Ion trap, trapped ion quantum computer, and method for generating magnetic field

Abstract

An ion trap is provided that comprises a first current source, a first pair of parallel wires that form a plane and have a space between them, each of the wires connected to the first current source such that current flows in opposite directions along each of the parallel wires, a second current source, and a second pair of parallel wires that are disposed in the plane of the first pair of parallel wires and in the space between the first pair of parallel wires, approximately perpendicular to the first pair of wires, and connected to the second current source such that each of the second pair of parallel wires flows in opposite directions along each of the second pair of parallel wires, At a center point of the first pair of parallel wires and the second pair of parallel wires, a magnetic field generated by a current from the first current source passing through the first pair of parallel wires is in an opposite direction to a magnetic field generated by a current from the second current source passing through the second pair of parallel wires.

Description

[Technical field]

[0001] The present invention relates to improvements in or relating to quantum computing, and in particular to improved magnetic field gradient generation in ion trap quantum computers. [Background technology]

[0002] In general, unlike so-called "classical computing", quantum computing relies on the quantum mechanical properties of particles or matter to produce or modify data. Data can be represented by quantum bits or "qubits", which are two-state quantum mechanical systems. Unlike classical computing, qubits can be in a superposition of quantum states. Another feature of quantum computing is entanglement between qubits, where the state of one particle or atom is influenced by another particle or atom.

[0003] Quantum mechanical qubits can simultaneously encode information as combinations of zeros and ones. Such properties enable many complex numerical applications that have traditionally been difficult with classical computers. Examples include artificial intelligence, image processing and recognition, cryptography, or secure communications.

[0004] Within an ion hyperfine electronic state (Zeeman split state) this can be revealed by the use of magnetic fields and different electronic levels used as different qubit states, and electrons moving between the levels using microwave radiation or lasers.

[0005] Magnetic field gradients are often used to generate multi-qubit gates, as discussed in [1]. Optimally, the magnitude of the magnetic field is nulled around the position of the ion.

[0006] In Non-Patent Document 2, the magnetic gradient is generated using permanent magnets. However, the inability to switch them on and off limits the application of this to large-scale quantum computers.

[0007] In Non-Patent Document 3, the magnetic field can be switched on and off, but the magnetic field around the ions is not nullified, which reduces the performance of the quantum gate. It is therefore desirable to provide an improved ion trap with a magnetic field gradient in which the magnetic field is nulled around the position of the ions and can be switched on and off. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] "Ion-Trap Quantum Logic Using Lon-Wavelength Radiation", Florian Mintert et al., Phys. Rev. Lett., Volume 87, p. 257904, Publication date: November 29, 2001 [Non-Patent Document 2] A. Khromova et al., “Designer spin pseudomolecule implemented with trapped ion in a magnetic gradient”, Phys. Rev. Lett., Vol. 108, No. 22, pp. 1-5, (2012) [Non-Patent Document 3] J. Welzel et al., “Spin and motion dynamics with zigzag ion crystals in transverse magnetic gradients”, J.Phys.B At.Mol.Opt. Phys., Vol. 52, No. 2, p.025301, (2019) Summary of the Invention

[0009] It is against this background that the present invention was born.

[0010] According to the invention, a current source and a first pair of parallel wires, the first pair forming a plane and having spaces therebetween, each of the wires being connected to the first current source such that current flows in opposite directions along each of the parallel wires, the first pair being linear wires, and a second pair of parallel wires, disposed in the plane of the first pair of parallel wires and in the spaces between the first pair of parallel wires and perpendicular to the first pair of parallel wires, each of the second pair of wires being arranged such that each of the currents in the second pair is parallel to the currents in the second pair of parallel wires. An ion trap is provided in which each of the second pair of parallel wires is connected to a second current source so as to flow in an opposite direction along each of the wires, each of the second pair of parallel wires being linear wires and defining a secondary line, the first pair of parallel wires extending at least between the secondary lines, and a magnetic field generated by a current from the first current source through the first pair of parallel wires is in an opposite direction to a magnetic field generated by a current from the second current source through the second pair of parallel wires at a center point between the first pair of parallel wires and the second pair of parallel wires. The current through the second pair of wires generates a magnetic field gradient along a direction parallel to the first pair of wires. The magnetic field generated by the current through the first pair of wires can be used to nullify the absolute value of the magnetic field at a center position between the first and second pairs of parallel wires. At the center point between the first and second pairs of parallel wires, the component of the magnetic field gradient in a direction parallel to the first wire should be maximized, but the absolute value of the magnetic field is approximately nulled. The gradient of the magnetic field along a direction parallel to the first pair of parallel wires at a midpoint between the first pair of parallel wires and the second pair of parallel wires is greater than ±100 T / m.

[0011] Although the term "wire" is used, a "wire" may be a segment of a wire or a portion of a wire. A wire or wire segment is a linear or straight wire segment. A linear wire segment may be at least 10 μm.

[0012] A first pair of parallel wires or wire segments extend such that they at least overlap one another, i.e., the second wire segment overlaps at a right angle to the first wire segment. The first pair of parallel wire segments define a space between their overlapping portions, and the second pair of parallel wire segments are disposed within the space between the overlapping portions of the first pair of wire segments. There is a rectangular space bounded by the first pair of parallel wire segments and the second pair of parallel wire segments.

[0013] The secondary wire extends to intersect each of the first pair of parallel wire segments.

[0014] The ions are suspended above the wires at a height of 10-1000 μm, typically offset 1-500 μm from the center point between the first and second pairs of parallel wires.

[0015] The magnetic field at the center point between the parallel wires of the pair is nearly nulled, but a gradient remains in the magnetic field component parallel to the first wire along a direction parallel to the first wire, and the ion is located above the wire and slightly offset from the center position.

[0016] In other words, the addition of the first wire (second wire) does not affect the magnetic field gradient along the direction parallel to the first wire, but nulls the magnetic field at the central position.

[0017] The ion trap may be a microstructure ion trap, in particular a surface ion trap, however also multipole ion traps, for example quadrupoles or octopoles, may be used.

[0018] The spacing between the first pair of parallel wires is preferably in the range of 100 to 10,000 μm, and each of the first pair of parallel wires may include multiple wires. The multiple wires may lie in the same plane as the first and second wires, or each may be disposed in parallel planes on either side of the second set of wires. The spacing between the second pair of parallel wires is preferably in the range of 10 to 1,000 μm.

[0019] Through the use of the present invention, the magnetic field at the center point between the first pair of parallel wires and the second pair of parallel wires is nulled, preferably less than 1 mT. The magnetic field gradient in the direction parallel to the first pair of parallel wires at the position of the ion 10-1000 μm above the center point between the first pair of parallel wires and the second pair of parallel wires is in the range of 10-10,000 T / m, preferably in the range of 100-1000 T / m. There may also be a magnetic field gradient in the direction parallel to the second pair of parallel wires and perpendicular to both the first and second pairs of parallel wires at the center point between the first pair of parallel wires and the second pair of parallel wires.

[0020] There may be a single current source for both pairs of wires, or there may be a current source for each pair of wires.

[0021] The second pair of parallel wires is formed from a U-shaped deformation in a first wire of the first pair of parallel wires, with the branch of the U forming the second pair of wires. This arrangement is advantageously easy to manufacture. The second wire of the first pair of parallel wires is thinner than normal adjacent the U-shaped deformation to accommodate the U-shape.

[0022] Alternatively, the first wires of the second set of parallel wires are formed from a U-shape of wires, with two branches of the U parallel to the first pair of parallel wires and a bridge forming the U forming the first wires of the second set of parallel wires. The second wires of the second set of parallel wires are formed from a U-shape of wires, with two branches of the U parallel to the first pair of parallel wires and a bridge forming the U forming the second wires of the second set of parallel wires.

[0023] Alternatively, the second set of first wires of the parallel wires is formed from a U-shaped wire configuration, with a wire bridge forming the second set of first wires of the parallel wires, the branch being perpendicular to the plane of the first and second sets of parallel wires, and the second set of second wires of the parallel wires is formed from a U-shaped wire configuration, with a wire bridge forming the second set of second wires of the parallel wires, the branch being perpendicular to the plane of the first and second sets of parallel wires.

[0024] For ease of manufacture, the wire typically has a rectangular cross-section, although the wire can have any cross-section.

[0025] According to the present invention there is provided a trapped ion quantum technique comprising a surface ion trap as described above.

[0026] According to the present invention there is provided an ion trap as described above, and a method of generating a magnetic field comprising: a current flowing from a first current source through a first pair of parallel wires generating a magnetic field at a centre point of both the first pair of parallel wires and the second pair of parallel wires that is opposite in direction to a magnetic field generated by a current flowing from a second current source through a second pair of parallel wires.

[0027] According to the present invention there is provided a method of trapping ions which includes generating the magnetic field as described above and providing ions for levitation above the ion trap. [Brief description of the drawings]

[0028] The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

[0029] [Figure 1] FIG. 1 shows a current configuration according to the invention. [Diagram 2] FIG. 2 shows a wire arrangement according to the invention. [Diagram 3] FIG. 3 shows an alternative wire arrangement according to the present invention. [Figure 4] FIG. 4 shows the magnetic field generated by a wire according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Figure 1 shows some currents according to the invention that can be used to generate a magnetic field at the location of an ion above the plane of the wires at the location marked X, and also to generate a magnetic field gradient along the dashed line marked AA. Figure 1 shows a first pair of parallel wires 1, 2, and a second pair of wires 3, 4. The second pair of wires 3, 4 have anti-parallel currents that generate a magnetic field that varies in the x-direction along line AA. The magnetic field generated by these wires also varies in the z-direction, but is constant in the y-direction.

[0031] The first pair of wires runs perpendicular to the second pair of wires and also has anti-parallel currents. They also generate a magnetic field around them. This magnetic field is used to adjust the absolute value of the magnetic field strength at the location of the ion around X (preferably in the range of 0.1-3 mT). The ion is usually located slightly above the parallel wires. Thus, there is a magnetic field gradient at the location of the ion, but the absolute magnetic field is minimal. At the center point between the parallel wires of both pairs, the magnetic field strength is almost nullified. However, at the location of the ion, offset from the center by about 1-500 μm and at a height of 10-10,000 μm above the plane of the wires, the magnetic field is minimal.

[0032] A first pair of wires is connected to a first current source and a second pair of wires is connected to a second current source. The current through the first pair of wires, and therefore the strength of the surrounding magnetic field, is controlled by the first current source. The current through the second pair of wires, and therefore the strength of the surrounding magnetic field, is controlled by the second current source.

[0033] The current output by the first current source can be adjusted to substantially nullify the magnetic field at a center point of the first and second pairs of wires (designated X in FIG. 1 ), where a magnetic field gradient may exist but is significantly reduced or nullified due to the presence of the first pair of wires.

[0034] FIG. 2 shows a particular arrangement of copper wires arranged in a substrate 10 according to the invention. In this embodiment, there is a first pair of wires 11, 12 in a plane, with anti-parallel currents flowing through them from a first current source. The distance between these wires is 1000 μm, but can be in the range of 100 to 10,000 μm. In this embodiment, there is an additional pair of first wires 111, 121, which are in the same plane as the first wires, run parallel to the first wires, and are positioned outside the first pair of wires. The additional pair of first wires is also connected to the first current source, the current in each of these wires flows in the same direction as the wires of the first pair, and the current in these wires serves to increase the magnetic field, thereby making it possible to use larger magnetic field gradients.

[0035] A second pair of wires 13, 14 are also shown in the figure and lie in the same plane as the first pair of wires. The second pair of wires is U-shaped with bridges U131, 141 at approximately right angles to the first pair of wires. The branches of the U are at approximately right angles to the first pair of wires.

[0036] The bridges U131, 141 generate a magnetic field gradient along the x-direction. The distance between the bridges U131, 141 is 100 μm, and is preferably in the range of 10-500 μm. The location of the ion is located near the center of both the bridges of the first wire and the second pair of wires. The ion is typically located 100 μm above the plane of the wires, but can be in the range of 10-1000 μm.

[0037] The currents through the first and second pairs of wires are selected such that the magnetic field from the first pair of wires cancels the absolute value of the magnetic field at the center point of the first and second pairs of wires, and therefore the magnetic field at the location of the ion is significantly reduced.

[0038] For ease of manufacture, the wires typically have a rectangular cross-section with a depth of approximately 15 μm. However, the thickness can be in the range of 100 nm to 1000 μm. The wires are often manufactured using electroplating. The magnetic field gradient at the position of the ion 10-1000 μm above position X is typically in the range of 100-1000 T / m.

[0039] A first pair of parallel wires is connected to a first current source and a second pair of parallel wires is connected to a second current source. The current sources generate anti-parallel currents in each of the pairs of wires. A current of approximately 10 A (preferably in the range of 1-100 A) is used in each of the pairs of wires to generate a magnetic field. Alternatively, the first current source may generate a first level of current and the second current source may generate a second level of current, whereby the magnetic field gradient near the location of the ion is maximized but the magnetic field is substantially nulled.

[0040] Two current sources can be used, although a single current source can alternatively be used. Another alternative is the use of one or more voltage sources.

[0041] Additional pairs of wires can be used if desired. The additional pairs of wires typically lie in the same plane as the first pair of wires and the second pair of wires. However, they may lie in a plane parallel to the plane of the first and second pairs of wires. As an example, the first pair of parallel wires may include multiple wires. As a further example, the second pair of parallel wires may include multiple wires.

[0042] In alternative embodiments, the wires of the first pair lie in a different but parallel plane than the wires of the second pair. Additionally, the individual wires of each pair of wires may themselves lie in additional planes relative to each other.

[0043] For ease, the first pair of wires may be connected at one end to create a loop. Although the wires are described as being made of copper, any conductive material may be used.

[0044] A second arrangement of wires is shown in Figure 3, where a second pair of wires 23, 24 is formed into a U-shape from one of the first pair of wires 21, 22. Advantageously, this formation is interdigitated and easily reproducible.

[0045] Similar to the arrangement of Figure 2, the magnetic field at the center points of the first and second pairs of wires is substantially nulled. The centerline of the second pair of wires is indicated by line 40, and the location of the ion slightly offset from the centerline is indicated by line 41. The direction of the magnetic field gradient at the offset ion location (41) from the centerline is indicated by the dashed arrow in Figure 3.

[0046] The first pair of wires has a width of approximately 500 μm (preferably 50 μm to 1,000 μm), except for the portion adjacent to the U-shaped deformation. If these wires were thinner, their resistance would increase and therefore power consumption would also increase, which could cause heat dissipation problems.

[0047] The second pair of wires has a width of 50 μm, but can be in the range of 10 to 200 μm. The thinner the second pair of wires, the steeper the magnetic field gradient that can be obtained.

[0048] The magnetic field generated by the arrangement shown in Figure 3 is shown in Figure 4. As can be seen, the y component of the magnetic field along the x direction is nearly nulled. The z component of the magnetic field along the x direction has a knee point around the location of the ion, so that the gradient of the magnetic field in the x direction is maximized around the location of the ion, but the overall magnetic field is nulled. In this example, the gradient of the magnetic field in the x direction along the x axis is approximately 160 T / m, but may be any value greater than 100 T / m.

[0049] Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure.

[0050] As used herein, "and / or" should be taken as a specific disclosure of each of the two specified features or components with or without the other. For example, "A and / or B" should be taken as a specific disclosure of each of (i) A, (ii) B, and (iii) A and B, as if each were individually set forth herein.

[0051] Unless the context dictates otherwise, the above feature descriptions and definitions are not limited to any particular aspect or embodiment of the invention, but apply equally to all aspects and embodiments described.

[0052] Those skilled in the art will further appreciate that the present invention has been described by way of example with reference to certain embodiments, and is not limited to the disclosed embodiments, alternative embodiments may be constructed without departing from the scope of the invention as defined in the appended claims.

Claims

1. An ion trap comprising: A current source; a first pair of parallel wire segments that form a plane and have a space therebetween, each of the wire segments being connected to the first current source such that current flows in opposite directions along each of the parallel wires, the first pair of parallel wire segments being linear wire segments; a second pair of parallel wire segments disposed within the plane of the first pair of parallel wire segments and within the spaces between the first pair of parallel wire segments and generally perpendicular to the first pair of wire segments, each of the second pair of wire segments being connected to the current source such that current flows in opposite directions along each of the second pair of parallel wire segments, each of the second pair of parallel wire segments being a linear wire segment and defining a secondary line; 11. An ion trap, wherein each of the first pair of parallel wire segments extends between at least the secondary wires, and a magnetic field generated by the current passing from the current source through the first pair of parallel wire segments is in an opposite direction to a magnetic field generated by the current passing from the current source through the second pair of parallel wire segments at a center point of the first pair of parallel wire segments and the second pair of parallel wire segments.

2. The ion trap of claim 1 wherein the spacing between the first pair of parallel wire segments is in the range of 100 to 10,000 μm.

3. The ion trap of claim 1 or claim 2, wherein each of the first pair of parallel wire segments comprises a plurality of parallel wire segments.

4. 2. An ion trap as claimed in any one of the preceding claims, wherein each of the second pair of parallel wire segments comprises a plurality of wire segments.

5. 10. An ion trap according to any one of the preceding claims, wherein the current source comprises a first current source connected to the first pair of parallel wires and a second current source connected to the second pair of parallel wires.

6. An ion trap according to any one of the preceding claims, wherein the spacing between the second pair of parallel wire segments is in the range 10 to 1,000 μm.

7. 10. An ion trap as claimed in any one of the preceding claims, wherein the second pair of parallel wire segments is formed from a U-shaped deformation in a first wire of the first pair of parallel wire segments, a branch of the U forming the second pair of wire segments.

8. The ion trap of claim 7 wherein the second wire segment of the first pair of parallel wire segments is thinner adjacent the U-shaped deformation.

9. 7. The ion trap of claim 1, wherein a first wire segment of a second set of parallel wire segments is formed from a U-shaped wire configuration, and wherein the two branches of the U are parallel to the first pair of parallel wire segments and the bridge of the U forms the first wire segment of the second set of parallel wire segments, and a second wire segment of the second set of parallel wire segments is formed from a U-shaped wire configuration, and wherein the two branches of the U are parallel to the first pair of parallel wire segments and the bridge of the U forms the second wire segment of the second set of parallel wire segments.

10. 2. An ion trap as claimed in any one of the preceding claims, wherein each of the first and second parallel wire segments is formed from a conductive material.

11. 2. An ion trap as claimed in any one of the preceding claims, wherein the first and second parallel wire segments each have a rectangular cross-section.

12. 10. An ion trap according to any one of the preceding claims, wherein the ion trap is a surface ion trap.

13. A trapped ion quantum computer comprising an ion trap according to any one of the preceding claims.

14. 13. A method of generating a magnetic field comprising providing an ion trap as claimed in any one of claims 1 to 12, wherein current flowing from the current source through the first pair of parallel wire segments generates a magnetic field at a centre point of both the first pair of parallel wire segments and the second pair of parallel wire segments that is in an opposite direction to the magnetic field generated by current flowing from the current source through the second pair of parallel wire segments.

15. 10. A method according to any one of the preceding claims, wherein the magnetic field between the first and second pairs of parallel wire segments, 10-1000 μm above the centre point, is less than 10 mT.

16. 10. The method of claim 1, wherein the magnetic field gradient in a direction parallel to the first pair of parallel wire segments at the midpoint between the first and second pair of parallel wire segments is in the range of 10 to 10,000 T / m.

17. 16. The method of claim 15, wherein the magnetic field gradient in a direction parallel to the first pair of parallel wires at the center point between the first pair of parallel wire segments and the second pair of parallel wire segments is in the range of 100 to 1000 T / m.

18. 10. The method of claim 9, wherein a gradient of a component of the magnetic field in a direction parallel to the first pair of parallel wire segments at the midpoint between the first pair of parallel wire segments and the second pair of parallel wire segments is greater than ±100 T / m along a direction parallel to the first pair of parallel wire segments.

19. 19. A method of trapping ions comprising generating a magnetic field according to any one of claims 14 to 18 and providing ions for levitation above at least a portion of the ion trap.

20. 10. The method of claim 1, wherein a gradient of the magnetic field strength along a direction parallel to the first pair of parallel wire segments at the midpoint between the first pair of parallel wire segments and the second pair of parallel wire segments is greater than ±100 T / m.

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