Superconducting quantum bit control reflected wave calibration method

Abstract

The invention relates to a superconducting quantum bit control reflected wave calibration method, which comprises the following steps of: integrating a reflected wave engineering mechanism in a pulse control system, pre-generating a reflected wave offset waveform which has the same frequency and the same shape as a reflected pulse and is opposite to the phase of the reflected pulse, and inhibiting a system error caused by reflection to 105 magnitude under the premise of not introducing additional hardware by combining DRAG parameter optimization; the defects that in a traditional scheme, the gate operation duration is increased, and the error rate is accumulated are overcome, finally, the overall single-bit gate fidelity is improved, the gate operation fidelity anisotropy is remarkably weakened, the single-bit gate fidelity remarkably approaches the coherence time limit of a current quantum bit, meanwhile, the modular expansion capacity is achieved, and the implementation cost is reduced. And the method can be adapted to various chip structures and large-scale parallel quantum bit systems.

Description

Technical Field

[0001] This invention relates to the technical fields of superconducting quantum bit control, microwave engineering, and quantum optimized gate control. Background Technology

[0002] Superconducting qubits offer a promising platform for realizing large-scale quantum computers, with a key advantage being their ability to achieve high-fidelity quantum logic gate operations on a nanosecond scale. Compared to other advanced quantum computing platforms, this characteristic promises to significantly improve computational speed. In superconducting quantum computing architectures, single-qubit gates, as the basic units of quantum logic operations, directly determine the correctness of the overall quantum algorithm and the system's fault tolerance based on their operational fidelity. Currently, the single-qubit gate fidelity of mainstream superconducting qubits has exceeded 99.9%, but there is still a gap to reach the theoretical limit determined by relaxation time.

[0003] The success of any computing architecture depends on its ability to execute a large number of gates and meet a fault tolerance threshold for gate errors. For large-scale computation, gate errors need to be below the fault tolerance threshold, conservatively estimated as follows: One of the fundamental requirements for the reliable realization of circuit-based quantum computing is a sufficiently large ratio between coherence time and gate length. To increase this ratio, a common approach to achieving high-fidelity gates is to increase the coherence time of the quantum device, including the energy relaxation time and dephase time. The coupling between TLS defects and the transmon can be suppressed by optimizing the geometry; solutions include keeping the transmon well isolated from its environment, such as reducing its coupling with the drive lines and readout resonators.

[0004] However, the above approach clearly contradicts the goal of achieving fast qubit control, which requires qubits to be easily actuated. Therefore, balancing coherence time and gate length becomes particularly important for realizing high-fidelity single-qubit gates. Long qubit pulses are limited by decoherence, while short pulses face the risk of energy level leakage (requiring DRAG suppression). Furthermore, regardless of pulse length, reflected wave interference caused by line impedance mismatch will be superimposed on the main pulse, resulting in waveform distortion and operational asymmetry. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, this invention proposes a superconducting quantum bit manipulation and reflection wave calibration method. The focus of this invention is to eliminate the manipulation and reflection waves to improve fidelity. Traditional calibration processes include frequency scanning, pulse amplitude and DRAG ratio calibration, which can suppress leakage and phase error to a certain extent, but cannot solve the problem of microwave reflection wave interference caused by line impedance mismatch.

[0006] The technical solution adopted in this invention is a superconducting quantum bit manipulation and reflection wave calibration method, the method comprising: determining the waveform characteristics of the anti-pulse formed after the main pulse signal is emitted, wherein the waveform characteristics include at least the occurrence time, occurrence frequency, phase, and waveform shape of the anti-pulse; A compensation pulse is generated based on the waveform characteristics. The compensation pulse and the inverse pulse have the same occurrence time, the same occurrence frequency, the same waveform shape, and opposite phase.

[0007] Preferably, the method for determining the occurrence time of the compensation pulse is as follows: obtaining the time point of the main pulse signal transmission, determining the delay duration from the transmission of the main pulse signal to the generation of the anti-pulse, and determining the occurrence time of the compensation pulse based on the time point and the delay duration.

[0008] Preferably, the method further includes calibrating the waveform characteristics of the inverse pulse.

[0009] The present invention also proposes a superconducting quantum bit control system, including a pulse transmission module and a terminal chip, characterized in that the pulse transmission module includes an arbitrary waveform generator, a digital-to-analog converter, and an IQ mixer connected in sequence, and the IQ mixer is connected to the terminal chip; The arbitrary waveform generator is further calibrated according to the calibration method described in any one of claims 1-3 for the pulse transmission module.

[0010] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention solves the problem of microwave reflection caused by impedance mismatch in traditional calibration lines by pre-generating anti-phase compensation pulses, thereby improving the signal purity of quantum bit control; 2. This invention can achieve error suppression without additional devices. It achieves intervention and control of the residual reflection field by adjusting the signal delay, phase and amplitude relationship in the transmission and reflection paths, while avoiding the complexity and instability brought about by traditional consumables or additional matching networks.

[0011] 3. This invention significantly improves the shape of quantum random benchmark measurement curves. After optimization, the fidelity decay in RB measurements is smoother and the fitting is more stable. It eliminates fitting anomalies or residual biases caused by non-unitary excitation channels and improves statistical stability. 4. This invention is beneficial for extending the calibration of multi-bit systems. The proposed method has modular characteristics and can be used as a basic unit for single-bit error compensation. It can be embedded in larger-scale quantum control systems and provides underlying support for the whole-chip uniformity optimization of single-bit gates in large-scale superconducting chips. Attached Figure Description

[0012] The present invention will now be described in detail with reference to the embodiments and accompanying drawings, wherein: Figure 1 The background diagram shows the path of the pulse signal being reflected in the transmission line and a schematic diagram of the superconducting experimental equipment.

[0013] Figure 2 This is a schematic diagram illustrating the Tbuffer buffering scheme used in pulse control to solve the problem of reflected waves in related technologies.

[0014] Figure 3 This is an engineering structural diagram of the reflected wave in the scheme of this application, which illustrates the mechanism of reflected wave cancellation.

[0015] Figure 4 This is a schematic diagram of the experimental waveform after calibration following reflection wave cancellation in the scheme of this application.

[0016] Figure 5 A graph showing the comparison of randomized benchmark (RB) results for different gate operations before and after optimization. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar components or components having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0018] In superconducting quantum bit control systems, such as Figure 1 As shown, quantum gate operations typically involve generating a preset pulse using an arbitrary waveform generator (AWG), which is then modulated by modules such as a DAC and IQ mixer before being input to the quantum chip to drive energy level transitions in superconducting qubits. Due to impedance mismatches at the line termination and direct echo paths, the emitted microwave preset pulse will be reflected upon encountering the structural boundary. Part of the reflected wave will return after several nanoseconds and superimpose onto the pulse tail of the qubit, which is still in the dynamic evolution stage, forming an unexpected secondary excitation. This affects the final quantum state, especially in short-time gate operations, where it manifests as a decrease in fidelity.

[0019] Traditional calibration procedures, including frequency scanning, pulse amplitude and proportional calibration, can suppress leakage and phase errors to some extent, but cannot solve the problem of microwave reflected wave interference caused by line impedance mismatch. Existing experiments have confirmed that even after high-fidelity calibration, the following problems still occur: inconsistent fidelity across different Clifford gates leads to gate operation asymmetry, with -X / -Y gates performing significantly worse than +X / +Y gates. Fidelity decreases significantly as the pulse time interval shortens. Specifically, for example... Figure 2As shown, the traditional approach is to forcibly insert a Tbuffer buffer of a certain duration after each pulse to ensure no crosstalk between pulses in subsequent long sequences. This method of dealing with pulse reflection has certain drawbacks: it reduces the algorithm's execution speed, exposes the system to noise for more time, leading to a higher error rate accumulation, and increases gate operation time, thus reducing quantum computing efficiency.

[0020] To address the aforementioned issues, this application proposes a superconducting quantum bit manipulation reflection wave calibration method. By designing a reflection wave engineering (RWE) mechanism integrated into the pulse control system, the method significantly suppresses the non-ideal evolution of quantum states caused by signal reflection without introducing additional hardware structures, thereby improving gate fidelity and operational stability.

[0021] In one embodiment, the superconducting quantum bit manipulation reflected wave calibration method includes: determining the waveform characteristics of the antipulse formed after the main pulse signal is emitted, wherein the waveform characteristics include at least the occurrence time, occurrence frequency, phase, and waveform shape of the antipulse; A compensation pulse is generated based on the waveform characteristics. The compensation pulse and the inverse pulse have the same occurrence time, the same occurrence frequency, the same waveform shape, and opposite phase.

[0022] Preferably, the method for determining the occurrence time of the compensation pulse is as follows: obtaining the time point of the main pulse signal transmission, determining the delay duration from the transmission of the main pulse signal to the generation of the anti-pulse, and determining the occurrence time of the compensation pulse based on the time point and the delay duration. In this embodiment, the delay duration is generally fixed and mainly depends on the transmission link itself, and can be obtained through multiple experimental measurements.

[0023] Preferably, the method further includes calibrating the waveform characteristics of the inverse pulse. Specifically, this calibration is achieved using a DRAG parameter optimization method.

[0024] To further illustrate the scheme of this application, the following explanation is provided in conjunction with experiments: like Figure 3 As shown, the mechanism for generating reflected waves to cancel interference in this application is as follows: After the main pulse is applied, the reflected signal returns with a fixed delay, and its frequency shape is the same as the main pulse. An additional phase perturbation and amplitude ratio are added, which may partially overlap with the evolution interval, equivalent to applying an additional perturbation field to the evolution path. The intervention pulse is a pulse with the same frequency and shape as the reflected pulse, but with an opposite phase. By experimentally calibrating the delay time, phase, and amplitude information, the reflected waveform is canceled out.

[0025] like Figure 4The diagram shown is a schematic of the experimental waveform after reflection waveform calibration. By adding reflection cancellation waveform, the actual line waveform is almost perfect, and two consecutive waveforms can be closely adjacent without overlapping or interfering with each other. Figure 4 The process of eliminating the pulse waveform is shown in the diagram. The upper Pulse drive section displays both the compensation pulse and the anti-pulse, which interact with each other. The final actual waveform is shown in the lower Actual drive section, which has eliminated the reflected waveform, making the actual line waveform almost perfect.

[0026] like Figure 5 As shown, experiments conducted on a superconducting chip demonstrate that... Figure 5 Part A represents the experimental data before optimization, which shows that... Door and The RB fidelity of the door is significantly high. The gate performance is significantly inferior to Door, ; Figure 5 Part B presents the experimental data after engineering processing of the reflected waves using the above method. It can be seen that the fidelity of the two types of gate operations tends to be consistent, indicating that the reflection effect is effectively suppressed. The gate operation optimized for reflection exhibits stronger robustness under different conditions, suppressing the systematic error caused by reflection to a minimum. The order of magnitude makes the total fidelity primarily limited by the coherence time of the qubits, and the random reference decay curve is smoother with smaller residuals.

[0027] It should be noted that this invention does not depend on a specific chip structure or bit type, and is applicable to systems under various physical boundary conditions, such as transmission line ends, cross-capacitor loading structures, and 3D packaging. For massively parallel qubit structures, this method can also be extended and deployed through channel-independent modeling and modular pulse shapers, thereby providing a foundation for building highly consistent, multi-channel gate operating systems.

[0028] In summary, this invention, by introducing a reflection wave engineering mechanism and employing a three-step approach of structural identification, intervention design, and experimental feedback, effectively solves the problem of non-ideal interference caused by microwave reflection in quantum gate operations, significantly improves the fidelity of gate operations, and provides key technical support for realizing a high-precision, scalable superconducting quantum computing system.

[0029] In the description of this specification, the use of terms such as "Embodiment 1," "this embodiment," or "in one embodiment" indicates that the specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example; moreover, the specific features, structures, materials, or characteristics described may be combined in any appropriate manner in one or more embodiments or examples.

[0030] In the description of this specification, the terms "connection," "installation," "fixing," "setting," and "having" are interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0031] In the description of this specification, relational terms such as “first” and “second” are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, 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.

[0032] The above description of the embodiments is intended to enable those skilled in the art to understand and apply the technology of this invention. Those skilled in the art can easily make various modifications to these examples and apply the general principles described herein to other embodiments without creative effort. Therefore, this invention is not limited to the above embodiments. Modifications in the following situations should be within the scope of protection of this invention: ① New technical solutions implemented based on the technical solution of this invention and combined with existing common knowledge, where the technical effects of the new technical solution do not exceed the technical effects of this invention; ② Equivalent substitutions of some features of the technical solution of this invention using known technology, resulting in the same technical effects as those of this invention; ③ Extendable technical solutions based on the technical solution of this invention, where the substantive content of the extended technical solution does not exceed the technical solution of this invention; ④ Equivalent transformations made using the content of this specification and drawings, directly or indirectly applied to other related technical fields.

Claims

1. A method for calibrating reflected waves by manipulating superconducting quantum bits, characterized in that, The method includes: determining the waveform characteristics of the anti-pulse formed after the main pulse signal is transmitted, wherein the waveform characteristics include at least the occurrence time, occurrence frequency, phase, and waveform shape of the anti-pulse; A compensation pulse is generated based on the waveform characteristics. The compensation pulse and the inverse pulse have the same occurrence time, the same occurrence frequency, the same waveform shape, and opposite phase.

2. The superconducting quantum bit manipulation and reflection wave calibration method according to claim 1, characterized in that, The method for determining the occurrence time of the compensation pulse is as follows: obtain the time point of the main pulse signal transmission, determine the delay time from the transmission of the main pulse signal to the generation of the anti-pulse, and determine the occurrence time of the compensation pulse based on the time point and the delay time.

3. The superconducting quantum bit manipulation and reflection wave calibration method according to claim 1, characterized in that, It also includes calibrating the waveform characteristics of the inverse pulse.

4. A superconducting quantum bit control system, comprising a pulse transmission module and a terminal chip, characterized in that, The pulse transmission module includes an arbitrary waveform generator, a digital-to-analog converter, and an IQ mixer connected in sequence, and the IQ mixer is connected to the terminal chip; The arbitrary waveform generator is further calibrated according to the calibration method described in any one of claims 1-3 for the pulse transmission module.

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