Quantum computing device and quantum computer

Abstract

A quantum computing device is identified that includes a permanent magnet device that includes a plurality of permanently magnetized segments. [Solution] The quantum computing device is configured to implement a Paul trap for trapping ions along a predetermined line, each segment having a magnetization direction, and the segments are arranged such that the magnetization directions of at least some of the segments differ from one another and such that a magnetic field is established that varies in magnitude along the predetermined line. Further, a quantum computer comprising the quantum computing device is specified.

Description

[Technical Field]

[0001] The present disclosure relates to quantum computing devices and quantum computers. [Background technology]

[0002] In many quantum computing processes that use quantum computing arrangements, the arrangements are configured to trap quantum particles, such as ions. During operation, the trapped quantum particles form quantum bits, or qubits for short. To perform computations, the trapped quantum particles must be controlled and manipulated. For trapped quantum particles, interactions, such as Coulomb repulsion, can create coupling between neighboring trapped quantum particles, thus enabling entanglement. To perform quantum computing processes using trapped quantum particles, the trapped quantum particles must be individually controllable and addressable relative to one another.

[0003] Individual addressing of multiple trapped quantum particles, e.g., qubit registers, is desirable to have negligible crosstalk. However, crosstalk between adjacent trapped quantum particles is typically a source of error that is difficult to control in quantum computing processes and can hinder meaningful application, and therefore scalability, of quantum error correction protocols.

[0004] Therefore, one object to be achieved is to provide an improved quantum computing device, for example a quantum computing device that allows improved controllability. A further object to be achieved is to provide a quantum computer using such a quantum computing device.

[0005] These objects are solved, inter alia, by the subject matter of claims 1 and 16. Advantageous embodiments and further developments are the subject matter of the dependent claims and can also be extracted from the following description and drawings. Summary of the Invention

[0006] First, a quantum computing device is identified.

[0007] In accordance with at least one embodiment, a quantum computing device comprises a permanent magnet device, the permanent magnet device including a plurality of permanently magnetized segments.

[0008] The segments may all be identical within the limits of manufacturing tolerances. For example, a permanent magnet device may be symmetrical with respect to a plane of symmetry, in particular geometrically symmetrical. This means that the geometry or shape of the permanent magnet device is symmetrical with respect to the plane of symmetry, respectively. The shape of the permanent magnet device may also have rotational symmetry, for example n-fold rotational symmetry, where n is at least 3, at least 4, at least 6, or at least 8.

[0009] The permanent magnet device may include at least four, at least eight, at least 16, or at least 32 segments. Each segment includes or consists of a permanent magnetic material. For example, the permanent magnetic material is a ferromagnetic material. The segments may each include or consist of the same material. For example, each segment may be integrally formed. Alternatively, each segment may be formed from at least two sub-segments, where the at least two sub-segments have the same material and / or magnetization properties.

[0010] According to at least one embodiment, the quantum computing device is configured to implement a Paul trap for trapping ions along a predetermined line, i.e., the ions are aligned along the predetermined line. In other words, during operation, the quantum computing device, i.e., at least a portion thereof, constitutes a Paul trap. A Paul trap is also known as a quadrupole ion trap or a radio frequency (RF) trap. This is a type of ion trap that uses a dynamic electric field to trap charged particles.

[0011] The Paul trap comprises multiple electrodes, e.g., at least two RF electrodes, at least two DC electrodes, and at least two end cap electrodes. The electrodes may be distinct from the permanently magnetized segments of the permanent magnet device. Thus, the Paul trap may be a separate device of the quantum computing device, distinct from the permanent magnet arrangement. Alternatively, one or more of the segments of the permanent magnet device also form the electrodes of the Paul trap, such that the Paul trap is at least partially formed by the permanent magnet device.

[0012] The Paul trap is configured to trap two or more ions along a given line, for example at least 8, or at least 20, or at least 100, and / or up to 1000 ions.

[0013] During operation, the electrodes of the Paul trap generate an oscillating electrical potential configured to trap ions, with the ions aligned parallel to a predetermined line and perpendicular to the predetermined line, also referred to herein as the radial direction. Effectively, at least one electrical potential well is created in which ions are trapped in all spatial directions and is formed such that ions are positioned back and forth along the predetermined line. Multiple ions trapped in the same static potential well are also referred to herein as an ion crystal.

[0014] The predetermined line, also called the trap line, is defined by the potential generated by the Paul trap and therefore depends on the geometry of the Paul trap. Trapped ions are arranged along the predetermined line. For example, each ion crosses and / or oscillates around the predetermined line. In other words, in a Paul trap, ions are arranged in an ion chain that extends along the predetermined line.

[0015] In addition to the electrodes for the Paul trap, the quantum computing device may include components for powering the electrodes, such as a power supply and / or a control unit.

[0016] According to at least one embodiment, each segment has a magnetization direction. The magnetization of each segment is defined by a vector field representing the dipole moment of the respective permanent magnetic material. That is, each permanent magnetic material exhibits a dipole moment. The vector field, and in particular the dipole moment of the permanent magnetic material, defines the respective magnetization direction. The dipole moment primarily refers to the magnetization direction.

[0017] In accordance with at least one embodiment, the segments are arranged such that the magnetization directions of at least some of the segments differ from one another, such that the permanent magnet device establishes a magnetic field whose magnitude varies along a predetermined line.

[0018] For example, the magnetization directions of every two directly adjacent segments differ from each other. The magnetization directions may differ from each other by an angle of at least 5°, or at least 10°, and / or at most 90°, or at most 45°. By way of example, if there are m segments, where m is an even natural number of at least 4, the magnetization directions of each of two directly adjacent segments are rotated by 360°·3 / m with respect to each other.

[0019] The vector field defined by the magnetization directions of the segments and their positions in space may be symmetric with respect to the above-mentioned plane of symmetry. In particular, this vector field may have the same symmetry as the geometry of the permanent magnet device. Alternatively, the vector field may be asymmetric with respect to the plane of symmetry and / or may have a different symmetry than the geometry of the permanent magnet device, or may even be asymmetric.

[0020] A magnetic field is understood herein to be a magnetic flux density, and the magnitude of the magnetic field is therefore the absolute value of the magnetic flux density.

[0021] The magnetic field generated by the permanent magnet device may be or include, for example, a magnetic quadrupole field. Higher multipole moments may also be present. At the center of the magnetic field, the absolute value of the magnetic field may be zero. The center of the magnetic field may coincide with the geometric center of the permanent magnet device and / or the Paul trap. For example, the center of the magnetic field may be in the plane of symmetry of the permanent magnet device and / or on a predetermined line. The magnetic field may be point-symmetric about its center.

[0022] The magnitude of the magnetic field varies along a given line, meaning that the magnitude of the magnetic field at different locations on the given line is different from one another. The variation in the magnitude of the magnetic field along a given line is also referred to herein as the gradient of the magnetic field along the given line.

[0023] The change in the magnitude of the magnetic field can be monotonic, e.g., strictly monotonic, at least in part. For example, starting from the center of the magnetic field, the change in the magnetic field can be monotonic in both directions along a given line, or strictly monotonic. The direction of the magnetic field can change along a given line, or can remain constant along a given line.

[0024] In at least one embodiment, a quantum computing device includes a permanent magnet device having a plurality of permanently magnetized segments. The quantum computing device is configured to implement a Paul trap for trapping ions along a predetermined line. Each segment has a magnetization direction. The segments are arranged such that the magnetization directions of at least some of the segments differ from one another, thereby establishing a magnetic field that varies in magnitude along the predetermined line.

[0025] Trapped ions provide an excellent quantum system for quantum control and metrology. In the present invention, they are stored in a Paul trap and form at least one ion crystal oriented along a predetermined line. For certain tasks in quantum computing and metrology with trapped ions, individual control over single ions is desirable. When ions are manipulated with RF radiation, this single-ion control cannot be achieved by focusing the radiation because the wavelength typically exceeds the ion separation in the ion crystal by several orders of magnitude. Also, coupling between internal and external quantum states, as quantified by the Lamb-Dicke parameter, cannot be achieved with RF radiation.

[0026] The present invention is based, inter alia, on the idea of ​​using an inhomogeneous magnetic field provided by a permanent magnet device to resolve the degeneracy of the resonance of individual trapped ions. This offers the possibility of individually addressing ions in frequency space by RF radiation. On the other hand, the superposition of the electric potential induced by the Paul trap and the magnetic field of the permanent magnet device makes the equilibrium position of the ions dependent on their respective quantum states. As a result, an effective spin-spin coupling is achieved due to the Coulomb interaction between the trapped ions. This allows for the entanglement of the ions' quantum states.

[0027] In summary, using the described quantum computing device for quantum information processing allows for individual single-qubit rotation with high addressability in frequency space and therefore low crosstalk, and introduces effective coupling between ions, thus enabling multi-qubit gates. This can also be used in conjunction with RF frequencies, where addressing by focusing radiation is not an option due to long wavelengths, but RF fields may offer advantages in terms of miniaturization and integration. According to at least one embodiment, the permanent magnet device includes NdFeB. In particular, the permanent magnet device includes NdFeB N52. Illustratively, each segment includes or consists of NdFeB, in particular NdFeB N52.

[0028] According to at least one embodiment, the segments are arranged in a Halbach arrangement, which is a special arrangement of permanent magnets that enhances the magnetic field on one side of the arrangement and cancels it to near zero on the other side. Specifically, this is achieved by having a spatially rotating pattern of the magnetization directions of the segments.

[0029] Using such a Halbach array, particularly high magnetic fields and magnetic field gradients can be achieved. Halbach arrays are particularly useful because the effective spin-spin coupling and the difference in resonance of adjacent ions depend on the inhomogeneity and magnitude of the magnetic field. In fact, Halbach arrays allow for large gradients even when the distance between any surface (including the trapping electrodes and magnet surfaces) and the trapped ions should be large, which is desirable for high-fidelity gates with trapped ions.

[0030] According to at least one embodiment, the permanent magnet device surrounds the Paul trap. That is, the Paul trap is a separate device from the permanent magnet device. In particular, the segments of the permanent magnet device are distinct from the electrodes of the Paul trap. For example, the permanent magnet device has a ring shape or a polygonal contour or perimeter shape, respectively. Thus, the Paul trap can be surrounded by a ring-shaped or polygonal contour-shaped permanent magnet device. The permanent magnet device can then increase the magnetic field inside the ring or contour and cancel out the magnetic field outside the ring or contour to near zero.

[0031] In accordance with at least one embodiment, at least some of the electrodes of the Paul trap are formed by segments of a permanent magnet device, for example, the end cap electrodes are formed by segments of a permanent magnet device.

[0032] According to at least one embodiment, the Paul trap is a linear Paul trap for trapping ions along a predetermined line or axis, respectively. The predetermined line is thus a predetermined line or a defined axis, respectively. Alternatively, the Paul trap may be a circular Paul trap.

[0033] According to at least one embodiment, the quantum computing device further includes a yoke structure for increasing the magnetic field and / or the change in magnetic field magnitude along a predetermined line established by the permanent magnet device. The yoke structure is positioned to increase the magnetic field or magnetic field gradient, particularly in the region of the trapped ions, i.e., along the predetermined line. For example, the yoke structure may include or consist of a soft magnetic material. It may have a coercivity of at most 1000 A / m, or at most 100 A / m. The soft magnetic material may be a ferromagnetic material configured to be magnetized by the magnetic field established by the permanent magnet device. The soft magnetic material may have a relative magnetic permeability of at least 300, or at least 1000, or at least 10,000. Illustratively, the soft magnetic material has a relative magnetic permeability of about 12,000. The saturation magnetic flux density of the soft magnetic material may be at least 0.5 T, or at least 2 T. For example, the soft magnetic material includes at least one of iron-cobalt, vanadium, manganese, niobium, silicon, and carbon.

[0034] The yoke structure may extend along or parallel to a predetermined line. For example, the yoke structure may include two portions spaced apart from each other in a direction parallel to the predetermined line. Each of the two portions may be elongated and may extend, for example, along or parallel to the predetermined line. That is, the elongated portion may be oriented parallel to the predetermined line. A portion of the yoke structure may intersect the predetermined line.

[0035] The steepness of the magnetic gradient can be further enhanced by using a yoke structure to concentrate the magnetic flux, for example, located in a region where the magnetic field magnitude of the permanent magnet device is already small and concentrating the field in a small cross-section of the yoke structure without exceeding the saturation magnetization of the yoke structure, thus substantially boosting the achievable gradient magnitude and enabling lower crosstalk, stronger coupling, and faster quantum gates.

[0036] According to at least one embodiment, the yoke structure is at least partially formed by components of the quantum computing device that constitute the end cap electrodes of the Paul trap (hereinafter simply referred to as Paul trap end cap electrodes). The end cap electrodes, whether part of the yoke structure or not, are formed, for example, as elongated elements extending parallel to or along a predetermined line. The end cap electrodes may each have a cylindrical main body. Furthermore, each end cap electrode may have a tapered portion, for example, a cone-shaped portion. The tapered portions taper toward each other or toward the trapped ions, respectively.

[0037] For example, each of the end cap electrodes may form part of a yoke structure, and the end cap electrodes may intersect a predetermined line.

[0038] Further electrodes of the Paul trap may also be part of the yoke structure, i.e., at least some of the electrodes of the Paul trap may include or consist of a soft magnetic material to increase the magnetic field or magnetic field gradient established by the permanent magnet device.

[0039] According to at least one embodiment, the yoke structure is disposed between the end cap electrodes of the Paul trap, e.g., portions of the yoke structure are disposed between the end cap electrodes in a direction parallel to the predetermined line.

[0040] In accordance with at least one embodiment, the yoke structure includes or consists of an iron-cobalt alloy, which may include vanadium, for example, in a concentration of at least 1.5% and at most 3%.

[0041] In accordance with at least one embodiment, the quantum computing device includes a vacuum chamber. During operation, ions are trapped within the vacuum chamber. The Paul trap or its electrodes may also be disposed within the vacuum chamber. The vacuum chamber may be an ultra-high vacuum chamber, an extremely high vacuum chamber, and / or a cryostat.

[0042] According to at least one embodiment, the permanent magnet device is located outside the vacuum chamber. This can be advantageous because creating an ultra-high vacuum (UHV) can include steps such as baking, which may be incompatible with many magnetic materials, especially those with low Curie temperatures. Even when the permanent magnet device is located outside the vacuum chamber, it still generates a sufficiently high magnetic field or magnetic field gradient in the ion region. Alternatively, the permanent magnet device can also be located inside the vacuum chamber. An optional yoke structure can be located inside or outside the vacuum chamber to increase the magnetic field (gradient).

[0043] According to at least one embodiment, the permanent magnet device establishes a substantially two-dimensional magnetic field that is primarily concentrated in the magnetic field plane. The center of the magnetic field may be in the magnetic field plane. The symmetry plane of the permanent magnet device is, for example, perpendicular to the magnetic field plane. For example, all segments of the permanent magnet device are positioned in the magnetic field plane.

[0044] Starting from the magnetic field plane and moving in a direction perpendicular to the magnetic field plane, the magnetic field decays, e.g., the average magnitude of the magnetic field decays to approximately zero. The decay length depends on the dimensions of the permanent magnet device, e.g., the inner and / or outer diameter and / or thickness of the segments measured perpendicular to the magnetic field plane. In particular, the decay length is proportional to the inner and / or outer diameter and thickness of the segments.

[0045] For example, the average magnitude of the magnetic field has a full width half maximum (FWHM) in a direction perpendicular to the magnetic field plane of at least 1 μm, or at least 10 μm, and / or at most 10 mm, or at most 500 μm. For example, in this case, the average magnitude of the magnetic field outside the magnetic field plane, e.g., at a distance of 1 mm from the magnetic field plane, is at least one order of magnitude smaller than the average magnitude of the magnetic field in the magnetic field plane. In other words, the magnetic field plane is the main extension plane of the magnetic field magnitude.

[0046] For example, in a segment of a permanent magnet device arranged in the form of a ring, the main extension plane of the ring defining the xy plane, the magnetic flux density corresponding to the magnetic field

number

number

[0047] B R is the remanence of the segment, and R i is the inner diameter of the ring, and R o is the outer diameter of the ring, and x and y are the coordinates within the permanent magnet device. In this case, the magnetic field plane is the xy plane or main extension plane of the ring, respectively.

[0048] According to at least one embodiment, the predetermined line extends parallel to the magnetic field plane, for example, the predetermined line extends in the magnetic field plane.

[0049] In accordance with at least one embodiment, the components of the quantum computing device that make up the RF electrodes of the Paul trap, hereinafter simply referred to as the RF electrodes of the Paul trap, are positioned outside the magnetic field plane. For example, two RF electrodes of the Paul trap are positioned on different sides of the magnetic field plane. Similarly, the DC electrodes of the Paul trap may be positioned outside the magnetic field plane, and, for example, are positioned on different sides of the magnetic field plane.

[0050] According to at least one embodiment, the end cap electrodes of the Paul trap are positioned in the magnetic field plane, i.e., intersect the magnetic field plane. For example, the end cap electrodes are positioned on a predetermined line, i.e., intersect the predetermined line. Alternatively, the end cap electrodes may each be segmented into at least two sub-electrodes, with the two sub-electrodes of each end cap electrode positioned on different sides of the magnetic field plane, e.g., symmetrically with respect to the magnetic field plane.

[0051] For example, a Paul trap includes at least two end cap electrodes and at least four radial electrodes. The end cap electrodes may be arranged on a predetermined line and spaced apart from one another in a direction parallel to the predetermined line. The radial electrodes may be arranged around the predetermined line. The radial electrodes may be blade electrodes. Two of the radial electrodes may be RF electrodes and are supplied with an AC voltage during operation. The other two radial electrodes may be DC electrodes that are at a static potential, e.g., ground, during operation. The RF electrodes may, for example, be diagonally opposite one another.

[0052] Instead of a Paul trap with electrodes arranged on both sides of the magnetic field plane generated by the permanent magnet device, the Paul trap may be a so-called planar Paul trap in which all electrodes are arranged in a common electrode plane and, for example, on one side of the magnetic field plane.

[0053] According to at least one embodiment, the segments of the permanent magnet device are arranged in the magnetic field plane, which means, for example, that each of the segments intersects the magnetic field plane.

[0054] According to at least one embodiment, the Paul trap is configured to trap 171Yb+ ions.

[0055] According to at least one embodiment, the Paul trap is configured such that during operation, the minimum distance between directly adjacent trapped ions is at least 0.1 μm, or at least 1 μm, and / or at most 30 μm, or at most 20 μm. The minimum distance between directly adjacent trapped ions is, for example, 5 μm. The distance between directly adjacent trapped ions can vary along a given line. For example, two different adjacent ion crystals can have a greater distance, for example, at least 50 μm, or at least 100 μm. The distance between ions can be set by setting the potential of the electrodes of the Paul trap.

[0056] According to at least one embodiment, the trapped ions each have σ± transitions of varying magnetic quantum numbers, where the frequency difference between the σ± transitions between directly adjacent trapped ions is at least 50 kHz, or at least 100 kHz, or at least 1 MHz, and / or at most 100 MHz. The frequency difference between the σ+ / - transitions between directly adjacent trapped ions is, for example, between 15 MHz and 50 MHz. The σ+ / - transitions can be excited by left- or right-handed circularly polarized electromagnetic waves.

[0057] According to at least one embodiment, the trapped ions each have a π-transition whose magnetic quantum number remains unchanged, and the frequency difference between the π-transitions between directly adjacent trapped ions is at least 200 Hz, or at least kHz, and / or at most 10 MHz. The frequency difference between the π-transitions between directly adjacent trapped ions is, for example, between 0.001 MHz and 0.5 MHz. Such π-transitions are excited by linearly polarized electromagnetic waves with polarization parallel to the local magnetic field.

[0058] According to at least one embodiment, the edges of the segments of the permanent magnet device that are arranged in opposite regions and that face each other have a minimum distance from each other of at least 10 μm, or at least 0.01 cm, and / or at most 100 cm. In this context, opposite means, for example, opposite with respect to the center of gravity of the permanent magnet device and / or with respect to the center of the magnetic field.

[0059] According to at least one embodiment, each segment has an extent along a corresponding minimum distance of at least 10 μm, or at least 0.01 cm, and / or at most 100 cm. For example, each segment is formed as a ring segment. The extent along the minimum distance is therefore the radial extension of that segment.

[0060] According to at least one embodiment, the remanence of each of the segments of the permanent magnet device is at least 0.5 T and / or at most 5 T.

[0061] According to at least one embodiment, the change in magnetic field along a predetermined line, e.g., at the center of the magnetic field, is at least 0.5 T / m, or at least 50 T / m, or at least 100 T / m, and / or at most 500 T / m, which can be achieved, for example, by a minimum distance between opposing segments and the remanence of the segments, as described above.

[0062] Next, a quantum computer is identified, which includes the quantum computing device described herein, and therefore, all features disclosed for a quantum computing device are also disclosed for a quantum computer, and vice versa.

[0063] Quantum computers are configured to perform quantum computing processes by using quantum computing devices, the trapped ions of which can be particularly well controlled and manipulated using the permanent magnet devices described herein to perform given quantum computations.

[0064] According to at least one embodiment, the quantum computer further comprises a cooling and / or read-out system, e.g., laser-based. The cooling and / or read-out system is configured to cool the ions to prepare them in a low motional state and trap them in their respective ground states. The read-out system is configured to determine the state of each ion. For example, the ions are cooled and / or read-out by impinging a laser beam or scattering photons of a laser beam, respectively. [Brief explanation of the drawings]

[0065] Hereinafter, the quantum computer device and quantum computer will be described in more detail based on exemplary embodiments with reference to the drawings. The accompanying drawings are included to provide a further understanding. In the drawings, elements of the same structure and / or function may be referred to by the same reference numerals. It should be understood 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 different figures correspond to each other in terms of their functionality, the description will not be repeated for each of the following figures. For clarity, elements may not appear with corresponding reference numerals in all figures. [Figure 1] FIG. 1 illustrates an exemplary embodiment of a quantum computing device. [Figure 2] FIG. 2 shows a detailed view of an exemplary embodiment of a Paul trap. [Figure 3] FIG. 3 shows a detailed view of an exemplary embodiment of a Paul trap in a different view. [Figure 4] FIG. 4 shows a further exemplary embodiment of a Paul trap. [Figure 5] FIG. 5 illustrates an exemplary embodiment of a quantum computing device. [Figure 6] FIG. 6 illustrates different exemplary embodiments of a quantum computing device. [Figure 7] FIG. 7 illustrates an exemplary embodiment of a quantum computer. DETAILED DESCRIPTION OF THE INVENTION

[0066] FIG. 1 illustrates a first exemplary embodiment of a quantum computing device 1. The quantum computing device 1 includes a permanent magnet arrangement 2. The permanent magnet arrangement 2 includes 16 permanently magnetized segments 3. The segments 3 surround Paul traps 100. The Paul traps 100 are each configured to trap a plurality of ions 6 along a predetermined line 7, i.e., a trapping line 7. In this exemplary embodiment, the Paul traps 100 are linear Paul traps for trapping ions 6 along the line 7. The line 7 defines the x-axis.

[0067] The permanent magnet device 2 has the shape of a ring, and the Paul trap 100 is located in the center of the ring. The thickness of each segment 3 is, for example, approximately 100 μm. The ring extends in the xy plane. Each segment 3 has the shape of a ring segment. The minimum distance between two opposing segments 3, i.e., the inner ring diameter 2Ri, is approximately 10 cm. Furthermore, each segment 3 has an extent along the corresponding minimum distance of approximately 20 cm. The outer diameter 2Ro of the permanent magnet device 2 is therefore approximately 50 cm. The edges of the mutually opposing, directly adjacent segments 3 have a mutual distance of, for example, approximately 10 mm.

[0068] Furthermore, each segment 3 has a magnetization direction 4, which is depicted as an arrow in the segment 3 in FIG. 1 . The segments 3 are each formed of, for example, NdFeB N52. The magnetization directions 4 of the segments 3 located in opposite regions relative to the center of the permanent magnet device 2 are oriented in opposite directions. A predetermined line 7 extends through the center of the permanent magnet device 2 and intersects two opposing segments 3. Here, the magnetization directions 4 of these two segments 3 are parallel to the predetermined line 7.

[0069] Each magnetization direction 4 forms an angle with a given line 7. All of these angles are formed differently from one another. For example, the angles of two directly adjacent segments 3 differ from one another by 67.5°. The magnetization directions 4 are all in the xy plane.

[0070] The permanent magnet device of Figure 1 is a Halbach arrangement that establishes a quadrupole field with a field magnitude that varies along a predetermined line 7. In other words, the field has a field gradient along the predetermined line 7. For example, each of the trapped ions positioned along the predetermined line sees a different magnetic field.

[0071] Using the permanent magnet device shown in Figure 1, the ideal magnetic flux density is

number

number

[0072] The remanence B of each segment 3 R is, for example, 1 T. As can be extracted from this ideal magnetic flux density, the magnetic field is a two-dimensional magnetic field, mainly concentrated in the xy plane, which constitutes the magnetic field surface.

[0073] Figures 2 and 3 show detailed views of the Paul trap 100 of Figure 1. Figure 2 shows the xy plane, while Figure 3 shows a plan view of the yz plane, i.e., a view along the x axis.

[0074] The Paul trap 100 includes two end cap electrodes 40 and four radial electrodes 20, 30. The two radial electrodes 20, which are diagonally opposed on different sides of the magnetic field plane BP (xy plane), are RF electrodes to which an AC voltage is supplied during operation. The other two diagonally opposed radial electrodes 30 are DC electrodes operated at a constant potential, e.g., ground.

[0075] The end cap electrodes 40 operate at an electrostatic potential. The potential V(x,0,0) along the x-axis generated by Paul trap 100 is shown in FIG.

[0076] 3 shows the potentials on the y-axis and z-axis generated by Paul trap 100. At time t1, the potential V(0,y,0,t1) along the y-axis is attractive. At this time t1, the potential V(0,0,z,t1) along the z-axis is repulsive or defocusing, respectively. At time t2, i.e., after half an RF cycle, the potential V(0,0,z,t2) along the z-axis is attractive. Along the y-axis, the potential V(0,y,0,t2) is repulsive or defocusing, respectively. These alternating potentials in the y and z directions create an attractive pseudo-potential such that ions 6 are ultimately trapped radially.

[0077] Overall, the potentials in different directions form a potential well W that traps ions 6. Ions 6 in the potential well W are arranged in a linear ion crystal 6a, as shown in FIG.

[0078] 2 and 3 also show the magnitude of the electric field, i.e., the magnetic flux density |B|, established by the permanent magnet device 2. As can be seen, the magnitude of the magnetic flux density B varies in the x and y directions, i.e., along the magnetic field plane BP. At the center of the magnetic field, the magnetic field magnitude is zero.

[0079] The ions 6 shown in FIGS. 1 to 3 are, for example, 171Yb+ ions. The distance d between directly adjacent trapped ions is approximately 3 μm. The degeneracy of the excited quantum states is resolved by the magnetic field generated by the permanent magnet device 2. The energy of the π-transition from the ground quantum state to the excited m=0 quantum state weakly depends on the magnetic field experienced by the ions. Similarly, the energy of the σ±-transition from the ground quantum state to the excited m=±1 quantum state depends on the magnetic field experienced by the ions. Since the magnitude of the magnetic field depends on the position of the ions 6 along the predetermined line 7, the energy of the transition depends on the position along the predetermined line 7. For example, for each of two adjacent ions 6, the frequency difference between the σ+ / − transitions is at least 1 MHz and at most 100 MHz. Furthermore, for each of two adjacent ions 6, the frequency difference between the π-transitions is at least 0.001 MHz and at most 10 MHz.

[0080] Furthermore, due to the geometry of the potential well along the predetermined line 7 and the magnetic field provided by the permanent magnet arrangement 2, the equilibrium positions of the ions 6 depend on their respective quantum states. Thus, an effective spin-spin coupling between the ions 6 due to Coulomb interactions is achieved, which allows the quantum states of the ions 6 to be entangled.

[0081] In particular, the coupling strength between two directly adjacent trapped ions 6 depends on the square of the magnetic field gradient. Furthermore, the relaxation time, in particular the spin relaxation time T2, is inversely proportional to the decoherence rate. Therefore, to provide multi-qubit gates, the magnetic field gradient must be relatively high to provide a large number of gates in a given time. This can be achieved by the permanent magnet devices described herein.

[0082] 4 shows a further exemplary embodiment of a Paul trap 100 in which end cap electrodes 40 are part of a yoke structure 60. The yoke structure 60 is configured to increase the magnetic field along a predetermined line 7 in the region where ions 6 are trapped. Each of the end cap electrodes 40 forms an elongated portion of the yoke structure 60. For example, the end cap electrodes 40 may be made from a soft magnetic material, such as Hiperco®.

[0083] 5 illustrates a further exemplary embodiment of a quantum computing device 1 or a Paul trap 100, respectively. In contrast to the previous exemplary embodiments, the permanent magnet device 2 is not separate from the Paul trap 100, but instead, the Paul trap 100 itself forms the permanent magnet device 2. This is achieved by different electrodes 20, 30, 40 forming segments 3 of the permanent magnet device 2. Each electrode 20, 30, 40 is made of a ferromagnetic material and has a magnetization direction 4. The magnetization directions 4 of at least some of the electrodes 20, 30, 40 are different from one another, thereby establishing a magnetic field having a field magnitude that varies along a predetermined line 7.

[0084] 6, the permanent magnet device 2 surrounds the Paul trap 100 in the form of a polygonal outline. Each segment 3 has a square shape. Adjacent segments 3 are rotated relative to each other.

[0085] 6, the Paul trap 100 is disposed in a chamber 10, and the chamber 10 is surrounded by a permanent magnet device 2. The chamber 10 is, for example, an ultra-high vacuum chamber.

[0086] One exemplary embodiment of a quantum computer 8 is shown in Figure 7. The quantum computer 8 comprises a quantum computing device 1 according to one of the exemplary embodiments described herein. A Paul trap 100 is connected to components external to the quantum computer 8 through a chamber 10 by a number of connections 11. For example, connections 11 connect the Paul trap 100 to external control electronics 12 and a classical computer 13.

[0087] The quantum computing device 1 is configured to trap ions, manipulate the trapped ions, and perform measurements. To this end, the quantum computing device 1 may include, in addition to the permanent magnet device 2 and any components of the Paul trap 100, a light guide and / or internal electronics, including electronic devices. The electronic devices may include circuitry, integrated electronics, a power supply, and / or detectors, such as photon detectors and / or charge detectors, controllers, etc. Illustratively, the internal electronics are provided for preprocessing. For example, these components enable measurement of the respective states of the ions and enable gating operations on the ions. Thus, the quantum computing device 1 is configured to trap ions and perform operations and measurements on the trapped ions.

[0088] The Paul trap 100 is mounted in a chamber 10, which may be an ultra-high vacuum chamber, an extremely high vacuum chamber, and / or a cryostat. The permanent magnet device 2 may be located outside the chamber 10. In this case, the permanent magnet device 2 surrounds the chamber 10. Alternatively, the permanent magnet device 2 may be located inside the chamber 10 (not shown here).

[0089] Quantum computing device 1, in particular Paul trap 100, is connected to external electronics 12 via connection 11. External electronics 12 may be located at least partially inside chamber 10 and partially outside chamber 10. Furthermore, external electronics 12 is connected to a classical computer 13.

[0090] The external electronics 12 may include, for example, an analog-to-digital converter and a signal generator, such as a radio frequency generator, a microwave signal generator, a low frequency signal generator, and / or a DC signal generator. Additionally, the external electronics 12 may include transistor-transistor logic (TTL).

[0091] Additionally, the external electronics 12 may further comprise at least one laser-based system configured to cool the trapped ions, and the laser-based system may further be configured to excite and / or read out particular states of the trapped ions.

[0092] Classical computer 13 is configured to provide and receive, for example, digital signals that correspond to control signals used to operate on qubits / ions as well as measurement signals that correspond to the states of the qubits.

[0093] External electronics 12 is configured, among other things, to convert digital signals to analog signals and vice versa, and thus to provide converted analog signals for manipulating ions (qubits) to quantum computing device 1. Furthermore, external electronics 12 is configured to process measured analog signals from quantum computing device 1 to classical computer 13, or to directly initiate any response signal generated by control electronics 12.

[0094] Classical computer 13 is illustratively configured with a particular algorithm, i.e., a predefined quantum computation that solves a particular problem. Classical computer 13 is then configured to translate compiled code corresponding to the algorithm into commands for quantum computing device 1. The commands are then transmitted to quantum computing device 1 via external control electronics 12. Additionally, classical computer 13 is configured to receive measured results of the particular algorithm.

[0095] For example, all elements of the quantum computer 8, in particular all electronic elements of the quantum computer 8, are synchronized, for example, by an atomic clock reference.

[0096] The present invention is not limited to the exemplary embodiments described therein, but rather encompasses any novel feature and any combination of features, and in particular includes any combination of features in the claims, even if that feature or combination itself is not explicitly set forth in the claims or exemplary embodiments. [Explanation of symbols]

[0097] 1. Quantum computing device 2. Permanent magnet device 3 segments 4 Magnetization direction 6. Ion 6a Ion Crystal 7 Default Lines 8. Quantum Computers 10 Chambers 11 Connection 12 Control electronic devices 13 Classical Computers 20 RF electrodes 30 DC electrode 40 End cap electrode 60 yoke structure 100 Pole Trap d distance Ri inner radius Ro outer radius BP magnetic field W potential well V(x,y,z) potential B(x,y,z) magnetic flux density

Claims

1. A quantum computing device a permanent magnet device including a plurality of permanently magnetized segments; the quantum computing device is configured to implement a Paul trap for trapping ions along a predetermined line; Each segment has a magnetization direction, the segments are arranged such that the magnetization directions of at least some of the segments differ from one another and such that a magnetic field is established that varies in magnitude along the predetermined line; Quantum computing device.

2. The segments are arranged in a Halbach array.

10. The quantum computing device of claim 1.

3. the permanent magnet device surrounds the Paul trap in the form of a ring or in the form of a polygonal profile; 3. The quantum computing device of claim 1 or 2.

4. at least some of the electrodes of the Paul trap are formed by segments of the permanent magnet device; 4. A quantum computing device according to any one of claims 1 to 3.

5. the Paul trap is a linear Paul trap for trapping ions along a predetermined line; 5. A quantum computing device according to any one of claims 1 to 4.

6. The quantum computing device further comprises: a yoke structure for increasing the magnetic field and / or the change in the magnitude of the magnetic field along the predetermined line established by the permanent magnet arrangement; 6. The quantum computing device of claim 1, comprising:

7. the yoke structure is at least partially formed by an end cap electrode of the Paul trap.

7. The quantum computing device of claim 6.

8. the yoke structure includes a soft magnetic material; 8. A quantum computing device according to claim 6 or 7.

9. The quantum computing device further comprises: a vacuum chamber in which the ions are trapped during operation; the permanent magnet device is disposed outside the vacuum chamber; 9. A quantum computing device according to any one of claims 1 to 8.

10. the permanent magnet device establishes a substantially two-dimensional magnetic field that is primarily concentrated in a magnetic field plane; the predetermined line extends parallel to the magnetic field plane; 10. A quantum computing device according to any one of claims 1 to 9.

11. the RF electrodes of the Paul trap are disposed outside the magnetic field plane and on different sides of the magnetic field plane; 11. The quantum computing device of claim 10.

12. end cap electrodes of the Paul trap are disposed on the magnetic field plane; 12. A quantum computing device according to claim 10 or 11.

13. The segments are arranged on the magnetic field plane.

13. A quantum computing device according to any one of claims 10 to 12.

14. the Paul trap is configured to trap Yb ions during operation; the minimum distance between directly adjacent trapped ions is at least 0.1 μm and at most 30 μm; the trapped ions each have σ± transitions of varying magnetic quantum numbers, the frequency difference between the σ± transitions between directly adjacent trapped ions being at least 100 kHz and at most 100 MHz; and / or the trapped ions each have a π transition that does not change magnetic quantum number, and the frequency difference between π transitions between directly adjacent trapped ions is at least 1 kHz and at most 10 MHz; 14. A quantum computing device according to any one of claims 1 to 13.

15. the edges of the segments that are arranged in opposite regions and that face each other have a minimum distance from each other of at least 10 μm and at most 100 cm; each segment having an extent along a corresponding minimum distance of at least 10 μm and at most 100 cm; 14. A quantum computing device according to any one of claims 1 to 13.

16. 16. A quantum computing device according to any one of claims 1 to 15, configured to perform quantum computations. Quantum computer.

17. The quantum computer further comprises: a laser-based cooling and / or readout system; 17. The quantum computer of claim 16.

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