Magnetic component, in particular quantum component

Abstract

The invention relates to a magnetic component comprising a substrate (6) supporting at least one pair of permanent magnets (2) extending in a first direction (X), each magnet (2) having an interaction end (21a, 21b), the interaction ends (21a, 21b) being arranged facing one another, the pair of magnets (2) being arranged so as to exert an antisymmetric magnetic field with a high magnetic field gradient along a second direction (Z) orthogonal to the first direction (X), under the effect of a magnetic field produced by external magnetic means.

Description

MAGNETIC COMPONENT, ESPECIALLY QUANTUM COMPONENT

[0001] The present invention relates to a magnetic component in the field of micro and nanoelectronics, in particular a quantum component. The quantum component is intended in particular, but not exclusively, for the manufacture of quantum computers. It may also relate to the fields of spintronics, topological superconductivity, for the magnetic actuation of nano-elements and nano-balls, or for near-field magnetic detection by scanning probe.

[0002] There are devices arranged to generate a magnetic field in particular directions via magnets, designated by the person skilled in the art as micro-magnets in the field of micro and nano electronics.

[0003] One aim of the invention is to propose a new magnetic component architecture making it possible to optimize the shape of the profile of the magnetic field generated by micro-magnets, and thus improve the performance of these components. SUBJECT OF THE INVENTION

[0004] To this end, and according to a first aspect, the invention proposes a magnetic component comprising a substrate supporting at least one pair of permanent magnets extending in the first direction, each magnet having an interaction end, the interaction ends being arranged opposite each other, the pair of magnets being arranged to exert an antisymmetric magnetic field with respect to the plane X=0, with a strong magnetic field gradient along a second direction orthogonal to the first direction, and a symmetrical magnetic field with respect to the plane X=0 along the first direction (X) orthogonal to the directions Y and Z, under the effect of a magnetic field produced by external magnetic means.

[0005] For the above and for the remainder of the description, the following terms are understood to mean:

[0006] – quantum component, an assembly of electronic circuits and / or devices using nanotubes as conductive or semiconductive elements thereof, the circuits having single, double or multiple quantum dots or boxes, in series or in parallel, using a single nano-object having selected properties as channel elements, or a plurality of separately selected nano-objects;

[0007] - a quantum dot, or quantum box, a portion of the nano-object in which an electron is trapped / confined in three dimensions; it can only occupy discrete energy levels;

[0008] – a nano-object, an object having at least one of its external dimensions (typically among its height, width, thickness, length) less than 100 nanometers; if its three external dimensions (defined along three orthogonal axes) are less than 100 nanometers: it is a nanoparticle; if two of its external dimensions (preferably defined along two orthogonal axes) are less than 100 nanometers: it is for example a hollow single- or multi-walled nanotube which can be closed at at least one end or a nanofiber, i.e. a solid fiber. An electrically conductive or semiconducting nanofiber will be referred to hereinafter as a nanowire. If an external dimension is less than 100 nm (typically its thickness), it is a nanosheet;

[0009] – an electrode, one end of an electrical conductor arranged to release or capture an electric current;

[0010] – a grid electrode, an electrode which carries a microwave signal and / or which allows the potentials to be fixed (in Volts);

[0011] – a microwave grid electrode, a grid electrode that carries and radiates a microwave signal that enables interaction between a microwave cavity and a nano-object;

[0012] – a low-frequency grid electrode, a grid electrode that allows electrostatic potentials to be fixed and a double quantum dot to be created;

[0013] – a magnet, a magnetic element which becomes magnetized under the effect of an external magnetic field;

[0014] – electrostatic potentials allowing the formation of the two quantum dots, the electrostatic potentials which allow the modulation of the potential energy barriers and the creation of a double quantum dot;

[0015] - Spin-photon coupling, the controllable interaction or "coupling" between the magnetic aspect of the qubit, i.e. its spin, and a microwave electric field coming from a microwave cavity. Since the electric field is made up of photons, we speak of spin-photon coupling;

[0016] - Quantum gate, a logic operation that can change the superposition state of a qubit. For example, a qubit may have a fifty-fifty chance of ending up in one of two states;

[0017] – inhomogeneous magnetic field, a magnetic field generated so as to generate a magnetic dipole, preferably by any variation of the magnetic field around and / or along the at least one nano-object element; for example, a vertical and / or horizontal component of the magnetic field changes sign along or around the at least one nano-object element, preferably at or directly above the at least one magnetic grid electrode; according to a particular example, a horizontal magnetic field gradient or along the at least one nano-object element which makes the total field inhomogeneous along said at least one nano-object element, preferably the component of the magnetic field along the axis or direction of the at least one nano-object changes sign along the at least one nano-object element;

[0018] – spatial extent, the area located along and / or around, preferably radially, the at least one nano-object element, preferably between the suspension electrodes, according to one embodiment an extent corresponding to the distance between two quantum dots;

[0019] – substrate, an element of the component having a high resistivity, for example a dielectric constant higher than air, particularly at low temperatures.

[0020] According to a second aspect of the invention, there is provided a quantum component comprising:

[0021] at least two suspension electrodes: a source electrode connected to an electron source and a drain electrode connected to a reference potential, designed to receive a quantum element incorporating a double quantum box,

[0022] at least three grid electrodes arranged between the two suspension electrodes, the two suspension electrodes being raised relative to the at least three grid electrodes,

[0023] a magnetic component according to the invention, intended to exert an antisymmetric magnetic field with a high magnetic field gradient along a second direction orthogonal to the first direction, under the effect of a magnetic field produced by external magnetic means, this antisymmetric magnetic field being applied to said quantum element.

[0024] According to a third aspect of the invention, there is provided a method of manufacturing a quantum component according to the invention, comprising the following steps:

[0025] -engrave a substrate to receive magnetic elements,

[0026] -depositing at least one pair of magnets extending in a first direction (X), each magnet having an interaction end, the interaction ends being arranged opposite each other,

[0027] - engrave at grazing incidence the substrate on which at least one pair of magnets has been deposited,

[0028] -deposit a layer of oxide on the substrate thus treated,

[0029] -deposit suspension electrodes and gate electrodes on the oxide layer.

[0030] Preferably, according to any preceding aspect, the component or method may comprise one or more of the following features:

[0031] - the pair of magnets generates by itself an antisymmetric magnetic field (component along the z axis) between the two dots (relative to the x=0 plane), and the applied external magnetic field makes it possible to generate a symmetrical field between the two dots;

[0032] - between quantum dots separated by a distance of between 60 and 120 nanometers, this or these gradients result in an asymmetric component of the field which can reach approximately 30mT or 40mT (mili-Tesla);

[0033] - If we consider points placed symmetrically with respect to the field distribution, the fields in the two points of the double quantum dot will be composed of a symmetric part and an antisymmetric part.

[0034] It is possible to define, for each component of the field: i = u, v, w:

[0035] or L;R refer to the left (L) and right (R) quantum dot respectively. This definition of the symmetric / asymmetric magnetic field for each vector component i (where u,v,w refer equivalently to directions in x,y,z space). This definition makes sense in the context of a double quantum dot.

[0036] The effects of stray fields on the energies in the left and right parts of the double quantum dot can then be expressed by:

[0037] Or

[0038] is the probability density of the electron being present in point p (left or right), the prefactor 2 represents the Landé factor of the electron spin and μB is the Bohr magneton.

[0039] This corresponds to the mathematical definition of the magnetic coupling constant between the electron in quantum dots and the symmetric, antisymmetric magnetic field, respectively. We will see later which is considered the quantity to be optimized (maximized).

[0040] The gradient must therefore be considered as an inhomogeneity between the two quantum dots of the fields averaged on each point.

[0041] A pair of dots with linear confinement is now considered, as found in a double quantum dot in a nanowire. The dots are aligned along x and defined between -250nm and -150nm for the L-dot, and between 150nm and 250nm for the R-dot.

[0042] The nanowire is suspended at z = 200 nm, above a magnetic layer extending

[0043] on -100nm < z < 100 nm.

[0044] Since the external magnetic field is preferably applied along the nanowire, while a transverse gradient is required, we assume a uniform magnetization m along +x.

[0045] As we now consider points above the magnetic system, it is used:

[0046] where L and R are swapped, with respect to the above. The definition of Q is a quantity that is optimized (see the previous coupling constant between the magnetic field and the points).

[0047] To ensure practical shapes, a constraint is added so that the magnet is homogeneous along z.

[0048] Thus, this optimization consists of deciding the presence or absence of a magnet in each or one more cell(s) or one or more elements of the total thickness along the Z axis at all X and Y positions. This method of optimizing the quantity Q becomes linear with respect to the individual magnetic elements / cells;

[0049] Larger MS magnetic saturation directly promotes larger stray fields and gradients, it also facilitates the formation of magnetic domains in nanomagnets and therefore requires a larger external field to reach saturation.

[0050] This external field is added as a term

[0051] has coming from the symmetrical part of the stray fields in the formation of the energy levels of the points.

[0052] By defining the inhomogeneity of the fields acting on the points as ,

[0053] This figure of merit value decreases when a large external field is used.

[0054] To optimize inhomogeneity, it is therefore necessary to identify the pairs of MS and Bext values ​​which provide the highest value of

[0055] This last point corresponds to the definition of the contribution of the external magnetic field to the symmetrical component. BRIEF DESCRIPTION OF THE FIGURES

[0056] Other characteristics and advantages of the invention will emerge from the detailed description of the invention which follows with reference to the appended figures and in which:

[0057] This is a schematic representation of a quantum component comprising electrodes extending substantially perpendicular to the two sets of magnets according to one embodiment;

[0058] It represents two series of magnets parallel to each other in the same series and between the two series, the ends of the magnets of the first series being opposite the ends of the magnets of the second series, the two series of magnets being arranged in the same plane;

[0059] The is a schematic representation of two ends of magnets facing each other and a nanotube connecting the two ends according to an embodiment of a quantum component, this representation being arranged in a three-dimensional frame;

[0060] is a nanoscale illustration of the saturation of the magnetic field at the ends of the two magnets;

[0061] shows curves of the components of the magnetic field along a carbon nanotube, in particular the distribution of the magnetic field along a carbon nanotube obtained with the micro-magnets conforming to the;

[0062] shows the impact of the external magnetic field on different physical quantities, with three different materials for the magnet.

[0063] For clarity, identical or similar elements of the different embodiments are identified by identical reference signs throughout the figures. DETAILED DESCRIPTION OF THE INVENTION

[0064] In relation to figures 1 and 2, there is shown an embodiment of a quantum component 1 comprising:

[0065] a substrate 6, made of a high resistivity material, for example,

[0066] a magnetic device 2, acting as a magnetic electrode, arranged to generate a magnetic field to which the quantum component 1 is subjected, comprising two comb-shaped parts 2A, 2B arranged opposite each other and separated by a central gap 22 in which a dedicated magnetic field is produced,

[0067] a set of grid electrodes 8 placed above the central gap 22, these grid electrodes being surrounded by a source electrode 9.1, a cut-source type electrode 9.2, a cut-drain type electrode 9.3, and a drain electrode 9.4,

[0068] a nanotube or nanowire (not visible in the) connected to the suspension electrodes, the nanotube or nanowire being suspended in a rectilinear manner above the grid electrodes and above a set of magnets arranged in a substantially parallel manner, this nanotube or nanowire preferably being made of carbon.

[0069] The source and drain electrodes are placed on a conductive layer via an insulating layer. They constitute suspension electrodes for the nanotube or nanowire and are raised above the gate electrodes. This arrangement is specific to a quantum component including a carbon nanotube.

[0070] With reference to the, the magnetic device 8 comprises permanent magnets arranged in the form of two combs 2A, 2B facing each other, a first comb and a second comb. Each comb 2A, 2B comprises a plurality of magnets 20A, 21A; 21A, 21B of generally rectangular shape arranged parallel to each other. The series of magnets of each comb is connected along the Z axis to the two opposite ends of the opposite comb.

[0071] According to the embodiment shown, each comb 2A, 2B comprises 15 magnets. Each magnet has a width of 1.5 micrometers and a length of 8.5 micrometers. The width is chosen so as to make the magnetic moments parallel to the boundaries due to the internal dipole energies. Preferably, each magnet is spaced laterally, along the Y axis, by a distance of 0.75 micrometers. Preferably, each comb 2A, 2B has a thickness of 400 nanometers. Preferably, each magnet comprises iron and cobalt, preferably with high remanence.

[0072] Each magnet 21A of a first comb 2A has, with reference to FIGS. 2 and 3, an interaction end or magnetic pole 41A, arranged to be opposite an interaction end or pole 41B of a magnet 21B of the second comb 2B. Each transverse face is opposite a transverse face of a magnet of the second comb. Preferably, the spacing between two interaction ends or poles of magnets facing each other is between 0.4 and 1 micrometer. The spacing is measured between the distal points of said interaction ends.

[0073] Preferably, each interaction end has a rounded shape viewed along a two-dimensional plane, or longitudinal plane, illustrated by the XY plane of the. Furthermore, Figures 3, 4 and 5 illustrate the optimal shapes of a saturated nanomagnet in the case of finite extension quantum dots, in particular the uniform magnetization imposed along x, maximizing a field difference Bz. Preferably, the distal portion in rounded shape, in particular ovoid in shape in three dimensions, contributes most to the optimization of the magnetic field. The shape of the interaction end allows the magnetic moments to be aligned in a single direction.

[0074] Furthermore, each magnet 21A has a connecting end 31A, opposite the interaction end 41A. Each comb 2A, 2B further comprises a connecting piece 200A, 200B of the magnets, such that each magnet of a comb 2A, 2B is connected to the connecting piece 200A, 200B of said comb 2A, 2B via the connecting end. According to the embodiment shown, the connecting piece 200A, 200B has a width of 4 micrometers.

[0075] The embodiment allows to propose an anisotropic shape and to produce a homogeneous magnetic field in the Y direction towards the nanotube. The reduced dimensions of the magnets lead to a shape anisotropy, the magnetic moments tend to be parallel to the boundaries due to the internal dipole energies.

[0076] Preferably the two magnet combs 2A, 2B are embedded in the substrate 6.

[0077] In addition, the quantum component comprises external magnetic means (not shown) arranged to exert a magnetic field along the X direction. For example, a torus (not shown) surrounds the electrodes and the combs. Preferably, this torus generates a magnetic field between 200 and 500 milli-Tesla.

[0078] The quantum component thus proposes to exert an antisymmetric magnetic field with a strong magnetic field gradient along the Z direction orthogonal to the X direction, under the effect of a magnetic field generated by external magnetic means. For example, according to tests carried out, the antisymmetric field constant reaches 26.8 micro-eV and the symmetric field constant reaches 29 micro-eV, making it possible to optimize the spin-photon coupling.

[0079] The quantum component makes it possible to optimize the distribution of magnetic moments around the quantum dots, the magnetic field gradient, and thus the interaction between the magnet and the nano-object or nanotube comprising at least two quantum dots. Preferably, the nano-object or nanotube is located above the considered magnet couple by approximately 100 nanometers.

[0080] Lamontre the results of micromagnetic simulations of a shape optimized for an inhomogeneous Bz component, with an external field Bext and magnetization along x. As a function of the external magnetic field, (a) magnetization mx, (b) symmetric (alpha s), (c) antisymmetric (alpha as) coupling constants due to nanomagnets, and (d) the ratio of the antisymmetric field to the total symmetric field

[0081] The different colors correspond to CoFe (line with squares), Co (line with triangles) and NiFe (line with circles).

Claims

Magnetic component comprising a substrate (6) receiving at least one pair of permanent magnets extending in the first direction (X), each magnet having an interaction end, the interaction ends being arranged opposite each other, the pair of magnets being arranged to exert an antisymmetric magnetic field with respect to the plane X=0, with a strong magnetic field gradient along a second direction (Z) orthogonal to the first direction (X), and a symmetrical magnetic field with respect to the plane X=0 along the first direction (X) orthogonal to the directions Y and Z, under the effect of a magnetic field produced by external magnetic means. Magnetic component according to claim 1, comprising several pairs of magnets facing each other so as to form two combs. A magnetic component according to any preceding claim, wherein each magnet has a rectilinear shape. A magnetic component according to any preceding claim, wherein each magnet interacting end has a rounded shape. Magnetic component according to the preceding claim, characterized in that the rounded shape is curvilinear with a predefined radius of curvature. A magnetic component according to one of the two preceding claims, wherein each magnet end is rounded in all three dimensions. A magnetic component according to any preceding claim, wherein each magnet interaction end has a non-protrusion shape. A magnetic component according to any preceding claim, wherein the at least one magnet is embedded in the substrate. Magnetic component according to any one of claims 1 to 7, wherein the at least one magnet is deposited on the substrate. Quantum component comprising:a source electrode connected to an electron source and a drain electrode connected to a reference potential, designed to receive a quantum element integrating a double quantum box,at least three gate electrodes (9.1, 9.2, 9.3, 9.4) arranged between the two source and drain electrodes,a magnetic component (1) according to any one of the preceding claims, designed to exert an antisymmetric magnetic field with a high magnetic field gradient along a second direction (Z) orthogonal to the first direction (X), under the effect of a magnetic field produced by external magnetic means, this antisymmetric magnetic field being applied to said quantum element. Quantum component according to the preceding claim, characterized in that the source and drain electrodes constitute suspension electrodes raised relative to the at least three gate electrodes. Quantum component according to the preceding claim, further comprising at least, as quantum element, one nano-object element suspended (11) between the two suspension electrodes, and electrically connected to them, the at least one nano-object element being arranged above the at least three gate electrodes. Quantum component according to claim 10, further comprising, as a quantum element, an electron gas located in a substrate disposed between the two source and drain electrodes. Quantum component according to one of the four preceding claims, wherein the quantum element is arranged at a distance of approximately 100 nm above the at least one magnet pair. Quantum component according to one of the five preceding claims, in which the magnets of a pair are arranged symmetrically with respect to a plane orthogonal to the direction of the at least one quantum element. A method of manufacturing a quantum component according to one of claims 10 to 15, comprising the following steps: etching a substrate to receive magnetic elements therein, depositing at least one pair of magnets extending in a first direction (X), each magnet having an interaction end, the interaction ends being arranged opposite each other, etching at grazing incidence the substrate on which at least one pair of magnets has been deposited, depositing an oxide layer on the substrate thus treated, depositing suspension electrodes and gate electrodes on the oxide layer.

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