A quantum bit reading optimization method, device and computer medium

Abstract

The present invention relates to the quantum field, and specifically provides a method for optimizing the reading of quantum bits, wherein the first part is the calibration of a driving signal for changing a quantum bit from a |1> state to a |2> state, and the second part is to add a driving signal for converting a quantum bit from a |1> state to a |2> state before reading the quantum bit, so as to improve the reading contrast between the |0> state and the |1> state. Compared with the prior art, the present invention utilizes a higher energy level outside the quantum computing subspace to improve the quantum bit state distinction, thereby improving the quantum bit state resolution capability, and at the same time provides a signal calibration method for driving a quantum bit from a |1> state to a |2> state.

Description

Technical Field

[0001] The present invention relates to the quantum field, and specifically provides a quantum bit reading optimization method, device and computer medium. Background Art

[0002] Quantum computing is a potential solution for people to continue to significantly improve computing power at a time when Moore's Law is facing failure. However, there are still some technical problems that need to be solved before quantum computing can actually generate application value. One of the current problems is that the fidelity of reading the state of quantum bits needs to be improved. Because quantum systems are very fragile, direct measurement of the state of quantum bits will generally affect the stability of the quantum computing subspace. Therefore, it is necessary to indirectly read the quantum bits through the influence of different states of quantum bits on the measurement system, thereby achieving quantum non-destructive measurement. Specifically, quantum bits exist in two different states in the quantum computing subspace, |0> and |1>, and the measurement system will reflect different response characteristics when the quantum bits are in |0> and |1> respectively.

[0003] Taking the superconducting quantum computing system as an example, when the superconducting quantum bit is in different states, the planar waveguide resonant cavity used for reading will reflect different microwave transmission characteristics. Therefore, the transmission intensity of the transmission signal at a specific frequency can be selected as the basis for distinguishing the quantum bit state. However, since the final read signal collected after passing through the quantum chip reading transmission line is very weak, it needs to be amplified multiple times before the read signal can be collected and analyzed. The read signal will inevitably introduce noise when it is amplified by the amplifier. Therefore, when the quantum bit is in the |0> state and |1> state, the transmission signal intensity of the reading transmission line is normally distributed within a certain range, and the distribution range has a certain overlap. This makes it impossible to judge the current state of the quantum bit in the overlap interval, which has an adverse effect on the fidelity of quantum bit reading.

[0004] like Figure 4 As shown in the figure, the horizontal axis represents the transmission intensity of the microwave transmission line. The larger the vertical axis of the curve in the figure, the more times the measurement results are distributed in the corresponding transmission intensity in multiple measurements. It can be seen from the figure that when the transmission intensity falls in the rectangular area, since the quantum bit is in the |0> and |1> states, it is impossible to judge the current bit state based on the transmission intensity, resulting in a decrease in the fidelity of quantum bit reading. Summary of the invention

[0005] The present invention aims to overcome the deficiencies of the above-mentioned prior art and provides a highly practical quantum bit reading optimization method.

[0006] A further technical task of the present invention is to provide a quantum bit reading optimization device.

[0007] The technical task of the third aspect of the present invention is to provide a computer-readable medium.

[0008] The technical solution adopted by the present invention to solve its technical problem is:

[0009] A quantum bit reading optimization method has the following steps:

[0010] S1. Obtain the X-gate parameters by the standard calibration process. The X-gate is used to change the quantum bit from the |0> state to the |1> state or from the |1> state to the |0> state.

[0011] S2. Define X 1→2 Door, X 1→2 The gate changes the quantum bit from the |1> state to the |2> state or from the |2> state to the |1> state;

[0012] S3, calibrate to get X 1→2 The characteristic frequency of the gate, X 1→2 The characteristic frequency of the gate is equal to the frequency corresponding to the energy level difference between the |1> and |2> states of the qubit;

[0013] S4, calibrate to get X 1→2 Microwave parameters of the door;

[0014] S5. Add X to the quantum bit before reading it. 1→2 Door;

[0015] S6. In application X 1→2 The quantum bit reading result after the gate becomes the |0> state and the |2> state;

[0016] S7, map the |0> state |2> state to the |0> state |1> state for analysis. When the result of a single read is the |2> state, simply consider the result of this read to be the |1> state.

[0017] S8. Mapping the |2> state back to the |1> state in step S7 will not cause any adverse effect on the analysis of quantum computing results. The read signals between the |0> state and the |2> state have a higher degree of distinction than those between the |0> state and the |1> state.

[0018] Further, in step S3, the calibration method is:

[0019] S301, applying an X gate to the quantum bit in the initial |0> state, so that the quantum bit changes from the |0> state to the |1> state;

[0020] S302, then apply a variable frequency microwave signal to the bit, the frequency range of the signal depends on the anharmonicity of the designed quantum bit, if the anharmonicity is negative, the frequency scanning range of the driving signal is (a, f 01 ), where f01 is the driving frequency of the X gate, and a <f 01 , if the anharmonicity is positive, the frequency sweep range of the drive signal is (f 01 ,b), where f 01 is the driving frequency of the X gate, and b>f 01 ;

[0021] S303, when the frequency of the driving microwave is equal to X 1→2 When the characteristic frequency of the gate is reached, the change in the transmission intensity of the reading resonant cavity will be observed. The driving frequency at this time is selected as X 1→2 The characteristic frequency of the gate.

[0022] Preferably, in step S4, the microwave parameters include microwave amplitude and length, and the calibration method fixes the microwave amplitude and changes the microwave length or fixes the microwave length and changes the microwave amplitude.

[0023] Further, in step S6, as described in step S5, after applying X to the quantum bit 1→2 When the gate is on, for the |0> state, due to X 1→2 The characteristic frequency of the gate is different from the frequency corresponding to the energy level difference between the |0> state and the |1> state, so this operation is invalid for the |0> state. For the |1> state, X 1→2 The gate will drive the |1> state to the |2> state, that is, when X is applied 1→2 The quantum bit reading results after the gate become |0> state and |2> state.

[0024] Further, in step S7, there is a one-to-one correspondence between the |0> state and the |0> state, and between the |1> state and the |2> state, and the |0> state |2> state is mapped to the |0> state |1> state for analysis. In a single read, when the result read is the |2> state, it can be simply considered that the read result is the |1> state.

[0025] Furthermore, in step S8, the output of the quantum computing result is limited to binary coding, so the |2> state is actually redundant information, and mapping the |2> state back to the |1> state will not cause any adverse effects on the analysis of the quantum computing results. The read signal between the |0> state and the |2> state has a higher degree of distinction than that between the |0> state and the |1> state.

[0026] A quantum bit reading optimization device, comprising: at least one memory and at least one processor;

[0027] The at least one memory is used to store a machine-readable program;

[0028] The at least one processor is used to call the machine-readable program to execute a quantum bit reading optimization method.

[0029] A computer-readable medium stores computer instructions, which, when executed by a processor, cause the processor to execute a quantum bit reading optimization method.

[0030] Compared with the prior art, the quantum bit reading optimization method, device and computer medium of the present invention have the following outstanding beneficial effects:

[0031] The present invention utilizes higher energy levels outside the quantum computing subspace to improve the quantum bit state distinction, thereby improving the quantum bit state resolution capability, and at the same time provides a signal calibration method for driving the quantum bit from the |1> state to the |2> state. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Attached Figure 1 It is a state distribution diagram under different reading microwave transmission line transmission intensities when the quantum bit is in the |0> state and |2> state in a quantum bit reading optimization method;

[0034] Attached Figure 2 It is a quantum bit reading optimization method. 1→2 Schematic diagram of the transmission line transmission intensity change during the gate characteristic frequency calibration;

[0035] Attached Figure 3 It is a schematic diagram of Rabi oscillation between quantum bit |1> state |2> state in a quantum bit reading optimization method;

[0036] Attached Figure 4 It is a schematic diagram of the state distribution under different reading microwave transmission line transmission intensities when the quantum bit is in the |0> state and |1> state in a quantum bit reading optimization method. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the solution of the present invention, the present invention is further described in detail below in conjunction with specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] A best embodiment is given below:

[0039] like Figure 1-3 As shown, a quantum bit reading optimization method in this embodiment has the following steps:

[0040] S1. The X-gate parameters are obtained by the standard calibration process. The function of the X-gate is to change the quantum bit from the |0> state to the |1> state or from the |1> state to the |0> state.

[0041] S2. Define X 1→2 Door, X 1→2 The gate changes the quantum bit from the |1> state to the |2> state or from the |2> state to the |1> state.

[0042] S3, calibrate to get X 1→2 The characteristic frequency of the gate, X 1→2 The characteristic frequency of the gate is equal to the frequency corresponding to the energy level difference between the quantum bit |1> state and |2> state. The calibration method is:

[0043] S301, applying an X gate to the quantum bit in the initial |0> state, so that the quantum bit changes from the |0> state to the |1> state;

[0044] S302, then apply a variable frequency microwave signal to the bit, the frequency range of the signal depends on the anharmonicity of the designed quantum bit, if the anharmonicity is negative, the frequency scanning range of the driving signal is (a, f 01 ), where f 01 is the driving frequency of the X gate, and a <f 01 , if the anharmonicity is positive, the frequency sweep range of the drive signal is (f 01 ,b), where f01 is the driving frequency of the X gate, and b>f 01 ;

[0045] S303, when the frequency of the driving microwave is equal to X 1→2 When the characteristic frequency of the gate is reached, the change in the transmission intensity of the reading resonant cavity will be observed. See the attached figure for an example. Figure 2 , the driving frequency at this time can be selected as X 1→2 The characteristic frequency of the gate.

[0046] S4, calibrate to get X 1→2 The microwave parameters of the door include the amplitude and length of the microwave. There are two calibration schemes at this time. One is to change the microwave length with a fixed microwave amplitude, and the other is to change the microwave amplitude with a fixed microwave length. Taking the first calibration scheme as an example, the specific calibration method is:

[0047] S401, applying an X gate to the quantum bit in the initial |0> state, so that the quantum bit changes from the |0> state to the |1> state;

[0048] S402, then apply a fixed amplitude, variable length drive signal to the qubit, and the signal frequency is the characteristic frequency obtained by calibration in the previous step. At this time, Rabi oscillations between the qubit |1> state and |2> state can be observed. See the example diagram Figure 3 , this fixed amplitude and T / 2 are the required X 1→2 Gate microwave parameters, T represents the Rabi oscillation period.

[0049] S5. Add X to the quantum bit before reading it. 1→2 Door;

[0050] S6, when applying X to the quantum bit 1→2 When the gate is on, for the |0> state, due to X 1→2 The characteristic frequency of the gate is different from the frequency corresponding to the energy level difference between the |0> state and the |1> state, so this operation is invalid for the |0> state. For the |1> state, X 1→2 The gate will drive the |1> state to the |2> state. That is, when X is applied 1→2 The quantum bit reading results after the gate become |0> state and |2> state.

[0051] S7. Since there is a one-to-one correspondence between the |0> state and the |0> state, and between the |1> state and the |2> state, the reading result in step S6 can be simply and directly mapped from the |0> state |2> state to the |0> state |1> state for analysis, that is, in a single reading, when the result read is the |2> state, it can be simply considered that the reading result is the |1> state.

[0052] S8, the output of quantum computing results is limited to binary coding, so the |2> state is redundant information, that is, mapping the |2> state back to the |1> state in step S7 will not cause any adverse effect on the analysis of quantum computing results. Figure 4 and attached Figure 1 It can be seen that the read signal between the |0> state and the |2> state has a higher degree of distinction than that between the |0> state and the |1> state. Therefore, the scheme proposed in the present invention can effectively improve the fidelity of quantum bit reading.

[0053] A quantum bit reading optimization device, comprising: at least one memory and at least one processor;

[0054] The at least one memory is used to store a machine-readable program;

[0055] The at least one processor is used to call the machine-readable program to execute a quantum bit reading optimization method.

[0056] A computer-readable medium stores computer instructions, which, when executed by a processor, cause the processor to execute a quantum bit reading optimization method.

[0057] The above-mentioned specific implementations are only specific cases of the present invention. The patent protection scope of the present invention includes but is not limited to the above-mentioned specific implementations. Any quantum bit reading optimization method, device and computer medium claims that conform to the present invention and any appropriate changes or substitutions made by a person of ordinary skill in the technical field shall fall within the patent protection scope of the present invention.

[0058] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A quantum bit reading optimization method, characterized in that: The steps are as follows: S1. Obtain the X-gate parameters by the standard calibration process. The X-gate is used to change the quantum bit from the |0> state to the |1> state or from the |1> state to the |0> state. S2. Define X 1→2 Door, X 1→2 The gate changes the quantum bit from the |1> state to the |2> state or from the |2> state to the |1> state; S3, calibrate to get X 1→2 The characteristic frequency of the gate, X 1→2 The characteristic frequency of the gate is equal to the frequency corresponding to the energy level difference between the |1> and |2> states of the qubit; Calibration methods include: S301, applying an X gate to the quantum bit in the initial |0> state, so that the quantum bit changes from the |0> state to the |1> state; S302, then apply a variable frequency microwave signal to the bit, the frequency range of the signal depends on the anharmonicity of the designed quantum bit, if the anharmonicity is negative, the frequency scanning range of the driving signal is (a, f 01 ), where f 01 is the driving frequency of the X gate, and a <f 01 , if the anharmonicity is positive, the frequency sweep range of the drive signal is (f 01 ,b), where f 01 is the driving frequency of the X gate, and b>f 01 ; S303, when the frequency of the driving microwave is equal to X 1→2 When the characteristic frequency of the gate is reached, the change in the transmission intensity of the reading resonant cavity will be observed. The driving frequency at this time is selected as X 1→2 The characteristic frequency of the gate; S4, calibrate to get X 1→2 Microwave parameters of the door; The microwave parameters include microwave amplitude and length, and the calibration method fixes the microwave amplitude and changes the microwave length or fixes the microwave length and changes the microwave amplitude; S5. Add X to the quantum bit before reading it. 1→2 Door; S6. In application X 1→2 The quantum bit reading result after the gate becomes the |0> state and the |2> state; S7, map the |0> state |2> state to the |0> state |1> state for analysis. When the result of a single read is the |2> state, simply consider the result of this read to be the |1> state. S8. Mapping the |2> state back to the |1> state in step S7 will not cause any adverse effect on the analysis of quantum computing results. The read signals between the |0> state and the |2> state have a higher degree of distinction than those between the |0> state and the |1> state.

2. A quantum bit reading optimization method according to claim 1, characterized in that: In step S6, as described in step S5, after applying X to the quantum bit 1→2 When the gate is on, for the |0> state, due to X 1→2 The characteristic frequency of the gate is different from the frequency corresponding to the energy level difference between the |0> state and the |1> state, so this operation is invalid for the |0> state. For the |1> state, X 1→2 The gate will drive the |1> state to the |2> state, that is, when X is applied 1→2 The quantum bit reading results after the gate become |0> state and |2> state.

3. A quantum bit reading optimization method according to claim 2, characterized in that: In step S7, there is a one-to-one correspondence between the |0> state and the |0> state, and between the |1> state and the |2> state, and the |0> state and the |2> state are mapped to the |0> state and the |1> state for analysis. In a single read, when the result read is the |2> state, it can be simply considered that the read result is the |1> state.

4. A quantum bit reading optimization method according to claim 3, characterized in that: In step S8, the output of the quantum computing result is limited to binary coding, so the |2> state is actually redundant information. Mapping the |2> state back to the |1> state will not cause any adverse effects on the analysis of the quantum computing results. The read signal between the |0> state and the |2> state has a higher degree of distinction than that between the |0> state and the |1> state.

5. A quantum bit reading optimization device, characterized in that: include: at least one memory and at least one processor; The at least one memory is used to store a machine-readable program; The at least one processor is configured to call the machine-readable program to execute the method according to any one of claims 1 to 4.

6. A computer-readable medium, characterized in that The computer readable medium stores computer instructions, and when the computer instructions are executed by a processor, the processor executes the method according to any one of claims 1 to 4.

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