Ultra-fast control germanium hole spin quantum bit device and preparation method thereof

Abstract

The invention provides an ultrafast control germanium hole spinning quantum bit device and a preparation method thereof. The preparation method comprises the steps of providing a substrate, and forming a germanium quantum well, a dielectric layer and a metal electrode on the substrate in sequence. A first interval and second intervals located on the two sides of the first interval are formed in the germanium quantum well. Silicon element doping is carried out in a second interval along a preset crystal orientation, so that the second interval can continuously provide uniaxial tensile strain in a preset direction and size for a first interval, and two-dimensional grid-control quantum dots are formed in the first interval of the germanium quantum well by applying an in-plane static magnetic field to the germanium quantum well based on an electric dipole spin resonance technology. The preparation of the germanium hole spin quantum bit with high quality and ultrafast control can be realized, so that the problems of insufficient coupling strength of the existing germanium quantum well hole state linear spin orbit and slow control speed of the germanium hole quantum bit are solved.

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 has become a hot topic for basic research and technological breakthroughs at home and abroad due to its exponentially growing computing power. Among many schemes, semiconductor gate-controlled quantum dots have attracted great attention due to their deep compatibility with mature microelectronic complementary metal oxide semiconductor (CMOS) processes. In the semiconductor gate-controlled quantum dot scheme, the spin of the carriers in the quantum dots can be used as a carrier to construct quantum bits. People have currently realized the control of ten quantum bits in the hole spin system of two-dimensional gate-controlled germanium quantum dots. Compared with silicon electron spin, germanium hole spin has the following four advantages: 1. Holes have p-type wave functions, and the probability of being scattered by nuclear spins is greatly reduced. In addition, like silicon, germanium can also further increase the spin decoherence time through isotope purification; 2. Germanium holes have strong spin-orbit coupling (SOC), which can increase the speed of spin manipulation; 3. Germanium holes do not suffer from the interference of valley degeneracy; 4. Germanium holes have a smaller effective mass, so larger gate-controlled quantum dots can be prepared, which is easier for spin manipulation.

[0003] The Rabi spin flip frequency (abbreviated as Rabi frequency) can be used to characterize the speed of spin manipulation. To achieve full electrical manipulation of hole spins in a two-dimensional gate-controlled germanium quantum dot system, it is necessary to use the Electron Dipole Spin Resonance (EDSR) technology. The principle of EDSR technology is: 1. Apply a static magnetic field to the two-dimensional gate-controlled quantum dots to cause Zeeman spin splitting of the energy levels, and the spins on the two split sub-energy levels are opposite (parallel or antiparallel to the direction of the external magnetic field); 2. Apply an alternating electric field or microwave to couple the quantum states with the same spin in adjacent low energy levels of the two-dimensional gate-controlled quantum dots; 3. The electric field generated by the gate voltage drives the linear SOC, provides electric dipole transitions, couples the quantum states of different spins in adjacent low energy levels, and forms a two-level system with different spin states, thereby causing spin resonance, and each resonant spin state is a quantum bit. Compared with the Electron Spin Resonance (ESR) technology, the hole EDSR technology does not require the design of a fine micromagnetic structure in a low-dimensional system to provide a gradient magnetic field to flip the spin, but instead uses an equivalent magnetic field generated by an electrically controlled linear Rashba SOC. Electrical control instead of magnetic control further expands the application prospects of semiconductor quantum dot quantum computing with hole spins as carriers.

[0004] The realization 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 there is no linear Rashba SOC in two-dimensional hole gas due to the absence of light-heavy hole coupling. However, recent studies have shown that there is electric field-adjustable linear Rashba SOC in the two-dimensional hole gas of germanium quantum wells in the

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

[110] growth direction, applying a strong anisotropic electric field on a small size, 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, so far, no ultrafast controllable germanium hole spin quantum bit devices have been successfully prepared experimentally with a control frequency of GHz, which seriously hinders 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 some extent.

[0007] To this end, the first purpose of the present 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 control speed of germanium hole spin qubits cannot be further improved experimentally.

[0008] To achieve the above-mentioned purpose, the first embodiment of the present application provides a method for preparing an ultrafast controlled germanium hole spin quantum bit, 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 for silicon doping 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 the 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] Electric dipole spin resonance technology is used to form two-dimensional gate-controlled quantum dots in the germanium quantum well.

[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 comprises:

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

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

[0019] Doping a silicon element with a preset crystal orientation at a preset position of the germanium layer to form the second interval;

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

[0021] Optionally, a method for doping a 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 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.

[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 magnetic field and is perpendicular to the direction of the second electric field.

[0035] To achieve the above-mentioned purpose, the first embodiment of the present application provides an ultrafast controlled germanium hole spin quantum bit 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 in sequence 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 the metal electrodes comprises 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] Among them, 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 quantum bit device and the preparation method thereof provided in the present 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, including providing a substrate, and sequentially forming a germanium quantum well, a dielectric layer and a metal electrode on the substrate. The interior of the germanium quantum well is formed with a first interval and a second interval located on both sides of the first interval. 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 control 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 the present application can improve 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 the 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 quantum bit according to an embodiment of the present application.

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

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

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

[0051] Figure 5 It is a 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 variation 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] Fig. 9 Schematic diagram of the variation of the linear SOC coefficient of a two-dimensional gate-controlled quantum dot with biaxial strain under a uniaxial tensile strain of 0.4% in the

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

[0056] Fig.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 magnetic field with a Lamour frequency of 5 GHz according to an embodiment of the present application.

[0057] Fig.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] Embodiments of the present application are described in detail below, and examples of the embodiments 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 prior art 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 method for preparing the same. It is expected that on this basis, it is possible to realize the preparation of single and multiple two-dimensional gate-controlled quantum dot high-quality hole spin qubits, providing a new solution for semiconductor quantum computing.

[0061] The study found that the strong SOC of the germanium quantum well holes can quickly drive the spin flip of its two-dimensional gate-controlled quantum dot qubits, and the IV group elements can provide a long spin decoherence time due to almost zero nuclear spin scattering, and are deeply compatible with microelectronic CMOS processes, so high-quality scalable spin qubits can be prepared. At present, high-quality charge manipulation of four-by-four (sixteen) quantum dot arrays has been achieved in germanium quantum wells internationally. However, the further development of spin qubits is still limited by slower spin manipulation and shorter decoherence time.

[0062] The basic units of quantum computing include quantum bits and quantum logic gates. Among them, the preparation of a single quantum bit state requires the application of an external magnetic field to introduce the Zeeman effect to generate the two energy levels required for quantum bit encoding, while the realization of quantum logic gates requires the flipping between different spin states (bits). For holes, EDSR technology is used, which involves quantum states of different spin components. Since the external alternating electric field or microwave can only cause coupling between quantum states of the same spin component, it is inevitable to introduce SOC. Since the spin direction generated by the Zeeman effect is always parallel or antiparallel to the direction of the external static magnetic field, the combined action of SOC and the alternating electric field fundamentally provides a driving force for spin flipping. In EDSR technology, when the frequency of the external alternating electric field or microwave is equal to the Lamour precession frequency caused by the external static magnetic field, the spin state resonates. At this time, the spin orientation shows periodic changes, and the corresponding spin flip frequency is the Rabi frequency.

[0063] How to improve the manipulation speed (Rabi frequency) of hole qubits is a core concern for quantum computing, and the key to responding to this concern is to provide a stronger linear SOC. Studies have shown that the linear SOC of the two-dimensional hole gas in the germanium quantum well comes from the coupling of light and heavy holes. However, for a long time in the past, researchers generally believed that there was no linear SOC in the two-dimensional hole gas in the semiconductor quantum well because the coupling of light and heavy holes was symmetry forbidden. Recent theoretical studies have shown that in the germanium / silicon quantum well in the

[001] growth direction (referred to as the

[001] direction), the coupling of light and heavy holes caused by the interface effect induces the linear Rashba SOC, which has led to several schemes that induce linear SOC by reducing the symmetry of the germanium quantum well to induce the coupling of light and heavy holes. However, the existing theoretical schemes are difficult to implement and control experimentally, and are not enough for practical application. The latest theoretical research has found that after the uniaxial strain compatible with CMOS process commonly used in the integrated circuit industry is applied to the germanium quantum well, the coupling between light and heavy holes can be significantly enhanced, thereby inducing a linear SOC intensity that is two orders of magnitude greater than that of the traditional germanium quantum well two-dimensional hole gas. Correspondingly, the Rabi frequency will be increased to the GHz level. However, this theoretical research has not yet been implemented in experiments.

[0064] The core idea of ​​this application is to increase the spin manipulation rate by applying uniaxial tensile strain on traditional quantum wells, and the manipulation rate can be characterized by the Rabi frequency. This application is compatible with the existing mature microelectronic CMOS process, provides a solution for preparing germanium quantum wells with uniaxial strain, and uses the strong linear SOC in the quantum wells with uniaxial strain to prepare high-quality hole spin qubits with two-dimensional gate-controlled quantum dots and GHz-level Rabi frequencies, paving the way for the further development of semiconductor quantum computing.

[0065] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings. The x direction in the following example diagram is the first direction, which is also the

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

[001] direction.

[0066] The first embodiment of the present application provides a method for preparing a germanium hole spin quantum bit that realizes ultrafast control compatible with CMOS process, such as Figure 1 to Figure 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 doped with 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 group of metal electrodes 400 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.

[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 by 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 element doped along a preset crystal direction in the second interval 202 can continuously provide a stable uniaxial tensile strain for the first interval 201. That is to say, by controlling the doping direction and doping concentration of the silicon element 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] Therefore, the EDSR technology is used to form a two-dimensional gate-controlled quantum dot in the first interval 201 in the germanium quantum well 200, and when the frequency of the alternating electric field or microwave is equal to the intrinsic frequency of the in-plane static magnetic field, the two-dimensional gate-controlled quantum dot 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, ultra-fast 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 lateral driving electric field, and the lateral 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, which is used to provide a binding potential for trapping two-dimensional holes, and to confine the two-dimensional gate-controlled quantum dots in 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 the linear Rashba SOC under the control of the gate voltage 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) 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 correspondingly formed inside the germanium quantum well 200.

[0078] like Figure 4 As shown, in some embodiments, the step of epitaxially forming a 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 a silicon element with a preset crystal orientation at a preset 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, and improve the epitaxial quality of the silicon germanium layer 220. At the same time, by utilizing the lattice mismatch between the silicon germanium buffer layer 210 and the germanium layer 220, a biaxial strain can also be provided for the second interval 202, and the magnitude of the biaxial strain can be adjusted by the content of silicon in the silicon germanium buffer layer 210 and the thickness of the silicon germanium buffer layer 210.

[0084] In addition, since the second interval 202 is formed on both sides of the first interval 201 along the first direction, the silicon element doped along the preset crystal direction in the second interval 202 can provide the first interval 201 with a uniaxial tensile strain along the preset direction. For example, the direction of doping the silicon element at the preset position of the

[001] germanium layer 220 can be along the

[110] crystal direction of the germanium layer 220. Therefore, the direction of the uniaxial tensile strain provided by the second interval 202 to the first interval 201 is

[110] , and the greater the doping concentration of the silicon element in the second interval 202, the greater the uniaxial tensile strain provided by the second interval 202 to the first interval 201.

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

[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 as 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 of the silicon element doping at the preset position of the germanium layer 220 is only used as an example, and the present application does not specifically limit this. In other embodiments, the doping of the silicon element for providing uniaxial tensile strain can also be in directions other than the

[110] direction. The specific method of doping the element in the second interval 202 includes but is not limited to thermal diffusion, electrochemical injection, or ion injection.

[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 step 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 magnetic field, and the direction of the second electric field is perpendicular to the surface of the substrate 100 .

[0096] Combination Figure 2 and Figure 6It can be known that when a static magnetic field is applied to the two-dimensional gate-controlled quantum dots formed in the germanium quantum well 200, the two-dimensional gate-controlled quantum dots will have discrete energy levels of spin polarization under the combined action of the quantum confinement effect and the Zeeman effect. The quantum state corresponding to the discrete energy level is called the Fock-Darwin state, which can be represented by the three quantum numbers of the principal quantum number n, the angular quantum number l and the spin quantum number s: |n, l, s>. The external alternating electric field or microwave can only couple adjacent quantum states containing the same spin component, that is, it is necessary to simultaneously satisfy Δn=±1 and Δs=0. In the absence of SOC, there is no coupling between quantum states of different spin components, so the spin control of the two-level system cannot be achieved; when linear SOC exists, it will cause coupling between adjacent quantum states containing different spin components, that is, it will simultaneously satisfy Δn=±1 and Δs≠0, forming a two-level system in which each energy level contains different spin components. 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 realizing spin flip and spin manipulation using EDSR technology, it was generally believed in the past that since quantum wells prohibit light and heavy hole coupling, there is no linear Rashba SOC for heavy holes in quantum wells, but only cubic Rashba SOC, and the central inversion symmetry of quantum wells also prohibits 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 schemes 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 vertical electric field with a strength 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 Fig. 9 As shown. It can be seen that under the action of 0.4% uniaxial tensile strain, The Dresselhaus-type linear SOC coefficient (α1 in the figure) and The Rashba-like linear SOC coefficient (α2 in the figure) is two orders of magnitude higher than the linear SOC coefficient without uniaxial strain. This is because after applying uniaxial strain, the symmetry of the quantum well is broken, resulting in 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 applying 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. Among the currently reported quantum wells and two-dimensional gate-controlled quantum dots, the maximum Rabi frequency that can be obtained is in the order of hundreds of MHz, while the two-dimensional gate-controlled quantum dots designed in this application with uniaxial strain can obtain a Rabi frequency in the order of GHz.

[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: Fig.10 As shown, under a gate voltage of 100 kV / cm and a vertical electric field, 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 Rabi frequency of hole spins in the two-dimensional gate-controlled quantum dots reach the GHz level.

[0101] Theoretical calculations show that the quantum well with uniaxial strain has a larger linear SOC and Rabi frequency than the quantum well without uniaxial strain. Since the linear SOC can be regulated by gate voltage, the uniaxial strain also has a wider range of parameter selection in the experiment, and various factors can be comprehensively considered to select appropriate parameters in the experiment. For example, in the above example, the thickness of the germanium layer 220 is about 18nm, and continuing to increase the thickness of the germanium layer 220 within a certain range can also further increase the Rabi frequency.

[0102] Furthermore, theoretical calculations show that Fig.11 As shown, when the gate voltage is adjusted, in the gate voltage range of 200 kV / cm to 250 kV / cm, the linear SOC coefficient does not change with the gate voltage. Theory shows that this characteristic can offset the charge noise problem caused by large linear SOC, further improving the usability of the two-dimensional gate-controlled quantum dots in quantum computing according to the embodiment of the present invention.

[0103] It should be noted that in the above embodiment, the direction of the first electric field and the direction of the in-plane magnetic field are the same and are only used as examples. The present application does not specifically limit the direction of the first electric field and the direction of the second electric field. That is to say, the in-plane magnetic field and the first electric field may also be in other directions than those in the above embodiment.

[0104] The second aspect 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 in sequence from bottom to top;

[0107] A dielectric layer 300 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 spaced apart from each other along a first direction, and the second interval 202 contains silicon elements doped along a preset crystal direction; the first interval 201 is located between the two second intervals 202 spaced apart from each other, 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 qubit device provided in this embodiment, please refer to the details disclosed in the ultrafast controlled germanium hole spin qubit preparation method in the embodiment of the present 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 method for preparing the same. 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 achieving the preparation of high-quality two-dimensional gate-controlled quantum dots with fast spin flipping.

[0112] In the description of the aforementioned embodiments, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means 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 representations 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, without contradiction.

[0113] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

Claims

1. A method for preparing an ultrafast controlled germanium hole spin quantum bit, characterized in that: include: providing a substrate; 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 for silicon doping 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 the 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; Electric dipole spin resonance technology is used to form two-dimensional gate-controlled quantum dots in the germanium quantum well.

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 step of epitaxially forming a germanium quantum well on the substrate comprises: forming a silicon germanium buffer layer on the substrate; forming a germanium layer on the buffer layer; Doping a silicon element with a preset crystal orientation at a preset position of the germanium layer to form the second interval; A silicon germanium barrier layer is formed on the germanium layer.

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

6. The preparation method according to claim 4, 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.

7. The preparation method according to claim 4, characterized in that: The silicon content in the silicon germanium buffer layer is not higher than 50%.

8. The preparation method according to claim 4, 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.

9. The preparation method according to claim 1, characterized in that: The step of preparing two-dimensional gate-controlled quantum dots in the germanium quantum well using electric dipole spin resonance technology comprises: 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; 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.

10. The preparation method according to claim 1, characterized in that: The dielectric material of the dielectric layer includes at least one of SiO2 and Al2O3, and the thickness of the dielectric layer ranges from a dozen nanometers to several tens of nanometers.

11. 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.

12. 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.

13. The preparation method according to claim 1, characterized in that: The diameter size of the two-dimensional gate-controlled quantum dots ranges from 60nm to 100nm.

14. 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.

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

16. An ultrafast controlled germanium hole spin quantum bit device, 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 in sequence 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 the 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; Among them, 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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