will definitely be the value at operating point E. As long as the oscillation frequencies measured by the Ramsey experiment at these two points are not equal, then we can conclude that the quantum bit has drifted.

[0093] Specifically, in this embodiment, determining whether the operating point of the sub-bit to be measured has drifted based on the results of two Ramsey experiments includes:

[0094] Two oscillation frequencies were obtained through two Ramsey experiments;

[0095] The difference between the two oscillation frequencies is used to determine whether the operating point of the sub-bit to be measured has drifted.

[0096] Specifically, in this embodiment, determining whether the operating point of the sub-bit to be measured has drifted based on the difference between the two oscillation frequencies includes:

[0097] Determine whether the difference between the two oscillation frequencies is greater than a preset threshold;

[0098] If so, it is determined that the operating point of the sub-bit to be measured has drifted;

[0099] If not, it is determined that the operating point of the sub-bit to be measured has not drifted.

[0100] Those skilled in the art will understand that the preset threshold can be set according to the actual application scenario. For example, in some application scenarios with high requirements for quantum bit frequency, the preset threshold can be set to: the absolute value of the difference between the two oscillation frequencies is less than or equal to 0.001MHz; while in some application scenarios with low requirements for quantum bit frequency, the preset threshold can be set to: the absolute value of the difference between the two oscillation frequencies is less than or equal to 0.02MHz; there are many other cases for the preset threshold, which will not be elaborated here. The specific threshold can be selected according to actual needs or actual application scenarios.

[0101] In addition to using the oscillation frequency from the Ramsey experiment to determine whether the qubit has drifted, we can also directly determine this by measuring the frequency of the qubit. As described above, we can also use the Ramsey experiment to obtain the frequency of the qubit.

[0102] Specifically, in this embodiment, determining whether the operating point of the sub-bit to be measured has drifted includes:

[0103] The actual frequency of the sub-bit to be measured at the first operating point and the second operating point is obtained respectively, wherein the first operating point and the second operating point are two operating points symmetrical about the degeneracy point before the drift occurs;

[0104] Based on the two actual frequencies obtained, it is determined whether the operating point of the sub-bit to be measured has drifted.

[0105] Specifically, in this embodiment, obtaining the drift of the degeneracy point of the sub-bit to be measured using gradient optimization algorithm and Ramsey experiment includes:

[0106] Ramsey experiments were performed on the sub-bit to be measured at the first operating point and the second operating point, respectively, wherein the first operating point and the second operating point are two operating points symmetrical about the degeneracy point before the drift occurred;

[0107] The working voltage value of the first working point is adjusted using a gradient optimization algorithm so that the difference between the value of the first oscillation frequency and the value of the second oscillation frequency is within a first preset range, and the working voltage value corresponding to the first working point at this time is obtained as the calibrated voltage. Here, the first oscillation frequency is the result of the Ramsey experiment performed on the sub-bit to be measured at the first working point, and the second oscillation frequency is the result of the Ramsey experiment performed on the sub-bit to be measured at the second working point.

[0108] The drift of the degeneracy point of the sub-bit to be measured is obtained based on the calibrated voltage and the second voltage, wherein the second voltage is the operating voltage corresponding to the second operating point.

[0109] Optionally, obtaining the drift of the degeneracy point of the sub-bit to be measured based on the calibrated voltage and the first voltage includes:

[0110] The calibrated degeneracy point of the sub-bit to be measured is obtained based on the calibrated voltage and the second voltage;

[0111] The drift of the degeneracy point of the sub-bit to be measured is obtained based on the calibrated degeneracy point.

[0112] To avoid wasting computing resources, an adjustment threshold can be set, that is, a threshold can be set for the number of iterations. Once a certain threshold is exceeded, the result can be considered to have converged or has fallen into a local optimum. At this point, the solution obtained can be considered the optimal solution.

[0113] Specifically, in this embodiment, adjusting the operating voltage value of the first operating point using a gradient optimization algorithm includes:

[0114] Get the number of times n has been used to update the operating voltage of the first operating point;

[0115] If the number of times n is less than a first preset value, then a first guess value is obtained based on the first voltage, where the first voltage is the initial operating voltage of the first operating point before adjustment, and the value of the operating voltage of the first operating point is adjusted to the first guess value according to the first voltage and the preset adjustment range.

[0116] Optionally, adjusting the operating voltage value of the first operating point using a gradient optimization algorithm further includes:

[0117] If the number of times n is greater than or equal to the first preset value, then obtain the first voltage V0 and the current guessed value V1, as well as the initial oscillation frequency f0 corresponding to the first voltage and the oscillation frequency f1 corresponding to the current guessed value;

[0118] Based on the first voltage and the current guessed value V1, and the initial oscillation frequency f0 and the oscillation frequency f1 corresponding to the current guessed value, adjust the value of the first voltage to the second guessed value V2:

[0119] Where f is the second oscillation frequency.

[0120] The first voltage is adjusted by obtaining a guess value, and the oscillation frequency is obtained based on the current guess value. The guess value includes a first guess value and several second guess values. The second guess values ​​are obtained by using a first slope, the current oscillation frequency, the first frequency, and the current guess value. Iteratively obtaining the guess values ​​based on the change in the magnitude of the first slope will cause the oscillation frequency to continuously approach the first frequency. Furthermore, using the first slope for iteration can effectively reduce the number of adjustments to the first voltage, thus effectively improving the efficiency of automatically calibrating the frequency of the superconducting quantum bit. The first slope is k, and k can be obtained according to Formula 10:

[0121]

[0122] Where f1 is the current oscillation frequency, f0 is the initial oscillation frequency, V1 is the current guess value, and V0 is the initial operating voltage at point E.

[0123] Specifically, in this embodiment, adjusting the operating voltage value of the first operating point using a gradient optimization algorithm further includes:

[0124] Obtain the oscillation frequency f2 corresponding to the second guessed value V2;

[0125] Determine whether |f2-f| is less than |f1-f|;

[0126] If so, then update the first voltage V0 to the second guessed value V2 and the initial oscillation frequency f0 to f2.

[0127] Based on the same inventive concept, please refer to Figure 3 The present invention also proposes a qubit calibration device, comprising:

[0128] The judgment unit is used to determine whether the operating point of the quantum bit to be measured has drifted, wherein the operating point includes the operating voltage and the quantum bit frequency corresponding to the operating voltage;

[0129] An optimization unit is used to obtain the drift amount of the degeneracy point of the sub-bit to be measured by using a gradient optimization algorithm and Ramsey experiments when drift occurs.

[0130] A calibration unit is used to calibrate all operating points of the sub-bit to be measured based on the drift of the degeneracy point of the sub-bit to be measured.

[0131] It is understood that the judgment unit 100, the optimization unit 200, and the calibration unit 300 can be implemented in a single device, or any one of these modules can be divided into multiple sub-modules. Alternatively, at least some of the functions of one or more modules of the judgment unit 100, the optimization unit 200, and the calibration unit 300 can be combined with at least some of the functions of other modules and implemented in a single functional module. According to embodiments of the present invention, at least one of the judgment unit 100, the optimization unit 200, and the calibration unit 300 can be at least partially implemented as a hardware circuit, such as a field-programmable gate array (FPGA), a programmable logic array (PLA), a system-on-a-chip, a system-on-a-substrate, a system-on-package, an application-specific integrated circuit (ASIC), or can be implemented in hardware or firmware in any other reasonable manner of integrating or packaging the circuit, or in a suitable combination of software, hardware, and firmware implementations. Alternatively, at least one of the judgment unit 100, the optimization unit 200, and the calibration unit 300 can be at least partially implemented as a computer program module, which, when run by a computer, can execute the functions of the corresponding module.

[0132] Based on the same inventive concept, embodiments of the present invention also propose a quantum control system that calibrates a quantum chip using the calibration method of the qubit described in any of the above-described features, or includes a calibration device for the qubit described in the above-described features.

[0133] Based on the same inventive concept, embodiments of the present invention also propose a quantum computer, including the quantum control system described in the above feature description.

[0134] Based on the same inventive concept, embodiments of the present invention also propose a readable storage medium storing a computer program thereon, which, when executed by a processor, can implement the calibration method for the qubit described in any of the above features.

[0135] The readable storage medium can be a tangible device capable of holding and storing instructions for use by an instruction execution device, such as, but not limited to, electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination thereof. More specific examples of readable storage media (a non-exhaustive list) include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination thereof. The computer programs described herein can be downloaded from the readable storage medium to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network can include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. Each computing / processing device's network adapter card or network interface receives the computer program from the network and forwards it for storage in a readable storage medium within the respective computing / processing device. The computer program used to perform the operations of this invention can be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as "C" or similar languages. The computer program can be executed entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving remote computers, the remote computer can be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or it can be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuits, such as programmable logic circuits, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), are personalized by utilizing state information from a computer program. These electronic circuits can execute computer-readable program instructions, thereby realizing various aspects of the present invention.

[0136] Various aspects of the present invention are described herein with reference to flowchart illustrations and / or block diagrams of methods, systems, and computer program products according to embodiments of the invention. It should be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by a computer program. These computer programs can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing apparatus to produce a machine such that, when executed by the processor of the computer or other programmable data processing apparatus, they create means for implementing the functions / actions specified in one or more blocks of the flowchart illustrations and / or block diagrams. These computer programs can also be stored in a readable storage medium that causes a computer, programmable data processing apparatus, and / or other device to operate in a particular manner; thus, the readable storage medium storing the computer program comprises an article of manufacture including instructions for implementing aspects of the functions / actions specified in one or more blocks of the flowchart illustrations and / or block diagrams.

[0137] A computer program may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable data processing apparatus, or other device to produce a computer-implemented process, thereby causing the computer program executing on the computer, other programmable data processing apparatus, or other device to perform the functions / actions specified in one or more boxes of a flowchart and / or block diagram.

[0138] 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.

[0139] 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 calibrating qubits, characterized in that, include: Determine whether the operating point of the quantum bit to be measured has drifted, wherein the operating point includes the operating voltage and the quantum bit frequency corresponding to the operating voltage; If a drift occurs, the drift amount of the degeneracy point of the sub-bit to be measured is obtained using gradient optimization algorithm and Ramsey experiment; All operating points of the sub-bit to be measured are calibrated based on the drift of the degeneracy point of the sub-bit to be measured; The process of obtaining the degeneracy point drift of the sub-bit to be measured using gradient optimization algorithms and Ramsey experiments includes: A first oscillation frequency and a second oscillation frequency are obtained by performing a Ramsey experiment on the sub-bit to be measured at a first operating point and a second operating point with a second voltage, respectively, wherein the first operating point and the second operating point are two operating points symmetrical about the degeneracy point before the drift occurs; The working voltage value of the first working point is adjusted using a gradient optimization algorithm so that the working voltage value corresponding to the first working point is the calibrated voltage when the difference between the value of the first oscillation frequency and the value of the second oscillation frequency is within a first preset range. The drift of the degeneracy point of the sub-bit to be measured is obtained based on the calibrated voltage and the second voltage.

2. The method as described in claim 1, characterized in that, The determination of whether the operating point of the sub-bit to be measured has drifted includes: Ramsey experiments were performed on the sub-bit to be measured at the first operating point and the second operating point, respectively, wherein the first operating point and the second operating point are two operating points symmetrical about the degeneracy point before the drift occurred; Based on the results of two Ramsey experiments, it was determined whether the operating point of the sub-bit to be measured had drifted.

3. The method as described in claim 2, characterized in that, The determination of whether the operating point of the sub-bit to be measured has drifted based on the results of two Ramsey experiments includes: Two oscillation frequencies were obtained through two Ramsey experiments; The difference between the two oscillation frequencies is used to determine whether the operating point of the sub-bit to be measured has drifted.

4. The method as described in claim 3, characterized in that, The method of determining whether the operating point of the sub-bit to be measured has drifted based on the difference between two oscillation frequencies includes: Determine whether the difference between the two oscillation frequencies is greater than a preset threshold; If so, it is determined that the operating point of the sub-bit to be measured has drifted; If not, it is determined that the operating point of the sub-bit to be measured has not drifted.

5. The method as described in claim 1, characterized in that, The determination of whether the operating point of the sub-bit to be measured has drifted includes: The actual frequency of the sub-bit to be measured at the first operating point and the second operating point is obtained respectively, wherein the first operating point and the second operating point are two operating points symmetrical about the degeneracy point before the drift occurs; Based on the two actual frequencies obtained, it is determined whether the operating point of the sub-bit to be measured has drifted.

6. The method as described in claim 1, characterized in that, The step of obtaining the drift of the degeneracy point of the sub-bit to be measured based on the calibrated voltage and the second voltage includes: The calibrated degeneracy point of the sub-bit to be measured is obtained based on the calibrated voltage and the second voltage; The drift of the degeneracy point of the sub-bit to be measured is obtained based on the calibrated degeneracy point.

7. The method as described in claim 1, characterized in that, The step of adjusting the operating voltage value of the first operating point using a gradient optimization algorithm includes: Get the number of times n has been used to update the operating voltage of the first operating point; If the number of times n is less than a first preset value, then a first guess value is obtained based on the first voltage, where the first voltage is the initial operating voltage of the first operating point before adjustment, and the value of the operating voltage of the first operating point is adjusted to the first guess value according to the first voltage and the preset adjustment range.

8. The method as described in claim 7, characterized in that, The step of adjusting the operating voltage value of the first operating point using a gradient optimization algorithm further includes: If the number of times n is greater than or equal to the first preset value, then obtain the first voltage V0 and the current guessed value V1, as well as the initial oscillation frequency f0 corresponding to the first voltage and the oscillation frequency f1 corresponding to the current guessed value; Based on the first voltage and the current guessed value V1, and the initial oscillation frequency f0 and the oscillation frequency f1 corresponding to the current guessed value, adjust the value of the first voltage to the second guessed value V2: , where f is the second oscillation frequency.

9. The method as described in claim 8, characterized in that, The step of adjusting the operating voltage value of the first operating point using a gradient optimization algorithm further includes: Obtain the oscillation frequency f2 corresponding to the second guessed value V2; Determine whether |f2-f| is less than |f1-f|; If so, then update the first voltage V0 to the second guessed value V2 and the initial oscillation frequency f0 to f2.

10. A calibration device for qubits, characterized in that, include: The judgment unit is used to determine whether the operating point of the quantum bit to be measured has drifted, wherein the operating point includes the operating voltage and the quantum bit frequency corresponding to the operating voltage; An optimization unit is used to obtain the drift amount of the degeneracy point of the sub-bit to be measured by using a gradient optimization algorithm and Ramsey experiments when drift occurs. A calibration unit is used to calibrate all operating points of the sub-bit to be measured based on the drift of the degeneracy point of the sub-bit to be measured; The optimization unit is specifically used for: A first oscillation frequency and a second oscillation frequency are obtained by performing a Ramsey experiment on the sub-bit to be measured at a first operating point and a second operating point with a second voltage, respectively, wherein the first operating point and the second operating point are two operating points symmetrical about the degeneracy point before the drift occurs; The working voltage value of the first working point is adjusted using a gradient optimization algorithm so that the working voltage value corresponding to the first working point is the calibrated voltage when the difference between the value of the first oscillation frequency and the value of the second oscillation frequency is within a first preset range. The drift of the degeneracy point of the sub-bit to be measured is obtained based on the calibrated voltage and the second voltage.

11. A quantum control system, characterized in that, A quantum chip is calibrated using the calibration method for qubits as described in any one of claims 1-9, or a calibration device for qubits as described in claim 10 is used.

12. A quantum computer, characterized in that, Including the quantum control system as described in claim 11.

13. A readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it can implement the calibration method for the qubits according to any one of claims 1 to 9.

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