Device and method for constructing spin quantum bit baseband control gate

Abstract

The invention provides a device and method for constructing a spin quantum bit baseband control gate. The device comprises a spin quantum bit unit and one or more SOT magnetic structure units. The spin quantum bit unit can form a planar spin quantum bit; the SOT magnetic structure unit is arranged on the spin quantum bit unit, and when an adjustable current pulse is applied to the SOT magnetic structure unit, an initial magnetic field of the SOT magnetic structure unit can be edited, and a specific magnetic field corresponding to the adjustable current pulse is obtained; an auxiliary external magnetic field is provided or other specific magnetic fields are provided through other SOT magnetic structure units to jointly act on the spin quantum bits, the spin quantization axes of the spin quantum bits are located in the superposition and direction of the total magnetic field, and the states of the specific magnetic fields can be changed by setting the time sequence of adjustable current pulses. Therefore, the state of the spin quantization axis of the spin quantum bit is changed, and the spin quantum bit baseband control gate is realized.

Description

Devices and methods for constructing baseband control gates for spin qubits Technical Field

[0001] This disclosure relates to the fields of quantum and semiconductor technology, and in particular to a device and method for constructing a baseband control gate for spin qubits. Background Technology

[0002] Silicon-based quantum dot (QD) spin qubits are considered a platform with significant advantages for realizing semiconductor quantum computing due to their long coherence time. Furthermore, their compatibility with CMOS industrial production is a core advantage of semiconductor spin qubits as a candidate for large-scale quantum computing and simulation in gate-defined quantum dots. In spin qubits, the intrinsic spin-orbit coupling (SOC) constructed using the magnetic field of a micromagnet is crucial in various aspects. Currently, the electric dipole spin resonance (EDSR) operation based on the synthetic SOC generated by the stray field gradient of the micromagnet or the intrinsic SOC of the material has achieved a 99% fidelity single-qubit to two-qubit gate, demonstrating the advantages and importance of this approach. However, many operations of spin qubits, including those of EDSR, rely on microwave driving technology. But with the need for large-scale qubit expansion, this technology has obvious limitations: microwave-driven quantum gates are susceptible to environmental noise and driving field drift, leading to decreased operational accuracy. Excessive operation time can also cause decoherence of the qubits, thereby reducing the fidelity of qubit operations. At the same time, in large-scale qubit expansion, microwave driving also faces problems such as crosstalk and frequency congestion, which further reduce fidelity.

[0003] To address the challenges of microwave manipulation, recent research has focused on hopping gates, constructed using baseband control of single-spin qubits based on baseband manipulation, due to their high fidelity, fast operation, and scalability. A key feature is the manipulation of the spin quantization axis. However, controlling the quantization axis via ultrafast magnetic fields has been extremely difficult in previous architectures. Researchers have attempted to achieve baseband manipulation using anisotropic spin-orbit coupling (SOC), for example, by constructing different spin quantization axes at different positions through magnetic field gradients and material parameters. Then, baseband voltage pulses cause the qubit to jump between different positions, inducing Larmor precession of the spin after its quantization axis changes, allowing it to rotate to the target position. However, this approach also has some drawbacks, such as high material selectivity, generally requiring materials with intrinsic spin-orbit coupling and g-factor anisotropy. For example, in materials like Si, an external magnetic field combined with a complex magnetic structure is needed to construct specific magnetic field direction and magnitude anisotropy. Furthermore, electrons in current baseband control gate schemes need to move, a process that can easily lead to decoherence, thus affecting operational fidelity. Summary of the Invention

[0004] In view of the above, in order to at least partially solve at least one of the aforementioned technical problems, this disclosure provides a device and method for constructing a spin qubit baseband control gate, the technical solution of which is as follows:

[0005] According to embodiments of this disclosure, a device for constructing a spin qubit baseband control gate is provided, comprising a spin qubit unit and a SOT magnetic structure unit: the spin qubit unit is capable of forming a planar spin qubit; the SOT magnetic structure unit is disposed on the spin qubit unit, and when an adjustable current pulse is applied to the SOT magnetic structure unit, the initial magnetic field of the SOT magnetic structure unit can be edited to obtain a specific magnetic field corresponding to the adjustable current pulse; an auxiliary external magnetic field is provided and acts on the spin qubit together with the specific magnetic field, the spin quantization axis of the spin qubit is located in the superposition direction of the specific magnetic field and the auxiliary external magnetic field, and the state of the specific magnetic field can be changed by setting the timing of the adjustable current pulse, thereby changing the state of the spin quantization axis of the spin qubit, and realizing the spin qubit baseband control gate.

[0006] According to embodiments of this disclosure, another device for constructing a spin qubit baseband control gate includes a spin qubit unit and at least two SOT magnetic structure units. The spin qubit unit can form a planar spin qubit; at least two SOT magnetic structure units are disposed on the spin qubit unit. When an adjustable current pulse is applied to each of the at least two SOT magnetic structure units, the initial magnetic field of each SOT magnetic structure unit can be edited to obtain at least two specific magnetic fields corresponding to the adjustable current pulse. The at least two specific magnetic fields act together on the spin qubit, and the spin quantization axis of the spin qubit is located in the direction of the superposition of the at least two specific magnetic fields. By setting the timing of the adjustable current pulse, the state of the at least two specific magnetic fields can be changed, thereby changing the state of the spin quantization axis of the spin qubit and realizing a spin qubit baseband control gate.

[0007] According to an embodiment of this disclosure, the adjustable current pulse is a square wave current pulse, and the timing of the square wave current pulse controls the reciprocating reversal of the magnetization direction of the specific magnetic field generated by the SOT magnetic structure unit. Before the magnetization direction of the specific magnetic field generated by the SOT magnetic structure unit is reversed, the superposition and direction of the specific magnetic field at the spin qubit and the auxiliary external magnetic field is the first direction S1. After the magnetization direction of the specific magnetic field generated by the SOT magnetic structure unit is reversed, the superposition and direction of the specific magnetic field at the spin qubit and the auxiliary external magnetic field becomes the second direction S2, thereby realizing the precession of the spin qubit axis around the second direction S2.

[0008] According to an embodiment of this disclosure, the strength of the auxiliary external magnetic field is less than the strength of the coercive field of the SOT magnetic structure unit, and the angle between the first direction S1 and the second direction S2 is controlled by adjusting the magnitude of the auxiliary external magnetic field.

[0009] According to an embodiment of this disclosure, the adjustable current pulse is a square wave current pulse. The timing of the square wave current pulse controls the reciprocating reversal of the magnetization direction of the specific magnetic field corresponding to the SOT magnetic structure unit. By adjusting the timing of the square wave current pulse applied to each SOT magnetic structure unit, the state of the specific magnetic field generated by each SOT magnetic structure unit is changed, causing the total magnetic field acting on the spin qubit to switch between a first state and a second state. In the first state, the superposition and direction of the total magnetic field of each specific magnetic field is the first direction S. 1， The total magnetic field, in the second state, is superimposed on the specific magnetic fields and its direction changes to the second direction S. 2， Achieve precession of the spin quantization axis around the second direction S2.

[0010] According to an embodiment of this disclosure, the adjustable current pulse is a square wave current pulse. By adjusting the timing of the square wave current pulse, the magnetization direction of the specific magnetic field corresponding to the SOT magnetic structure unit is controlled to reciprocate. By adjusting the timing of the square wave current pulse, the magnetization directions of the two SOT magnetic structure units are made parallel or antiparallel. When the magnetization directions of the two SOT magnetic structure units are parallel, the superposition and direction of the two specific magnetic fields at the spin qubit is the first direction S1. When the magnetization directions of the two SOT magnetic structure units are antiparallel, the superposition and direction of the two specific magnetic fields at the spin qubit becomes the second direction S2, thereby realizing the precession of the spin qubit axis around the second direction S2.

[0011] According to an embodiment of this disclosure, the angle between the first direction S1 and the second direction S2 is 90°. The spin precession angle is adjusted by adjusting the duty cycle of the square wave current pulse, thereby realizing the spin quantum bit baseband control gate.

[0012] According to an embodiment of this disclosure, the spin qubit unit is a spin qubit architecture based on silicon-based quantum dots.

[0013] According to an embodiment of this disclosure, the SOT magnetic structural unit comprises, from bottom to top, a heavy metal layer, a magnetic layer, and an oxide capping layer; the heavy metal layer is prepared from materials selected from Ta, W, and Pt, and the magnetic layer is prepared from materials selected from CoFeB and Co; the oxide capping layer comprises an oxide isolation layer and a capping layer, wherein the oxide isolation layer is selected from MgO, amorphous alumina, HfO2, and TiO2, and the capping layer is selected from Ta, Ru, Ti, and Pt.

[0014] According to embodiments of this disclosure, a method for constructing a spin qubit baseband control gate is also provided, comprising: fabricating a spin qubit unit capable of forming a spin qubit; fabricating an SOT magnetic structure unit on the spin qubit unit; applying a tunable current pulse to the SOT magnetic structure unit to edit the initial magnetic field of the SOT magnetic structure unit to obtain a specific magnetic field corresponding to the tunable current pulse; introducing other magnetic fields to superimpose with the specific magnetic field vector and act together on the spin qubit; and changing the state of the specific magnetic field corresponding to the SOT magnetic structure unit by adjusting the timing of the tunable current pulse, thereby changing the state of the spin quantization axis of the spin qubit and realizing a spin qubit baseband control gate. Attached Figure Description

[0015] The above and other objects, features and advantages of this disclosure will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0016] Figure 1a is a schematic diagram of the top structure of the device for constructing a spin qubit baseband control gate according to Embodiment 1 of this disclosure.

[0017] Figure 1b is a schematic cross-sectional view of the device for constructing a spin qubit baseband control gate according to Embodiment 1 of this disclosure, along AA′ in Figure 1a.

[0018] Figure 2a is a schematic diagram of the top structure of the device for constructing a spin qubit baseband control gate according to Embodiment 2 of this disclosure.

[0019] Figure 2b is a schematic cross-sectional view of the device for constructing a spin qubit baseband control gate according to Embodiment 2 of this disclosure along AA′ in Figure 2a.

[0020] Figure 3a is a schematic diagram of the timing of the square wave current pulse and the change of the spin state of the spin qubit when the angle θ between the first direction S1 and the second direction S2 is 22.5° according to an embodiment of the present disclosure.

[0021] Figure 3b is a schematic diagram of the timing of the square wave current pulse and the change of the spin state of the spin qubit when the angle θ between the first direction S1 and the second direction S2 is 45° according to an embodiment of the present disclosure.

[0022] Figure 3c is a schematic diagram of the timing of the square wave current pulse and the change of the spin state of the spin qubit when the angle θ between the first direction S1 and the second direction S2 is 90° according to an embodiment of the present disclosure.

[0023] Figure 4 is a schematic diagram of the specific magnetic field and auxiliary external magnetic field at the spin qubit before and after the magnetization direction of the SOT magnetic structure unit in Embodiment 1 of this disclosure is switched.

[0024] Figure 5 is a schematic diagram showing the distribution of the specific magnetic field and the total magnetic field of the auxiliary external magnetic field at the spin qubit before and after the magnetization direction switching of the SOT magnetic structure unit in Embodiment 1 of this disclosure.

[0025] Figure 6 is a schematic diagram of the direction of the normalized total magnetic field at the spin qubit before and after the magnetization direction switching of the SOT magnetic structure unit in Embodiment 1 of this disclosure.

[0026] Figure 7 is a schematic diagram showing the relationship between the spin precession angle and time of the spin qubit before and after the magnetization direction switching of the SOT magnetic structure unit in Embodiment 1 of this disclosure.

[0027] Figure 8 is a schematic diagram showing the distribution of the total magnetic field at the spin qubits of the two SOT magnetic structure units in different states in Embodiment 2 of this disclosure.

[0028] Figure 9 is a schematic diagram showing the direction of the total magnetic field at the spin qubit of the two SOT magnetic structure units in different states of Embodiment 2 of this disclosure.

[0029] Figure 10 is a schematic diagram showing the relationship between the spin precession angle and time at the spin qubits of the two SOT magnetic structural units in different states of Embodiment 2 of this disclosure.

[0030] Figure 11 is a flowchart illustrating a method for constructing a spin qubit baseband control gate according to an embodiment of this disclosure.

[0031] Figure label:

[0032] 101-Heavy metal layer; 102-Source; 103-Shielding plate; 104-Drain; 105-Oxide capping layer; 106-Barrier gate; 107-Top gate; 201-Silicon germanium barrier layer; 202-Silicon germanium substrate; 203-Oxide capping layer; 204-Magnetic layer; 205-Oxide insulating layer; 206-Strained silicon. Detailed Implementation

[0033] This disclosure provides a silicon-based semiconductor quantum bit baseband control gate based on a spin-orbit torque device. By using a spin-orbit torque (SOT) device, the magnetization direction of the device can be reversed through the manipulation of square wave current.

[0034] Theoretically, the magnetization direction of a SOT device can be reversed by manipulating it with square wave current pulses. When current flows through materials such as heavy metals, due to the Spin Hall Effect (SHE), a spin current is generated that is simultaneously perpendicular to the charge flow and the spin polarization direction. This leads to directional spin accumulation at the thin film interface, exerting a torque on the magnetic moment of the adjacent magnetic layer, causing the magnetic moment to flip in the easy magnetization direction. This flip allows the magnetic stray field around the device to be changed in a very short time by altering the magnetization, thereby directly changing the spin quantization axis without the need for actual charge displacement. Bit gate operations can be achieved by manipulating the DC electrical properties of the SOT device. Currently, several studies have reported that the magnetic layer flip time of spin orbital moment magnetic random access memory (SOT-MRAM) can reach the nanosecond or sub-nanosecond order of magnitude, which is much smaller than the decoherence time of a bit. This gives SOT devices the potential to replace traditional micromagnets for bit manipulation.

[0035] This invention utilizes the electron spin polarization current generated by the spin Hall effect in heavy metal materials (such as Ta / W / Pt), and then achieves rapid magnetization reversal of the adjacent magnetic layer (such as CoFeB / Co) in the plane of the thin film or in the direction perpendicular to the thin film plane through the spin orbital torque effect generated therein. When current flows through heavy metal materials in a SOT device, due to its spin Hall effect, the heavy metal layer generates a spin current that is simultaneously perpendicular to the charge flow and the spin polarization direction, resulting in directional spin accumulation at the thin film interface. This generates a torque on the magnetic moment of the adjacent magnetic layer, causing the magnetic moment to reverse in the easy magnetization direction. This reversal allows the magnetic field or magnetic stray field around the SOT device to be changed in a very short time by changing the magnetization, thereby directly changing the spin quantization axis of the qubit without the need for actual charge displacement. The gate operation of the qubit is achieved by controlling the DC electrical properties of the SOT device. Several studies have reported that the magnetic layer flip time of spin-orbit torque magnetic random access memory (SOT-MRAM) can reach the order of nanoseconds or sub-nanoseconds, which is much smaller than the decoherence time of qubits. This gives SOT devices the potential to replace traditional micromagnets for bit manipulation.

[0036] The SOT device of this invention, which rapidly switches stray fields, not only allows for the simple and direct acquisition of specific magnetic field angles, but also eliminates the need for materials with g-factor anisotropy and the requirement for charge movement. Theoretically, this reduces noise caused by spatial inhomogeneities in quantum dots and offers greater operability. By placing magnets around the qubits and switching their magnetization states, magnetic field manipulation is achieved, controlling the precession of the qubit spin quantization axis. By setting a reasonable flip sequence, a non-adiabatic spin qubit baseband control gate can be realized.

[0037] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0038] In the embodiments of this disclosure, a device for constructing a spin qubit baseband control gate is provided. This device mainly includes spin qubit units and SOT magnetic structure units (referred to as magnets or magnetic units). In Embodiment 1, as shown in Figures 1a and 1b, one SOT magnetic structure unit can be provided, and an external auxiliary magnetic field needs to be introduced. In Embodiment 2, as shown in Figures 2a and 2b, two SOT magnetic structure units are provided. It should be noted that more SOT magnetic structure units can be provided as needed.

[0039] In embodiments of this disclosure, a method for constructing a spin qubit baseband control gate is also provided, as shown in Figure 11. The method includes:

[0040] S1: Prepare spin qubit units capable of forming spin qubits;

[0041] S2: Fabricate SOT magnetic structure units on the spin qubit units;

[0042] S3: Apply an adjustable current pulse to the SOT magnetic structure unit to edit the initial magnetic field of the SOT magnetic structure unit and obtain a specific magnetic field corresponding to the adjustable current pulse;

[0043] S4: Introduce other magnetic fields to superimpose them with the specific magnetic field vector and act on the spin qubit; and

[0044] S5: By adjusting the timing of the adjustable current pulse, the state of the specific magnetic field corresponding to the SOT magnetic structure unit is changed, thereby changing the state of the spin quantization axis of the spin qubit and realizing the baseband control gate of the spin qubit.

[0045] According to embodiments of this disclosure, the spin qubit unit is a spin qubit architecture based on silicon-based quantum dots.

[0046] According to embodiments of this disclosure, the SOT magnetic structural unit comprises, from bottom to top, a heavy metal layer, a magnetic layer, and an oxide capping layer; the heavy metal layer is prepared from materials selected from Ta, W, and Pt, and the magnetic layer is prepared from materials selected from CoFeB and Co; the oxide capping layer comprises an oxide isolation layer and a capping layer, wherein the oxide isolation layer is selected from MgO, amorphous alumina, HfO2, and TiO2, and the capping layer is selected from Ta, Ru, Ti, and Pt. When there is one SOT magnetic structural unit, the thickness of the SOT magnetic structural unit is between 2-5 nm, and the horizontal distance between the SOT magnetic structural unit and the plane projection of the silicon-based quantum dot is between 50-100 nm. When there are two SOT magnetic structural units, the two SOT magnetic structural units are symmetrically distributed, the thickness of the SOT magnetic structural units is between 2-5 nm, and the spacing between the two SOT magnetic structural units is between 100-200 nm. It should be noted that both single and multiple SOT magnetic structural units can be achieved through in-plane or out-of-plane magnetization configurations. When there are multiple SOT magnetic structural units, the magnetization configuration of all SOT magnetic structural units needs to be consistent, for example, all of them should be in-plane magnetization configurations or all of them should be out-of-plane magnetization configurations.

[0047] The fabrication of devices with spin qubit baseband control gates mainly includes the following steps:

[0048] a) Through simulation calculations, the magnetic field parameters required for a specific spin qubit unit are calculated, and the parameters of the SOT magnetic structure unit are designed accordingly. For example, referring to Figures 1a and 1b, and Figures 2a and 2b, the SOT magnetic structure unit size is designed as length × width = 200 nm × 100 nm, where the thickness of the perpendicularly magnetized SOT magnetic structure unit is 2 nm, and the thickness of the in-plane magnetized SOT magnetic structure unit is 5 nm. The horizontal distance of the SOT magnetic structure unit from the quantum dot plane projection is 80 nm. If two symmetrical SOT magnetic structure units are set, the horizontal spacing between the two SOT magnetic structure units is 160 nm. The height difference between the bottom of the SOT magnetic structure unit and the xy plane where the quantum dot is located is set to 40 nm to simulate the height of the isolation layer and the heavy metal layer. The saturation magnetization of the magnetic layer material is set to 2.23 × 10⁻⁶. 6 A / m.

[0049] b) Complete the fabrication of the silicon-based spin qubit unit and fabricate one or more magnetic layers around the qubit, magnetized in-plane or out-of-plane in an SOT magnetic structure unit. Then, perform testing and characterization in the qubit's measurement and control environment, such as a dilution refrigerator and cryogenic layer.

[0050] The testing principle and process are as follows:

[0051] 1) Applying a square wave current pulse to the SOT magnetic structure unit generates a spin current through the SOT effect of its heavy metal layer, flipping the magnetization direction of one or more SOT magnetic structure units, causing the superposition and direction of the specific magnetic field at the bit to change, and the spin quantization axis of the qubit jumps from the first direction S1 (e.g., S1 is defined as the polar direction) to the second direction S2.

[0052] 2) Wait for a duration of τ1, allowing the spin qubit to precess by an angle φ1 around the second direction S2. The magnitude of the precession angle φ1 accumulated during this operation can be controlled by adjusting the waiting duration τ1.

[0053] 3) Restore the magnetization parallel state of the two SOT magnetic structure units, so that the spin quantization axis jumps back to the first direction S1, the qubit state restarts precession around the first direction S1, and maintains a waiting time τ2.

[0054] 4) Repeat steps 1-4 zero or more until the spin position of the spin qubit reaches the equator at a 90° angle to the initial spin quantization axis. At this point, the spin qubit moves around the initial spin quantization axis S1 on the equator, completing X. 90 A gate. If, by adjusting the magnetic field angle or by adjusting the waiting time τ, it is possible to rotate the gate to any position on the Bloch sphere, then any gate control operation based on this technical concept should fall within the protection scope of this invention.

[0055] In Embodiment 1 of this disclosure, as shown in Figures 1a and 1b, a device for constructing a spin qubit baseband control gate is provided, including a spin qubit unit and an SOT magnetic structure unit. The spin qubit unit can form a planar spin qubit. The spin qubit unit is fabricated based on a silicon-germanium substrate and includes, from bottom to top: a silicon-germanium substrate 202, strained silicon 206, and a silicon-germanium barrier layer 201. An electrode structure (source 102, drain 104, barrier gate 106, planar gate 107, and shielding plate 103) is fabricated on the silicon-germanium barrier layer 201. An oxide insulating layer 205 is covered on the electrode structure. The spin qubit is formed directly below the top gate at the junction of the silicon-germanium barrier layer 201 and the strained silicon 206. The SOT magnetic structure unit is disposed on the spin qubit unit and includes, from bottom to top, a heavy metal layer 101, a magnetic layer 204, and an oxide capping layer 203. When an adjustable current pulse is applied to the SOT magnetic structure unit, the initial magnetic field of the SOT magnetic structure unit can be edited to obtain a specific magnetic field corresponding to the adjustable current pulse. An auxiliary external magnetic field is provided by a magnetic field generator, so that the auxiliary external magnetic field and the specific magnetic field act together on the spin qubit. The spin quantization axis of the spin qubit is located in the superposition direction of the specific magnetic field and the auxiliary external magnetic field. By setting the timing of the adjustable current pulse, the state of the specific magnetic field can be changed, thereby changing the state of the spin quantization axis of the spin qubit, realizing the baseband control gate of the spin qubit.

[0056] In Embodiment 1 of this disclosure, the adjustable current pulse is a square wave current pulse. The timing of the square wave current pulse controls the reciprocating reversal of the magnetization direction of the specific magnetic field generated by the SOT magnetic structure unit. Before the magnetization direction of the specific magnetic field generated by the SOT magnetic structure unit is reversed, the superposition and direction of the specific magnetic field at the spin qubit and the auxiliary external magnetic field is the first direction S1. After the magnetization direction of the specific magnetic field generated by the SOT magnetic structure unit is reversed, the superposition and direction of the specific magnetic field at the spin qubit and the auxiliary external magnetic field becomes the second direction S2, realizing the precession of the spin qubit axis around the second direction S2. As shown in Figure 3a, it represents the extreme case where the angle θ between the first direction S1 and the second direction S2 is 22.5°, and the baseband control gate is completed through two cycles. If the angle θ is less than 22.5° or greater than 157.5°, more steps are required to complete the baseband control gate. Figure 3b shows the extreme case where the angle θ between the first direction S1 and the second direction S2 is 45°. When the angle θ is between 45° and 135°, the gate operation can be completed in one loop. Figure 3c shows the case where the angle θ between the first direction S1 and the second direction S2 is 90°, and the baseband control gate operation is completed in one loop.

[0057] In Embodiment 1 of this disclosure, the strength of the auxiliary external magnetic field is less than the strength of the coercive field of the SOT magnetic structure unit, and the angle between the first direction S1 and the second direction S2 is controlled by adjusting the magnitude of the auxiliary external magnetic field.

[0058] More specifically, devices that construct spin qubit baseband control gates based on a single SOT magnetic structural unit:

[0059] The first step is to fabricate the core structure of the qubit, namely, to prepare spin qubit units based on silicon quantum dots. The fabrication process is roughly as follows:

[0060] 1. Perform semiconductor processes such as Mesa etching, ion implantation, annealing, and gate oxide growth on a silicon-germanium substrate to complete the fabrication of spin qubit units.

[0061] 2. On the substrate, a heavy metal layer (e.g., Ta), a magnetic layer (e.g., CoFeB), and an oxide capping layer (including an oxide isolation layer, such as MgO, and a capping layer, such as Ta) are grown in one step using magnetron sputtering technology. The magnetic layer can be designed to have its thickness and whether it undergoes a post-annealing process involving the oxide isolation layer, so that the orientation of the easy magnetization axis of the SOT magnetic structural unit is out-of-plane or in-plane.

[0062] 3. The core part of the invention, the SOT magnetic structural unit morphology, is patterned using photolithography or electron beam lithography.

[0063] 4. The structure of the SOT magnetic structural unit is obtained by one or more patterned RIE etching processes.

[0064] 5. The control electrodes of the spin qubit are patterned by exposure using a precision electron beam.

[0065] 6. After Al coating and resist removal, the gated electrode is obtained.

[0066] 7. Use equipment such as ALD to oxidize the top capping layer of the electrode to prevent short circuits.

[0067] 8. Repeat steps 5, 6, and 7 three times to obtain all the overlapping Al electrodes, thus completing the entire fabrication process for constructing a spin qubit baseband control gate device.

[0068] Due to the operating characteristics of qubits, the test environment for the samples is located in a dilution refrigerator, and the tests are generally conducted at extremely low temperatures (such as millikelvin).

[0069] Excitation and control of spin polarization current: A dedicated high-precision current control module (such as an arbitrary waveform generator (AWG)) generates DC current pulses to precisely control the flipping of SOT magnetic structural units. Through a purely electrical DC application, the magnetization flipping of SOT magnetic structural units in the vertical direction can be achieved on the order of ps to ns. Furthermore, for SOT magnetic structural units with a specific bias direction, controlling the DC current flowing through them allows control of the flipping orientation of the spin polarization current generated by the current. Therefore, precise control of the direction and magnitude I of the DC current is sufficient. w Duration t pulse The evolution of the magnetic field distribution of each SOT magnetic structural unit can be arbitrarily defined by the waiting time τ between currents, where t pulse The magnitude is on the order of nanoseconds, determined by the inherent properties of the device. The waiting time τ is calculated from the precession velocity, and the amplitude I... w It needs to be greater than the flipping critical current threshold I of the SOT magnetic structure unit. c To complete the flip.

[0070] Realization of magnetic field control at the qubit: By setting up a SOT magnetic structure unit on one side of the qubit and switching the magnetization direction of the SOT magnetic structure unit through the above-mentioned current pulse manipulation method, the direction of the stray field at the spin bit can be quickly defined. The specific magnetic field generated by the SOT magnetic structure unit before and after the operation is equal in magnitude and opposite in direction.

[0071] Construction of a fast non-adiabatic baseband control gate: A sufficiently large stray field will cause the spin quantization axes of the qubits to align along it. Changes in the magnetic field can directly change the state of the spin quantization axes. This process is completed in nanoseconds, causing the electron spin quantization axes to change abruptly. During this time, the system does not remain in the instantaneous energy eigenstate, that is, the spin state will undergo non-adiabatic evolution. Specifically, the spin precesses around the new quantization axis direction. By designing a reasonable magnetic field state angle and the jump timing of the adjustable current pulse, the spin can be made to evolve non-adiabatically on the Bloch sphere.

[0072] In Embodiment 1 of this disclosure, since the magnetic field generated by a single SOT magnetic structural unit is equal in magnitude and opposite in direction before and after the flip, with an angle of 180°, direct gate operation is not possible. Therefore, an additional auxiliary external magnetic field needs to be applied. This auxiliary external magnetic field needs to be smaller than the coercive field of the SOT magnetic structural unit's magnetic layer itself to avoid changing the magnetization state of the SOT magnetic structural unit. Simultaneously, it needs to be approximately equal in magnitude to the magnetic field generated by the magnetic layer itself, thereby effectively modulating the magnetic field angle between the before and after states. Furthermore, this applied magnetic field does not need to be changed, and therefore will not affect bit gate operation. In addition, since the flipping of an SOT magnetic structural unit with its magnetic layer magnetized out-of-plane has symmetry, an external field along the current direction is generally required to break the symmetry. Therefore, this magnetic field also serves as an auxiliary external magnetic field in the out-of-plane magnetized SOT magnetic structural unit scheme.

[0073] First, an external magnetic field larger than the device coercive field is applied along the easy magnetization axis of the SOT magnetic structure unit to magnetize the magnetic layer of the SOT magnetic structure unit in a specific direction. Then, the magnetic field is removed, and a small auxiliary external magnetic field is applied. This auxiliary external magnetic field is generally aligned with the write current path of the SOT magnetic structure unit, and in this case, it is located perpendicular to the line connecting the SOT magnetic structure unit and the qubit position. The qubit ratio spin quantization axis lies in the superposition direction of the stray field generated by the SOT magnetic structure unit and the auxiliary external magnetic field, denoted as the first direction S1, as shown in Figure 6. At time T1, a DC signal I in a specific direction is applied to the SOT magnetic structure unit. w Length t pulse After the time is up, the magnetization flips to another state. At this time, the stray field generated by the SOT magnetic structure unit will reverse, while the auxiliary external magnetic field remains unchanged. The superposition of the two is denoted as the second direction S2, as shown in Figure 6. The angle between the directions S1 and S2 is between 0 and 180°. The size of this angle can be changed by setting the size of the auxiliary external magnetic field.

[0074] After a waiting period τ1 between currents, the spin quantization axis will precess around the second direction S2, and the qubit spin will precess by an angle φ1. At time T2, the flipped SOT magnetic structure unit will again be supplied with a reverse DC signal -I. w Length t pulse When the magnetization direction of a specific magnetic field flips back to the downward state, the sum of the magnetic fields at the qubit will again follow the initial direction, and the qubit will precess again around the initial first direction S1. Calculations show that if the angle between the magnetic fields, or the angle between S1 and S2, is between 22.5° and 157.5°, since the maximum precession angle (i.e., the state where the electron spin has precessed 180° around S2) is twice the angle formed by the straight line containing the spin quantization axis, two cycles of repeated operation are needed to complete the spin rotation around the initial quantization axis by 90°, thus completing X. 90The gate operation can be completed in a single cycle when the quantization axis angle is between 45° and 135°. Furthermore, the angle and total magnetic field strength can be controlled by an auxiliary external magnetic field. As shown in Figure 4, an in-plane magnetized SOT magnetic structure unit is set in the -x direction. Under the auxiliary field in the y direction, the magnetic field state at the qubit before and after switching the magnetization direction of the SOT magnetic structure unit is illustrated. The blue curve represents the change in the angle between the magnetic field states with the magnitude of the external auxiliary magnetic field, while the green and red curves represent the change in the total magnetic field strength with the magnitude of the external auxiliary magnetic field. The total magnetic field strength remains unchanged before and after the flip, thus the precession angular velocity remains constant. The range of 45° to 135° is marked, within which the gate operation can be completed by a single flip sequence. According to the Larmor precession principle, the precession speed is positively correlated with the magnitude of the auxiliary external magnetic field, which can be used to control the waiting time and thus design the duration of the entire gate operation. If the 90° precession has not yet been completed, after a waiting time τ2, the spin precession angle φ2 is increased, and a DC signal I is applied again at time T3. w Length t pulse This process is repeated until the control gate operation is completed. Referring to Figures 4 and 5, an in-plane magnetized SOT magnetic structure unit is set in the -x direction, while an auxiliary external magnetic field B is applied. ex = 19.77mT along the y-direction. Figure 5(a) and (b) show the distribution of the total magnetic field in the xyz direction within the xy plane of the qubit when the magnetization direction of the SOT magnetic structure unit is along the +x and -x directions, respectively. Figure 6 shows the normalized direction of the total magnetic field when a specific auxiliary external magnetic field is set so that the angle between the first direction S1 and the second direction S2 is 45°. Figure 7 shows the relationship between the precession angle of the bit spin and time under the switched magnetic field, where the time to complete the target precession angle of 180°, i.e., the waiting time τ, is marked.

[0075] In addition to introducing an auxiliary external magnetic field as described in Example 1, other magnetic fields can be introduced by setting other SOT magnetic structure units, such as setting at least two SOT magnetic structure units; the spin qubit unit can form a planar spin qubit; at least two SOT magnetic structure units are set on the spin qubit unit, and when an adjustable current pulse is applied to the at least two SOT magnetic structure units respectively, the initial magnetic field of each SOT magnetic structure unit can be edited to obtain at least two specific magnetic fields corresponding to the adjustable current pulse; the at least two specific magnetic fields act together on the spin qubit, and the spin quantization axis of the spin qubit is located in the superposition and direction of the at least two specific magnetic fields. By setting the timing of the adjustable current pulse, the state of the at least two specific magnetic fields can be changed, thereby changing the state of the spin quantization axis of the spin qubit and realizing the spin qubit baseband control gate. The adjustable current pulse is a square wave current pulse. By adjusting the timing of the square wave current pulse, the magnetization direction of the specific magnetic field corresponding to the SOT magnetic structure unit is controlled to reciprocate. By adjusting the timing of the square wave current pulse applied to each SOT magnetic structure unit, the state of the specific magnetic field generated by each SOT magnetic structure unit is changed, so that the total magnetic field of each specific magnetic field acting on the spin qubit switches between the first state and the second state. In the first state, the superposition and direction of each specific magnetic field is the first direction S1. In the second state, the superposition and direction of each specific magnetic field becomes the second direction S2, realizing the precession of the spin qubit axis around the second direction S2.

[0076] In Embodiment 2 of this disclosure, as shown in Figures 2a and 2b, the device for constructing a spin qubit baseband control gate includes two SOT magnetic structure units and a spin qubit unit. The spin qubit is formed directly below the top gate, located at the interface between the silicon-germanium barrier layer and strained silicon. By adjusting the timing of the square wave current pulse, the magnetization directions of the two SOT magnetic structure units are made parallel or antiparallel. When the magnetization directions of the two SOT magnetic structure units are parallel, the superposition and direction of the two specific magnetic fields at the spin qubit is the first direction S1. When the magnetization directions of the two SOT magnetic structure units are antiparallel, the superposition and direction of the two specific magnetic fields at the spin qubit becomes the second direction S2, realizing the precession of the spin qubit axis around the second direction S2. The angle between the first direction S1 and the second direction S2 is 90°. By adjusting the duty cycle of the square wave current pulse, the spin precession angle is adjusted, thus realizing the spin qubit baseband control gate.

[0077] More specifically, the device in Example 2, which constructs a spin qubit baseband control gate based on two SOT magnetic structure units, does not require an additional auxiliary external magnetic field. The device fabrication process is basically the same as that in Example 1, except for the difference in the number of SOT magnetic structure units.

[0078] Realization of magnetic field control at the qubit: By setting symmetrical SOT magnetic structural units on both sides of the qubit, the in-plane magnetized SOT magnetic structural units do not require an auxiliary external field. Therefore, the relative state (parallel or antiparallel) of the two SOT magnetic structural units can be switched by simply applying an adjustable current pulse. The total magnetic field direction of the two specific magnetic fields at the spin bit can be quickly defined, and the magnetic field angle between the two states can be 90°, as shown in Figure 9. In Figure 8, parts (a) and (b) show the distribution of the total magnetic field in the xy plane where the qubit is located when the two SOT magnetic structural units are magnetized along the parallel and antiparallel directions, respectively. It can be seen that the total magnetic field basically has only the x component or only the z component. The direction of the normalized total magnetic field when the angle between the first direction S1 and the second direction S2 is 45° is shown in Figure 9.

[0079] Construction of a fast, non-adiabatic baseband control gate: First, the two SOT magnetic structural units are initialized to a parallel magnetization state and demagnetized using a saturated external magnetic field. Due to the symmetrical distribution of the magnetic field generated at the qubit, some components will cancel each other out, leaving only one direction. For example, for two parallel in-plane magnetized devices, the magnetic field generated at the quantum dot is also in-plane, while for two parallel out-of-plane magnetized devices, it is out-of-plane. At time T1, a DC signal I in a specific direction is applied to one of the SOT magnetic structural units. w Length t pulse After the time expires, the magnetization direction flips, becoming antiparallel to the SOT magnetic structure unit on the other side. At this point, the magnetic fields generated at the qubits by both will cancel each other out: for two antiparallel in-plane magnetization devices, the magnetic field generated at the quantum dot is out-of-plane; for two antiparallel out-of-plane magnetizations, it is in-plane. In short, through this design, we can make the angle between the first direction S1 and the second direction S2 equal to 90°. Then, we only need to set the waiting time τ and the qubit precession angle φ1 = / 2, thus directly completing the gate operation through only one set of square wave current pulse sequences. The advantage of Example 2 is that it does not require an additional auxiliary external magnetic field and theoretically has higher controllability. After the two SOT magnetic structural units (magnetic units) are switched from parallel to antiparallel, the relationship between the precession angle of the qubit spin and time under the total magnetic field after the switch is shown in Figure 10, where the time to complete the target precession angle of 90° is marked, i.e., the waiting time τ.

[0080] In fact, by setting an auxiliary external magnetic field to combine with the magnetic field change of the SOT device flipping to form a specific angle, or by setting two or more SOT magnetic structure units, or by using the geometry and position of the SOT magnetic structure units, as long as the corresponding angle can be formed before and after the magnetization direction of the SOT magnetic structure unit is flipped, and the angle range is reasonable, the non-adiabatic control gate regulation and calculation described in this invention can be performed.

[0081] This disclosure discloses a device and method for constructing a baseband control gate for spin qubits based on a method for rapidly manipulating the magnetic field at the qubit using purely electrical means of the SOT magnetic structure unit. Based on this, high-fidelity and practical adiabatic baseband control gate operation is achieved. It is not only applicable to the planar silicon-based system in the embodiments but can also be extended to other planar electron spin qubit systems, such as electron spin qubits in two-dimensional materials, demonstrating good versatility and scalability. The gate operation speed of this disclosure is only limited by the flipping speed of the SOT magnetic structure unit, which is much shorter than the time requirement of traditional microwave driving schemes, thus significantly shortening the operation time of non-adiabatic baseband control gates. Furthermore, compared to the traditional Hopping Gate scheme used in non-adiabatic baseband control gates, this scheme does not require materials with g-tensor anisotropy, nor does it require moving the quantum dot charge during operation, greatly improving the simplicity and robustness of operation. Using square wave current pulses to drive the magnetization flipping of the SOT magnetic structure unit avoids the crosstalk and frequency congestion problems present in traditional microwave driving schemes. Furthermore, since the flipping of SOT magnetic structural units is insensitive to waveform distortion and the scheme does not involve charge noise as in traditional schemes, the reliability and accuracy of the operation are further improved. The fabrication method of silicon-based qubits and SOT magnetic structural units is highly compatible with existing experimental fabrication processes and can be seamlessly integrated into existing silicon-based semiconductor manufacturing processes. Simultaneously, this scheme can be combined with other quantum manipulation experimental schemes based on SOT magnetic structural units, such as electric dipole spin resonance (EDSR), providing technical support for the multifunctional integration of quantum computing systems. By freely combining the stray fields generated by the flippable SOT magnetic structural units, the externally applied constant auxiliary magnetic field, or freely setting the spatial positions of multiple SOT magnetic structural units, the magnetic field at the qubit can be rapidly and almost omnidirectionally changed, which has a significant advantage over the complex quantized axis direction calculations in traditional systems.

[0082] The embodiments of this disclosure have been described in detail above with reference to the accompanying drawings. It should be noted that implementations not illustrated or described in the drawings or the main text of the specification are forms known to those skilled in the art and are not described in detail. Furthermore, the definitions of the various elements and methods described above are not limited to the specific structures, shapes, or methods mentioned in the embodiments, and those skilled in the art can easily modify or substitute them.

[0083] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A device for constructing a baseband control gate for spin qubits, comprising: Spin qubit units can form planar spin qubits; A SOT magnetic structure unit is disposed on the spin qubit unit. When an adjustable current pulse is applied to the SOT magnetic structure unit, the initial magnetic field of the SOT magnetic structure unit can be edited to obtain a specific magnetic field corresponding to the adjustable current pulse. An auxiliary external magnetic field is provided and acts on the spin qubit together with the specific magnetic field. The spin quantization axis of the spin qubit is located in the superposition direction of the specific magnetic field and the auxiliary external magnetic field. By setting the timing of the adjustable current pulse, the state of the specific magnetic field can be changed, thereby changing the state of the spin quantization axis of the spin qubit, realizing the baseband control gate of the spin qubit.

2. A device for constructing a baseband control gate for spin qubits, comprising: Spin qubit units can form planar spin qubits; At least two SOT magnetic structure units are disposed on the spin qubit unit. When an adjustable current pulse is applied to the at least two SOT magnetic structure units, the initial magnetic field of each SOT magnetic structure unit can be edited to obtain at least two specific magnetic fields corresponding to the adjustable current pulse. The at least two specific magnetic fields act together on the spin qubit, and the spin quantization axis of the spin qubit is located in the superposition and direction of the at least two specific magnetic fields. By setting the timing of the adjustable current pulse, the state of the at least two specific magnetic fields can be changed, thereby changing the state of the spin quantization axis of the spin qubit and realizing the baseband control gate of the spin qubit.

3. The device for constructing a spin qubit baseband control gate according to claim 1, wherein the adjustable current pulse is a square wave current pulse, and the timing of the square wave current pulse controls the reciprocating reversal of the magnetization direction of the specific magnetic field generated by the SOT magnetic structure unit; before the magnetization direction of the specific magnetic field generated by the SOT magnetic structure unit is reversed, the superposition and direction of the specific magnetic field at the spin qubit and the auxiliary external magnetic field is the first direction S1; after the magnetization direction of the specific magnetic field generated by the SOT magnetic structure unit is reversed, the superposition and direction of the specific magnetic field at the spin qubit and the auxiliary external magnetic field becomes the second direction S2, thereby realizing the precession of the spin qubit axis around the second direction S2.

4. In the device for constructing a spin qubit baseband control gate according to claim 3, the strength of the auxiliary external magnetic field is less than the strength of the coercive field of the SOT magnetic structure unit, and the angle between the first direction S1 and the second direction S2 is controlled by adjusting the magnitude of the auxiliary external magnetic field.

5. The device for constructing a spin qubit baseband control gate according to claim 2, wherein the adjustable current pulse is a square wave current pulse, and the magnetization direction of the specific magnetic field corresponding to the SOT magnetic structure unit is repeatedly flipped by adjusting the timing of the square wave current pulse; by adjusting the timing of the square wave current pulse applied to each SOT magnetic structure unit, the state of the specific magnetic field generated by each SOT magnetic structure unit is changed, so that the total magnetic field of each specific magnetic field acting on the spin qubit switches between a first state and a second state; in the first state, the superposition and direction of the total magnetic field of each specific magnetic field is the first direction S. 1， The total magnetic field, in the second state, is superimposed on the specific magnetic fields and its direction changes to the second direction S. 2， Achieve precession of the spin quantization axis around the second direction S2.

6. The device for constructing a spin qubit baseband control gate according to claim 2, wherein the adjustable current pulse is a square wave current pulse, and the magnetization direction of the specific magnetic field corresponding to the SOT magnetic structure unit is reciprocated by adjusting the timing of the square wave current pulse; the magnetization directions of the two SOT magnetic structure units are made parallel or antiparallel by adjusting the timing of the square wave current pulse; when the magnetization directions of the two SOT magnetic structure units are parallel, the superposition and direction of the two specific magnetic fields at the spin qubit is the first direction S1; when the magnetization directions of the two SOT magnetic structure units are antiparallel, the superposition and direction of the two specific magnetic fields at the spin qubit becomes the second direction S2, thereby realizing the precession of the spin qubit axis around the second direction S2.

7. The device for constructing a spin qubit baseband control gate according to claim 6, wherein the angle between the first direction S1 and the second direction S2 is 90°, and the spin precession angle is adjusted by adjusting the duty cycle of the square wave current pulse to realize the spin qubit baseband control gate.

8. The device for constructing a spin qubit baseband control gate according to claim 1 or 2, wherein the spin qubit unit is a spin qubit architecture based on silicon quantum dots.

9. The device for constructing a spin qubit baseband control gate according to claim 1 or 2, wherein the SOT magnetic structure unit comprises, from bottom to top, a heavy metal layer, a magnetic layer, and an oxide capping layer; the heavy metal layer is prepared from materials selected from Ta, W, and Pt, and the magnetic layer is prepared from materials selected from CoFeB and Co; the oxide capping layer comprises an oxide isolation layer and a capping layer, wherein the oxide isolation layer is selected from MgO, amorphous alumina, HfO2, and TiO2, and the capping layer is selected from Ta, Ru, Ti, and Pt.

10. A method for constructing a baseband control gate for spin qubits, comprising: Fabricate spin qubit units capable of forming spin qubits; SOT magnetic structure units are fabricated on the spin qubit units; An adjustable current pulse is applied to the SOT magnetic structure unit to edit the initial magnetic field of the SOT magnetic structure unit, thereby obtaining a specific magnetic field corresponding to the adjustable current pulse; other magnetic fields are introduced to superimpose with the specific magnetic field vector and act together on the spin qubit; and the state of the specific magnetic field corresponding to the SOT magnetic structure unit is changed by adjusting the timing of the adjustable current pulse, thereby changing the state of the spin quantization axis of the spin qubit and realizing the baseband control gate of the spin qubit.

Images