CN-122021958-A - Screening method, system, medium and quantum circuit for working frequency of two-bit gate

CN122021958ACN 122021958 ACN122021958 ACN 122021958ACN-122021958-A

Abstract

The invention discloses a screening method, a system, a medium and a quantum circuit of two-bit gate working frequency, which comprise the steps of carrying out energy spectrum scanning on two quantum bits in the two-bit gate to obtain an energy spectrum scanning result and relaxation time, processing according to the relaxation time to obtain a first dephasing time of the quantum bits under a preset error threshold, carrying out quantum state chromatography on the quantum bits to obtain corresponding residual coupling, obtaining the relation between the residual coupling and bit frequency based on the energy spectrum scanning result, determining a first frequency range, adjusting the bit frequency to the first frequency range, respectively measuring second dephasing time of the two quantum bits under different signal frequencies through the quantum phase chromatography, determining the corresponding second frequency range based on the first dephasing time and the second dephasing time, obtaining the bit frequency corresponding to the minimum residual coupling as the working frequency, and saving experimental resources and scanning time without repeated calibration, and improving experimental efficiency.

Inventors

ZHU SONG
DONG YUQIAN
GU GANGXU
WANG ZHICHUAN

Assignees

量子科技长三角产业创新中心

Dates

Publication Date: 20260512
Application Date: 20251205

Claims (11)

1. A method for screening the operating frequency of a two-bit gate, comprising: Carrying out energy spectrum scanning on two quantum bits in the two-bit gate to obtain an energy spectrum scanning result and relaxation time; processing according to the relaxation time to obtain a first dephasing time of the quantum bit under a preset error threshold; Carrying out quantum state chromatography on the quantum bit to obtain corresponding residual coupling, obtaining the relation between the residual coupling and bit frequency based on the energy spectrum scanning result, and determining a first frequency range; Adjusting the bit frequency to the first frequency range, and respectively measuring second dephasing time of two quantum bits under different signal frequencies through quantum phase chromatography; And determining a corresponding second frequency range based on the first dephasing time and the second dephasing time, and acquiring a bit frequency corresponding to the minimum residual coupling as a working frequency.
2. The method of claim 1, wherein said energy spectrum scanning two qubits in a two-bit gate comprises: Obtaining the bit frequency by measuring the quantum bit; Determining a range of energy spectrum scanning based on the bit frequency, and performing energy spectrum scanning through bias voltages with different magnitudes to obtain an energy spectrum scanning result; and determining the relation between the bit frequency and the bias voltage based on the energy spectrum scanning result.
3. The method of claim 1, wherein the processing the relaxation time to obtain a first dephasing time of the qubit below a predetermined error threshold comprises: Establishing an error calculation model of the two-bit gate, and processing the error calculation model to obtain an error of the two-bit gate, wherein the error comprises an error caused by depolarization and an error caused by quasi-static noise, and the error is respectively configured to be characterized by relaxation time and dephasing time; and determining first dephasing time corresponding to the two quantum bits under the preset error threshold value based on the error calculation model.
4. The method of claim 3, wherein the error calculation model is configured as a sum of a ratio of a time to perform quantum gates to a relaxation time and a square of a ratio of the time to perform quantum gates to the dephasing time.
5. The method of claim 1, wherein said subjecting the qubit to quantum state chromatography to obtain a corresponding residual coupling comprises: Adjusting two qubits to the positions of desserts, wherein the desserts are points with the bit frequency and the magnetic flux change rate of 0; preparing the first qubit to an overlapped state; Preparing second quantum bits to a ground state and an excited state respectively, and performing quantum state chromatography processing by applying bias signals to the first quantum bits to obtain corresponding phases; and obtaining a conditional phase based on phase difference processing corresponding to the ground state and the excited state, wherein the conditional phase is a phase corresponding to residual coupling of the first quantum bit and the second quantum bit.
6. The method of claim 2, wherein determining the first frequency range based on the residual coupling versus bit frequency obtained from the spectral scan results comprises: Obtaining the relation between the residual coupling and the amplitude of the bias signal by adjusting the strength of the bias signal; based on the energy spectrum scanning result, determining the corresponding relation among the residual coupling, the bias voltage and the bit frequency; and determining the first frequency range corresponding to the bit frequency according to a preset bias voltage threshold.
7. The method of claim 5, wherein measuring the second dephasing time of two of the qubits at different signal frequencies by quantum phase chromatography, respectively, comprises: adjusting the bit frequency corresponding to the first quantum bit to the first frequency range; Applying bias signals to the first quantum bit and the second quantum bit to perform quantum phase chromatography to obtain phase distribution and phase standard deviation; Obtaining the relation between the phase standard deviation and the second dephasing time through Gaussian dephasing model processing; And adjusting the amplitude of the bias signal to obtain second dephasing time of the two quantum bits under different signal frequencies.
8. The method of claim 1, wherein determining the corresponding second frequency range based on the first dephasing time and the second dephasing time comprises: and based on the first dephasing time, acquiring bit frequency conforming to the quantum bit at the second dephasing time, and determining the second frequency range.
9. A two-bit gate operating frequency screening system, comprising: The measuring module is used for carrying out energy spectrum scanning on two quantum bits in the two-bit gate to obtain an energy spectrum scanning result and relaxation time; the processing module is used for processing the first dephasing time of the quantum bit under a preset error threshold according to the relaxation time; The chromatographic adjustment module is used for carrying out quantum state chromatography on the quantum bits to obtain corresponding residual coupling, obtaining the relation between the residual coupling and bit frequency based on the energy spectrum scanning result, and determining a first frequency range; And the screening module is used for determining a corresponding second frequency range based on the first dephasing time and the second dephasing time and obtaining a bit frequency corresponding to the minimum residual coupling as a working frequency.
10. A computer readable storage medium, characterized in that it stores a computer program for running a method, wherein the computer program causes a computer to perform the method according to any one of claims 1-8.
11. A quantum wire through which the bit frequency and relaxation time of claim 1 are obtained, comprising: A quantum chip; The quantum chip is connected with the pulse generation unit through the reading unit, the reading signal, the control signal and the bias signal sent by the pulse generation unit are sent to the quantum chip, and the control signal and the bias signal are used for adjusting the quantum state of the corresponding quantum bit of the two-bit gate and carrying out quantum state chromatography; The quantum chip is connected with the signal acquisition unit through the reading unit, sends a reading signal to the signal acquisition unit, reads the bit frequency of the quantum bit, and measures the relaxation time of the quantum bit.

Description

Screening method, system, medium and quantum circuit for working frequency of two-bit gate Technical Field The invention relates to the technical field of quantum measurement and control, in particular to a screening method, a screening system, a screening medium and a quantum circuit for working frequency of a two-bit gate. Background In superconducting quantum computing, two-bit gates can realize condition control and state association between quantum bits, and quantum entanglement is generated by utilizing the two-bit quantum gates, so that the whole quantum system shows non-classical co-evolution behavior, and the fundamental point of quantum computing is that quantum computing is superior to classical computing. The existing screening mode of the working frequency of the two-bit gate is to introduce a SQUID ring (a superconducting loop consisting of two Josephson junctions) on the Josephson junctions, so that the equivalent Josephson energy is adjustable along with the change of external magnetic flux, and the working frequency of the quantum bit is determined by adjusting the bit frequency of the quantum bit by adjusting the external magnetic flux to change the Josephson energy. When the working frequency is selected, the working frequency of one bit is fixed, then the external magnetic flux of the other bit is regulated, the bit frequency is reduced, and the residual coupling between the first bit and the second bit is reduced. And then according to the type of the two-bit gate, adjusting the bit to the frequency when the two-bit gate operation is performed, calibrating and measuring the decoherence time under the frequency point, if the decoherence time does not meet the requirement of the gate operation, changing the bit frequency, and re-performing calibration measurement until the decoherence time of the two bits when the gate operation is performed meets the requirement. A great deal of experimental resources are required to continuously adjust the frequency of the quantum bit and calibrate the quantum bit, so that the experimental efficiency is seriously affected. Disclosure of Invention The invention aims to solve the defects in the prior art and provides a screening method, a screening system, a screening medium and a quantum circuit for the working frequency of a two-bit gate. In order to achieve the above purpose, the invention adopts the following technical scheme that the screening method of the working frequency of the two-bit gate comprises the following steps: Carrying out energy spectrum scanning on two quantum bits in the two-bit gate to obtain an energy spectrum scanning result and relaxation time; processing according to the relaxation time to obtain a first dephasing time of the quantum bit under a preset error threshold; Carrying out quantum state chromatography on the quantum bit to obtain corresponding residual coupling, obtaining the relation between the residual coupling and bit frequency based on an energy spectrum scanning result, and determining a first frequency range; Adjusting the bit frequency to the first frequency range, and respectively measuring second dephasing time of two quantum bits under different signal frequencies through quantum phase chromatography; And determining a corresponding second frequency range based on the first dephasing time and the second dephasing time, and acquiring a bit frequency corresponding to the minimum residual coupling as a working frequency. As a further description of the above technical solution, the performing energy spectrum scanning on two qubits in the two-bit gate includes: Obtaining the bit frequency by measuring the quantum bit; Determining a range of energy spectrum scanning based on the bit frequency, and performing energy spectrum scanning through bias voltages with different magnitudes to obtain an energy spectrum scanning result; and determining the relation between the bit frequency and the bias voltage based on the energy spectrum scanning result. As a further description of the above technical solution, the processing according to the relaxation time to obtain the first dephasing time of the qubit under a preset error threshold includes: Establishing an error calculation model of the two-bit gate, and processing the error calculation model to obtain an error of the two-bit gate, wherein the error comprises an error caused by depolarization and an error caused by quasi-static noise, and the error is respectively configured to be characterized by relaxation time and dephasing time; and determining first dephasing time corresponding to the two quantum bits under the preset error threshold value based on the error calculation model. As a further description of the above solution, the error calculation model is configured to sum the square of the ratio of the time to perform quantum gates to the relaxation time to the ratio of the time to perform quantum gates to the dephasing time. As a further description of the above