Ion trap, quantum computer array and method for operating an ion trap and / or a quantum computer array

Abstract

An ion trap (1) for a quantum computer arrangement (10) comprises an arrangement (9) of permanent magnets (2, 3) that generate a magnetic field on an ion trap axis (T) and a magnetic coil (4) for modifying a gradient and / or field strength of the magnetic field at a position along the ion trap axis (T) at least during one stage of a quantum computer algorithm.

Description

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

[0002] A typical repeated iteration of a trapped ion quantum algorithm begins with initialization, which includes cooling and optical pumping, continues with gate sequence execution, and ends with state detection. While a large magnetic field gradient is advantageous for the gate sequence, initialization and state detection require little or no gradient.

[0003] To generate the required field gradient, a permanent magnet can be used, which has the advantage of low power loss. Publication DE 102022124674 B4 discloses an ion trap for a quantum computer array using a Halbach array of permanent magnets. Alternatively, time-dependent magnetic fields can be generated using magnetic coils, but at the cost of significant power loss. This is particularly critical when used in cryogenic setups.

[0004] One task to be solved is the provision of an improved ion trap for a quantum computer setup.

[0005] This problem is solved by the subject matter of independent claim 1. Advantageous embodiments, implementations, and further developments are the subject matter of the respective dependent claims.

[0006] According to a first aspect, an ion trap for a quantum computer setup comprises an array of permanent magnets that generate a magnetic field along an ion trap axis. The ion trap further comprises a magnetic coil for changing the gradient and / or field strength of the magnetic field at a position along the ion trap axis, at least during one phase of a quantum computer algorithm.

[0007] The permanent magnet arrangement can generate a base gradient and / or a base magnetic field strength. Generating the magnetic field with permanent magnets has the advantage of lower power loss compared to generation with coils. The gradient and / or the magnetic field can be modified by the magnetic coil. For example, in phases where a gradient and / or magnetic field strength is not required or is detrimental, the gradient and / or magnetic field strength can be reduced by the magnetic coil.

[0008] The arrangement of permanent magnets can include a first permanent magnet and a second permanent magnet. The magnetization directions can be aligned along a line connecting the magnets. This line can coincide with the axis of the ion trap. In one embodiment, the corresponding poles of the permanent magnets point towards each other. In this case, the permanent magnets can be arranged symmetrically about a plane perpendicular to the axis. In such an arrangement, a large magnetic gradient can be generated along the axis.

[0009] The arrangement of permanent magnets can be a Halbach array. This arrangement can generate a quadrupole field. A Halbach array is a special arrangement of permanent magnets that strengthens the magnetic field on one side of the array and almost cancels it out on the other. This can be achieved by a spatially rotating pattern of the magnetization directions of the permanent magnets. The permanent magnets can be segments of the Halbach array.

[0010] In another embodiment, the opposite poles of the permanent magnets point towards each other. In this case, the second permanent magnet can be displaced relative to the first permanent magnet along the ion trap axis. The permanent magnet arrangement generates a uniform field along the ion trap axis.

[0011] A homogeneous magnetic field, i.e., a field with little or no gradient, can be useful for initialization (e.g., Doppler cooling, sub-Doppler cooling, optical pumping) and for detection.

[0012] In some embodiments, the magnetic coil incorporates an anti-Helmholtz coil. An anti-Helmholtz coil comprises a first coil and a second coil, with the current flowing in opposite directions in the first and second coils. Each coil may, for example, have a single turn. It is also possible for one or both coils to have multiple turns.

[0013] Such a coil can generate a magnetic field along the line connecting the permanent magnets, the field strength of which increases from a central point in opposite directions along the line. This allows a magnetic field gradient generated by the permanent magnet array to be compensated, at least at a central point along the line. It is also possible to compensate for the field gradient in a region along the axis. This region could be the relevant area occupied by the ion register.

[0014] In other embodiments, the magnetic coil is designed as a helical coil. This allows for the generation of a homogeneous field, i.e., a field with parallel field lines and a homogeneous field strength. With such an arrangement, the magnetic field strength can be reduced or set to zero, at least at a central point along the axis. It is also possible to compensate for the field gradient in a region along the axis. This region can be the relevant area occupied by the ion register.

[0015] The magnetic coil is configured, for example, to decrease a gradient and / or field strength during an initialization phase and / or a state detection phase of a quantum computer algorithm. The magnetic coil can also be configured to increase or maintain a gradient and / or field strength of a magnetic field in a gate sequence of the quantum computer algorithm.

[0016] In another example, the magnetic coil is configured to generate a sinusoidally modulated magnetic field gradient. This can enhance the coupling of ions participating in the same mode. It is also possible for the magnetic coil to generate a field to reduce and / or cancel a magnetic field strength and / or gradient, in addition to a sinusoidally modulated gradient. For example, a sinusoidally modulated gradient can be generated during a gate sequence, and a different field during initialization and / or detection.

[0017] The ion trap can have electrodes for capturing one or more ions along the ion trap axis. The ion trap can have first electrodes configured to generate a time-varying electric field and second electrodes configured to generate a static electric field. The one or more ions can be arranged along the trap axis and / or oscillate around it. The one or more ions can intersect the trap axis and / or oscillate around it. For example, the ions are arranged in an ion chain along the trap axis.

[0018] The ion trap axis may coincide with the line connecting the permanent magnets. It is also possible that the ion trap axis does not coincide with the line connecting the permanent magnets.

[0019] According to another aspect, a quantum computer setup is described, which includes the ion trap as described above. The quantum computer setup further includes a device for manipulating the trapped ions. This device could be a laser device.

[0020] According to a further aspect, a method for operating an ion trap and / or a quantum computer arrangement is disclosed. The method can be carried out with the ion trap and / or the quantum computer arrangement as disclosed in the preceding descriptions. The method comprises the steps of generating a current flow through the magnetic coil such that a gradient and / or a field strength of the magnetic field at a position along the ion trap axis is changed, at least during one phase of a quantum computer algorithm.

[0021] The method may include the steps of initializing the quantum algorithm, executing a gate sequence, and performing state detection. In some embodiments, the current flow in the magnetic coil may be such that the magnetic field gradient and / or the magnetic field strength at a position along the ion trap axis is lower during initialization and / or detection than during the gate sequence.

[0022] For example, the current flow can be switched off during a gate sequence, while the current flows through the solenoid during initialization and / or state detection. As another example, the direction of current flow during a gate sequence can be reversed compared to initialization and / or state detection.

[0023] It is also possible that, at least during a gate sequence, the current flow in the magnetic coil is such that a sinusoidally modulated gradient of the magnetic field is generated.

[0024] The present disclosure has several aspects and embodiments. Every feature described in relation to one of the aspects and embodiments is also disclosed here in relation to the other aspects and embodiments, even if the respective feature is not expressly mentioned in this context.

[0025] Further features, refinements, and advantages will become apparent from the following description of the exemplary embodiments in conjunction with the figures. In the figures, elements of the same structure and / or functionality can be designated by the same reference numerals. It is understood that the embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale. Fig. Figure 1 shows a schematic representation of an ion trap. Fig. Figure 2 shows an embodiment of the ion trap made of Fig. 1 with electrodes in a schematic view, Fig. Figure 3 shows an embodiment of a quantum computer arrangement, Fig. Figure 4 shows another embodiment of an ion trap in a schematic view. Fig. Figure 5 shows another embodiment of an ion trap in a schematic view. Fig. Figure 6 shows another embodiment of an ion trap in a schematic view. Fig. Figure 7 shows an embodiment of a quantum computer method in a schematic process diagram. Fig. Figure 8 shows an embodiment of a quantum computer method in a schematic diagram of the current flow through a magnetic coil over time. Fig. Figure 9 shows an ion trap with a Halbach arrangement.

[0026] Fig. Figure 1 shows an embodiment of an ion trap 1 comprising a permanent magnet arrangement 9. The permanent magnet arrangement 9 includes a first permanent magnet 2 and a second permanent magnet 3. The permanent magnets 2 and 3 generate a magnetic field with a field gradient along a line connecting the permanent magnets 2 and 3. The axis A can coincide with the ion trap axis T, along which the ions are trapped.

[0027] In the illustrated embodiment, the permanent magnets 2, 3 are arranged such that like poles face each other. For example, the like poles facing each other can be the south poles S.

[0028] The permanent magnet arrangement 9 could be a Halbach arrangement. An example of a Halbach arrangement for the ion trap 1 is shown in Fig. 9 shown. The Halbach arrangement shows the in Fig. 1. Permanent magnets 2, 3 and others shown, in Fig. 1 additional permanent magnets not shown, which are present when using a Halbach arrangement.

[0029] The permanent magnets 2 and 3 generate a permanent magnetic field gradient along the connecting line A with little or no power loss. Such a magnetic gradient is advantageous for certain sequences of a quantum computer operation. However, for other sequences, a large magnetic gradient can be detrimental. In particular, a large gradient can create ideal conditions for executing a gate sequence. The field strength varies for different positions along the trap axis T. Consequently, the resonance frequency of each ion at the trap axis T, upon which the magnetic field gradient acts, can be unique for each trapped ion due to the magnetic field gradient.

[0030] For certain phases, such as initialization and state detection, a low or zero gradient is advantageous. To cancel or reduce the magnetic field gradient along the ion trap axis T during specific phases of a quantum algorithm, the ion trap 1 incorporates a magnetic coil 4 to generate a superimposed gradient. Specifically, the magnetic field gradient can be reduced or canceled during initialization and state detection, and may remain unchanged during a gate sequence. This simplifies cooling and detection.

[0031] The magnetic coil 4 is configured as an anti-Helmholtz coil, comprising a first coil 5 and a second coil 6. The current in the first coil 5 and the second coil 6 flows in opposite directions around the common axis C of the coils 5 and 6. It is also possible for the first coil 5 and / or the second coil 6 to have multiple turns. The coils 5 and 6 generate a superimposed magnetic field that is zero at the midpoint between the coils 5 and 6 and increases in both directions along the coil axis. The coil axis C coincides with the line connecting the permanent magnets 2 and 3 and with the trapping axis T. This allows the magnetic field gradient along the trapping axis T to be reduced or eliminated. Alternatively, the magnetic field gradient can be increased by reversing the current direction or by modulation with an alternating current.

[0032] Various structures are possible for the ion trap 1. For example, the magnetic coil 4 and / or the permanent magnets 2, 3 can be implemented as planar structures in ion trap chips.

[0033] Fig. Figure 2 shows an ion trap 1 which includes the permanent magnet arrangement 9, the magnet coil 4 and electrodes 7, 8 for trapping the ions.

[0034] Electrodes 7 and 8 feature first electrodes 7 in the form of blade electrodes for radial confinement and second electrodes 8 for axial confinement. The first electrodes 7 can generate a time-varying electric field, and the second electrodes 8 a static electric field. This traps one or more ions along the trap axis T. For example, ion 11, and in particular each of the ions, may intersect the trap axis T, and / or there may be an oscillation along the trap axis T and another oscillation perpendicular to the trap axis T. The ion trap 1 may be a Paul trap.

[0035] Fig. Figure 3 shows a schematic view of a quantum computer setup 10 comprising an ion trap 1, a device 12 for manipulating the trapped ions, and a detector 13. The device 12 can be a laser device, and the detector 13 can be a single-photon detector. The ion trap 1 can be the ion trap 1 of the Fig. 1 and Fig. 2. The device 12 is configured to irradiate the trapped ions with laser light in order to manipulate the ions in a gate sequence. The detector 13 serves to detect the state of the ions.

[0036] Fig. Figure 4 shows another embodiment of an ion trap 1, which has an arrangement 9 of permanent magnets 2, 3 and a magnetic coil 4. Here too, the permanent magnets 2, 3 are arranged along a connecting line A, which can be the trap axis T.

[0037] In this case, the opposite poles of permanent magnets 2 and 3 point towards each other. The magnetic coil 4 is designed as a helical coil. When current flows through the magnetic coil 4, an offset field is generated along the connecting line A. This can reduce or eliminate the electric field along the connecting line A. Alternatively, the electric field can be increased by reversing the current direction or by modulating it with an alternating current.

[0038] The Fig. 5 and Fig. Figure 6 shows further embodiments of ion traps 1. In these embodiments, the magnetic coil 4 generates an offset field for an ion 11 that is displaced from the connecting line A of the permanent magnet arrangement 9. The magnetic field generated by the magnetic coil 4 serves to compensate for the displacement and cancels out the magnetic field of the permanent magnet arrangement 9 at the location of the ion 11 and / or in a region along the trap axis T.

[0039] In Fig. 5 The ion 11 is displaced along the axial direction of the connecting line A. The magnet coil 4 is designed as a helical coil and generates a magnetic field perpendicular to the connecting line A of the permanent magnet arrangement 9 along the trap axis T.

[0040] In Fig. 6 the ion 11 is displaced perpendicular to the connecting line A. The magnetic coil 4 is designed as a helical coil and generates a magnetic field perpendicular to the connecting line A of the permanent magnet arrangement 9 along the trap axis T. The winding axis C of the magnetic coil 4 is perpendicular to the trap axis T. In the embodiments of the Fig. 1, Fig. 2 and Fig. 4 is the winding axis C of the magnet coil 4 parallel to the trap axis T.

[0041] The embodiments of Fig. 5 and Fig. 6 can be modified so that two magnetic coils are provided in the same ion trap 1, with one magnetic coil 4 as in Fig. 5 and a second magnetic coil 4 as in Fig. 6 is arranged. Additionally or alternatively, in the embodiments of the Fig. 4 and Fig. 6. A further magnetic coil may be provided in a third direction. In particular, the further magnetic coil may have an axis C pointing in the direction of the image plane.

[0042] The magnetic coils 4 of the Fig. 5 and Fig. Six qubits can be configured to generate a magnetic field during a gate sequence. The magnetic field can only be generated during one gate sequence. Alternatively, the magnetic field can also be generated only during two qubit-gate sequences.

[0043] Fig. Figure 7 shows the steps of a quantum algorithm in a schematic representation.

[0044] A run of the quantum algorithm begins with initialization in step A. During the initialization phase, the trapped ions are cooled and optically pumped. In a subsequent step B, a gate sequence is performed in which the trapped ions are manipulated, for example, by laser beams. In the following step C, the state of the trapped ions is detected, for example, by a detector.

[0045] The quantum algorithm can be carried out with the ion trap 1 and the quantum computer arrangement 10 of the preceding figures, in particular with a permanent magnet arrangement 9 and a magnetic coil 4.

[0046] Fig. Figure 8 shows a schematic diagram of the current flow through a magnetic coil 4 in the quantum computer steps of Fig. 7 according to an embodiment of a quantum computer method.

[0047] At time t0, the initialization begins and the current I c= I init , with |I init A current of >0 A flows through the magnetic coil 4, thus canceling or reducing the magnetic field gradient of the permanent magnet arrangement 9 along the ion trap axis. At time t1, a gate sequence begins and the current through the magnetic coil 4 is switched off (I gate =0 A). At time t2, state detection begins and the current I c = I detect , with |I detect The current I flows through the magnetic coil 4 again, thus canceling or reducing the magnetic field gradient of the permanent magnet arrangement 9 along the ion trap axis. init , I detect This can vary during initialization and state detection.

[0048] In comparison to an ion trap where a magnetic field gradient is generated only by coils instead of permanent magnets 2, 3, the power loss averaged over a repetition is reduced by a factor (t init +t detect) / (t init +t gate +t detect ) reduced. Here, t denotes init (=t1-t0) the time for initialization, t gate = (t2-t1) is the time for executing the gate sequence and t detect (=t3-t2) is the time for state detection. The reduction in power loss is particularly large in the case of t gate >> t init , t detect .

[0049] It is also possible that during the gate sequence the current flowing through the magnetic coil 4 is reversed compared to the initialization (I gate = - I init ). In this case, the gradient during the gate sequence is increased by a factor of two, so that the gate sequence can be accelerated by a factor of four.

[0050] It is also possible that, in addition to the gradient generated by the permanent magnet assembly 9, the magnetic coil 4 generates a sinusoidally modulated gradient. This gradient is generated by current modulation in the magnetic coil 4, which can enhance the coupling of ions participating in the same mode while saving a large portion of the power loss that would occur with a larger, constant gradient. Due to the gradient generated by the magnetic coil 4, the gradient generated by the permanent magnet assembly 9 can be smaller. This reduces the power loss during initialization and detection. Furthermore, it is possible that the magnetic coil 4 provides a sinusoidally modulated gradient and a field to reduce or cancel the gradient and / or the field strength.

[0051] The magnetic coils 4 can be configured to generate a magnetic field during a gate sequence. The magnetic field can only be generated during a single gate sequence. Alternatively, the magnetic field can also be generated only during two qubit gate sequences.

[0052] Fig. Figure 9 shows an ion trap 1 with an arrangement 9 of segments 14 of permanent magnets in the form of a Halbach arrangement. The arrangement 9 and further details of the ion trap 1 can be provided in any of the embodiments disclosed above. The permanent magnets 2, 3 of the aforementioned embodiments are, in this case, segments 14 of the Halbach arrangement. The ion trap 1 has a planar Paul trap 16. The planar Paul trap 16 is configured to capture an ionic crystal with a plurality of ions arranged along a capture axis T. The Paul trap 16 is arranged in a chamber 17 surrounded by the permanent magnet arrangement 9. The permanent magnet arrangement 9 is located between an inner radius R i and arranged with an outer radius R0. The ion trap 1 can also be non-planar, as for example in Fig. 2 shown.

[0053] The arrangement 9 has the form of a ring in the center of which the ions are trapped. The magnetization directions 15 of the segments 14, which are arranged in opposite regions with respect to a center of the permanent magnet arrangement 9, are directed in opposite directions. The capture axis T passes through the center of the permanent magnet arrangement 9 and intersects with two opposite segments 14, which correspond to the permanent magnets 2, 3 of the embodiments described below. The magnetization directions 15 of these two segments 14 run parallel to the capture axis T.

[0054] The Halbach arrangement generates a magnetic quadrupole field, the magnitude of which changes along the capture axis T. As a result, each of the trapped ions arranged along the capture axis T experiences a different magnetic field. Reference sign 1 ion trap 2 first permanent magnet 3 second permanent magnet 4 magnetic coil 5 first coil 6 second coil 7 first electrodes 8 second electrodes 9 Permanent magnet arrangement 11 Ion 10 quantum computer array 12 Device 13 Detector 14 segments 15 Magnetization direction 16 Paul Trap A connecting line of the permanent magnets T ion trap axis C Winding axis of the magnet coil R i inner radius R0 outer radius I c Current through magnetic coil I init Power during initialization I gate Current during gate sequence I detect Current during detection t0, t1, t2, t3 Time points in the quantum algorithm QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 102022124674 B4

[0003]

Claims

[1] Ion trap (1) for a quantum computer arrangement (10), comprising - an arrangement (9) of permanent magnets (2, 3) that generate a magnetic field on an ion trap axis (T), and - a magnetic coil (4) for changing a gradient and / or field strength of the magnetic field at a position along the ion trap axis (T) at least during a phase of a quantum computer algorithm. [2] Ion trap (1) according to claim 1, wherein the magnetic coil (4) is configured to reduce a gradient and / or a field strength in an initialization phase and / or a state detection phase of a quantum computer algorithm. [3] Ion trap (1) according to one of claims 1 and 2, wherein the magnetic coil (4) is configured to amplify or maintain a gradient and / or field strength of a magnetic field in a gate sequence of a quantum computer algorithm. [4] Ion trap (1) according to one of the preceding claims, wherein the arrangement (9) of permanent magnets (2, 3) comprises a first permanent magnet (2) and a second permanent magnet (3) with magnetizations (15) in the direction of a connecting line of the magnets (3). [5] Ion trap (1) according to one of the preceding claims, wherein the magnetic coil (4) has an anti-Helmholtz coil. [6] Ion trap (1) according to one of the preceding claims, wherein the magnet coil (4) comprises a helical coil. [7] Ion trap (1) according to one of the preceding claims, wherein the magnetic coil (4) is configured to generate a magnetic field with field lines parallel to an ion trap axis (T). [8] Ion trap (1) according to any one of claims 1 to 6, wherein the magnetic coil (4) is configured to generate a magnetic field with field lines perpendicular to an ion trap axis (T). [9] Ion trap (1) according to one of the preceding claims, comprising several magnetic coils (4) for generating magnetic field lines in different directions relative to an ion trap axis (T). [10] Quantum computer arrangement (10), comprising - the ion trap (1) according to one of the preceding claims, and - a device (12) for manipulating trapped ions (11) . [11] Method for operating the ion trap (1) and / or the quantum computer arrangement (10) according to any one of the preceding claims, comprising the steps: Generating a current flow through the magnetic coil (4) such that a gradient and / or a field strength of the magnetic field at a position along the ion trap axis (A) is changed at least during one phase of a quantum computer algorithm. [12] Method according to claim 9, showing the steps: A) Initialization of the quantum algorithm, B) Execution of a gate sequence, C) Performing a condition detection, wherein the current flow in the magnetic coil (4) is such that the magnetic field gradient and / or the magnetic field strength at a position along the ion trap axis (T) in step A and / or C is smaller than in step B. [13] Method according to claim 12, wherein in step B the current flow in the magnet coil (4) is switched off. [14] Method according to claim 12, wherein in step B the direction of the current flow in the magnet coil (4) is reversed compared to step A and / or step C. [15] Method according to one of claims 11 to 14, wherein at least in step B a sinusoidally modulated gradient of the magnetic field is generated by the magnetic coil (4).

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