charged particle trap

Abstract

A charged particle trap is disclosed. The charged particle trap comprises a substrate (31) and a layer structure (33, 37, 39) disposed on the substrate, the layer structure including an antenna layer (33) and an electrode layer (39). The antenna layer comprises a coplanar conductive serpentine wire (12) with at least three elongated arms (13) that are parallel and coplanar and symmetric about a central axis (15). The electrode layer comprises a set of electrodes (45, 46, 47) arranged to trap charged particles (16) along a trapping axis (17) parallel to the central axis and to generate a pseudopotential symmetric about the trapping axis.

Description

[Technical Field]

[0001] The present invention relates to a charged particle trap. [Background technology]

[0002] A promising approach to ion-trap quantum computing is to implement quantum gates without laser fields. In this configuration, the quantum gates are driven by strong magnetic field gradients. These gradients can be generated by passing electric currents through wires on the ion trap chip.

[0003] The ideal setup for a multi-qubit quantum gate is one in which the magnetic field strength is essentially zero (referred to herein as a "no-field gradient"), but has a very high magnetic field gradient, because the gradient is responsible for generating the desired coupling, while the magnetic field can generate undesired coupling, increasing errors and / or weakening the effective interaction strength.

[0004] Two techniques have been used to generate field-free gradients.

[0005] C. Ospelkaus et al., "Microwave quantum logic gates for trapped ions," https: / / arxiv.org / pdf / 1104.3573.pdf (2011), describes a first approach in which multiple current lines are formed on the trap chip and their respective phases and currents are adjusted to form the desired quadrupole. M. Wahnschaffe et al., "Single-ion microwave near field quantum sensor," https: / / arxiv.org / pdf / 1601.06460.pdf (2021), describes a second approach in which a three-segment meander is formed on the top surface of the ion trap. The dimensions of the meander are simulated to create a quadrupole at the location of the ion, and then a meander with those dimensions is fabricated.

[0006] However, these approaches have one or more drawbacks. The first approach requires multiple, individually adjustable current sources and low differential noise between the separate conductors, which can be difficult to achieve. The second approach can be difficult to align the ion position with the zero magnetic field, for example, due to imperfections in fabrication. In both cases, AC current flowing through the conductors generates an AC electric field that displaces the ions from their zero magnetic field locations. Finally, the design rules for the current-carrying conductor design tend to conflict with the design rules for the trapping electrodes.

[0007] Proposals have been made to resolve these competing requirements, such as providing a meandering path through a multilayer structure, with only a small region near the ion entering the top layer (see H. Hahn et al., "Multilayer ion trap with three-dimensional microwave circuitry for scalable quantum logic applications," https: / / arxiv.org / pdf / 1812.02445.pdf (2021)). However, this only partially alleviates the problem, as the current-carrying electrodes on the top layer remain a significant design constraint for the trap electrodes. Furthermore, this technology relies on high-current interlayer interconnects, which can be difficult to fabricate and introduce significant resistance if the footprint cannot be afforded, as shown, for example, in A. Bautista-Salvador et al., "Multilayer ion trap technology for scalable quantum computing and quantum simulation," New Journal of Physics, volume 21, 043011 (2019)).

[0008] UK Patent Application No. 2593901A describes a technique for partially nulling the magnetic field in a certain direction to minimize the magnetic field's effect on a quantum gate. The partially nulled magnetic field can still affect the qubit, for example in the form of rapid frequency modulation or diffuse qubit frequency shifts. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] UK Patent Application No. 2593901A [Non-patent literature]

[0010] [Non-Patent Document 1] C. Ospelkaus et al., “Microwave quantum logic gates for trapped ion,” https: / / arxiv.org / pdf / 1104.3573.pdf (2011) [Non-patent document 2] M. Wahnschaffe et al., “Single-ion microwave near field quantum sensor”, https: / / arxiv.org / pdf / 1601.06460.pdf (2021) [Non-patent document 3] H. Hahn et al., “Multilayer ion trap with three-dimensional microwave circuitry for scalable quantum logic applications”, https: / / arxiv.org / pdf / 1812.02445.pdf (2021) [Non-patent document 4] A. Bautista-Salvador et al., “Multilayer ion trap technology for scalable quantum computing and quantum simulation”, New Journal of Physics, volume 21, 043011 (2019) Summary of the Invention [Means for solving the problem]

[0011] According to a first aspect of the present invention, a charged particle trap is provided. The charged particle trap comprises a substrate and a layer structure disposed on the substrate. The layer structure includes an antenna layer and an electrode layer. The antenna layer comprises a coplanar conductive serpentine wire having at least three elongated arms that are parallel and coplanar and symmetric about a central axis. The electrode layer comprises a set of electrodes configured to trap charged particles along a trapping axis parallel to the central axis and to generate a pseudopotential that is symmetric about the trapping axis. For example, the pseudopotential can be symmetric about the trapping axis in a direction in a plane perpendicular to the trapping axis (i.e., parallel to the electrode layer).

[0012] This configuration can help to create a magnetic field gradient and provide magnetic field cancellation at the point where charged particles become trapped.

[0013] The antenna layer may be interposed between the substrate and the electrode layer, and may be above or below (in other words, not coplanar with) the electrode layer.

[0014] The electrode layers are preferably symmetric about the trapping axis, at least in the section along the trapping axis where charged particles are to be trapped.

[0015] The coplanar conductive serpentine line may have an odd number of elongated arms and may include a central arm, with the central axis running along the central arm. The serpentine line may have an even number of elongated arms and may include a pair of central arms, with the central axis running between the pair of central arms.

[0016] The coplanar conductive serpentine lines may have a width between 5 μm and 500 μm. The conductive serpentine lines may have a thickness t between 0.3 μm and 2 μm. The conductive serpentine lines may comprise a superconducting material.

[0017] The layer structure may further include a conductive layer interposed between the antenna layer and the electrode layer. The conductive layer may provide a ground plane. The conductive layer may be sheet-shaped. The conductive layer may be formed of a metal such as aluminum.

[0018] The layer structure may further include a conductive connection layer (e.g., including a set of traces or wires) interposed between the antenna layer and the electrode layer. The conductive connection layer may be formed of a metal such as aluminum. The conductive connection layer may be used to transmit signals to the surface electrodes. The layer structure may further include at least one conductive via or at least two conductive vias connecting the conductive connection layer to at least one or at least two of the electrodes in the electrode layer.

[0019] The coplanar conductive serpentine line may be arranged to pass through at least two adjacent bundles of parallel strands, and three or more bundles may be symmetrical about a central axis.

[0020] The set of electrodes has a shielding effect of S=20log 10 The trap may include a set of surface electrodes having [B0' / B1']≦20 dB or <1 dB, where B0' is the magnetic field gradient at the charged particle when trapped by the charged particle trap without the set of surface electrodes and B1' is the magnetic field gradient at the charged particle when trapped by the charged particle trap with the set of surface electrodes.

[0021] The elongate arms are preferably straight, for example, in the region through which the elongate arms and the central axis pass.

[0022] According to a second aspect of the present invention, a quantum information processing system is provided. The quantum information processing system includes a charged particle trap and a control system. The charged particle trap includes a substrate and a layer structure disposed on the substrate. The layer structure includes an antenna layer and an electrode layer. The antenna layer is interposed between the substrate and the electrode layer. The antenna layer includes at least three parallel, coplanar, and symmetrical wires about a central axis, and the electrode layer includes a set of electrodes arranged to trap charged particles along a trapping axis parallel to the central axis. The control system is for controlling the charged particle trap, applying biases to the set of electrodes to trap at least one ion, and implementing at least one quantum logic gate for the at least one charged particle. The control system is arranged to drive currents through the at least three wires such that each current has a respective phase and the currents are symmetrical about the central axis.

[0023] This configuration can be useful for creating a magnetic field gradient and providing magnetic field cancellation where charged particles would be trapped without the use of a serpentine path.

[0024] The control system may include at least two bias sources.

[0025] The control system may include N bias sources, each configured to drive a respective current through a respective wire or through a respective bundle of at least two adjacent parallel wires, at a respective phase.

[0026] The control system may include a first bias source and a second bias source, the first bias source configured to drive a first current through the first set of at least one wire or the first set of at least one bundle of at least two adjacent parallel wires with a first phase, and the second bias source configured to drive a second current through the first set of at least one wire or the first set of at least one bundle of at least two adjacent parallel wires with a second phase.

[0027] The at least three wires may comprise an odd number of wires, the odd number of wires including a central wire, the central axis running along the central wire. The at least three wires may comprise an even number of wires, the even number of wires including a central pair of wires, the central axis running between the central pair of wires.

[0028] The wire may have a width between 5 μm and 500 μm. The wire may have a thickness t between 0.3 μm and 2 μm. The wire may comprise a superconducting material.

[0029] The layer structure may further include a conductive layer interposed between the antenna layer and the electrode layer. The conductive layer may provide a ground plane. The conductive layer may be sheet-shaped. The conductive layer may be made of a metal such as aluminum.

[0030] The layer structure may further include a conductive connection layer (e.g., including a set of traces or wires) interposed between the antenna layer and the electrode layer. The conductive connection layer may be formed of a metal such as aluminum. The conductive connection layer may be used to transmit signals to the surface electrodes. The layer structure may further include at least one conductive via or at least two conductive vias connecting the conductive connection layer to at least one or at least two of the electrodes in the electrode layer.

[0031] The wires may be arranged to run in bundles of at least two adjacent parallel wires, and three or more bundles may be symmetrical about a centerline.

[0032] The set of electrodes has a shielding effect of S=20log 10 The trap may include a set of surface electrodes having [B0' / B1']≦20 dB or <1 dB, where B0' is the magnetic field gradient at the charged particle when trapped by the charged particle trap without the set of surface electrodes and B1' is the magnetic field gradient at the charged particle when trapped by the charged particle trap with the set of surface electrodes.

[0033] The wire is preferably straight, for example in the region through which the elongate arms and central axis pass.

[0034] According to a third aspect of the present invention, there is provided a quantum information processing system comprising the charged particle trap of the first aspect and a control system for controlling the charged particle trap for applying a bias to a set of electrodes to trap at least one ion and for implementing at least one quantum logic gate on the at least one charged particle.

[0035] The control system may be configured to pass a current having a frequency of 1 GHz or less through the coplanar conductive serpentine or wire.

[0036] According to a third aspect of the present invention, there is provided a method of operating the charged particle trap of the first aspect and the quantum information processing system of the second or third aspect, the method comprising the steps of trapping at least one charged particle in the charged particle trap, each charged particle providing a respective qubit, providing an initial qubit state, and applying one or more sequences of gates to the qubit, wherein applying the one or more sequences of gates to the qubit comprises driving a current through a coplanar conductive serpentine line or wire having a frequency of 1 GHz or less.

[0037] The method may further comprise reading the qubit state.

[0038] The charged particles are calcium ions ( 40 Ca + or 43 Ca + The charged particle can be an atom or molecule with a net charge, or an elementary charged particle such as an electron or positron.

[0039] Some embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0040] [Figure 1] FIG. 2 is a schematic plan view of a first antenna structure comprising wires for generating a magnetic field gradient. [Figure 2] FIG. 10 is a schematic plan view of a second antenna structure comprising a two-arm serpentine path for generating a magnetic field gradient. [Figure 3] FIG. 10 is a schematic plan view of a third antenna structure comprising a three-arm serpentine structure for generating a magnetic field gradient. [Figure 4] FIG. 10 is a schematic plan view of a fourth antenna structure comprising a four-arm serpentine structure for generating a magnetic field gradient. [Figure 5] 4 is a plot of simulated magnetic fields and field gradients for the three-arm serpentine structure shown in FIG. 3. [Figure 6] FIG. 1 is a schematic diagram of a quantum information processing system including a surface electrode trap and a control system. [Figure 7] 1 is a schematic orthographic view of a charged particle trap including an antenna with a four-arm serpentine path. [Figure 8] FIG. 8 is a schematic plan view of the charged particle trap shown in FIG. 7. [Figure 9] FIG. 2 is a plan view of the antenna layer of the charged particle trap. [Figure 10] FIG. 2 is a plan view of the electrode layer of the charged particle trap. [Figure 11] FIG. 10 is a schematic plan view of a fifth antenna comprising a multi-turn three-arm serpentine path for generating a magnetic field gradient. [Figure 12] FIG. 10 is a schematic plan view of a sixth antenna comprising a multi-turn four-arm serpentine path for generating a magnetic field gradient. [Figure 13] FIG. 1 is a schematic diagram of a single source drive configuration. [Figure 14] FIG. 1 is a schematic diagram of a first multi-source driving configuration. [Figure 15] FIG. 10 is a schematic diagram of a second multi-source drive configuration. [Figure 16] 1 is a schematic plan view of a charged particle trap with a surface antenna. DETAILED DESCRIPTION OF THE INVENTION

[0041] introduction An antenna structure is described herein. The structure can be driven by a single or multiple sources. The structure can be positioned to aid in aligning the magnetic field zero with the trapped ions. Because the structure can be buried, it can provide AC electric field shielding and allow greater freedom for the design of the top layer. The structure is planar, thus eliminating the need for low-resistance, low-footprint interconnects, which can help simplify fabrication. Signals can be supplied to the structure, for example, through large interconnects located away from other structures or through wire bonds attached directly to the buried layer structure. Finally, the structure can be adapted to generate large gradients at low currents, helping to reduce overall power consumption.

[0042] Structure for generating a magnetic field gradient Referring to Figures 1 and 2, a first antenna structure 11 and a second antenna structure 12 are shown.

[0043] The first antenna structure 11 takes the form of a single straight wire 2 along a central axis 5 (in this case parallel to the x-axis) through which a current i can be driven. The first antenna structure 11 can be used to apply a magnetic field gradient (not shown) to one or more charged particles 6 on an axis 7 that is parallel to and offset perpendicularly (along the z-axis) from the central axis 5.

[0044] The second antenna structure 12 takes the form of a serpentine path wire structure 2 (also referred to herein as a "two-wire serpentine path structure," "two-arm serpentine path structure," "one-turn serpentine path structure," or "single-segment serpentine path structure") having first and second elongated wire sections 3 (or "arms") that are straight and parallel (in this case parallel to the x-axis) and coplanar (in this case lying in the x-y plane) joined by a transverse section 4 (or "bridge") and symmetrical about a central axis 5 (parallel to the x-axis). The second antenna structure 12 can be used to apply a magnetic field gradient (not shown) to one or more charged particles 6 on an axis 7 that is parallel to and perpendicularly offset (along the z-axis) from the central axis 5.

[0045] Although the first antenna structure 11 and the second antenna structure 12 may be used to generate a magnetic field gradient (not shown), they cannot cause magnetic field cancellation, i.e., they cannot generate a region of zero magnetic field by themselves (e.g., without additional wires).

[0046] Structure for generating magnetic field gradients and for magnetic field cancellation 3 and 4, a third antenna structure 111 and a fourth antenna structure 112 are shown.

[0047] The third antenna structure 111 takes the form of a serpentine wire structure 12 (also referred to herein as a "three-wire serpentine structure," "three-arm serpentine structure," "two-turn serpentine structure," or "1.5-segment serpentine structure") having straight, parallel first, second, and third elongated wire sections 13 (or "arms") joined by first and second transverse sections 14 (or "bridges") and symmetrical about a central axis 15. The wires 12 are therefore boustrophedonic. The third antenna structure 111 can be used to apply a magnetic field gradient (not shown) to one or more charged particles 16 on an axis 17 that is parallel to and offset perpendicularly (in this case, along the z-axis) from the central axis 15.

[0048] A pseudopotential (not shown) for the charged particle is generated by electrodes that are symmetric about an axis 17, specifically about the trapping axis 17 in an in-plane direction y that is orthogonal to the trapping axis, and about a plane P that is orthogonal to the z axis and in which the central axis 15 and the trapping axis 17 lie. Charged particles 16 may be trapped in a chain, e.g., more than one, for use in, e.g., a two-qubit gate.

[0049] The fourth antenna structure 112 takes the form of a serpentine path wire structure 12 (also referred to herein as a “four-wire serpentine path structure,” “four-arm serpentine path structure,” “three-turn serpentine path structure,” or “two-segment serpentine path structure”) having straight, parallel first, second, third, and fourth elongated wire sections 13 joined by first, second, and third transverse sections 14 and symmetrical about a central axis 15. The fourth antenna structure 112 may be used to apply a magnetic field gradient (not shown) to one or more charged particles 16 on an axis 17 that is parallel to and offset perpendicularly (in this case, along the z-axis) from the central axis 15.

[0050] A pseudopotential (not shown) for the charged particle is generated by electrodes that are symmetric about an axis 17, specifically about the trapping axis 17 in an in-plane direction y that is orthogonal to the trapping axis, and about a plane P that is orthogonal to the z axis and in which the central axis 15 and the trapping axis 17 lie. Charged particles 16 may be trapped in a chain, e.g., more than one, for use in, e.g., a two-qubit gate.

[0051] Referring to Figure 5, a plot of the magnetic field along the y-axis (B y ), magnetic field along the z-axis (B z ), the y- and z-field gradients (dB y / dy,dB z / dz), and the z- and y-field gradients along the y- and z-axes (dB z / dy,dB y / dz) is shown for a 3-wire serpentine at z=40 μm (where z=0 is the plane of the serpentine) when a current of 1 A flows through the serpentine.

[0052] At y=0, the magnetic field is set to zero (B y =B z =0). At the same time, the two slope components (dB z / dy and dB y / dz) is not 0, but is actually strong, at 125 T / m.

[0053] By symmetry, B z = 0 is achieved. On the other hand, B y = 0 is true only when the spacing is chosen appropriately. In the simulation, the wires are assumed to be very thin. In that case, the optimal spacing is equal to the ion height (40 μm). In a real device, the optimal spacing may be different due to the finite width of the wires (as well as the presence of nearby structures). Therefore, more granular simulations can be used to find the optimal spacing for a real device.

[0054] Quantum Information Processing System 21 Referring to FIG. 6, a quantum information processing system 21 is shown that includes a surface electrode trap 22 and a control system 23 .

[0055] The surface electrode trap 22 can be used to trap and control one or more charged particles 16 that provide respective quantum bits along a trapping axis 17 .

[0056] The charged particles 16 are calcium ions ( 40 Ca + ), however, they may also take the form of atoms or molecules with a net electric charge, or elementary charged particles such as electrons or positrons.

[0057] The surface electrode trap 22 may be housed in a cryogenic freezer (not shown) for cooling the surface electrode trap 22 to a suitable low temperature T (e.g., less than 77 K or 4.2 K). The surface electrode trap 22 may operate at room temperature. The surface electrode trap 22 may be housed in a vacuum chamber (not shown), which provides an ultra-high vacuum environment that allows individual charged particles to be isolated.

[0058] Multilayer charged particle trap 7 and 8, an example of a surface electrode trap 22 is shown.

[0059] The surface electrode trap 22 includes a substrate 31 having a top surface 32, e.g., sapphire, supporting an antenna layer 33; a first dielectric layer (not shown) comprising silicon dioxide and having a top surface (not shown) supporting a conductive layer 37, e.g., gold, aluminum, or another suitable metal, or degenerately doped silicon, or another suitable semiconductor layer; and a second dielectric layer (not shown) comprising silicon dioxide and having a top surface (not shown) supporting a charged particle trap layer 39 having a top surface 40 on which one or more charged particles 16 can be trapped. The conductive layer 37 may provide a ground plane. Additional layers (not shown) providing conductive paths (not shown) may be provided, along with vias (not shown) to provide signal lines to the surface electrodes and wires. The antenna layer 33 and the charged particle trap layer 39 are not coplanar; in this case, the antenna layer 33 is below the charged particle trap layer 39.

[0060] The antenna layer 33 comprises antenna structures 11 for magnetic field gradient generation and magnetic field cancellation, such as, for example, the third antenna structure 111 (FIG. 3) or the fourth antenna structure 112 (FIG. 4) previously described.

[0061] The antenna layer 33 comprises a coplanar conductive serpentine line 12 with at least three elongated arms 13 that are parallel and coplanar and symmetrical about a central axis 15 that is parallel to the trapping axis 17. The central axis 15 and the trapping axis 17 lie in a plane P that is perpendicular to the top surface 40, and the trapping axis 17 lies above the central axis 15.

[0062] The serpentine lines 12 may be formed from metals such as gold, silver, or aluminum, superconductors such as rare earth barium copper oxide (ReBCO), niobium or alloys containing niobium, or semiconductors such as doped silicon. The lines 12 may have a width w (transverse to the current flow) between 5 μm and 500 μm, and a thickness t between 0.3 μm and 20 μm.

[0063] The control system 23 includes a signal source 42 attached to a first end 43 and a second end 44 of the antenna structure 11 .

[0064] The charged particle trapping layer 39 comprises an arrangement of electrodes 45, 46, 47 that can be used to trap and control one or more charged particles 16. In this case, the charged particles 16 are shown trapped in pairs for use in a two-qubit gate. However, the charged particles 16 may also be trapped singly or in longer chains of three or more particles 16.

[0065] The electrodes 45, 46, 47 include a central electrode 45 in the form of a strip extending along a longitudinal axis 48 parallel to the trapping axis 17, and first and second electrodes 46 in the form of respective strips extending on either side of the central electrode 45 such that the central electrode 45 is interposed between the first and second electrodes 46. An AC signal at an RF frequency to produce a ponderomotive confining potential is applied to the first and second electrodes 46 (also referred to herein as the “first and second RF electrodes”). The electrodes 45, 46, 47 generate a pseudopotential (not shown) that is symmetric about the plane P. Specifically, the pseudopotential (not shown) is symmetric about the trapping axis 17 in the y direction. Along the z direction, the pseudopotential (not shown) is asymmetric.

[0066] The control system 10 applies appropriate DC and AC currents and voltage biases to the electrodes 45 , 46 , 47 of the surface electrode trap 22 .

[0067] Referring to FIG. 9, the antenna layer 33 is shown.

[0068] Referring to FIG. 10, a charged particle trapping layer 39 is shown.

[0069] The serpentine line 12 is perfectly symmetric about y=0. This helps to provide magnetic field cancellation along one axis, i.e., y or z, depending on the design. In the four-wire configuration shown in Figure 10, the symmetry ensures magnetic field cancellation along the y axis. Cancellation along the other axis (z for the four-wire design) can be configured by judicious setting of conductor spacing and width. Cancellation along the x direction can be achieved by making the structure sufficiently long along the x direction.

[0070] The ability to make both the trap and the serpentine symmetrical greatly aids in cancelling the magnetic fields, which may make the configuration less susceptible to fabrication and simulation uncertainties.

[0071] The antenna layer 33 takes the form of a single buried layer. This can lead to one or more advantages. The geometry of the serpentine path can be tailored for optimal performance without restricting the geometry of the top electrode. The width w of the wiring can be made relatively large to reduce resistance and thereby reduce power consumption. Similarly, the thickness t of the wiring can be increased without compromising the quality of the fabrication of the top electrode. The need for low-footprint, low-resistance vias can be eliminated. This also makes the structure more suitable for the use of superconducting wiring, as superconducting planar structures tend to be easier to fabricate than superconducting vias. The serpentine wiring material can be freely chosen for optimal performance, regardless of its effect on ions such as electric field noise.

[0072] The layers above the antenna layer 33 provide a shielding structure that may help reduce the AC electric fields created by the serpentine line 2, which may help ameliorate the problem of aligning the ion position with the magnetic field 0. These electric fields may be reduced by connecting additional wiring to the conductive surface 37 at a single point close to the charged particle 16 and driving it with a differential feed.

[0073] The frequency of the current can be adjusted to help ensure that a sufficient magnetic field gradient is generated. Low-frequency magnetic fields are less susceptible to shielding, making this structure more suitable for quantum gates generated by low-frequency gradients.

[0074] Although thick, highly conductive layers shield both electric and magnetic fields more effectively than thin, less conductive layers, electric fields are generally attenuated much more strongly than magnetic fields, at least at frequencies near DC, e.g., below 100 Hz. Therefore, tailoring the geometry and conductivity of the shielding layers allows the use of structures that provide sufficient shielding for electric fields while ensuring sufficient penetration of magnetic fields.

[0075] operation The control system 23 applies a low frequency (<1 GHz) current to the serpentine wire 12. This can help improve performance, as applying a higher frequency to the wire 12 can result in fields that are susceptible to induced currents, ground bounce, and phase shifts. Applying a low frequency current helps reduce currents in other layers and minimizes the phase shift of the wave across the antenna.

[0076] Further Structure Referring again to Figures 3 and 4, the third antenna structure 111 and the fourth antenna structure 112 comprise a single wire 12 that is repeatedly bent in a single strand to form a serpentine path (referred to herein as a "multi-turn single-wire serpentine path").

[0077] 11 and 12, a fifth antenna structure 113 and a sixth antenna structure 114 are shown that also comprise a single wire 12, where the wire 12 is made up of three or more parallel strands that are repeatedly bent together (e.g., in pairs, triplets, or other multi-wire bundles) to form a serpentine path (referred to herein as a "multi-turn multi-wire serpentine path"), with straight, parallel strands within each bundle.

[0078] In the fifth antenna structure 113 and the sixth antenna structure 114, the wires may be thinner than in the third antenna structure 111 and the fourth antenna structure 112. This may help to reduce power consumption, as one wire section of width w carrying a current I may be replaced with N parallel wire sections, each with width w / N and each carrying a current I / N, to produce an equivalent magnetic field gradient while reducing power losses by a factor N.

[0079] The fifth antenna structure 113 and the sixth antenna structure 114 are examples of multi-turn three-wire serpentine and multi-turn four-wire serpentine structures, respectively.

[0080] Drive Configuration 13, a single source 42 may be used to drive current I(t) through elongated wire sections 13 or bundles 18 of strands connected in series (FIG. 11). A serpentine path structure 12 including one or more bridges 14 ensures that the current in a given wire section 13 or a given bundle 18 of strands and the current in an adjacent wire section 13 or adjacent bundle 18 of strands flow antiparallel but have the same magnitude.

[0081] This configuration, i.e., using one source 42 to drive two or more elongated wire sections 13 that are electrically connected in series, is referred to herein as a "passive configuration," a "common source configuration," or a "series wire drive configuration."

[0082] However, this effect can be achieved differently.

[0083] Referring to FIG. 14, multiple sources 421, 422, 423 may be used, where source 42 idrives each elongated wire 131, 132, 133 (or each bundle of strands), and the elongated wires 13 (or bundles) are not electrically connected in series. Instead, the current in a given wire, say the second wire 132, is driven with a given phase φ, and the currents in adjacent wires (in this case the first wire 131 and the third wire 133) are driven with the same magnitude but in opposite phase.

[0084] This configuration, i.e., N elongated wires 13 that are not electrically connected in series. i or N sources 42 to drive N bundles (i=1,...,N) i Configurations using (i=1,...,N) are referred to herein as "active configurations," "separate source configurations," or "parallel wire drive configurations."

[0085] Referring to FIG. 15, the same effect may be achieved using two sources 42, where a first source 421 drives a first set 201 of one or more alternating wires 13 or alternating bundles of strands through which current flows in parallel, and a second source 422 drives a second set 202 of one or more wires 13 or alternating bundles of strands through which current flows anti-parallel to the first set.

[0086] This configuration, i.e., using two sources 42 to drive N elongated wires 13, with the wires in one set connected in parallel and the wires in another set also connected in parallel, but the two sets not electrically connected, is called a "semi-active configuration," a "shared source configuration," or a "split parallel wire drive configuration."

[0087] Shielding of surface electrodes The surface electrode traps described above may include one or more antennas (not shown) disposed below the surface electrode, i.e., inserted between the substrate and the surface electrode. The antennas may take the form of electrically conductive paths (or "wires") carrying current that generate a magnetic field that can act on the trapped charged particles. A dielectric layer, such as silicon dioxide, having a thickness of, for example, 1 μm to 10 μm, may be deposited over the antenna to electrically insulate the antenna and the surface electrode, such that the dielectric layer is inserted between the antenna and the surface electrode.

[0088] The shielding effectiveness S in dB is S=20log 10 (B0' / B1') (1) where B0' is the magnetic field gradient for a charged particle without a shielding structure, and B1' is the magnetic field gradient for a charged particle with a shielding structure.

[0089] The shielding effect can be in three forms, namely: - "Low shielding": S<1dB (i.e. B1'>0.9B0') - "Medium shielding": 20dB≧S≧1dB (i.e., 0.1B0'≦B1'≦0.9B0') - "High Shielding": S>20dB (i.e., B1'<0.1B0') It can be divided into:

[0090] The surface electrodes are preferably positioned so as not to shield charged particles from the antenna, in other words to provide low shielding, although moderate shielding may also be acceptable.

[0091] Low shielding can be achieved by (a) choosing an appropriate material for the electrodes and an electrode thickness that is much smaller than the skin depth δ of the material (i.e., t<<δ), and (b) configuring the electrode layout to have, for example, slots and / or spacing.

[0092] The shielding effectiveness can be estimated by modeling the layer above the antenna as a solid ground plane of thickness t and conductivity σ. For example, for a 500 nm thick copper layer (t = 500 nm and σ = 5.96 × 10) at room temperature, 7 S / m) is considered a poor shielding layer at frequency f = 10 MHz because S < 1 dB. A 5 μm thick copper layer (t = 5 μm and σ = 5.96 × 10 7 S / m) is a high shielding layer at frequency f = 300 MHz, since S>20 dB.

[0093] The shielding effectiveness S is altered by the electrode geometry, especially the presence of slots and notches. However, the shielding effectiveness of a sheet without slots or notches can be used as an approximation.

[0094] Surface Antenna The surface electrode traps described previously utilize embedded antennas. However, the antenna may also be located on the surface. This may be used, for example, if surface electrodes are too shielded.

[0095] Referring to FIG. 16, another example of a surface electrode trap 22' is shown.

[0096] The surface electrode trap 22' is similar to the previously described surface electrode trap 22 (FIG. 8). However, an antenna structure 11, in this case a three-arm structure, is formed on the top surface. The antenna structure 11 in this case comprises a conductive serpentine path 12 with three straight arms 13 that are parallel and symmetric about a central axis 15 that is parallel to the trap axis 17.

[0097] Second electrodes 46 (or "RF electrodes") are also provided on the top surface between the arms 13. Third electrodes 47 (or "DC electrodes") are disposed on either side of the serpentine path 12, on either side of the trap axis 17.

[0098] Electrodes 46, 47 are arranged to generate a pseudopotential (not shown) for trapping charged particles along a central section S of trap 22' that is symmetric about trapping axis 17. The pseudopotential (not shown) is symmetric about trapping axis 17, which is parallel to the layers along the y direction.

[0099] Modification It will be understood that various modifications may be made to the previously described embodiments. Such modifications may involve equivalent and other features which are already known in the design, manufacture, and use of charged particle traps and their components and which may be used instead of, or in addition to, features already described herein. Features of one embodiment may be replaced by, or supplemented by, features of another embodiment.

[0100] The traps described herein have one layer of electrodes or two layers of electrodes (in which case one of the layers of electrodes is buried). Traps with three or more layers (which include at least two buried layers of electrodes) may also be used.

[0101] Although claims in this application are formulated to particular combinations of features, the scope of the present disclosure should be understood to include any novel feature or any novel combination of features explicitly or implicitly disclosed herein, or any generalization thereof, whether or not it relates to the same invention as presently asserted in any claim, and whether or not it alleviates any or all of the same technical problems as the present invention. Applicants hereby give notice that new claims may be formulated to such features and / or combinations of such features during prosecution of this application or any further application derived therefrom. [Explanation of symbols]

[0102] 1, 11 Antenna structure 2 wire, straight wire, meandering wire structure, meandering wire 3 Serpentine wire structure, long and thin wire section 4 Crossing Section 5 Center axis 6. Charged Particles 7 axes 10. Control System 11 First antenna structure 12 Second Antenna Structure 111Third Antenna Structure 112 Fourth Antenna Structure 113 Fifth Antenna Structure 114 6th Antenna Structure 13 Wire section 14 Crossing Sections, Bridges 15 Center axis 16 Charged Particles 17 Trap shaft, shaft 18 strand bundles 201 First Set 21 Quantum Information Processing System 22 Surface Electrode Trap 23 Control System 31 PCB 32 Top side 33 Antenna Layer 37 Conductive layer 39 Charged particle trap layer 40 Top side 42 source, signal source 421 Source, First Source 422 Source, Second Source 423 source 43 First end 44 Second end 45 electrode, center electrode 46 electrodes, first electrode and second electrode 47 Electrode, Third Electrode 48 Longitudinal Axis

Claims

1. 1. A charged particle trap comprising: A substrate; A layer structure disposed on the substrate, an antenna layer; an electrode layer; and a layer structure including the electrode layer, the antenna layer comprises a coplanar conductive meander line with at least three elongated arms that are parallel and coplanar and symmetrical about a central axis; 1. A charged particle trap, wherein the electrode layer comprises a set of electrodes configured to trap charged particles along a trapping axis parallel to the central axis and to generate a pseudopotential symmetric about the trapping axis.

2. 2. The charged particle trap of claim 1, wherein the antenna layer is interposed between the substrate and the electrode layer.

3. the coplanar conductive serpentine line comprises an odd number of elongated arms; the odd number of elongate arms includes a central arm; 3. The charged particle trap of claim 1, wherein the central axis is along the central arm.

4. the coplanar conductive serpentine line comprises an even number of elongated arms; the even number of elongate arms includes a pair of central arms; 3. A charged particle trap as claimed in claim 1 or 2, wherein the central axis passes between the pair of central arms.

5. 3. A charged particle trap according to claim 1 or 2, wherein the coplanar conductive serpentine lines have a width between 5 μm and 500 μm.

6. 3. A charged particle trap according to claim 1 or 2, wherein the coplanar conductive serpentine lines have a thickness between 0.3 μm and 2 μm.

7. The charged particle trap of claim 1 or 2, wherein the coplanar conductive serpentine lines comprise a superconducting material.

8. 3. A charged particle trap according to claim 1, wherein the layer structure further comprises a conductive layer interposed between the antenna layer and the electrode layer.

9. 3. A charged particle trap according to claim 1, wherein the layer structure further comprises an electrically conductive connecting layer interposed between the antenna layer and the electrode layer.

10. the coplanar conductive serpentine line is arranged to pass through a bundle of two or more parallel strands; 3. A charged particle trap according to claim 1, wherein three or more bundles are symmetric about said central axis.

11. The set of electrodes has a shielding effectiveness S=20 log １０ a set of surface electrodes with [B0' / B1']≦20 dB; B0' is the magnetic field gradient at a charged particle when trapped by the charged particle trap without the set of surface electrodes; 3. The charged particle trap of claim 1, wherein B1' is the magnetic field gradient across a charged particle when trapped by the charged particle trap in the presence of the set of surface electrodes.

12. 1. A quantum information processing system, comprising:

1. A charged particle trap comprising: A substrate; A layer structure disposed on the substrate, the layer structure comprising: an antenna layer; an electrode layer; the antenna layer comprises at least three elongated arms that are parallel and coplanar and symmetric about a central axis; a layer structure, the electrode layer comprising a set of electrodes configured to trap charged particles along a trapping axis parallel to the central axis and to generate a pseudopotential symmetric about the trapping axis; a control system for controlling the charged particle trap, applying a bias to the set of electrodes to trap at least one ion, and implementing at least one quantum logic gate on at least one charged particle; The quantum information processing system, wherein the control system is configured to drive currents through the at least three elongate arms such that each current has a respective phase and the currents are symmetric about the central axis.

13. The quantum information processing system of claim 12 , wherein the control system comprises at least two bias sources.

14. the control system comprises N bias sources; 14. The quantum information processing system of claim 12 or 13, wherein each of the N bias sources is configured to drive a respective current through a respective elongate arm or through each bundle of at least two adjacent parallel strands with a respective phase.

15. the control system includes a first bias source and a second bias source; the first bias source is configured to drive a first current at a first phase through a first set of at least one arm or a first set of at least one bundle of at least two adjacent parallel strands; 14. The quantum information processing system of claim 12 or 13, wherein the second bias source is configured to drive a second current through a first set of at least one arm or a first set of at least one bundle of at least two adjacent parallel strands with a second phase.

16. A charged particle trap according to claim 1 or 2; a control system for controlling the charged particle trap, applying a bias to the set of electrodes to trap at least one ion, and implementing at least one quantum logic gate on at least one charged particle.

17. 14. The quantum information processing system of claim 12 or 13, wherein the control system is configured to pass a current having a frequency of 1 GHz or less through the coplanar conductive serpentine lines.

18. A method of operating a charged particle trap according to claim 1 or 2 or a quantum information processing system according to claim 12 or 13, comprising the steps of: Trapping at least one charged particle in the charged particle trap, each charged particle providing a respective quantum bit; providing an initial qubit state; applying a sequence of one or more gates to the qubit; 10. The method of claim 1, wherein applying the sequence of one or more gates to the qubit comprises driving a current having a frequency of 1 GHz or less through a coplanar conductive serpentine or wire.

19. 20. The method of claim 18, further comprising reading out the qubit state.

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