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

Abstract

The invention discloses a quantum bit calibration method and device, a quantum control system and a quantum computer, whether a working point of a to-be-measured sub-bit drifts is judged, and the working point comprises a working voltage and a quantum bit frequency corresponding to the working voltage. And if drift occurs, acquiring the drift distance of the degeneracy point of the to-be-measured sub-bit by using a gradient optimization algorithm and a Ramsey experiment. And calibrating all working points of the to-be-measured sub-bit based on the drift distance of the degeneracy point of the to-be-measured sub-bit. According to the scheme, the drift distance of the degeneracy point of the to-be-measured sub-bit is obtained through the gradient optimization algorithm and the Ramsey experiment, calibration of the quantum bit working point can be effectively achieved, only the drift distance of the degeneracy point needs to be tested, and the quantum bit calibration efficiency is effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of quantum computing technology, and in particular to a quantum bit calibration method, device, quantum control system and quantum computer. Background Art

[0002] Quantum computing and quantum information is an interdisciplinary subject based on the principles of quantum mechanics to achieve computing and information processing tasks. It has a very close connection with quantum physics, computer science, informatics and other disciplines. It has developed rapidly in the past two decades. Quantum algorithms based on quantum computers in scenarios such as factorization and unstructured search have shown performance far beyond the existing algorithms based on classical computers, and this direction has also been expected to exceed existing computing capabilities. In general, each quantum bit can include one or more Josephson junctions, and the Josephson junction is shunted by a capacitor in parallel with the junction. The quantum bit is capacitively coupled to a 2D or 3D microwave cavity, and the electromagnetic energy associated with the quantum bit is stored in the Josephson junction and in the capacitor and inductor elements that form the quantum bit. As a realization of the operation of the quantum bit, a flux modulation line is coupled to the quantum bit. Usually, the flux modulation signal provided by the flux modulation line regulates the electromagnetic energy associated with the quantum bit, thereby controlling the working performance of the quantum bit.

[0003] Since quantum computing has the potential to far exceed the performance of classical computers in solving specific problems, in order to realize a quantum computer, it is necessary to obtain a quantum chip that contains a sufficient number and quality of quantum bits, and can perform extremely high-fidelity quantum bit logic gate operations and read the quantum bits. However, the quantum bit frequency parameters of the quantum bits will fluctuate with the environment. If this fluctuation is ignored, the fidelity of the quantum bit logic gate operation will decrease, and the reading efficiency will also be affected. Therefore, the parameters of the quantum chip, especially the quantum bit frequency parameters, need to be calibrated regularly to ensure long-term stability and optimal performance, that is, the optimal execution of the quantum algorithm. Since quantum bits will randomly and probabilistically drift in frequency, and the existing technical means of quantum bit frequency calibration rely on a lot of manpower and time consumption, it is not practical in large-scale quantum chip applications.

[0004] Therefore, how to realize the automatic calibration function of quantum bits has become a technical problem that needs to be solved urgently in this field.

[0005] It should be noted that the information disclosed in the background technology section of this application is only intended to deepen the understanding of the general background technology of this application, and should not be regarded as an admission or suggestion in any form that the information constitutes prior art already known to those skilled in the art. Summary of the invention

[0006] The purpose of the present invention is to provide a quantum bit calibration method, device, quantum control system and quantum computer, which are used to solve the problem that the existing technical means for quantum bit frequency calibration rely on a large amount of manpower and time consumption and are not practical in large-scale quantum chip applications.

[0007] In order to solve the above technical problems, the present invention proposes a quantum bit calibration method, comprising:

[0008] Determining whether an operating point of a quantum bit to be measured has drifted, the operating point comprising an operating voltage and a quantum bit frequency corresponding to the operating voltage;

[0009] If drift occurs, the drift amount of the degenerate point of the subbit to be measured is obtained by using a gradient optimization algorithm and a Ramsey experiment;

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

[0011] Optionally, the determining whether the working point of the sub-bit to be measured drifts includes:

[0012] Performing a Ramsey experiment on the subbit to be measured at a first working point and a second working point respectively, wherein the first working point and the second working point are two working points symmetrical along a degenerate point before the drift occurs;

[0013] Based on the results of the two Ramsey experiments, it is determined whether the working point of the sub-bit to be measured drifts.

[0014] Optionally, judging whether the working point of the subbit to be measured drifts based on the results of the two Ramsey experiments includes:

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

[0016] It is determined whether the working point of the sub-bit to be measured drifts based on the difference between the two oscillation frequencies.

[0017] Optionally, judging whether the working point of the sub-bit to be measured drifts based on the difference between the two oscillation frequencies includes:

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

[0019] If yes, it is determined that the working 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, the determining whether the working point of the sub-bit to be measured drifts includes:

[0022] Respectively obtaining actual frequency magnitudes of the subbit to be measured at a first working point and a second working point, wherein the first working point and the second working point are two working points symmetrical along a degenerate point before drift occurs;

[0023] Based on the two acquired actual frequencies, it is determined whether the working point of the sub-bit to be measured drifts.

[0024] Optionally, the obtaining the drift amount of the degenerate point of the sub-bit to be measured by using a gradient optimization algorithm and a Ramsey experiment includes:

[0025] Performing a Ramsey experiment on the subbit to be measured at a first working point and a second working point respectively, wherein the first working point and the second working point are two working points symmetrical along a degenerate point before the drift occurs;

[0026] Using a gradient optimization algorithm to adjust the operating voltage value of the first operating point, so that the difference between the first oscillation frequency and the second oscillation frequency is within a first preset range, and obtaining the operating voltage value corresponding to the first operating point at this time as a calibrated voltage, wherein the first oscillation frequency is a result of a Ramsey experiment performed on the sub-bit to be measured at the first operating point, and the second oscillation frequency is a result of a Ramsey experiment performed on the sub-bit to be measured at the second operating point;

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

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

[0029] Acquire a calibrated degenerate point of the sub-bit to be measured based on the calibrated voltage and the second voltage;

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

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

[0032] Obtaining the number n of times the working voltage of the first working point is currently updated;

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

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

[0035] If the number n is greater than or equal to the first preset value, the first voltage V0 and the current guess value V1, as well as the initial oscillation frequency f0 corresponding to the first voltage and the oscillation frequency f1 corresponding to the current guess value are obtained;

[0036] According to the first voltage and the current guess value V1, as well as the initial oscillation frequency f0 and the oscillation frequency f1 corresponding to the current guess value, the value of the first voltage is adjusted to a second guess value V2:

[0037] Wherein, f is the second oscillation frequency.

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

[0039] Obtaining an oscillation frequency f2 corresponding to the second guess value V2;

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

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

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

[0043] A judging unit, used to judge whether a working point of a quantum bit to be measured has drifted, wherein the working point includes a working voltage and a quantum bit frequency corresponding to the working voltage;

[0044] An optimization unit, used for obtaining the drift amount of the degenerate point of the sub-bit to be measured by using a gradient optimization algorithm and a Ramsey experiment when drift occurs;

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

[0046] Based on the same inventive concept, the present invention also proposes a quantum control system, which calibrates a quantum chip using the quantum bit calibration method described in any one of the above characteristic descriptions, or includes a quantum bit calibration device described in the above characteristic descriptions.

[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 on which a computer program is stored. When the computer program is executed by a processor, it can implement the quantum bit calibration method described in any one of the above-mentioned feature descriptions.

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

[0050] The quantum bit calibration method proposed in the present invention determines whether the working point of the sub-bit to be measured drifts, and the working point includes an operating voltage and a quantum bit frequency corresponding to the operating voltage. If drift occurs, the drift amount of the degenerate point of the sub-bit to be measured is obtained by using a gradient optimization algorithm and a Ramsey experiment. All working points of the sub-bit to be measured are calibrated based on the drift amount of the degenerate point of the sub-bit to be measured. The scheme of the present application uses a gradient optimization algorithm and a Ramsey experiment to obtain the drift amount of the degenerate point of the sub-bit to be measured, which can effectively realize the calibration of the quantum bit working point, and only needs to test the drift amount of the degenerate point, which effectively improves the calibration efficiency of the quantum bit.

[0051] The quantum bit calibration device, quantum control system, quantum computer and readable storage medium proposed in the present 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 A schematic diagram of a flow chart of a quantum bit calibration method proposed in an embodiment of the present invention;

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

[0054] Figure 3 This is a simplified schematic diagram of a quantum bit calibration device according to another embodiment of the present invention. DETAILED DESCRIPTION

[0055] The specific implementation of the present invention will be described in more detail below in conjunction with the schematic diagram. 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 are not in exact proportions, and are only used to facilitate and clearly assist in explaining the purpose of the embodiments of the present invention.

[0056] In the description of the present invention, it is necessary to understand that the terms "center", "up", "down", "left", "right", etc. indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0057] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0058] In order to better understand the technical solution of the present application, the invention concept of the present application and the related technologies involved are briefly described below:

[0059] The Ramsey experiment refers to the process of applying two π / 2 quantum logic gate operations to a quantum bit, with the time interval between the two operations being τ, applying a read pulse to the quantum bit after the second π / 2 quantum logic gate operation to obtain the excited state distribution P1(τ) of the quantum bit, and changing the time interval τ to obtain P1(τ). The result of a typical Ramsey experiment is that P1(τ) satisfies the mathematical model of exponential oscillation decay with the time interval τ as follows:

[0060]

[0061] In formula 1, A and B are fitting coefficients, T0 is the decoherence time of the quantum bit, and f d is the carrier frequency of the microwave pulse signal corresponding to the π / 2 quantum logic gate operation, f0 is the oscillation frequency of the quantum bit, and f0 is related to the real frequency f of the quantum bit. q , the carrier frequency of the π / 2 quantum logic gate operation satisfies:

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

[0063] To sum up and combine with formula 2, we can get: the result of the Ramsey experiment, that is, 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 quantum bit. Therefore, in addition to being able to be used to obtain the decoherence time of the quantum bit, the Ramsey experiment can also accurately obtain the true frequency of the quantum bit at the same time.

[0064] In the bit coordinate system (Bloch Sphere), if the microwave pulse frequency and the superconducting quantum bit frequency are the same, it can be equivalent to assume that there is no phase accumulation in the middle, and the result is pure e-exponential oscillation; if the microwave frequency and the superconducting quantum bit frequency are inconsistent, there will be sine oscillation. Please refer to Figure 3 , add a phase with fringe as the oscillation frequency to the second π / 2. If the microwave pulse and the bit frequency are the same, the oscillation frequency is fringe. If they are different, the oscillation frequency is fringe±frequency difference. Therefore, the actual oscillation frequency is: f_osc=fringe±frequency difference. Assuming that the superconducting quantum bit frequency of a superconducting quantum bit operating point is fq, and the frequency of the microwave pulse is fp (fixed), then the frequency difference Δf=fq–fp, and the calculation formula of 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 is equal to fq, the theoretical value of the frequency difference Δf = 0, and the value of the oscillation frequency f_osc is equal to fringe;

[0067] When the superconducting bit frequency drifts, the frequency difference Δf = fq_offset-fq, and 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 fq-v function parameters measured previously have changed, it is impossible to get the voltage v_offset corresponding to fq_offset, so we need to modify the voltage value and try it. For example, V_dc is increased to V_dc1 (if Δf<0, the voltage value needs to be reduced). At the voltage value of V_dc1, f_osc1 can be measured through the Ramsey interferometer experiment, which is obtained from the previous oscillation frequency calculation formula:

[0069] f_osc1=fringe + (fq1–fq) (4)

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

[0071] f_osc–f_osc1 = fq–fq1 (5)

[0072] Please refer to Figure 1 , an embodiment of the present invention provides a quantum bit calibration method, comprising:

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

[0074] S200: If drift occurs, a gradient optimization algorithm and a Ramsey experiment are used to obtain a drift amount of the degenerate point of the subbit to be measured;

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

[0076] The difference from the prior art is that the quantum bit calibration method proposed in the embodiment of the present invention determines whether the working point of the sub-bit to be measured drifts, and the working point includes the working voltage and the quantum bit frequency corresponding to the working voltage. If drift occurs, the drift amount of the degenerate point of the sub-bit to be measured is obtained by using the gradient optimization algorithm and the Ramsey experiment. All working points of the sub-bit to be measured are calibrated based on the drift amount of the degenerate point of the sub-bit to be measured. The scheme of the present application uses the gradient optimization algorithm and the Ramsey experiment to obtain the drift amount of the degenerate point of the sub-bit to be measured, which can effectively realize the calibration of the quantum bit working point, and only needs to test the drift amount of the degenerate point, which effectively improves the calibration efficiency of the quantum bit.

[0077] For the quantum bit, the voltage V of the frequency control signal it feels qubit It actually contains two parts: one is the degenerate point voltage V sweet_point , the other is the offset voltage V idle_point , the offset voltage can be positive or negative, that is, 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 working point corresponding to the point where the quantum bit is insensitive to the 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 quantum bit modulation spectrum. Therefore, when the offset voltage V idle_point When it is 0, it means that the quantum bit is at a degenerate point.

[0078] Please refer to Figure 2 , Figure 2 is a schematic diagram of the processed modulation spectrum of a quantum bit to be measured. The horizontal axis can be regarded as the working voltage, and the vertical axis is the frequency of the quantum bit. Figure 2 One of the curves is the modulation spectrum before the working point of the quantum bit to be measured drifts, and the other curve is the modulation spectrum after the working point of the quantum bit to be measured drifts. It should be noted that for a quantum bit, its modulation spectrum is a curve that is symmetrical along the degenerate point. For ease of understanding, Figure 2 The modulation spectrum is simply processed, and the horizontal coordinate at the degenerate point before drift is set to the reference, that is, 0. The modulation spectrum after drift is shifted to the right as a whole. Figure 2 Point A and point B in the figure are two symmetrical working points where the drift front of the sub-bit to be measured occurs. From the previous analysis, we can know that the offset voltage V idle_point The absolute value of is 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 drift, then the frequency we measure must be the value at working point E. At this time, the working point symmetrical to working point D in the modulation spectrum after drift is point C. Since points C and D are symmetrical along the degenerate point after drift, as long as we obtain points C and D, we can determine the degenerate point after drift. The working voltage and frequency of point D can be directly obtained. What we need to obtain is the working voltage of point C with the same frequency as point D.

[0079] In order to obtain the working voltage at point C, the applicant proposes to use a gradient optimization algorithm. Specifically, we assume that (V_q, fq) represents the working point C after the sub-bit to be measured drifts, and fq_0 represents the frequency value corresponding to the voltage after the sub-bit to be measured drifts (before calibration) (that is, the frequency corresponding to the working point E). Since the specific parameters of the curve function after the drift are unknown, V_q cannot be obtained when fq is known; therefore, the problem needs to be converted.

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

[0081]

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

[0083] It can be understood by those skilled in the art that the tangent slope requires at least two sets of coordinates to be calculated. If we move the voltage by a very small increment and obtain a guessed voltage V1, the tangent slope at this point is approximately equivalent to:

[0084] k=(fq_step–fq_0) / (V1–V0) (7)

[0085] V0 is the initial working voltage at point E. According to the above content, the specific parameters of the drift function are unknown. Therefore, fq_step and fq_0 are unknown. It can be understood by those skilled in the art that, however, it can be obtained from formula 5:

[0086] f1–f0=fq_step–fq_0 (8)

[0087] k=(f1–f0) / (V1–V0) (9)

[0088] Among them, the oscillation frequency f1 is measured by performing a Ramsey experiment after setting the sub-bit to be measured to the guessed voltage V1; f0 is the initial oscillation frequency measured by performing a Ramsey experiment using the initial value V0; therefore, the approximate slope can be calculated by only measuring the oscillation frequency through the Ramsey experiment. The frequency f at the working 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 believe that the working point C of the sub-bit to be measured has been found. It can be understood that in this embodiment, the convergence condition can be set to: 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 may also be other situations. For example, in some application scenarios with higher requirements for quantum bit frequency, the convergence condition may be set to: the absolute value of the difference between the current oscillation frequency and the oscillation frequency at the working point D is less than or equal to 0.001 MHz; and in some application scenarios with lower requirements for quantum bit frequency, the convergence condition may be set to: the absolute value of the difference between the current oscillation frequency and the oscillation frequency at the working point D is less than or equal to 0.02 MHz; there are many other situations for the convergence condition, which are not elaborated here one by one, and can be selected according to actual needs or actual application scenarios.

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

[0090] Performing a Ramsey experiment on the subbit to be measured at a first working point and a second working point respectively, wherein the first working point and the second working point are two working points symmetrical along a degenerate point before the drift occurs;

[0091] Based on the results of the two Ramsey experiments, it is determined whether the working point of the sub-bit to be measured drifts.

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

[0093] Specifically, in this embodiment, judging whether the working point of the subbit to be measured drifts based on the results of the two Ramsey experiments includes:

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

[0095] It is determined whether the working point of the sub-bit to be measured drifts based on the difference between the two oscillation frequencies.

[0096] Specifically, in this embodiment, judging whether the working point of the sub-bit to be measured drifts based on the difference between the two oscillation frequencies includes:

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

[0098] If yes, it is determined that the working 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 appreciate that the preset threshold may be set according to the actual application scenario. For example, in certain application scenarios with higher requirements for the frequency of quantum bits, the preset threshold may be set to: the absolute value of the difference between the two oscillation frequencies is less than or equal to 0.001 MHz; and in certain application scenarios with lower requirements for the frequency of quantum bits, the preset threshold may be set to: the absolute value of the difference between the two oscillation frequencies is less than or equal to 0.02 MHz. There are many other situations for the preset threshold, which are not elaborated here one by one, and can be selected according to actual needs or actual application scenarios.

[0101] In addition to judging whether the quantum bit to be measured drifts by the oscillation frequency in the experimental results of the Ramsey experiment, it can also be judged directly by measuring the frequency of the quantum bit to be measured. From the previous description, we can know that we can also use the Ramsey experiment to obtain the frequency of the quantum bit.

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

[0103] Respectively obtaining actual frequency magnitudes of the subbit to be measured at a first working point and a second working point, wherein the first working point and the second working point are two working points symmetrical along a degenerate point before drift occurs;

[0104] Based on the two acquired actual frequencies, it is determined whether the working point of the sub-bit to be measured drifts.

[0105] Specifically, in this embodiment, the use of the gradient optimization algorithm and the Ramsey experiment to obtain the drift amount of the degenerate point of the sub-bit to be measured includes:

[0106] Performing a Ramsey experiment on the subbit to be measured at a first working point and a second working point respectively, wherein the first working point and the second working point are two working points symmetrical along a degenerate point before the drift occurs;

[0107] Using a gradient optimization algorithm to adjust the operating voltage value of the first operating point, so that the difference between the first oscillation frequency and the second oscillation frequency is within a first preset range, and obtaining the operating voltage value corresponding to the first operating point at this time as a calibrated voltage, wherein the first oscillation frequency is a result of a Ramsey experiment performed on the sub-bit to be measured at the first operating point, and the second oscillation frequency is a result of a Ramsey experiment performed on the sub-bit to be measured at the second operating point;

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

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

[0110] Acquire a calibrated degenerate point of the sub-bit to be measured based on the calibrated voltage and the second voltage;

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

[0112] In order to avoid wasting computing resources, you can also set a threshold for the number of adjustments, that is, set a threshold for the number of iterations. When a certain threshold is exceeded, it can be considered that the result has converged, or has fallen into a local optimal solution. At this time, the solution obtained can be considered the optimal solution.

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

[0114] Obtaining the number n of times the working voltage of the first working point is currently updated;

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

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

[0117] If the number n is greater than or equal to the first preset value, the first voltage V0 and the current guess value V1, as well as the initial oscillation frequency f0 corresponding to the first voltage and the oscillation frequency f1 corresponding to the current guess value are obtained;

[0118] According to the first voltage and the current guess value V1, as well as the initial oscillation frequency f0 and the oscillation frequency f1 corresponding to the current guess value, the value of the first voltage is adjusted to a second guess value V2:

[0119] Wherein, 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 value is obtained by the first slope, the current oscillation frequency, the first frequency and the current guess value, and the guess value is obtained by continuously iterating according to the size change of the first slope, which will make the oscillation frequency approach the first frequency continuously, and the method of iterating using the first slope can effectively reduce the number of times the first voltage is adjusted, and can effectively improve the efficiency of automatically calibrating the superconducting quantum bit frequency. The first slope is k, and k can be obtained according to formula 10:

[0121]

[0122] Among them, f1 is the current oscillation frequency, f0 is the initial oscillation frequency, V1 is the current guessed value, and V0 is the initial working voltage at point E.

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

[0124] Obtaining an oscillation frequency f2 corresponding to the second guess value V2;

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

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

[0127] Based on the same invention concept, please refer to Figure 3 , an embodiment of the present invention further provides a quantum bit calibration device, comprising:

[0128] A judging unit, used to judge whether a working point of a quantum bit to be measured has drifted, wherein the working point includes a working voltage and a quantum bit frequency corresponding to the working voltage;

[0129] An optimization unit, used for obtaining the drift amount of the degenerate point of the sub-bit to be measured by using a gradient optimization algorithm and a Ramsey experiment when drift occurs;

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

[0131] It can be understood that the judgment unit 100, the optimization unit 200 and the calibration unit 300 can be combined in one device, or any one of the modules can be split into multiple sub-modules, or at least part of the functions of one or more modules in the judgment unit 100, the optimization unit 200 and the calibration unit 300 can be combined with at least part of the functions of other modules and implemented in one functional module. According to an embodiment 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 a package, an application specific integrated circuit (ASIC), or can be implemented in hardware or firmware in any other reasonable way of integrating or packaging the circuit, or in a proper combination of software, hardware and firmware. 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, and when the program is run by a computer, the function of the corresponding module can be executed.

[0132] Based on the same inventive concept, an embodiment of the present invention further proposes a quantum control system, which calibrates a quantum chip using the quantum bit calibration method described in any one of the above characteristic descriptions, or includes a quantum bit calibration device described in the above characteristic descriptions.

[0133] Based on the same inventive concept, an embodiment of the present invention further proposes a quantum computer, including the quantum control system described in the above feature description.

[0134] Based on the same inventive concept, an embodiment of the present invention further proposes a readable storage medium having a computer program stored thereon, and when the computer program is executed by a processor, the quantum bit calibration method described in any one of the above-mentioned feature descriptions can be implemented.

[0135] The readable storage medium can be a tangible device that can keep and store the instructions used by the instruction execution device, such as but not limited to an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device or any suitable combination of the above. The more specific example (non-exhaustive list) of the readable storage medium includes: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a convex structure in a groove on which instructions are stored, and any suitable combination of the above. The computer program described here can be downloaded from the readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device through a network, such as the Internet, a local area network, a wide area network and / or a wireless network. The network can include copper transmission cables, optical fiber transmission, wireless transmission, routers, firewalls, switches, gateway computers and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer program from the network and forwards the computer program for storage in a readable storage medium in each computing / processing device. The computer program for performing the operation of the present invention may be an assembly instruction, an instruction set architecture (ISA) instruction, a machine instruction, a machine-dependent instruction, a microcode, a firmware instruction, a state setting data, or a 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" language or similar programming languages. The computer program may be executed entirely on the user's computer, partially on the user's computer, as an independent software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., using an Internet service provider to connect through the Internet). In some embodiments, by utilizing the state information of a computer program to personalize an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), the electronic circuit can execute computer-readable program instructions to implement various aspects of the present invention.

[0136] Here, various aspects of the present invention are described with reference to the flowchart and / or block diagram of the method, system and computer program product according to the embodiment of the present invention. It should be understood that each square frame of the flowchart and / or block diagram and the combination of the square frames in the flowchart and / or block diagram can be realized by a computer program. These computer programs can be provided to the processor of a general-purpose computer, a special-purpose computer or other programmable data processing device, so as to produce a machine, so that these programs, when executed by the processor of a computer or other programmable data processing device, produce a device for realizing the function / action specified in one or more square frames in the flowchart and / or block diagram. These computer programs can also be stored in a readable storage medium, and these computer programs make the computer, programmable data processing device and / or other equipment work in a specific way, so that the readable storage medium storing the computer program includes a manufactured product, which includes instructions for realizing various aspects of the function / action specified in one or more square frames in the flowchart and / or block diagram.

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

[0138] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example" or "specific example" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

[0139] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any technician in the relevant technical field, without departing from the scope of the technical solution of the present invention, makes any form of equivalent replacement or modification to the technical solution and technical content disclosed in the present invention, which does not depart from the content of the technical solution of the present invention and still falls within the protection scope of the present invention.

Claims

1. A method for calibrating a quantum bit, characterized in that: include: Determining whether an operating point of a quantum bit to be measured has drifted, the operating point comprising an operating voltage and a quantum bit frequency corresponding to the operating voltage; If drift occurs, the drift amount of the degenerate point of the subbit to be measured is obtained by using a gradient optimization algorithm and a Ramsey experiment; All the working points of the sub-bit to be measured are calibrated based on the drift amount of the degenerate point of the sub-bit to be measured.

2. The method according to claim 1, characterized in that The determining whether the working point of the sub-bit to be measured has drifted includes: Performing a Ramsey experiment on the subbit to be measured at a first working point and a second working point respectively, wherein the first working point and the second working point are two working points symmetrical along a degenerate point before the drift occurs; Based on the results of the two Ramsey experiments, it is determined whether the working point of the sub-bit to be measured drifts.

3. The method according to claim 2, characterized in that The determining, based on the results of the two Ramsey experiments, whether the working point of the subbit to be measured drifts, includes: Two oscillation frequencies were obtained through two Ramsey experiments; It is determined whether the working point of the sub-bit to be measured drifts based on the difference between the two oscillation frequencies.

4. The method according to claim 3, characterized in that The determining whether the working point of the sub-bit to be measured drifts based on the difference between the two oscillation frequencies includes: Determining whether the difference between the two oscillation frequencies is greater than a preset threshold; If yes, it is determined that the working 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 according to claim 1, characterized in that The determining whether the working point of the sub-bit to be measured has drifted includes: Respectively obtaining actual frequency magnitudes of the subbit to be measured at a first working point and a second working point, wherein the first working point and the second working point are two working points symmetrical along a degenerate point before drift occurs; Based on the two acquired actual frequencies, it is determined whether the working point of the sub-bit to be measured drifts.

6. The method according to claim 1, characterized in that The method of obtaining the drift amount of the degenerate point of the subbit to be measured by using the gradient optimization algorithm and the Ramsey experiment includes: Performing a Ramsey experiment on the subbit to be measured at a first working point and a second working point respectively, wherein the first working point and the second working point are two working points symmetrical along a degenerate point before the drift occurs; Using a gradient optimization algorithm to adjust the operating voltage value of the first operating point, so that the difference between the first oscillation frequency and the second oscillation frequency is within a first preset range, and obtaining the operating voltage value corresponding to the first operating point at this time as a calibrated voltage, wherein the first oscillation frequency is a result of a Ramsey experiment performed on the sub-bit to be measured at the first operating point, and the second oscillation frequency is a result of a Ramsey experiment performed on the sub-bit to be measured at the second operating point; The drift amount of the degenerate point of the sub-bit to be measured is obtained based on the calibrated voltage and a second voltage, wherein the second voltage is an operating voltage corresponding to the second operating point.

7. The method according to claim 6, characterized in that The obtaining the drift amount of the degenerate point of the sub-bit to be measured based on the calibrated voltage and the first voltage includes: Acquire a calibrated degenerate point of the sub-bit to be measured based on the calibrated voltage and the second voltage; The drift amount of the degenerate point of the sub-bit to be measured is obtained based on the calibrated degenerate point.

8. The method according to claim 6, characterized in that The step of adjusting the operating voltage value of the first operating point by using a gradient optimization algorithm includes: Obtaining the number n of times the working voltage of the first working point is currently updated; If the number n is less than a first preset value, a first guess value is obtained based on a first voltage, where the first voltage is the initial working voltage of the first working point before adjustment, and based on the first voltage and a preset adjustment range, the working voltage of the first working point is adjusted to a first guess value.

9. The method according to claim 8, characterized in that The step of adjusting the operating voltage value of the first operating point by using a gradient optimization algorithm further includes: If the number n is greater than or equal to the first preset value, the first voltage V0 and the current guess value V1, as well as the initial oscillation frequency f0 corresponding to the first voltage and the oscillation frequency f1 corresponding to the current guess value are obtained; According to the first voltage and the current guess value V1, as well as the initial oscillation frequency f0 and the oscillation frequency f1 corresponding to the current guess value, the value of the first voltage is adjusted to a second guess value V2: Wherein, f is the second oscillation frequency.

10. The method according to claim 9, characterized in that The step of adjusting the operating voltage value of the first operating point by using a gradient optimization algorithm further includes: Obtaining an oscillation frequency f2 corresponding to the second guess value V2; Determine whether |f2-f| is less than |f1-f|; If so, the first voltage V0 is updated to the second guessed value V2, and the initial oscillation frequency f0 is updated to f2.

11. A quantum bit calibration device, characterized in that: include: A judging unit, used to judge whether a working point of a quantum bit to be measured has drifted, wherein the working point includes a working voltage and a quantum bit frequency corresponding to the working voltage; An optimization unit, used for obtaining the drift amount of the degenerate point of the sub-bit to be measured by using a gradient optimization algorithm and a Ramsey experiment when drift occurs; A calibration unit is used to calibrate all working points of the sub-bit to be measured based on the drift amount of the degenerate point of the sub-bit to be measured.

12. A quantum control system, characterized in that: A quantum chip is calibrated using the quantum bit calibration method described in any one of claims 1 to 10, or a quantum bit calibration device including the quantum bit calibration device described in claim 11.

13. A quantum computer, characterized in that: Comprising the quantum control system as claimed in claim 12.

14. 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 quantum bit calibration method according to any one of claims 1 to 10.

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