Method and device for correcting cz link distortion of tunable coupler and quantum computer

Abstract

The application discloses a CZ link distortion correction method and device of an adjustable coupler and a quantum computer, and belongs to the technical field of quantum computing. The method comprises the following steps: acquiring a plurality of pre-distortion digital filters corresponding to a plurality of quantum bits associated with a target adjustable coupler to be corrected to form a candidate filter list; wherein each pre-distortion digital filter is used for performing distortion correction on a Z link of the quantum bit; according to each pre-distortion digital filter in the candidate filter list, a frequency control signal is applied to a CZ link of the target adjustable coupler, and two-qubit gate operation is performed on two quantum bits connected with the target adjustable coupler to obtain the fidelity of the two-qubit gate operation; and the pre-distortion digital filter with the highest fidelity is determined as the distortion correction filter of the CZ link of the target adjustable coupler. The application can simplify the distortion test process of the adjustable coupler and improve the distortion test efficiency.

Description

Technical Field

[0001] This application relates to the field of quantum computing, and in particular to a method, apparatus and quantum computer for CZ link distortion correction of an adjustable coupler. Background Technology

[0002] In the superconducting qubit extension architecture based on tunable couplers, two superconducting qubits are coupled through a tunable coupler whose coupling coefficient can be adjusted. The coupling parameter of the tunable coupler can be positive or negative, thus achieving complete decoupling under certain parameters. The working principle of the tunable coupler is to apply a frequency control signal through the CZ link of the tunable coupler to adjust the frequency of the tunable coupler, thereby changing the effective coupling between the two superconducting qubits and achieving isolation or two-qubit gate operation.

[0003] Specifically, at the static operating point of the tunable coupler, the coupling between qubits is turned off. When executing a two-qubit gate, the coupling between qubits is quickly turned on by applying a dynamic waveform to the CZ link to adjust the frequency of the tunable coupler. Similar to qubit Z-line distortion, waveform distortion on the CZ link of the tunable coupler can also cause the actual waveform arriving at the tunable coupler to differ from the expected waveform, resulting in a decrease in the fidelity of the two-qubit gate. Therefore, it is necessary to perform distortion correction on the CZ link of the tunable coupler. Summary of the Invention

[0004] The purpose of this application is to provide a CZ link distortion correction method, device, and quantum computer for tunable couplers, in order to overcome the shortcomings of the prior art, simplify the distortion testing process of tunable couplers, and improve the distortion testing efficiency.

[0005] To address the aforementioned technical problems, the first aspect of this application provides a CZ link distortion correction method for an adjustable coupler, comprising:

[0006] Obtain predistortion digital filters corresponding to several qubits associated with the target tunable coupler to be corrected, to form a candidate filter list; wherein each of the predistortion digital filters is used to perform distortion correction on the Z-link of the qubit; According to each predistortion digital filter in the candidate filter list, a frequency control signal is applied to the CZ link of the target tunable coupler, and a two-qubit gate operation is performed on the two qubits connected to the target tunable coupler to obtain the fidelity of the two-qubit gate operation; The predistorted digital filter with the highest fidelity is selected as the distortion correction filter for the CZ link of the target tunable coupler.

[0007] The CZ link distortion correction method for the tunable coupler described above may optionally include the step of obtaining predistortion digital filters corresponding to the plurality of qubits associated with the target tunable coupler to be corrected, respectively, comprising: Based on the topology of the quantum chip, determine a number of neighboring qubits adjacent to the target tunable coupler; Obtain predistortion digital filters that perform distortion correction on the Z-links of each of the neighboring qubits.

[0008] The CZ link distortion correction method for the tunable coupler described above may optionally include the step of obtaining predistortion digital filters corresponding to the plurality of qubits associated with the target tunable coupler to be corrected, respectively, comprising: Based on the physical location of the CZ link of the target tunable coupler in the quantum measurement and control link, determine the predistortion digital filter corresponding to the qubit with the nearest physical location.

[0009] The CZ link distortion correction method for the tunable coupler described above may optionally include obtaining pre-distortion digital filters corresponding to several qubits associated with the target tunable coupler to be corrected, including: Candidate filters are pre-screened through a distortion sensitivity experiment; wherein, the candidate filters include pre-distortion digital filters corresponding to all qubits on the quantum chip, and the distortion sensitivity experiment is used to test the effect of changes in the control signal applied to the CZ link of the target tunable coupler on the two connected qubits.

[0010] The CZ link distortion correction method for the adjustable coupler described above may optionally include the distortion sensitivity experiment comprising: A target control signal is applied to the CZ link of the target tunable coupler so that the frequency of the target tunable coupler produces a target adjustment range for the frequencies of the two qubits connected to the tunable coupler; Multiple control signals, including dynamic waveforms, are applied to the CZ link, and the single-qubit phase of each of the two qubits corresponding to each dynamic waveform is measured.

[0011] The CZ link distortion correction method for the tunable coupler described above can optionally include pre-screening of candidate filters through distortion sensitivity experiments, including: Calculate the standard deviation of the single-qubit phase of each of the two qubits, and calculate the sum of the two standard deviations; The predistortion digital filters corresponding to qubits whose sum of standard deviations is less than a preset threshold are selected into the candidate filter list.

[0012] In the CZ link distortion correction method for the tunable coupler described above, optionally, the candidate filter includes pre-distortion digital filters from a seed library of multiple quantum chips; wherein, the seed library includes multiple seeds, each seed representing a pre-distortion digital filter for distortion correction of the Z link of a quantum bit.

[0013] Optionally, the CZ link distortion correction method for the adjustable coupler described above may further include: Save the distortion correction filter and its corresponding two-qubit gate parameters and fidelity results.

[0014] A second aspect of this application provides a CZ link distortion correction device for an adjustable coupler, comprising: An acquisition module is used to acquire predistortion digital filters corresponding to several qubits associated with the target tunable coupler to be corrected, so as to form a candidate filter list; wherein, each of the predistortion digital filters is used to perform distortion correction on the Z link of the qubit; The measurement module is used to apply frequency control signals to the CZ link of the target tunable coupler according to each predistortion digital filter in the candidate filter list, and to perform a two-qubit gate operation on the two qubits connected to the target tunable coupler to obtain the fidelity of the two-qubit gate operation. A determination module is used to determine the predistortion digital filter with the highest fidelity as the distortion correction filter for the CZ link of the target tunable coupler.

[0015] A third aspect of this application provides a quantum computer that uses the CZ link distortion correction method for the tunable coupler as described in any of the first aspects above to correct the tunable coupler on the quantum chip, or includes the CZ link distortion correction device as described in the second aspect above.

[0016] Compared to existing technologies, this application simplifies the complex coupler distortion correction problem into a screening problem of predistortion digital filters corresponding to existing corrected qubits, greatly simplifying the process. It eliminates the need for characterizing the tunable coupler and avoids the complex CZ link distortion measurement steps for tunable couplers, thus improving distortion testing efficiency and the automation pass rate of the two-qubit gate correction process. Furthermore, by using two-qubit gate fidelity as a metric, the complex process of finely optimizing the CZ link distortion of tunable couplers lacking separate XY control lines and readout cavities is transformed into a simple predistortion digital filter screening task, thereby improving both two-qubit gate fidelity and connectivity on large-scale quantum chips. In addition, its reuse and screening mechanism allows it to be applied to various types of qubits, exhibiting strong generalization ability and scalability.

[0017] The CZ link distortion correction device and quantum computer for the tunable coupler provided in this application belong to the same concept as the CZ link distortion correction method for the tunable coupler, and therefore have the same beneficial effects, which will not be elaborated here. Attached Figure Description

[0018] Figure 1 A flowchart illustrating a CZ link distortion correction method for an adjustable coupler provided in this application embodiment; Figure 2 This is a schematic diagram of the structure of a CZ link distortion correction device with an adjustable coupler provided in an embodiment of this application. Detailed Implementation

[0019] 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.

[0020] 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.

[0021] 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.

[0022] The quantum measurement and control link includes XY links and Z links. The XY links connect to the XY control lines of each qubit on the quantum chip, and the Z links connect to the Z control lines of each qubit on the quantum chip. When these links transmit quantum signals, they not only cause transmission delays but also distortions. This is because the coaxial cables included in the quantum measurement and control link, as well as the devices mounted on them, are not ideal. During the research process, the applicant summarized the factors that may cause quantum signal distortion as follows:

[0023] First, there's the issue of imperfect signal generation. The quantum signal generation process relies on the control pulses generated by an arbitrary waveform generator, which has limited bandwidth and may experience overshoot. This results in the output waveform deviating from the original design waveform. Second, the quantum control link incorporates various devices such as filters, DC blockers, and bias tees, each with its own frequency response. The skin effect of coaxial cables also lengthens the rise time of the system response. Third, there's the reflection caused by impedance mismatch, especially when the quantum chip is mounted on the package, requiring impedance control of the wiring bonding line.

[0024] Distortions occurring during the generation and transmission of quantum signals can cause the waveform arriving at the qubit to deviate from the original design, severely impacting the fidelity of operations in quantum computing and quantum simulation. For example, two-qubit gates in frequency-tunable qubit systems are typically implemented by applying a pulse of tens of nanoseconds to the Z-line to adjust the qubit frequency. Quantum simulations also use fast Z-pulses to tune the qubit to a specific frequency for evolution. Specifically, pulse tailing caused by Z-line distortion affects the qubit frequency when a single-qubit gate is subsequently applied, resulting in a decrease in the fidelity of the corrected single-qubit gate. For two-qubit gates, such as control phase gates, short-timescale distortions can cause the qubit evolution to deviate from its carefully designed trajectory, leading to control phase errors and the leakage of the qubit state into non-computational subspaces. More serious are long-timescale tailing distortions, which can cause the effect of the current waveform to be influenced by historical waveforms applied before it, impairing the reproducibility of logic gates. Therefore, testing and compensating for Z-control line distortion is crucial for achieving high-fidelity quantum operations.

[0025] In addition to qubits, the quantum chip also includes tunable couplers for coupling between two qubits. The tunable coupler has a CZ control line connected to a CZ link (similar to the Z link of a qubit). For the characterization of the tunable coupler, each qubit has its corresponding XY and Z control lines and a readout cavity. However, although the tunable coupler is also a transmon structure, it only has one CZ control line and its connected CZ link, used to adjust the frequency of the tunable coupler and thus the interaction between qubits. The state of a qubit can be read using the coupling between the qubit and the readout cavity, and the state of the tunable coupler can be read using the interaction between the tunable coupler and the qubit via the qubit. The XY control of the tunable coupler can be achieved through signal crosstalk from the XY control line of the qubit.

[0026] There are generally two existing methods for characterizing tunable couplers. The first approach involves treating the tunable coupler as a single qubit for XY and Z control and readout. The unit step response test method for the qubit's Z control line is also applicable to tunable couplers. However, this method requires two qubits surrounding the tunable coupler, one for driving the coupler and the other for reading its state, making the testing process complex. Furthermore, since the coherence time of the tunable coupler is much shorter than that of the qubit, the testing accuracy of the unit step response is poor, resulting in poor distortion correction.

[0027] Another approach is to adjust the frequency of the tunable coupler to a position close to the qubit frequency. In this case, due to the strong coupling between the tunable coupler and the qubit, the qubit frequency will change significantly with the frequency of the tunable coupler, i.e., the voltage applied to the CZ link of the tunable coupler. That is, the voltage on the CZ link can have a wide range of adjustment over the qubit frequency. In this case, the unit step response test method for qubits can be used to test the distortion of the CZ link. However, this approach has two drawbacks. First, the adjustment range of the CZ link over the qubit frequency is limited, making the qubit frequency less sensitive to voltage changes on the CZ link. Second, at positions with relatively high sensitivity, the strong interaction between the qubit and the tunable coupler can lead to a deterioration in coherence time, affecting the test accuracy.

[0028] Based on this, such as Figure 1 As shown, this application provides a Z-line distortion correction method for tunable couplers to correct the distortion of the CZ link of tunable couplers on quantum chips, thereby ensuring the undistorted frequency control signal of the tunable coupler. Specifically, the distortion correction method of this application includes the following steps.

[0029] Step S10: Obtain the predistortion digital filters corresponding to several qubits associated with the target tunable coupler to be corrected, so as to form a candidate filter list; wherein, each predistortion digital filter is used to correct the distortion of the Z link of the qubit.

[0030] Each qubit's Z-link (used to control the qubit frequency) on the quantum chip has undergone fine predistortion correction, and the corresponding predistortion digital filter parameters have been stored. These predistortion digital filters can effectively compensate for waveform distortion in the Z-link. Since the Z-links of qubits on the same chip and the CZ-links of tunable couplers share a large number of identical microwave components (such as high-density cables, coaxial cables, PCB traces, etc.), and the transmission characteristics of the measurement and control links are highly consistent, the predistortion digital filters used for qubit Z-link correction are also applicable to the CZ-links of adjacent tunable couplers; that is, the predistortion digital filters corresponding to several qubits associated with the target tunable coupler to be corrected can be obtained to form a candidate filter list.

[0031] When selecting predistortion digital filters corresponding to several qubits associated with the target tunable coupler to form a candidate filter list, the qubits can be selected according to the proximity principle. This proximity principle can refer to the proximity between qubits and tunable couplers in the topology of a quantum chip, or the proximity between quantum measurement and control circuitry and tunable couplers in a quantum computer.

[0032] In accordance with the proximity principle of the topology of a quantum chip, the predistortion digital filters corresponding to several qubits associated with the target tunable coupler to be corrected are obtained, including the following steps.

[0033] Step S101: Based on the topology of the quantum chip, determine several neighboring qubits near the target tunable coupler; Step S102: Obtain the predistortion digital filter that performs distortion correction on the Z-link of each neighboring qubit.

[0034] For example, the quantum chip in this embodiment adopts a two-dimensional grid topology, containing multiple superconducting qubits and multiple tunable couplers. Each qubit has an independent XY control line, Z control line, and readout cavity, while the tunable coupler only has a CZ link for adjusting its frequency. The target tunable coupler to be calibrated is connected to at least two qubits.

[0035] Based on the topology diagram of the quantum chip, identify several qubits that are physically adjacent to the target tunable coupler to be calibrated. For example, for a tunable coupler connecting Qubit A and Qubit B, Qubit A and Qubit B are themselves the nearest neighbors. Obtain the predistortion digital filters for the Z-links used to calibrate Qubit A and Qubit B, respectively, and add them to the candidate list. Alternatively, predistortion digital filters corresponding to other qubits not directly connected to the vicinity of the tunable coupler can also be included in the candidate list.

[0036] In the principle of proximity between the quantum measurement and control circuit and the tunable coupler, obtaining the predistortion digital filters corresponding to several qubits associated with the target tunable coupler to be calibrated also includes: determining the predistortion digital filters corresponding to the qubits with adjacent physical locations based on the physical location of the CZ link of the tunable coupler in the quantum measurement and control link.

[0037] Long-term distortions often originate from high-density coils in quantum telemetry and control links. Since the crosstalk and transmission characteristics between adjacent lines in a high-density coil are similar, the qubits corresponding to other signal lines physically adjacent to the target tunable coupler in the physical high-density coil can be selected based on the CZ link's location within that coil. Obtaining pre-distortion digital filters for these qubits as candidates can effectively characterize common distortion modes introduced by physical link sharing.

[0038] Step S20: Apply frequency control signals to the CZ link of the target tunable coupler according to each predistortion digital filter in the candidate filter list, and perform a two-qubit gate operation on the two qubits connected to the target tunable coupler to obtain the fidelity of the two-qubit gate operation.

[0039] For each digital filter in the candidate filter list generated in step S10, the following evaluation is performed: specifically, the currently evaluated predistortion digital filter is loaded into the digital predistortion module of the arbitrary waveform generator (AWG) corresponding to the CZ link of the target tunable coupler. Near the determined optimal operating point (voltage) of the CZ gate, an automated two-bit CZ gate parameter correction procedure is performed. This procedure typically includes correcting the amplitude, width, shape, etc., of the gate pulse to ensure a standard CZ gate operation.

[0040] The two-bit CZ gate parameter correction process can be executed based on the Nelder-Mead optimization algorithm. By adjusting the pulse amplitude and duration parameters of the CZ gate, the conditional phase of the two-bit gate is made close to the target value π. In this embodiment, the duration ranges from 20 to 200 nanoseconds, and the automated correction process converges to the optimal parameter combination through iterative optimization.

[0041] After completing the CZ gate parameter correction, the fidelity of the CZ gate is accurately characterized using the standard two-qubit cross-entropy benchmark (XEB) experiment. The XEB experiment obtains the two-qubit gate fidelity by comparing the cross-entropy between the output probability distribution of the ideal quantum circuit and the probability distribution obtained by actual measurement.

[0042] Specifically, the XEB experiment applies a random quantum circuit consisting of random single-bit gates and CZ gates to two qubits and another qubit, measures the probability distribution of the output state, and compares it with the probability distribution under ideal conditions to calculate the fidelity of the two-bit gate. In this embodiment, the circuit depth of the XEB experiment is set to 100 layers, the number of random circuits is 20, and the fidelity measurement of each predistortion digital filter is repeated multiple times and the average value is taken.

[0043] Step S30: Determine the predistortion digital filter with the highest fidelity as the distortion correction filter for the CZ link of the tunable coupler.

[0044] Through the above evaluation process, this embodiment obtains two-bit gate fidelity data corresponding to several candidate predistorted digital filters. For example, the fidelity of predistorted digital filter 1 (corresponding to qubit 1) is 98.2%, the fidelity of predistorted digital filter 2 (corresponding to qubit 2) is 98.5%, the fidelity of predistorted digital filter 3 (corresponding to qubit 3) is 98.0%, the fidelity of predistorted digital filter 4 (corresponding to qubit 4) is 98.3%, the fidelity of predistorted digital filter 5 (corresponding to qubit 5) is 98.7%, the fidelity of predistorted digital filter 6 (corresponding to qubit 6) is 98.4%, the fidelity of predistorted digital filter 7 (corresponding to qubit 7) is 99.1%, the fidelity of predistorted digital filter 8 (corresponding to qubit 8) is 98.6%, and the fidelities of the remaining four predistorted digital filters are 97.8%, 98.1%, 98.9%, and 98.2%, respectively.

[0045] Based on the fidelity data measured in step 20, this embodiment selects the predistortion digital filter 7 with the highest fidelity as the distortion correction filter for the CZ link of the target tunable coupler to be corrected. In this embodiment, the fidelity of the predistortion digital filter 7 is 99.1%, which is higher than other candidate predistortion digital filters, thus determining it as the optimal filter.

[0046] Existing method 1 employs a scheme that treats the coupler as a qubit for unit step response testing, requiring two surrounding qubits to drive and read them separately. This results in a complex testing process, with the complete characterization and calibration time for a single coupler exceeding two hours. In contrast, the method in this embodiment eliminates the need for complex characterization of coupler 1, and the optimization time for a single coupler is only half an hour, thus improving calibration efficiency.

[0047] Existing method 2 employs an indirect distortion test by adjusting the coupler frequency. However, due to the limited range of frequency adjustment for qubits via the CZ link and the decrease in qubit coherence time, the final optimized two-qubit gate fidelity is typically between 97.5% and 98.2%. In contrast, the method in this embodiment directly uses two-qubit gate fidelity as the evaluation criterion, achieving goal-oriented optimization and ultimately reaching a fidelity of 99.1%, thus improving the two-qubit gate fidelity.

[0048] Furthermore, the method in this embodiment has a high degree of automation. The entire process only requires setting the target tunable coupler to be calibrated and the source of the candidate filter list at the beginning. The subsequent predistortion digital filter configuration, CZ gate calibration, fidelity measurement and optimal filter selection are all automatically completed by the quantum computing system. The proportion of manual intervention steps is less than 5%, and the degree of automation exceeds 95%.

[0049] This application simplifies the complex coupler distortion correction problem into a screening problem of predistortion digital filters corresponding to existing corrected qubits, greatly simplifying the process. It eliminates the need for characterizing the tunable coupler and avoids the complex CZ link distortion measurement steps for tunable couplers, thus improving distortion testing efficiency and the automation pass rate of the two-qubit gate correction process. Furthermore, by using two-qubit gate fidelity as a metric, the complex process of finely optimizing the CZ link distortion of tunable couplers lacking separate XY control lines and readout cavities is transformed into a simple predistortion digital filter screening task, thereby improving both two-qubit gate fidelity and connectivity on large-scale quantum chips. In addition, its multiplexing and screening mechanism allows it to be applied to various types of qubits, exhibiting strong generalization and scalability.

[0050] In one implementation, the method further includes: saving the distortion correction filter and its corresponding two-qubit gate parameters and fidelity results. The optimal predistortion digital filter determined in step 30 is used as the distortion correction filter for the CZ link of the target tunable coupler, and it, along with the two-qubit CZ gate parameters (such as pulse amplitude and duration) measured under this filter and the final fidelity results, are saved to the configuration database or file of the measurement and control system. This allows the optimized parameters to be loaded and used at any time in subsequent quantum computing tasks, ensuring high-quality CZ gate operation.

[0051] When the number of qubits on a quantum chip is very large, the corresponding number of predistortion digital filters is also large. When there are many candidate filters, directly performing a complete two-qubit gate fidelity test on all candidates would consume a lot of time. Therefore, a fast and sensitive pre-screening experiment can be designed.

[0052] In one implementation, obtaining predistortion digital filters corresponding to a plurality of qubits associated with the target tunable coupler to be calibrated includes: pre-screening candidate filters through a distortion sensitivity experiment; wherein the candidate filters include predistortion digital filters corresponding to all qubits on the quantum chip, and the distortion sensitivity experiment is used to test the effect of changes in the control signal applied to the CZ link of the tunable coupler on the two connected qubits.

[0053] The pre-screening of candidate filters through distortion sensitivity experiments aims to select a subset of predistorted digital filters (candidate filters) from all qubits to form a candidate filter list; that is, the filters in the candidate filter list are those selected through distortion sensitivity experiments, not all candidate filters. Then, formal screening is performed through subsequent steps S20-S30 to select the predistorted digital filter with the highest fidelity from the candidate filter list.

[0054] For example, a distortion-sensitive experiment includes the following steps.

[0055] Step S111: Apply a target control signal to the CZ link of the tunable coupler so that the frequency of the tunable coupler produces a target adjustment range for the frequencies of the two qubits connected to the tunable coupler.

[0056] Adjust the target control signal applied to the tunable coupler CZ link so that its frequency falls into the region most sensitive to frequency changes of the two connected qubits, where small fluctuations in the coupler frequency can significantly affect the bit frequency.

[0057] Step S112: Apply multiple control signals, including dynamic waveforms, to the CZ link and measure the single-qubit phase of each of the two qubits corresponding to each dynamic waveform.

[0058] A series of control signals, including dynamic waveforms (such as square waves, step waves, or CZ gate pulses), are repeatedly applied to the CZ link. Each time a control signal of a waveform is applied, the single-bit phase of each of the two qubits connected to the coupler is immediately measured using methods such as standard quantum state tomography or Ramsey interferometry. The single-bit phase corresponding to each dynamic waveform is different.

[0059] For example, during testing, waveforms 1, 2, 3, 4, and N are applied sequentially on the CZ link, and the accumulated phases P1, P2, P3, and P4 are measured. These phases are then differentiated to obtain P1, P2-P1, P3-P2, and P4-P3, which correspond to the accumulated phases of the 1st, 2nd, 3rd, and Nth waveforms.

[0060] Distortion correction targets control signals including dynamic waveforms. The amplitude of these dynamic waveforms significantly affects the coupler's adjustment of the bit frequency. When the CZ link exhibits significant long-term IIR distortion, the distortion of the dynamic waveform causes a change in the phase accumulated by the bit after each waveform application. Without IIR distortion, subsequent waveforms are not affected by the long-term distortion of preceding waveforms, and the phase accumulated by each dynamic waveform should be the same, i.e., repeatable; in this case, the standard deviation of the single-bit phase is 0.

[0061] In one implementation, candidate filters are pre-screened through a distortion sensitivity experiment, including the following steps.

[0062] Step S121: Calculate the standard deviation of the single-qubit phase of each of the two qubits, and calculate the sum of the two standard deviations.

[0063] Step S122: Select the predistortion digital filters corresponding to qubits whose sum of standard deviations is less than a preset threshold and add them to the candidate filter list.

[0064] For a predistortion digital filter F to be evaluated, it is applied to the CZ link of the coupler, and the distortion sensitivity experiment described above is repeated. The phase accumulated for each dynamic waveform is calculated using differential operations, and then the standard deviation of these phases is calculated. For example, the standard deviation σ1 of the phase sequence of qubit 1 and the standard deviation σ2 of the phase sequence of qubit 2 are obtained. The sum of the two is calculated as S = σ1 + σ2. The smaller the value of S, the better the compensation effect of the predistortion digital filter on the distortion of the CZ link, and the higher the phase repeatability.

[0065] The S-value can be compared with a preset threshold (or the S-values ​​of all candidate filters can be sorted), and filters with smaller S-values ​​(e.g., S < preset threshold or ranked in the top K) can be selected to form a simplified candidate filter list. In specific implementations, this preset threshold can be set according to the chip noise level and accuracy requirements.

[0066] In one implementation, the candidate filter includes predistorted digital filters from a seed library of multiple quantum chips; wherein the seed library includes multiple seeds, each representing a predistorted digital filter that performs distortion correction on the Z-link of a quantum bit.

[0067] In practice, candidate filters are not limited to the filters corresponding to the qubits that have already undergone distortion optimization on the current quantum chip, but can also be extended to a pre-built "seed library." This seed library contains high-performance pre-distortion digital filters collected from the calibration processes of multiple different quantum chips and batches. By traversing and filtering through a seed library containing a richer set of distortion modes, it is sometimes possible to find an optimal solution for the coupler under test that is more suitable than any qubit filter on the current chip, especially when the reference filter on the current chip itself is poorly calibrated.

[0068] Based on the same application concept, such as Figure 2 As shown, this embodiment also provides a CZ link distortion correction device for an adjustable coupler, including an acquisition module, a measurement module, and a determination module.

[0069] Specifically, the acquisition module acquires predistortion digital filters corresponding to several qubits associated with the target tunable coupler to be corrected, forming a candidate filter list; each predistortion digital filter is used to correct the distortion of the Z-link of the qubits. The measurement module applies frequency control signals to the CZ-link of the target tunable coupler according to each predistortion digital filter in the candidate filter list, and performs a two-qubit gate operation on the two qubits connected to the target tunable coupler to obtain the fidelity of the two-qubit gate operation. The determination module determines the predistortion digital filter with the highest fidelity as the distortion correction filter for the CZ-link of the target tunable coupler.

[0070] The aforementioned acquisition and determination modules can be functional modules integrated into a classical computer, while the measurement can be a specific measurement device, such as a quantum computing measurement and control system, used to output various control signals and perform measurements. The device provided in this embodiment can automatically and efficiently execute the above correction method, realizing the processization and automation of coupler CZ link distortion correction, significantly reducing the complexity of manual intervention and debugging, and improving the correction efficiency and final performance of the quantum chip.

[0071] Based on the same concept, this embodiment also provides a quantum computer that uses the CZ link distortion correction method of the tunable coupler as described above to correct the tunable coupler on the quantum chip, or includes the CZ link distortion correction device as described above.

[0072] This quantum computer includes a quantum computer system comprising a quantum chip system (also called a quantum processor), a quantum computer control system, a quantum computer environment support system (also called a dilution refrigerator), and a quantum computer operating system integrated into the classical computer. The quantum chip integrates multiple qubits and tunable couplers for connecting these qubits. The quantum computer operating system can execute CZ link distortion correction methods using the aforementioned tunable couplers. Alternatively, it can integrate the aforementioned CZ link distortion correction device.

[0073] Integrating the method or apparatus of this application into a quantum computer directly improves the overall performance, resulting in higher two-qubit gate fidelity, higher chip connectivity (more available high-quality couplers), and a more robust automated correction process. This is an important technical means for quantum computing systems to become practical.

[0074] The systems, devices, modules, or units described in the above embodiments can be implemented by computer chips or entities, or by products with certain functions. A typical implementation device is a computer, which can take the form of a personal computer, laptop computer, cellular phone, camera phone, smartphone, personal digital assistant, media player, navigation device, email sending and receiving device, game console, tablet computer, wearable device, or any combination of these devices.

[0075] In a typical configuration, a computer includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0076] Memory may include non-persistent storage in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0077] Computer-readable media, including both permanent and non-permanent, removable and non-removable media, can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, disk storage, quantum memory, graphene-based storage media or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0078] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0079] The foregoing has described specific embodiments of this specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in a different order than that shown in the embodiments and may still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require the specific or sequential order shown to achieve the desired result. In some embodiments, multitasking and parallel processing are possible or may be advantageous.

[0080] The terminology used in one or more embodiments of this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of one or more embodiments of this specification. The singular forms “a,” “described,” and “the” used in one or more embodiments of this specification and in the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0081] It should be understood that although the terms first, second, third, etc., may be used to describe various information in one or more embodiments of this specification, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, first information may also be referred to as second information without departing from the scope of one or more embodiments of this specification, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to a determination." The above description is merely a preferred embodiment of one or more embodiments of this specification and is not intended to limit one or more embodiments of this specification. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of one or more embodiments of this specification should be included within the scope of protection of one or more embodiments of this specification.

[0082] The above description, based on the embodiments shown in the drawings, details the structure, features, and effects of this application. The above description is only a preferred embodiment of this application, but this application does not limit the scope of implementation to what is shown in the drawings. Any changes made in accordance with the concept of this application, or modifications to equivalent embodiments, that do not exceed the spirit covered by the specification and drawings, should be within the protection scope of this application.

Claims

1. A method for correcting CZ link distortion in an adjustable coupler, characterized in that, include: Obtain predistortion digital filters corresponding to several qubits adjacent to the target tunable coupler to be corrected, to form a candidate filter list; wherein each of the predistortion digital filters is used to perform distortion correction on the Z-link of the qubit; According to each predistortion digital filter in the candidate filter list, a frequency control signal is applied to the CZ link of the target tunable coupler, and a two-qubit gate operation is performed on the two qubits connected to the target tunable coupler to obtain the fidelity of the two-qubit gate operation; The predistorted digital filter with the highest fidelity is selected as the distortion correction filter for the CZ link of the target tunable coupler.

2. The CZ link distortion correction method for the adjustable coupler according to claim 1, characterized in that, The acquisition of predistortion digital filters corresponding to several qubits adjacent to the target tunable coupler to be corrected includes: Based on the topology of the quantum chip, determine a number of neighboring qubits adjacent to the target tunable coupler; Obtain predistortion digital filters that perform distortion correction on the Z-links of each of the neighboring qubits.

3. The CZ link distortion correction method for the adjustable coupler according to claim 1, characterized in that, The acquisition of predistortion digital filters corresponding to several qubits adjacent to the target tunable coupler to be corrected includes: Based on the physical location of the CZ link of the target tunable coupler in the quantum measurement and control link, determine the predistortion digital filter corresponding to the qubit with the nearest physical location.

4. The CZ link distortion correction method for the adjustable coupler according to claim 1, characterized in that, Obtain the predistortion digital filters corresponding to several qubits adjacent to the target tunable coupler to be corrected, including: Candidate filters are pre-screened through a distortion sensitivity experiment; wherein, the candidate filters include pre-distortion digital filters corresponding to all qubits on the quantum chip, and the distortion sensitivity experiment is used to test the effect of changes in the control signal applied to the CZ link of the target tunable coupler on the two connected qubits.

5. The CZ link distortion correction method for the adjustable coupler according to claim 4, characterized in that, The distortion sensitivity experiment includes: A target control signal is applied to the CZ link of the target tunable coupler so that the frequency of the target tunable coupler produces a target adjustment range for the frequencies of the two qubits connected to the tunable coupler; Multiple control signals, including dynamic waveforms, are applied to the CZ link, and the single-qubit phase of each of the two qubits corresponding to each dynamic waveform is measured.

6. The CZ link distortion correction method for the adjustable coupler according to claim 5, characterized in that, Candidate filters are pre-screened through distortion sensitivity experiments, including: Calculate the standard deviation of the single-qubit phase of each of the two qubits, and calculate the sum of the two standard deviations; The predistortion digital filters corresponding to qubits whose sum of standard deviations is less than a preset threshold are selected into the candidate filter list.

7. The CZ link distortion correction method for the adjustable coupler according to claim 4, characterized in that, The candidate filters include predistorted digital filters from a seed library of multiple quantum chips; wherein, the seed library includes multiple seeds, each seed representing a predistorted digital filter for distortion correction of a Z-link of a quantum bit.

8. The CZ link distortion correction method for the adjustable coupler according to claim 1, characterized in that, The method further includes: Save the distortion correction filter and its corresponding two-qubit gate parameters and fidelity results.

9. A CZ link distortion correction device with an adjustable coupler, characterized in that, include: An acquisition module is used to acquire predistortion digital filters corresponding to several qubits adjacent to the target tunable coupler to be corrected, so as to form a candidate filter list; wherein, each of the predistortion digital filters is used to perform distortion correction on the Z link of the qubit; The measurement module is used to apply frequency control signals to the CZ link of the target tunable coupler according to each predistortion digital filter in the candidate filter list, and to perform a two-qubit gate operation on the two qubits connected to the target tunable coupler to obtain the fidelity of the two-qubit gate operation. A determination module is used to determine the predistortion digital filter with the highest fidelity as the distortion correction filter for the CZ link of the target tunable coupler.

10. A quantum computer, characterized in that, The tunable coupler on the quantum chip is corrected using the CZ link distortion correction method of the tunable coupler as described in any one of claims 1-8, or the tunable coupler CZ link distortion correction device as described in claim 9 is also used.

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