An ultrafast manipulation germanium hole spin qubit device and a preparation method thereof

Abstract

The application provides a germanium hole spin quantum bit device capable of ultrafast operation and a preparation method thereof. The device comprises the following steps: providing a substrate, and sequentially forming a germanium quantum well, a dielectric layer and a metal electrode on the substrate. The germanium quantum well has a first interval and a second interval on both sides of the first interval. The second interval can continuously provide the first interval with uniaxial tensile strain of a preset direction and size by doping silicon elements in the second interval along a preset crystal direction. The preparation of a germanium hole spin quantum bit capable of high-quality and ultrafast operation can be realized by applying an in-plane static magnetic field to the germanium quantum well and forming a two-dimensional gate-controlled quantum dot in the first interval of the germanium quantum well based on the electric dipole spin resonance technology. Thus, the problems of insufficient linear spin-orbit coupling strength of a germanium quantum well hole state and slow operation speed of a germanium hole quantum bit are overcome.

Description

Technical Field

[0001] The present application relates to the field of semiconductor production process technology, and in particular to an ultrafast controlled germanium hole spin quantum bit device and a preparation method thereof. Background Art

[0002] In recent years, quantum computing, due to its exponentially growing computing power, has become a hot topic in both basic research and technological advancements both domestically and internationally. Among various approaches, semiconductor gate-controlled quantum dots (QDs) have garnered significant attention due to their deep compatibility with established microelectronics complementary metal-oxide-semiconductor (CMOS) processes. In this approach, the spins of the charge carriers in the QDs can be used as a basis for constructing quantum bits (qubits). Currently, researchers have achieved the manipulation of ten qubits in a two-dimensional, gated germanium quantum dot hole spin system. Germanium hole spins have the following four advantages over silicon electron spins: 1. Holes have p-type wave functions, which greatly reduce the probability of being scattered by nuclear spins. In addition, like silicon, germanium can also be further improved through isotope purification to increase its spin decoherence time. 2. Germanium holes have strong spin-orbit coupling (SOC), which can increase the speed of spin manipulation. 3. Germanium holes are not subject to the interference of valley degeneracy. 4. Germanium holes have a small effective mass, which allows the preparation of larger gate-controlled quantum dots, making spin manipulation easier.

[0003] The Rabi spin flip frequency (Rabi frequency) can be used to characterize the speed of spin manipulation. Achieving fully electrical manipulation of hole spins in a two-dimensional gated germanium quantum dot system requires the use of electric dipole spin resonance (EDSR). The EDSR principle is as follows: 1. Applying a static magnetic field to the two-dimensional gated quantum dot causes Zeeman spin splitting of the energy levels, with the spins of the two split sub-levels oriented in opposite directions (parallel or antiparallel to the direction of the applied magnetic field); 2. Applying an alternating electric field or microwaves couples quantum states with the same spin in adjacent low-energy levels of the two-dimensional gated quantum dot; 3. The electric field generated by the gate voltage drives a linear SOC, providing electric dipole transitions that couple quantum states with different spins in adjacent low-energy levels, forming a two-level system with different spin states, thereby generating spin resonance. Each resonant spin state is a quantum bit. Compared to electron spin resonance (ESR) technology, hole EDSR technology does not require the design of sophisticated micromagnetic structures in low-dimensional systems to provide a gradient magnetic field to induce spin flips. Instead, it uses an equivalent magnetic field generated by electrically controlled linear Rashba SOC. This substitution of electrical control for magnetic control further expands the application prospects of semiconductor quantum dots for quantum computing using hole spins as carriers.

[0004] The implementation of EDSR technology in two-dimensional gate-controlled germanium quantum dots relies on linear SOC, but the bulk phase of germanium does not allow linear Dresselhaus SOC due to the existence of central inversion symmetry. On the other hand, it has been believed that linear Rashba SOC does not exist in two-dimensional hole gases due to the absence of light-heavy hole coupling. However, recent studies have shown that electric field-adjustable linear Rashba SOC exists in two-dimensional hole gases in germanium quantum wells along the

[001] growth direction. This is caused by light-heavy hole coupling caused by interface effects, but the intensity of the linear Rashba SOC caused by interface effects is relatively weak. Researchers have tried several theoretical schemes to enhance the linear Rashba SOC in germanium quantum well hole gases, such as preparing germanium quantum wells along the

[110] growth direction, applying a strongly anisotropic electric field on a small scale, and applying a gradient shear strain along the growth direction. However, these theoretical schemes are difficult to implement and control experimentally and have not been actually applied to quantum bit devices based on germanium holes.

[0005] Although quantum bit devices based on two-dimensional gate-controlled germanium quantum dots have attractive application prospects, to date, no ultrafast control of germanium hole spin quantum bit devices has been successfully prepared experimentally, with a control frequency of GHz, which has seriously hindered the development of semiconductor quantum dot quantum computing. Summary of the Invention

[0006] The present application aims to solve one of the technical problems in the related art at least to a certain extent.

[0007] To this end, the first purpose of this application is to provide an ultrafast-controlled germanium hole spin qubit device and a preparation method thereof, which can successfully prepare high-quality and ultrafast-controlled germanium hole spin qubits, and solve the problem that the experimental control speed of germanium hole spin qubits cannot be further improved.

[0008] To achieve the above objectives, the first embodiment of the present application provides a method for preparing an ultrafast controlled germanium hole spin qubit, comprising:

[0009] providing a substrate;

[0010] Epitaxially forming a germanium quantum well on the substrate, wherein the interior of the germanium quantum well includes a first region for forming a two-dimensional gate-controlled quantum dot and a second region doped with silicon along a preset crystal direction, wherein the second region is located on both sides of the first region along a first direction;

[0011] forming a dielectric layer on the germanium quantum well structure;

[0012] forming at least one group of metal electrodes on the dielectric layer, each group of metal electrodes comprising a first electrode, a second electrode, and a third electrode spaced apart from each other along a second direction, the third electrode being located between the first electrode and the second electrode;

[0013] Two-dimensional gate-controlled quantum dots are formed in the germanium quantum well using electric dipole spin resonance technology.

[0014] Optionally, the germanium quantum well is formed on the substrate using a CMOS process.

[0015] Optionally, the substrate comprises a

[001] silicon substrate.

[0016] Optionally, the epitaxially forming a germanium quantum well on the substrate includes:

[0017] forming a silicon germanium buffer layer on the substrate;

[0018] forming a germanium layer on the buffer layer;

[0019] Doping a predetermined position of the germanium layer with silicon in a predetermined crystal direction to form the second region;

[0020] A silicon germanium barrier layer is formed on the germanium layer.

[0021] Optionally, a method for doping the preset position of the germanium layer with silicon elements in a preset crystal orientation includes thermal diffusion, electrochemical implantation, or ion implantation.

[0022] Optionally, the preset crystal orientation of the silicon element doping in the second interval includes a

[110] crystal orientation, which is used to provide a uniaxial tensile strain in the

[110] crystal orientation for the two-dimensional gate-controlled quantum dots formed in the first interval.

[0023] Optionally, the silicon content in the silicon germanium buffer layer is not higher than 50%.

[0024] Optionally, the thickness of the germanium layer ranges from tens of nanometers to hundreds of nanometers, and the thickness of the silicon germanium buffer layer and the silicon germanium barrier layer ranges from several nanometers to tens of nanometers.

[0025] Optionally, the step of preparing two-dimensional gate-controlled quantum dots in the germanium quantum well using electric dipole spin resonance technology includes:

[0026] Providing an in-plane static magnetic field in the germanium quantum well;

[0027] applying a first threshold voltage and a second threshold voltage to the first electrode and the second electrode respectively, so as to provide a first electric field for the germanium quantum well;

[0028] A third threshold voltage is applied to the third electrode to provide a second electric field for the germanium quantum well to form the two-dimensional gate-controlled quantum dot in the first interval; the direction of the second electric field is perpendicular to the substrate surface.

[0029] Optionally, the dielectric material of the dielectric layer includes at least one of SiO 2 and Al 2 O 3 , and the thickness of the dielectric layer ranges from a dozen nanometers to several tens of nanometers.

[0030] Optionally, the material of the metal electrode includes at least one of Al and Au, and the thickness of the metal electrode ranges from several nanometers to tens of nanometers.

[0031] Optionally, a vertical projection of the third electrode on the substrate covers a vertical projection of the first interval.

[0032] Optionally, the diameter size of the two-dimensional gate-controlled quantum dots ranges from 60 nm to 100 nm.

[0033] Optionally, the bulk phase of the germanium material of the germanium quantum well is a crystal structure with regular tetrahedral covalent bonds.

[0034] Optionally, the direction of the first electric field is the same as the direction of the in-plane static magnetic field and is perpendicular to the direction of the second electric field.

[0035] To achieve the above objectives, the first embodiment of the present application provides an ultrafast controlled germanium hole spin qubit device, characterized in that it includes:

[0036] substrate;

[0037] A germanium quantum well is formed on the substrate, comprising a silicon germanium buffer layer, a germanium layer and a silicon germanium barrier layer stacked sequentially from bottom to top;

[0038] a dielectric layer formed on the germanium quantum well;

[0039] at least one group of metal electrodes formed on the dielectric layer, each group of metal electrodes comprising a first electrode, a second electrode, and a third electrode spaced apart from each other along a second direction, the third electrode being located between the first electrode and the second electrode;

[0040] In which, the interface between the germanium layer and the silicon germanium barrier layer includes a first interval, the first interval is used to form a two-dimensional gate-controlled quantum dot, the germanium layer includes two second intervals spaced apart from each other along a first direction, the second interval contains silicon elements doped along a preset crystal direction; the first interval is located between the two second intervals spaced apart from each other, and the second interval is used to provide a uniaxial tensile strain in a preset direction for the two-dimensional gate-controlled quantum dot formed in the first interval.

[0041] The ultrafast controlled germanium hole spin qubit device and its preparation method provided in this application have at least the following beneficial effects:

[0042] The present application provides an ultrafast controlled germanium hole spin quantum bit device and a preparation method thereof, comprising providing a substrate, and sequentially forming a germanium quantum well, a dielectric layer and a metal electrode on the substrate. A first interval and a second interval located on both sides of the first interval are formed inside the germanium quantum well. By doping silicon elements along a preset crystal direction in the second interval, the second interval can continuously provide a uniaxial tensile strain of a preset direction and magnitude to the first interval, and by applying an in-plane static magnetic field to the germanium quantum well and forming a two-dimensional gate-controlled quantum dot in the first interval of the germanium quantum well based on the EDSR technology, the preparation of high-quality ultrafast controlled germanium hole spin quantum bits can be achieved, thereby overcoming the problems of insufficient linear spin-orbit coupling strength of the hole state in the existing germanium quantum well and slow manipulation speed of the germanium hole quantum bit.

[0043] Compared with the traditional germanium quantum well without uniaxial strain, the germanium quantum well with uniaxial strain applied in this application can increase the linear SOC intensity by two orders of magnitude and can provide a Rabi frequency of the GHz order.

[0044] The germanium quantum well provided in this application is deeply compatible with existing mature microelectronic CMOS processes and is expected to be used to achieve large-scale integration of quantum bits.

[0045] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0047] Figure 1 Schematic diagram of the structure of a germanium hole spin qubit according to an embodiment of the present application.

[0048] Figure 2 Based on Figure 1 A top-down view of a germanium hole spin qubit is shown.

[0049] Figure 3 Schematic diagram of the process of preparing a germanium hole spin quantum bit according to an embodiment of the present application.

[0050] Figure 4 Schematic diagram of the process of preparing a germanium quantum well according to an embodiment of the present application.

[0051] Figure 5 Schematic diagram of the process of preparing two-dimensional gate-controlled quantum dots according to an embodiment of the present application.

[0052] Figure 6 Schematic diagram of the principle of EDSR caused by linear SOC.

[0053] Figure 7 Schematic diagram of spin splitting of a germanium quantum well subjected to 0.4% uniaxial tensile strain in the

[110] direction and a gate voltage of 100 kV / cm according to an embodiment of the present application.

[0054] Figure 8 Schematic diagram of the change of the linear SOC coefficient of the two-dimensional gate-controlled quantum dots with uniaxial strain under a fixed biaxial strain of 0.61% compressive strain according to an embodiment of the present application.

[0055] Figure 9 Schematic diagram of the change of the linear SOC coefficient of the two-dimensional gate-controlled quantum dots with biaxial strain under a uniaxial tensile strain of 0.4% in the

[110] direction according to an embodiment of the present application.

[0056] Figure 10 Schematic diagram of the relationship between the Rabi frequency of a two-dimensional gate-controlled quantum dot and the uniaxial strain in the

[110] direction under an in-plane static magnetic field with a Lamour frequency of 5 GHz according to an embodiment of the present application.

[0057] Figure 11 Schematic diagram of the relationship between the linear SOC coefficient of a two-dimensional gate-controlled quantum dot under a uniaxial tensile strain of 0.4% in the

[110] direction and the gate voltage according to an embodiment of the present application.

[0058] 100 substrate; 200 germanium quantum well; 201 first interval; 202 second interval; 210 silicon germanium buffer layer; 220 germanium layer; 230 silicon germanium barrier layer; 300 dielectric layer; 400 metal electrode; 410 first electrode; 420 second electrode; 430 third electrode. DETAILED DESCRIPTION

[0059] The following describes in detail embodiments of the present application, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, and should not be construed as limiting the present application.

[0060] In view of the shortcomings of the existing technology mentioned above, the present invention provides a germanium hole spin qubit device that is deeply compatible with CMOS processes and applies uniaxial tensile strain in a specific direction, and a preparation method thereof. It is expected that on this basis, the preparation of single and multiple two-dimensional gate-controlled quantum dot high-quality hole spin qubits can be realized, providing a new solution for semiconductor quantum computing.

[0061] Research has found that the strong SOC of holes in germanium quantum wells can rapidly drive the spin flips of their two-dimensional gated quantum dot qubits. Furthermore, Group IV elements, due to their near-zero nuclear spin scattering, offer long spin decoherence times and are deeply compatible with microelectronic CMOS processes, enabling the fabrication of high-quality, scalable spin qubits. Currently, high-quality charge manipulation of a four-by-four (sixteen) quantum dot array in a germanium quantum well has been achieved internationally. However, further development of spin qubits remains limited by slow spin manipulation and short decoherence times.

[0062] The basic units of quantum computing include qubits and quantum logic gates. The preparation of a single qubit state requires the application of an external magnetic field to induce the Zeeman effect, generating the two energy levels required for qubit encoding. The implementation of quantum logic gates relies on flipping between different spin states (bits). For holes, EDSR technology is used, which involves quantum states with different spin components. Since an applied alternating electric field or microwave can only induce coupling between quantum states with the same spin component, the introduction of SOC is unavoidable. Because the spin orientation generated by the Zeeman effect is always parallel or antiparallel to the direction of the applied static magnetic field, the combined action of SOC and the alternating electric field fundamentally provides the driving force for spin flipping. In EDSR technology, when the frequency of the applied alternating electric field or microwave is equal to the Lamour precession frequency induced by the applied static magnetic field, the spin states resonate, and the spin orientation exhibits periodic changes. The corresponding spin flip frequency is the Rabi frequency.

[0063] Improving the manipulation speed (Rabi frequency) of hole qubits is a core concern for quantum computing, and the key to addressing this concern lies in providing a strong linear SOC. Research has shown that the linear SOC of a two-dimensional hole gas in a germanium quantum well originates from light-heavy hole coupling. However, for a long time, researchers generally believed that linear SOC did not exist in a two-dimensional hole gas in a semiconductor quantum well because light-heavy hole coupling was symmetry-forbidden. Recent theoretical studies have shown that in a germanium / silicon quantum well in the

[001] growth direction (abbreviated as the

[001] direction), light-heavy hole coupling caused by interface effects induces a linear Rashba SOC. This has led to several schemes that induce linear SOC by reducing the symmetry of the germanium quantum well to induce light-heavy hole coupling. However, existing theoretical schemes are difficult to implement and control experimentally, making them insufficient for practical application. Recent theoretical research has found that applying uniaxial strain, a technique compatible with CMOS processes commonly used in the integrated circuit industry, to a germanium quantum well significantly enhances the coupling between light and heavy holes, thereby inducing a linear SOC intensity two orders of magnitude greater than that of a conventional two-dimensional hole gas in a germanium quantum well. Consequently, the Rabi frequency can be increased to the GHz range. However, this theoretical research has not yet been put into practice experimentally.

[0064] The core concept of this application is to increase the spin manipulation rate, which can be characterized by the Rabi frequency, by applying uniaxial tensile strain to conventional quantum wells. This application is compatible with existing mature microelectronic CMOS processes and provides a method for preparing uniaxially strained germanium quantum wells. By leveraging the strong linear SOC in uniaxially strained quantum wells, this application enables the preparation of high-quality hole spin qubits in two-dimensional gated quantum dots with GHz-level Rabi frequencies, paving the way for the further development of semiconductor quantum computing.

[0065] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments and accompanying drawings. In the following exemplary drawings, the x-direction is the first direction, also the

[110] direction; the y-direction is the second direction, also the [-110] direction; and the z-direction is the third direction, also the

[001] direction.

[0066] The first embodiment of the present application provides a method for preparing a germanium hole spin quantum bit that can realize ultrafast manipulation compatible with CMOS process, such as Figures 1 to 3 As shown, the following steps are included:

[0067] S1, providing a substrate 100.

[0068] S2, epitaxially forming a germanium quantum well 200 on the substrate 100, the interior of the germanium quantum well 200 includes a first interval 201 for forming a two-dimensional gate-controlled quantum dot and a second interval 202 for doping silicon elements along a preset crystal direction, and the second interval 202 is located on both sides of the first interval 201 along the first direction.

[0069] S3 , forming a dielectric layer 300 on the germanium quantum well 200 .

[0070] S4, forming at least one set of metal electrodes 400 on the dielectric layer 300, each set of metal electrodes 400 includes a first electrode 410, a second electrode 420 and a third electrode 430 spaced apart from each other along the second direction, and the third electrode 430 is located between the first electrode 410 and the second electrode 420.

[0071] S5, using EDSR technology to form two-dimensional gate-controlled quantum dots in germanium quantum wells.

[0072] It can be understood that the technical solution provided in the present application forms a germanium quantum well 200 by epitaxial growth on a substrate 100, and forms a first interval 201 and a second interval 202 inside the germanium quantum well 200, and the second interval 202 is located on both sides of the first interval 201 along the first direction, so that the silicon elements doped along the preset crystal direction in the second interval 202 can continuously provide stable uniaxial tensile strain for the first interval 201. That is to say, by controlling the doping direction and doping concentration of the silicon elements in the second interval 202, the direction and magnitude of the uniaxial strain of the first interval 201 in the germanium quantum well 200 can be controlled.

[0073] Thus, EDSR technology is used to form two-dimensional gate-controlled quantum dots in the first interval 201 of the germanium quantum well 200. When the frequency of the alternating electric field or microwave is equal to the eigenfrequency of the in-plane static magnetic field, the two-dimensional gate-controlled quantum dots formed in the first interval 201 can achieve a strong linear SOC under the action of the alternating electric field, the external static magnetic field and the uniaxial strain in the preset direction provided by the second interval 202, thereby realizing the preparation of high-quality, ultrafast controlled germanium hole spin quantum bits with a Rabi frequency of the GHz order.

[0074] As an example, the alternating electric field includes a vertical electric field and a transverse driving electric field, and the transverse driving electric field is applied in the plane of the germanium quantum well 200 through the first electrode 410 and the second electrode 420. The vertical electric field is applied to the germanium quantum well 200 through the third electrode 430, and the third electrode 430 is located between the first electrode 410 and the second electrode 420, and is used to provide a binding potential for trapping two-dimensional holes, and to confine the two-dimensional gate-controlled quantum dots within the first interval 201, and to provide a controllable gate voltage for the formation of the two-dimensional gate-controlled quantum dots, so that the two-dimensional gate-controlled quantum dots can generate and regulate linear Rashba SOC under the gate voltage control of the third electrode 430. As a result, the vertical projection of the third electrode 430 on the substrate 100 also covers the vertical projection of the first interval 201.

[0075] As an example, the hole mobility in the germanium quantum well 200 can reach 10 5 cm 2 / (V∙s) order of magnitude.

[0076] As an example, the substrate 100 may be made of a

[001] silicon substrate material, and the germanium quantum well 200 epitaxially formed on the substrate 100 is also a

[001] germanium quantum well 200 .

[0077] It should be noted that the at least one group of metal electrodes 400 in the above step S4 indicates that the metal electrodes 400 formed on the dielectric layer 300 include but are not limited to one group, and when multiple groups of metal electrodes 400 are formed on the dielectric layer 300, multiple first intervals 201 will be formed correspondingly inside the germanium quantum well 200.

[0078] like Figure 4 As shown, in some embodiments, the step of epitaxially forming the germanium quantum well 200 on the substrate 100 may specifically include:

[0079] S21, forming a silicon germanium buffer layer 210 on the substrate 100,

[0080] S22, forming a germanium layer 220 on the silicon germanium buffer layer 210;

[0081] S23, doping silicon elements with a predetermined crystal orientation at a predetermined position of the germanium layer 220 to form a second region 202;

[0082] S24 , forming a silicon-germanium barrier layer 230 on the germanium layer 220 .

[0083] The silicon germanium buffer layer 210 is represented by

[001] -Ge x Si 1-x , and

[001] -Ge x Si 1-xThe proportion of silicon in the silicon-germanium buffer layer 210 should be less than 50%. The silicon-germanium buffer layer 210 can alleviate the lattice mismatch between the silicon substrate and the germanium layer 220, thereby improving the epitaxial quality of the silicon-germanium layer 220. Furthermore, the lattice mismatch between the silicon-germanium buffer layer 210 and the germanium layer 220 can also be utilized to provide biaxial strain in the second region 202. The magnitude of the biaxial strain can be adjusted by adjusting the silicon content in the silicon-germanium buffer layer 210 and the thickness of the silicon-germanium buffer layer 210.

[0084] Furthermore, because the second region 202 is formed on both sides of the first region 201 along the first direction, the silicon doped along a predetermined crystal orientation within the second region 202 can provide the first region 201 with uniaxial tensile strain along a predetermined direction. For example, the direction in which silicon is doped at a predetermined position of the

[001] germanium layer 220 can be along the

[110] crystal orientation of the germanium layer 220. Thus, the direction in which the uniaxial tensile strain provided by the second region 202 to the first region 201 is also

[110] , and the greater the silicon doping concentration within the second region 202, the greater the uniaxial tensile strain provided by the second region 202 to the first region 201.

[0085] As an example, the epitaxial growth method of the germanium quantum well 200 may include physical vapor deposition and plasma chemical vapor deposition, and the metal electrode 400 may be prepared by electron beam exposure and / or electron beam evaporation.

[0086] As an example, the thickness of the silicon germanium buffer layer 210 ranges from a few nanometers to tens of nanometers, the thickness of the germanium layer 220 ranges from tens of nanometers to hundreds of nanometers, the thickness of the silicon germanium barrier layer 230 ranges from a few nanometers to tens of nanometers, the thickness of the dielectric layer 300 ranges from more than ten nanometers to tens of nanometers, and the thickness of the metal electrode 400 ranges from tens of nanometers.

[0087] As an example, the dielectric layer 300 is composed of a dielectric material, including but not limited to one of SiO2 or Al2O3; the metal electrode 400 is composed of a metal material with low resistivity, including but not limited to aluminum (Al) or gold (Au).

[0088] As an example, the diameter size of the two-dimensional gate-controlled quantum dots prepared above ranges from 60 nm to 100 nm, and the bulk phase of the germanium material of the germanium quantum well 200 is a crystal structure with regular tetrahedral covalent bonds.

[0089] It should be noted that the specific doping direction for silicon doping at the predetermined position of the germanium layer 220 is provided as an example only and is not specifically limited in this application. In other embodiments, the silicon doping for providing uniaxial tensile strain may be in directions other than the

[110] direction. Specific methods for doping the second interval 202 include, but are not limited to, thermal diffusion, electrochemical implantation, or ion implantation.

[0090] In addition, the doping elements in the second interval 202 may include but are not limited to silicon. Other elements that can be doped in the second interval 202 and provide uniaxial strain for the first interval 201 should also be included in the scope disclosed in this application.

[0091] like Figure 2 and Figure 5 As shown, in some embodiments, the steps of forming a two-dimensional gate-controlled quantum dot in the first interval 201 using the EDSR technology may include:

[0092] S51, providing an in-plane static magnetic field for the germanium quantum well 200;

[0093] S52 , applying a first threshold voltage and a second threshold voltage to the first electrode 410 and the second electrode 420 , respectively, to provide a first electric field for the germanium quantum well 200 .

[0094] S53 , applying a third threshold voltage to the third electrode 430 to provide a second electric field for the germanium quantum well 200 , so as to form a two-dimensional gate-controlled quantum dot in the first interval 201 .

[0095] The first electric field is a lateral driving electric field, and the second electric field is a vertical electric field. The direction of the first electric field is the same as the direction of the in-plane static magnetic field, and the direction of the second electric field is perpendicular to the surface of the substrate 100 .

[0096] Combine Figure 2 and Figure 6It can be seen that when an in-plane static magnetic field is applied to the two-dimensional gated quantum dot formed in the germanium quantum well 200, the gated quantum dot will exhibit discrete spin-polarized energy levels due to the combined effects of quantum confinement and the Zeeman effect. The quantum states corresponding to these discrete energy levels are called Fock-Darwin states and can be represented by the principal quantum number n, the angular quantum number l, and the spin quantum number s: |n,l,s>. An applied alternating electric field or microwave can only couple adjacent quantum states containing the same spin component, that is, ∆n=±1 and ∆s=0 must both be satisfied. In the absence of SOC, quantum states with different spin components do not couple, making spin control of a two-level system impossible. However, when linear SOC is present, adjacent quantum states with different spin components couple, that is, ∆n=±1 and ∆s≠0 must both be satisfied, forming a two-level system in which each energy level contains a different spin component. The alternating electric field or microwave continuously couples the same spin components in the two-level system, thereby continuously changing the spin components of each energy level, realizing time-dependent spin flip and spin manipulation.

[0097] Although linear SOC is the key to achieving spin flip and spin manipulation using EDSR technology, it was generally believed in the past that due to the forbidden coupling of light and heavy holes in quantum wells, there is no linear Rashba SOC for heavy holes in quantum wells, but only cubic Rashba SOC. The central inversion symmetry of quantum wells also forbids Dresselhaus SOC. Recent studies have shown that there is light and heavy hole coupling in quantum wells, and thus linear SOC. However, since the light and heavy hole coupling in the

[001] quantum well comes from the contribution of the wave function at the interface, the SOC is relatively weak. Several existing studies have attempted to enhance the light and heavy hole coupling, but their solutions are difficult to implement and control experimentally.

[0098] The first-principles calculation results of the empirical pseudopotential method for spin splitting are as follows: Figure 7 As shown, when a gate voltage perpendicular electric field with an intensity of 100 kV / cm is applied to the quantum well through the third electrode 430, before and after applying a 0.4% uniaxial tensile strain in the

[110] direction, (Ge) 120 / (Ge 0.8 Si 0.2 ) 60 The spin splitting of the quantum well increases significantly near the Γ point and is anisotropic. The linear SOC coefficient is fitted from the energy band and its relationship with strain is obtained as follows: Figure 8 and Figure 9 As shown in the figure, it can be seen that under the action of 0.4% uniaxial tensile strain, a Dresselhaus-type linear SOC coefficient of 102.3 meVÅ can be obtained (see the figure). α 1) and a Rashba-like linear SOC coefficient of -13.6 meVÅ (see figure)α 2) The linear SOC coefficient increases by two orders of magnitude compared to the case without uniaxial strain. This is because the symmetry of the quantum well is broken after uniaxial strain is applied, leading to the intrinsic light-heavy hole coupling of the light and heavy hole states. Therefore, the light-heavy hole coupling strength in the quantum well after uniaxial strain is much greater than that without uniaxial strain.

[0099] Within a certain range, the Rabi frequency is proportional to the linear SOC coefficient. Currently reported quantum wells and two-dimensional gated quantum dots have achieved Rabi frequencies of up to hundreds of MHz, while the two-dimensional gated quantum dots designed in this application, subjected to uniaxial strain, can achieve Rabi frequencies in the GHz range.

[0100] As an example, a magnetic field is applied in the quantum well plane, and the Lamour frequency of the transverse driving electric field is fixed at 5 GHz. The calculation results of the Rabi frequency are as follows: Figure 10 As shown in the figure, under a gate voltage perpendicular electric field of 100 kV / cm, a two-dimensional gate-controlled quantum dot subjected to 0.4% uniaxial tensile strain can achieve a Rabi frequency of about 4 GHz, thereby making the hole spin Rabi frequency in the two-dimensional gate-controlled quantum dot reach the GHz level.

[0101] Theoretical calculations show that quantum wells with uniaxial strain have higher linear SOC and Rabi frequency than quantum wells without uniaxial strain. Since linear SOC can be controlled by gate voltage, uniaxial strain also has a wide range of parameter selection in experiments, and appropriate parameters can be selected experimentally based on various factors. For example, in the above example, the thickness of the germanium layer 220 is approximately 18 nm, and further increasing the thickness of the germanium layer 220 within a certain range can further increase the Rabi frequency.

[0102] Furthermore, theoretical calculations show that Figure 11 As shown in the graph, when adjusting the gate voltage, the linear SOC coefficient remains essentially unchanged within the gate voltage range of 200 kV / cm to 250 kV / cm. Theoretical evidence suggests that this characteristic can offset the charge noise problem caused by a large linear SOC, further enhancing the applicability of the two-dimensional gate-controlled quantum dots in quantum computing.

[0103] It should be noted that, in the above embodiment, the direction of the first electric field and the direction of the in-plane static magnetic field are the same and are only used as an example. The present application does not make any specific limitations on the direction of the first electric field and the direction of the second electric field. That is to say, the in-plane static magnetic field and the first electric field can also be in other directions than those in the above embodiment.

[0104] The second embodiment of the present application provides a germanium hole spin quantum bit device that realizes ultrafast control compatible with CMOS process, such as Figure 1As shown, the device includes:

[0105] substrate 100;

[0106] The germanium quantum well 200 is formed on the substrate 100 and includes a silicon germanium buffer layer 210, a germanium layer 220 and a silicon germanium barrier layer 230 stacked sequentially from bottom to top;

[0107] A dielectric layer 300 is formed on the germanium quantum well 200;

[0108] At least one group of metal electrodes 400 is formed on the dielectric layer 300 , each group of metal electrodes 400 includes a first electrode 410 , a second electrode 420 , and a third electrode 430 spaced apart from each other along the second direction, and the third electrode 430 is located between the first electrode 410 and the second electrode 420 ;

[0109] Among them, the interface between the germanium layer 220 and the silicon germanium barrier layer 230 includes a first interval 201, the first interval 201 is used to form a two-dimensional gate-controlled quantum dot, the germanium layer 220 includes two second intervals 202 arranged at intervals along the first direction, and the second intervals 202 contain silicon elements doped along a preset crystal direction; the first interval 201 is located between the two second intervals 202 arranged at intervals, and the second interval 202 is used to provide a uniaxial tensile strain in a preset direction for the two-dimensional gate-controlled quantum dot formed in the first interval 201.

[0110] It should be noted that for details not disclosed in the ultrafast-controlled germanium hole spin quantum bit device provided in this embodiment, please refer to the details disclosed in the ultrafast-controlled germanium hole spin quantum bit preparation method in the embodiment of this application, and no further details will be given here.

[0111] In summary, the present invention provides a germanium hole spin qubit quantum device that is compatible with CMOS technology and can achieve ultrafast control, and a preparation method thereof. By locally injecting doped silicon elements into the germanium quantum well 200, uniaxial strain in a fixed direction in the local area is achieved, thereby realizing the preparation of high-quality two-dimensional gate-controlled quantum dots with fast spin flipping.

[0112] In the descriptions of the foregoing embodiments, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are mutually inconsistent.

[0113] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

Claims

1. A method for preparing ultrafast controlled germanium hole spin qubits, characterized in that: include: providing a substrate; forming a germanium quantum well on the substrate, wherein the interior of the germanium quantum well includes a first region for forming a two-dimensional gate-controlled quantum dot and a second region doped with silicon along a preset crystal direction, wherein the second region is located on both sides of the first region along a first direction; forming a dielectric layer on the germanium quantum well structure; forming at least one group of metal electrodes on the dielectric layer, each group of metal electrodes comprising a first electrode, a second electrode, and a third electrode spaced apart from each other along a second direction, the third electrode being located between the first electrode and the second electrode; The method uses electric dipole spin resonance technology to form a two-dimensional gate-controlled quantum dot in the germanium quantum well, comprising: Providing an in-plane static magnetic field in the germanium quantum well; applying a first threshold voltage and a second threshold voltage to the first electrode and the second electrode respectively, so as to provide a first electric field for the germanium quantum well; Applying a third threshold voltage to the third electrode to provide a second electric field to the germanium quantum well to form the two-dimensional gate-controlled quantum dot in the first interval; the direction of the second electric field is perpendicular to the substrate surface; The germanium quantum well includes a silicon germanium buffer layer, a germanium layer and a silicon germanium barrier layer which are sequentially epitaxially formed on the substrate, and the second interval is formed at a preset position of the germanium layer.

2. The preparation method according to claim 1, characterized in that The germanium quantum well is formed on the substrate by using a CMOS process.

3. The preparation method according to claim 1, characterized in that The substrate includes a [001] silicon substrate.

4. The preparation method according to claim 1, characterized in that The method of doping the preset position of the germanium layer with silicon elements in a preset crystal orientation includes thermal diffusion, electrochemical implantation or ion implantation.

5. The preparation method according to claim 1, characterized in that The preset crystal orientation of the silicon element doped in the second interval includes a [110] crystal orientation, which is used to provide a uniaxial tensile strain in the [110] crystal orientation for the two-dimensional gate-controlled quantum dots formed in the first interval.

6. The preparation method according to claim 1, characterized in that The silicon content in the silicon germanium buffer layer is not higher than 50%.

7. The preparation method according to claim 1, characterized in that The thickness of the germanium layer ranges from tens of nanometers to hundreds of nanometers, and the thickness of the silicon germanium buffer layer and the silicon germanium barrier layer ranges from several nanometers to tens of nanometers.

8. The preparation method according to claim 1, characterized in that The dielectric material of the dielectric layer includes at least one of SiO 2 and Al 2 O 3 , and the thickness of the dielectric layer ranges from more than ten nanometers to several tens of nanometers.

9. The preparation method according to claim 1, characterized in that The material of the metal electrode includes at least one of Al and Au, and the thickness of the metal electrode ranges from several nanometers to tens of nanometers.

10. The preparation method according to claim 1, characterized in that A vertical projection of the third electrode on the substrate covers a vertical projection of the first interval.

11. The preparation method according to claim 1, wherein The diameter of the two-dimensional gate-controlled quantum dots ranges from 60 nm to 100 nm.

12. The preparation method according to claim 1, characterized in that The bulk phase of the germanium material of the germanium quantum well is a crystal structure with regular tetrahedral covalent bonds.

13. The preparation method according to claim 1, characterized in that The direction of the first electric field is the same as the direction of the in-plane static magnetic field and is perpendicular to the direction of the second electric field.

14. An ultrafast controlled germanium hole spin qubit device, prepared by the preparation method of claim 1, characterized in that: include: substrate; A germanium quantum well is formed on the substrate, comprising a silicon germanium buffer layer, a germanium layer and a silicon germanium barrier layer stacked sequentially from bottom to top; a dielectric layer formed on the germanium quantum well; at least one group of metal electrodes formed on the dielectric layer, each group of metal electrodes comprising a first electrode, a second electrode, and a third electrode spaced apart from each other along a second direction, the third electrode being located between the first electrode and the second electrode; In which, the interface between the germanium layer and the silicon-germanium barrier layer includes a first interval, the first interval is used to form a two-dimensional gate-controlled quantum dot, the germanium layer includes two second intervals spaced apart from each other along a first direction, the second interval contains silicon elements doped along a preset crystal direction; the first interval is located between the two second intervals spaced apart from each other, and the second interval is used to provide a uniaxial tensile strain in a preset direction for the two-dimensional gate-controlled quantum dot formed in the first interval.

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