Superconducting quantum computing circuit package

Abstract

To provide a device that provides a cleaner frequency space for an operation of a quantum arithmetic circuit.SOLUTION: A superconducting quantum arithmetic circuit package (1) includes a substrate (2) in which a circuit having a plurality of circuit elements is formed. The substrate (2) includes a pore (8) that is arranged between the circuit elements and that is extended through the thickness of the substrate (2). The package also comprises a holder (3) that has a surface (9) for housing the substrate (2), and a cover (4) that is arranged on the other side of the substrate (2). The holder (3) and the cover (4) are formed of metal and / or a superconductor. The holder (3) also includes a protrusion (12) that is arranged on the surface (9) and that protrudes from the surface (9). The protrusion (12) protrudes through the pore (8) within the substrate (2), and comes into contact with the cover (4) so as to suppress an electromagnetic mode within an operation frequency range of a quantum arithmetic circuit.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a superconducting quantum operation circuit package, and more particularly to a superconducting quantum operation circuit package that includes a holder for a substrate of a superconducting quantum operation circuit. [Background technology]

[0002] In quantum computing architectures, it is desirable to build circuit chips containing multiple qubits to enable useful computations. However, as chips are scaled, the physical space they occupy increases to a size that supports electromagnetic (EM) modes with frequencies comparable to the operating frequencies of the quantum computing circuits on the chip. For example, a rectangular chip encased in a conductive material with side lengths longer than a few millimeters (both sides longer than its thickness) and a high dielectric constant of around 10 can support EM modes in the range of several gigahertz to tens of gigahertz.

[0003] Such electromagnetic "chip-like" modes are undesirable in most cases, especially in the frequency range of several gigahertz to tens of gigahertz. Because these frequencies are approximately the same as the desired operating frequencies of quantum computing circuits, they can interfere with the operation of quantum computing circuits through interactions with "circuit-like" modes, e.g., qubit modes, and other circuit elements and control signals used. Maintaining circuit coherence is important for extending the circuit's operating lifetime and enabling effective quantum processing, and such interference can result in a loss of circuit coherence.

[0004] As quantum computing circuit chips increase in size, the frequency of the lowest frequency chip-like mode that can be supported decreases, causing the chip to host a large number of unwanted modes within the circuit's operating frequency space. Another problem that arises when scaling quantum computing circuit chips to increase the number of circuit elements within the circuit is the possibility of unwanted interactions between circuit-like modes (e.g., crosstalk interactions between qubits) that can interfere with the operation of the quantum computing circuit.

[0005] This means that the problem of troublesome interactions between chip-like and circuit-like modes, and between circuit-like and circuit-like modes, will often only get worse as quantum computing circuits are scaled up in both physical dimensions and the number of circuit elements. For example, scaling quantum computing circuits on high-dielectric substrates to sizes larger than about 1 cm x 1 cm will be difficult without measures to eliminate spurious (unwanted) chip-like modes and / or their interactions with circuit-like modes.

[0006] One way to attempt to suppress spurious chip modes and crosstalk is to form vias through the thickness of the circuit substrate, introducing conductors between circuit elements that serve to disrupt and suppress spurious chip modes by reducing the effective length scale over which standing waves can form within the chip; providing conductors between circuit elements also reduces crosstalk (e.g., between qubits) by shielding field (capacitive and / or inductive) interactions. Summary of the Invention [Problem to be solved by the invention]

[0007] However, including vias in a circuit chip increases the complexity of manufacturing the chip and can adversely affect the operation of superconducting quantum computing circuits, as such circuits are particularly sensitive to the presence of impurities and defects, which cannot be helped by introducing additional steps into the manufacturing process.

[0008] It is an object of the present invention to provide an apparatus that provides a cleaner frequency space for the operation of quantum computing circuits. [Means for solving the problem]

[0009] Viewed from a first aspect, the present invention provides a superconducting quantum operation circuit package comprising: a substrate on which a superconducting quantum operation circuit having a plurality of circuit elements is formed, the substrate being disposed between the plurality of circuit elements and including one or more holes extending through the thickness of the substrate; a holder having a surface for accommodating the substrate and including one or more protrusions disposed on the surface and protruding from the surface, the holder being formed of a metal and / or a superconductor; and a cover disposed on the opposite side of the substrate from the holder and formed of a metal and / or a superconductor, the one or more protrusions protruding so as to pass through the one or more holes in the substrate and coming into contact with the cover, thereby suppressing electromagnetic modes within the operating frequency range of the quantum operation circuit.

[0010] The present invention provides a superconducting quantum operation circuit package. The package includes a substrate, a substrate holder, and a cover on the opposite side of the substrate from the holder. The substrate has a superconducting quantum operation circuit formed on its surface, for example, including a plurality of circuit elements such as quantum bits. One or more holes are formed to extend (completely) through the substrate, with the holes disposed between the circuit elements (for example, two or more circuit elements).

[0011] The substrate is positioned on a holder made of metal and / or superconductor. The holder has one or more protrusions formed on and protruding from the surface that accommodates the substrate. The one or more protrusions on the holder correspond to one or more holes in the substrate and are configured to protrude through the holes and contact the inner surface of the cover (when the cover is placed on the holder), thereby passing through the thickness of the substrate between multiple circuit elements. This current path between the holder and the cover via the protrusions acts to disrupt the formation of standing waves within the chip (e.g., across the chip) and suppress (e.g., substantially eliminate) EM modes consisting of such standing waves within the chip. This changes the field shape and frequency of EM "chip-like" modes (e.g., confines any modes between the edge of the substrate and the protrusions, or between the protrusions if multiple protrusions are present), thereby helping to prevent electromagnetic modes present in the package that could harm the operation of the quantum computing circuit.

[0012] It should be appreciated that the separate substrate and holder of the package thus provide conductive elements (i.e., protrusions of the holder) between circuit elements of the quantum computing circuit. The presence of the protrusions reduces the length scale over which standing waves can occur, thereby increasing the frequency of the lowest frequency EM modes. This helps to suppress (e.g., substantially eliminate) EM chip-like modes that occur at frequencies approximately the same as the desired operating frequency of the quantum computing circuit. This helps to reduce interference between undesired chip-like modes and the quantum computing circuit during operation.

[0013] The presence of holes and protrusions between circuit elements also helps to confine generated chip-like modes (e.g., modes that exist substantially within the "chip," i.e., the substrate and the circuitry formed thereon) and circuit-like modes (e.g., quantum modes, resonator modes, control line modes, etc.) to predetermined regions of, for example, the package and thus the quantum computing circuit, e.g., the regions between the protrusions. This can help to improve the addressability of circuit elements (their ability to be individually addressed) and reduce undesired interactions (e.g., qubit crosstalk) in an operating quantum computing circuit.

[0014] Separate holders, covers, and substrates also help minimize the number of fabrication steps required to manufacture the substrate and quantum computing circuitry. The substrate, holder, and cover are preferably formed as individual components. For example, the holder and cover may be manufactured separately from the substrate (and separately from each other), and the substrate may simply require the formation of holes through its thickness. This helps minimize the number of defects or impurities in these components.

[0015] Reducing interference, crosstalk, and the presence of impurities and defects in quantum computing circuits all help to provide a cleaner electromagnetic environment for quantum computing circuits to operate in, and allows quantum computing circuits to be scaled with more, e.g., qubits, on larger chips without increasing the number of spurious EM mode interactions, which helps improve the conditions for performing quantum computing by prolonging the coherence of the quantum computing circuit elements during operation.

[0016] Applicant also recognizes that the separate holder, cover, and substrate configuration of the present invention offers numerous advantages over substrates with integrally formed vias. This is because vias can only filter out chip-like modes. Therefore, if there is a gap between the chip and the housing surrounding it, spurious modes that can interfere with the quantum computing circuitry may exist in this gap without being filtered out by the vias. When the projections of the holder of the present invention pass through the holes in the substrate and contact the cover, the projections pass through all gap regions near the qubits, protecting the qubits from spurious gap modes as well.

[0017] The substrate may be any suitable and desirable substrate on which to form superconducting quantum computing circuits, for example for use in a superconducting environment. Preferably, the substrate comprises a high dielectric substrate. The substrate may be formed of any suitable and desirable material, for example, silicon or sapphire.

[0018] The substrate may be of any suitable and desirable shape, hi one embodiment, the substrate is substantially planar (except for holes extending through the thickness of the substrate).

[0019] The plurality of circuit elements of the quantum computing circuit may comprise any suitable and desirable circuit elements. In one embodiment, the plurality of circuit elements comprises one or more (e.g., all) of a quantum bit (e.g., comprising a Josephson junction or a superconducting electrode), a control line, and a readout element (e.g., a resonator). Preferably, the plurality of circuit elements comprises a plurality of sets of a quantum bit, a control line, and a readout element. The circuit elements may be arranged in any suitable and desirable manner, for example, as described in the applicant's previous application published as WO 2017 / 021714 A1, in which the superconducting electrodes of a quantum bit are coaxial and coplanar, and the control line and / or readout element are arranged out-of-plane with respect to the quantum bit. It should be understood that the quantum computing circuit package configuration of the present invention (at least in the preferred embodiment) is suitable for comprising such a quantum computing circuit layout.

[0020] In a preferred embodiment, the plurality of circuit elements comprises a plurality of qubits, e.g., control lines and readout elements. The qubits may be any suitable and desirable size and spaced apart from one another by any suitable and desirable distance. In one embodiment, the largest dimension of a qubit is between 0.1 mm and 1 mm. In one embodiment, the plurality of qubits are spaced apart from adjacent qubits by between 0.2 mm and 2 mm.

[0021] The circuit elements of the quantum operation circuit are preferably formed on a surface of a substrate. Preferably, the thickness of the substrate is significantly smaller than the other two dimensions (e.g., length and width), for example, in directions perpendicular to the thickness of the substrate. Thus, the substrate preferably has two opposing surfaces (separated by the thickness of the substrate) on either side of the substrate on which the circuit elements can be formed. One of these surfaces preferably faces the surface of the holder when the substrate is placed on the holder.

[0022] In one embodiment, the circuitry is formed on only one side of the substrate, e.g., the side opposite the holder surface. In another embodiment, the circuitry is formed on both sides of the substrate. It should be understood that this is possible due to the package design, since the conductive elements (i.e., the holder protrusions) are separate from the substrate. In contrast, substrates that include vias (integral with the substrate) may allow for circuitry on both sides of the substrate, but this requires a complex, multi-step fabrication process. In this manner, the package design of the present invention can accommodate a wide range of circuit designs.

[0023] In one embodiment, the substrate is not fixedly attached (e.g., glued or bonded) to the holder or cover within the package. Instead, for example, (e.g., a face of) the substrate may simply rest on the surface of the holder and / or cover. This also helps in some embodiments to allow circuit elements of the quantum computing circuit to be formed on the face of the substrate opposite the face of the holder (and thus, for example, on both faces of the substrate).

[0024] The holder and cover may be formed of any suitable and desirable metal and / or superconductor, such as a superconducting metal, hi one embodiment, the metal comprises aluminum.

[0025] The holder may be of any suitable and desired shape for receiving the substrate. In one embodiment, the surface receiving the substrate is generally planar (apart from the protrusions). In one embodiment, the holder is generally rectangular.

[0026] In one embodiment, the surface that receives the substrate is recessed from the face of the holder, for example a rectangular parallelepiped face, In other words, the holder may be provided with a rim around (protruding from) the surface that receives the substrate.

[0027] The surface may be recessed to any suitable and desirable depth. In one embodiment, the surface is recessed from the face of the holder by a depth approximately equal to the thickness of the substrate, e.g., the rim has a height approximately equal to the thickness of the substrate. Thus, when the substrate is placed on the surface, the substrate (e.g., its outer face) is preferably substantially flush with the face of the holder (and e.g., the rim).

[0028] In one embodiment, the protrusions disposed on the surface protrude in a direction generally perpendicular to the (e.g., planar) surface, and therefore the holes in the substrate preferably extend in a direction generally perpendicular to the surface (e.g., face) of the substrate.

[0029] The one or more protrusions on the surface of the holder may have any suitable and desirable shape, size, and spacing from one another. A plurality of protrusions disposed on and protruding from the surface is preferred. The protrusions may be arranged relative to the circuit elements (e.g., qubits) (e.g., in terms of position and / or number) in any suitable and desirable manner. In one embodiment, the holder comprises at least as many protrusions as there are qubits in the quantum operation circuit on the substrate. In one embodiment, the protrusions are arranged such that multiple circuit elements (e.g., qubits) are located between each protrusion. Thus, for example, there may be at least as many circuit elements (e.g., qubits) as there are protrusions.

[0030] Preferably, the holes in the substrate correspond in shape and size to the protrusions of the holder (they are slightly larger than the protrusions), and the holes accommodate the protrusions of the holder when the substrate is placed on the holder. Preferably, the substrate has a plurality of holes. Like the protrusions, the substrate may also have at least as many holes as there are qubits in a quantum operation circuit on the substrate. In one embodiment, the holes are arranged so that multiple circuit elements (e.g., qubits) are located between each hole. Thus, for example, there may be at least as many circuit elements (e.g., qubits) as there are holes. Preferably, the substrate includes as many holes as there are protrusions on the surface of the holder.

[0031] The one or more holes (and thus the corresponding one or more protrusions) may be arranged between the plurality of circuit elements in any suitable and desirable manner, for example, in a configuration that serves to suppress chip-like modes within the operating frequency range of the quantum computing circuit. Preferably, the one or more holes are arranged between the plurality of circuit elements, and the one or more protrusions protrude from the holder surface through at least a portion of the thickness of the substrate between the plurality of circuit elements.

[0032] Preferably, the one or more holes (and thus the one or more protrusions) are arranged surrounded by (e.g., between (e.g., to distribute the qubits)) the qubits of a quantum computing circuit formed on the substrate. Preferably, the one or more protrusions (and thus the one or more holes) are arranged to pass between (e.g., adjacent) qubits. This helps to reduce undesired interactions between circuit-like modes (e.g., reduce crosstalk between adjacent qubits) in addition to suppressing spurious electromagnetic modes. In one embodiment, the protrusions are arranged in a (e.g., regular geometric) lattice that corresponds, for example, to the (e.g., regular geometric) lattice of the qubits of the quantum computing circuit.

[0033] It will be appreciated that the holes and their corresponding protrusions may be arranged in any suitable and desirable configuration to suppress chip-like and, e.g., circuit-like modes in the operating frequency range of the quantum operations circuit and to confine modes, e.g., to the vicinity of individual qubits (so that the modes do not extend across multiple qubits). In preferred embodiments, the maximum spacing between adjacent holes and / or protrusions corresponds to (e.g., can support) chip-like modes having frequencies that exceed (e.g., significantly) the maximum operating frequency of the quantum operations circuit.

[0034] Preferably, the arrangement (e.g., size and spacing) of the protrusions and their corresponding holes relates to (e.g., matches) the arrangement (e.g., size and spacing) of the circuit elements (e.g., qubits) of the quantum operation circuit on the substrate. In one embodiment, when the holder includes multiple protrusions, the multiple protrusions are spaced apart from adjacent protrusions by 0.2 mm to 2 mm (and similarly for the holes accommodating the corresponding protrusions).

[0035] Preferably, the one or more protrusions (eg each) have a height (ie the height in the direction in which the protrusion protrudes from the surface of the holder) of between 0.2 mm and 1 mm (eg about 0.5 mm).

[0036] For contacting the cover, one or more protrusions may extend partway through the thickness of the substrate, while the cover may comprise corresponding protrusions (protruding from a surface of the cover) that also extend partway through the thickness of the substrate (from the opposite side of the substrate), so that one or more protrusions of the holder come into contact with one or more corresponding protrusions of the cover. When the cover comprises one or more protrusions, any or preferred features described herein with respect to one or more protrusions of the holder may preferably also apply to one or more protrusions of the cover.

[0037] As noted above, it should be understood that the height of the protrusions depends on how far the protrusions protrude through the substrate. Thus, in one embodiment, the height of (e.g., each of) one or more protrusions is greater than or equal to half the thickness of the substrate, e.g., is approximately equal to the thickness of the substrate.

[0038] However, it is preferred that one or more protrusions (of the holder) extend through the thickness of the substrate and contact the cover. Therefore, it is preferred that the height of (e.g., each of) the one or more protrusions is equal to or greater than the thickness of the substrate. Applicant has found that having protrusions extending through the thickness of the substrate can be particularly effective in suppressing (e.g., substantially eliminating) electromagnetic modes in the operating frequency range of the quantum computing circuit.

[0039] If the holder includes a recess or a rim, the depth of the recess or the height of the rim is preferably approximately equal to the height of one or more protrusions. Therefore, the depth of the recess or the height of the rim is preferably 0.2 mm to 1 mm (for example, about 0.5 mm).

[0040] The width (i.e., the width in a direction parallel to the surface of the holder) of (e.g., each of) one or more protrusions is preferably 0.2 mm to 1 mm (e.g., about 0.5 mm). Accordingly, the width (i.e., the width in a direction parallel to the surface of the substrate) of (e.g., each of) one or more holes is preferably 0.2 mm to 1 mm (e.g., about 0.5 mm).

[0041] The one or more protrusions and (e.g., each of) the one or more corresponding holes are preferably substantially cylindrical. Thus, for example, the cross section (in a plane substantially parallel to the surface of the holder) of the one or more protrusions (e.g., each of) is substantially constant in the direction in which the one or more protrusions protrude, e.g., in a direction substantially perpendicular to the surface of the holder. Correspondingly, for example, the cross section (in a plane substantially parallel to the surface of the substrate, i.e., substantially perpendicular to the thickness of the substrate) of the one or more holes (e.g., each of) is substantially constant in the direction in which the hole extends through the substrate, e.g., in a direction substantially perpendicular to the surface of the substrate (i.e., substantially parallel to the thickness of the substrate).

[0042] Thus, the (e.g., each of) one or more protrusions may take the form of a wall or a pillar, and the (corresponding) (e.g., each of) one or more holes may take the form of a channel or a pillar-shaped hole. In one embodiment, the (e.g., each of) one or more protrusions and one or more holes have a circular cross-section (and the cylindrical axis of the protrusion or hole) oriented in a direction generally perpendicular to the surface of the holder or the plane of the substrate (i.e., generally parallel to the thickness of the substrate).

[0043] In a preferred embodiment, the tip of one or more of the protrusions (e.g., each of them) is tapered, e.g., rounded or pointed. This helps ensure that the tip of the one or more protrusions makes contact with the cover. Applicant has recognized that in at least some embodiments of the present invention, even a small gap between the protrusion and the cover can cause problems with modes not being suppressed. For example, even a gap as small as 1 μm can cause problems.

[0044] The one or more protrusions (and their corresponding holes) may be arranged (e.g., shaped, sized, and / or positioned) to suppress (e.g., substantially eliminate) any appropriate and desired electromagnetic (e.g., tip-like) modes in the operating frequency range of the quantum operations circuit. In one embodiment, the one or more protrusions are arranged to suppress (e.g., substantially eliminate) all electromagnetic (e.g., tip-like) modes in the operating frequency range of the quantum operations circuit.

[0045] However, in some embodiments, one or more protrusions may be arranged (e.g., positioned) to suppress some (but not all) electromagnetic (e.g., tip-like) modes in the operating frequency range of the quantum computing circuit. For example, one or more protrusions may be arranged (e.g., positioned) to manipulate and utilize tip-like modes. This may be used, for example, to mediate long-range interactions between qubits that can be used to create quantum circuits with specific connectivity.

[0046] For example, if the package includes multiple protrusions, some of the protrusions (and corresponding holes in the substrate) may be positioned closely together (e.g., to suppress modes and confine them from extending beyond the individual qubits), while other protrusions may be positioned farther apart (or, for example, away from the edge of the substrate) to allow modes to exist and extend between the qubits. Thus, the spacing of the protrusions and corresponding holes may be selected accordingly.

[0047] The operating frequency range of the quantum operation circuit may be any suitable and desirable frequency range suitable for performing operations in the quantum operation circuit. In one embodiment, the operating frequency range is 4 GHz to 12 GHz. The protrusions protruding into the holes in the substrate may suppress only electromagnetic modes within the operating frequency range of the quantum operation circuit, but preferably the protrusions protruding into the holes in the substrate are positioned to suppress electromagnetic modes within a wider frequency range.

[0048] In one embodiment, the protrusions that protrude into the holes in the substrate are arranged to suppress electromagnetic modes having frequencies below 12 GHz, such as below 15 GHz, such as below 20 GHz.

[0049] In one embodiment, the holder includes one or more openings formed through a surface of the holder, and the quantum operation circuit package includes one or more wires arranged to pass through the one or more openings and connect to (e.g., multiple circuit elements of) the quantum operation circuit, respectively. Providing openings in the holder is useful for routing control wiring for the quantum operation circuit, for example, for addressing qubits.

[0050] It will be appreciated that when circuit elements are arranged such that the control lines and / or readout elements are not flush with the qubits, as described, for example, in Applicant's previous application published as WO 2017 / 021714 A1, providing openings in the holder for routing the control lines and / or readout elements (and, e.g., their connecting wires) can help provide a package with a compact and neat arrangement. Accordingly, embodiments of the present invention are well suited to accommodating off-chip control wiring (and quantum computing circuitry including such wiring). Such configurations may be more scalable than configurations that implement control wiring on-chip.

[0051] The one or more openings in the holder are preferably positioned between (e.g., interspersed with) one or more protrusions, for example, to correspond with circuit elements (e.g., qubits) of a quantum operation circuit formed on the substrate, which serves to connect the circuit elements of the quantum operation circuit to off-chip control wiring.

[0052] The cover is located on the opposite side of the substrate from the holder, e.g., the substrate is sandwiched between the holder and the cover. The cover protects the circuit elements from external electromagnetic radiation and also helps to reduce possible spurious electromagnetic modes. In one embodiment, for example, when the holder has a rim, the cover is positioned to surround the substrate together with the holder.

[0053] The cover may be of any suitable and desirable size, and preferably extends at least beyond the periphery of the substrate (e.g., the dimensions of the cover's surface facing the substrate are equal to or greater than the corresponding dimensions of the substrate's surface facing the cover).

[0054] In one embodiment, the cover includes one or more openings formed therethrough, and the quantum operations circuit package includes one or more wires arranged to pass through each of the one or more openings and connect to (e.g., multiple circuit elements of) the quantum operations circuit. For example, if the quantum operations circuit has off-chip control wiring, and particularly if the circuit elements of the quantum operations circuit are formed on both sides of the substrate, the openings through the cover, like the openings through the holder, also serve to provide paths for connecting wires to the quantum operations circuit. In the latter case, providing openings through both the holder and the cover allows for easy access to and connection to the circuit elements on both sides of the substrate.

[0055] The cover (e.g., a surface thereof) is preferably configured to space the circuit elements on the substrate (e.g., a surface thereof) so that the cover does not contact the circuit elements formed on the substrate (e.g., when at least some of the circuit elements are disposed on the surface of the substrate facing the cover). This helps to avoid shorting out the circuit elements of the quantum computing circuit (e.g., to the surface of the cover facing the substrate).

[0056] The cover may be of any suitable and desirable shape. In one embodiment, the cover is generally planar. In one embodiment, the cover is generally rectangular. The cover is preferably shaped to complement the shape of the holder (and e.g., the substrate), e.g., to surround the substrate.

[0057] In one embodiment, the cover has cutouts on its surface that correspond to and face the circuit elements on the substrate (e.g., the circuit elements arranged on the side of the substrate facing the cover) so as to space the cover from the circuit elements on the substrate.

[0058] In one embodiment, the cover is spaced from (eg, all sides of) the substrate to space the circuit elements on the substrate.

[0059] The cover may be spaced from the substrate in any appropriate and desirable manner. For example, a recess in the holder may be deeper than the thickness of the substrate, such that the surface of the substrate facing the cover is spaced from the cover. In another example, the cover may have a recess that spaces the cover from the substrate. In another example, a protrusion on the holder may be taller than the thickness of the substrate, such that the protrusion penetrates the thickness of the substrate and also protrudes from the surface of the substrate facing the cover, thereby spacing the cover from the substrate (e.g., positioned to abut against the protrusion).

[0060] When the substrate has circuit elements on the surface of the substrate facing the holder, it is preferable that the holder (e.g., the surface) is configured to be spaced apart from the circuit elements on the substrate (e.g., the surface) in the same manner as the cover, for example. Thus, for example, the holder may have cutouts on its surface that correspond to and face the circuit elements on the substrate (e.g., the circuit elements arranged on the surface of the substrate facing the holder) so as to be spaced apart from the circuit elements on the substrate.

[0061] The one or more protrusions may contact the cover in any suitable and desirable manner. Preferably, the (e.g., each) one or more protrusions is positioned to form conductive contact with the cover.

[0062] In one embodiment, the cover includes one or more recesses (on the surface of the cover facing the substrate) that correspond (e.g., in shape, size, and / or location) to one or more protrusions of the holder (and one or more holes in the substrate), and the recesses are arranged to receive the one or more protrusions (e.g., tapered tips of the protrusions) so that the one or more protrusions contact the cover within the corresponding one or more recesses. The recesses help to position the corresponding one or more protrusions and also help to form good contact between the protrusions and the cover.

[0063] Preferably, the cover comprises a quantity of conductive material within (e.g., each of) the one or more recesses, which material is softer (e.g., more malleable and / or ductile) than the metal of the cover. The conductive material within the recesses helps to form good (e.g., conductive) contact between the protrusions and the cover (i.e., the (e.g., each of) the one or more protrusions is positioned to contact the conductive material within a respective one of the one or more recesses). Preferably, the conductive material deforms when the one or more protrusions make contact. It should be appreciated that this deformation helps to offset manufacturing tolerances of the cover and the protrusions, eliminating the need to match the shape and / or size of the (e.g., recesses of) the cover to the shape and / or size of the protrusions. Preferably, the conductive material comprises a metal, such as indium.

[0064] In one embodiment, the holder and cover include (i.e., have) a surface treatment. This helps to provide (e.g., ultra-) clean surfaces and helps to avoid impurities and defects in the quantum computing circuit package. The surface treatment can be provided in any suitable and desirable manner, such as by etching.

[0065] The holder, substrate, and cover may be manufactured in any suitable and desirable manner. In one embodiment, one or more of the holder, substrate, and cover may be manufactured using laser machining, computer numerical control (CNC) machining, or mechanical micromachining. The formation of holes in the substrate may occur before or after the circuit elements are fabricated on the substrate.

[0066] Preferably, the quantum operation circuit package, in particular the holder and cover, are arranged to be cooled by a (e.g., cryogenic) cooling system, for example when the holder is formed of a superconductor. The present invention therefore extends to a superconducting quantum operation system comprising a superconducting quantum operation circuit package according to an embodiment of the present invention, and to a (e.g., cryogenic) cooling system arranged to cool the holder and cover (e.g., to a superconducting temperature). Thus, in order to cool the substrate (e.g., to a superconducting temperature), the holder and cover, which are formed of a metal or a superconductor, are preferably cooled by a cooling system.

[0067] It will be appreciated that, at least in preferred embodiments, the design of the holder and cover helps to maximize the area of surface contact with the substrate (on which the circuit elements are mounted), which helps to improve the thermal connectivity of the substrate to a cooling system (and thus helps to maximize thermal conductivity from the substrate) for cooling the substrate (e.g., to superconducting temperatures).

[0068] Any suitable and desirable (eg, cryogenic) cooling system may be used, such as, for example, a dilution refrigerator.

[0069] Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0070] [Figure 1] 1 shows a superconducting quantum operation circuit package according to an embodiment of the present invention. [Figure 2] 2 shows a substrate of the superconducting quantum operation circuit package shown in FIG. 1. [Figure 3] 2 shows the cover of the superconducting quantum operation circuit package shown in FIG. 1. [Figure 4] 1 shows a cross section of a portion of a superconducting quantum operation circuit package according to an embodiment of the present invention. [Figure 5] 1 shows a diagram of the lowest frequency electromagnetic modes generated by a superconducting quantum computing circuit. [Figure 6]1 shows a diagram of the lowest frequency electromagnetic modes generated by a superconducting quantum computing circuit. [Figure 7] 1 shows diagrams of the frequency spectra of electromagnetic modes generated in different superconducting quantum computing circuit packages. DETAILED DESCRIPTION OF THE INVENTION

[0071] As quantum computing chips are scaled to accommodate multiple qubits, the physical space occupied by the chip increases to a size that supports electromagnetic modes with frequencies comparable to the operating frequencies of the quantum computing circuits on the chip. Such spurious EM chip-like modes can interfere with the operation of the quantum computing circuits, resulting in detrimental loss of qubit coherence. As described below, embodiments of the present invention provide superconducting quantum computing circuits in which these spurious modes, as well as crosstalk, are suppressed.

[0072] 1 shows a superconducting quantum operation circuit package 1 according to an embodiment of the present invention. The package 1 includes a substrate 2, a holder 3 for the substrate 2, and a cover 4. In FIG. 1, the package 1 is shown in, for example, an unfolded configuration before assembly.

[0073] Fig. 2 shows the substrate 2 of the superconducting quantum operation circuit package 1 shown in Fig. 1. This substrate is generally made of silicon or sapphire. A quantum operation circuit 5 is formed on the surface of the substrate 2 (a similar circuit may be formed on the opposite surface of the substrate 2).

[0074] The quantum computing circuit 5 includes a plurality of qubits 6 arranged in a regular geometric lattice. The qubits 6 are connected to each other by respective wires 7. The qubits 6 are addressed by respective control lines and readout elements, for example as disclosed in the applicant's previous application published as WO2017 / 021714A1.

[0075] A plurality of holes 8 are formed (e.g., machined) through the thickness of the substrate 2. The holes 8 are arranged in a regular geometric grid that distributes the qubits 6. (Similarly, qubits and wiring are formed between the holes 8 on the back side of the substrate 2.)

[0076] 1 , the holder 3 of the superconducting quantum operation circuit package 1 is made of aluminum (or other suitable superconducting metal) and has a generally rectangular parallelepiped shape. A recess 10 is formed in the upper surface 9 of the holder 3 so that a rim 11 extends along the periphery of the upper surface 9. The depth of the recess 10 is generally equal to the thickness of the substrate 2, and when the substrate 2 is placed on the upper surface 9 of the holder 3, the upper surface of the substrate 2 is flush with the rim 11 of the holder 3.

[0077] A plurality of cylindrical protrusions 12 are formed on the upper surface 9 of the holder 3 within the recess 10. The positions and number of the protrusions 12 correspond to the holes 8 formed through the substrate 2. The diameter of the cylinder of the protrusions 12 is slightly smaller than the corresponding diameter of the hole 8 of the substrate 2, and the height of the protrusions 12 is slightly greater than the thickness of the substrate 2. When the substrate 2 is placed on the upper surface 9 of the holder 3 and the cover 4 is placed on the holder 3 so as to surround the substrate 2, the protrusions 12 pass through the corresponding hole 8 and the tops of the protrusions 12 come into contact with the inner surface of the cover 4.

[0078] A plurality of openings 13 are formed within recess 10, penetrating holder 3. Similarly, a plurality of openings 14 are formed through cover 4. The positions and number of openings 13, 14 penetrating holder 3 and cover 4 correspond to the quantum bits 6 formed on substrate 2. Openings 13, 14 allow off-chip control wiring to be routed through holder 3 and cover 4 and connected to quantum bits 6 of quantum operation circuit 5.

[0079] FIG. 3 shows the underside of cover 4. Openings 14 penetrating cover 4 are visible, as are cutout channels 15 extending between openings 14. The positions and number of cutout channels 15 correspond to the wiring 7 between qubits 6 of quantum operation circuit 5. The width of cutout channels 15 is wider than the width of wiring 7, so that when cover 4 is placed on substrate 2, cover 4 does not come into contact with (i.e., short-circuit) the circuit elements of quantum operation circuit 5. (If a quantum operation circuit is formed on the opposite side of substrate 2, similar cutout channels may be provided between openings 13 penetrating holder 3.)

[0080] 3 also shows a plurality of recesses 16 formed on the underside of the cover 4. The positions and number of the recesses 16 correspond to the holes 8 formed through the substrate 2, and therefore also correspond to the protrusions 12 of the holder 3.

[0081] 4 shows a cross section of a portion of the superconducting quantum operation circuit package 1. FIG. 4 shows the holder 3, cover 4, and substrate 2 around the recess 16 in the cover 4, the hole 8 in the substrate 2, and the protrusion 12 of the holder 3. The protrusion 12 has a tapered tip 17 that passes through the hole 8 in the substrate 2, and is aligned with the recess 16 in the cover 4. The cylindrical diameter of this recess 16 (and all other recesses 16 in the cover 4) is slightly larger than the corresponding diameter of the protrusion 12, so that the protrusion 12 is received in the recess 16.

[0082] This recess 16 (and all other recesses 16 in the cover 4) is substantially filled with a quantity of indium 18. Indium 18 is a soft metal that deforms when the substrate 2 is sandwiched between the cover 4 and the holder 3, so that the tapered tips 17 of the protrusions 12 protrude into the quantity of indium 18. This contributes to a good conductive connection between the holder 3 and the cover 4.

[0083] The components of the superconducting quantum operation circuit package 1 are manufactured using laser processing, computer numerical control (CNC) processing, or mechanical micromachining.

[0084] The use of the superconducting quantum operation circuit package 1 will now be described with reference to Figures 1, 2, 3, 4, 5, 6, and 7. Figure 5 shows a diagram of the electric field magnitude distribution of the lowest frequency chip-like mode on a 1 cm x 1 cm sapphire substrate 2 that has no through holes (and no protrusions through the substrate 2). Figure 6 shows a diagram of the electric field magnitude distribution of the lowest frequency chip-like mode generated by a superconducting quantum operation circuit on a 1 cm x 1 cm sapphire substrate 2 surrounded by the holder 3 and cover 4 shown in Figures 1 to 4. Figure 7 shows diagrams of the frequency spectrum of the electromagnetic mode generated by each of the different superconducting quantum operation circuit packages.

[0085] Once the quantum operation circuit 5 is formed on the substrate 2, the elements of the quantum operation circuit 5 are connected to off-chip wiring used to control the operations performed by the quantum operation circuit 5. The substrate 2 is inserted into the recess 10 of the holder 3 so that the substrate 2 rests on the upper surface 9 of the holder 3 with the protrusions 12 penetrating the thickness of the substrate. The cover 4 is placed on the substrate 2 so that the holder 3 and cover 4 surround the substrate 2, causing the protrusions 12 to contact the underside of the cover 4 via a quantity of indium 18 in a recess 16 on the underside of the cover 4. The off-chip control wiring passes through openings 13, 14 in the holder 3 and cover 4 and is connected to the appropriate control circuitry.

[0086] The superconducting quantum operation circuit package 1 is placed in an appropriate cryogenic system so that it can operate at superconducting temperatures.

[0087] During operation of the quantum processing circuit 5, electromagnetic modes are generated on the substrate 2. If the quantum processing circuit 5 were formed on a substrate 2 that did not have any through holes (and protrusions passing through the holes), the distribution of the lowest frequency electromagnetic modes 20 that would be generated (in one particular mode of operation) would be as shown in the diagram of Figure 5. This distribution of the lowest frequency modes 20 shows that the generated modes 20 extend throughout the entire substrate 2, and thus pass between the qubits 6 of the quantum processing circuit 5. Because these modes are at around 7 GHz, they are likely to interfere with the qubits 6 and cause crosstalk between the qubits 6.

[0088] FIG. 7 shows the frequency spectrum of the four lowest-frequency electromagnetic modes that occur during operation of the quantum operation circuit in this configuration (i.e., a configuration without holes penetrating the substrate 2 and protrusions passing through the holes). FIG. 7 shows that the four lowest-frequency chip modes 22 that occur are in the range of 6 GHz to 14 GHz. Thus, the frequencies of these undesired electromagnetic modes 20, 22 partially overlap with the microwave frequencies in the range of 4 GHz to 12 GHz used to operate the quantum operation circuit 5 (see FIG. 7). Spurious electromagnetic modes 20, 22 at these frequencies and crosstalk between qubits 6 due to the distribution of these spurious modes 20, 22 interfere with the operation of the quantum operation circuit 5, resulting in a detrimental loss of coherence in the qubits 6.

[0089] FIG. 6 shows the distribution of the lowest-frequency electromagnetic mode 21 generated when the substrate 2 is placed inside the holder 3 and cover 4 shown in FIGS. 1 to 4 . As can be seen from FIG. 6 , although the lowest-frequency electromagnetic mode 21 is generated during operation of the quantum operation circuit 5, when the substrate 2 is placed on the surface 9 of the holder 3, the lowest-frequency electromagnetic mode 21 penetrates the thickness of the substrate 2 and is confined to the volume between each pair of adjacent protrusions 12 by the protrusions 12 of the holder 3 located between the circuit elements (including the quantum bits 6) of the quantum operation circuit 5. This mode is approximately 20 GHz, which is significantly detuned from the operating frequency of the quantum bits 6, and is therefore unlikely to interfere with the quantum bits 6 or cause crosstalk between the quantum bits 6. Furthermore, the protrusions serve to localize the circuit mode within the volume immediately adjacent to each pair of adjacent protrusions 12, further reducing crosstalk between the quantum bits 6.

[0090] Furthermore, as shown in Figure 7, which shows the frequency spectrum of the four lowest frequency electromagnetic modes 23 generated during operation of the quantum operation circuit in this configuration (i.e., a configuration having holes penetrating the substrate 2 and protrusions passing through the holes as shown in Figures 1 to 4), the minimum frequencies of the spurious electromagnetic modes 21, 23 are higher than the microwave frequency used to operate the quantum operation circuit 5 because the modes are confined within a smaller volume (see Figure 6).

[0091] Thus, FIG. 7 shows the effect on suppression of electromagnetic modes in the operating frequency range of the quantum operation circuit, due to the frequency increase of the lowest frequency spurious modes using a superconducting quantum operation circuit package according to an embodiment of the present invention.

[0092] For these reasons, when the quantum operation circuit 5 is operated using the superconducting quantum operation circuit package 1 shown in Figures 1 to 4, spurious electromagnetic modes and crosstalk are significantly suppressed. This helps to realize a clean frequency space for the operation of the quantum operation circuit 5 and helps to increase the coherence time of the quantum bits 6.

Claims

1. a substrate on which a superconducting quantum operation circuit including a plurality of circuit elements is formed, the substrate including one or more holes disposed between the plurality of circuit elements and extending through a thickness of the substrate; a holder having a surface for receiving the substrate, the holder including one or more protrusions disposed on and protruding from the surface, the holder being made of a metal and / or a superconductor; a cover disposed on the opposite side of the substrate from the holder and made of a metal and / or a superconductor; the one or more protrusions protrude through the one or more holes in the substrate and contact the cover, thereby suppressing electromagnetic modes within an operating frequency range of the quantum operation circuit; the cover has cutouts on a surface thereof that correspond to and face the plurality of circuit elements on the substrate; the surface that receives the substrate is recessed from a face of the holder; Superconducting quantum computing circuit package.

2. the plurality of circuit elements include one or more of one or more quantum bits, one or more control lines, and one or more readout elements; The superconducting quantum operation circuit package according to claim 1 .

3. a maximum spacing between adjacent holes in the substrate and / or adjacent protrusions on the holder corresponds to a chip-like mode having a frequency higher than a maximum operating frequency of the quantum operation circuit; The superconducting quantum operation circuit package according to claim 2 .

4. the one or more holes are disposed between the one or more quantum bits, and the one or more protrusions are disposed so as to pass between adjacent quantum bits.

4. The superconducting quantum operation circuit package according to claim 2 or 3.

5. the surface is recessed from the face of the holder by a depth approximately equal to the thickness of the substrate and / or the height of the one or more protrusions; The superconducting quantum operation circuit package according to any one of claims 1 to 4.

6. the one or more holes correspond in shape and size to the one or more protrusions, and when the substrate is on the holder, the one or more holes receive the corresponding one or more protrusions; The superconducting quantum operation circuit package according to any one of claims 1 to 5.

7. the one or more protrusions have a height equal to or greater than half the thickness of the substrate; The superconducting quantum operation circuit package according to any one of claims 1 to 6.

8. the one or more protrusions projecting into the one or more holes in the substrate are positioned to suppress electromagnetic modes having frequencies less than 12 GHz. The superconducting quantum operation circuit package according to any one of claims 1 to 7.

9. a cover separating the plurality of circuit elements on the substrate; The superconducting quantum operation circuit package according to any one of claims 1 to 8.

10. The holder and the cover are surface-treated. The superconducting quantum operation circuit package according to any one of claims 1 to 9.

11. the cover includes one or more recesses corresponding to the one or more protrusions; the one or more recesses are arranged to receive the one or more protrusions, and the one or more protrusions contact the cover within a corresponding one or more recesses; The superconducting quantum operation circuit package according to any one of claims 1 to 10.

12. the cover having a quantity of conductive material within the one or more recesses; The material is softer than the metal of the cover. The superconducting quantum operation circuit package according to claim 11.

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