Ion trap, quantum computer and method for manufacturing an ion trap

Abstract

According to at least one embodiment, the ion trap (100) comprises a first (1) and a second (2) permanent magnets spaced apart from each other. The ion trap is configured to capture ions (6) such that the ions are aligned along a predetermined line (7). The magnetic moments of the permanent magnets point in the same direction. The permanent magnets are arranged such that the magnitude of the magnetic field generated by the permanent magnets changes along the predetermined line.

Description

[0001] The present disclosure relates to an ion trap, a quantum computer, and a method for manufacturing an ion trap.

[0002] One problem to be solved is to provide an ion trap that can be manufactured easily and / or inexpensively. Further problems to be solved include providing a quantum computer with such an ion trap and a method for manufacturing such an ion trap.

[0003] First, the ion trap is introduced. The ion trap is specifically an ion trap for quantum computing.

[0004] In at least one embodiment, the ion trap comprises a first and a second permanent magnet spaced apart from each other. The ion trap is configured to trap ions such that the ions are aligned along a predetermined line. The magnetic moments of the permanent magnets point in the same direction. The permanent magnets are arranged such that the magnitude of the magnetic field generated by the permanent magnets changes along the predetermined line.

[0005] In an ion trap for quantum computers, it can be advantageous to have a magnetic field whose magnitude is different for different ions, i.e., to have a varying magnetic field magnitude along the line along which the trapped ions are aligned. The present invention is based, among other things, on the discovery that such a magnetic field can be generated using two permanent magnets magnetized in the same direction, i.e., whose magnetic moments point in the same direction. Such an ion trap is easy to manufacture because the permanent magnets can be magnetized in a homogeneous field after the ion trap has been assembled. In contrast, the use of pre-magnetized permanent magnets magnetized in different directions complicates the assembly of a small ion trap because of the considerable forces involved during assembly.

[0006] The first and second permanent magnets are each made of a ferromagnetic material, such as neodymium iron boron (NdFeB), samarium cobalt (SmCo), aluminum nickel cobalt (AlNiCo), or a combination thereof. When reference is made to "the two permanent magnets" here, this refers to the first and second permanent magnets.

[0007] During operation of the ion trap, ions are trapped inside the ion trap along a predetermined line. The ion trap is designed, for example, to trap at least one ion crystal with two or more ions, e.g., at least eight, or at least 20, or at least 100, and / or at most 1000 ions, aligned along the predetermined line. The predetermined line can be a straight line. The fact that the ions are trapped along the predetermined line means, in particular, that each of the trapped ions overlaps the predetermined line and / or oscillates around the predetermined line.

[0008] The magnetic moments of the first and second permanent magnets point in the same direction. The magnetic moment m⇀ of a permanent magnet is defined as m⇀=∫∫∫m⇀ dV where M⇀ is the magnetization field. The volume integral extends over the entire volume of the respective permanent magnet.

[0009] "Pointing in the same direction" means that the magnetic moments point in the same direction within the manufacturing tolerances. For example, the deviation between the directions of the magnetic moments of the two permanent magnets is at most 5° or at most 1°. In addition, the amplitudes of the magnetic moments of the first and second permanent magnets, i.e. |m⇀|, be identical within the manufacturing tolerance, e.g., with a deviation of no more than 10% or no more than 5%. In particular, the magnitude of the magnetic moments is greater than zero. Thus, the magnitude of the magnetic moment of the two permanent magnets is between 0.3 T and 1.8 T, in particular between 0.9 T and 1.1 T.

[0010] The first and second permanent magnets are arranged such that the magnitude of the magnetic field they generate varies along the predetermined line. Specifically, the magnitude of the magnetic field generated by the two permanent magnets is minimum at a specific point on the predetermined line and increases in both directions from that point along the predetermined line. During operation, for example, ions are trapped on two sides of that specific point along the predetermined line. Preferably, the total static magnetic field to which the trapped ions are exposed during operation of the ion trap is such that its magnitude varies along the predetermined line.

[0011] For example, the static magnetic field to which the ions are exposed during operation is primarily generated by the first and second permanent magnets. For example, more than 50%, e.g., at least 75%, or 100% of the magnitude of the static magnetic field experienced by the trapped ions during operation of the ion trap is generated by the first and second permanent magnets.

[0012] According to at least one embodiment, the two permanent magnets are arranged such that the magnitude of the magnetic field generated by them is zero at a point on the predetermined line and increases in two directions away from this point along the predetermined line. This can be achieved, for example, if the predetermined line is offset from the two permanent magnets and, in particular, does not intersect with either of the two permanent magnets. Additionally or alternatively, this can be achieved by an additional magnetic field (in addition to the magnetic field generated by the two permanent magnets) that is homogeneous in the region of the enclosed ions and / or in the region of the first and second permanent magnets. With such an additional homogeneous magnetic field, the location of the minimum of the total magnetic field and / or the magnitude of the minimum of the total magnetic field can be influenced.Especially in the area around the magnetic field zero point, the magnetic field is equal to or almost equal to a magnetic quadrupole field.

[0013] The additional magnetic field can be provided by a further permanent magnet arranged at a distance from the predetermined line and / or from the first and second permanent magnets, wherein this distance is large compared to the distance between the first and second permanent magnets, e.g., at least a factor of 10 or 100 larger. The spatial extent of the further permanent magnet can be larger than the distance between the first and second permanent magnets, e.g., at least a factor of 10 or 100 larger.

[0014] According to at least one embodiment, the centers of the two permanent magnets lie on a first axis and are spaced apart from each other in a first direction parallel to this first axis. The distance in the first direction is 2 Δx. The centers of the two permanent magnets are, for example, the centers of mass of the two permanent magnets.

[0015] According to at least one embodiment, the magnetic moments of the two permanent magnets point in a second direction parallel to a second axis. This second axis is perpendicular to the first axis. In other words, the magnetic moments of the first and second permanent magnets are perpendicular to the straight connecting line connecting the centers of the first and second permanent magnets.

[0016] According to at least one embodiment, the predefined line runs parallel to the first axis, i.e., it is a straight line. "Parallel to the first axis" again means parallel within the manufacturing tolerances. For example, the predefined line and the first axis form an angle of at most 10°, at most 5°, or at most 1°. The predefined line can lie in the plane spanned by the first and second axes.

[0017] According to at least one embodiment, the predetermined line is spaced from the first axis. For example, the distance of the predetermined line from the first axis is smaller than the distance between the centers of the first and second permanent magnets. In particular, the predetermined line is spaced from the first axis in the second direction by a distance Δx / √2 ± 35%. At such a distance between the predetermined line and the first axis, the magnetic field generated by the two permanent magnets is equal to or nearly equal to a magnetic quadrupole field, which is particularly advantageous for quantum computations.

[0018] According to at least one embodiment, the ion trap further comprises a substrate with a top surface. The substrate is formed, for example, from a diamagnetic or paramagnetic material. In particular, the substrate can be formed from an electrically insulating material and / or a semiconductor material. The substrate is formed, for example, from sapphire or silicon or SiC, or from a dielectric material such as plastic or polyamide.

[0019] The top side of the substrate can be a main side of the substrate, i.e., a side parallel to a main extension plane of the substrate. The top side can be substantially flat. The thickness of the substrate, measured in the direction from the top side to a bottom side, is, for example, smaller than the extension of the top side. The first axis or the first direction runs, for example, parallel to the top side of the substrate.

[0020] According to at least one embodiment, the predetermined line is located vertically above the upper side. The vertical direction is a direction perpendicular to the upper side and / or perpendicular to the main extension plane of the substrate. Preferably, the predetermined line does not intersect with the substrate, i.e., it is offset from the substrate. For example, the vertical direction is parallel to the second direction or the second axis.

[0021] According to at least one embodiment, the two permanent magnets are arranged on or in the substrate. For example, the permanent magnets are arranged on the top side of the substrate or on the bottom side of the substrate, or they are embedded in the substrate. In particular, the permanent magnets are arranged such that a plane running parallel to the top side intersects the two permanent magnets, e.g., at their centers.

[0022] According to at least one embodiment, the magnetic moments of the two permanent magnets point in the vertical direction or at least in a direction oblique to the top surface. For example, the angle between the magnetic moments of the first and second permanent magnets and the vertical direction is at most 20°, at most 10°, or at most 5°.

[0023] Alternatively, the magnetic moments can both be perpendicular to the vertical direction.

[0024] According to at least one embodiment, the ion trap comprises electrodes for generating an electrical trapping potential in which the ions are trapped along the predetermined line. The ion trap can be a so-called quadrupole trap. In particular, the ion trap is a Paul trap. The electrodes can comprise at least two direct current electrodes and at least two or at least four alternating current electrodes. The electrodes can be arranged on the top side of the substrate, on the underside of the substrate, or in the substrate. The ion trap is, for example, a planar ion trap in which the electrodes on the top side are metallized.

[0025] According to at least one embodiment, the electrodes are arranged in a plane vertically between the predetermined line and the permanent magnets.

[0026] According to at least one embodiment, the ion trap comprises exactly two permanent magnets, i.e., only the first and second permanent magnets. In particular, only the first and second permanent magnets are arranged on or in the substrate.

[0027] According to at least one embodiment, the permanent magnets are identical in size and / or shape. This, in turn, relates to the manufacturing tolerances. For example, the difference between the volumes of the two permanent magnets is at most 10% or at most 5%.

[0028] According to at least one embodiment, the two permanent magnets are each plate-shaped, e.g., disc-shaped. This means that the thickness of each permanent magnet is smaller than the smallest lateral dimension. The thickness is measured, e.g., in the second direction and / or in the vertical direction. The lateral dimensions of a permanent magnet are measured, e.g., in directions perpendicular to the second direction and / or parallel to the top side of the substrate.

[0029] According to at least one embodiment, the thickness of each of the two permanent magnets is in the range between 1 µm and 200 µm, e.g., between 10 µm and 100 µm. The limits are inclusive.

[0030] According to at least one embodiment, the maximum lateral extent of each of the two permanent magnets is in the range between 20 µm and 2 mm, e.g., between 50 µm and 800 µm. The limits are included.

[0031] According to at least one embodiment, the distance between the two permanent magnets, e.g., measured in the first direction, is at most 1 mm or at most 500 µm. The limits are included. The distance between the permanent magnets is defined as the shortest distance between any two points on the two permanent magnets. As the size of the permanent magnets increases, the distance may increase.

[0032] According to at least one embodiment, the two permanent magnets each have a circular shape, an elliptical shape, or a rectangular shape in a plan view. The plan view is, in particular, a view in a direction parallel to the vertical direction and / or parallel to the second direction. Alternatively, the permanent magnets can each have a freeform shape in the plan view. For example, the extent of each of the permanent magnets is greater in a direction perpendicular to the first direction and perpendicular to the second direction than in any other direction.

[0033] For example, the first and second permanent magnets are mirror-symmetrical to each other with respect to a virtual mirror plane. The first direction is, for example, oblique or perpendicular to the virtual mirror plane.

[0034] For example, the first and second permanent magnets each have a shape defined by the following equation: μ−15x2(1+x2+y2)72+3(1+x2+y2)52+λ(3(1+x2+y2)52−1(1+x2+y2)32)=0, where x and y are coordinates that define the outer closed perimeter in lateral directions. Specifically, x and y in this equation are given in relative units, with a height—i.e., the z-coordinate at which the magnitude of the magnetic field is zero—being set to 1. µ and λ are numbers. For example, µ and / or λ are nonzero.

[0035] Next, the quantum computer is specified. The quantum computer comprises the ion trap according to one of the embodiments described here. The quantum computer is configured to perform quantum computations.

[0036] The method for producing an ion trap is then described. The method is particularly suitable for producing an ion trap according to one of the embodiments described here. Therefore, all features described in connection with the ion trap are also disclosed for the method, and vice versa.

[0037] In at least one embodiment, the method comprises a step of providing a preliminary ion trap comprising two ferromagnetic elements spaced apart from each other, the preliminary ion trap being configured to trap ions such that the ions are aligned along a predetermined line. The method further comprises a step of magnetizing the ferromagnetic elements in an external magnetic field so that they become permanent magnets whose magnetic moments point in the same direction. The permanent magnets are arranged such that the magnitude of the magnetic field generated by the permanent magnets changes along the predetermined line.

[0038] The preliminary ion trap can be identical to the ion trap described above, except that the ferromagnetic elements have not yet been converted into permanent magnets. This means that the preliminary ion trap can already include the substrate and / or the electrodes. The ferromagnetic elements can be arranged on or within the substrate by applying a ferromagnetic film or by selecting and placing the ferromagnetic elements.

[0039] The external magnetic field used to permanently magnetize the ferromagnetic elements can be homogeneous, at least in the region of the ferromagnetic elements and / or the region where the ions are trapped.

[0040] To permanently magnetize the ferromagnetic elements, they can, for example, be heated, then exposed to the external magnetic field and then cooled in the external magnetic field.

[0041] The ion trap, the quantum computer, and the method for producing an ion trap are explained in more detail below using exemplary embodiments with reference to the drawings. The attached figures serve to further understand the invention. In the figures, elements of the same structure and / or functionality may be designated by the same reference numerals. It goes without saying that the embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale. To the extent that elements or components in the various figures have the same function, their description will not be repeated for each of the following figures. For reasons of clarity, elements may not appear with the corresponding reference symbols in all figures. The Fig. 1 and Fig. 4 show different embodiments of the ion trap, The Fig. 2 and Fig. 3 show embodiments of the static magnetic field generated by the ion trap, Fig. 5 shows an embodiment of a quantum computer, and Fig. 6 shows a flowchart of an embodiment of the method for manufacturing an ion trap.

[0042] The first embodiment of the ion trap from Fig. 1 comprises a first permanent magnet 1 and a second permanent magnet 2, both of which are identical, namely plate-shaped and cylindrical. The magnetic moments of the two permanent magnets 1, 2 are indicated by the arrows. As shown, the magnitude and direction of the magnetic moments are identical. The permanent magnets 1, 2 are formed, for example, with NdFeB.

[0043] The centers of the permanent magnets 1, 2 lie on a first axis, which here forms the x-axis of a Cartesian coordinate system. The magnetic moments are parallel to a second direction, which is a direction parallel to the z-axis of the Cartesian coordinate system. The thickness of the permanent magnets 1, 2 is measured in the second direction and is smaller than the lateral dimensions of the permanent magnets 1, 2, measured in the xy plane.

[0044] The ion trap 100 from Fig. 1 has captured a multitude of ions 6 lined up along a given line 7. The given line 7 is a straight line parallel to the x-axis. The position of the straight line 7 is at y = 0 and z = Δx / √2, where the distance between the centers of the permanent magnets 1, 2 measured along the x-axis is 2·Δx.

[0045] Fig. 2 shows the two permanent magnets 1, 2 from Fig. 1 generated magnetic field in the xz-plane. Here, Δx = 1. The given line 7 at z = 1 / √2 is also shown.

[0046] Fig. 3 shows an enlargement of Fig. 2. As shown, the magnetic field generated by the two permanent magnets 1, 2 along the given line 7 is identical or almost identical to a quadrupole magnetic field. In particular, at the point (x,z)=(0,1 / √2), i.e., at the position of the given line 7 centered over the two permanent magnets 1, 2, the amplitude of the magnetic field is zero and increases in two directions along the given line 7 away from the point (x,z)=(0,1 / √2).

[0047] Fig. Figure 4 shows another embodiment of the ion trap 100. Here, the ion trap is a planar Paul trap comprising a substrate 3 with a top surface 30. The permanent magnets 1, 2 are embedded in the substrate 3, and the predetermined line 7 is arranged vertically above the top surface 30, with the vertical direction being a direction parallel to the z-axis. Electrodes 40 for establishing the electrical trapping potential are arranged on the top surface 30 of the substrate 3.

[0048] The substrate 3 comprises two layers 31, 32. The first layer 31 is formed, for example, from sapphire, Si, or SiC. The permanent magnets 1, 2 are arranged on top of the first layer 31. After the permanent magnets 1, 2 are arranged on the first layer 31, the second layer 32 is applied to the top of the first layer 31 so that the permanent magnets 1, 2 are covered by the second layer 32. The second layer 32 is formed, for example, from polyamide. The electrodes 40 are then applied to the polyamide layer 32.

[0049] The implementation of the quantum computer by Fig. 5 comprises an ion trap 100, e.g., that of Fig. 4, as the computing unit of the quantum computer, which is located in a chamber 200. The ion trap 100 is connected to external components of the quantum computer via the chamber 200 through a plurality of connections 11. For example, the connections 11 connect the ion trap 100 to electronic devices 12 and a classical computer 13.

[0050] The electronic devices 12 include, for example, a laser, a wave measuring device, an acousto-optic modulator, an electro-optic modulator, a detector, a signal generator, an amplifier, a power supply, a piezo controller, a motor, analog-to-digital converters, signal generators such as high-frequency generators, microwave signal generators, low-frequency signal generators, and / or DC signal generators. The electronic devices 12 can also be partially arranged within the chamber 200.

[0051] In the embodiment of the method for producing an ion trap according to the flow chart of Fig. 6, a step S1 is carried out in which a preliminary ion trap is provided. The preliminary ion trap comprises two ferromagnetic elements that are spaced apart from each other. The preliminary ion trap is designed to trap ions such that the ions are lined up along a predetermined line. For example, in step S1, a preliminary ion trap as in Fig. 4 shown, with the difference that the elements 1, 2 are not yet permanently magnetized, but are ferromagnetic elements with a magnetic moment of, for example, zero.

[0052] In step S2 of the process, the ferromagnetic elements are then magnetized in an external magnetic field so that they become permanent magnets whose magnetic moments point in the same direction. This results in, for example, in permanent magnets 1, 2 made of Fig. 4. In particular, the permanent magnets 1, 2 then generate a magnetic field, with the magnitude of the magnetic field changing along the given line.

[0053] The invention is not limited to the embodiments described herein. Rather, the invention encompasses any novel feature and any combination of features, including, in particular, any combination of features in the claims, even if this feature or combination itself is not explicitly recited in the claims or embodiments. Reference symbol 1 first permanent magnet 2 second permanent magnet 3 Substrat 6 Ion 7 predefined line 11 Connection 12 electronic devices 13 classic computers 30 Top of the substrate 31 first layer 32 second layer 40 electrodes 100 ion traps 200 chambers X x-axis Y y-axis Z z-axis S1 Process step S2 process step

Claims

[1] Ion trap (100) with - a first (1) and a second (2) permanent magnet which are spaced apart from each other, wherein - the ion trap (100) is designed to capture ions (6) such that the ions (6) are lined up along a predetermined line (7), - the magnetic moments of the permanent magnets (1, 2) point in the same direction, - the permanent magnets (1, 2) are arranged so that the size of the magnetic field generated by the permanent magnets (1, 2) changes along the predetermined line. [2] Ion trap (100) according to claim 1, wherein - the two permanent magnets (1, 2) are arranged such that the magnitude of the magnetic field generated by them is zero at a point on the predetermined line (7) and increases in two directions along the predetermined line (7) away from this point. [3] Ion trap (100) according to claim 1 or 2, wherein - centers of the two permanent magnets (1, 2) lie on a first axis (x) and are spaced apart from each other in a first direction parallel to the first axis (x), the distance in the first direction being 2·Δx, - the magnetic moments of the two permanent magnets (1, 2) point in a second direction which is parallel to a second axis (z), and this second axis (z) is perpendicular to the first axis (x), - the predetermined line (7) runs parallel to the first axis (x) and is spaced from the first axis (x) in the second direction by a distance Δx / √2 ± 35%. [4] Ion trap (100) according to one of the preceding claims, further comprising - a substrate (3) having a top side (30), wherein - the predetermined line (7) is located vertically above the top side (30), the vertical direction being a direction perpendicular to the top side (30), - the two permanent magnets (1, 2) are arranged on or in the substrate (3). [5] Ion trap (100) according to claim 4, wherein - the magnetic moments of the two permanent magnets (1, 2) point in the vertical direction or at least in a direction which is oblique to the upper side (30). [6] Ion trap (100) according to claim 4 or 5, further comprising - electrodes (40) for generating an electrical trapping potential in which the ions are trapped along the predetermined line (7), wherein - the electrodes (40) are arranged in a plane vertically between the predetermined line (7) and the permanent magnets (1, 2). [7] Ion trap (100) according to one of the preceding claims, wherein - the ion trap (100) comprises exactly two permanent magnets (1, 2). [8] Ion trap (100) according to one of the preceding claims, wherein - the permanent magnets (1, 2) are the same in size and / or shape. [9] Ion trap (100) according to one of the preceding claims, wherein - the permanent magnets (1, 2) are each plate-shaped, - a thickness of each permanent magnet (1, 2) is in the range between 1 µm and 200 µm, - a maximum lateral extension of each permanent magnet (1, 2) is in the range between 20 µm and 2 mm, - a distance between the two permanent magnets (1, 2) is not more than 1 mm. [10] Ion trap (100) according to one of the preceding claims, wherein - the two permanent magnets (1, 2) each have a circular or elliptical or rectangular shape in a plan view. [11] Quantum computers encompassing - the ion trap (100) according to one of the preceding claims, wherein - the quantum computer is designed to perform quantum calculations. [12] A method for manufacturing an ion trap comprising the following steps - providing a preliminary ion trap comprising two ferromagnetic elements spaced apart from each other, the preliminary ion trap being designed to trap ions (6) such that the ions (6) are lined up along a predetermined line (7), - magnetizing the ferromagnetic elements in an external magnetic field so that they become permanent magnets (1, 2) whose magnetic moments point in the same direction, where - the permanent magnets (1, 2) are arranged such that the size of the magnetic field generated by the permanent magnets (1, 2) changes along the predetermined line (7).

Images