Method for obtaining a drive crosstalk coefficient between quantum bits

Abstract

The application provides an acquisition method of a driving crosstalk coefficient between quantum bits, and the method comprises the following steps: providing a quantum chip, wherein the quantum chip is provided with a first quantum bit and a second quantum bit; applying a driving signal with a first amplitude to the first quantum bit for a certain length of time; acquiring an amplitude of a pull-push oscillation on the second quantum bit as a second amplitude; and acquiring a crosstalk coefficient of the driving signal of the first quantum bit to the second quantum bit based on the first amplitude and the second amplitude. The technical scheme of the application can acquire the influence degree of the driving crosstalk between two quantum bits, so that the researchers can optimize the quantum chip according to the crosstalk coefficient.

Description

Technical Field

[0001] The present invention belongs to the field of quantum computing technology, and in particular relates to a method and device for obtaining a driving crosstalk coefficient between quantum bits, a quantum computer, and a readable storage medium. Background Art

[0002] The physical systems that enable quantum computing include superconducting quantum computing, semiconductor quantum computing, and ion trap quantum computing. The core of superconducting quantum computing is the superconducting quantum chip, which is equipped with a number of qubits. To control the qubits in the superconducting quantum chip, XY control lines (or microwave drive lines) are used to transmit microwave drive signals to the corresponding qubits to control the qubit's energy level transitions.

[0003] During the execution of a multi-qubit quantum circuit, a single qubit is easily affected by microwave pulses from the XY control lines (or microwave drive lines) that drive other qubits, leading to the excitation of undesirable quantum states. This phenomenon is called drive crosstalk.

[0004] In order to characterize the impact of the driven crosstalk between quantum bits, we need to propose a method to obtain the driven crosstalk coefficient between quantum bits.

[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 any form of implication 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 method for obtaining the driven crosstalk coefficient between quantum bits, a method for obtaining the crosstalk matrix, a device for obtaining the crosstalk coefficient between quantum bits, a readable storage medium and a quantum control system. The method for obtaining the driven crosstalk coefficient between quantum bits can measure the driven crosstalk coefficient of the driving signal on the first quantum bit on the quantum chip on the second quantum bit, thereby calibrating the degree of influence of the driven crosstalk between quantum bits, which is convenient for R&D personnel to optimize the quantum chip according to the driven crosstalk coefficient.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a method for obtaining a driven crosstalk coefficient between quantum bits, the method comprising:

[0008] Providing a quantum chip, wherein a first quantum bit and a second quantum bit are provided on the quantum chip;

[0009] Applying a driving signal with a first amplitude for a certain time length to the first qubit, wherein the frequency of the driving signal is consistent with the frequency of the second qubit within a first allowable error range;

[0010] obtaining an amplitude of the Rabi oscillation on the second quantum bit as a second amplitude;

[0011] A crosstalk coefficient of the driving signal of the first quantum bit on the second quantum bit is obtained based on the first amplitude and the second amplitude.

[0012] Optionally, obtaining a crosstalk coefficient of a driving signal of the first qubit on the second qubit based on the first amplitude and the second amplitude includes:

[0013] Using the formula:

[0014]

[0015] A crosstalk coefficient of the driving signal of the first quantum bit on the second quantum bit is calculated.

[0016] Optionally, the driving signal is a π pulse.

[0017] Optionally, the time length is 100 to 1000 nanoseconds.

[0018] Optionally, the first error allowable range is 0 to 2 MHz.

[0019] Optionally, obtaining the amplitude of the Rabi oscillation as a second amplitude includes: fitting the Rabi oscillation with a cosine function to obtain the second amplitude.

[0020] In a second aspect, the present invention provides a method for obtaining a driving crosstalk matrix, comprising:

[0021] A quantum chip is provided, on which N quantum bits are arranged;

[0022] Repeat the following steps: selecting one qubit from the N qubits as a first qubit, and then selecting one qubit from the N qubits as a second qubit; applying a driving signal having a first amplitude for a certain time length to the first qubit; obtaining the amplitude of the Rabi oscillation on the second qubit as a second amplitude; obtaining a crosstalk coefficient of the driving signal of the first qubit on the second qubit based on the first amplitude and the second amplitude; until,

[0023] The selection of the first qubit and the second qubit has traversed the N qubits to obtain N2 crosstalk coefficients;

[0024] An N×N driving crosstalk matrix is ​​obtained according to the N2 crosstalk coefficients.

[0025] In a third aspect, the present invention provides a device for obtaining a crosstalk coefficient between quantum bits, comprising:

[0026] A quantum chip, wherein a first quantum bit and a second quantum bit are provided on the quantum chip;

[0027] a driving signal applying module, configured to apply a driving signal having a first amplitude for a certain time length to the first qubit, wherein the driving signal is configured to induce Rabi oscillation in the second qubit;

[0028] A second amplitude acquisition module, configured to acquire the amplitude of the Rabi oscillation as a second amplitude;

[0029] A crosstalk coefficient acquisition module is used to obtain a crosstalk coefficient of the driving signal of the first quantum bit on the second quantum bit based on the first amplitude and the second amplitude.

[0030] In a fourth aspect, the present invention provides a readable storage medium having a computer program stored thereon, which, when executed, can implement the method for obtaining the driven crosstalk coefficient between quantum bits provided in the first aspect of the present invention.

[0031] In a fifth aspect, the present invention provides a quantum control system, which includes the device for obtaining the crosstalk coefficient between quantum bits provided in the third aspect of the present invention.

[0032] Compared with the existing technology, it has the following beneficial effects:

[0033] The present invention provides a method for obtaining a driven crosstalk coefficient between quantum bits. The first step is to provide a quantum chip on which a first quantum bit and a second quantum bit are disposed. The second step is to apply a driving signal having a first amplitude to the first quantum bit for a certain length of time, wherein the frequency of the driving signal is consistent with the frequency of the second quantum bit within a first error tolerance range. The third step is to obtain the amplitude of the Rabi oscillation on the second quantum bit as a second amplitude. The fourth step is to obtain the crosstalk coefficient of the driving signal of the first quantum bit on the second quantum bit based on the first amplitude and the second amplitude. The method for obtaining a driven crosstalk coefficient between quantum bits of the present invention induces Rabi oscillation in the second quantum bit through the driving signal on the driving line of the first quantum bit. The crosstalk coefficient is calibrated using the amplitude of the Rabi oscillation and the amplitude of the driving signal. The degree of influence of the driven crosstalk between the two quantum bits can be obtained, allowing researchers to optimize the quantum chip based on the crosstalk coefficient.

[0034] The method for obtaining the driving crosstalk matrix provided by the present invention can obtain the driving crosstalk coefficients between each quantum bit on a quantum chip, so that researchers can optimize the quantum chip based on the obtained driving crosstalk matrix.

[0035] The device for obtaining the crosstalk coefficient between quantum bits, the readable storage medium, and the quantum control system proposed in the present invention, and the method for obtaining the driving crosstalk coefficient between the quantum bits, belong to the same inventive concept and therefore have the same beneficial effects, and will not be elaborated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0037] Figure 1 1 is a flow chart of a method for obtaining a driving crosstalk coefficient between quantum bits according to an embodiment of the present invention;

[0038] Figure 2 FIG. 4 is a schematic diagram of a driving crosstalk matrix according to an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The following describes specific embodiments of the present invention in more detail with reference to schematic diagrams. The advantages and features of the present invention will become more apparent from the following description and claims. It should be noted that the drawings are greatly simplified and not to exact scale, and are intended solely to facilitate and clearly illustrate the embodiments of the present invention.

[0040] In the description of the present invention, it should be understood that the terms "center", "up", "down", "left", "right", etc., indicating directions or positional relationships, are 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.

[0041] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0042] The frequency of a quantum bit when performing an operation is called a working point, and when performing a quantum gate operation, due to the interference of some other factors, the quantum bit will have some errors when working, and we want to find the ideal working point of each quantum bit when performing a specific operation, and reduce the errors as much as possible when they operate. When performing a single-bit gate, the main error sources are drive crosstalk and ZZ coupling, and the present application is a calibration method for the drive crosstalk coefficient, so only the drive crosstalk is explained as necessary. As described in the background art, drive crosstalk refers to applying a drive signal to the drive line of a certain quantum bit, and due to energy leakage, a certain anharmonic drive will be generated on other quantum bits, causing other quantum bits to have a certain excitation probability.

[0043] The core idea of the present application is to provide a method for obtaining the drive crosstalk coefficient between quantum bits, so as to calibrate the size of the drive crosstalk coefficient, thereby characterizing the influence degree of the drive crosstalk between quantum bits.

[0044] <Embodiment I>

[0045] The present embodiment provides a method for obtaining the drive crosstalk coefficient between quantum bits, please refer to Figure 1 , Figure 1 The flowchart of the method for obtaining the drive crosstalk coefficient between quantum bits provided by the present embodiment can be seen from Figure 1 , the method comprises:

[0046] S1: providing a quantum chip, the quantum chip is provided with a first quantum bit and a second quantum bit;

[0047] S2: applying a drive signal with a first amplitude to the first quantum bit for a certain length of time, the frequency of the drive signal is consistent with the frequency of the second quantum bit within a first error allowed range;

[0048] S3: obtaining the amplitude of the pull-in oscillation of the second quantum bit as a second amplitude;

[0049] S4: obtaining the crosstalk coefficient of the drive signal of the first quantum bit to the second quantum bit based on the first amplitude and the second amplitude.

[0050] In step S1, in addition to the first quantum bit and the second quantum bit, the quantum chip may also include other quantum bits, and the quantum bits are coupled to each other. Each quantum bit is coupled to an XY signal transmission line and a Z signal transmission line, and the XY signal transmission line is used to transmit a quantum state control signal, and the Z signal transmission line is used to transmit a magnetic flux control signal; each quantum bit is also coupled to a resonant cavity, and the end of the resonant cavity away from the corresponding quantum bit is connected to a data transmission bus integrated on the quantum chip, and the data transmission bus is used to receive a quantum bit read signal and transmit a quantum bit read feedback signal, by applying the quantum bit read signal to the resonant cavity, and then reading the quantum bit read feedback signal transmitted or reflected from the resonant cavity, and determining the state of the quantum bit by measuring the response of the resonant cavity to microwaves.

[0051] In step S2, the purpose of applying the drive signal to the first qubit is to induce the second qubit to generate Rabi oscillations. Rabi oscillations are explained here as the physical process in which a quantum state of a two-level system periodically oscillates between two energy levels under the drive of resonant microwaves. By observing the state of the second qubit, if the second qubit does not undergo Rabi oscillations, then there is no drive crosstalk from the drive signal of the first qubit to the second qubit. If Rabi oscillations occur on the second qubit, then there is drive crosstalk from the drive signal of the first qubit to the second qubit, and the degree of drive crosstalk can be calibrated based on the amplitude of the Rabi oscillations.

[0052] Similarly, in step S2, the drive signal is transmitted to the first qubit via the XY signal transmission line coupled to the first qubit. A portion of the energy of the drive signal from the first qubit leaks to the second qubit through coupling, causing the second qubit to enter a Rabi oscillation state. The drive signal has a duration that ensures the Rabi oscillation generated by the second qubit is sufficiently long for observation. The amplitude of the drive signal is a first amplitude, which is set before the drive signal is applied to the first qubit, and therefore does not need to be measured.

[0053] In step S3, if Rabi oscillation does not occur on the second quantum bit, the Rabi oscillation on the second quantum bit cannot be obtained, and the crosstalk coefficient of the driving signal of the first quantum bit on the second quantum bit does not exist; if Rabi oscillation occurs on the second quantum bit, the state of the second quantum bit can be read through the resonant cavity, and the amplitude of the Rabi oscillation on the second quantum bit is obtained as the second amplitude.

[0054] In step S4, a crosstalk coefficient of the first qubit driving signal on the second qubit is obtained based on the first amplitude and the second amplitude; the crosstalk coefficient can calibrate the degree of influence of the first qubit driving signal on the second qubit.

[0055] The method for obtaining the drive crosstalk coefficient between quantum bits provided by the present invention can calibrate the degree of influence of the drive crosstalk of the drive signal on one quantum bit on another quantum bit on the same quantum chip, making it convenient for researchers to optimize the quantum chip based on the drive crosstalk coefficient.

[0056] It should also be noted that in step S2, the driving signal applied to the first quantum bit is a π pulse, which can flip the state of the quantum bit. Continuously applying a π pulse to a quantum bit can flip the state of the quantum bit back and forth between the ground state and the excited state; when part of the energy leaks to other quantum bits through coupling, the quantum state of other quantum bits will also flip back and forth between the ground state and the excited state.

[0057] Similarly, in step S2, the time length is 100 to 1000 nanoseconds, which can facilitate the reading of the Rabi oscillation amplitude on the second quantum bit.

[0058] In addition, the frequency of the driving signal approaches or remains consistent with the frequency of the second quantum bit, generally within the first allowable error range, which is 0 to 2 MHz; the frequency of the driving signal applied to the first quantum bit approaches or remains consistent with the frequency of the second quantum bit, which is conducive to inducing Rabi oscillation in the second quantum bit.

[0059] In step S3, obtaining the amplitude of the Rabi oscillation on the second quantum bit as the second amplitude specifically includes: fitting the curve of the Rabi oscillation with a cosine function to obtain the second amplitude.

[0060] In step S4, obtaining a crosstalk coefficient of a driving signal of the first quantum bit on the second quantum bit based on the first amplitude and the second amplitude includes:

[0061] Using the formula:

[0062]

[0063] A crosstalk coefficient of the driving signal of the first quantum bit on the second quantum bit is calculated.

[0064] The crosstalk coefficient calculated using the above formula has a smaller value, which is convenient for statistics and calculation.

[0065] In addition, the crosstalk coefficient may also be directly represented by the ratio of the first amplitude to the second amplitude, which is not specifically limited here.

[0066] In summary, the present invention provides a method for obtaining a drive crosstalk coefficient between qubits, comprising: providing a quantum chip having a first qubit and a second qubit disposed thereon; applying a drive signal having a first amplitude to the first qubit for a certain duration; obtaining the amplitude of the Rabi oscillation on the second qubit as a second amplitude; and obtaining the crosstalk coefficient of the drive signal from the first qubit on the second qubit based on the first and second amplitudes. The method for obtaining a drive crosstalk coefficient between qubits provided by the present invention can calibrate the degree of drive crosstalk influence of a drive signal from one qubit on another qubit in a quantum chip, thereby facilitating quantum chip optimization by researchers.

[0067] <Example 2>

[0068] This embodiment provides a method for obtaining a driving crosstalk matrix, which is used to obtain driving crosstalk coefficients between quantum bits on a quantum chip. The method for obtaining the driving crosstalk matrix includes:

[0069] A quantum chip is provided, on which N qubits are arranged; the qubits are coupled to each other, and each qubit is coupled to an XY signal transmission line and a Z signal transmission line, the XY signal transmission line is used to transmit a quantum state control signal, and the Z signal transmission line is used to transmit a magnetic flux control signal; each qubit is also coupled to a resonant cavity, and the end of the resonant cavity away from the corresponding qubit is connected to a data transmission bus integrated on the quantum chip, the data transmission bus is used to receive a qubit read signal and transmit a qubit read feedback signal, by applying the qubit read signal to the resonant cavity, and then reading the qubit read feedback signal transmitted or reflected from the resonant cavity, and determining the state of the qubit by measuring the response of the resonant cavity to microwaves.

[0070] Repeat the following steps: selecting one qubit from the N qubits as a first qubit, and then selecting one qubit from the N qubits as a second qubit; applying a driving signal having a first amplitude for a certain time length to the first qubit; obtaining the amplitude of the Rabi oscillation on the second qubit as a second amplitude; obtaining a driving crosstalk coefficient of the driving signal of the first qubit on the second qubit based on the first amplitude and the second amplitude; until,

[0071] The selection of the first qubit and the second qubit has traversed the N qubits to obtain N2 crosstalk coefficients;

[0072] An N×N driving crosstalk matrix is ​​obtained according to the N2 crosstalk coefficients.

[0073] The method for obtaining the driven crosstalk coefficient is the same as the method for obtaining the driven crosstalk coefficient between the quantum bits provided in the first embodiment of the present invention, and will not be repeated here; it should be noted that, in this embodiment, the selection of the first quantum bit and the second quantum bit should traverse all situations. When the first quantum bit is selected, the second quantum bit should also traverse N quantum bits. Since the first quantum bit also needs to traverse N quantum bits, there are a total of N2 situations, and N2 driven crosstalk coefficients can be obtained.

[0074] See Figure 2 , Figure 2 Schematic diagram of a crosstalk matrix obtained in this embodiment, wherein the horizontal axis represents different quantum bits, and the vertical axis represents the driving lines of different quantum bits.

[0075] It should be noted that the data in the figure is based on the formula:

[0076]

[0077] The calculated crosstalk coefficient may also be obtained by other calculation methods to obtain the driving crosstalk coefficient, which is not limited here.

[0078] See Figure 2 , Figure 2 This is a schematic diagram of the drive crosstalk matrix of this embodiment, wherein "Z1, Z2, Z3, Z4, X1, X2, X3, X4" in the horizontal axis represent different quantum bits, and "DLZ1, DLZ2, DLZ3, DLZ4, DLX1, DLX2, DLX3, DLX4" in the vertical axis correspond to the drive signals of different quantum bits, for example, DLZ1 represents the drive signal of quantum bit Z1; the diagonal elements in the figure mean that the crosstalk coefficient of the drive signal of a quantum bit on the quantum chip to itself is 0, and the off-diagonal elements represent the drive crosstalk coefficient of the drive signal of a quantum bit to another quantum bit. For example, the element in the first row and second column indicates that the drive crosstalk coefficient of the drive signal of quantum bit Z1 to quantum bit Z2 is -1.4; in addition, the figure only shows a part of the drive crosstalk coefficients, and does not fully show the drive crosstalk coefficients between all quantum bits in the quantum chip.

[0079] In summary, this embodiment provides a method for obtaining a driving crosstalk matrix, which can obtain the driving crosstalk coefficient between each quantum bit on a quantum chip, so that researchers can optimize the quantum chip based on the obtained driving crosstalk matrix.

[0080] <Example 3>

[0081] This embodiment provides a device for obtaining driven crosstalk between quantum bits, including:

[0082] A quantum chip, wherein a first quantum bit and a second quantum bit are provided on the quantum chip;

[0083] a driving signal applying module, configured to apply a driving signal having a first amplitude for a certain time length to the first qubit, wherein the driving signal is configured to induce Rabi oscillation in the second qubit;

[0084] A second amplitude acquisition module, configured to acquire the amplitude of the Rabi oscillation as a second amplitude;

[0085] A crosstalk coefficient acquisition module is used to obtain a crosstalk coefficient of the driving signal of the first quantum bit on the second quantum bit based on the first amplitude and the second amplitude.

[0086] The device for obtaining the driven crosstalk between quantum bits and the method for obtaining the driven crosstalk between quantum bits provided in this embodiment belong to the same inventive concept, and therefore have the same beneficial effects, and will not be described in detail here.

[0087] <Example 4>

[0088] This embodiment provides a readable storage medium having a computer program stored thereon. When the computer program is executed, the method for obtaining the driving crosstalk coefficient between quantum bits provided by the present invention can be implemented.

[0089] <Example 5>

[0090] This embodiment provides a quantum control system, which includes the device for obtaining the driving crosstalk coefficient between quantum bits provided in the embodiment of the present invention.

[0091] The above description is only a description of the preferred embodiments of the present invention and does not limit the scope of the present invention. Any changes and modifications made by ordinary technicians in the field of the present invention based on the above disclosure shall fall within the scope of protection of the claims.

Claims

1. A method for obtaining a driving crosstalk coefficient between quantum bits, characterized in that: include: Providing a quantum chip, wherein a first quantum bit and a second quantum bit are provided on the quantum chip; Applying a driving signal with a first amplitude for a certain time length to the first qubit, wherein the frequency of the driving signal is consistent with the frequency of the second qubit within a first allowable error range; obtaining an amplitude of the Rabi oscillation on the second quantum bit as a second amplitude; A crosstalk coefficient of the driving signal of the first quantum bit on the second quantum bit is obtained based on the first amplitude and the second amplitude.

2. The method for obtaining the driving crosstalk coefficient between quantum bits according to claim 1, characterized in that: The obtaining, based on the first amplitude and the second amplitude, a crosstalk coefficient of the driving signal of the first quantum bit on the second quantum bit includes: Using the formula: A crosstalk coefficient of the driving signal of the first quantum bit on the second quantum bit is calculated.

3. The method for obtaining the driving crosstalk coefficient between quantum bits according to claim 1, characterized in that: The driving signal is a π pulse.

4. The method for obtaining the driving crosstalk coefficient between quantum bits according to claim 1, characterized in that: The time length is 100 to 1000 nanoseconds.

5. The method for obtaining the driving crosstalk coefficient between quantum bits according to claim 1, characterized in that: The first error allowable range is 0~2Mhz.

6. The method for obtaining the driving crosstalk coefficient between quantum bits according to claim 1, characterized in that: The obtaining the amplitude of the Rabi oscillation as a second amplitude includes: fitting the Rabi oscillation with a cosine function to obtain the second amplitude.

7. A method for obtaining a driving crosstalk matrix, characterized in that: include: A quantum chip is provided, on which N quantum bits are arranged; Repeating the following steps: selecting one qubit from the N qubits as a first qubit, and then selecting one qubit from the N qubits as a second qubit; applying a driving signal having a first amplitude for a certain time length to the first qubit; obtaining the amplitude of the Rabi oscillation on the second qubit as a second amplitude; and obtaining a crosstalk coefficient of the driving signal of the first qubit on the second qubit based on the first amplitude and the second amplitude. Until, The selection of the first qubit and the second qubit has traversed the N qubits, obtaining N² crosstalk coefficients; An N×N driving crosstalk matrix is ​​obtained according to the N² crosstalk coefficients.

8. A device for obtaining crosstalk coefficients between quantum bits, characterized in that: include: A quantum chip, wherein a first quantum bit and a second quantum bit are provided on the quantum chip; a driving signal applying module, configured to apply a driving signal having a first amplitude for a certain time length to the first qubit, wherein the driving signal is configured to induce Rabi oscillation in the second qubit; A second amplitude acquisition module, configured to acquire the amplitude of the Rabi oscillation as a second amplitude; A crosstalk coefficient acquisition module is used to obtain a crosstalk coefficient of the driving signal of the first quantum bit on the second quantum bit based on the first amplitude and the second amplitude.

9. A readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed, it can implement the method for obtaining the driven crosstalk coefficient between quantum bits according to any one of claims 1 to 6, and the method for obtaining the driven crosstalk matrix according to claim 7.

10. A quantum control system, characterized in that: The quantum control system includes the device for obtaining the driving crosstalk coefficient between quantum bits as claimed in claim 8.

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