Single-bit gate operation method and related equipment based on dynamic decoupling

Abstract

The present application belongs to the field of quantum computer technology, and relates to a single-bit gate operation method based on dynamic decoupling and related equipment, including receiving a single-bit gate operation instruction, determining the first quantum bit and the second quantum bit of the sample according to the single-bit gate operation instruction; performing a single-bit gate operation on the first quantum bit, and applying a decoupling pulse to the second quantum bit at the same time, respectively obtaining the corresponding first decoupled quantum bit and the second decoupled quantum bit. The technical solution provided by the present application can largely offset the coupling evolution generated between the two quantum bits, thereby improving the fidelity of the single-bit gate.

Description

Technical Field

[0001] The present application relates to the field of quantum computer technology, and more specifically, to a single-bit gate operation method based on dynamic decoupling and related equipment. Background Art

[0002] Quantum computers are physical devices that follow the laws of quantum mechanics to perform high-speed mathematical and logical operations, store and process quantum information. The nuclear magnetic resonance (NMR) quantum computing system can implement a variety of quantum computing algorithms at room temperature and pressure, has mature radio frequency measurement and control technology, and simple experimental conditions.

[0003] In liquid NMR quantum computing, the internal Hamiltonian of the sample, driven by the indirect coupling term between nuclear spins, will cause the quantum bits to evolve in a coupled manner. This coupling evolution between quantum bits is the basis for the construction of two-bit logic gates, but it is also one of the main causes of quantum dephasing. Dynamical decoupling is an important technology in NMR quantum computing. It is generally used to eliminate the interaction between other bits when constructing a specific two-bit interaction gate, or to eliminate the influence of inter-bit coupling when measuring the dephasing time T2. When performing dynamical decoupling, it is necessary to apply π pulses to different quantum bits at certain time points during the evolution of the quantum system to rotate the quantum bits by 180°, in order to achieve the purpose of removing or retaining the coupling between quantum bits. See Figure 1 The four-qubit kinetic decoupling sequence shown in the figure, the black rectangle is a π pulse, the positive sign indicates that the evolution is in the forward direction, and the negative sign indicates that the evolution is in the reverse direction. Over a period of time, the number of positive and negative signs of the qubit is equal, and the positive and negative evolutions of the qubit cancel each other out, which is called the qubit being refocused. Once only one of the two bits is refocused, the two bits will be kinetically decoupled.

[0004] Dynamically decoupled pulse sequences are often designed using so-called Hadamard matrices. This scheme can realize specified two-bit logic gates without relying on GRAPE to optimize the control pulses. Dynamic decoupling is generally used to decouple unwanted inter-bit coupling when constructing two-bit gates, but the influence of coupling between nuclear spins exists not only in two-bit gate operations, but also in single-bit gate operations. In nuclear magnetic resonance quantum computing where the sample is heteronuclear, hard pulses are often used to manipulate quantum bits for single-bit gate operations. If the hard pulse duration is too long or the coupling strength of the sample is too strong, the fidelity of the single-bit gate will be affected by the coupling evolution. Summary of the invention

[0005] The technical problem to be solved by the embodiments of the present application is that the coupled evolution of quantum bits in the prior art will affect the fidelity of single-bit gates.

[0006] In order to solve the above technical problems, the embodiment of the present application provides a single-bit gate operation method based on dynamic decoupling, which adopts the following technical solution:

[0007] Receiving a single-bit gate operation instruction, and determining a first quantum bit and a second quantum bit of the sample according to the single-bit gate operation instruction;

[0008] A single-bit gate operation is performed on the first quantum bit, and a decoupling pulse is applied to the second quantum bit, so as to obtain corresponding first decoupled quantum bits and second decoupled quantum bits respectively.

[0009] Further, the step of determining the first quantum bit and the second quantum bit of the sample according to the single-bit gate operation instruction includes:

[0010] Determine the atomic nucleus to be operated in the sample according to the single-bit gate operation instruction, and determine the corresponding coupled atomic nucleus according to the atomic nucleus to be operated;

[0011] Pre-applying a test pulse to the atomic nucleus to be operated and the coupled atomic nucleus to obtain a corresponding first operating pulse width and a second operating pulse width respectively;

[0012] The first qubit and the second qubit are determined based on the first operation pulse width and the second operation pulse width.

[0013] Further, the step of determining the first quantum bit and the second quantum bit based on the first operation pulse width and the second operation pulse width includes:

[0014] Determining that the first operation pulse width is greater than the second operation pulse width;

[0015] The atomic nucleus to be operated corresponding to the first operation pulse width is used as the first quantum bit, and the coupled atomic nucleus corresponding to the second operation pulse width is used as the second quantum bit.

[0016] Furthermore, the step of performing a single-bit gate operation on the first quantum bit and applying a decoupling pulse to the second quantum bit comprises:

[0017] Applying a logic gate pulse of the single-bit gate operation to the first quantum bit, and determining a rotation direction and a corresponding rotation angle of the first quantum bit after applying the logic gate pulse;

[0018] Obtaining an operation pulse duration of the single-bit gate operation according to the rotation angle and the pulse width of the first quantum bit, and determining a decoupling time for applying the decoupling pulse based on the operation pulse duration and the rotation direction;

[0019] While applying the logic gate pulse to the first quantum bit, a decoupling pulse of a preset duration is applied to the second quantum bit at the decoupling moment, wherein the preset duration is obtained according to the pulse width of the second quantum bit.

[0020] Furthermore, the step of performing a single-bit gate operation on the first quantum bit and applying a decoupling pulse to the second quantum bit comprises:

[0021] Applying a logic gate pulse of the single-bit gate operation to the first quantum bit, and determining a rotation direction and a corresponding rotation angle of the first quantum bit after applying the logic gate pulse;

[0022] Obtaining an operation pulse duration of the single-bit gate operation according to the rotation angle and the pulse width of the first quantum bit;

[0023] Determining the rotation angle of the second quantum bit and the pulse width of the second quantum bit to which the decoupling pulse is applied to obtain a decoupling pulse duration;

[0024] Based on the operation pulse duration and the decoupling pulse duration, a decoupling flip angle and a total decoupling pulse duration are obtained, and a target decoupling pulse is determined according to the decoupling flip angle;

[0025] The logic gate pulse is applied to the first quantum bit within the operation pulse duration, and the target decoupling pulse with the total decoupling pulse duration is applied to the second quantum bit.

[0026] Furthermore, the step of obtaining the decoupling flip angle and the total decoupling pulse duration based on the operation pulse duration and the decoupling pulse duration includes:

[0027] Calculating the number of rotation cycles based on the operation pulse duration and the decoupling pulse duration;

[0028] Obtaining a decoupling flip angle according to the number of rotation cycles and the rotation angle of the decoupling pulse;

[0029] The total duration of the decoupling pulse is obtained according to the decoupling flip angle and the pulse width of the second quantum bit.

[0030] Further, after the step of performing a single-bit gate operation on the first quantum bit and applying a decoupling pulse to the second quantum bit to obtain the corresponding first decoupled quantum bit and second decoupled quantum bit respectively, the method further includes:

[0031] A fidelity test is performed on the first decoupled quantum bit and the second decoupled quantum bit to obtain a fidelity result of a single-bit gate.

[0032] In order to solve the above technical problems, the embodiment of the present application further provides a single-bit gate operation device based on dynamic decoupling, which adopts the following technical solution:

[0033] A determination module, configured to receive a single-bit gate operation instruction, and determine a first quantum bit and a second quantum bit of the sample according to the single-bit gate operation instruction;

[0034] A decoupling module is used to perform a single-bit gate operation on the first quantum bit and apply a decoupling pulse to the second quantum bit to obtain corresponding first decoupled quantum bits and second decoupled quantum bits respectively.

[0035] In order to solve the above technical problems, the embodiment of the present application further provides a quantum computer, which adopts the following technical solution:

[0036] The quantum computer includes a memory and a processor, wherein the memory stores computer-readable instructions, and when the processor executes the computer-readable instructions, the steps of the single-bit gate operation method based on dynamic decoupling as described above are implemented.

[0037] In order to solve the above technical problems, the embodiment of the present application further provides a computer-readable storage medium, which adopts the following technical solution:

[0038] The computer-readable storage medium stores computer-readable instructions, and when the computer-readable instructions are executed by a processor, the steps of the single-bit gate operation method based on dynamic decoupling as described above are implemented.

[0039] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0040] The present application applies a decoupling pulse to the second quantum bit while performing a single-bit gate operation on the first quantum bit, which can largely offset the coupling evolution generated between the two quantum bits, thereby improving the fidelity of the single-bit gate. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the solutions in the present application or the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0042] Figure 1It is the existing four-bit kinetic decoupling sequence;

[0043] Figure 2 is a flow chart of an embodiment of a single-bit gate operation method based on dynamic decoupling according to the present application;

[0044] Figure 3 is a schematic diagram of the principle of the single-bit gate operation method based on dynamic decoupling according to the present application;

[0045] Figure 4 yes Figure 2 A flowchart of a specific implementation of step S102;

[0046] Figure 5 yes Figure 2 A flowchart of another specific implementation of step S102;

[0047] Figure 6 It is a schematic diagram of the decoupling solution provided by this application;

[0048] Figure 7 It is the result of the nuclear magnetic resonance spectrum tested on a desktop nuclear magnetic resonance quantum computer;

[0049] Figure 8 yes Figure 2 A schematic diagram of the structure of a specific implementation of the computing module shown;

[0050] Fig. 9 It is a schematic diagram of the structure of an embodiment of a quantum computer according to the present application. DETAILED DESCRIPTION

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by technicians in the technical field of this application; the terms used in the specification of the application herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned drawings are intended to cover non-exclusive inclusions. The terms "first", "second", etc. in the specification and claims of this application or the above-mentioned drawings are used to distinguish different objects, not to describe a specific order.

[0052] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0053] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings.

[0054] The present application embodiment provides a single-bit gate operation method based on dynamic decoupling, see Figure 2 , a flowchart of an embodiment is shown, comprising the following steps:

[0055] Step S101, receiving a single-bit gate operation instruction, and determining a first quantum bit and a second quantum bit of a sample according to the single-bit gate operation instruction.

[0056] In this embodiment, the atomic nucleus to be operated in the sample is determined according to the single-bit gate operation instruction, and the corresponding coupled atomic nucleus is determined according to the atomic nucleus to be operated; a test pulse is pre-applied to the atomic nucleus to be operated and the coupled atomic nucleus to obtain the corresponding first operation pulse width and second operation pulse width, respectively; and the first quantum bit and the second quantum bit are determined based on the first operation pulse width and the second operation pulse width.

[0057] Among them, the single-bit gate operation instruction is the quantum computer measurement and control system responding to the user's selection of the corresponding operation instruction according to the single-bit gate operation, and transmitting the operation instruction to the quantum computer, and the quantum computer executes the corresponding operation after receiving it.

[0058] The nucleus has a magnetic moment, which comes from the spin of the nucleus itself. Spin is a kind of angular momentum and an intrinsic property of particles. There are coupling interactions between different nuclei. There are usually two types of magnetic coupling between nuclear spins: one is the dipole-dipole interaction between the magnetic moments of nuclear spins, and the other is the indirect interaction carried by electrons in chemical bonds, called J coupling. In liquid NMR samples, the dipole-dipole interaction is often averaged out, leaving only the J coupling effect.

[0059] The molecules selected as quantum computing samples must have larger J coupling, longer coherence time, better spectral resolution, etc.

[0060] This embodiment facilitates subsequent single-bit gate operations and dynamic decoupling operations on different quantum bits by determining the first quantum bit and the second quantum bit.

[0061] In this embodiment, the step of determining the first quantum bit and the second quantum bit based on the first operation pulse width and the second operation pulse width includes:

[0062] Determining that the first operating pulse width is greater than the second operating pulse width;

[0063] The atomic nucleus to be operated corresponding to the first operation pulse width is used as the first quantum bit, and the coupled atomic nucleus corresponding to the second operation pulse width is used as the second quantum bit.

[0064] In this embodiment, it is necessary to ensure that the hard pulse width for controlling the first quantum bit is greater than the hard pulse width for controlling the second quantum bit. Comparing the first operation pulse width and the second operation pulse width, the first operation pulse width of the atomic nucleus to be operated must be significantly greater than the second operation pulse width of the coupled atomic nucleus, otherwise, the operation is stopped.

[0065] It should be understood that for the NMR system, the RF pulse is the RF electromagnetic field pulse, and the RF magnetic field is the power source that drives the excitation magnetization vector and generates the NMR signal, so different RF pulse forms have different effects. A hard pulse refers to a very narrow and strong rectangular RF pulse. The spectrum corresponding to this rectangular pulse is very wide, and the central part of the main lobe of the spectrum is sufficient to cover the range of the sample absorption spectrum.

[0066] In this embodiment, the atomic nucleus to be operated with a large pulse width is used as the first quantum bit, and the coupled atomic nucleus with a small pulse width is used as the second quantum bit, which is helpful for subsequent dynamic decoupling and the process is simple.

[0067] Step S102, performing a single-bit gate operation on the first quantum bit, and applying a decoupling pulse to the second quantum bit, to obtain corresponding first decoupled quantum bits and second decoupled quantum bits, respectively.

[0068] The internal Hamiltonian of the sample, driven by the indirect coupling term between nuclear spins, will cause the qubit to undergo coupled evolution. In nuclear magnetic resonance quantum computing where the sample is heteronuclear, hard pulses are often used to manipulate qubits for single-bit gate operations. If the hard pulse duration is too long or the coupling strength of the sample is too strong, the fidelity of the single-bit gate will be affected by the coupling evolution, which will reduce the fidelity of the single-bit gate.

[0069] Single-bit gates include but are not limited to Hadamard gates, X gates, and T gates.

[0070] See also Figure 3 As shown, in this embodiment, the hard pulse width for controlling the first quantum bit is greater than the hard pulse width for controlling the second quantum bit, there is a difference between the gate operation duration of the first quantum bit and the gate operation duration of the second quantum bit, and a kinetic decoupling pulse is applied to the second quantum bit while a single-bit gate operation is performed on the first quantum bit, thereby achieving the purpose of improving the fidelity of the single-bit gate.

[0071] join Figure 4 In some embodiments, the step of performing a single-bit gate operation on the first qubit and applying a decoupling pulse to the second qubit includes:

[0072] Step S201, applying a logic gate pulse of a single-bit gate operation to the first quantum bit, and determining a rotation direction and a corresponding rotation angle of the first quantum bit after the logic gate pulse is applied;

[0073] Step S202, obtaining the operation pulse duration of the single-bit gate operation according to the rotation angle and the pulse width of the first quantum bit, and determining the decoupling time of applying the decoupling pulse based on the operation pulse duration and the rotation direction;

[0074] Step S203, while applying a logic gate pulse to the first quantum bit, at the decoupling moment, a decoupling pulse of a preset duration is applied to the second quantum bit, wherein the preset duration is obtained according to the pulse width of the second quantum bit.

[0075] The pulse width of the quantum bit at a preset angle can be directly obtained by querying data or experiments, and the logic gate pulse applied to the first quantum bit is set according to the actual situation.

[0076] For example, assuming that the preset angle is 90°, when the angle is 90°, the pulse width of the first quantum bit is PW1, and the pulse width of the second quantum bit is PW2. To implement a single-bit gate operation on the first quantum bit, it is necessary to apply and R x (π) logic gate pulse, where represents the rotation around the Bloch sphere The control operation of the axis rotation angle θ, where The axis rotation is the rotation direction. According to the logic gate pulse applied to the first quantum bit gate, it can be determined that the logic gate pulse rotates 90° around the y-axis, and the pulse duration of the rotation around the y-axis is PW1, and the logic gate pulse rotates 180° around the x-axis, and the pulse duration of the rotation around the x-axis is 2*PW1, and then the total pulse duration of the single-bit gate operation on the first quantum bit is 3*PW1.

[0077] While applying a logic gate pulse to the first qubit, a decoupling pulse of a preset duration is applied to the second qubit. x (π) The time starting position and time middle position of the logic gate pulse, a decoupling pulse is applied to the second quantum bit, and the time point of the decoupling pulse application is the decoupling moment. Assuming that the decoupling pulse is a π pulse, the pulse duration of the decoupling pulse (i.e., the preset duration) is 2*PW2, and the rotation axis (rotation direction) of the decoupling pulse can be an axis at any angle on the xy plane of the Bloch sphere. Assuming that the rotation axis is the y axis, the decoupling pulse is R y (π).

[0078] See also Figure 5In some embodiments, the step of performing a single-bit gate operation on the first qubit and applying a decoupling pulse to the second qubit includes:

[0079] Step S301, applying a logic gate pulse of a single-bit gate operation to a first quantum bit, and determining a rotation direction and a corresponding rotation angle of the first quantum bit after the logic gate pulse is applied;

[0080] Step S302, obtaining the operation pulse duration of the single-bit gate operation according to the rotation angle and the pulse width of the first quantum bit;

[0081] Step S303, determining the rotation angle of the second quantum bit to which the decoupling pulse is applied and the pulse width of the second quantum bit to obtain the decoupling pulse duration;

[0082] Step S304, based on the operation pulse duration and the decoupling pulse duration, a decoupling flip angle and a total decoupling pulse duration are obtained, and a target decoupling pulse is determined according to the decoupling flip angle;

[0083] Step S305 , applying a logic gate pulse to the first quantum bit within the operation pulse duration, and applying a target decoupling pulse with a total decoupling pulse duration to the second quantum bit.

[0084] Among them, the implementation of steps S301 to S302 is the same as that of the above-mentioned steps S201 to S202, and will not be repeated here.

[0085] In step S303 , assuming that the decoupling pulse is a π pulse and the rotation angle is 180°, the decoupling pulse duration is 2*PW2.

[0086] In step S304, due to the limitation of pulse length, it is often difficult to decouple all hard pulse durations with π pulses, so the decoupling scheme of this embodiment is adopted: during the time of single-bit gate operation on one quantum bit, a decoupling pulse is applied to another quantum bit to make it flip continuously, and the flipping angle is 2nπ (n is an integer), where 2n is the number of rotation cycles. If the duration of the flipping decoupling pulse is not exactly equal to the duration of the single-bit gate operation, n can be selected so that the decoupling pulse duration is shorter than the single-bit gate operation duration, or no more operations are performed within the duration when the decoupling pulse duration exceeds the single-bit gate operation. In this way, the coupling evolution between the two bits can be averaged out as much as possible in the forward and reverse directions within the time of the single-bit gate operation, and the quantum bit to which the decoupling pulse is applied can return to the original quantum state.

[0087] Specifically, the number of rotation cycles is calculated based on the operation pulse duration and the decoupling pulse duration; the decoupling flip angle is obtained according to the rotation cycle number and the rotation angle of the decoupling pulse; and the decoupling duration is obtained according to the decoupling flip angle and the second pulse width.

[0088] For example, assuming PW1 = 70us, PW2 = 20us, the pulse duration of the logic gate pulse is 210us, the decoupling pulse duration is 40us, and a value of n is selected so that 2*n*40 is closest to 210, then n = 3 is calculated, the number of rotation cycles is 2*3, and according to the number of rotation cycles 2*3 and the rotation angle π of the decoupling pulse, the final decoupling flip angle 6π can be obtained, and the target decoupling pulse is R y (6π), based on the decoupling flip angle of 6π and the pulse width of the second quantum bit of 20us, the final decoupling duration is 240us.

[0089] In step S307, taking the above example, the operation pulse duration is 210us, the total decoupling pulse duration is 240us, and the operation pulse duration is 30us less than the total decoupling pulse duration. The operation pulse duration is the operation duration of the single-bit gate operation. Within the 30us longer than the single-bit gate operation, there is no need to operate the first quantum bit, and decoupling pulses are continuously applied to the second quantum bit to make it rotate.

[0090] Assuming that the duration of the operation pulse is greater than the total duration of the decoupling pulse, the first quantum bit is operated continuously.

[0091] It should be noted that, according to the hard pulse width of the nuclear magnetic resonance quantum computer for different nuclear spins, the first solution (steps S201 to S203) and the second solution (steps S301 to S305) can be flexibly selected for use.

[0092] This embodiment can eliminate the coupling effect between the two quantum bits to a large extent by applying logic gate pulses and decoupling pulses to the two quantum bits respectively, thereby improving the fidelity of the single-bit gate.

[0093] In some optional embodiments, after the step of performing a single-bit gate operation on the first qubit and applying a decoupling pulse to the second qubit to obtain the corresponding first decoupled qubit and second decoupled qubit, the step further includes:

[0094] The fidelity test is performed on the first decoupled quantum bit and the second decoupled quantum bit to obtain the fidelity result of the single-bit gate.

[0095] The step of performing a fidelity test on the first decoupled qubit and the second decoupled qubit to obtain a fidelity result of a single-bit gate includes:

[0096] applying an observation pulse to the second decoupled quantum bit to obtain an observation signal;

[0097] Determining a quantum state of a first decoupled quantum bit according to an observation signal;

[0098] The fidelity results of single-bit gates are obtained based on the quantum states.

[0099] In this embodiment, the first qubit is in a superposition state, and the signal of the second qubit will be split. The height of the two signal peaks depends on the occupancy of the quantum state of the first qubit. The ideal single-bit gate is to rotate the qubit from the |0> state to the |0> state and the |1> state with equal occupancy. state (theoretical quantum state), observing the signal spectrum line of the second quantum bit should produce two peaks of the same height.

[0100] The second decoupled qubit obtained by applying a decoupling pulse to the second qubit can obtain the signal spectrum of the observation signal of the second qubit by applying an observation pulse. By comparing the heights of the two signal peaks of the signal spectrum, if the height ratio is close to 1:1, it means that the quantum state of the first decoupled qubit is close to the theoretical quantum state. state, further indicating that the single-bit gate makes the quantum state of the first quantum bit evolve to an equal-weighted superposition state of |0> and |1>, which is consistent with the numerical simulation results, and the fidelity is high.

[0101] In this embodiment, the quantum state of the first decoupled quantum bit is close to the theoretical quantum state states, assuming that the occupancy of the |0> state of the first decoupled qubit is D1, and the occupancy of the |1> state is D2. or , it indicates that the quantum state of the first decoupled quantum bit is close to the theoretical quantum state.

[0102] This embodiment determines the quantum state of the first decoupled quantum bit through the observation signal of the second decoupled quantum bit, and then obtains the fidelity through the quantum state of the first decoupled quantum bit. The test method is simple, the test result is accurate, and the obtained fidelity result is reliable.

[0103] The above scheme is further described below in conjunction with specific implementation examples. The preferred embodiments of the present application are described in detail as follows:

[0104] Taking the nuclear magnetic resonance quantum computing of dimethyl phosphite molecule as an example, the single-bit gate operation is the Hadamard gate single-bit operation.

[0105] From the molecular structure of dimethyl phosphite, we can see that there are 7 H atoms and 1 P atom in this molecule. 31 P nucleus is directly coupled to a 1 H nucleus. 1 H nuclei and 31 The P nuclei are used as two quantum bits. The pulse width of the hard pulse controlling the hydrogen nuclei is larger than that of the hard pulse controlling the phosphorus nuclei. 1 H is the first qubit, 31P serves as the second quantum bit.

[0106] For convenience, assume 1 The 90° pulse width of H is 70us, 31 The 90° pulse width of P is 20us. 1 To implement a Hadamard gate single-bit operation on H qubits, 1 H is applied successively and R x (π) hard pulse (logic gate pulse), where represents the rotation around the Bloch sphere Control operation of the shaft rotation angle θ.

[0107] Based on the above logic gate pulses, it can be seen that 1 The total pulse duration of the Hadamard gate operation of the H quantum bit is 210us. 1 H nuclei and 31 The coupling strength of the P nucleus is J = 696 Hz, and the time scale of the coupling evolution is about From this we can see that 1 The Hadamard gate operation of the H quantum bit is already at the same order of magnitude as the time scale required for the coupling evolution. Starting from the pseudopure state |00>, 1 H and 31 P coupling interaction and 1 The Hadamard gate operation of H is performed simultaneously, and the numerical simulation shows that 1 The quantum state of H after the operation is The populations of the |0> state and the |1> state are 0.5943 and 0.4057 respectively. 31 P qubits impose a Observation pulses of Figure 7 As shown in (a), we can see that 1 Caused by H 31 The P spectrum line is split into two peaks of different heights, with a height ratio of about 6:4. However, an ideal Hadamard gate is to rotate the quantum bit from the |0> state to the |0> state and the |1> state with equal population. state, observation 31 The signal spectrum of P should have two peaks of equal height.

[0108] In view of the above situation, under the same conditions as above, 1 While the H quantum bit performs the Hadamard gate operation, 31 The P qubit is subjected to a kinetic decoupling pulse.

[0109] The principles of this application are:

[0110] The Hamiltonian is in the form The two-bit coupling interaction always has This means That is to say, within a period of time, if a π pulse is applied to one of the two quantum bits, the coupled evolution of the two quantum bits sandwiched between the two π pulses will become reverse evolution. The coupled evolution can be offset by simply adjusting the time of the forward evolution and the reverse evolution.

[0111] Since this embodiment is in 1 While applying logic gate pulses to the H quantum bit to perform single-bit gate operations, 31 P qubits are decoupled, so the forward coupling evolution U J (t) and the reverse coupled evolution U J (-t) cannot be completely consistent, but the results of numerical simulation and actual machine testing show that the decoupling effect is still obvious.

[0112] Specific operations such as Figure 6 As shown in (a) and (b). Figure 6 The scheme shown in (a) is to use π pulses for dynamic decoupling. 1 H applies 140us to R x (π) The time starting position and time midpoint position of the hard pulse 31 P applies a π pulse that flips the qubit 180°. The rotation axis of this π pulse used for decoupling can be an axis at any angle in the xy plane. In this example, R is used. y (π), at 140us 1 During the H operation, the coupled evolution is reverse evolution in the first 70us. The evolution is positive in the last 70us. Although and Not completely consistent, but 1 H and 31 The coupling interactions between P can still be eliminated to a large extent.

[0113] Figure 6 The solution shown in (b) is Figure 6 A variation of solution (a). Due to the limitation of pulse length, it is often difficult to decouple all hard pulse durations with π pulses. In this case, another decoupling solution can be used:

[0114] like Figure 6 As shown in (b), 1 The total time for H to perform Hadamard gate operation is 210us. 31P applies R y (6π) hard pulse, in order to make up the flip angle of integer multiples of 2π, 31 The total decoupling pulse duration of P is 240us, and there is no need to adjust the decoupling pulse duration of P within 30us longer than the Hadamard gate operation. 1 H to operate.

[0115] Based on the above decoupling scheme, the numerical simulation results are as follows:

[0116] In the above case, after the unoptimized Hadamard gate action, 1 The quantum state of the H qubit is go through Figure 6 The Hadamard gate action after the decoupling scheme is optimized as shown in (a). 1 The quantum state of the H qubit is go through Figure 6 The Hadamard gate action after the decoupling scheme is optimized as shown in (b). 1 The quantum state of the H qubit is From the results, we can see that the optimized Hadamard gate operation makes 1 H is closer to the theoretical quantum state

[0117] Figure 7 The results are tested on a desktop NMR quantum computer. Figure 7 (a)) and the Hadamard gate after optimization by the above scheme ( Figure 7 (b) 1 H is operated, and then 31 P qubits impose a The observation pulse, observation 31 P signal.

[0118] like Figure 7 As shown in (a), 31 The ratio of the two signal peak heights of P is about 4:6, which means that the unoptimized Hadamard gate does not make 1 The quantum state of H evolves to an equal-weight superposition state of |1> and |1>. This is very close to the result of numerical simulation. Figure 7 (b) 31 The ratio of the two signal peak heights of P is about 1:1, which shows that the Hadamard gate optimized by decoupling in this invention can make 1 The quantum state of H evolves to an equal-weight superposition state of |1> and |1>, which is consistent with the numerical simulation results.

[0119] In summary, in a heteronuclear desktop NMR quantum computer, the present application can improve the fidelity of single-bit gates.

[0120] Further references Figure 8 , as a response to the above Figure 2 The present application provides an embodiment of a single-bit gate operation device based on dynamic decoupling, and the device embodiment is similar to Figure 2 Corresponding to the method embodiment shown, the device can be specifically applied to various electronic devices.

[0121] like Figure 8 As shown, the single-bit gate operation device 800 based on dynamic decoupling of this embodiment includes: a selection module 801 and a decoupling module 802. Among them:

[0122] The determination module 801 is used to receive a single-bit gate operation instruction, and determine a first quantum bit and a second quantum bit of the sample according to the single-bit gate operation instruction;

[0123] The decoupling module 802 is used to perform a single-bit gate operation on the first quantum bit and apply a decoupling pulse to the second quantum bit to obtain the corresponding first decoupled quantum bit and second decoupled quantum bit respectively.

[0124] Based on the above-mentioned single-bit gate operation device based on dynamic decoupling, while performing a single-bit gate operation on the first quantum bit, applying a decoupling pulse to the second quantum bit can largely offset the coupling evolution generated between the two quantum bits, thereby improving the single-bit gate fidelity.

[0125] In this embodiment, the determination module 801 includes a selection submodule, an acquisition submodule and a determination submodule, wherein:

[0126] The selection submodule is used to determine the atomic nuclei to be operated in the sample according to the single-bit gate operation instruction, and determine the corresponding coupled atomic nuclei according to the atomic nuclei to be operated;

[0127] The acquisition submodule is used to pre-apply a test pulse to the atomic nucleus to be operated and the coupled atomic nucleus to obtain the corresponding first operation pulse width and second operation pulse width respectively;

[0128] The determination submodule is used to determine the first quantum bit and the second quantum bit based on the first operation pulse width and the second operation pulse width.

[0129] In this embodiment, the determination submodule is further used to: determine that the first operation pulse width is greater than the second operation pulse width; use the to-be-operated atomic nucleus corresponding to the first operation pulse width as the first quantum bit, and the coupled atomic nucleus corresponding to the second operation pulse width as the second quantum bit.

[0130] In some optional implementations of this embodiment, the decoupling module 802 includes an acquisition submodule, a time determination submodule and a decoupling submodule, wherein:

[0131] The acquisition submodule is used to apply a logic gate pulse of a single-bit gate operation to the first quantum bit, and determine the rotation direction and corresponding rotation angle of the first quantum bit after the logic gate pulse is applied;

[0132] The time determination submodule is used to obtain the operation pulse duration of the single-bit gate operation according to the rotation angle and the pulse width of the first quantum bit, and determine the decoupling time of applying the decoupling pulse based on the operation pulse duration and the rotation direction;

[0133] The decoupling submodule is used to apply a decoupling pulse of a preset duration to the second quantum bit at the decoupling moment while applying a logic gate pulse to the first quantum bit, wherein the preset duration is obtained according to the pulse width of the second quantum bit.

[0134] In some optional implementations, the decoupling module 802 further includes a first duration submodule, a second duration submodule, and a decoupling pulse determination submodule, wherein:

[0135] The acquisition submodule is used to apply a logic gate pulse of a single-bit gate operation to the first quantum bit, and determine the rotation direction and corresponding rotation angle of the first quantum bit after the logic gate pulse is applied;

[0136] The first duration submodule is used to obtain the operation pulse duration of the single-bit gate operation according to the rotation angle and the pulse width of the first quantum bit;

[0137] The second duration submodule is used to determine the rotation angle of the second quantum bit and the pulse width of the second quantum bit to which the decoupling pulse is applied, and obtain the decoupling pulse duration;

[0138] The decoupling pulse determination submodule is used to obtain a decoupling flip angle and a total decoupling pulse duration based on the operation pulse duration and the decoupling pulse duration, and determine a target decoupling pulse according to the decoupling flip angle;

[0139] The decoupling submodule is used to apply the logic gate pulse to the first quantum bit within the operation pulse duration, and simultaneously apply the target decoupling pulse of the total decoupling pulse duration to the second quantum bit.

[0140] In this embodiment, the decoupling pulse determination submodule is further used to: calculate the number of rotation cycles based on the operation pulse duration and the decoupling pulse duration; obtain the decoupling flip angle according to the number of rotation cycles and the rotation angle of the decoupling pulse; obtain the total decoupling pulse duration according to the decoupling flip angle and the pulse width of the second quantum bit.

[0141] In some optional embodiments, the single-bit gate operation device based on dynamic decoupling also includes a testing module for performing a fidelity test on the first decoupled quantum bit and the second decoupled quantum bit to obtain a fidelity result of the single-bit gate.

[0142] To solve the above technical problems, the present application also provides a quantum computer. Fig. 9 , Fig. 9 This is a basic structural block diagram of the quantum computer of this embodiment.

[0143] The quantum computer 9 includes a memory 91, a processor 92, and a network interface 93 that are interconnected through a system bus. It should be noted that the figure only shows a quantum computer 9 with components 91-93, but it should be understood that it is not required to implement all the components shown, and more or fewer components can be implemented instead. Among them, those skilled in the art can understand that the quantum computer here is a device that can automatically perform numerical calculations and / or information processing according to pre-set or stored instructions, and its hardware includes but is not limited to microprocessors, application specific integrated circuits (Application Specific Integrated Circuit, ASIC), programmable gate arrays (Field-Programmable Gate Array, FPGA), digital processors (Digital Signal Processor, DSP), embedded devices, etc.

[0144] The quantum computer can be a computing device such as a desktop computer, a notebook, a PDA, a cloud server, etc. The quantum computer can interact with the user through a keyboard, a mouse, a remote control, a touch pad, or a voice control device.

[0145] The memory 91 includes at least one type of readable storage medium, and the readable storage medium includes flash memory, hard disk, multimedia card, card-type memory (for example, SD or DX memory, etc.), random access memory (RAM), static random access memory (SRAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), programmable read-only memory (PROM), magnetic memory, disk, optical disk, etc. In some embodiments, the memory 91 can be an internal storage unit of the quantum computer 9, such as a hard disk or memory of the quantum computer 9. In other embodiments, the memory 91 can also be an external storage device of the quantum computer 9, such as a plug-in hard disk equipped on the quantum computer 9, a smart memory card (Smart Media Card, SMC), a secure digital (Secure Digital, SD) card, a flash card (FlashCard), etc. Of course, the memory 91 can also include both the internal storage unit of the quantum computer 9 and its external storage device. In this embodiment, the memory 91 is generally used to store the operating system and various application software installed on the quantum computer 9, such as computer-readable instructions of a single-bit gate operation method based on dynamic decoupling, etc. In addition, the memory 91 can also be used to temporarily store various types of data that have been output or are to be output.

[0146] The processor 92 may be a central processing unit (CPU), a controller, a microcontroller, a microprocessor, or other data processing chips in some embodiments. The processor 92 is generally used to control the overall operation of the quantum computer 9. In this embodiment, the processor 92 is used to run computer-readable instructions or process data stored in the memory 91, such as computer-readable instructions for running the single-bit gate operation method based on kinetic decoupling.

[0147] The network interface 93 may include a wireless network interface or a wired network interface, and the network interface 93 is generally used to establish a communication connection between the quantum computer 9 and other electronic devices.

[0148] This embodiment implements the steps of the single-bit gate operation method based on dynamic decoupling as in the above embodiment when the processor executes the computer-readable instructions stored in the memory.

[0149] The present application also provides another embodiment, namely, providing a computer-readable storage medium, which stores computer-readable instructions, and the computer-readable instructions can be executed by at least one processor to enable the at least one processor to perform the steps of the single-bit gate operation method based on kinetic decoupling as described above.

[0150] Through the description of the above implementation methods, those skilled in the art can clearly understand that the above-mentioned embodiment methods can be implemented by means of software plus a necessary general hardware platform, and of course by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present application, or the part that contributes to the prior art, can be embodied in the form of a software product, which is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk), and includes a number of instructions for a terminal device (which can be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in each embodiment of the present application.

[0151] Obviously, the embodiments described above are only some embodiments of the present application, rather than all embodiments. The preferred embodiments of the present application are given in the accompanying drawings, but they do not limit the patent scope of the present application. The present application can be implemented in many different forms. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive. Although the present application is described in detail with reference to the aforementioned embodiments, for those skilled in the art, it is still possible to modify the technical solutions recorded in the aforementioned specific implementation methods, or to perform equivalent replacement of some of the technical features therein. Any equivalent structure made using the contents of the specification and drawings of this application, directly or indirectly used in other related technical fields, is similarly within the scope of patent protection of this application.

Claims

1. A single-bit gate operation method based on dynamic decoupling, characterized in that: include: Receiving a single-bit gate operation instruction, and determining a first quantum bit and a second quantum bit of the sample according to the single-bit gate operation instruction; Performing a single-bit gate operation on the first qubit and applying a decoupling pulse to the second qubit to obtain corresponding first decoupled qubits and second decoupled qubits, respectively; The step of determining the first quantum bit and the second quantum bit of the sample according to the single-bit gate operation instruction comprises: Determine the atomic nucleus to be operated in the sample according to the single-bit gate operation instruction, and determine the corresponding coupled atomic nucleus according to the atomic nucleus to be operated; Pre-applying a test pulse to the atomic nucleus to be operated and the coupled atomic nucleus to obtain a corresponding first operating pulse width and a second operating pulse width respectively; The first qubit and the second qubit are determined based on the first operation pulse width and the second operation pulse width.

2. The single-bit gate operation method based on dynamic decoupling according to claim 1, characterized in that: The step of determining the first quantum bit and the second quantum bit based on the first operation pulse width and the second operation pulse width comprises: Determining that the first operation pulse width is greater than the second operation pulse width; The atomic nucleus to be operated corresponding to the first operation pulse width is used as the first quantum bit, and the coupled atomic nucleus corresponding to the second operation pulse width is used as the second quantum bit.

3. The single-bit gate operation method based on dynamic decoupling according to claim 1, characterized in that: The step of performing a single-bit gate operation on the first quantum bit and applying a decoupling pulse to the second quantum bit comprises: Applying a logic gate pulse of the single-bit gate operation to the first quantum bit, and determining a rotation direction and a corresponding rotation angle of the first quantum bit after applying the logic gate pulse; Obtaining an operation pulse duration of the single-bit gate operation according to the rotation angle and the pulse width of the first quantum bit, and determining a decoupling time for applying the decoupling pulse based on the operation pulse duration and the rotation direction; While applying the logic gate pulse to the first quantum bit, a decoupling pulse of a preset duration is applied to the second quantum bit at the decoupling moment, wherein the preset duration is obtained according to the pulse width of the second quantum bit.

4. The single-bit gate operation method based on dynamic decoupling according to claim 1, characterized in that: The step of performing a single-bit gate operation on the first quantum bit and applying a decoupling pulse to the second quantum bit comprises: Applying a logic gate pulse of the single-bit gate operation to the first quantum bit, and determining a rotation direction and a corresponding rotation angle of the first quantum bit after applying the logic gate pulse; Obtaining an operation pulse duration of the single-bit gate operation according to the rotation angle and the pulse width of the first quantum bit; Determining the rotation angle of the second quantum bit and the pulse width of the second quantum bit to which the decoupling pulse is applied to obtain a decoupling pulse duration; Based on the operation pulse duration and the decoupling pulse duration, a decoupling flip angle and a total decoupling pulse duration are obtained, and a target decoupling pulse is determined according to the decoupling flip angle; The logic gate pulse is applied to the first quantum bit within the operation pulse duration, and the target decoupling pulse with the total decoupling pulse duration is applied to the second quantum bit.

5. The single-bit gate operation method based on dynamic decoupling according to claim 4, characterized in that: The step of obtaining the decoupling flip angle and the total decoupling pulse duration based on the operation pulse duration and the decoupling pulse duration comprises: Calculating the number of rotation cycles based on the operation pulse duration and the decoupling pulse duration; Obtaining a decoupling flip angle according to the number of rotation cycles and the rotation angle of the decoupling pulse; The total duration of the decoupling pulse is obtained according to the decoupling flip angle and the pulse width of the second quantum bit.

6. The single-bit gate operation method based on dynamic decoupling according to claim 1, characterized in that: After the step of performing a single-bit gate operation on the first qubit and applying a decoupling pulse to the second qubit to obtain the corresponding first decoupled qubit and second decoupled qubit, the step further includes: A fidelity test is performed on the first decoupled qubit and the second decoupled qubit to obtain a fidelity result of a single-bit gate.

7. A single-bit gate operation device based on dynamic decoupling, characterized in that: include: A determination module, configured to receive a single-bit gate operation instruction, and determine a first quantum bit and a second quantum bit of the sample according to the single-bit gate operation instruction; a decoupling module, configured to perform a single-bit gate operation on the first qubit and apply a decoupling pulse to the second qubit, to obtain corresponding first decoupled qubits and second decoupled qubits, respectively; The determination module includes a selection submodule, an acquisition submodule and a determination submodule, wherein: The selection submodule is used to determine the atomic nuclei to be operated in the sample according to the single-bit gate operation instruction, and determine the corresponding coupled atomic nuclei according to the atomic nuclei to be operated; The acquisition submodule is used to pre-apply a test pulse to the atomic nucleus to be operated and the coupled atomic nucleus to obtain the corresponding first operation pulse width and second operation pulse width respectively; The determination submodule is used to determine the first quantum bit and the second quantum bit based on the first operation pulse width and the second operation pulse width.

8. A quantum computer, comprising a memory and a processor, wherein the memory stores computer-readable instructions, and when the processor executes the computer-readable instructions, the steps of the single-bit gate operation method based on dynamic decoupling as described in any one of claims 1 to 6 are implemented.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer-readable instructions, which, when executed by a processor, implement the steps of the single-bit gate operation method based on dynamic decoupling as described in any one of claims 1 to 6.

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