Method for rapidly detecting read crosstalk between quantum bits

Abstract

The invention discloses a method for quickly detecting read crosstalk between quantum bits, which comprises the following steps of: for an N quantum bit system, randomly generating M bit character strings, preparing initial states of all the bit character strings and measuring a single quantum bit read result; and then, according to a target bit and a control bit, classifying random bit character string measurement results, calculating an average value of probabilities that the target bit is in a preparation state based on a classification result, and traversing all bit pairs to obtain crosstalk information. According to the invention, the number of measurement times required for detecting the read crosstalk between the quantum bits can be reduced from 2N (N-1) to a constant number of times, that is, the number of measurement times is not increased along with the scale expansion of a quantum processor.

Description

Technical Field

[0001] The present invention relates to the field of quantum bit measurement technology, and in particular to a method for rapidly detecting read crosstalk between quantum bits. Background Art

[0002] Qubits are the fundamental building blocks of quantum processors, and measuring them is essential for quantum computing. Errors in these measurements can lead to read errors. Read errors are a common type of error on current quantum computing platforms, and their presence can cause biased estimates of the observables measured by the quantum processor. Researchers have developed a variety of read error mitigation techniques, the most common of which uses a response matrix to describe the read error model and infer (e.g., through matrix inversion) the observables that would have been obtained without read errors.

[0003] Read crosstalk is a significant factor contributing to read errors. Specifically, the measurement result of one qubit (the target bit) is affected by the state of another qubit (the control bit). The presence of read crosstalk significantly increases the complexity of read error mitigation. When read crosstalk exists between qubits, the time required to construct the response matrix increases exponentially with the number of qubits, making it unscalable. However, when read crosstalk is negligible, the response matrix can be efficiently derived by performing a tensor product on the response matrix of a single qubit. Therefore, a crucial step in optimizing qubit reads is to quickly detect and specifically address read crosstalk between qubits, thereby efficiently mitigating read errors.

[0004] According to the existing technical solutions, when searching for qubit pairs with read crosstalk, it is necessary to select two qubits from N qubits as the target bit and the control bit and test them in sequence. Each test requires preparing the target bit and the control bit to the |i> state and |j> state (i, j = 0, 1) respectively, and then measure the target bit to obtain the probability F of it being in the |i> state. ij , here traversing i,j includes four cases. Finally, calculate |F 01 -F 00 |和|F 11 -F 10 |, when either of these two values ​​is significantly greater than 0, it means that the state of the control bit will affect the measurement result of the target bit, that is, there is read crosstalk. After traversing all quantum bit pairs in the above way, the complete |F 01 -F 00 |和|F 11 -F 10 |, need to be The existing quantum bit read crosstalk detection technology has a very low detection efficiency. As the scale of quantum processors continues to expand, the time resources consumed when the number of quantum bits increases is unacceptable. Summary of the Invention

[0005] The purpose of the present invention is to address the deficiencies of the existing technology and propose a method for rapidly detecting read crosstalk between quantum bits.

[0006] The object of the present invention is achieved through the following technical solution: a method for rapidly detecting read crosstalk between quantum bits, characterized in that the method comprises the following steps:

[0007] (1) For an N-qubit system, randomly generate M bit strings;

[0008] (2) Prepare the initial state of all bit strings and measure the single quantum bit reading results;

[0009] (3) Classify the random bit string measurement results according to the target bits and control bits;

[0010] (4) calculating the average value of the probability that the target bit is in the prepared state based on the classification results;

[0011] (5) Repeat steps (3) to (4) to traverse all bit pairs to obtain crosstalk information.

[0012] Furthermore, in step (2), the initial states corresponding to all bit strings are prepared in sequence on the quantum processor, and the probability of each quantum bit being in the |1> state is measured and recorded.

[0013] Furthermore, in step (3), for each pair of target bits and control bits, the M random bit strings are classified according to the bit string type (00, 01, 10, 11) of the pair of quantum bits.

[0014] Furthermore, in step (4), based on the classification results, the probability average of the target bit being in the |i> state is extracted to obtain F ij .

[0015] Furthermore, in step (5), all qubit pairs are traversed to obtain the complete |F 01 -F 00 |和|F 11 -F 10 |, when either of these two values ​​is significantly greater than 0, it indicates that the state of the control bit affects the measurement result of the target bit, that is, read crosstalk exists.

[0016] Beneficial effects of the present invention: The method of the present invention can reduce the number of measurements required to detect read crosstalk between quantum bits from 2N(N-1) to a constant number, that is, it does not increase with the expansion of the scale of the quantum processor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] 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 creative work.

[0018] Figure 1 Figure 1 is a schematic diagram of typical measurement data of the effect of control bit crosstalk on target bit readout;

[0019] Figure 2 This is a schematic diagram of the random bit string measurement scheme and its data processing. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described below with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are only used to explain the present invention and are not intended to limit the present invention.

[0021] like Figure 2 As shown, the present invention provides a method for rapidly detecting read crosstalk between quantum bits, which adopts a random bit string measurement method and is specifically implemented as follows:

[0022] The core of random bit string measurement is to extract the read crosstalk information (i.e., obtain F ij Each measurement is no longer limited to two specific qubits, but focuses on all qubits to obtain as many F as possible. ij For an N-qubit system, the present invention needs to randomly generate M bit strings, then sequentially prepare the initial states corresponding to these bit strings on the quantum processor, and measure and record the probability of each qubit being in the |1> state. Figure 2 The left picture in .

[0023] After the data is measured, the crosstalk information needs to be extracted and read from it. For each pair of target bits and control bits, the M random bit strings need to be classified according to the bit string type (00, 01, 10, 11) of the pair of quantum bits when processing the data. Figure 2Since the bit string is randomly generated, each of the four bit string types corresponds to approximately M / 4 sets of measurement data. From these data, the average probability of the target bit being in the |i> state can be extracted to obtain F ij For example, for the measurement data with a bit string type of 01 (the target bit is prepared to the |0> state and the control bit is prepared to the |1> state), the probability of the target qubit being in the |0> state can be extracted and averaged to obtain F 01 By traversing all quantum bit pairs in the above way, we can quickly get the complete |F 01 -F 00 |和|F 11 -F 10 In principle, the M required by the present invention does not increase with the number of qubits, which greatly reduces the time required to find qubit pairs with read crosstalk.

[0024] The above process can be summarized as follows: (1) Generate a random bit string; (2) Generate the corresponding initial state on the quantum processor based on the generated random bit string and measure the single quantum bit reading result; (3) Measurement data processing: Classify the random bit string measurement results according to the target bit and control bit, and calculate the average value F of the probability that the target bit is in the prepared state for each category of results ij , traverse all bit pairs in this way to get the complete |F 01 -F 00 |和|F 11 -F 10 |.

[0025] Figure 1 Typical measurement data for extracting read crosstalk information using a random bit string measurement scheme is shown. Figure 1 The dark red square on the right side of the figure shows that the second qubit has read crosstalk on the fifth qubit.

[0026] Figure 2 Figure 1 is a schematic diagram of the random bit string measurement scheme and its data processing. Each blue rectangle in the figure represents a measurement. Figure 2 The left figure in explicitly shows the quantum circuit corresponding to the first bit string, and the remaining quantum circuits are determined by the bit strings corresponding to each measurement. Figure 2 The right figure in the figure shows the results of classifying the bit strings shown in the left figure according to the bit string types (00, 01, 10, 11) of the first quantum bit and the second quantum bit.

[0027] The above embodiments are used to illustrate the present invention rather than to limit the present invention. Any modifications and changes made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for rapidly detecting read crosstalk between quantum bits, characterized in that: The method comprises the following steps: (1) For an N-qubit system, randomly generate M bit strings; (2) Prepare the initial state of all bit strings and measure the single quantum bit reading results; (3) Classify the random bit string measurement results according to the target bits and control bits; (4) calculating the average value of the probability that the target bit is in the prepared state based on the classification results; (5) Repeat steps (3) to (4) to traverse all bit pairs to obtain crosstalk information.

2. A method for rapidly detecting inter-qubit read crosstalk according to claim 1, characterized in that: In step (2), the initial states corresponding to all bit strings are prepared in sequence on the quantum processor, and the probability of each quantum bit being in the |1> state is measured and recorded.

3. The method for rapidly detecting read crosstalk between quantum bits according to claim 1, wherein: In step (3), for each pair of target bits and control bits, the M random bit strings are classified according to the bit string type (00, 01, 10, 11) of the pair of quantum bits.

4. A method for rapidly detecting read crosstalk between quantum bits according to claim 2, characterized in that: In step (4), based on the classification results, the probability average of the target bit being in the |i> state is extracted to obtain F ij .

5. A method for rapidly detecting read crosstalk between quantum bits according to claim 4, characterized in that: In step (5), all qubit pairs are traversed to obtain the complete |F 01 -F 00 | and |F 11 -F 10 |. When any one of these two values is significantly greater than 0, it indicates that the state of the control qubit affects the measurement result of the target qubit, that is, there is readout crosstalk.

Images