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

Abstract

In at least one embodiment, the ion trap (100) comprises a first (1) and a second (2) permanent magnet which are spaced apart from each other. The ion trap is configured to trap ions (6) such that the ions are lined up along a predefined 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 predefined line.

Description

[0001] Description

[0002] Ion trap, quantum computer and method for producing an ion trap

[0003] The present disclosure relates to an ion trap, a quantum computer and a method for producing an ion trap .

[0004] One obj ect to be solved is to provide an ion trap that can be easily and / or cheaply produced . Further obj ects to be solved are to provide a quantum computer with such an ion trap and a method for producing such an ion trap .

[0005] First , the ion trap is speci fied . The ion trap is , in particular, an ion trap for quantum computing .

[0006] In at least one embodiment , the ion trap comprises a first and a second permanent magnet which are spaced apart from each other . The ion trap is configured to trap ions such that the ions are lined up along at least one predefined line of at least one processing zone . 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 predefined line . Exclusively the first and a second permanent magnet are configured to generate the magnetic field in the at least one processing zone .

[0007] In an ion trap for quantum computing, it may be advantageous to have a magnetic field whose magnitude is di f ferent for di f ferent 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, inter alia, on the recognition that such a magnetic field can be produced with two permanent magnets which are magnetized in the same direction, i.e. which have magnetic moments pointing in the same direction. Such an ion trap can be easily produced because the permanent magnets can be magnetized in a homogeneous field after assembly of the ion trap. In contrast to that, using pre-magnetized permanent magnets which are magnetized in different directions makes the assembly of a small ion trap more difficult since substantial forces appear during assembly.

[0008] The first and the second permanent magnet each consist of a ferromagnetic material, like neodymium iron boron (NdFeB) , samarium cobalt (SmCo) , aluminium nickel cobalt (AlNiCo) or a combination thereof. Herein, when talking about "the two permanent magnets", the first and the second permanent magnet are meant.

[0009] During operation of the ion trap, ions are trapped inside the ion trap along at least one predefined line of at least one processing zone. The ion trap is, for example, configured 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 lined up along the at least one predefined line of the at least one processing zone. For example, the ion trap can comprise one processing zone or a plurality of processing zones. In each processing zone a respective predefined line can be located. In particular, each processing zone is assigned to two permanent magnets as described herein. The predefined line may be a straight line. The fact that the ions are trapped along the predefined line means, in particular, that each of the trapped ions intersects with the predefined line and / or oscillates around the predefined line. The magnetic moments of the first and the second permanent magnets point in the same direction. The magnetic moment m of a permanet magnet is defined as wherein M is the magnetization field. The volume integral is over the whole volume of the respective permanent magnet.

[0010] "Point in the same direction" means that the magnetic moments point in the same direction within the limits of manufacturing tolerances. For example, a deviation between the directions of the magnetic moments of the two permanent magnets is at most 5° or at most 1°. Moreover, the amplitudes of the magnetic moments of the first and the second permanent magnet, i.e. |m|, may be the same within the limits of manufacturing tolerance, e.g. with a deviation of at most 10% or at most 5%. Particularly, the magnitude of the magnetic moments is greater than zero. For instance, the magnitude of the magnetic moment of each the two permanent magnets is between 0.3 T and 1.8 T, particularly between 0.9 T and 1.1 T .

[0011] The first and the second permanent magnet are arranged such that the magnitude of the magnetic field generated by them changes along the predefined line. Particularly, the magnitude of the magnetic field generated by the two permanent magnets has a minimum at a certain point of the predefined line and increases in both directions away from this point along the predefined line. For example, during operation, ions are trapped on both sides of this certain point along the predefined line. Preferably, the whole static magnetic field felt by the trapped ions during operation of the ion trap is such that the magnitude thereof changes along the predefined line .

[0012] The static magnetic field felt by the ions during operation is , for example , mainly generated by the first and the second permanent magnet . For instance , more than 50% , e . g . at least 75% or 100% , of the magnitude of the static magnetic field felt by the trapped ions during operation of the ion trap is generated by the first and the second permanent magnet .

[0013] According to at least one embodiment , the two permanent magnets are arranged such that the magnitude of the magnetic field generated with the help of them is zero at one point of the predefined line and increases in both directions along the predefined line away from that point . This can be achieved, for example , when the predefined line is of fset from the two permanent magnets and particularly does not intersect with any of the two permanent magnets . Additionally or alternatively, this can be achieved by an additional magnetic field ( additional to the magnetic field established by the two permanent magnets ) , which is homogeneous in the region of the trapped ions and / or in the region of the first and the second permanent magnet . 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 . Particularly in the region around that point of zero magnetic field, the magnetic field is equal or almost equal to a magnetic quadrupole field .

[0014] The additional magnetic field may be provided by a further permanent magnet which is arranged at a distance from the predefined line and / or from the first and the second permanent magnet, wherein said distance is large compared to the distance between the first and the second permanent magnet, e.g. at least a factor of 10 or 100 larger. The spatial extent of the further permanent magnet may be larger than the distance between the first and the second permanent magnet, e.g. at least a factor of 10 or 100 larger.

[0015] According to at least one embodiment, centers of the two permanent magnets lie on a first axis and are spaced apart from each other in a first direction which is parallel to this first axis. The distance in the first direction is 2 • Ax . The centers of the two permanent magnets are, for instance, the centers of mass of the two permanent magnets.

[0016] According to at least one embodiment, the magnetic moments of the two permanent magnets point in a second direction which is parallel to a second axis. Said second axis is perpendicular to the first axis. In other words, the magnetic moments of the first and the second permanent magnet are perpendicular to the straight connection line connecting the centers of the first and the second permanent magnet.

[0017] According to at least one embodiment, the predefined line runs parallel to the first axis, i.e. is a straight line. "Parallel to the first axis" again means parallel within the limits of manufacturing tolerances. For instance, the predefined straight line and the first axis enclose an angle of at most 10° or at most 5° or at most 1°. The predefined line may lie in the plan spanned by the first and the second axis . According to at least one embodiment , the predefined line is spaced apart from the first axis . For example , the distance of the predefined line from the first axis is smaller than the distance between the centers of the first and the second permanent magnet . Particularly, the predefined line is spaced apart from the first axis in the second direction by the distance Ax / 2 ± 35% . With such a distance between the predefined line and the first axis , the magnetic field generated by the two permanent magnets is equal or almost 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 side . The substrate is , for example , of a diamagnetic or paramagnetic material . Particularly, the substrate may be of an electrically insulating material and / or of a semiconductor material . For example , the substrate is of or comprises sapphire or silicon or SiC or a dielectric material , like plastic or polyamide .

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

[0020] According to at least one embodiment , the predefined line is located vertically above the top side . Thereby, the vertical direction is a direction perpendicular to the top side and / or perpendicular to the main extension plane of the substrate . Preferably, the predefined line does not intersect with the substrate , i . e . is of fset from the substrate . For instance , the vertical direction is parallel to the second direction or the second axis , respectively .

[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 . Particularly, the permanent magnets are arranged such that a plane running parallel to the top side intersects with both permanent magnets , e . g . with the centers thereof .

[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 which is oblique to the top side . For example , an angle between the magnetic moments of the first and the second permanent magnet and the vertical direction is at most 20 ° or at most 10 ° or at most 5 ° .

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

[0024] According to at least one embodiment , the ion trap comprises electrodes for establishing an electric trapping potential in which the ions are trapped along the predefined line . The ion trap may be a so-called quadrupole trap . Particularly, the ion trap is a Paul trap . The electrodes may comprise at least two DC electrodes and at least two or at least four AC electrodes . The electrodes may be arranged on the top side of the substrate or on the bottom side of the substrate or may be arranged in the substrate . For example , the ion trap is a planar ion trap with the electrodes being metallizations at the top side.

[0025] According to at least one embodiment, the electrodes are arranged in a plane vertically between the predefined 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 the second permanent magnet. Particularly, only the first and the second permanent magnets are arranged on or in the substrate.

[0027] According to at least one embodiment, the permanent magnets are equal in size and / or shape. This again refers to the limits of manufacturing tolerances. For example, the difference of 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 platelet-shaped, e.g. disc-shaped. That is, for each permanent magnet, the thickness is smaller than the smallest lateral extension. The thickness is, for example, measured in the second direction and / or in the vertical direction. The lateral extensions of a permanent magnet are, for example, measured in directions perpendicular to the second direction and / or parallel to the top side of the substrate .

[0029] According to at least one embodiment, a thickness of each of the two permanent magnets is in the range between 1 pm and 200 pm, e.g. between 10 pm and 100 pm. The borders are included . According to at least one embodiment, the maximum lateral extension of each of the two permanent magnets is in the range between 20 pm and 2 mm, e.g. between 50 pm and 800 pm. The borders are included.

[0030] 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 pm. The borders are included. The distance between the permanent magnets is defined as the shortest distance between any two points of the two permanent magnets. With greater sizes of the permanent magnets, the distance may increase.

[0031] According to at least one embodiment, the two permanent magnets each have a circular shape or an elliptic shape or a rectangular shape when viewed in a top view. The top view is, particularly, a view in a direction parallel to the vertical direction and / or parallel to the second direction. Alternatively, in the top view, the permanent magnets may each have a free-form shape. For example, the extension of each of the permanent magnets in a direction perpendicular to the first direction and perpendicular to the second direction is greater than in any other direction.

[0032] For example, the first and the second permanent magnet are mirror symmetric to one another with respect to a virtual mirror plane. The first direction is, for example, oblique or perpendicular to the virtual mirror plane.

[0033] For example, the first and the second permanent magnets each have a shape defined by the following equation: wherein x and y are coordinates defining the outer closed circumference in lateral directions . In particular, in this equation x and y are in relative units , where a height , i . e . the z-coordinate , at which the magnitude of the magnetic field is zero is set to 1 . / i and are numbers . For example , / z and / or are di f ferent from zero .

[0034] Next , the quantum computer is speci fied . The quantum computer comprises the ion trap according to any of the embodiments described herein . The quantum computer is configured to perform quantum computations .

[0035] Next , the method for producing an ion trap is speci fied . The method is , in particular, suited for producing an ion trap according to any of the embodiments described herein . Therefore , all features described in connection with the ion trap are also disclosed for the method and vice versa .

[0036] In at least one embodiment , the method comprises a step of providing a preliminary ion trap comprising two ferromagnetic elements which are spaced apart from each other, wherein the preliminary ion trap is configured to trap ions such that the ions are lined up along a predefined line . The method further comprises a step of magneti zing the ferromagnetic elements in an external magnetic field so that they become permanent magnets which have magnetic moments pointing 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 predefined line . The preliminary ion trap may be identical to the above described ion trap except that the ferromagnetic elements are not yet trans formed into permanent magnets . That is , the preliminary ion trap may already comprise the substrate and / or the electrodes . The ferromagnetic elements may be arranged on or in the substrate by depositing a ferromagnetic film or by a pick-and-place of the ferromagnetic elements .

[0037] The external magnetic field used for permanently magneti zing the ferromagnetic elements may be homogeneous , at least in the region of the ferromagnetic elements and / or the region where the ions are trapped .

[0038] For example , to permanently magneti ze the ferromagnetic elements , they may be heated up, then exposed to the external magnetic field and then cooled down inside the external magnetic field .

[0039] Hereinafter, the ion trap, the quantum computer and the method for producing an ion trap are explained in more detail with reference to the drawings on the basis of exemplary embodiments . The accompanying figures are included to provide a further understanding . In the figures , elements of the same structure and / or functionality may be referenced by the same reference signs . It is to be understood that the embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale . Insofar as elements or components correspond to one another in terms of their function in di f ferent figures , the description thereof is not repeated for each of the following figures . For the sake of clarity, elements might not appear with corresponding reference symbols in all figures . Figures 1 and 4 show di f ferent exemplary embodiments of the ion trap,

[0040] Figures 2 and 3 show exemplary embodiments of the static magnetic field generated by the ion trap,

[0041] Figure 5 shows an exemplary embodiment of a quantum computer, and

[0042] Figure 6 shows a flowchart of an exemplary embodiment of the method for producing an ion trap .

[0043] The first exemplary embodiment of the ion trap of figure 1 comprises a first permanent magnet 1 and a second permanent magnet 2 which are both formed identically, namely with a platelet , cylindrical shape . The magnetic moments of both permanent magnets 1 , 2 are indicated by the arrows . As can be seen, the magnitude of the magnetic moments and the direction of the magnetic moments are identical . For example , the permanent magnets 1 , 2 are of NdFeB .

[0044] The centers of the permanent magnets 1 , 2 lie on a first axis , which herein 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 extensions of the permanent magnets 1 , 2 , measured in the x-y-plane .

[0045] The ion trap 100 of figure 1 has trapped a plurality of ions 6 which are lined up along a predefined line 7 . The predefined line 7 is a straight line parallel to the x-axis . The position of the straight line 7 is at y = 0 and z = Ax / 2, wherein the distance between the centers of the permanent magnets 1, 2 measured along the x-axis is 2 • Ax .

[0046] Figure 2 shows the magnetic field generated by the two permanent magnets 1, 2 of figure 1 in the x-z plane. Here, Ax = 1. The predefined line 7 at z= 1 / 2 is indicated as well.

[0047] Figure 3 shows a zoom-in of figure 2. As can be seen, the magnetic field generated by the two permanent magnets 1, 2 along the predefined line 7 is identical or almost identical to a quadrupole magnetic field. Particularly, at the point (x, z) = (0, 1 / 2) , i.e. at the position of the predefined line 7 centrally above the two permanent magnets 1, 2, the amplitude of the magnetic field is zero and increases in both directions along the predefined line 7 away from the point (x, z) = (0, 1 / 2) .

[0048] Figure 4 shows another exemplary embodiment of the ion trap 100. Here, the ion trap is a planar Paul trap comprising a substrate 3 with a top side 30. The permanent magnets 1, 2 are embedded in the substrate 3 and the predefined line 7 is arranged vertically above the top side 30, wherein the vertical direction is a direction parallel to the z-axis. Electrodes 40 for establishing the electric trapping potential are arranged on the top side 30 of the substrate 3.

[0049] The substrate 3 comprises two layers 31, 32. The first layer 31 is, for example, formed of sapphire or Si or SiC. The permanent magnets 1, 2 are arranged on a top side of the first layer 31. After arrangement of the permanent magnets 1, 2 on the first layer 31, the second layer 32 is applied to the top side of the first layer 31 so that the permanent magnets 1, 2 are covered by the second layer 32. The second layer 32 is, for example, of polyamide. The electrodes 40 are then applied onto the polyamide layer 32.

[0050] The exemplary embodiment of the quantum computer of figure 5 comprises an ion trap 100, e.g. that of figure 4, as a processing unit of the quantum computer located within a chamber 200. The ion trap 100 is connected to external components of the quantum computer through the chamber 200 by a plurality of connections 11. For example, the connections 11 connect the ion trap 100 with electronic devices 12 and a classical computer 13.

[0051] The electronic devices 12 comprise, exemplarily, a laser, a wavemeter, 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 radio frequency generators, microwave signal generators, low-frequency signal generators and / or direct current signal generators. The electronic devices 12 can be also partially arranged within the chamber 200.

[0052] In the exemplary embodiment of the method for producing an ion trap according to the flowchart of figure 6, a step SI is executed in which a preliminary ion trap is provided. The preliminary ion trap comprises two ferromagnetic elements which are spaced apart from each other. The preliminary ion trap is configured to trap ions such that the ions are lined up along a predefined line. For example, in step SI, a preliminary ion trap as shown in figure 4 is provided, with the difference that the elements 1, 2 are not yet permanently magnetized but are ferromagnetic elements with a magnetic moment of, e.g., zero.

[0053] In a step S2 of the method, the ferromagnetic elements are then magnetized in an external magnetic field so that they become permanent magnets which have magnetic moments pointing in the same direction. For example, the permanent magnets 1, 2 of figure 4 are produced thereby. Particularly, the permanent magnets 1, 2 then generate a magnetic field, wherein the magnitude of the magnetic field changes along the predefined line.

[0054] The invention is not limited to the exemplary embodiments by their description. Rather, the invention encompasses any new feature as well as any combination of features, which in particular includes any combination of features in the claims, even if this feature or combination itself is not explicitly indicated in the claims or exemplary embodiments.

[0055] Reference signs :

[0056] 1 first permanent magnet

[0057] 2 second permanent magnet

[0058] 3 substrate

[0059] 6 ion

[0060] 7 predefined line

[0061] 11 connection

[0062] 12 electronic devices

[0063] 13 classical computer

[0064] 30 top side of substrate

[0065] 31 first layer

[0066] 32 second layer

[0067] 40 electrodes

[0068] 100 ion trap

[0069] 200 chamber x x-axis y y-axis z z-axis

[0070] 51 method step

[0071] 52 method step

Claims

Claims1. Ion trap (100) comprising- a first (1) and a second (2) permanent magnet which are spaced apart from each other, wherein- the ion trap (100) is configured to trap ions (6) such that the ions (6) are lined up along at least one predefined line (7) of at least one processing zone,- the magnetic moments of the permanent magnets (1, 2) point in the same direction,- the first (1) and the second (2) permanent magnets are arranged such that the magnitude of the magnetic field generated by the permanent magnets (1, 2) changes along the predefined line of the at least one processing zone, and- exclusively the first (1) and a second (2) permanent magnet are configured to generate the magnetic field in the at least one processing zone.

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 with the help of them is zero at one point of the predefined line (7) and increases in both directions along the predefined line (7) away from that 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 which is parallel to the first axis (x) , wherein the distance in the first direction is 2 -Ax,- the magnetic moments of the two permanent magnets (1, 2) point in a second direction which is parallel to a secondaxis (z) and said second axis (z) is perpendicular to the first axis (x) ,- the predefined line (7) runs parallel to the first axis (x) and, in the second direction, is spaced apart from the first axis (x) by the distance Ax / 2 ± 35%.

4. Ion trap (100) according to any one of the preceding claims, further comprising- a substrate (3) with a top side (30) , wherein- the predefined line (7) is located vertically above the top side (30) , wherein the vertical direction is 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 top side (30) .

6. Ion trap (100) according to claim 4 or 5, further comprising- electrodes (40) for establishing an electric trapping potential in which the ions are trapped along the predefined line (7) , wherein- the electrodes (40) are arranged in a plane vertically between the predefined line (7) and the permanent magnets (1, 2) .

7. Ion trap (100) according to any one of the preceding claims, wherein- the ion trap (100) comprises exactly two permanent magnets (1, 2) .

8. Ion trap (100) according to any one of the preceding claims, wherein- the permanent magnets (1, 2) are equal in size and shape.

9. Ion trap (100) according to any one of the preceding claims, wherein- the permanent magnets (1, 2) are each platelet-shaped,- a thickness of each permanent magnet (1, 2) is in the range between 1 pm and 200 pm,- a maximum lateral extension of each permanent magnet (1, 2) is in the range between 20 pm and 2 mm,- a distance between the two permanent magnets (1, 2) is at mo st 1 mm .

10. Ion trap (100) according to any one of the preceding claims, wherein- in a top view, the two permanent magnets (1, 2) each have a circular shape or an elliptical shape or a rectangular shape.

11. Quantum computer comprising- the ion trap (100) according to any one of the preceding claims, wherein- the quantum computer is configured to perform quantum computations .

12. Method for producing an ion trap comprising the steps of- providing a preliminary ion trap comprising two ferromagnetic elements which are spaced apart from each other, wherein the preliminary ion trap is configured to trap ions (6) such that the ions (6) are lined up along a predefined line (7) ,- magnetizing the ferromagnetic elements in an external magnetic field so that they become permanent magnets (1, 2) which have magnetic moments pointing in the same direction, wherein- the permanent magnets (1, 2) are arranged such that the magnitude of the magnetic field generated by the permanent magnets (1, 2) changes along the predefined line (7) .

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