Quantum Gate Phase Control Method Based on a Controllable Flip Magnet and the Controllable Flip Magnet

Abstract

The present invention provides a quantum gate phase control method based on a controllable flipping magnet and the controllable flipping magnet, mainly relating to the technical field of quantum computing. The quantum gate phase control method includes: performing an initialization process on the magnetization direction of the controllable flipping magnet; driving the controllable flipping magnet to flip by using a current pulse sequence, so that the local magnetic fields of the controllable flipping magnet are vectorially superposed at the qubit to form an equivalent rotating magnetic field; when it is determined that the equivalent rotating magnetic field rotates one circle along the forward path and the energy level spacing of the qubit satisfies the adiabatic approximation condition, driving the initial quantum state of the qubit to flip by using a first microwave pulse; based on the principle of time symmetry, driving the controllable flipping magnet to flip again by using the current pulse sequence, so that the equivalent rotating magnetic field rotates one circle along the reverse path to convert the dynamic phase of the quantum state into a global phase, and obtaining a quantum state only with geometric phase information.

Description

Technical Field

[0001] The present invention relates to the technical field of quantum computing, and more specifically, to a method for controlling the phase of a quantum gate based on a controllable flipping magnet and a controllable flipping magnet. Background Art

[0002] Quantum computing provides a new way to solve complex problems that are difficult to handle by classical computers by utilizing characteristics such as quantum superposition and quantum entanglement. Among many quantum bit implementation schemes, silicon-based spin qubits have become one of the ideal platforms for realizing large-scale quantum computing due to their long coherence time, good compatibility with existing semiconductor manufacturing processes, and excellent scalability.

[0003] To overcome the limitations of spin qubit operations that rely on microwave driving technology, existing technologies have proposed high-fidelity quantum bit operation schemes based on quantum geometric phase gates. However, the operation time of existing adiabatic geometric phase gate implementation schemes is often comparable to or even longer than the decoherence time of the qubits, resulting in a significant reduction in the fidelity of gate operations and making it difficult to meet the actual application requirements. In addition, although the operation scheme of directly and rapidly rotating the magnetic field has potential in theory, there are lack of efficient and controllable means for generating and regulating the magnetic field in the silicon-based platform, making it difficult to achieve high-precision and high-speed magnetic field rotation at the nanosecond level. Summary of the Invention

[0004] In view of this, the present invention provides a method for controlling the phase of a quantum gate based on a controllable flipping magnet and a controllable flipping magnet.

[0005] One aspect of the present invention provides a method for controlling the phase of a quantum gate based on a controllable flipping magnet. The method for controlling the phase of the quantum gate includes: initializing the magnetization direction of the controllable flipping magnet; driving the controllable flipping magnet to flip by using a current pulse sequence, so that the local magnetic fields of the controllable flipping magnet are vectorially superposed at the quantum bit to form an equivalent rotating magnetic field; when it is determined that the equivalent rotating magnetic field rotates one circle along the forward path and the energy level spacing of the quantum bit satisfies the adiabatic approximation condition, driving the initial quantum state of the quantum bit to flip by using a first microwave pulse; based on the principle of time symmetry, driving the controllable flipping magnet to flip again by using the current pulse sequence, so that the equivalent rotating magnetic field rotates one circle along the reverse path to convert the dynamic phase of the quantum state into a global phase, and obtaining a quantum state with only geometric phase information.

[0006] According to an embodiment of the present invention, the initializing the magnetization direction of the controllable flipping magnet includes: applying an external magnetic field in a specific direction to the controllable flipping magnet, so that the initial magnetization direction of the controllable flipping magnet is aligned with the preset coordinate axis direction.

[0007] According to an embodiment of the present invention, before driving the controllable flipping magnet to flip by using the current pulse sequence, the quantum gate phase control method further includes: initializing the quantum state of the qubit by using a second microwave pulse to obtain the initial quantum state of the qubit.

[0008] According to an embodiment of the present invention, the controllable flipping magnet includes a plurality of magnetic units. Among them, driving the controllable flipping magnet to flip by using the current pulse sequence, so that the local magnetic fields of the controllable flipping magnet are vectorially superposed at the qubit to form an equivalent rotating magnetic field, includes: determining the flipping timing and flipping direction of each of the plurality of magnetic units based on the pulse amplitude, pulse interval, duration, and direction of the current pulse sequence; based on the flipping timing and flipping direction of each of the plurality of magnetic units, sequentially applying current pulses to the plurality of magnetic units to drive the plurality of magnetic units to flip and form the equivalent rotating magnetic field.

[0009] According to an embodiment of the present invention, the quantum gate phase control method further includes: when the energy level spacing of the qubit does not satisfy the adiabatic approximation condition, applying a vertical external magnetic field to the qubit to adjust the energy level spacing of the qubit so that the energy level spacing of the qubit satisfies the adiabatic approximation condition.

[0010] Another aspect of the present invention provides a controllable flipping magnet applied to the quantum gate phase control method described in any one of the above. The controllable flipping magnet includes a heavy metal thin film layer, a plurality of magnetic units, and a current channel structure, wherein: the heavy metal thin film layer is disposed on the surface of the substrate; the current channel structure is embedded in the heavy metal thin film layer, and the current channel structure is used to generate a spin-polarized current at the contact surface between the heavy metal thin film layer and the plurality of magnetic units under the action of a pulsed current sequence; the plurality of magnetic units are symmetrically arranged around the qubit, and each of the magnetic units is in direct contact with the heavy metal thin film layer, and the plurality of magnetic units are used to complete the flipping of the magnetization direction under the drive of the spin-polarized current.

[0011] According to an embodiment of the present invention, the plurality of magnetic units are arranged in a cross symmetry centered on the qubit.

[0012] According to an embodiment of the present invention, the substrate is configured as a planar germanium-silicon heterojunction.

[0013] According to an embodiment of the present invention, the heavy metal thin film layer is obtained by performing a thin film deposition operation on a heavy metal material having a spin-orbit coupling effect on the substrate.

[0014] According to an embodiment of the present invention, the above-mentioned multiple magnetic units are obtained by performing micro-nano processing on a magnetic material on the above-mentioned heavy metal thin film layer to form a shape.

[0015] In an embodiment of the present invention, a controllable flipped magnet is driven by a current pulse sequence to generate a rapidly rotating magnetic field, providing a controllable parameter space path for quantum state evolution. In addition, by combining the quantum state flip of a microwave π pulse with the time symmetry operation of the reverse path, the operation time of the adiabatic geometric phase gate is shortened, and the random phase accumulation caused by environmental noise is eliminated, solving the problem of too long operation time in the traditional microwave driving scheme, thereby improving the fidelity and practicality of the adiabatic geometric phase gate operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Through the following description of the embodiments of the present invention with reference to the drawings, the above and other objects, features, and advantages of the present invention will become more clear.

[0017] Figure 1 FIG. shows a schematic diagram of a quantum gate phase control method based on a controllable flipped magnet according to an embodiment of the present invention.

[0018] Figure 2a FIG. shows a schematic diagram of changing the geometric phase accumulated by a spin qubit by applying an external magnetic field in the z direction according to a specific embodiment of the present invention.

[0019] Figure 2b FIG. shows a schematic diagram of the change of adiabatic parameters during the quantum state evolution according to a specific embodiment of the present invention.

[0020] Figure 3a FIG. shows a top view of a single-bit device for implementing an adiabatic geometric phase gate in strained silicon according to a specific embodiment of the present invention.

[0021] Figure 3b FIG. shows a cross-sectional view of a single-bit device for implementing an adiabatic geometric phase gate in strained silicon according to a specific embodiment of the present invention.

[0022] Figure 4 FIG. shows a schematic diagram of the configuration of the magnetization directions of multiple magnets according to a specific embodiment of the present invention.

[0023] Figure 5 FIG. shows a schematic diagram of the configuration change of the magnetization directions of multiple magnets according to a specific embodiment of the present invention.

[0024] Figure 6 FIG. shows a schematic diagram of a magnetic field path according to a specific embodiment of the present invention.

[0025] Figure 7a FIG. shows a schematic diagram of the spatial magnetic field distribution generated by the x-direction magnetic field component of configuration 402 in the region near the quantum dot according to a specific embodiment of the present invention.

[0026] Figure 7b Shows a schematic diagram of the spatial magnetic field distribution generated by the y-direction magnetic field component of Configuration 402 according to a specific embodiment of the present invention in the region near the quantum dot.

[0027] Figure 7c Shows a schematic diagram of the spatial magnetic field distribution generated by the z-direction magnetic field component of Configuration 402 according to a specific embodiment of the present invention in the region near the quantum dot.

[0028] Figure 8a Shows a schematic diagram of the spatial magnetic field distribution generated by the x-direction magnetic field component of Configuration 404 according to a specific embodiment of the present invention in the region near the quantum dot.

[0029] Figure 8b Shows a schematic diagram of the spatial magnetic field distribution generated by the y-direction magnetic field component of Configuration 404 according to a specific embodiment of the present invention in the region near the quantum dot.

[0030] Figure 8c Shows a schematic diagram of the spatial magnetic field distribution generated by the z-direction magnetic field component of Configuration 404 according to a specific embodiment of the present invention in the region near the quantum dot.

[0031] Figure 9 Shows a block diagram of a quantum gate phase control device based on a controllable flip magnet according to an embodiment of the present invention. Detailed implementation manners

[0032] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In the following detailed description, for the sake of explanation, many specific details are set forth to provide a thorough understanding of the embodiments of the present invention. However, obviously, one or more embodiments can also be implemented without these specific details. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily obscuring the concepts of the present invention.

[0033] The terms used herein are merely for describing specific embodiments and are not intended to limit the present invention. The terms "including", "comprising", etc. used herein indicate the presence of the described features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0034] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0035] In the case of using expressions such as "at least one of A, B, and C, etc.", generally, it should be interpreted according to the meaning that those skilled in the art usually understand this expression (for example, "a system having at least one of A, B, and C" should include but not be limited to a system having only A, only B, only C, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.).

[0036] As a rapidly developing frontier technology in recent years, quantum computing provides a new approach to solving complex problems that are difficult to handle by classical computers by utilizing characteristics such as quantum superposition and quantum entanglement. Among numerous quantum bit implementation schemes, silicon-based spin qubits have become one of the ideal platforms for realizing large-scale quantum computing due to their relatively long coherence time, good compatibility with existing semiconductor manufacturing processes, and excellent scalability. However, to achieve universal quantum computing, the quantum bit gate operation must reach the fault-tolerant quantum computing threshold and improve the operation fidelity as much as possible, which poses extremely high requirements for operation accuracy.

[0037] Currently, the operation of spin qubits mainly relies on microwave driving technology, but this technology has certain limitations: the quantum gates driven by microwaves are easily affected by environmental noise and driving field drift, resulting in a decrease in operation accuracy; at the same time, in large-scale qubit expansion, microwave driving also faces problems such as crosstalk and frequency crowding, further reducing the qubit operation fidelity.

[0038] To overcome the above problems, the prior art has proposed a high-fidelity quantum bit operation scheme based on the quantum geometric phase gate. Quantum geometric phase refers to the phase that is independent of dynamics accumulated when a quantum state evolves along a closed path in the parameter space. Its characteristic is that it only depends on the geometric properties of the evolution path and is independent of the specific time information of the evolution process. This characteristic makes the geometric phase gate naturally robust to certain types of noise, thus becoming one of the preferred schemes for constructing high-fidelity quantum gates.

[0039] According to whether the system evolution satisfies the adiabatic approximation, geometric phase gates can be divided into two types: non-adiabatic geometric phase gates and adiabatic geometric phase gates. Among them, non-adiabatic geometric phase gates have relatively high requirements for the accuracy of microwave pulses and are easily affected by waveform distortion in actual operations, resulting in a decrease in operation reliability. In contrast, adiabatic geometric phase gates only depend on the ratio between parameters and are insensitive to changes in the absolute value of parameters, showing stronger parameter robustness. This characteristic makes it a more stable and anti-interference quantum operation scheme, especially suitable for the requirements of high-fidelity operations in fault-tolerant quantum computing.

[0040] However, existing implementation schemes of adiabatic geometric phase gates usually rely on microwave driving, suffering from the problem of overly long operation time. Their operation time is often comparable to or even longer than the decoherence time of qubits, leading to a significant reduction in the fidelity of gate operations and making it difficult to meet the requirements of practical applications. In addition, although the operation scheme of directly and rapidly rotating the magnetic field has potential in theory, there are lack of efficient and controllable means for magnetic field generation and regulation in a silicon-based platform, making it difficult to achieve high-precision and high-speed magnetic field rotation at the nanosecond level.

[0041] In view of this, the quantum gate phase control method based on a controllable flipping magnet proposed in the implementation of the present invention drives a controllable flipping magnet through a current pulse sequence to generate a rapidly rotating magnetic field, providing a controllable parameter space path for the evolution of quantum states. In addition, by combining the quantum state flipping of a microwave π pulse with the time symmetry operation of the reverse path, the operation time of the adiabatic geometric phase gate is shortened, and the random phase accumulation caused by environmental noise is eliminated, solving the problem of overly long operation time in traditional microwave driving schemes, thereby improving the fidelity and practicality of adiabatic geometric phase gate operations.

[0042] Specifically, the embodiments of the present invention provide a quantum gate phase control method based on a controllable flipping magnet. The quantum gate phase control method includes: initializing the magnetization direction of the controllable flipping magnet; driving the controllable flipping magnet to flip by using a current pulse sequence, so that the local magnetic fields of the controllable flipping magnet are vectorially superimposed at the qubit to form an equivalent rotating magnetic field; when it is determined that the equivalent rotating magnetic field rotates one circle along the forward path and the energy level spacing of the qubit satisfies the adiabatic approximation condition, driving the initial quantum state of the qubit to flip by using a first microwave pulse; based on the time symmetry principle, driving the controllable flipping magnet to flip again by using a current pulse sequence, so that the equivalent rotating magnetic field rotates one circle along the reverse path to convert the dynamic phase of the quantum state into a global phase, obtaining a quantum state with only geometric phase information.

[0043] It should be noted that the quantum gate phase control method based on a controllable flipping magnet and the controllable flipping magnet determined in the embodiments of the present invention can be used in the field of quantum computing technology. The quantum gate phase control method based on a controllable flipping magnet and the controllable flipping magnet determined in the embodiments of the present invention can also be used in any field other than the field of quantum computing technology, such as the fields of quantum information processing and spintronics technology. The application fields of the quantum gate phase control method based on a controllable flipping magnet and the controllable flipping magnet determined in the embodiments of the present invention are not limited.

[0044] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to specific embodiments and the accompanying drawings.

[0045] Figure 1Shows a schematic diagram of a quantum gate phase control method based on a controllable flipping magnet according to an embodiment of the present invention.

[0046] As Figure 1 shown, this quantum gate phase control method includes operations S110 to S140.

[0047] In operation S110, the magnetization direction of the controllable flipping magnet is initialized.

[0048] In operation S120, a current pulse sequence is used to drive the controllable flipping magnet to flip, so that the local magnetic fields of the controllable flipping magnet are vectorially superposed at the qubit to form an equivalent rotating magnetic field.

[0049] In operation S130, when it is determined that the equivalent rotating magnetic field rotates one circle along the forward path and the rotation rate of the equivalent rotating magnetic field satisfies the adiabatic approximation condition, a first microwave pulse is used to drive the initial quantum state of the qubit to flip.

[0050] In operation S140, based on the principle of time symmetry, a current pulse sequence is used to drive the controllable flipping magnet to flip again, so that the local magnetic field rotates one circle along the reverse path, to convert the dynamic phase of the quantum state into a global phase, and obtain a quantum state only with geometric phase information.

[0051] According to an embodiment of the present invention, the magnetization direction of the controllable flipping magnet is adjusted to a preset initial direction, such as along the x, y, -x, -y axes of the coordinate system, to provide consistent initial conditions for subsequent magnetic field rotation operations and avoid operation errors caused by magnetization direction deviation.

[0052] According to an embodiment of the present invention, a time-sequenced current pulse is applied to the controllable flipping magnet to drive multiple magnets included in the controllable flipping magnet to flip in sequence, so that the direction of the local magnetic field around the qubit continuously changes along a predetermined path (such as rotating one week around the z-axis) and is vectorially superposed at the qubit to form a closed evolution path as the equivalent rotating magnetic field. Among them, the current pulse can be configured as a square wave pulse current.

[0053] Among them, the equivalent rotating magnetic field can be used to represent the rotating magnetic field formed after magnetic field superposition around the qubit.

[0054] According to an embodiment of the present invention, when the equivalent rotating magnetic field rotates one circle along the forward path and satisfies the adiabatic condition, a first microwave pulse resonant with the qubit energy level is applied to the qubit to drive the initial quantum state to flip, for example, the quantum state is flipped from to , and then rotate one full circle at the same time as the reverse path. The forward and reverse rotations convert the dynamical phase accumulated during the evolution of the quantum state into a global phase, and thus its influence is eliminated. Among them, the first microwave pulse may include a microwave π pulse, and the frequency of the microwave π pulse is matched and resonant with the energy level difference of the qubit.

[0055] According to an embodiment of the present invention, a current pulse with a reverse time sequence is applied to the controllable flipping magnet again to drive the multiple magnets included in the controllable flipping magnet to flip in sequence, and the magnetic field rotation rate is kept consistent with the forward path, so that the local magnetic field rotates one full circle along the original path in the reverse direction.

[0056] For example, in the actual evolution process, the system accumulates both the geometric phase and the dynamical phase. To eliminate the influence of the dynamical phase, the Echo method can be used. The evolution process is as follows:

[0057] (1);

[0058] (2);

[0059] In the formula, and represent the initial two quantum states of the qubit, one of which is the ground state and the other is the excited state; and respectively represent the accumulated dynamical phase and geometric phase. and respectively represent the accumulated dynamical phase and geometric phase; represents the forward path, represents the reverse path.

[0060] In this specific embodiment, first adiabatically evolve one full circle along the forward path , then apply a microwave π pulse to flip the quantum state, and then evolve reversely along the opposite path , and apply a second microwave π pulse to restore the initial state. The phase change during the overall evolution is as shown in the above formulas (1) and (2). After the overall operation is finally completed, both the ground state and the excited state will accumulate of the dynamical phase, and this dynamical phase is converted into a global phase factor to be eliminated, leaving only the accumulated geometric phase and the accumulated geometric phase .

[0061] Based on this, embodiments of the present invention drive a controllable flipping magnet through a current pulse sequence to generate a rapidly rotating magnetic field, providing a controllable parameter space path for quantum state evolution. In addition, by combining the quantum state flipping of microwave π pulses with the time symmetry operation of the reverse path, the operation time of the adiabatic geometric phase gate is shortened, and the random phase accumulation caused by environmental noise is eliminated, solving the problem of too long operation time in traditional microwave drive schemes, thereby improving the fidelity and practicality of the adiabatic geometric phase gate operation.

[0062] In addition, embodiments of the present invention use a square wave current pulse to drive the magnet to flip, avoiding the crosstalk and frequency crowding problems existing in traditional microwave drive schemes. In addition, since the magnet flipping is insensitive to waveform distortion, the reliability and accuracy of the operation are further improved.

[0063] According to an embodiment of the present invention, the initialization process of the magnetization direction of the controllable flipping magnet includes: applying an external magnetic field in a specific direction to the controllable flipping magnet, so that the preset initial magnetization direction of the controllable flipping magnet is aligned with the preset coordinate axis direction.

[0064] According to an embodiment of the present invention, the controllable flipping magnet can be driven to generate a spin polarization current by applying an external magnetic field in a specific direction to the controllable flipping magnet or by applying a current pulse to the controllable flipping magnet, so as to achieve rapid initialization. Among them, the external magnetic field can be generated by a permanent magnet array or an electromagnetic coil.

[0065] According to an embodiment of the present invention, before driving the controllable flipping magnet to flip by using a current pulse sequence, the quantum gate phase control method further includes: initializing the quantum state of the qubit by using a second microwave pulse to obtain the initial quantum state of the qubit.

[0066] According to an embodiment of the present invention, a second microwave pulse is applied to the qubit to drive it to transition from an excited state (such as state) to a ground state (such as state), so as to provide a clean initial quantum state (such as ), reducing the background noise in subsequent phase operations and ensuring the accuracy of the dynamic phase conversion.

[0067] According to an embodiment of the present invention, driving the controllable flipping magnet to flip by using a current pulse sequence, so that the local magnetic fields of the controllable flipping magnet are vectorially superimposed at the qubit to form an equivalent rotating magnetic field, includes: determining the flipping timing and flipping direction of each of a plurality of magnetic units based on the pulse amplitude, pulse interval, duration, and direction of the current pulse sequence; driving each of the plurality of magnetic units to flip based on the flipping timing and flipping direction of each of the plurality of magnetic units to form an equivalent rotating magnetic field.

[0068] According to an embodiment of the present invention, by adjusting the pulse amplitude, duration (pulse width), and direction of the current pulse sequence, the flipping timing and flipping direction of multiple magnets in the controllable flipping magnet can be precisely controlled, thereby generating a fast and stable equivalent rotating magnetic field.

[0069] According to a specific embodiment of the present invention, the flipping speed of the controllable flipping magnet can be controlled by the pulse amplitude of the current pulse. For example, based on the flipping characteristics of the magnet material of the controllable flipping magnet, the initial pulse amplitude range can be determined, and then adjusted by a high-precision current source to achieve the control of the current pulse amplitude. Among them, the larger the pulse amplitude, the stronger the spin-orbit torque (SOT), and the faster the magnet flips.

[0070] According to an embodiment of the present invention, the pulse width of the current pulse sequence can be controlled to ensure that the magnet flips completely. Specifically, the initial pulse width can be set according to the magnet flipping time, a fast switching circuit (such as a MOSFET or GaN device) is used to generate a narrow pulse, and the magnet flipping state is monitored in real time by a magnetoresistive sensor to dynamically adjust the pulse width.

[0071] Based on this, the embodiment of the present invention controls the amplitude, duration, and direction of the pulsed current to optimize the magnetic field rotation path and parameters, thereby achieving precise control of the flipping moment and sequence of each magnet, ensuring that the magnets flip in sequence according to a predetermined order, using the generated spin-polarized current to drive the magnets to flip quickly, so as to complete the magnetic field rotation within a time scale of ten nanoseconds, far exceeding the magnetic field rotation time (microsecond level) of the traditional adiabatic method, to achieve a fast adiabatic geometric phase gate operation, while maintaining high parameter robustness, being insensitive to parameter changes, and significantly improving the stability and anti-interference ability of the operation.

[0072] According to an embodiment of the present invention, the phase control method further includes: when the rotation rate of the equivalent rotating magnetic field does not satisfy the adiabatic approximation condition, applying a vertical external magnetic field to the qubit to adjust the energy level spacing of the qubit, so that the rotation rate of the equivalent rotating magnetic field satisfies the adiabatic approximation condition.

[0073] According to an embodiment of the present invention, the adiabatic approximation condition is used to characterize that the adiabatic parameter is much less than 1, that is . Among them, the adiabatic parameter is used to characterize the relative relationship between the system evolution rate and the energy level spacing of the qubit. When , the system evolution rate is much less than the change rate of the energy level spacing, and the quantum state always remains in the instantaneous eigenstate, satisfying the adiabatic approximation condition. Among them, the expression of the adiabatic parameter is as follows:

[0074] (3);

[0075] In the formula, represents the adiabatic parameter, represents the first instantaneous eigenenergy of the qubit, represents the second instantaneous eigenenergy of the qubit, represents the energy level spacing of the qubit, represents the Hamiltonian, represents the Hamiltonian the rate of change with time, represents the reduced Planck constant, where the larger the energy level spacing of the qubit, the easier it is for the adiabatic parameter to be satisfied.

[0076] According to an embodiment of the present invention, in the case where the energy level spacing of the qubit does not satisfy the adiabatic approximation condition, the energy level spacing of the qubit can be adjusted by applying a vertical external magnetic field to the qubit.

[0077] For example, the energy level spacing and the Hamiltonian rate of change in the case of, the adiabatic parameter is calculated by the above formula (3), and by applying a vertical external magnetic field of 0.5 T to the qubit, the energy level spacing is increased to and the is recalculated by the above formula (3), so as to satisfy the adiabatic approximation condition .

[0078] Figure 2a shows a schematic diagram of changing the geometric phase accumulated by the spin qubit by applying an external magnetic field in the z direction according to a specific embodiment of the present invention.

[0079] Figure 2b shows a schematic diagram of the change of the adiabatic parameter during the quantum state evolution according to a specific embodiment of the present invention.

[0080] As Figure 2a shown, by applying a vertical external magnetic field such as the external magnetic field B in the z direction ext (T), the geometric phase accumulated by the spin qubit is changed , and then different adiabatic geometric gate operations are realized. For example, when B ext (T) = 19 mT, the geometric phase accumulated by the spin qubit in a single closed path. As Figure 2b shown, based on the calculation formula (3) of the adiabatic parameter, the adiabatic parameter calculated in a specific embodiment of the present invention satisfies the adiabatic approximation condition.

[0081] Based on this, the adiabatic geometric phase quantum gate control method proposed in the embodiment of the present invention adjusts the energy level spacing of the qubit by applying a vertical external magnetic field to make the adiabatic parameter , ensure that the adiabatic approximation condition holds, so as to ensure that the qubit still satisfies the adiabatic evolution condition under the rapid magnetic field rotation, avoid the errors caused by non-adiabatic transitions, and support long-time quantum state evolution. In addition, by adjusting the external magnetic field strength, the geometric phase accumulated by the qubit is controlled, so as to realize the operations of different adiabatic geometric gates (such as Pauli-Z gate, phase gate), support the flexible switching of various quantum gate operations, and meet the requirements of complex quantum algorithms.

[0082] On the other hand, the present invention provides a controllable flipping magnet, wherein the controllable flipping magnet includes a heavy metal thin film layer, a plurality of magnetic units, and a current channel structure. The heavy metal thin film layer is arranged on the surface of the substrate; the current channel structure is embedded in the heavy metal thin film layer, and the current channel is used to generate a spin-polarized current at the contact surface between the heavy metal thin film layer and the plurality of magnetic units under the action of a pulsed current sequence; the plurality of magnetic units are symmetrically arranged around the qubit, and each magnetic unit is in direct contact with the heavy metal thin film layer, and the plurality of magnetic units are used to complete the flipping of the magnetization direction under the drive of the spin-polarized current.

[0083] According to an embodiment of the present invention, the heavy metal thin film layer is arranged on the surface of the substrate, and a heavy metal material with a strong spin-orbit coupling effect (such as Pt, Ta, or W, etc.) can be selected, and a heavy metal thin film with a nanoscale thickness is prepared on a suitable substrate by magnetron sputtering, electron beam evaporation, or other thin film deposition techniques, ensuring sufficient spin-orbit coupling effect on the basis of ensuring the uniformity and consistency of the thin film.

[0084] According to an embodiment of the present invention, on the heavy metal thin film layer, a plurality of flippable magnetic units are symmetrically arranged around the qubit through micro-nano processing technology, and each magnetic unit is in direct contact with the heavy metal thin film layer. Among them, each magnetic unit can select a magnetic material with a high magnetic susceptibility (such as CoFeB, NiFe, etc.) so as to achieve high-speed and stable flipping after applying the spin-polarized current.

[0085] Among them, the plurality of magnetic units are arranged in a cross symmetry centered on the qubit. The cross-symmetrical layout makes the magnetic field components of each magnet orthogonally superposed at the quantum dot, forming a continuously rotating synthetic magnetic field. In the case of flipping the magnets in sequence (such as clockwise or counterclockwise), the magnetic field direction can be gradually rotated , which is convenient for timing control.

[0086] In a specific embodiment of the present invention, the micro-nano processing technology includes any one or a combination of the following: laser direct writing, electron beam lithography, reactive ion etching, ion implantation, rapid thermal processing, atomic layer deposition, electron beam evaporation, wet etching, and magnetron sputtering, etc. The micro-nano processing technology is not limited in the embodiments of the present invention.

[0087] According to an embodiment of the present invention, a current channel structure is constructed on the surface of the heavy metal thin film layer, so as to generate a spin-polarized current on the surface where the heavy metal thin film contacts the magnetic unit by applying a pulsed current, enabling the magnetic unit to complete the magnetization direction reversal under the drive of the spin-polarized current. Among them, the spin-polarized current is used to represent an electron current with a determined spin polarization direction.

[0088] According to a specific embodiment of the present invention, the substrate can be configured as a planar germanium-silicon heterojunction, which is compatible with the silicon-based quantum dot process and is convenient to be integrated into the existing semiconductor quantum computing platform. In addition, the high thermal conductivity of germanium helps to dissipate heat in a low-temperature (millikelvin) environment and reduce the interference of Joule heat on qubits. During the preparation process, the surface roughness can be made less than or equal to 0.5 nm by chemical mechanical polishing (CMP) to ensure uniform deposition of the heavy metal thin film.

[0089] Figure 3a The top view of a single-bit device for implementing an adiabatic geometric phase gate in strained silicon according to a specific embodiment of the present invention is shown.

[0090] As Figure 3a shown, in the single-bit device of this specific embodiment, the quantum dot is located at the center of the single-bit device and is used to trap electron spin qubits. The heavy metal thin film layer 103 covers the area between the magnetic unit and the quantum dot to generate a spin-polarized current through the spin Hall effect.

[0091] In the single-bit device of this specific embodiment, the controllable flip magnet includes four magnetic units 104, which are symmetrically distributed around the quantum dot and are in direct contact with the heavy metal thin film layer 103 to complete the magnetization direction reversal under the drive of the spin-polarized current and generate an equivalent rotating magnetic field.

[0092] In a specific embodiment of the present invention, all four magnetic units 104 can adopt cuboid magnets, and the magnet size is , the four magnetic units 104 are arranged in a cross shape with the central quantum dot as the symmetry point. The distance from each magnetic unit to the plane projection of the quantum dot is 50 nm, and the horizontal distance between the magnetic units is 160 nm. The magnet material uses CoFe with a relatively large saturation magnetization to obtain a larger magnetic field, and its saturation magnetization is .

[0093] As Figure 3a shown, the gate structure of this single-bit device includes a shielding gate 101, a side top gate 102, and a top gate 105, which are used to regulate the quantum dot potential and electron states.

[0094] As Figure 3a shown, this single-bit device also includes a planar silicon substrate 106 to serve as the support substrate of the single-bit device.

[0095] As shown Figure 3a in the figure, the single-bit device further includes an electrode lead 107, where the electrode lead 107 can be configured to provide electron injection for the quantum dot.

[0096] Among them, the current injection point included in the current channel structure is located at the contact interface between the four magnetic units 104 and the heavy metal thin film layer 103. The embedded low-impedance wire included in the current channel structure can be configured to be arranged along the symmetric distribution direction of the four magnetic units 104 to ensure the generation of a spin-polarized current at the current injection point.

[0097] Figure 3b The figure shows a cross-sectional view of a single-bit device for implementing an adiabatic geometric phase gate in strained silicon according to a specific embodiment of the present invention.

[0098] Figure 3b For Figure 3a the cross-sectional view along the dashed line in the figure. As shown Figure 3b in the figure, the single-bit device further includes an insulating layer 201, a germanium-silicon substrate 202, a germanium-silicon barrier layer 203, and a strained silicon layer 204. Among them, the insulating layer 201 covers between the gates to prevent leakage due to overlapping contact between different gates. The germanium-silicon substrate 202 serves as the bottom support of the device. The germanium-silicon barrier layer 203 is located above the germanium-silicon substrate 202 and is used to confine the electron wave function. The strained silicon layer 204 is located on the germanium-silicon barrier layer 203, and quantum dots are formed at the interface between it and the germanium-silicon barrier layer 203.

[0099] As shown Figure 3b in the figure, the current channel structure is embedded inside the heavy metal thin film layer 103, near the contact surface between the four magnetic units 104 and the heavy metal thin film layer 103, is in direct contact with the four magnetic units 104, and is isolated from the top gate 105 above through the insulating layer 201. The electron spin qubit is formed directly below the top gate 105, at the junction of the strained silicon layer 204 and the germanium-silicon barrier layer 203.

[0100] In the single-bit device of this specific embodiment, when a pulsed current is directly applied to the heavy metal thin film layer 103, due to its strong spin-orbit coupling effect itself, spin-polarized currents will accumulate on the upper and lower interfaces. The spin-polarized currents are injected into the contact surface between the four magnetic units 104 and the heavy metal thin film layer 103, and the four magnetic units 104 are driven to flip in the magnetization direction through the spin-orbit torque (SOT) of the spin-polarized current. By sequentially triggering the current channels corresponding to the four magnetic units 104, the pulsed current flows through each magnet region in sequence to drive the magnetic field direction to gradually rotate (for example, driving the magnetic field direction of the magnet to rotate clockwise respectively), so as to generate an equivalent rotating magnetic field at the quantum dot.

[0101] Based on this, embodiments of the present invention use a germanium-silicon substrate as the substrate, which is compatible with the silicon-based quantum dot process and is convenient for integration into existing semiconductor quantum computing platforms. In addition, the high thermal conductivity of germanium helps to dissipate heat in a low-temperature environment and reduce the interference of Joule heat on qubits. Moreover, since the embodiments of the present invention only rely on the spin Hall effect of heavy metal thin films (Pt, Ta, W), rather than a specific substrate material, it is not only applicable to planar silicon-based systems, but also can be extended to other planar electron spin qubit systems, such as electron spin qubits in two-dimensional materials like graphene, transition metal sulfides (such as MoS 2 ) etc., demonstrating good versatility and scalability.

[0102] Figure 4 The schematic configuration diagram of the magnetization directions of multiple magnets according to a specific embodiment of the present invention is shown.

[0103] As Figure 4 shown, the four magnetic units of the controllable flip magnet are distributed in a cross symmetry centered on the quantum dot, and the arrows indicate the directions of magnetization of each magnetic unit. By independently controlling the flip states of each magnetic unit, the system can achieve a total of 2 4 = 16 different magnetization direction configurations. Specifically, it can include configurations 401 to 416 as Figure 4 shown.

[0104] Figure 5 The schematic diagram of the configuration change of the magnetization directions of multiple magnets according to a specific embodiment of the present invention is shown.

[0105] As Figure 5 shown, 8 (such as configuration 403, configuration 409, configuration 405, configuration 402, configuration 411, configuration 413, configuration 406, configuration 404) can be selected from the above 16 configurations to construct the magnetic field path, and these configurations are related by rotational symmetry. Each time a magnetic unit is flipped, the configuration of the magnetization direction changes and finally returns to the initial state, completing a closed evolution path. For example, the initial state is configuration 405, and flipping the right magnetic unit changes it to configuration 406. By sequentially flipping each magnetic unit, a closed evolution path is finally formed such as configuration 402 → configuration 404 → configuration 403 → configuration 411 → configuration 409 → configuration 413 → configuration 405 → configuration 406 → configuration 402.

[0106] Figure 6 The schematic diagram of the magnetic field path according to a specific embodiment of the present invention is shown.

[0107] As Figure 6 shown, based on the flipping process of the above multiple magnetic units, Figure 6The evolution trajectory of the quantum state shown on the Bloch sphere is a closed evolution path. When the magnetization direction configuration of the magnet changes in sequence as configuration 402 → configuration 404 → configuration 403 → configuration 411 → configuration 409 → configuration 413 → configuration 405 → configuration 406 → configuration 402, the trajectory of the quantum state on the Bloch sphere is from A to H and finally returns to A.

[0108] Figure 7a Fig. shows a schematic diagram of the spatial magnetic field distribution generated by the x-direction magnetic field component of configuration 402 according to a specific embodiment of the present invention in the region near the quantum dot.

[0109] Figure 7b Fig. shows a schematic diagram of the spatial magnetic field distribution generated by the y-direction magnetic field component of configuration 402 according to a specific embodiment of the present invention in the region near the quantum dot.

[0110] Figure 7c Fig. shows a schematic diagram of the spatial magnetic field distribution generated by the z-direction magnetic field component of configuration 402 according to a specific embodiment of the present invention in the region near the quantum dot.

[0111] As Figures 7a - 7c shown, based on the magnetic field distribution of configuration 402 to determine the micro-magnetism at the central quantum dot. Specifically, as Figure 7a shown, Bx = 12.2 mT, as Figure 7b shown, By = 0 mT, as Figure 7c shown, Bz = -8.37 mT. Among them, By≈0 indicates that the symmetry of the magnet layout effectively suppresses the magnetic field components in non-target directions, and the negative sign of Bz indicates the downward direction. Since configurations 403, 409, and 405 are similar to configuration 402 and are formed by rotating configuration 402 by a certain angle, and the formed magnetic field distributions are also similar, the magnetic field distributions are not given separately.

[0112] Figure 8a Fig. shows a schematic diagram of the spatial magnetic field distribution generated by the x-direction magnetic field component of configuration 404 according to a specific embodiment of the present invention in the region near the quantum dot.

[0113] Figure 8b Fig. shows a schematic diagram of the spatial magnetic field distribution generated by the y-direction magnetic field component of configuration 404 according to a specific embodiment of the present invention in the region near the quantum dot.

[0114] Figure 8c Fig. shows a schematic diagram of the spatial magnetic field distribution generated by the z-direction magnetic field component of configuration 404 according to a specific embodiment of the present invention in the region near the quantum dot.

[0115] As Figures 8a - 8c shown, based on the magnetic field distribution of configuration 404 to determine the micro-magnetism at the central quantum dot. Specifically, as Figure 8aAs shown, Bx = 12.10 mT, as Figure 8b As shown, By = 12.10 mT, as Figure 8c As shown, Bz = 0.2 mT. Among them, based on Figures 7b to 8b the magnetic field changes shown in

[0116] it can be seen that during the process of changing from configuration 402 to configuration 404, the magnetic field direction rotates synchronously, thus verifying the feasibility of realizing continuous rotation of the magnetic field by flipping the magnet. Since configurations 411, 413, 406 are similar to configuration 404 and are formed by rotating configuration 404 by a certain angle respectively, and the formed magnetic field distributions are also similar, the magnetic field distributions are not given separately.

[0117] Figure 9 Fig. shows a block diagram of a quantum gate phase control device based on a controllable flipping magnet according to an embodiment of the present invention.

[0118] As Figure 9 shown, the quantum gate phase control device based on a controllable flipping magnet includes an initialization module 910, a first driving module 920, a second driving module 930, and a third driving module 940.

[0119] The initialization module 910 is used to perform an initialization process on the magnetization direction of the controllable flipping magnet.

[0120] The first driving module 920 is used to drive the controllable flipping magnet to flip by using a current pulse sequence, so that the local magnetic fields of the controllable flipping magnet are vectorially superimposed at the qubit to form an equivalent rotating magnetic field.

[0121] The second driving module 930 is used to drive the initial quantum state of the qubit to flip by using a first microwave pulse when it is determined that the equivalent rotating magnetic field rotates one circle along the forward path and the energy level spacing of the qubit satisfies the adiabatic approximation condition.

[0122] The third driving module 940 is configured to drive the controllable flipping magnet to flip again based on the time symmetry principle by using a current pulse sequence, so that the equivalent rotating magnetic field rotates one circle along the reverse path, thereby converting the dynamic phase of the quantum state into a global phase, and obtaining a quantum state with only geometric phase information.

[0123] According to an embodiment of the present invention, the initialization module 910 includes an initialization unit.

[0124] The magnetization direction initialization unit is configured to apply an external magnetic field in a specific direction to the controllable flipping magnet, so that the initial magnetization direction of the controllable flipping magnet is aligned with the preset coordinate axis direction.

[0125] According to an embodiment of the present invention, the quantum gate phase control device based on the controllable flipping magnet further includes a quantum state initialization module.

[0126] The quantum state initialization module is configured to initialize the quantum state of the qubit by using a second microwave pulse to obtain the initial quantum state of the qubit.

[0127] According to an embodiment of the present invention, the first driving module 920 includes a timing determination unit and a magnet driving unit.

[0128] The timing determination unit is configured to determine the flipping timing and flipping direction of each of the plurality of magnetic units based on the pulse amplitude, pulse interval, duration, and direction of the current pulse sequence.

[0129] The magnet driving unit is configured to sequentially apply current pulses to the plurality of magnetic units based on the flipping timing and flipping direction of each of the plurality of magnetic units to drive the plurality of magnetic units to flip and form an equivalent rotating magnetic field.

[0130] According to an embodiment of the present invention, the quantum gate phase control device based on the controllable flipping magnet further includes an energy level spacing adjustment module.

[0131] The energy level spacing adjustment module is configured to apply a vertical external magnetic field to the qubit when the energy level spacing of the qubit does not satisfy the adiabatic approximation condition, so as to adjust the energy level spacing of the qubit to make the energy level spacing of the qubit satisfy the adiabatic approximation condition.

[0132] Any plurality of modules, sub-modules, units, and sub-units according to embodiments of the present invention, or at least part of the functions of any of them, can be implemented in one module. Any one or more of the modules, sub-modules, units, and sub-units according to embodiments of the present invention can be split into multiple modules for implementation. Any one or more of the modules, sub-modules, units, and sub-units according to embodiments of the present invention can be at least partially implemented as a hardware circuit, such as a field programmable gate array (FPGA), a programmable logic array (PLA), a system on a chip, a system on a substrate, a system on a package, an application specific integrated circuit (ASIC), or can be implemented by any other reasonable way of integrating or packaging circuits, or in any one of the three implementation manners of software, hardware, and firmware, or in a suitable combination of any of them. Alternatively, one or more of the modules, sub-modules, units, and sub-units according to embodiments of the present invention can be at least partially implemented as a computer program module, and when the computer program module is run, the corresponding functions can be executed.

[0133] For example, any plurality of the initialization module 910, the first driving module 920, the second driving module 930, and the third driving module 940 can be combined and implemented in one module / unit / sub-unit, or any one of the modules / units / sub-units can be split into multiple modules / units / sub-units. Alternatively, at least part of the functions of one or more of these modules / units / sub-units can be combined with at least part of the functions of other modules / units / sub-units and implemented in one module / unit / sub-unit. According to embodiments of the present invention, at least one of the initialization module 910, the first driving module 920, the second driving module 930, and the third driving module 940 can be at least partially implemented as a hardware circuit, such as a field programmable gate array (FPGA), a programmable logic array (PLA), a system on a chip, a system on a substrate, a system on a package, an application specific integrated circuit (ASIC), or can be implemented by any other reasonable way of integrating or packaging circuits, or in any one of the three implementation manners of software, hardware, and firmware, or in a suitable combination of any of them. Alternatively, at least one of the initialization module 910, the first driving module 920, the second driving module 930, and the third driving module 940 can be at least partially implemented as a computer program module, and when the computer program module is run, the corresponding functions can be executed.

[0134] It should be noted that in the embodiments of the present invention, the part of the quantum gate phase control device based on the controllable flipping magnet corresponds to the part of the quantum gate phase control method based on the controllable flipping magnet. For the description of the part of the quantum gate phase control device based on the controllable flipping magnet, please refer to the part of the quantum gate phase control method based on the controllable flipping magnet, and details will not be repeated here.

[0135] The flowcharts and block diagrams in the accompanying drawings illustrate the possible architectures, functions, and operations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagram may represent a module, a program segment, or a part of code, and the above-mentioned module, program segment, or part of code contains one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than that marked in the accompanying drawings. For example, two consecutive blocks shown may actually be executed substantially in parallel, and they may sometimes be executed in the reverse order, depending on the functions involved. It should also be noted that each block in the block diagram or flowchart, as well as the combination of blocks in the block diagram or flowchart, can be implemented by a dedicated hardware-based system for performing the specified functions or operations, or can be implemented by a combination of dedicated hardware and computer instructions. Those skilled in the art can understand that the features described in various embodiments of the present invention can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in the present invention. In particular, without departing from the spirit and teachings of the present invention, the features described in various embodiments of the present invention can be combined and / or combined in various ways. All such combinations and / or combinations fall within the scope of the present invention.

[0136] The embodiments of the present invention have been described above. However, these embodiments are only for illustrative purposes and not for limiting the scope of the present invention. Although the embodiments have been described separately above, this does not mean that the measures in each embodiment cannot be used advantageously in combination. Without departing from the scope of the present invention, those skilled in the art can make various substitutions and modifications, and all such substitutions and modifications should fall within the scope of the present invention.

Claims

1. A quantum gate phase control method based on a controllable flip magnet, characterized in that: The quantum gate phase control method comprises: Initializing the magnetization direction of the controllable flip magnet; Using a current pulse sequence to drive the controllable flipping magnet to flip, so that the local magnetic field of the controllable flipping magnet is vector-superimposed at the quantum bit to form an equivalent rotating magnetic field; When it is determined that the equivalent rotating magnetic field rotates one circle along the forward path and the energy level spacing of the quantum bit satisfies the adiabatic approximation condition, a first microwave pulse is used to drive the initial quantum state of the quantum bit to flip, wherein the frequency of the first microwave pulse resonates with the energy level of the quantum bit; Based on the principle of time symmetry, the current pulse sequence is used to drive the controllable flip magnet to flip again, so that the equivalent rotating magnetic field rotates one circle along the reverse path to convert the dynamic phase of the quantum state into a global phase, thereby obtaining a quantum state with only geometric phase information.

2. The quantum gate phase control method according to claim 1, characterized in that: The initialization process of the magnetization direction of the controllable flip magnet includes: An external magnetic field in a specific direction is applied to the controllable flip magnet so that the initial magnetization direction of the controllable flip magnet is aligned to the preset coordinate axis direction.

3. The quantum gate phase control method according to claim 2, characterized in that: Before using the current pulse sequence to drive the controllable flip magnet to flip, the quantum gate phase control method further includes: The quantum state of the quantum bit is initialized using a second microwave pulse to obtain an initial quantum state of the quantum bit.

4. The quantum gate phase control method according to claim 1, characterized in that: The controllable flip magnet includes a plurality of magnetic units, wherein the current pulse sequence is used to drive the controllable flip magnet to flip, so that the local magnetic field of the controllable flip magnet is vector-superimposed at the quantum bit to form an equivalent rotating magnetic field, including: Determining the flipping timing and flipping direction of each of the plurality of magnetic units based on the pulse amplitude, pulse interval, duration and direction of the current pulse sequence; Based on the respective flipping timings and flipping directions of the plurality of magnetic units, current pulses are sequentially applied to the plurality of magnetic units to drive the plurality of magnetic units to flip and form the equivalent rotating magnetic field.

5. The quantum gate phase control method according to claim 1, characterized in that: The quantum gate phase control method further comprises: When the energy level spacing of the quantum bit does not satisfy the adiabatic approximation condition, a vertical external magnetic field is applied to the quantum bit to adjust the energy level spacing of the quantum bit so that the energy level spacing of the quantum bit satisfies the adiabatic approximation condition.

6. A controllable flip magnet, applied to the quantum gate phase control method according to any one of claims 1 to 5, characterized in that: The controllable flip magnet includes a heavy metal film layer, a plurality of magnetic units and a current channel structure, wherein: The heavy metal film layer is arranged on the surface of the substrate; The current channel structure is embedded in the heavy metal film layer, and the current channel structure is used to stimulate the contact surface between the heavy metal film layer and the plurality of magnetic units to generate spin polarized current under the action of a pulse current sequence; The multiple magnetic units are symmetrically arranged around the quantum bit, each of the magnetic units is in direct contact with the heavy metal film layer, and the multiple magnetic units are used to complete the magnetization direction reversal under the drive of the spin polarization flow.

7. The controllable flip magnet according to claim 6, characterized in that: The plurality of magnetic units are arranged in a cross-symmetrical manner with the quantum bit as the center.

8. The controllable flip magnet according to claim 6 or claim 7, characterized in that: The substrate is configured as a planar silicon-germanium heterojunction.

9. The controllable flip magnet according to claim 8, characterized in that: The heavy metal thin film layer is obtained by performing a thin film deposition operation on the substrate using a heavy metal material having a spin-orbit coupling effect.

10. The controllable flip magnet according to claim 6, characterized in that: The plurality of magnetic units are formed by performing micro-nano processing on the heavy metal film layer to form magnetic materials.

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