WO2024066730A1 - 一种量子芯片、量子计算电路及量子计算机 - Google Patents

一种量子芯片、量子计算电路及量子计算机 Download PDF

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Publication number
WO2024066730A1
WO2024066730A1 PCT/CN2023/110592 CN2023110592W WO2024066730A1 WO 2024066730 A1 WO2024066730 A1 WO 2024066730A1 CN 2023110592 W CN2023110592 W CN 2023110592W WO 2024066730 A1 WO2024066730 A1 WO 2024066730A1
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quantum
circuit
frequency
bit
quantum bit
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PCT/CN2023/110592
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English (en)
French (fr)
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杨振权
李松
李业
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本源量子计算科技（合肥）股份有限公司
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Priority claimed from CN202211220300.1A external-priority patent/CN115438794B/zh
Priority claimed from CN202211220357.1A external-priority patent/CN115438795B/zh
Application filed by 本源量子计算科技（合肥）股份有限公司 filed Critical 本源量子计算科技（合肥）股份有限公司
Publication of WO2024066730A1 publication Critical patent/WO2024066730A1/zh

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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06N—COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
    • G06N10/00—Quantum computing, i.e. information processing based on quantum-mechanical phenomena
    • G06N10/20—Models of quantum computing, e.g. quantum circuits or universal quantum computers
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06N—COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
    • G06N10/00—Quantum computing, i.e. information processing based on quantum-mechanical phenomena
    • G06N10/40—Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control

Definitions

  • the present application belongs to the field of quantum information, especially the field of quantum computing technology.
  • the present application relates to a quantum chip, a quantum computing circuit and a quantum computer.
  • Quantum chips are the core components of quantum computers.
  • the basic idea of constructing quantum chips with superconducting physics systems is to connect the Squid (Superconducting quantum interference device) formed based on the Josephson junction in parallel with the additional capacitor plates.
  • the superconducting quantum bit circuit formed based on the parallel structure is used as the basic unit for performing quantum computing on the quantum chip - the quantum bit.
  • the quantum bit can be controlled by an external electrical signal to achieve a series of quantum bit operations.
  • quantum chips when quantum chips perform quantum computing, they generally use a magnetic flux control signal line (Z-control line) located near the Squid.
  • the frequency of the quantum bit is controlled by applying a signal to control the magnetic flux of the Squid.
  • the control structure of the quantum bit is relatively limited. For example, it is limited to the structure described above. This situation urgently needs to be improved and optimized.
  • the present application provides a quantum chip, a quantum computing circuit and a quantum computer, which overcome the limitations of the frequency control structure of quantum bits in the prior art.
  • One aspect of the present application provides a quantum chip, comprising:
  • a quantum bit and a frequency-adjustable control structure, wherein the control structure is dispersion-coupled with the quantum bit, wherein the quantum bit includes a first capacitor plate and a single first Josephson junction connected to the first capacitor plate to form a first nonlinear oscillation circuit.
  • the quantum bit is one or more
  • the first Josephson junction in each quantum bit is connected to the first capacitor plate, and one end of the first capacitor plate is grounded.
  • the first Josephson junction in each quantum bit is connected in parallel with the first capacitor plate and one end of the first Josephson junction is connected to the ground.
  • one end of the first Josephson junction in each quantum bit is connected to a first capacitor plate, and the other end is connected to another first capacitor plate.
  • control structure includes a second nonlinear oscillation circuit.
  • the second nonlinear oscillation circuit includes: a first superconducting quantum interference device, and a magnetic flux control signal line inductively coupled to the first superconducting quantum interference device.
  • the first superconducting quantum interference device includes at least two second Josephson junctions, and the at least two second Josephson junctions form a parallel structure.
  • critical currents of the at least two second Josephson junctions are different.
  • the second nonlinear oscillation circuit further includes: two second capacitor plates, one end of the first superconducting quantum interference device is connected to one second capacitor plate, and the other end is connected to another second capacitor plate.
  • the second nonlinear oscillation circuit further includes: a second capacitor plate connected in parallel with the first superconducting quantum interference device.
  • a frequency-tunable coupling circuit when there are multiple quantum bits, a frequency-tunable coupling circuit is connected between adjacent quantum bits.
  • the coupling circuit includes a capacitor with one end grounded, and a second superconducting quantum interference device connected in parallel with the capacitor, and the second superconducting quantum interference device includes at least two Josephson junctions.
  • the number of Josephson junctions included in the second superconducting quantum interference device is an odd number.
  • the quantum chip further includes a reading circuit and/or a pulse control signal line, the reading circuit is coupled to the quantum bit, and the pulse control signal line is coupled to the quantum bit.
  • the frequency difference ⁇ and the quantity of the qubit and the control structure satisfies: ⁇ 3g.
  • the frequency of the control structure is lower than the frequency of the quantum bit.
  • Another aspect of the present application provides a quantum computing circuit, comprising:
  • a plurality of quantum bits wherein adjacent quantum bits are coupled to each other, and the quantum bits include a capacitor connected in parallel and having one end in common ground and a single Josephson junction;
  • a frequency-tunable control circuit is provided, wherein the control circuit is coupled to the quantum bit dispersion.
  • a frequency-tunable coupling circuit is connected between adjacent quantum bits.
  • the coupling circuit includes a capacitor with one end grounded, and a superconducting quantum interference device connected in parallel with the capacitor, and the superconducting quantum interference device includes at least two Josephson junctions.
  • the number of Josephson junctions included in the superconducting quantum interference device is an odd number.
  • Another aspect of the present application provides a quantum computer, which is a superconducting system and is provided with at least any one of the quantum computing circuits described above.
  • Another aspect of the present application provides a quantum computer, comprising:
  • a vacuum refrigeration system including a closed container
  • a plurality of transmission lines are provided in the vacuum refrigeration environment so as to guide electrical signals to at least one selected quantum bit in the quantum chip and receive electrical signals from the at least one selected quantum bit.
  • the quantum chip provided by the present application uses a single first Josephson junction and a first nonlinear oscillation circuit connected to a first capacitor plate to construct a quantum bit, and uses a frequency-adjustable control structure to couple with the quantum bit dispersion, so as to be able to control the frequency of the quantum bit.
  • the stability of the frequency control of the quantum bit is higher and is not easily affected by the magnetic flux noise.
  • FIG1 is a schematic diagram of the structure of a quantum bit on a quantum chip in the related art
  • FIG2 is a schematic diagram of an implementation structure of a quantum chip provided in an embodiment of the present application.
  • FIG3 is a schematic diagram of the implementation structure of another quantum chip provided in an embodiment of the present application.
  • FIG4 is a frequency of a quantum bit 1 of a specific design example of a quantum chip provided by an embodiment of the present application.
  • FIG5 is a frequency diagram of a control structure 2 of a specific design example of a quantum chip provided in an embodiment of the present application;
  • FIG6 is a dispersion criterion for a specific design example of a quantum chip provided in an embodiment of the present application.
  • FIG7 is a schematic diagram of a quantum computing circuit in the related prior art
  • FIG8 is a schematic diagram of a quantum computing circuit provided in an embodiment of the present application.
  • a qubit is a two-level system that follows the laws of quantum mechanics. It can be in any superposition state of 0 and 1 and is the basic unit for performing quantum computing.
  • Several physical systems have been suggested as potential implementation methods for qubits. Depending on the different physical systems used to construct qubits, the physical implementation methods of qubits include superconducting physical systems, semiconductor quantum dot physical systems, ion traps, diamond vacancies, topological quantum, photons, etc.
  • the superconducting physical system is currently the fastest and best method for implementing solid quantum computing.
  • the energy level structure of qubits based on superconducting physical systems can be controlled by external electrical signals, and the design and customization of quantum chips are highly controllable.
  • superconducting physical systems have scalability that is difficult to match with most quantum physical systems.
  • a Josephson junction is a three-layer structure formed by two superconductors separated by a thin insulating layer.
  • the intermediate insulating layer is thin enough to clearly show the quantum tunneling effect of Cooper pairs, the Josephson junction can show some behaviors different from those exhibited by ordinary superconductors or insulators.
  • the maximum current allowed is the critical current.
  • the superconducting quantum interference device Squid is usually a superconducting ring formed by two Josephson junctions in parallel, and its critical current is tuned by applying an external magnetic field.
  • the Transmons quantum bit is a commonly used quantum bit structure.
  • the quantum bit often includes a capacitor, and a superconducting quantum interference device Squid having one end grounded and the other end connected to the capacitor.
  • the size of the equivalent critical current Ic of the Squid is regulated by the external magnetic field ⁇ e , and the capacitor is often a cross-shaped capacitor.
  • the cross-shaped capacitor C q is surrounded by a ground plane (GND), and there is a gap between the cross-shaped capacitor C q and the ground plane (GND), and one end of the superconducting quantum interference device Squid is connected to the cross-shaped capacitor C q , and the other end is connected to the ground plane (GND).
  • the first end of the cross-shaped capacitor C q is usually used to connect the superconducting quantum interference device Squid, and the second end is used to couple with the reading resonant cavity, the second end is the opposite side of the first end; a certain space needs to be reserved near the first end and the second end for wiring. For example, a pulse modulation needs to be reserved near the first end.
  • the space for the control signal line (also known as the XY signal line) and the magnetic flux control signal line (also known as the Z signal line) of the cross-shaped capacitor C q , the other two ends (i.e., the ends other than the first end and the second end) can be used to couple with adjacent quantum bits.
  • the pulse control signal line is used to apply a quantum bit transition excitation pulse signal to the quantum bit
  • the magnetic flux control signal line is used to transmit a driving signal, which generates a magnetic field coupled to the quantum bit to achieve frequency control of the quantum bit.
  • the frequency control structure of quantum bits is limited to the flux control signal line structure described above, which is relatively simple in form.
  • problems of quantum computing are related to the frequency control of quantum bits, especially the way to achieve frequency control by applying an external magnetic field through the flux control signal line to tune the magnetic flux of the quantum bit squid.
  • the external magnetic field can reduce the energy of the Josephson junction, thereby introducing flux noise.
  • the frequency of the quantum bit is easily affected by the flux noise and deviates from the ideal position, thereby affecting the performance of the quantum bit.
  • the quantum chip provided in the embodiment of the present application can be expressed in the form of a circuit, so the quantum chip can also be called a quantum computing circuit.
  • the quantum bit in the quantum chip can also be expressed in the form of a circuit, so the quantum bit can also be called a quantum bit circuit.
  • the capacitor involved in this application can also be called a capacitor plate.
  • the control structure can also be called a control circuit.
  • the superconducting quantum interference device can also be called a superconducting quantum interference circuit.
  • a quantum chip may include one qubit or multiple qubits.
  • Figures 2 and 3 are both described by taking a quantum chip including one qubit as an example.
  • Figures 7 and 8 are both described by taking a quantum chip including multiple qubits as an example.
  • FIG2 is a schematic diagram of an implementation structure of a quantum chip provided in an embodiment of the present application
  • FIG3 is a schematic diagram of an implementation structure of another quantum chip provided in an embodiment of the present application
  • the embodiments of the present application can solve the limitations in the design solutions of the prior art.
  • a quantum chip comprising a frequency-adjustable control structure 2, and a quantum bit 1 dispersion-coupled with the control structure 2, and the quantum bit 1 comprises a first capacitor plate 11, and a single first Josephson junction 12 connected to the first capacitor plate 11, and the first capacitor plate 11 and the first Josephson junction 12 are connected to form a nonlinear oscillation circuit.
  • the various elements of the quantum bit 1 can be formed on a substrate, such as a wafer, and the wafer can be a silicon wafer, a sapphire wafer, or other substrate materials used for micromachining.
  • the distribution positions of the control structure 2 and the quantum bit 1 are not limited, and the two can be located on the same surface of the substrate and form dispersion coupling (see the forms described in FIG. 2 and FIG. 3 ). As another example, they can also be independently located on two different surfaces.
  • the control structure 2 can be an oscillating circuit. When it is implemented, the control structure 2 can be used as long as it has a tunable continuous frequency value or multiple dispersed frequency points. Combining Figures 2 and 3, it can be seen that there is a white blank area between the first capacitor plate 11 and the ground plane (GND), which means that there is a gap between the first capacitor plate 11 and the ground plane (GND).
  • the quantum chip provided in the embodiment of the present application uses a single first Josephson junction 12 and a nonlinear oscillation circuit connected to the first capacitor plate 11 to construct a quantum bit 1, and uses a frequency-adjustable control structure 2 to disperse couple with the quantum bit 1. Dispersion coupling helps to reduce or even avoid direct energy exchange between the two, so that the frequency of the quantum bit 1 can be controlled by the control structure 2.
  • the quantum chip structure is a new structure that can replace the use of a magnetic flux control signal line to directly control the quantum bit in the related art.
  • the magnetic flux of the Squid of the quantum bit is directly controlled by applying a signal to the magnetic flux control signal line (Z-control line) on the quantum chip to complete the frequency control of the quantum bit.
  • the quantum chip in the solution provided in the present application uses the control structure 2 to perform frequency control on the quantum bit 1. Since the magnetic flux of the Josephson junction in the quantum bit is not directly tuned by the magnetic flux control signal line, the energy of the Josephson junction in the quantum bit can be avoided from being affected by the magnetic field introduced by the magnetic flux control signal line, so that the stability of the frequency control is higher and it is not easily affected by the magnetic flux noise.
  • a quantum bit 1 is formed by a first capacitor plate 11 and a single first Josephson junction 12 connected to the first capacitor plate 11.
  • the frequency of the quantum bit 1 of this structural form has moderate adjustability, and because of electrical coupling, the frequency change of the control structure 2 causes the change of the frequency of the quantum bit 1.
  • the frequency tunable range of the quantum bit 1 in the embodiment of the present application is smaller (for example, about 100MHz), and the flux noise is not easy to adversely affect the sensitivity and decoherence time of the quantum state dephasing.
  • one end of the first Josephson junction 12 is connected to the first capacitor plate 11, and the other end is grounded.
  • one end of the first Josephson junction 12 is connected to a first capacitor plate 11, and the other end is connected to another first capacitor plate 11.
  • the first capacitor plate 11 is surrounded by the ground plane GND, and there is a gap between the first capacitor plate 11 and the ground plane GND, the first Josephson junction 12 is constructed in the gap, and the first A Josephson junction 12 is electrically and physically connected to the first capacitor plate 11 and the ground plane GND according to design requirements, that is, the electrical connection is achieved through physical contact.
  • the control structure 2 in the embodiment of the present application has the characteristic of adjustable frequency.
  • the frequency tuning of the control structure 2 causes the frequency shift of the quantum bit 1 to complete the frequency tuning of the quantum bit 1, and then the quantum state of the quantum bit 1 is manipulated by the pulse control signal line 3 configured in the quantum chip.
  • the control structure 2 includes a superconducting quantum interference device Squid (i.e., a first superconducting quantum interference device), and a flux control signal line 4 inductively coupled to the superconducting quantum interference device Squid. Based on the signal on the flux control signal line 4, an external magnetic field is generated and applied to the superconducting quantum interference device Squid, and the frequency of the control structure 2 is regulated by the external magnetic field.
  • the superconducting quantum interference device Squid includes at least two second Josephson junctions 22, for example, it can be a parallel structure formed by three second Josephson junctions 22.
  • the at least two second Josephson junctions 22 usually have different areas, which refers to the area of the overlap of the three layers of SIS (also referred to as the junction area), so as to ensure that the critical currents of the at least two second Josephson junctions 22 are different.
  • the at least two second Josephson junctions 22 may also have the same area.
  • control structure 2 includes a second capacitor plate 21, one end of the superconducting quantum interference device Squid is connected to the second capacitor plate 21, and the other end is grounded.
  • control structure 2 includes two second capacitor plates 21, one end of the superconducting quantum interference device Squid is connected to one second capacitor plate 21, and the other end is connected to another second capacitor plate 21.
  • the second capacitor plate 21 is surrounded by the ground plane GND, and there is a gap between the second capacitor plate 21 and the ground plane GND, the superconducting quantum interference device Squid is constructed in the gap, and the superconducting quantum interference device Squid is electrically and physically contacted with the second capacitor plate 21 and the ground plane GND as required by the design.
  • the control structure of the quantum bit described in the related art above tunes the frequency of the quantum bit by applying an external magnetic flux to the superconducting quantum interference device Squid contained in the quantum bit.
  • the frequency of the quantum bit The frequency of the quantum bit ⁇ 10 is related to the electrostatic energy E C of the capacitor and the energy of the squid.
  • the energy E J of Squid changes with the external magnetic field ⁇ e , so the frequency of the quantum bit can be controlled and adjusted by the energy E J of Squid in response to the change of the external magnetic field ⁇ e .
  • the external magnetic field ⁇ e is generated by the current applied to the magnetic flux control signal line (Z-control line), and the external magnetic field passes through the Squid region to cause the frequency of the quantum bit belonging to the Squid region to change.
  • the magnetic flux penetrating the Squid loop is affected by the mutual inductance M between the magnetic flux control signal line and the Squid loop, the magnetic field size generated by the electrical signal applied to the magnetic flux control signal line, and the magnetic flux noise.
  • the magnetic flux noise is the inherent noise caused by the current fluctuation in the magnetic flux control signal or the magnetic flux noise caused by the additional signal carried by the magnetic flux control signal.
  • the magnetic flux noise can cause the frequency of the quantum bit to fluctuate and deviate.
  • the frequency tuning of the quantum bit 1 can be achieved by the coupling strength g between the quantum bit 1 and the control structure 2, and the frequency difference ⁇ between the quantum bit 1 and the control structure 2, and the control structure 2 can reduce the influence of the magnetic flux noise on the frequency regulation of the quantum bit 1 when tuning the frequency of the quantum bit 1.
  • the frequency tuning of the quantum bit 1 in the embodiment of the present application is further introduced.
  • the initial frequency of the quantum bit 1 is ⁇ q
  • the frequency of the control structure 2 is ⁇ t
  • C t is the capacitance of the second capacitor plate to the ground
  • C q is the capacitance of the first capacitor plate to the ground
  • C qt is the coupling capacitance between the first capacitor plate and the second capacitor plate.
  • the frequency of the control structure 2 can be tuned by the signal of the flux control signal line 4, and the frequency of the quantum bit 1 can be further tuned based on the frequency of the control structure 2.
  • the frequency of the quantum bit 1 is not directly tuned by the flux control signal line 4, and the influence of the noise introduced by the flux control signal line 4 on the frequency of the quantum bit 1 is reduced. Therefore, it can be considered that this frequency tuning structure can avoid the direct interference of the flux noise of the flux control signal line 4 on the frequency of the quantum bit 1, thereby reducing the deviation of the frequency control, which helps to improve the decoherence time of the quantum bit 1.
  • the specific design properties of the quantum chip are as follows: the first capacitor plate 11 of the quantum bit 1 and the second capacitor plate 21 of the control structure 2 are both 88fF, the critical current of the first Josephson junction 12 is approximately 38nA, and the critical current of the second Josephson junction 22 of the Squid (i.e., the first superconducting quantum interference device) is approximately 15nA.
  • the numerical simulation results for this example are shown in Figures 4 to 6 ( ⁇ e is the external magnetic field flux, ⁇ 0 is the magnetic flux quantum). It can be seen that: in the range of 5.38 GHz to 5.51 GHz, the frequency of quantum bit 1 is tunable, and the tunable amplitude is about 134 MHz.
  • a larger tunable amplitude can be obtained by adjusting the design attribute parameters of the quantum chip during implementation; in addition, when the external magnetic field flux is 0, the frequency of quantum bit 1 is the smallest, the frequency of control structure 2 is the largest, and the detuning amount between the two is the smallest, which results in a smaller ⁇ / and weaker dispersion coupling. Therefore, in some implementation examples of the present application, when designing or regulating quantum bit 1 and control structure 2, the frequency of control structure 2 can be limited to be lower than the frequency of quantum bit 1, so that the frequency of quantum bit 1 and the frequency of control structure 2 maintain a sufficient detuning amount, for example, greater than 500 MHZ, thereby helping to enhance dispersion coupling.
  • the frequency difference ⁇ between the quantum bit 1 and the control structure 2 and the coupling strength g between the quantum bit 1 and the control structure 2 satisfy: ⁇ 3g.
  • the first capacitor plate 11, the second capacitor plate 21, the ground plane GND, the superconductor part of the first Josephson junction 12 and the second Josephson junction 22, as well as the pulse control signal line 3, the flux control signal line 4, the wires electrically connecting various components, etc. of the embodiment of the present application are made of superconducting materials.
  • the quantum chip can directly use mature semiconductor processes to obtain superconducting materials through deposition, patterning, etc.
  • the thickness of the deposition can be micrometer or nanometer.
  • the superconducting material is a material that exhibits superconducting properties at a temperature equal to or lower than the critical temperature, such as about 10-100 millikelvin (mK) or about 4K, such as aluminum, niobium, tantalum or titanium nitride, etc., which is not limited to these types in specific implementation.
  • Materials that exhibit superconducting properties at a temperature equal to or lower than the critical temperature can be used to form the above-mentioned structure, for example, one or more of aluminum (Al), niobium (Nb), niobium nitride (NbN), titanium nitride (TiN) and niobium titanium nitride (NbTiN).
  • the embodiment of the present application also provides a quantum computer, comprising: a vacuum refrigeration system including a sealed container; and a quantum chip as described in the above quantum chip embodiment, wherein the quantum chip is contained in A vacuum refrigeration environment defined by the sealed container; and a plurality of transmission lines arranged in the vacuum refrigeration environment so as to guide electrical signals to at least one selected quantum bit 1 in the quantum chip and receive electrical signals from the at least one selected quantum bit 1.
  • the quantum chip in the above quantum computer is similar in structure to the quantum chip described in other embodiments of the present application, and has the same beneficial effects as other quantum chip embodiments of the present application, so it will not be described in detail.
  • quantum computer embodiments of the present application those skilled in the art should refer to the description of the above quantum chip embodiments for understanding, and will not be described in detail here to save space.
  • the manufacture of a quantum chip provided in an embodiment of the present application may require the deposition of one or more materials, such as superconductors, dielectrics and/or metals. Depending on the selected material, these materials can be deposited using deposition processes such as chemical vapor deposition, physical vapor deposition (e.g., evaporation or sputtering) or epitaxial techniques and other deposition processes.
  • the preparation process of the quantum chip described in an embodiment of the present application may require the removal of one or more materials from the device during the manufacturing process. Depending on the material to be removed, the removal process may include, for example, wet etching technology, dry etching technology or lift-off process.
  • the materials forming the circuit elements described herein can be patterned using known exposure (lithographic) techniques (e.g., photolithography or electron beam exposure).
  • FIG. 7 is a schematic diagram of a quantum computing circuit in the related prior art.
  • the quantum bit circuit in a commonly used quantum computing circuit, the quantum bit circuit often uses a capacitor C q with one end grounded, and a circuit structure of a superconducting quantum interference circuit Squid connected in parallel with the capacitor C q .
  • the capacitor C q affects the anharmonicity of the quantum bit.
  • the anharmonicity parameter of the quantum bit is determined, and the capacitor C q is determined.
  • the structural form of the quantum computing circuit is relatively simple and limited to the structure described above.
  • several problems of quantum computing are related to the frequency control of the quantum bit, especially the form of the circuit structure of the frequency control.
  • the quantum computing circuit described above applies an external magnetic field through a magnetic flux control signal line Z (Z-control line, denoted as Z) to tune the magnetic flux of the superconducting quantum interference circuit Squid contained in the quantum bit to achieve frequency control, but it is easy to introduce sensitivity to magnetic flux noise, which makes the frequency of the quantum bit susceptible to the influence of magnetic flux noise, causing the frequency of the quantum bit to deviate from the ideal position, ultimately affecting the accuracy of quantum bit control, reducing the decoherence time of the quantum bit, etc.
  • Z magnetic flux control signal line
  • adjacent quantum bit circuits are coupled via frequency-tunable coupling circuits.
  • the coupling circuit is coupled with the two qubit circuits respectively, that is, the coupling is achieved through the capacitance between the coupling circuit and the two qubit circuits.
  • the coupling circuit includes a capacitor C t with one end grounded, a superconducting quantum interference circuit Squid connected in parallel with the capacitor C t , and a magnetic flux control signal line Z.
  • the quantum computing circuit in FIG7 further includes a read circuit, and the read circuit is coupled to the quantum bit circuit via a capacitor C qr .
  • the read circuit includes an LC oscillation circuit formed by a capacitive element Cr and an inductive element Lr .
  • the quantum bit circuit can also be coupled to a pulse control signal line XY (XY-control line, denoted as XY) via a capacitor.
  • the present application provides a quantum computing circuit and a quantum computer to solve the structural limitations in related technologies.
  • FIG8 is a schematic diagram of a quantum computing circuit provided in an embodiment of the present application.
  • an embodiment of the present application provides a quantum computing circuit, which includes a plurality of quantum bit circuits and a frequency-tunable control circuit, wherein the control circuit is dispersion-coupled with the quantum bit circuit, and adjacent quantum bit circuits are coupled to each other, and the coupling between adjacent quantum bit circuits may be through capacitor (C 1 ) coupling or resonant circuit coupling, and the quantum bit circuit includes a first capacitor C q and a single first Josephson junction JJ that are connected in parallel and have one end connected to the ground.
  • the frequency of the quantum bit circuit can be regulated by changing the frequency of the control circuit, and compared with the method of frequency regulation of the quantum bit in the related art by applying a signal to the magnetic flux control signal line Z on the quantum chip to control the magnetic flux of the Squid, based on the quantum computing circuit in the solution provided by the present application, the stability of the frequency regulation of the quantum bit circuit is higher and is not easily affected by the magnetic flux noise introduced by the magnetic flux control signal line Z.
  • any quantum bit circuit including a first capacitor C q and a single first Josephson junction JJ can also be connected in series, that is, one end of the single first Josephson junction JJ is connected to one end of the first capacitor C q , the other end of the single first Josephson junction JJ is used to connect other circuits, and the other end of the first capacitor C q is grounded.
  • the quantum bit circuit can also be coupled to the pulse control signal line XY via a capacitor.
  • the first capacitor Cq in the quantum bit circuit may also be an equivalent capacitor of multiple capacitive elements connected in series, in parallel, or partially in series and partially in parallel. The number and electrical connection relationship of the capacitive elements may be determined as needed.
  • the control circuit in the embodiment of the present application has the characteristic of adjustable frequency.
  • the frequency of the control circuit is tuned to make the qubit circuit frequency shift, thus completing the frequency tuning of the qubit circuit.
  • the state of the quantum bit circuit is controlled by the configured pulse control signal line XY.
  • the control circuit includes an oscillation circuit, such as an oscillation circuit formed by a capacitive element and an inductive element, as long as the self-frequency of the oscillation circuit can be adjusted to different frequency values.
  • the oscillation circuit is a nonlinear oscillation circuit, for example, an oscillation circuit formed by a capacitive element and a nonlinear inductive element.
  • the nonlinear oscillation circuit includes a second capacitor Ct and a superconducting quantum interference circuit Squid (i.e., a first superconducting quantum interference device) in parallel, and a magnetic flux control signal line Z coupled to the superconducting quantum interference circuit Squid, and the superconducting quantum interference circuit Squid includes at least two Josephson junctions, which are distinguished from the Josephson junctions included in the quantum bit circuit, and the Josephson junctions included in the superconducting quantum interference circuit Squid are recorded as second Josephson junctions.
  • a superconducting quantum interference circuit Squid i.e., a first superconducting quantum interference device
  • the number of second Josephson junctions included in the superconducting quantum interference circuit Squid in the control circuit is an odd number.
  • the first Josephson junction and the second Josephson junction may be tunnel junctions, point contacts, or other structures exhibiting the Josephson effect.
  • the frequency tuning of the quantum bit circuit can be achieved by the coupling strength g between the quantum bit circuit and the control circuit, and the frequency difference ⁇ between the quantum bit circuit and the control circuit, and the control circuit can reduce the influence of magnetic flux noise on the frequency regulation of the quantum bit circuit when tuning the frequency of the quantum bit circuit.
  • the frequency tuning of the quantum bit circuit in the embodiment of the present application is further introduced.
  • the initial frequency of the quantum bit circuit is ⁇ q
  • the frequency of the control circuit is ⁇ t
  • C qt is the coupling capacitance between the quantum bit circuit and the control circuit.
  • the frequency of the control circuit can be tuned by the signal of the flux control signal line Z, and the frequency of the quantum bit circuit can be further tuned based on the frequency of the control circuit.
  • the frequency of the quantum bit circuit is not directly tuned through the flux control signal line Z, and the influence of the noise introduced by the flux control signal line Z on the frequency of the quantum bit circuit is reduced. Therefore, it can be considered that this frequency tuning structure can avoid the direct interference of the flux noise of the flux control signal line Z on the frequency of the quantum bit circuit, reduce the deviation of the frequency control, and help to improve the decoherence time of the quantum bit circuit.
  • the design properties of a quantum computing circuit are as follows:
  • the first capacitor Cq of the quantum bit circuit and the second capacitor Ct of the control circuit are both 88fF, the critical current of the first Josephson junction JJ of the quantum bit circuit is about 38nA, and the critical current of the second Josephson junction of the superconducting quantum interference circuit Squid in the control circuit is about 15nA.
  • the numerical simulation results for this example are shown in Figures 4 to 6 ( ⁇ e is the external magnetic field flux, ⁇ 0 is the magnetic flux quantum). It can be seen that: in the range of 5.38 GHz to 5.51 GHz, the frequency of the quantum bit circuit is tunable, and the tunable amplitude is about 134 MHz.
  • the frequency of the control circuit can be limited to be lower than the frequency of the quantum bit circuit, so that the frequency of the quantum bit circuit and the frequency of the control circuit maintain a sufficient detuning amount, for example, greater than 500 MHZ, thereby helping to enhance dispersion coupling.
  • the frequency difference ⁇ between the quantum bit circuit and the control circuit and the coupling strength g between the quantum bit circuit and the control circuit satisfy: ⁇ 3g.
  • the adjacent qubit circuits in the quantum computing circuit are connected by a frequency-tunable coupling circuit, and the frequency-tunable coupling circuit facilitates the regulation of the coupling strength between adjacent qubit circuits, which helps to realize the execution of dual quantum logic gates.
  • the two qubit circuits are in adjacent positions, and the coupling circuit is coupled with both qubit circuits, that is, coupling is achieved through C2 and C3 in FIG8, thereby generating indirect coupling between the two qubit circuits, and by adjusting the frequency of the coupling circuit, the coupling strength between the qubit circuits can be adjusted.
  • the coupling circuit includes a capacitor C C with one end grounded, and a superconducting quantum interference circuit Squid (i.e., a second superconducting quantum interference device) connected in parallel with the capacitor C C.
  • a superconducting quantum interference circuit Squid i.e., a second superconducting quantum interference device
  • the superconducting quantum interference circuit Squid in the coupling circuit can be selected according to the need.
  • the superconducting quantum interference circuit Squid in the coupling circuit includes at least two Josephson junctions, and the Josephson junctions are connected in parallel, and the frequency of the coupling circuit can be adjusted by applying an external magnetic flux.
  • the number of Josephson junctions in the superconducting quantum interference circuit Squid is an odd number.
  • the Josephson junction is a tunnel junction, a point contact, Or other structures that exhibit the Josephson effect.
  • the quantum computing circuit further includes a reading circuit, the reading circuit is coupled to the quantum bit circuit, and the reading circuit is used to read the quantum state of the regulated quantum bit circuit.
  • the reading circuit includes an LC oscillation circuit formed by a capacitive element Cr and an inductive element Lr .
  • the reading circuit is capacitively coupled to the quantum bit circuit, for example, through a capacitor Cqr .
  • each quantum bit circuit has the reading circuit coupled thereto, and the other end of the plurality of reading circuits is coupled to a common reading signal transmission line, and the reading signal transmission line obtains information on the quantum state through the reading circuit corresponding to each quantum bit.
  • An embodiment of the present application further provides a quantum computer, wherein the quantum computer is a superconducting system, and the quantum computer is at least provided with the quantum computing circuit as described above.
  • quantum computing circuit involved in the above quantum computer embodiment is similar in structure to the above quantum computing circuit embodiment and has the same beneficial effects as the above quantum computing circuit embodiment, so it will not be described in detail.
  • quantum computing circuit for technical details not disclosed in the quantum computer embodiment of the present application, those skilled in the art should refer to the description of the above quantum computing circuit for understanding, and will not be described in detail here to save space.
  • the quantum computing circuit of the present application includes a plurality of quantum bit circuits, and the adjacent quantum bit circuits are coupled, the quantum bit circuit includes a first capacitor C q and a single first Josephson junction JJ, one end of which is in common ground, and the control circuit for dispersion coupling with the quantum bit circuit may include a second capacitor C t and a superconducting quantum interference circuit Squid in parallel, and a magnetic flux control signal line Z coupled to the superconducting quantum interference circuit Squid.
  • the frequency of the quantum bit circuit can be controlled by changing the frequency of the control circuit, and compared with the method of directly applying a signal to control the frequency of the quantum bit through the magnetic flux control signal line Z in the related art, the method of controlling the frequency of the quantum bit based on the control structure provided by the present application has higher stability and is not easily affected by the magnetic flux noise introduced by the magnetic flux control signal line Z.
  • the frequency of the quantum bit circuit is adjusted to the operating frequency by using a control circuit, and at this time, a quantum state control signal is applied through a pulse control signal line XY to control the quantum state of the quantum bit circuit in the initial state, and a read circuit is used to read the quantum state of the controlled quantum bit circuit, and a read detection signal (for example, a microwave signal with a frequency of 4-8 GHz) is applied to a read signal transmission line coupled to the read circuit, and the read signal is analyzed.
  • the read feedback signal (a signal in response to the read detection signal) output by the transmission line determines the quantum state of the quantum bit circuit.
  • the pulse control signal line XY and the read signal transmission line are not described in detail here.

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Abstract

一种量子芯片、量子计算电路及量子计算机，属于量子计算技术领域。一种量子芯片，包括：量子比特，及频率可调的控制结构，且控制结构与量子比特色散耦合，其中，所述量子比特包括第一电容极板及与第一电容极板连接形成非线性振荡电路的单个第一约瑟夫森结。本申请克服了现有技术中量子比特的频率调控结构的限制，可以通过将频率可调的控制结构与包含单个约瑟夫森结的量子比特耦合进行频率调控，并且量子比特的频率稳定性较高，不易受磁通噪声的影响。

Description

一种量子芯片、量子计算电路及量子计算机
本申请要求于2022年09月30日提交中国专利局、申请号为202211220357.1发明名称为“一种量子芯片及量子计算机”的中国专利申请，以及于2022年09月30日提交中国专利局、申请号为202211220300.1发明名称为“一种量子计算电路及一种量子计算机”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请属于量子信息领域，尤其是量子计算技术领域，特别地，本申请涉及一种量子芯片、量子计算电路及量子计算机。
背景技术
量子芯片是量子计算机的核心部件。超导物理体系构建量子芯片的基本思路是：将基于约瑟夫森结形成的Squid(Superconducting quantum interference device，超导量子干涉装置)与额外构建电容极板并联，基于该并联结构形成的超导量子比特电路即作为量子芯片上执行量子计算的基本单元——量子比特。量子比特可通过外加电信号进行调控，进而实现一系列的量子比特操作。目前，量子芯片执行量子计算时，普遍是采用位于Squid附近的磁通调控信号线(Z-control line)的结构形式，通过施加信号调控Squid的磁通量完成量子比特的频率的调控。量子比特的调控结构形式较局限，例如，局限于上文描述的结构，这种现状亟需进行改善优化。
发明内容
针对现有技术中量子比特的频率调控结构较为局限的问题，本申请提供一种量子芯片、量子计算电路及量子计算机，克服了现有技术中量子比特的频率调控结构的限制。
本申请的一个方面提供了一种量子芯片，包括：
量子比特，及频率可调的控制结构，且控制结构与量子比特色散耦合，其中，所述量子比特包括第一电容极板及与第一电容极板连接形成第一非线性振荡电路的单个第一约瑟夫森结。
在本申请的一些实施方式中，所述量子比特为一个或多个；
所述量子比特为多个时，相邻量子比特之间耦合连接。
在本申请的一些实施方式中，每一量子比特中的第一约瑟夫森结与第一电容极板连接，且该第一电容极板的一端接地。
在本申请的一些实施方式中，每一量子比特中的第一约瑟夫森结与第一电容极板并联且一端共地。
在本申请的一些实施方式中，每一量子比特中的第一约瑟夫森结的一端连接一个第一电容极板，另一端连接另一个第一电容极板。
在本申请的一些实施方式中，所述控制结构包括第二非线性振荡电路。
在本申请的一些实施方式中，所述第二非线性振荡电路包括：第一超导量子干涉装置，以及与所述第一超导量子干涉装置感应耦合连接的磁通调控信号线。
在本申请的一些实施方式中，所述第一超导量子干涉装置包括至少两个第二约瑟夫森结，所述至少两个第二约瑟夫森结形成并联结构。
在本申请的一些实施方式中，所述至少两个第二约瑟夫森结的临界电流不相同。
在本申请的一些实施方式中，所述第二非线性振荡电路还包括：两个第二电容极板，所述第一超导量子干涉装置的一端连接一个第二电容极板，另一端连接另一个第二电容极板。
在本申请的一些实施方式中，所述第二非线性振荡电路还包括：与所述第一超导量子干涉装置并联的第二电容极板。
在本申请的一些实施方式中，在所述量子比特为多个的情况下，相邻量子比特之间连接有频率可调谐的耦合电路。
在本申请的一些实施方式中，所述耦合电路包括一端接地的电容，以及与该电容并联的第二超导量子干涉装置，且所述第二超导量子干涉装置包括至少两个约瑟夫森结。
在本申请的一些实施方式中，所述第二超导量子干涉装置包括的约瑟夫森结的个数为奇数。
在本申请的一些实施方式中，所述量子芯片还包括读取电路和/或脉冲调控信号线，所述读取电路与所述量子比特耦合，所述脉冲调控信号线与所述量子比特耦合。
在本申请的一些实施方式中，所述量子比特与控制结构的频率差Δ及量 子比特与控制结构的耦合强度g满足：Δ≥3g。
在本申请的一些实施方式中，所述控制结构的频率低于量子比特的频率。
本申请的另一个方面提供了一种量子计算电路，包括：
多个量子比特，且相邻量子比特之间耦合连接，该量子比特包括并联且一端共地的电容和单个约瑟夫森结；以及，
频率可调谐的控制电路，且控制电路与量子比特色散耦合。
在本申请的一些实施方式中，相邻量子比特之间连接有频率可调谐的耦合电路。
在本申请的一些实施方式中，所述耦合电路包括一端接地的电容，以及与该电容并联的超导量子干涉装置，且该超导量子干涉装置包括至少两个约瑟夫森结。
在本申请的一些实施方式中，所述超导量子干涉装置包括的约瑟夫森结的个数为奇数。
本申请的另一个方面提供了一种量子计算机，所述量子计算机为超导体系，且所述量子计算机至少设置有上述任一所述的量子计算电路。
本申请的另一个方面提供了一种量子计算机，包括：
真空制冷系统，包括密闭容器；
如上述任一所述量子芯片，该量子芯片被包含在由该密闭容器限定的真空制冷环境内；以及
设于该真空制冷环境内的多个传输线路，以便将电信号引导到该量子芯片中的至少一个选定的量子比特并且从该至少一个选定的量子比特接收电信号。
与现有技术相比，本申请提供的量子芯片采用单个第一约瑟夫森结、与第一电容极板连接形成的第一非线性振荡电路一起构建量子比特，并利用频率可调的控制结构与量子比特色散耦合，从而能够调控量子比特的频率。并且，相对于相关技术中通过在量子芯片上的磁通调控信号线(Z-control line)施加信号调控量子比特中Squid的磁通量完成量子比特的频率调控的方式，基于本申请提供的方案，量子比特的频率调控的稳定性较高，不易受磁通噪声的影响。
附图说明
此处所说明的附图用来提供对本申请的进一步理解，构成本申请的一部分，本申请的示意性实施例及其说明用于解释本申请，并不构成对本申请的不当限定。
图1为相关技术中量子芯片上量子比特的结构示意图；
图2为本申请的实施例提供的一种量子芯片的实施结构示意图；
图3为本申请的实施例提供的另一种量子芯片的实施结构示意图；
图4为本申请的实施例提供的一种量子芯片特定设计示例的量子比特1的频率；
图5为本申请的实施例提供的一种量子芯片特定设计示例的控制结构2的频率；
图6为本申请的实施例提供的一种量子芯片特定设计示例的色散判据；
图7为相关现有技术中一种量子计算电路的示意图；
图8为本申请实施例提供的一种量子计算电路的示意图。
附图标记说明：
1-量子比特，11-第一电容极板，12-第一约瑟夫森结，
2-控制结构，21-第二电容极板，22-第二约瑟夫森结，
3-脉冲调控信号线，4-磁通调控信号线。
具体实施方式
为使本申请的目的、技术方案、及优点更加清楚明白，以下参照附图并举实施例，对本申请进一步详细说明。显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员所获得的所有其他实施例，都属于本申请保护的范围。
需要说明的是，本申请的说明书和权利要求书及上述附图中的术语“第一”、“第二”等是用于区别类似的对象，而不必用于描述特定的顺序或先后次序。应该理解这样使用的数据在适当情况下可以互换，以便这里描述的本申请的实施例能够以除了在这里图示或描述的那些以外的顺序实施。此外，术语“包括”和“具有”以及他们的任何变形，意图在于覆盖不排他的包含，例如，包含了一系列步骤或单元的过程、方法、系统、产品或设备不必限于清楚地列出的那些步骤或单元，而是可包括没有清楚地列出的或对于这些过 程、方法、产品或设备固有的其它步骤或单元。
另外，应该理解的是，当层(或膜)、区域、图案或结构被称作在衬底、层(或膜)、区域和/或图案“上”时，它可以直接位于另一个层或衬底上，和/或还可以存在插入层。另外，应该理解，当层被称作在另一个层“下”时，它可以直接位于另一个层下，和/或还可以存在一个或多个插入层。另外，可以基于附图进行关于在各层“上”和“下”的指代。
量子比特为一个遵循量子力学规律的二能级系统，可以处于0和1的任意叠加状态，是执行量子计算的基本单元。若干物理系统已被建议作为量子比特的潜在的实施方式，根据构建量子比特所采用的不同物理体系，量子比特在物理实现方式上包括超导物理体系、半导体量子点物理体系、离子阱、金刚石空位、拓扑量子、光子等。超导物理体系是目前进展最快最好的一种固体量子计算实现方法。基于超导物理体系的量子比特的能级结构可通过外加电信号进行调控，量子芯片的设计定制的可控性强。同时，得益于基于现有的成熟集成电路工艺，超导物理体系具有多数量子物理体系难以比拟的可扩展性。
约瑟夫森结(Josephson Junction)是一个由两个超导体中间隔绝一个薄的绝缘层形成的三层结构。当中间绝缘层薄到能明显体现出库珀对的量子遂穿效应时，约瑟夫森结就能体现出一些不同于一般超导体或是绝缘体所展现的行为。对于这种超导体-绝缘体-超导体(SIS)三层交叠形成的约瑟夫森结，允许的最大电流是临界电流。超导量子干涉装置Squid通常是两个约瑟夫森结并联形成的超导环，其临界电流通过施加的外部磁场来调谐。
在超导物理体系中，Transmons量子比特为一种常用的量子比特的构造，结合图1所示，量子比特常包括电容，及一端接地、另一端与该电容连接的超导量子干涉装置Squid，Squid的等效临界电流Ic的大小受到外磁场Φe的调节，并且该电容常为十字型电容，参见图1所示，十字型电容Cq被接地平面(GND)包围，且十字型电容Cq与接地平面(GND)之间具有间隙，且超导量子干涉装置Squid的一端连接至十字型电容Cq，另一端连接至接地平面(GND)，由于十字型电容Cq的第一端通常用于连接超导量子干涉装置Squid，第二端用于与读取谐振腔耦合，第二端为第一端的对侧；第一端和第二端的附近需要预留一定的空间用于布线，例如，第一端的附近需预留布置脉冲调 控信号线(又称XY信号线)和磁通调控信号线(Z-control line，又称Z信号线)的空间，十字型电容Cq的另外两端(即除第一端和第二端外的端)可以用于与相邻量子比特耦合。其中，脉冲调控信号线用于给量子比特施加量子比特跃迁激发脉冲信号，磁通调控信号线用于传输驱动信号，驱动信号产生耦合到量子比特的磁场进而实现对量子比特的频率控制。
目前，量子比特的频率调控结构局限于上文描述的磁通调控信号线结构，形式较为单一，然而，量子计算的若干问题与量子比特的频率调控有关，特别是与通过磁通调控信号线施加外部磁场来调谐量子比特的Squid的磁通量进而实现频率调控的方式有关。例如，外部磁场可降低约瑟夫森结的能量，由此引入对磁通噪声。量子比特的频率易受到磁通噪声的影响而偏离理想位置，进而影响量子比特的性能。
本申请实施例提供的量子芯片可以表示为电路的形式，因此，量子芯片也可以称为量子计算电路，相应的，量子芯片中的量子比特也可以表示为电路的形式，因此，量子比特也可以称为量子比特电路。本申请中涉及的电容也可以称为电容极板。控制结构也可以称为控制电路。超导量子干涉装置也可以称为超导量子干涉电路。
量子芯片可以包含一个量子比特，也可以包含多个量子比特。图2和图3均以量子芯片包含一个量子比特为例进行说明。图7和图8均以量子芯片包含多个量子比特为例进行说明。
图2为本申请的实施例提供的一种量子芯片的实施结构示意图，图3为本申请的实施例提供的另一种量子芯片的实施结构示意图；本申请的实施例能够解决在现有技术的设计方案中的限制。
结合图2和图3所示，根据本申请的一个或多个实施例，提供了一种量子芯片，包括频率可调的控制结构2，及与控制结构2色散耦合的量子比特1，并且该量子比特1包括第一电容极板11，及与第一电容极板11连接的单个第一约瑟夫森结12，第一电容极板11和第一约瑟夫森结12连接形成非线性振荡电路。量子比特1的各元件可形成在衬底上，诸如晶片，晶片可以是硅晶片、蓝宝石晶片或用于微加工的其它衬底材料。并且，控制结构2和量子比特1的分布位置不限，两者可以位于衬底的同一表面并形成色散耦合(参见图2和图3所描述的形式)。又示例性的，也可以分别独立的位于两个不同的 表面并形成色散耦合。控制结构2可以是振荡电路，具体实施时，只要控制结构2具有可以调谐的连续频率值或者多个分散频率点即可。结合图2和图3可以看出，第一电容极板11与接地平面(GND)之间存在白色空白区域，也就表示第一电容极板11与接地平面(GND)之间具有间隙。
本申请实施例提供的量子芯片采用单个第一约瑟夫森结12和与第一电容极板11连接形成的非线性振荡电路构建量子比特1，并利用频率可调的控制结构2与量子比特1色散耦合。色散耦合有助于降低甚至避免两者之间发生能量的直接交换，从而能够利用控制结构2调控量子比特1的频率，该量子芯片结构是一种可以替代相关技术中采用磁通调控信号线直接调控量子比特的新型结构。并且，相关技术中通过在量子芯片上的磁通调控信号线(Z-control line)施加信号直接调控量子比特的Squid的磁通量完成量子比特的频率调控，本申请提供的方案中的量子芯片，利用控制结构2对量子比特1进行频率调控，由于并非直接通过磁通调控信号线调谐量子比特中约瑟夫森结的磁通量，因此，能够避免量子比特中约瑟夫森结的能量受磁通调控信号线引入的磁场的影响，使得频率调控的稳定性较高，不易受磁通噪声的影响。
下面结合图2至图6进一步描述本申请实施例中的量子比特1和控制结构2。
量子比特1
本申请实施例中，由第一电容极板11，及与第一电容极板11连接的单个第一约瑟夫森结12形成量子比特1，这种结构形式的量子比特1的频率具有适度的可调性，并且因为电性耦合，控制结构2的频率变化引起量子比特1的频率的变化。相对于相关技术中由电容极板及与电容极板并联的超导量子干涉装置Squid直接构建形成量子比特而言，本申请实施例中的量子比特1的频率可调谐范围更小(例如，约100MHz)，磁通噪声不易对量子态去相位的敏感度及退相干时间产生不利影响。在本申请的一些实施例中，如图2所示，所述第一约瑟夫森结12的一端连接所述第一电容极板11，另一端接地。在本申请的另一些实施例中，如图3所示，所述第一约瑟夫森结12的一端连接一个第一电容极板11，另一端连接另一个第一电容极板11。在本申请的实施例中，第一电容极板11被接地平面GND包围，且第一电容极板11与接地平面GND之间具有间隙，所述第一约瑟夫森结12被构建在该间隙中，且所述第 一约瑟夫森结12按设计需要与第一电容极板11、接地平面GND电和物理的接触连接，即，通过在物理上的接触实现电连接。
控制结构2
本申请实施例中的控制结构2具有自身频率可调的特点，通过控制结构2的频率调谐进而使量子比特1发生频移，完成量子比特1的频率调谐，然后再通过量子芯片中配置的脉冲调控信号线3对量子比特1的量子态进行操控。在本申请的一些实施例中，所述控制结构2包括超导量子干涉装置Squid(即第一超导量子干涉装置)，以及与超导量子干涉装置Squid感应耦合连接的磁通调控信号线4，基于磁通调控信号线4上的信号产生施加于超导量子干涉装置Squid的外部磁场，通过外部磁场调控控制结构2的频率。在一些示例中，所述超导量子干涉装置Squid包括至少两个第二约瑟夫森结22，例如，可以是三个第二约瑟夫森结22形成的并联结构。示例性的，所述至少两个第二约瑟夫森结22通常具有不同的面积，该面积也就是指SIS三层交叠的面积(也可以称为结面积)，从而保证该至少两个第二约瑟夫森结22的临界电流不相同。通过在超导量子干涉装置Squid中设置具有不相似(即临界电流不同)的约瑟夫森结，降低控制结构2的频率对噪声的敏感性。另一种方式中，所述至少两个第二约瑟夫森结22也可以具有相同的面积。
在本申请的一些实施例中，如图2所示，所述控制结构2包括一个第二电容极板21，所述超导量子干涉装置Squid的一端连接所述第二电容极板21，另一端接地。本申请的另一些实施例中，如图3所示，所述控制结构2包括两个第二电容极板21，所述超导量子干涉装置Squid的一端连接一个第二电容极板21，另一端连接另一个第二电容极板21。在本申请的实施例中，第二电容极板21被接地平面GND包围，且第二电容极板21与接地平面GND之间具有间隙，超导量子干涉装置Squid被构建在该间隙中，且超导量子干涉装置Squid按设计需要与第二电容极板21、接地平面GND电和物理的接触连接。
再次结合图1，上文相关技术所描述的量子比特的调控结构通过施加于量子比特包含的超导量子干涉装置Squid的外部磁通量来调谐量子比特的频率。具体的，在上文相关技术所描述的量子比特的调控结构中，该量子比特的频率量子比特的频率ω10与电容的静电能EC及Squid的能 量EJ有关，Squid的能量EJ随外磁场Φe变化，因此可通过Squid的能量EJ对外磁场Φe的变化响应完成量子比特的频率的控制调节。利用施加在磁通调控信号线(Z-control line)上的电流产生外磁场Φe，外磁场穿过Squid区域引起该Squid区域所属量子比特的频率的变化。穿透该Squid环路的磁通量是受到由磁通调控信号线与该Squid环路之间的互感强度M、施加在磁通调控信号线的电信号产生的磁场大小、及磁通噪声等因素的影响的。磁通噪声是磁通调控信号中电流波动引起的固有噪声或磁通调控信号携带的额外信号引起的磁通量噪声，磁通噪声会使量子比特频率发生波动和偏离。
在本申请的实施例中，量子比特1的频率调谐可以通过量子比特1与控制结构2的耦合强度g，及量子比特1与控制结构2的频率差Δ实现，并且控制结构2在调谐量子比特1的频率时，可以降低磁通噪声对量子比特1的频率调控的影响。示例性的，结合图2所示，对本申请的实施例的针对量子比特1的频率调谐的进一步介绍，记量子比特1的初始频率为ωq，控制结构2的频率为ωt，Ct为第二电容极板的对地电容，Cq为第一电容极板的对地电容，Cqt为第一电容极板与第二电容极板之间耦合电容，则量子比特1被控制结构2调谐发生频移后的频率为：
其中，
结合上式，在本申请的实施例中，通过磁通调控信号线4的信号可以调谐控制结构2的频率，而基于控制结构2的频率又进一步可以调谐量子比特1的频率，但这个过程中，并不是直接通过磁通调控信号线4调谐量子比特1的频率，磁通调控信号线4引入的噪声对量子比特1的频率的影响程度被降低，因此，可以认为这种频率调谐的结构形式可以避免磁通调控信号线4的磁通噪声对量子比特1频率的直接干扰，从而降低了频率调控的偏离程度，这有助于提升量子比特1的退相干时间以保证基于量子比特1进行数据处理时得到的量子测量结果的有效性。可以理解的是，图3所示结构中量子比特1被控制结构2调谐后的频率，与图2相比，区别在于Ct需要考虑两个 第二电容极板的等效对地电容，Cq需要考虑两个第一电容极板的等效对地电容，Cqt为两个第一电容极板与两个第二电容极板之间耦合电容，在此不赘述。
为了进一步说明，在一个设计示例中，量子芯片的特定设计属性如下：量子比特1的第一电容极板11及控制结构2的第二电容极板21均为88fF，第一约瑟夫森结12的临界电流约为38nA，Squid(即第一超导量子干涉装置)的第二约瑟夫森结22的临界电流约为15nA。针对该示例的数值模拟结果参见图4至图6(Φe为外磁场通量，φ0为磁通量子)，可以看出：在5.38GHz～5.51GHz范围，量子比特1的频率可调谐，可调谐的幅度约为134MHz，可以理解的是，在实施时通过对量子芯片的设计属性参数进行调整可以获得更大的可调谐的幅度；另外，在外磁场通量为0时，量子比特1的频率最小，控制结构2的频率最大，两者的失谐量最小，这导致Δ/较小，色散耦合较弱，因此，本申请的一些实施示例中，在设计或调控量子比特1和控制结构2时，可以限定控制结构2的频率低于量子比特1的频率，以使量子比特1的频率和控制结构2的频率之间保持足够的失谐量，例如大于500MHZ，从而有助于增强色散耦合。
在本申请的实施例中，为使控制结构2与量子比特1间满足色散耦合，有效地降低甚至避免两者之间发生能量的直接交换，量子比特1与控制结构2的频率差Δ及量子比特1与控制结构2的耦合强度g满足：Δ≥3g。
本申请实施例的第一电容极板11、第二电容极板21、接地平面GND，及第一约瑟夫森结12和第二约瑟夫森结22的超导体部分，以及脉冲调控信号线3、磁通调控信号线4、电连接各种元件的线等由超导材料制成。量子芯片可以直接利用成熟的半导体工艺将超导材料经过沉积、图案化等获得，沉积的厚度可以是微米级或纳米级，超导材料为在等于或低于临界温度的温度时，例如在大约10-100毫开尔文(mK)或大约4K时，展现超导特性的材料，例如铝、铌、钽或氮化钛等等，具体实施时不限于这几种，在等于或低于临界温度的温度时展现超导特性的材料均可用于形成前文所述结构，例如，铝(Al)，铌(Nb)，氮化铌(NbN)，氮化钛(TiN)和铌钛氮化物(NbTiN)中的一种或多种。
本申请的实施例还提供了一种量子计算机，包括：包括密闭容器的真空制冷系统；及如上量子芯片实施例中描述的量子芯片，该量子芯片被包含在 由该密闭容器限定的真空制冷环境内；以及，设于该真空制冷环境内的多个传输线路，以便将电信号引导到该量子芯片中的至少一个选定的量子比特1并且从该至少一个选定的量子比特1接收电信号。
这里需要指出的是：以上量子计算机中的量子芯片与本申请的其他实施例中介绍的量子芯片的结构类似，且具有同本申请的其他量子芯片实施例相同的有益效果，因此不做赘述。对于本申请量子计算机实施例中未披露的技术细节，本领域的技术人员请参照上述量子芯片实施例的描述而理解，为节约篇幅，这里不再赘述。
本申请实施例提供的一种量子芯片的制造可能需要沉积一种或多种材料，例如超导体、电介质和/或金属。取决于所选择的材料，这些材料可以使用诸如化学气相沉积、物理气相沉积(例如，蒸发或溅射)的沉积工艺或外延技术以及其他沉积工艺来沉积。本申请实施例描述的量子芯片的制备工艺可能需要在制造过程期间从器件去除一种或多种材料。取决于要去除的材料，去除工艺可以包括例如湿蚀刻技术、干蚀刻技术或剥离(lift-off)工艺。可以使用已知的曝光(lithographic)技术(例如，光刻或电子束曝光)对形成本文所述的电路元件的材料进行图案化。
针对量子芯片包含多个量子比特的情况，参见图7和图8的相关介绍。
图7为相关现有技术中一种量子计算电路的示意图。
参见图7所示，目前，常用的一种量子计算电路中，量子比特电路常采用一个一端接地的电容Cq，及与该电容Cq并联连接的超导量子干涉电路Squid的电路结构。电容Cq影响量子比特的非谐性，在进行量子电路设计时，量子比特的非谐性参数确定，电容Cq即确定。目前，量子计算电路的结构形式较为单一并局限于上文描述的结构。然而，量子计算的若干问题与量子比特的频率调控有关，特别是与频率调控的电路结构的形式有关，前文描述的量子计算电路通过磁通调控信号线Z(Z-control line，记为Z)施加外部磁场来调谐量子比特包含的超导量子干涉电路Squid的磁通量进而实现频率调控，但是易引入对磁通噪声的敏感度，进而使得量子比特的频率易受到磁通噪声的影响，导致量子比特的频率偏离理想位置，最终影响量子比特调控的精度，降低量子比特的退相干时间等。
另外，图7中，相邻的量子比特电路之间通过频率可调谐的耦合电路进 行连接。图7中，耦合电路分别与两个量子比特电路均实现耦合，即，通过耦合电路与两个量子比特电路之间的电容实现耦合。耦合电路包括一端接地的电容Ct、与电容Ct并联的超导量子干涉电路Squid，以及磁通调控信号线Z。
图7中的量子计算电路还包括读取电路，读取电路与量子比特电路通过电容Cqr耦合。读取电路包括电容性元件Cr和电感性元件Lr形成的LC振荡电路。量子比特电路还可以通过电容与脉冲调控信号线XY(XY-control line，记为XY)耦合。
为此，本申请提供一种量子计算电路及一种量子计算机，以解决突破相关技术中的结构局限。
图8为本申请实施例提供的一种量子计算电路的示意图。
参见图8所示，本申请的实施例提供了一种量子计算电路，它包括多个量子比特电路及频率可调谐的控制电路，所述控制电路与所述量子比特电路色散耦合，且相邻的所述量子比特电路之间耦合，相邻的所述量子比特电路之间耦合的方式可以是通过电容(C1)耦合或谐振电路耦合，所述量子比特电路包括并联且一端共地的第一电容Cq和单个第一约瑟夫森结JJ。基于本申请的实施例提供的量子计算电路，通过改变控制电路的频率，能够调控量子比特电路的频率，并且相对于相关技术中通过在量子芯片上的磁通调控信号线Z施加信号调控Squid的磁通量完成量子比特的频率调控的方式，基于本申请提供的方案中的量子计算电路，量子比特电路的频率调控的稳定性较高，不易受磁通调控信号线Z引入的磁通噪声的影响。
另一种实现方式中，任一量子比特电路包含第一电容Cq和单个第一约瑟夫森结JJ也可以串联，即，单个第一约瑟夫森结JJ的一端与第一电容Cq的一端连接，单个第一约瑟夫森结JJ的另一端用于连接其他电路，第一电容Cq的另一端接地。
图8中，量子比特电路还可以通过电容与脉冲调控信号线XY耦合。
在本申请提供的实施例中，量子比特电路中的第一电容Cq也可以是多个电容性元件串联、并联，或者部分串联部分并联后的等效电容，电容性元件的数量和电连接关系可以根据需要确定。
本申请实施例中的控制电路具有自身频率可调的特点，通过控制电路的频率调谐进而使量子比特电路发生频移，完成量子比特电路的频率调谐，然 后再通过配置的脉冲调控信号线XY对量子比特电路所处的状态进行操控。在一些实施方式中，所述控制电路包括振荡电路，例如由电容性元件和电感性元件形成的振荡电路，只要该振荡电路的自身频率可调控为不同的频率值即可。所述振荡电路为非线性振荡电路，例如，由电容性元件和非线性电感性元件形成的振荡电路。如图8所示，所述非线性振荡电路包括并联的第二电容Ct和超导量子干涉电路Squid(即第一超导量子干涉装置)，以及与所述超导量子干涉电路Squid耦合的磁通调控信号线Z，且所述超导量子干涉电路Squid包括至少两个约瑟夫森结，为与量子比特电路中包含的约瑟夫森结区分，超导量子干涉电路Squid包含的约瑟夫森结记为第二约瑟夫森结。在一些示例中，为获得非对称结构的超导量子干涉电路Squid以使控制电路的频谱具有至少两个磁通量不敏感点，控制电路中该超导量子干涉电路Squid包含的第二约瑟夫森结的个数为奇数。在一些实施方式中，第一约瑟夫森结和第二约瑟夫森结可以为隧道结、点接触、或者其他呈现约瑟夫森效应的结构。
在本申请的实施例中，量子比特电路的频率调谐可以通过量子比特电路与控制电路的耦合强度g，及量子比特电路与控制电路的频率差Δ实现，并且控制电路在调谐量子比特电路的频率时，可以降低磁通噪声对量子比特电路的频率调控的影响。示例性的，结合图8所示，对本申请的实施例的针对量子比特电路的频率调谐的进一步介绍，记量子比特电路的初始频率为ωq，控制电路的频率为ωt，Cqt为量子比特电路与控制电路之间的耦合电容，则量子比特电路被控制电路调谐发生频移后的频率为：
其中，
结合上式，在本申请的实施例中，通过磁通调控信号线Z的信号可以调谐控制电路的频率，而基于控制电路的频率又进一步可以调谐量子比特电路的频率，但这个过程中，并不是直接通过磁通调控信号线Z调谐量子比特电路的频率，磁通调控信号线Z引入的噪声对量子比特电路的频率的影响程度被降低，因此，可以认为这种频率调谐的结构形式可以避免磁通调控信号线Z的磁通噪声对量子比特电路频率的直接干扰，降低了频率调控的偏离程度，有助于提升量子比特电路的退相干时间
为了进一步说明，在一个设计示例中，量子计算电路的设计属性如下： 量子比特电路的第一电容Cq及控制电路的第二电容Ct均为88fF，量子比特电路的第一约瑟夫森结JJ的临界电流约为38nA，控制电路中超导量子干涉电路Squid的第二约瑟夫森结的临界电流约为15nA。针对该示例的数值模拟结果参见图4至图6(Φe为外磁场通量，φ0为磁通量子)，可以看出：在5.38GHz～5.51GHz范围，量子比特电路的频率可调谐，可调谐的幅度约为134MHz，可以理解的是，在实施时通过对量子计算电路的设计属性参数进行调整可以获得更大的可调谐的幅度；另外，在磁通偏置为0时，量子比特电路的频率最小，控制电路的频率最大，两者的失谐量最小，这导致Δ/g较小，色散耦合较弱，因此，本申请的一些实施示例中，在设计或调控量子比特电路和控制电路时，可以限定控制电路的频率低于量子比特电路的频率，以使量子比特电路的频率和控制电路的频率之间保持足够的失谐量，例如大于500MHZ，从而有助于增强色散耦合。
在本申请的实施例中，为使控制电路与量子比特电路间满足色散耦合，有效地降低甚至避免两者之间发生能量的直接交换，量子比特电路与控制电路的频率差Δ及量子比特电路与控制电路的耦合强度g满足：Δ≥3g。
在一些实施方式中，所述量子计算电路中相邻的所述量子比特电路之间通过频率可调谐的耦合电路进行连接，频率可调谐的耦合电路便于实现对相邻量子比特电路之间耦合强度的调控，有助于实现双量子逻辑门的执行。例如，结合图8所示，两个量子比特电路处于相邻位置，耦合电路分别与两个量子比特电路均实现耦合，即，通过图8中的C2和C3实现耦合，从而产生了两个量子比特电路之间的间接耦合，并且，通过调节耦合电路的频率，可以调节量子比特电路之间的耦合强度。其中，作为示例性的，所述耦合电路包括一端接地的电容CC，以及与电容CC并联的超导量子干涉电路Squid(即第二超导量子干涉装置)，可以理解的是，耦合电路中的超导量子干涉电路Squid可以根据需要选择不同于控制电路中的Squid的参数设计。在一些示例中，耦合电路中的该超导量子干涉电路Squid包括至少两个约瑟夫森结，且所述约瑟夫森结之间并联，通过外加磁通能够对所述耦合电路的频率进行调节。并且，在一些示例中，为获得非对称结构的超导量子干涉电路Squid以使耦合电路的频谱具有至少两个磁通量不敏感点，该超导量子干涉电路Squid中的约瑟夫森结的个数为奇数。在一些实施方式中，所述约瑟夫森结为隧道结、点接触、 或者其他呈现约瑟夫森效应的结构。
在一些实施方式中，所述量子计算电路还包括读取电路，所述读取电路与所述量子比特电路耦合，采用读取电路读取调控后的量子比特电路的量子态。其中，作为示例性的，如图8所示，所述读取电路包括电容性元件Cr和电感性元件Lr形成的LC振荡电路。在一些示例中，所述读取电路与所述量子比特电路电容耦合，例如通过电容Cqr耦合。在本申请的实施例中，每个量子比特电路均有与其耦合的所述读取电路，多个所述读取电路的另一端与一共同的读取信号传输线耦合，读取信号传输线通过与每个量子比特对应的读取电路获取量子态的信息。
本申请的实施例还提供了一种量子计算机，所述量子计算机为超导体系，且所述量子计算机至少设置有如上所述的量子计算电路。
这里需要指出的是：以上量子计算机的实施例中涉及的量子计算电路与上述量子计算电路实施例中的结构类似，且具有同上述量子计算电路实施例相同的有益效果，因此不做赘述。对于本申请的量子计算机实施例中未披露的技术细节，本领域的技术人员请参照上述量子计算电路的描述而理解，为节约篇幅，这里不再赘述。
结合本申请文件的描述，与现有技术相比，本申请的量子计算电路，包括多个量子比特电路，且相邻的所述量子比特电路之间耦合，所述量子比特电路包括第一电容Cq和单个第一约瑟夫森结JJ，两者的一端共地，与所述量子比特电路色散耦合的控制电路可以包括并联的第二电容Ct和超导量子干涉电路Squid，以及与所述超导量子干涉电路Squid耦合的磁通调控信号线Z。基于本申请的实施例提供的量子计算电路，通过改变控制电路的频率，能够调控量子比特电路的频率，并且相对于相关技术中直接通过磁通调控信号线Z施加信号调控量子比特的频率调控的方式，基于本申请提供的基于调控结构调控量子比特频率调控的方式，其稳定性较高，不易受磁通调控信号线Z引入的磁通噪声的影响。在本申请提供的实施例中，利用控制电路将量子比特电路的频率调整到工作频率，此时通过脉冲调控信号线XY施加量子态调控信号对处于初始态的量子比特电路进行量子态调控，采用读取电路读取调控后的量子比特电路的量子态，通过在与读取电路耦合的读取信号传输线上施加读取探测信号(例如，频率为4-8GHz的微波信号)，通过解析经读取信号 传输线输出的读取反馈信号(响应于读取探测信号的信号)确定量子比特电路所处于的量子态，脉冲调控信号线XY和读取信号传输线在此不再赘述。
以上所述仅为本申请的较佳实施例，并不用以限制本申请，凡在本申请的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本申请保护的范围之内。

Claims (23)

  1. 一种量子芯片，其特征在于，包括：
    量子比特，及频率可调的控制结构，且控制结构与量子比特色散耦合，其中，所述量子比特包括第一电容极板及与第一电容极板连接形成第一非线性振荡电路的单个第一约瑟夫森结。
  2. 根据权利要求1所述的量子芯片，其特征在于，所述量子比特为一个或多个；
    所述量子比特为多个时，相邻量子比特之间耦合连接。
  3. 根据权利要求2所述的量子芯片，其特征在于，每一量子比特中的第一约瑟夫森结与第一电容极板连接，且该第一电容极板的一端接地。
  4. 根据权利要求3所述的量子芯片，其特征在于，每一量子比特中的第一约瑟夫森结与第一电容极板并联且一端共地。
  5. 根据权利要求2所述的量子芯片，其特征在于，每一量子比特中的第一约瑟夫森结的一端连接一个第一电容极板，另一端连接另一个第一电容极板。
  6. 根据权利要求2所述的量子芯片，其特征在于，所述控制结构包括第二非线性振荡电路。
  7. 根据权利要求6所述的量子芯片，其特征在于，所述第二非线性振荡电路包括：第一超导量子干涉装置，以及与所述第一超导量子干涉装置感应耦合连接的磁通调控信号线。
  8. 根据权利要求7所述的量子芯片，其特征在于，所述第一超导量子干涉装置包括至少两个第二约瑟夫森结，所述至少两个第二约瑟夫森结形成并联结构。
  9. 根据权利要求8所述的量子芯片，其特征在于，所述至少两个第二约瑟夫森结的临界电流不相同。
  10. 根据权利要求7-9任一所述的量子芯片，其特征在于，所述第二非线性振荡电路还包括：两个第二电容极板，所述第一超导量子干涉装置的一端连接一个第二电容极板，另一端连接另一个第二电容极板。
  11. 根据权利要求7-9任一所述的量子芯片，其特征在于，所述第二非线性振荡电路还包括：与所述第一超导量子干涉装置并联的第二电容极板。
  12. 根据权利要求2所述的量子芯片，其特征在于，在所述量子比特为多 个的情况下，相邻量子比特之间连接有频率可调谐的耦合电路。
  13. 根据权利要求12所述的量子芯片，其特征在于，所述耦合电路包括一端接地的电容，以及与该电容并联的第二超导量子干涉装置，且所述第二超导量子干涉装置包括至少两个约瑟夫森结。
  14. 根据权利要求13所述的量子芯片，其特征在于，所述第二超导量子干涉装置包括的约瑟夫森结的个数为奇数。
  15. 根据权利要求1-14任一所述的量子芯片，其特征在于，所述量子芯片还包括读取电路和/或脉冲调控信号线，所述读取电路与所述量子比特耦合，所述脉冲调控信号线与所述量子比特耦合。
  16. 根据权利要求1-15任一所述的量子芯片，其特征在于，所述量子比特与控制结构的频率差Δ及量子比特与控制结构的耦合强度g满足：Δ≥3g。
  17. 根据权利要求1-15任一项所述的量子芯片，其特征在于，所述控制结构的频率低于量子比特的频率。
  18. 一种量子计算电路，其特征在于，包括：
    多个量子比特，且相邻量子比特之间耦合连接，该量子比特包括并联且一端共地的电容和单个约瑟夫森结；以及，
    频率可调谐的控制电路，且控制电路与量子比特色散耦合。
  19. 根据权利要求18所述的量子计算电路，其特征在于，相邻量子比特之间连接有频率可调谐的耦合电路。
  20. 根据权利要求19所述的量子计算电路，其特征在于，所述耦合电路包括一端接地的电容，以及与该电容并联的超导量子干涉装置，且该超导量子干涉装置包括至少两个约瑟夫森结。
  21. 根据权利要求20所述的量子计算电路，其特征在于，所述超导量子干涉装置包括的约瑟夫森结的个数为奇数。
  22. 一种量子计算机，其特征在于，所述量子计算机为超导体系，且所述量子计算机至少设置有权利要求18至21中任一项所述的量子计算电路。
  23. 一种量子计算机，其特征在于，包括：
    真空制冷系统，包括密闭容器；
    如权利要求1至17中任一项所述量子芯片，该量子芯片被包含在由该密闭容器限定的真空制冷环境内；以及
    设于该真空制冷环境内的多个传输线路，以便将电信号引导到该量子芯片中的至少一个选定的量子比特并且从该至少一个选定的量子比特接收电信号。
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