Quantum information processing system
By designing coaxial superconducting qubits and arranging out-of-plane control readout elements, the problems of short coherence time and complex wiring in quantum computing systems are solved, achieving effective isolation of qubits and scalability of the system, supporting large-scale quantum computing.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- OXFORD UNIVERSITY INNOVATION LTD
- Filing Date
- 2016-07-29
- Publication Date
- 2026-05-12
AI Technical Summary
In existing quantum computing systems, the short coherence time of qubits makes it difficult to scale in two-dimensional arrays, and the complex control and readout wiring limits the system's size and efficiency.
The design employs a coaxial and coplanar superconducting qubit design, with control lines and readout elements arranged out of plane. Electromagnetic coupling is reduced through coaxial electrodes, achieving effective isolation of the qubits, and topological expansion is achieved through multiple building blocks.
It significantly extends the coherence time of qubits, simplifies wiring, supports the construction and expansion of large-scale multi-qubit systems, and improves the scalability and operational efficiency of the system.
Smart Images
Figure CN115545206B_ABST
Abstract
Description
[0001] This application is a divisional application of patent application No. 201680043930.2 filed on July 29, 2016, entitled "Quantum Information Processing System". Technical Field
[0002] The present invention relates to quantum information processing systems and building blocks for such systems, and particularly to superconducting building blocks for quantum information processing systems. Background Technology
[0003] In superconducting circuit implementations of quantum computers, the basic unit of quantum computing (qubit) can be physically implemented in a variety of different ways. Typically, one or more Josephson junctions are combined with capacitors and / or inductors to form a high-quality anharmonic circuit, where the lowest quantization level serves as the qubit. For example, a commonly implemented and successful design called a charge qubit or transporter lies in its simplest form: a single Josephson junction connected in parallel with a capacitor. The two electrodes of a qubit can be arranged in various ways; examples include arranging the electrodes collinearly in a geometry approximating a dipole antenna, using interdigitated capacitors, or having one electrode in a cross shape and the other implemented as a common ground plane. Control and measurement circuitry systems are typically implemented using planar circuitry systems integrated with the qubit on a chip, and / or using 3D electromagnetic waveguides and cavities in which the qubit chip is embedded.
[0004] A crucial consideration in the design of quantum information processing systems is maximizing the coherence time of qubits (the lifetime that must be preserved for the fragile quantum states of the qubits to perform quantum computations). This requires highly controlled electromagnetic environments for the qubits, designed to prevent leakage of their quantum information into these environments. A common approach to achieving this environmental control is to embed the qubits within or strongly couple them to high-quality electromagnetic resonators on a chip or in 3D, which have a resonant frequency different from that of the qubits. This prevents energy leakage due to the environment's inability to tolerate the energy at the qubit's frequency. Because the resonator experiences a measurable frequency shift when the qubit changes its quantum state, this method, known as circuit quantum electrodynamics, also provides a convenient way to measure the quantum state of the qubits.
[0005] The macroscopic size of superconducting qubits makes it easy to couple control signals to them, enabling relatively easy execution of fast operations. However, the linear arrangement of the superconducting electrodes of a qubit typically implies strong coupling to the environment, particularly to a uniform electromagnetic field that is often present in the environment at the size scale of the qubit. This results in a reduction in the coherence time of the quantum superposition states of the qubit, which is desired to be as long as possible to enable quantum computing using the qubit. This is because qubits readily radiate energy when coupled to an electromagnetic field.
[0006] To perform any useful quantum computing, an architecture consisting of a large number of qubits must be implemented, with coupling between the qubits and wiring that enables control and readout of all (or a critical subset) of the qubits. However, if such an architecture is implemented using in-plane coupling and control and readout wiring (e.g., on the surface of a fabricated chip or circuit board), the size becomes increasingly difficult to accommodate the necessary wiring in space. This is due to the fundamental fact that the edges of a two-dimensional array of N qubits extend in the square root of N, such that, for example, for a square arrangement of M × M qubits (totaling N = M² qubits), M²-order control and readout lines are needed across the edges (between 4M edge qubits). This can hinder the implementation of a practically useful-scale quantum computer with a 2D qubit array. Summary of the Invention
[0007] The present invention aims to provide an improved and scalable architecture for quantum computing systems.
[0008] When viewed from a first aspect, the present invention provides building blocks for a quantum information processing system, comprising:
[0009] A superconducting quantum bit comprising a Josephson junction connected between two superconducting electrodes, wherein the two superconducting electrodes are coaxial and coplanar;
[0010] A control line coupled to the superconducting qubit and arranged to control the state of the superconducting qubit; and / or a readout element coupled to the superconducting qubit and arranged to measure the state of the superconducting qubit;
[0011] The control lines and / or readout elements are arranged out of plane relative to the two superconducting electrodes.
[0012] When viewed from a second aspect, the present invention provides a quantum information processing system comprising a plurality of component blocks as described in the first aspect of the invention;
[0013] At least some (and preferably all) of the superconducting qubits in the plurality of building blocks are coupled to one or more of the other superconducting qubits in the plurality of building blocks.
[0014] This invention relates to a quantum information processing system that provides superconducting qubits as a fundamental building block. Superconducting qubits are formed by a Josephson junction connected between two coaxial and coplanar superconducting electrodes, i.e., a weak link in the Josephson junction, for example, by providing a barrier of insulating material between the two coaxial and coplanar superconducting electrodes. The Josephson junction, combined with the capacitance between these electrodes, implements charge qubits or transporters (where the Josephson energy is much greater than the charging energy associated with the capacitance).
[0015] Preferably, a control line is coupled to the superconducting qubit, and this control line is arranged to control the quantum state of the individual qubit (e.g., by exposing the qubit to microwave pulses of controlled amplitude and phase). This control line can also be used in implementations of multi-qubit operation in multi-qubit systems, such as those described in the second aspect of the invention. A readout element is also preferably coupled to the superconducting qubit, for example, during or after quantum computing, in implementations of quantum algorithms, or to obtain the results of quantum computing, and is arranged to measure the quantum state of the superconducting qubit. The control line and / or the readout element are arranged out of plane relative to the plane of the two superconducting electrodes of the qubit, i.e., these elements are positioned at locations not in the same plane as the two superconducting electrodes.
[0016] The invention also extends to quantum information processing systems comprising multiple component blocks, wherein each component block is (i.e., electromagnetically) coupled to at least one of the other component blocks in the system.
[0017] The applicant has recognized that because the electrodes of a qubit are not oriented in a single direction—that is, they are coaxial, for example, possessing circular symmetry—providing building blocks for a quantum information processing system in which superconducting qubits have coaxial electrodes helps to significantly reduce the electromagnetic coupling of the qubit to a uniform electromagnetic field, compared to qubits with linear geometry. A qubit can be coupled to an electromagnetic field having a coaxial component or a fundamental field gradient at its location; however, these fields are unlikely to exist naturally in the qubit's environment. Therefore, effectively isolating the qubit from its electromagnetic environment helps to increase the qubit's coherence time.
[0018] Furthermore, because the far-field radiation of a qubit with coaxial electrodes weakens very rapidly at distances larger than the qubit's size, the qubit is only very weakly coupled to other electromagnetic objects in the system, such as other qubits (if any), in addition to being isolated from the electromagnetic environment as described above. This electromagnetic isolation, in turn, helps increase the coherence time of the qubit and improves the practicality of constructing large-scale multi-qubit systems. This is in contrast to conventional qubits with linear constructions that typically have large dipole moments, and provides a significantly greater electromagnetic field at greater distances from the qubit.
[0019] The applicant has also recognized that by providing building blocks for a quantum information processing system in which the plane of the control and readout elements relative to the two superconducting electrodes of the qubit is arranged out of plane, the topology of a quantum information processing system comprising multiple building blocks can be expanded in the same manner as the number of building blocks. This is because, although multiple couplings are provided to the qubit, no space is required for the control and readout elements in the plane of the electrodes since the electrodes are arranged out of plane relative to the qubit. It should be understood that this is impossible for conventional quantum computing systems (e.g., implemented using in-plane geometry) because all components and connections must be arranged in the same plane, which becomes increasingly difficult as the system has more than a certain number of qubits.
[0020] The two superconducting electrodes of a qubit can be arranged in any suitable and desired coaxial and coplanar configuration. In a preferred embodiment, the two superconducting electrodes of the qubit are radially symmetrical, i.e., circular. Because there is no orientation in the plane of the electrodes with more orientations than other directions, this configuration of the two electrodes further helps to reduce the electromagnetic coupling of the qubit to the environment. The exterior of the two coaxial superconducting electrodes may include a ground plane, for example, shared with other qubits when the system includes multiple qubits.
[0021] The superconducting electrodes can be continuous, for example, in a circle. However, in one embodiment, the outer edges of the two electrodes are discontinuous, for example, at a (single) point. Therefore, a small gap can exist in the outer ring electrode of the qubit. This helps prevent continuous circulating current and trapped magnetic flux between the two superconducting electrodes.
[0022] Quantum bits can be formed in any suitable and desired manner. In a preferred embodiment, qubits (i.e., comprising two superconducting electrodes and a weak link) are formed by microfabrication of a low-loss superconducting material such as aluminum on a low-loss dielectric substrate such as sapphire or silicon.
[0023] In one embodiment, the qubits are arranged to be frequency-tunable, for example by incorporating two Josephson junctions connected in parallel between two superconducting electrodes and an out-of-plane control line controlling the magnetic flux passing through the gap enclosed by the superconducting electrodes and the Josephson junctions. This embodiment enables controllable operations requiring frequency-tunable qubits.
[0024] The control lines for the component blocks can be provided in any suitable and desired manner. In a preferred embodiment, the control lines are arranged coaxially with the two superconducting electrodes of the qubit. Alternatively or concurrently, the control lines comprise coaxial cables, for example, having geometry that matches or is similar to that of the coaxial electrodes of the qubit. This arrangement allows the control lines to be coupled directly to the qubit and to highly selectively control individual qubits from among multiple qubits in a multi-qubit system.
[0025] In another embodiment, the control line includes a magnetic flux control line. Such a magnetic flux control line preferably comprises a coaxial line with electrically shorted ends, wherein the coaxial line has a center conductor connected to an external ground conductor (e.g., in a manner that allows current in the coaxial cable to generate magnetic flux in a nearby qubit). For example, in embodiments where the qubit is frequency-tunable, this allows the control line to control the frequency of the qubit.
[0026] The control lines are arranged to control the state of the qubit in any suitable and desired manner. Preferably, the control lines are arranged to irradiate the qubit with electromagnetic radiation, such as microwaves. In a preferred embodiment, the control lines are arranged to apply pulses of electromagnetic radiation, such as microwaves, to the qubit. The length, phase, and / or amplitude of the electromagnetic radiation pulses can be varied to implement universal single-qubit control. Therefore, preferably, the control lines are arranged to provide universal control of the quantum state of the qubit.
[0027] The readout element for the component block can be provided in any suitable and desirable manner. In a preferred embodiment, the readout element comprises a (e.g., microwave) resonator coupled to the superconducting qubit (e.g., arranged coaxially with the two superconducting electrodes of the qubit). The microwave resonator may include a lumped-element microwave resonator, for example, having the same geometry as the qubit and differing only in that a linear inductor is used instead of a Josephson junction. Thus, in a particularly preferred embodiment, the two superconducting electrodes, control lines, and / or the readout element are arranged coaxially. In addition or alternatively, the readout element comprises a coaxial cable, for example, having a geometry that matches or is similar to the coaxial electrodes of the qubit. This arrangement allows the readout element to be coupled directly to the qubit and to perform highly selective measurements of individual qubits from multiple qubits in a multi-qubit system.
[0028] The readout element is arranged to measure the state of the qubit in any suitable and desired manner. In a preferred embodiment (when the readout element includes a coaxial cable and a microwave readout resonator), the coaxial cable of the readout element is arranged to measure the response of the readout microwave resonator (which is coupled to the qubit), for example at a certain frequency from which the state of the qubit can be inferred.
[0029] In one embodiment of the component block, the control line and the readout element may be formed as a single element, i.e. combined into the same element, preferably including a coaxial cable and a coaxial readout resonator, the single element being arranged for controlling and measuring both for a single qubit, for example, where the coaxial cable is arranged behind the readout resonator.
[0030] In a quantum information processing system, preferably, each control line and / or readout element is coupled to only a single qubit, i.e., preferably there is a one-to-one relationship between the qubit and its associated control line and / or readout element. Quantum information processing systems can be provided such that not all qubits have associated control lines and / or readout elements, for example, to implement specific quantum computing architectures such as surface codes.
[0031] In a quantum information processing system, each of a plurality of building blocks can be coupled to one or more of the other building blocks in any suitable and desired manner. In a preferred embodiment, one or more, and preferably all, of the plurality of building blocks are coupled to the other nearest building block. Coupling a building block to its nearest one or more neighboring building blocks helps to provide a simple and scalable architecture that enables fault-tolerant quantum computing schemes such as surface codes.
[0032] Preferably, the coupling includes capacitance between the external electrodes of adjacent qubits, which can be adjusted, for example, by changing the geometry and / or spacing of the qubit electrodes. Preferably, the quantum information processing system further includes one or more additional superconducting qubits that can be connected to one or more of the building blocks in any suitable and desired manner (such as via capacitance between the external electrodes of adjacent qubits). For example, the additional superconducting qubits may or may not be connected to control lines and / or readout elements.
[0033] Multiple building blocks in a quantum information processing system can be arranged in any suitable and desired manner. In a preferred embodiment, the building blocks are arranged, for example, in a regular array. The type of array may depend on the number of other building blocks that each building block is expected to couple to. For example, the array may include a square array (i.e., in which qubits are arranged in rows and columns), in which case each qubit may be coupled to up to four other qubits (assuming, for example, only the nearest neighbor couplings are used). In another embodiment, the array may include a triangular array, in which case each qubit may be coupled to up to six other qubits (assuming, for example, only the nearest neighbor couplings are used). In yet another embodiment, the array may include a hexagonal array, in which case each qubit may be coupled to up to three other qubits (assuming, for example, only the nearest neighbor couplings are used). Other geometries may be used in any suitable and desired manner.
[0034] In a quantum information processing system, multiple qubits can be arranged in a single plane (i.e., the plane of a superconducting electrode). However, embodiments are also envisioned in which multiple planes of qubits are provided, for example, stacked on top of each other such that the planes of the qubits are parallel.
[0035] A quantum information processing system may include any suitable and desired number of qubits. In one embodiment, the quantum information processing system includes 10 or more qubits, such as 20 or more qubits, such as 50 or more qubits, such as 100 or more qubits.
[0036] In one embodiment, the quantum information processing system includes a processing circuitry arranged to operate one or more of a plurality of qubits, such as manipulating the state of one or more qubits. Preferably, the processing circuitry is arranged to implement one or more quantum logic gates (e.g., high-fidelity single-qubit and two-qubit) throughout the qubit array in the system. More preferably, the processing circuitry is arranged to implement high-fidelity single-qubit measurements on at least a subset of the qubits in the array. Even more preferably, the processing circuitry is arranged to implement one or more error correction schemes, such as using a feedback algorithm. This enables the quantum information processing system to perform useful quantum computations. Attached Figure Description
[0037] Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which:
[0038] Figure 1 The diagram illustrates a component block for a quantum information processing system according to an embodiment of the present invention;
[0039] Figure 2 As shown Figure 1 The shown component blocks are grouped together;
[0040] Figure 3 and Figure 4 As shown Figure 1 The array of component blocks shown; and
[0041] Figure 5 The structure of a quantum information processing system according to a further embodiment of the present invention is shown. Detailed Implementation
[0042] Figure 1 A component block 1 for a quantum information processing system according to an embodiment of the present invention is schematically shown. Component block 1 includes a superconducting qubit 2 having two superconducting electrodes 3, 4 and a Josephson junction 5 between the two superconducting electrodes 3, 4. The two superconducting electrodes 3, 4 are arranged as a circular inner superconducting electrode 3 surrounded by a coaxial and coplanar circular outer superconducting electrode 4. The Josephson junction 5 is arranged to extend radially between the two superconducting electrodes 3, 4. The superconducting qubit 2 can be formed by microfabrication of a low-loss superconducting material such as aluminum on a low-loss dielectric substrate such as sapphire or silicon.
[0043] To control the quantum state of superconducting qubit 2, control line 6 is arranged coaxially with superconducting qubit 2. Control line 6 is arranged to irradiate superconducting qubit 2 with microwaves in order to set the state of superconducting qubit 2.
[0044] On the other side of the superconducting qubit 2, a readout resonator 7 and a readout line 8 are disposed, both of which are also arranged coaxially with the superconducting qubit 2. The readout resonator 7 is arranged to couple to the superconducting qubit 2 in such a way that its resonant frequency depends on the state of the superconducting qubit 2. The readout line 8 is arranged as a radiating resonator 7 and the frequency shift of the resonator 7 is measured via reflected microwave signals, and thus the state of the superconducting qubit 2 is measured.
[0045] Figure 2 The schematic diagram shows an arrangement in a straight line, such as Figure 1 The three components in block 1 shown are group 10. All superconducting qubits 2 are located in the same plane and therefore can be formed on the same substrate. Resonators 7 can be formed on the back side of the same substrate or on a separate substrate. (See reference...) Figure 4 As shown, but Figure 2 As not shown, the external superconducting electrode 4 of each superconducting qubit 2 is connected to the external superconducting electrode 4 of the nearest neighboring qubit 2 via a capacitor.
[0046] Figure 3 The schematic diagram illustrates an arrangement of elements in a square array, such as... Figure 1 The nine components in block 1 shown are grouped 20. The superconducting qubits 2 are in the same plane and therefore can be formed on the same substrate. The resonator 7 can be formed on the back side of the same substrate or on a separate substrate. (See reference...) Figure 4 As shown, but Figure 3 As not shown, the external superconducting electrode 4 of each superconducting qubit 2 is connected to the external superconducting electrode 4 of the nearest neighboring qubit 2 via a capacitor.
[0047] Figure 4 schematically shown Figure 3 The diagram shows a plan view of component block 1. As can be seen, component block 1 is arranged in a square array, wherein the external superconducting electrode 4 of each superconducting qubit 2 is connected to the external superconducting electrode 4 of the nearest adjacent superconducting qubit 2 via a capacitor 9.
[0048] In addition, in order to implement including such Figures 1 to 4 The quantum information processing system shown in component block 1 will include multiple standard control electronics (not shown), such as those connected to the ends of each in a coaxial cable, including control line 6 and readout line 8, as well as a suitable cooling system (not shown) required to keep the necessary components at superconducting temperatures.
[0049] For example, in operation, quantum information processing system 10 or quantum information processing system 20 is provided as part of a quantum computer. Control lines 6 apply pulses of microwave radiation to their respective superconducting qubits 2, the length, phase, and / or amplitude of which are used to control the state of the superconducting qubits 2, i.e., the state of the qubits, and to perform individual qubit operations. Multi-qubit (e.g., two-qubit) quantum logic operations are implemented in any desired manner (e.g., by applying appropriate microwave pulses to control lines 6, utilizing capacitive coupling between qubits, or otherwise coupling). The quantum state of the superconducting qubits 2 is thus manipulated through a series of quantum logic gates to perform computations using quantum information processing system 10 or quantum information processing system 20.
[0050] Once the calculation has been performed, the readout resonators 7 are used to measure the state of their respective superconducting qubits 2, for example, by measuring the amplitude and / or phase of a microwave signal applied to readout lines 8, which radiate the readout resonators 7 near their resonant frequencies, which depend on the state of their respective superconducting qubits 2. The state of the superconducting qubits 2 after the calculation is performed can then be used to determine the result of the calculation.
[0051] Figure 5 A component block 21 for a quantum information processing system according to a further embodiment of the present invention is illustrated schematically. This component block 21 is similar to... Figures 1 to 4 The component block shown includes a superconducting quantum bit 22 with two superconducting electrodes 23 and 24, which are arranged as a circular inner superconducting electrode 23 surrounded by a coaxial and coplanar circular outer superconducting electrode 24.
[0052] The difference lies in that the superconducting qubit 22 includes two Josephson junctions 25 and 26 extending radially between the two superconducting electrodes 23 and 24. This makes the flux of the superconducting qubit 22 tunable, meaning that its transition frequency can be adjusted by changing the magnetic flux through the two spaces between the two electrodes of the superconducting qubit 22.
[0053] Control line 27 is coaxially arranged with superconducting qubit 22 and is capable of providing magnetic flux control to superconducting qubit 22. Readout resonator 28 and readout line 29 are arranged on opposite sides of superconducting qubit 22, and readout line 29 also serves as a control line for implementing individual qubit control. Figure 1 In the embodiment shown, the control of this single qubit is implemented using control line 6.
[0054] Reference Figures 1 to 4 The component blocks shown are similar. Figure 5 The component block 21 is arranged as part of an array of component blocks to form a quantum information processing system.
[0055] Figure 5 The operation of component block 21 (as part of the quantum information processing system) is similar to Figures 1 to 4 The component block shown, namely control line 27, is arranged to set the quantum state of the superconducting qubit 22 by applying magnetic flux. The state of component block 21 (along with other elements in the quantum information processing system) is then manipulated and subsequently measured using readout resonator 28 and readout line 29.
[0056] Therefore, it should be understood that because the superconducting electrodes of a superconducting qubit are not oriented in a single direction, the building block and quantum information processing system of this invention significantly reduce the electromagnetic coupling of the building block to a uniform electromagnetic field compared to superconducting qubits with linear geometry. Thus, the building block is effectively isolated from the electromagnetic environment, which helps to increase the coherence time of the qubit.
[0057] It should also be understood that by providing building blocks for a quantum information processing system in which the control lines and readout elements are arranged out of plane relative to the plane of the two superconducting electrodes of the superconducting qubit, the topology of the information processing system comprising multiple building blocks can be expanded in the same way as the number of building blocks (qubits).
Claims
1. A building block for a quantum information processing system, comprising: A superconducting qubit comprising a Josephson junction connected between two superconducting electrodes, wherein the two superconducting electrodes are coaxial and coplanar; Control lines, coupled to the superconducting qubit and arranged to control the state of the superconducting qubit; and / or A readout element is coupled to the superconducting qubit and arranged to measure the state of the superconducting qubit; The control line and / or the readout element are arranged in a plane that is not parallel to the two superconducting electrodes.
2. The component block according to claim 1, wherein the exterior of the two superconducting electrodes includes a ground plane.
3. The component block according to claim 1 or 2, wherein the two superconducting electrodes of the superconducting qubit are radially symmetrical.
4. The component block according to claim 1 or 2, wherein the superconducting qubits are arranged in a frequency-tunable manner.
5. The component block according to claim 1 or 2, wherein the control line is arranged coaxially with the two superconducting electrodes of the superconducting qubit.
6. The component block according to claim 1 or 2, wherein the control line includes a magnetic flux control line.
7. The component block according to claim 1 or 2, wherein the control lines are arranged to provide universal control over the quantum state of the superconducting qubit.
8. The component block according to claim 1 or 2, wherein the control line is arranged to radiate the superconducting qubit with electromagnetic radiation.
9. The component block according to claim 1 or 2, wherein the control line is arranged to apply pulses of electromagnetic radiation to the superconducting qubit.
10. The component block according to claim 1 or 2, wherein the readout element is arranged coaxially with the two superconducting electrodes of the superconducting qubit.
11. The component block according to claim 1 or 2, wherein the two superconducting electrodes, the control line and / or the readout element are arranged coaxially.
12. The component block according to claim 1 or 2, wherein the readout element comprises a resonator coupled to the superconducting qubit.
13. The component block according to claim 1 or 2, wherein the control line and the readout element are formed as a single element.
14. A quantum information processing system, comprising a plurality of component blocks as described in claim 1; At least some of the plurality of component blocks are coupled to one or more of the other component blocks.
15. The system of claim 14, further comprising one or more additional superconducting qubits.
16. The system of claim 15, wherein one or more of the additional superconducting qubits are coupled to one or more of the plurality of building blocks.
17. The system of claim 14 or 15, wherein each control line is coupled to only a single superconducting qubit.
18. The system of claim 14 or 15, wherein each readout element is coupled to only a single superconducting qubit.
19. The system of claim 14 or 15, wherein one or more of the plurality of component blocks are coupled to the nearest other component block.
20. The system of claim 14 or 15, wherein the coupling between the component blocks includes a capacitor.
21. The system according to claim 14 or 15, wherein the component blocks are arranged in an array.
22. The system of claim 14 or 15, further comprising a processing circuitry system arranged to operate on one or more of the plurality of component blocks.
23. The system of claim 22, wherein the processing circuitry is arranged to implement one or more quantum logic gates.