Quantum bit working frequency determination method, storage medium and quantum computer

Abstract

The invention discloses a quantum bit working frequency determination method, a storage medium and a quantum computer, and belongs to the technical field of quantum computation.The method comprises the steps that after an initial microwave signal is applied to a drive line of a quantum bit, when the quantum bit is in a microwave crosstalk state, the drive line of the quantum bit drives the quantum bit to work; determining a first microwave signal actually transmitted on the driving line according to a preset crosstalk coefficient; determining an initial Hamiltonian of a quantum bit in a non-microwave crosstalk state, and performing spin wave approximation processing on the initial Hamiltonian to obtain a first Hamiltonian; updating a microwave signal in the first Hamiltonian into a first microwave signal to obtain a corresponding second Hamiltonian; constructing a matrix comprising a physical parameter of a quantum bit and a signal parameter of the first microwave signal according to the second Hamiltonian; and determining the working frequency of the quantum bits according to the physical parameters and the signal parameters. According to the invention, the working frequency of the quantum bit after microwave crosstalk influence can be determined without an experiment, and compensation and calibration are facilitated.

Description

Technical Field

[0001] This application relates to the field of quantum computing technology, and in particular to a method for determining the operating frequency of a qubit, a storage medium, and a quantum computer. Background Technology

[0002] A quantum computer is a physical device that performs high-speed mathematical and logical operations, stores and processes quantum information, following the laws of quantum mechanics. The main characteristics of quantum computers include high operating speed, strong information processing capabilities, and a wide range of applications. Compared to conventional computers, the greater the amount of information processed, the more advantageous it is for quantum computers to perform calculations, and the more accurately the calculations can be ensured.

[0003] Superconducting quantum processors composed of microwave-controlled qubit arrays represent the forefront of contemporary digital quantum computing, analog quantum simulation, and modeling. Microwave-controlled qubits enable controllable, high-fidelity single-qubit gates. A key requirement for quantum computing is precise microwave control applied to the drive lines of the qubits, allowing individual control over each qubit. However, microwave crosstalk is a major factor hindering the development of scalable quantum computing. Microwave crosstalk is defined as follows: although the microwave signal applied to a specific drive line is designed to control only one qubit, crosstalk propagation of that signal to other qubits occurs.

[0004] It is necessary to accurately determine the microwave crosstalk between individual qubits in order to compensate for or calibrate it.

[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 application is to provide a method for determining the operating frequency of a qubit, a storage medium, and a quantum computer, which can solve the problem of microwave crosstalk between qubits in the prior art. The operating frequency of the qubit after the influence of microwave crosstalk can be determined without experimentation, which facilitates compensation and calibration.

[0007] To address the above technical problems, the first aspect of this application proposes a method for determining the operating frequency of a qubit, the method comprising:

[0008] After an initial microwave signal is applied to the driving line of a qubit, when the qubit is in a state of microwave crosstalk, the first microwave signal actually transmitted on the driving line is determined according to a preset crosstalk coefficient.

[0009] The initial Hamiltonian of the qubit under non-microwave crosstalk state is determined, and the initial Hamiltonian is approximated by a vortex wave to obtain the first Hamiltonian.

[0010] The microwave signal in the first Hamiltonian is updated to the first microwave signal to obtain the corresponding second Hamiltonian.

[0011] A matrix comprising the physical parameters of the qubits and the signal parameters of the first microwave signal is constructed based on the second Hamiltonian, and the physical parameters and the signal parameters are extracted.

[0012] The operating frequency of the qubit is determined based on the physical parameters and the signal parameters.

[0013] Optionally, determining the initial Hamiltonian of the qubit in the non-microwave crosstalk state using the method described above includes:

[0014] The initial Hamiltonian of the qubit is determined based on the initial microwave signal, the capacitance of the qubit, and the coupling capacitance between the qubit and the driving line. The initial Hamiltonian is:

[0015]

[0016] Wherein, the H Qj This is the initial Hamiltonian. ω is Planck's constant. q For applied to the drive line

[0017] The frequency of microwave signals, 'a' is a raise or lower operator. It is the coupling capacitance between the qubit and the driving line.

[0018] C j It is the capacitance in a qubit, V Qj (t) is the initial microwave signal. It is the characteristic magnitude of the charge zero-point fluctuation of a qubit.

[0019] Optionally, in the method described above, when the qubit is in a microwave crosstalk state, determining the first microwave signal actually transmitted on the drive line based on a preset crosstalk coefficient includes:

[0020] Obtain the resonant frequencies of all qubits on the quantum chip;

[0021] When all qubits have the same resonant frequency, the first microwave signal is determined based on the initial microwave signal and the preset crosstalk coefficient between the two qubits.

[0022] The first microwave signal is:

[0023]

[0024] Where n is the total number of qubits and driving lines, It is the constant voltage of the signal on the driving line of the qubit, A i is the amplitude of the square envelope function of the initial microwave signal applied on the drive line, and t is the pulse duration of the initial microwave signal. It is the frequency of the initial microwave signal applied to the drive line. It is the driving phase of the initial microwave signal applied to the driving line, φ i→j R is the phase crosstalk coefficient from the driving line of the i-th qubit to the driving line of the j-th qubit. i→j It is the amplitude crosstalk coefficient from the driving line of the i-th qubit to the driving line of the j-th qubit.

[0025] Optionally, the method described above involves constructing a matrix comprising the physical parameters of the qubits and the signal parameters of the first microwave signal based on the second Hamiltonian, and extracting the physical parameters and signal parameters, including:

[0026] Obtain the initial unitary operator for the qubit;

[0027] Update the Hamiltonian in the initial unitary operator to the second Hamiltonian;

[0028] Convert the updated initial unitary operator into a matrix;

[0029] Extract a first factor from the matrix to characterize the physical parameters of the qubit and a second factor to characterize the signal parameters of the first microwave signal.

[0030] As described above, optionally, the matrix is:

[0031]

[0032] Among them, Ω Qj As the first factor, C Qj It is the second factor.

[0033] Optionally, the first factor can be:

[0034]

[0035] Wherein, the Ω Qj As the first factor, It is the coupling capacitance between the qubit and the driving line. C j It is the capacitance in a qubit. Let be Planck's constant. It is the characteristic order of magnitude of the charge zero-point fluctuation of a qubit;

[0036] The second factor is:

[0037]

[0038] Where n is the total number of qubits and driving lines, It is the constant voltage of the signal on the driving line of the qubit, A i It is the amplitude of the square envelope function of the microwave signal applied on the drive line, r i→j R is the amplitude crosstalk coefficient from the driving line of the i-th qubit to the driving line of the j-th qubit. z→j It is the amplitude crosstalk coefficient from the driving line of the z-th qubit to the driving line of the j-th qubit. It is the driving phase of the microwave signal applied to the driving line of the i-th qubit. It is the driving phase of the microwave signal applied to the driving line of the z-th qubit, φ i→j φ is the phase crosstalk coefficient of the crosstalk signal from the driving line of the i-th qubit to the driving line of the j-th qubit. z→j It is the phase crosstalk coefficient of the crosstalk signal from the driving line of the z-th qubit to the driving line of the j-th qubit.

[0039] Optionally, the operating frequency is as described above:

[0040]

[0041] Among them, the For the operating frequency, the Ω Qj As the first factor, the C Qj It is the second factor.

[0042] The second aspect of this application proposes a method for determining the qubit crosstalk coefficient, comprising:

[0043] The amplitude crosstalk coefficient and phase crosstalk coefficient of the preset qubit;

[0044] The operating frequency of the qubit is determined by the method described in any one of the first aspects based on the amplitude crosstalk coefficient and the phase crosstalk coefficient.

[0045] The Rabi oscillation experiment was performed on the qubit to obtain the measurement frequency of the qubit;

[0046] The amplitude crosstalk coefficient and phase crosstalk coefficient when the operating frequency is the same as the measurement frequency are determined as the target crosstalk coefficient.

[0047] A third aspect of this application provides a readable storage medium having a computer program stored thereon, which, when executed by a processor, can implement the method for determining the operating frequency of qubits as described in the first aspect or the method for determining the crosstalk coefficient of qubits as described in the second aspect.

[0048] The fourth aspect of this application proposes a quantum computer, characterized in that the operating frequency of each qubit on the quantum chip is determined by the method described in any one of the first aspects, or the crosstalk coefficient of each qubit on the quantum chip is determined by the method described in the second aspect.

[0049] Compared with the prior art, this application has the following beneficial effects:

[0050] This application first applies an initial microwave signal to the driving line of a qubit to determine the first microwave signal actually transmitted on the driving line of the qubit when microwave crosstalk exists. This first microwave signal is used to characterize the microwave crosstalk effect of microwave signals applied to the driving lines of other qubits on the target qubit. Then, the correspondence between the Hamiltonian of the qubit and the microwave signal applied to the driving line is obtained to determine the second Hamiltonian under the influence of crosstalk. Based on the second Hamiltonian, a matrix including the physical parameters of the qubit and the signal parameters of the first microwave signal is constructed to obtain the physical parameters of the qubit and the signal parameters of the first microwave signal. Finally, the operating frequency of the qubit is determined based on the extracted physical parameters and signal parameters. This application can determine the operating frequency of the qubit under the influence of microwave crosstalk without performing Rabi oscillation experiments on the qubit, and then calibrate and compensate for the crosstalk on the driving line based on the determined operating frequency.

[0051] The method for determining the qubit crosstalk coefficient, the quantum computer, and the readable storage medium proposed in this application belong to the same concept as the method for determining the qubit operating frequency, and therefore have the same beneficial effects, which will not be elaborated here. Attached Figure Description

[0052] Figure 1 This is a schematic diagram illustrating the effect of microwave crosstalk between adjacent qubits, as exemplified in an embodiment of this application.

[0053] Figure 2 This is a flowchart illustrating a method for determining the operating frequency of a qubit according to an embodiment of this application.

[0054] Figure 3 This is a schematic diagram of a process for determining the operating frequency of a qubit based on a unitary operator, as proposed in an embodiment of this application.

[0055] Figure 4 This is a flowchart illustrating a method for determining the qubit crosstalk coefficient proposed in an embodiment of this application. Detailed Implementation

[0056] The specific embodiments of this application will be described in more detail below with reference to the schematic diagrams. The advantages and features of this application 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 this application.

[0057] In the description of this application, 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 used only for the convenience of describing this application 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 application.

[0058] 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 application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0059] A quantum chip integrates multiple qubits, each with a corresponding driving line. Driving a qubit requires applying a driving signal (such as a microwave signal) to that driving line. Ideally, the driving signal applied to each qubit's driving line should only drive that specific qubit. However, in practical applications, the driving signal applied to each qubit's driving line can not only drive that qubit but also drive adjacent or nearby qubits through spatial radiation, affecting the driving of other qubits (crosstalk). Figure 1 The diagram shows the driving accuracy of two adjacent qubits. Crosstalk directly affects the driving accuracy of each qubit, and thus the computational accuracy of the qubits performing quantum computing tasks.

[0060] Figure 1The diagram illustrates two qubits (Qubit1 and Qubit2), each with corresponding drive lines (Drive Line1 and Drive Line2). The drive lines are frequency drive lines for the qubits, and the microwave signals applied to these lines drive the qubits' operating frequency. The operating frequency of a qubit when performing an operation is called its operating point. When performing quantum gate operations, the operating frequency directly affects the precision of the qubit's operation. When microwave signals are applied to the frequency drive lines of other qubits, they directly affect the frequency of the current qubit, causing its operating frequency to shift and thus reducing its precision in performing quantum gate operations. Therefore, it is necessary to determine the impact of crosstalk from the qubit's frequency drive lines on the microwave crosstalk of its operating frequency.

[0061] like Figure 2 As shown in the figure, this embodiment provides a method for determining the operating frequency of a qubit, which includes the following steps.

[0062] Step S10: After the initial microwave signal is applied to the driving line of the qubit, when the qubit is in a microwave crosstalk state, the first microwave signal actually transmitted on the driving line is determined according to the preset crosstalk coefficient.

[0063] In this embodiment, the initial microwave signal is applied to the frequency drive line of the qubit to control the common frequency of the qubit; taking the j-th qubit on the quantum chip as an example, the initial microwave signal applied to its drive line is expressed as follows:

[0064]

[0065] in, It is the constant voltage of the signal on the driving line of the qubit, A j is the amplitude of the square envelope function of the microwave signal applied on the drive line, and t is the pulse duration of the microwave signal. It is the frequency of the microwave signal applied to the drive line. It refers to the driving phase of the microwave signal applied to the driving line. In practice, an initial microwave signal is usually output by an instrument such as a signal source or microwave source and transmitted to the driving line of the qubit on the quantum chip through a quantum measurement and control link.

[0066] The initial microwave signal applied to the driving line of a qubit is the microwave signal output by the signal source. Ideally, when there is no crosstalk between the driving lines of adjacent qubits on the quantum chip, the microwave signal received by the qubit is consistent with the output of the signal source. However, in reality, crosstalk is difficult to avoid. The first microwave signal on the driving line of a qubit includes not only the initial microwave signal output by the signal source it is connected to, but also the crosstalk signal generated by the microwave signals applied to the driving lines of other qubits. That is, the crosstalk coefficients of other qubits can be preset, and the first microwave signal actually transmitted on the driving line of each qubit can be determined based on the preset crosstalk coefficients.

[0067]

[0068] Where n is the total number of qubits and driving lines, and i and j are used to represent the i-th qubit and the j-th qubit; A is the constant voltage of the signal on the driving line of the i-th qubit. i is the amplitude of the square envelope function of the initial microwave signal applied to the driving line of the i-th qubit, and t is the pulse duration of the initial microwave signal. It is the frequency of the initial microwave signal applied to the driving line of the i-th qubit. It is the driving phase of the initial microwave signal applied to the driving line of the i-th qubit, φ. i→j R is the phase crosstalk coefficient of the driving line of the j-th qubit to the driving line of the initial microwave signal applied from the driving line of the i-th qubit. i→j It is the amplitude crosstalk coefficient of the initial microwave signal applied from the driving line of the i-th qubit to the driving line of the j-th qubit.

[0069] Specifically, in the formula for the first microwave signal mentioned above, the j-th qubit can be exemplified as the target qubit, and i, ranging from 0 to n, represents all other qubits, each acting as a crosstalk bit to determine their microwave crosstalk influence on the microwave signal on the drive line of the target qubit. It can be understood that when i and j are the same, it represents the initial microwave signal applied by the signal source received by the drive line of the target qubit. By summing all the aforementioned microwave crosstalk influences and the initial microwave signal, the actual first microwave signal transmitted on the drive line of the target qubit when all other qubits on the quantum chip influence the microwave crosstalk of one of the target qubits can be determined.

[0070] It should be added that the phase crosstalk coefficient and amplitude crosstalk coefficient of the crosstalk signal mentioned above can be set in a preset way, and then compared and verified by the measurement experiment of the quantum bit operating frequency.

[0071] Furthermore, when determining the first microwave signal as described above, the frequency of the microwave signal applied to the driving line of each qubit needs to be considered individually, which is quite complex. Therefore, in this embodiment, it can be determined that the resonant frequency of all qubits on the quantum chip is the same, so that the frequency of the microwave signal applied to the driving line of all qubits is the same. At this time, the first microwave signal can be simplified to:

[0072]

[0073] Where n is the total number of qubits and driving lines, It is the constant voltage of the signal on the driving line of the qubit, A i is the amplitude of the square envelope function of the initial microwave signal applied on the drive line, and t is the pulse duration of the initial microwave signal. It is the frequency of the initial microwave signal applied to the drive line. It is the driving phase of the initial microwave signal applied to the driving line, φ i→j R is the phase crosstalk coefficient from the driving line of the i-th qubit to the driving line of the j-th qubit. i→j It is the amplitude crosstalk coefficient from the driving line of the i-th qubit to the driving line of the j-th qubit.

[0074] Step S20: Determine the initial Hamiltonian of the qubit under non-microwave crosstalk state, and perform a vortex approximation on the initial Hamiltonian to obtain the first Hamiltonian.

[0075] In this embodiment, the qubit is a superconducting qubit, whose physical structure is formed by a superconducting Josephson junction ring and a capacitor connected in parallel. The superconducting Josephson junction ring is equivalent to an inductor, and an oscillator is formed through the inductor and capacitor. The driving line is capacitively coupled to the superconducting qubit. The microwave signal applied to the driving line can adjust the inductance of the superconducting Josephson junction ring, thereby adjusting the oscillation frequency of the oscillator and thus adjusting the operating frequency of the qubit.

[0076] The system energy of the qubit resonator system can be represented by the Hamiltonian, which is related not only to the specific physical structural parameters of the qubit, such as capacitance and coupling capacitance, but also to the microwave signal transmitted on the qubit's driving line. Without considering crosstalk on the driving line, the initial Hamiltonian of the qubit is determined as:

[0077]

[0078] Where j can represent the j-th qubit, H Qj This is the initial Hamiltonian. ω is Planck's constant. q The frequency of the microwave signal applied to the drive line, 'a' is the lifting operator and 'decreasing operator, respectively. It is the coupling capacitance between the qubit and the driving line. C j It is the capacitance in the qubit (connected in parallel with the superconducting Josephson junction ring), V Qj (t) is the initial microwave signal. It is the characteristic magnitude of the charge zero-point fluctuation of a qubit.

[0079] Furthermore, the initial Hamiltonian mentioned above includes multiple oscillating terms. The high-frequency oscillation terms generally have a time integral that is approximately zero over a period of time. By using the vortex approximation to eliminate the high-frequency oscillation terms in the initial Hamiltonian, a simplified first Hamiltonian for the qubit is obtained, expressed as:

[0080]

[0081] Where j can represent the j-th qubit, H ′ Qj For the first Hamiltonian, ω q The frequency of the microwave signal applied to the drive line. 'a' is the lifting operator and 'decreasing operator, respectively. It is the coupling capacitance between the qubit and the driving line. C j It is the capacitance in the qubit (connected in parallel with the superconducting Josephson junction ring), V Qj (t) is the initial microwave signal. It is the characteristic magnitude of the charge zero-point fluctuation of a qubit.

[0082] Step S30: Update the microwave signal in the first Hamiltonian to the first microwave signal to obtain the corresponding second Hamiltonian.

[0083] By determining the first Hamiltonian in step S20, it can be seen that the first Hamiltonian is the Hamiltonian of the qubit system, which is related to the microwave signal applied to the driving line of the qubit. Therefore, considering the crosstalk effect on the driving line, the microwave signal in the first Hamiltonian can be updated to the first microwave signal to obtain the corresponding second Hamiltonian, which characterizes the system energy of the qubit under the influence of crosstalk, and is expressed as:

[0084]

[0085] in, It is the coupling capacitance between the qubit and the driving line. C j It is the capacitance in the qubit (connected in parallel with the superconducting Josephson junction ring). It represents the characteristic magnitude of the charge zero-point fluctuation of a qubit; n is the total number of qubits and driving lines, and i and j are used to represent the i-th qubit and the j-th qubit, respectively. A is the constant voltage of the signal on the driving line of the i-th qubit. i It is the amplitude of the square envelope function of the microwave signal applied to the driving line of the i-th qubit. It is the driving phase of the microwave signal applied to the driving line of the i-th qubit, φ. i→j R is the phase crosstalk coefficient of the crosstalk signal from the driving line of the i-th qubit to the driving line of the j-th qubit. i→j σ is the amplitude crosstalk coefficient of the crosstalk signal applied from the driving line of the i-th qubit to the driving line of the j-th qubit. x and σ y It is a Pauli operator.

[0086] Step S40: Construct a matrix including the physical parameters of the qubits and the signal parameters of the first microwave signal based on the second Hamiltonian, and extract the physical parameters and signal parameters.

[0087] The second Hamiltonian of the qubit can also be represented using a unitary operator, as shown in the example:

[0088]

[0089] Among them, U Qj H″ is the unitary operator for the j-th qubit. Qj This is the second Hamiltonian. is Planck's constant.

[0090] Furthermore, the unitary operator described above can be converted into matrix form, and H″ in step S30 above can be transformed into matrix form. Qj Substituting these into the unitary operator above, we can obtain a matrix that includes the physical parameters of the qubits and the signal parameters of the first microwave signal.

[0091] Step S50: Determine the operating frequency of the qubit based on the physical parameters and signal parameters.

[0092] Once the physical parameters of the qubit are determined, and the signal parameters of the first microwave signal applied to the driving line are also determined, the operating frequency of the qubit can be determined.

[0093] This application does not require performing Rabi oscillation experiments on the qubit. The operating frequency of the qubit under the influence of microwave crosstalk can be determined according to the above steps, and then the crosstalk on the driving line can be calibrated and compensated according to the determined operating frequency.

[0094] In this application, an initial microwave signal is first applied to the drive line of the qubit, and the first microwave signal actually transmitted on the drive line of the qubit when microwave crosstalk exists is determined, which is used to characterize the microwave crosstalk effect of the microwave signal applied on the drive line of other qubits on the target qubit. Then, the correspondence between the Hamiltonian of the qubit and the microwave signal applied on the drive line is obtained to determine the second Hamiltonian under the crosstalk effect, and a matrix including the physical parameters of the qubit and the signal parameters of the first microwave signal is constructed according to the second Hamiltonian, and the physical parameters of the qubit and the signal parameters of the first microwave signal are obtained. Finally, the operating frequency of the qubit is determined according to the extracted physical parameters and signal parameters. This application can determine the operating frequency of the qubit under the influence of microwave crosstalk without performing a Rabi oscillation experiment on the qubit, and then calibrate and compensate the crosstalk on the drive line according to the determined operating frequency.

[0095] For example, as Figure 3 shown, constructing a matrix including the physical parameters of the qubit and the signal parameters of the first microwave signal according to the second Hamiltonian, and extracting the physical parameters and signal parameters include the following steps:

[0096] Step S410: Obtain the initial unitary operator of the qubit.

[0097] The initial unitary operator of the qubit obtained in this step is the above unitary operator U Qj , and its representation is also described by the above formula.

[0098] Step S420: Update the Hamiltonian in the initial unitary operator to the second Hamiltonian.

[0099] Substituting the second Hamiltonian directly into the calculation of the above unitary operator, it can be updated to:

[0100]

[0101] where U' Qj is the unitary operator, is the coupling capacitance between the qubit and the drive line, C j is the capacitance in the qubit (in parallel with the superconducting Josephson junction loop), is the characteristic magnitude of the charge zero-point fluctuation of the qubit, is the Planck constant; n is the total number of qubits and drive lines, and i and j are used to represent the i-th qubit and the j-th qubit; is the constant voltage of the signal on the drive line of the i-th qubit, A i is the amplitude of the square envelope function of the microwave signal applied on the drive line of the i-th qubit, is the drive phase of the microwave signal applied on the drive line of the i-th qubit, φi→j R is the phase crosstalk coefficient of the crosstalk signal from the driving line of the i-th qubit to the driving line of the j-th qubit. i→j It is the amplitude crosstalk coefficient of the crosstalk signal applied from the driving line of the i-th qubit to the driving line of the j-th qubit.

[0102] Step S430: Convert the updated initial unitary operator into a matrix, specifically, the unitary operator U′ mentioned above. Qj It can also be represented in matrix form, as shown in the example:

[0103]

[0104] In the above formula:

[0105]

[0106] in, It is the capacitance between the qubit and the driving line. C j It is the capacitance in a qubit. Let be Planck's constant. It represents the characteristic magnitude of the charge zero-point fluctuation of a qubit; n is the total number of qubits and driving lines. It is the constant voltage of the signal on the driving line of the qubit, A i It is the amplitude of the square envelope function of the microwave signal applied on the drive line, r i→j R is the amplitude crosstalk coefficient of the crosstalk signal from the driving line of the i-th qubit to the driving line of the j-th qubit. z→j It is the amplitude crosstalk coefficient of the crosstalk signal from the driving line of the z-th qubit to the driving line of the j-th qubit. It is the driving phase of the microwave signal applied to the driving line of the i-th qubit. It is the driving phase of the microwave signal applied to the driving line of the z-th qubit, φ i→j φ is the phase crosstalk coefficient of the crosstalk signal from the driving line of the i-th qubit to the driving line of the j-th qubit. z→j It is the phase crosstalk coefficient of the crosstalk signal from the driving line of the z-th qubit to the driving line of the j-th qubit.

[0107] Step S440: Extract from the matrix a first factor for characterizing the physical parameters of the qubit and a second factor for characterizing the signal parameters of the first microwave signal.

[0108] In the above unitary operator U′ Qj In the formula, Ω QjThe first factor is determined to characterize the physical parameters of the qubit, such as capacitance parameters and the coupling capacitance between the driving line and the signal source output; C Qj It is determined as the second factor, used to characterize the signal parameters of the first microwave signal on the drive line.

[0109] After extracting the physical parameters from the matrix and the signal parameters of the first microwave signal through the above steps S410-S440, the operating frequency of the qubit can be determined.

[0110] For example, by combining the first and second factors in the matrix, the operating frequency of the qubit is determined as follows:

[0111]

[0112] in, For the operating frequency, Ω Qj As the first factor, C Qj It is the second factor.

[0113] like Figure 4 As shown, based on the same application concept, this embodiment also provides a method for determining the qubit crosstalk coefficient, including the following steps:

[0114] Step S11: Preset the amplitude crosstalk coefficient and phase crosstalk coefficient of the qubit.

[0115] In step S10 above, V′ Qj In (t), the amplitude crosstalk coefficient and phase crosstalk coefficient of the microwave signal on the driving line of adjacent qubits are defined. Therefore, by using the preset amplitude crosstalk coefficient and phase crosstalk coefficient of the qubits, the corresponding first microwave signal V′ can be determined. Qj (t).

[0116] Step S21: Determine the operating frequency of the qubit using the methods described in steps S10-S50 above, based on the amplitude crosstalk coefficient and the phase crosstalk coefficient.

[0117] Then, according to steps 10-S50 above, V′ Qj Substituting (t) into the Hamiltonian and the unitary operator, the operating frequency of the qubit can be determined.

[0118] Step S31: Perform a Rabi oscillation experiment on the qubit to obtain the measurement frequency of the qubit.

[0119] In this step, an experimental measurement method is adopted to perform a Rabi oscillation experiment on the target qubit and measure the measurement frequency of the qubit. The measurement frequency obtained by measurement is the measurement result under the influence of microwave crosstalk; therefore, it can be compared with the operating frequency determined by calculation in step S21.

[0120] Step S41: Determine the amplitude crosstalk coefficient and phase crosstalk coefficient when the operating frequency is the same as the measurement frequency as the target crosstalk coefficient.

[0121] Specifically, the operating frequency of the qubit obtained in steps S11-S21 is under the influence of microwave crosstalk, and the measurement frequency obtained in step S31 is also under the influence of microwave crosstalk. Therefore, when comparing the operating frequency and the measurement frequency, the amplitude crosstalk coefficient and phase crosstalk coefficient defined in step S11 are the crosstalk coefficients of the qubit.

[0122] Based on the same concept, embodiments of this application also provide a quantum computer that uses any of the methods described above to determine the operating frequency of each qubit on the quantum chip, or uses the methods described above to determine the crosstalk coefficient of each qubit on the quantum chip.

[0123] Based on the same concept, embodiments of this application also provide a readable storage medium storing a computer program thereon, which, when executed by a processor, can implement the above-described method for executing quantum computing tasks.

[0124] A 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. Networks can include copper transmission cables, fiber optic transmissions, wireless transmissions, 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 on a readable storage medium within the respective computing / processing device. The computer program used to perform the operations of this application 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 to implement various aspects of this application.

[0125] Various aspects of this application are described herein with reference to flowchart illustrations and / or block diagrams of methods, systems, and computer program products according to embodiments of this application. 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 includes an article of manufacture comprising instructions for implementing various aspects of the functions / actions specified in one or more blocks of the flowchart illustrations and / or block diagrams.

[0126] 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.

[0127] In the description of this specification, the 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 this application. 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.

[0128] The above are merely preferred embodiments of this application and do not constitute any limitation on this application. Any equivalent substitutions or modifications made by those skilled in the art to the technical solutions and content disclosed in this application without departing from the scope of the technical solutions of this application shall still fall within the protection scope of this application.

Claims

1. A method for determining the operating frequency of a qubit, characterized in that, The method comprises: After an initial microwave signal is applied to a driving line of a quantum bit, a first microwave signal actually transmitted on the driving line is determined according to a preset crosstalk coefficient when the quantum bit is in a microwave crosstalk state; An initial Hamiltonian of the quantum bit in a non-microwave crosstalk state is determined, and a first Hamiltonian is obtained by performing a rotating wave approximation on the initial Hamiltonian; The microwave signal in the first Hamiltonian is updated to the first microwave signal to obtain a corresponding second Hamiltonian; A matrix including physical parameters of the quantum bit and signal parameters of the first microwave signal is constructed according to the second Hamiltonian, and the physical parameters and the signal parameters are extracted; A working frequency of the quantum bit is determined according to the physical parameters and the signal parameters.

2. The method of claim 1, wherein, The initial Hamiltonian of the quantum bit in the non-microwave crosstalk state comprises: The initial Hamiltonian of the quantum bit is determined according to the initial microwave signal, a capacitance of the quantum bit, and a coupling capacitance between the quantum bit and the driving line, and the initial Hamiltonian is: where H0is the initial Hamiltonian, Qj H0= hωa†a+ 1 2 h is the Planck constant, ω q is the frequency of the initial microwave signal applied to the drive line, and a is the raising operator, C is the coupling capacitance between the qubit and the drive line, C j is the capacitance in the qubit, V Qj (t) is the initial microwave signal, is the characteristic magnitude of the charge zero-point fluctuation of the qubit.

3. The method of claim 1, wherein, When the quantum bit is in the microwave crosstalk state, the first microwave signal actually transmitted on the driving line is determined according to a preset crosstalk coefficient, which comprises: Resonant frequencies of all quantum bits on a quantum chip are obtained; When the resonant frequencies of all quantum bits are the same, the first microwave signal is determined according to the initial microwave signal and a preset crosstalk coefficient between two quantum bits; The first microwave signal is: where n is the total number of qubits and drive lines, is the constant voltage of the signal on the drive line of the qubit, A i is the amplitude of the square envelope function of the initial microwave signal applied on the drive line, t is the duration of the pulse of the initial microwave signal, is the frequency of the initial microwave signal applied on the drive line, is the drive phase of the initial microwave signal applied on the drive line, φ i→j is the phase crosstalk coefficient from the drive line of the i-th qubit to the drive line of the j-th qubit, r i→j is the amplitude crosstalk coefficient from the drive line of the i-th qubit to the drive line of the j-th qubit.

4. The method of claim 1, wherein, According to the second Hamiltonian, a matrix including physical parameters of the quantum bit and signal parameters of the first microwave signal is constructed, and the physical parameters and the signal parameters are extracted, which comprises: An initial unitary operator of the quantum bit is obtained; The Hamiltonian in the initial unitary operator is updated to the second Hamiltonian; The updated initial unitary operator is converted into a matrix; First factors for representing the physical parameters of the quantum bit and second factors for representing the signal parameters of the first microwave signal are extracted from the matrix.

5. The method of claim 4, wherein, The matrix is: wherein Ω Qj is a first factor, C Qj is a second factor.

6. The method of claim 5, wherein, The first factor is: wherein the Ω Qj is a first factor, is a coupling capacitance between the qubit and the drive line, C j is a capacitance in the qubit, h is Planck's constant, is a characteristic magnitude of the charge zero-point fluctuation of the qubit; The second factor is: where n is the total number of qubits and drive lines, is the constant voltage of the signal on the drive line of the i-th qubit, A i is the amplitude of the square envelope function of the microwave signal applied on the drive line, r i→j is the amplitude crosstalk coefficient from the drive line of the i-th qubit to the drive line of the j-th qubit, r z→j is the amplitude crosstalk coefficient from the drive line of the z-th qubit to the drive line of the j-th qubit, is the drive phase of the microwave signal applied on the drive line of the i-th qubit, φ is the drive phase of the microwave signal applied on the drive line of the z-th qubit, φ i→j is the phase crosstalk coefficient of the crosstalk signal from the drive line of the i-th qubit to the drive line of the j-th qubit, φ z→j is the phase crosstalk coefficient of the crosstalk signal from the drive line of the z-th qubit to the drive line of the j-th qubit.

7. The method of claim 5, wherein, The working frequency is: Wherein, the is the working frequency, the Ω Qj is the first factor, the C Qj is the second factor.

8. A method for determining the crosstalk coefficient of a qubit, characterized in that, It comprises: Preset amplitude crosstalk coefficients and phase crosstalk coefficients of quantum bits; According to the amplitude crosstalk coefficients and the phase crosstalk coefficients, the working frequency of the quantum bit is determined by using the method of any one of claims 1-7; A Rabi oscillation experiment is performed on the quantum bit to obtain a measurement frequency of the quantum bit; When the working frequency and the measurement frequency are the same, the amplitude crosstalk coefficient and the phase crosstalk coefficient are determined as target crosstalk coefficients.

9. A readable storage medium, having stored thereon a computer program, characterized in that, The computer program is executed by a processor to implement the method for determining the working frequency of the quantum bit according to claims 1-7 or the method for determining the crosstalk coefficient of the quantum bit according to claim 8.

10. A quantum computer, characterized by, The working frequency of each quantum bit on a quantum chip is determined by using the method of any one of claims 1-7, or the crosstalk coefficient of each quantum bit on the quantum chip is determined by using the method of claim 8.

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