WO2023226598A1 - 一种读取电路、读取方法及量子计算机 - Google Patents

一种读取电路、读取方法及量子计算机 Download PDF

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WO2023226598A1
WO2023226598A1 PCT/CN2023/086067 CN2023086067W WO2023226598A1 WO 2023226598 A1 WO2023226598 A1 WO 2023226598A1 CN 2023086067 W CN2023086067 W CN 2023086067W WO 2023226598 A1 WO2023226598 A1 WO 2023226598A1
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frequency
reading
resonant cavity
read
qubit
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PCT/CN2023/086067
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English (en)
French (fr)
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张辉
李松
李业
杨振权
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本源量子计算科技(合肥)股份有限公司
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Publication of WO2023226598A1 publication Critical patent/WO2023226598A1/zh

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    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06NCOMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
    • G06N10/00Quantum computing, i.e. information processing based on quantum-mechanical phenomena
    • G06N10/20Models of quantum computing, e.g. quantum circuits or universal quantum computers
    • GPHYSICS
    • G06COMPUTING; CALCULATING OR COUNTING
    • G06NCOMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
    • G06N10/00Quantum computing, i.e. information processing based on quantum-mechanical phenomena
    • G06N10/40Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control

Definitions

  • This application belongs to the field of quantum information, especially the field of quantum computing technology.
  • this application relates to a reading circuit, a reading method and a quantum computer.
  • the reading circuit structure mainly includes a resonant cavity coupled with the qubit to be read, and a reading bus coupled with the resonant cavity. Based on this circuit structure, the state information of the qubit is transferred from the qubit to the transmission line. Therefore, each qubit on the superconducting quantum chip is connected to the read bus through an independent resonant cavity.
  • this reading mechanism has certain limitations, and the objects read are specific.
  • this application provides a reading circuit, a reading method and a quantum computer.
  • An embodiment of the present application provides a read circuit, which includes: a transmission element coupled to an element to be read; a resonant cavity coupled to the transmission element; and a read signal line coupled to the resonant cavity .
  • the read circuit has a plurality of transmission elements coupled in sequence.
  • the transmission element includes at least one of the following types: qubit, frequency tunable coupler.
  • the transmission element includes sequentially coupled qubits and frequency-tunable couplers, and the qubits and the couplers are arranged alternately.
  • the element to be read includes one of the following types: quantum bits, frequency tunable couplers.
  • the coupler includes a superconducting quantum interferometer formed by having at least two Josephson junctions connected in parallel.
  • the qubit includes a superconducting quantum interferometer formed by having at least two Josephson junctions connected in parallel.
  • the resonant cavity is formed by a coplanar waveguide transmission line.
  • the resonant cavity is a half-wavelength resonant cavity or a quarter-wavelength resonant cavity.
  • Another embodiment of the present application provides a reading method for a reading circuit, including the following steps:
  • Adjust the first frequency of the element to be read and the second frequency of the transmission element and determine the spectrum with the largest dispersion frequency shift value as the target spectrum.
  • a magnetic flux signal is applied to the configured signal line to adjust the second frequency.
  • the step of adjusting the second frequency of the transmission element includes: adjusting the second frequency to the qubit. Degeneracy point.
  • the step of adjusting the second frequency of the transmission element includes: The frequency of the qubit is fixed at the degeneracy point, and the frequency of the coupler is adjusted.
  • a third embodiment of the present application provides a quantum computer including the reading circuit as described above.
  • an indirect coupling connection is established between the element to be read and the resonant cavity through the coupling of the transmission element to the element to be read and the resonant cavity, and then based on The reading signal line coupled with the resonant cavity enables reading of the element to be read, thereby breaking through the limitation in the related technology that reading can only be achieved through the resonant cavity directly coupled with the element to be read.
  • two qubits can be read in an integrated extended quantum chip using a resonant cavity coupled to a qubit and a coupler between the two qubits.
  • the resonant cavity directly coupled to one qubit fails, the resonant cavity of the adjacent qubit coupled to the qubit can also be used to achieve reading.
  • Figure 1 is a schematic structural diagram of a qubit on a quantum chip in related technology
  • Figure 2 is a schematic structural diagram of a reading circuit provided by an embodiment of the present application.
  • Figure 3 is a flow chart of a reading method provided by an embodiment of the present application.
  • the physical implementation methods of qubits include superconducting quantum circuits, semiconductor quantum dots, ion traps, diamond vacancies, topological quantum, photons, etc.
  • Quantum computing in superconducting quantum circuits is currently the fastest and best way to implement solid-state quantum computing. Since the energy level structure of superconducting quantum circuits can be controlled by external electromagnetic signals, the design and customization of the circuits are highly controllable. Thanks to the existing mature integrated circuit technology, superconducting quantum circuits have scalability that is unmatched by most quantum physics systems.
  • qubits include Josephson junctions.
  • the Josephson junction is a structure formed by separating two thin film superconducting layers with a non-superconducting material. When the temperature is reduced to a specific low temperature, the superconducting layer becomes superconducting, and electron pairs can tunnel from one superconducting layer through the non-superconducting layer to another superconducting layer.
  • a Josephson junction (which acts as a nonlinear inductive device) is connected in parallel with one or more capacitive devices to form a nonlinear microwave oscillator.
  • a qubit has a resonant/transition frequency determined by the values of the inductor and capacitor within it.
  • a readout circuit is a circuit coupled to a qubit to capture, read and measure quantum information.
  • the structure of a qubit includes a single capacitor to ground and a superconducting quantum interference device with one end connected to ground and the other end connected to the capacitor.
  • This capacitor is often a cross-type parallel plate capacitor.
  • the cross-shaped capacitor plate C q is surrounded by a ground plane (GND).
  • GND ground plane
  • One end of the superconducting quantum interference device squid is connected to the cross-shaped capacitor plate C q , and the other end is connected to the ground plane (GND).
  • the first end is usually used to connect the superconducting quantum interference device squid, and the second end is used to couple with a reading structure such as a resonant cavity. Therefore, a certain space needs to be reserved near the first end and the second end for wiring. For example, space needs to be reserved near the first end to arrange the xy signal line and z signal line.
  • the other two ends of the cross-shaped capacitive plate C q are used to couple with adjacent qubits.
  • Qubits utilizing this structure are arranged according to a one-dimensional chain array to achieve integrated expansion of qubits. Qubits in adjacent positions are coupled and share a read signal line (ReadOut Line).
  • the read circuit structure mainly includes a resonant cavity coupled to the qubit to be read, and a read signal line coupled to the resonant cavity. Each qubit is connected to the read signal line through an independent resonant cavity. Based on the respective resonant cavities and the read signal lines coupled with the resonant cavities, the state information of the qubits is transferred from the qubits to the transmission lines.
  • this reading mechanism has great limitations, including but not limited to the following two aspects.
  • this application provides a reading circuit, a reading method and a quantum computer to solve the deficiencies in the existing technology. It breaks through the related technology and can only achieve reading through a resonant cavity directly coupled with the element to be read. limits. Embodiments of the present application will be introduced in detail below with reference to Figures 2 to 3.
  • FIG. 2 is a schematic structural diagram of a reading circuit provided by an embodiment of the present application.
  • Figure 3 is a flow chart of a reading method provided by an embodiment of the present application.
  • FIG. 2 schematically shows the relationship between the read signal line 1, the resonant cavity 2, the qubit 3, and the frequency tunable coupler 4.
  • each qubit 3 has an independently configured resonant cavity 2 .
  • the resonant cavity 2 is coupled to the read signal line.
  • a coupling relationship is established between adjacent qubits 3 through a coupler 4 .
  • the resonant cavity 2 includes a first resonant cavity 21, a second resonant cavity 22... and an Nth resonant cavity 23.
  • Qubit 3 includes a first bit 31, a second bit 32... and an Nth bit 33.
  • the coupler 4 includes a first coupler 41, a second coupler 42... and an Nth coupler 43.
  • an embodiment of the present application provides a A reading circuit includes: a transmission element coupled with the element to be read; a resonant cavity 2 coupled with the transmission element; and a read signal line 1 coupled with the resonant cavity 2 .
  • the resonant cavity 2 has a first end configured to be coupled to the transmission element and a second end configured to be coupled to the read signal line 1 .
  • the coupling may be in the form of capacitive coupling or inductive coupling.
  • the element to be read, the transmission element, and the resonant cavity 2 are coupled in sequence, thereby indirectly coupling the element to be read and the resonant cavity 2, and then based on the reading signal line 1 coupled with the resonant cavity 2, the realization
  • the reading of the element to be read thus breaks through the limitation in the related art that reading can only be achieved through the resonant cavity 2 directly coupled with the element to be read.
  • the transmission element is an electrical element with a coupling connection function.
  • An indirect coupling connection is established between the element to be read and the resonant cavity through the transmission element.
  • the transmission element may have a first end configured to be coupled to the element to be read and a second end configured to couple to the resonant cavity 2 .
  • the transmission element may be a qubit 3 coupled to the element to be read. The coupling between the element to be read and the qubit 3 may be directly adjacent to each other, or may be coupled through other electrical structural elements.
  • the resonant cavity 2 coupled to the qubit 3 and the coupler 4 between the two qubits 3 can be used to realize the reading of the two qubits 3 based on the solution of the embodiment of the present application. Based on the solution of this application, the resonant cavity 2 of an adjacent qubit 3 coupled to a qubit 3 can also be used to realize the reading of the qubit 3, thereby solving the problem of resonant cavity directly coupled to the qubit 3. The problem of not being able to read it when it fails.
  • the first bit 31 and the second bit 32 are coupled through the first coupler 41 .
  • the read circuit for the first bit 31 may include: a first coupler 41, a second bit 32, a second resonant cavity 22 and a read signal line 1 coupled in sequence.
  • the first bit 31 is coupled to the first coupler 41
  • the first coupler 41 is coupled to the second bit 32
  • the second bit 32 is coupled to the second resonant cavity 22
  • the second resonant cavity 22 is coupled to the read signal line 1 .
  • the reading signal line 1 is used to measure the state information of a specific element to be read (the first bit 31) using the principle of dispersive readout technology.
  • the dispersive readout is based on the dispersive interaction of the first bit 31 with the second resonant cavity 22, which dispersion shift causes the frequency of the second resonant cavity 22 to change depending on the state of the first bit 31.
  • the first bit 31 can achieve indirect coupling with the second resonant cavity 22 through the first coupler 41 and the second bit 32, the frequency of the second resonant cavity 22 changes according to the state of the first bit 31.
  • the second resonant cavity 22 is probed with microwave pulses and the phase and amplitude of the reflected signal are used To distinguish the status information of the first bit 31.
  • the reading circuit may have a plurality of transmission elements coupled and connected in sequence.
  • a plurality of the transmission elements are coupled and connected in sequence to form a transmission link.
  • One end of the transmission link is coupled to the element to be read, and the other end is coupled to the resonant cavity, thereby ensuring that the element to be read establishes an indirect coupling connection with the resonant cavity through the transmission link.
  • the spectrum reading of the element to be read is realized.
  • the first bit 31 can form an indirect coupling with the N-th resonant cavity 23 by means of a transmission link formed by sequential coupling and connection of the first coupler 41, the second bit 32, the second coupler 42... and the N-th bit 33.
  • the frequency of the N-th resonant cavity 23 changes according to the state of the first bit 31 .
  • the Nth resonant cavity 23 is probed with microwave pulses, and the phase and amplitude of the reflected signal are used to distinguish the state information of the first bit 31 .
  • the transmission element includes qubit 3.
  • the indirect coupling of the first resonant cavity 21 and the first coupler 41 can be realized by means of the first bit 31 , or the second resonant cavity 22 can be realized by means of the second bit 32
  • microwave pulses can be used to detect the first resonant cavity 21 or the second resonant cavity 22 to achieve reading of the first coupler 41.
  • the transmission element may also include a frequency-tunable coupler 4 .
  • the indirect coupling between the first coupler 41 and the N-th resonant cavity 23 is achieved through the transmission link formed by the qubit 3 and the coupler, so that the N-th resonant cavity 23 can be probed with microwave pulses to realize the coupling of the first coupler 41 of reading.
  • the transmission element includes a qubit 3 and a frequency-tunable coupler 4 .
  • the transmission link can be formed by coupling and connecting multiple qubits 3 and multiple couplers 4 .
  • the qubit 3 and the coupler 4 are arranged alternately in the transmission link.
  • the frequency tunable coupler 4 is capable of controlling the coupling between adjacent bits (first bit 31 and second bit 32) in order to reduce or eliminate coupling between bits during readout or during application of control pulses to qubit 3.
  • Microwave crosstalk and/or frequency conflict Tuning the frequency of the first coupler 41 enables adjustment of the coupling strength between the first bit 31 and the second bit 32 to allow the coupling between the first bit 31 and the second bit 32 to be adjusted from weak coupling to strong coupling. .
  • the frequency of coupler 4 may be tuned to be the same as or close to the transition frequency (qubit resonance frequency) of qubit 3, or may be tuned to be at the far end of the frequency range from qubit 3.
  • the coupler 4 is connected to the quantum bit 3. Bit 3 resonates.
  • coupler 4 does not resonate with qubit 3.
  • the element to be read includes one of the following types: qubit 3, frequency tunable coupler 4.
  • the coupler 4 includes a superconducting quantum interference device squid formed by at least two Josephson junctions connected in parallel. It can be understood that the coupler 4 is configured with a signal line for frequency tuning. The frequency of the coupler 4 can be adjusted based on the magnetic flux signal applied on the signal line.
  • the qubit 3 includes a superconducting quantum interference device squid formed by at least two Josephson junctions connected in parallel. It can be understood that qubit 3 is configured with an xy signal line and a z signal line.
  • the resonant cavity 2 is formed by a coplanar waveguide transmission line.
  • the resonant cavity 2 is a half-wavelength resonant cavity or a quarter-wavelength resonant cavity.
  • the present application also provides a spectrum reading method for the reading circuit as described above.
  • the reading method includes steps S601 to S602.
  • Step S601 Apply a measurement microwave signal on the reading signal line 1, and obtain the response spectrum of the resonant cavity 2. For example, what is obtained may be a graph of spectrum S21. Probing the resonant cavity 2 with microwave pulses. The microwave pulse is typically at a frequency close to the midpoint corresponding to the resonant frequencies of the ground and excited states. The phase and amplitude of the reflected signal are used to distinguish the status information of the element to be read.
  • Step S602 Adjust the first frequency of the element to be read and the second frequency of the transmission element, and determine that the spectrum when the dispersion frequency shift value is the maximum is the target spectrum, and the target spectrum is used as the reading result.
  • the embodiment of the present application provides a reading method for the reading circuit as described above. It applies a measurement microwave signal on the reading signal line 1, obtains the spectrum of the response of the resonant cavity 2, and then adjusts the to-be-measured microwave signal. Read the first frequency of the element and the second frequency of the transmission element, and determine the spectrum when the dispersion frequency shift value is the maximum as the target spectrum to achieve reading of the element to be read.
  • the reading method of the embodiment of the present application is particularly suitable for the following situation: when the resonant cavity 2 directly coupled to the qubit 3 fails, the reading is realized through the resonant cavity 3 corresponding to the adjacent qubit 2 coupled to the qubit 2. Pick.
  • the coupling mechanism between the qubit 2 and the adjacent qubit 2 can be realized by the frequency-tunable coupler 4, or the frequency-tunable coupler 4 and the qubit 3 can be coupled and connected in sequence to form a transmission link.
  • the second frequency is adjusted by applying a magnetic flux signal on the configured signal line.
  • the transmission element includes one of the following types: qubit 3, frequency tunable coupler 4.
  • the coupler 4 includes a superconducting quantum interference device squid formed by at least two Josephson junctions connected in parallel.
  • the coupler 4 is configured with a signal line for frequency tuning, and the frequency of the coupler 4 can be adjusted based on the magnetic flux signal applied on the signal line.
  • the qubit 3 includes a superconducting quantum interference device squid formed by at least two Josephson junctions connected in parallel. Qubit 3 is configured with a z signal line for frequency control.
  • the coupling strength of the nearby qubit 3 and the resonant cavity 2 in the reading circuit can be adjusted to the maximum.
  • the step of adjusting the second frequency of the transmission element may include: adjusting the second frequency to the degeneracy point of qubit 3.
  • the step of adjusting the second frequency of the transmission element includes: changing the frequency of the qubit 3 The frequency is fixed at the degeneracy point and the frequency of the coupler 4 is adjusted.
  • the reading circuit When reading for the first coupler 41, the reading circuit includes the first bit 31, the first resonant cavity 21 and the reading signal line 1 coupled in sequence, which can fix the frequency of the first bit 31 at the degeneracy point, so that Maximizing the coupling strength between the first bit 31 and the first resonant cavity 21 facilitates obtaining the modulation spectrum of the first coupler 41 .
  • the reading circuit may include: a first coupler 41, a second bit 32, a second resonant cavity 22 and a reading signal line 1 coupled in sequence, and the second bit may be The frequency of 32 is fixed at the degeneracy point, and the frequency of the first coupler 41 is adjusted.
  • An embodiment of the present application also provides a quantum computer, including the reading circuit as described above.
  • the quantum computer has a reading circuit with the above structure and has the same beneficial effects as the above reading circuit embodiment, so no further description is given.
  • those skilled in the art should refer to the description of the reading circuit above to understand them. To save space, they will not be described again here.
  • Embodiments of the present application use the same or similar processing techniques used in integrated circuit manufacturing (such as photolithography, material deposition such as sputtering or chemical vapor deposition, and material removal such as etching or lift-off) to fabricate qubits and resonant cavities. , transmission components and read signal lines.
  • the qubits, resonators, transmission elements and read signal lines can each be on the same chip (such as the same silicon or sapphire substrate or wafer) and operate at temperatures below the critical temperature of the superconducting material from which they are formed.
  • superconducting materials include, but are not limited to, aluminum (eg, superconducting critical temperature of 1.2 Kelvin), niobium (eg, superconducting critical temperature of 9.3 Kelvin), and titanium nitride (eg, superconducting critical temperature of 5.6 Kelvin).
  • the superconducting circuit elements are cooled within a cryostat to allow the superconducting material to behave super Conductivity temperature.

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Abstract

一种读取电路、读取方法及量子计算机,属于量子计算技术领域。在所述读取电路中,通过传输元件与谐振腔的耦合,将与传输元件耦合的待读取元件与谐振腔建立间接的耦合连接,进而可以基于与谐振腔耦合的读取信号线实现对待读取元件的读取,从而突破了相关技术中仅能通过与待读取元件直接耦合的谐振腔实现读取的限制。还提供了针对上述读取电路的读取方法,通过在所述读取信号线上施加测量微波信号,并获取所述谐振腔响应的频谱,然后调整所述待读取元件的第一频率以及所述传输元件的第二频率,将色散频移值为最大的所述频谱确定为目标频谱,即实现对待读取元件的读取。

Description

一种读取电路、读取方法及量子计算机
相关申请的交叉引用
本专利申请要求于2022年05月27日提交的、发明名称为“一种读取电路、读取方法及量子计算机”、申请号为CN202210596911.X的中国专利申请的优先权,该专利申请在此全部引入作为参考。
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,本申请涉及一种读取电路、读取方法及量子计算机。
背景技术
目前,超导量子比特的读取采用色散读取的方式,读取的电路结构主要包括与待读取量子比特耦合的谐振腔、及与谐振腔耦合的读取总线。基于这种电路结构实现将量子比特的状态信息从量子比特到传输线的传递。因此,超导量子芯片上的每个量子比特通过独立的谐振腔与读取总线的连接。然而,这种读取机制有一定的限制性,读取的对象特定。
发明内容
为克服相关技术中读取机制的限制,本申请提供一种读取电路、读取方法及量子计算机。
本申请的一个实施例提供了一种读取电路,它包括:与待读取元件耦合的传输元件;与所述传输元件耦合的谐振腔;以及,与所述谐振腔耦合的读取信号线。
如上所述的读取电路,在一些实施方式中,所述读取电路具有多个依次耦合连接的所述传输元件。
如上所述的读取电路,在一些实施方式中,所述传输元件包括以下类型至少之一:量子比特、频率可调谐的耦合器。
如上所述的读取电路,在一些实施方式中,所述传输元件包括依次耦合连接的量子比特和频率可调谐的耦合器,且所述量子比特和所述耦合器相间布置。
如上所述的读取电路,在一些实施方式中,所述待读取元件包括以下类型之一:量子比特、频率可调谐的耦合器。
如上所述的读取电路,在一些实施方式中,所述耦合器包括由具有至少两个约瑟夫森结并联形成的超导量子干涉器。
如上所述的读取电路,在一些实施方式中,所述量子比特包括由具有至少两个约瑟夫森结并联形成的超导量子干涉器。
如上所述的读取电路,在一些实施方式中,所述谐振腔由共面波导传输线形成。
如上所述的读取电路,在一些实施方式中,所述谐振腔为半波长谐振腔或四分之一波长谐振腔。
本申请的另一个实施例提供了一种读取电路的读取方法,包括如下步骤:
在所述读取信号线上施加测量微波信号,并获取所述谐振腔响应的频谱;
调整所述待读取元件的第一频率以及所述传输元件的第二频率,确定色散频移值为最大的所述频谱为目标频谱。
如上所述的读取方法,在一些实施方式中,在配置的信号线上施加磁通信号实现对所述第二频率的调整。
如上所述的读取方法,在一些实施方式中,所述传输元件为量子比特时,调整所述传输元件的第二频率的步骤,包括:将所述第二频率调整至所述量子比特的简并点。
如上所述的读取方法,在一些实施方式中,所述传输元件为依次耦合连接的频率可调谐的耦合器及量子比特时,调整所述传输元件的第二频率的步骤,包括:将所述量子比特的频率固定在简并点,并调整所述耦合器的频率。
本申请的第三个实施例提供了一种量子计算机,包括如上所述的读取电路。
与现有技术相比,在本申请提供的读取电路中,通过传输元件与待读取元件和谐振腔的耦合,将待读取元件与谐振腔建立间接的耦合连接,进而基于 与谐振腔耦合的读取信号线实现对待读取元件的读取,从而突破了相关技术中仅能通过与待读取元件直接耦合的谐振腔实现读取的限制。根据本申请的实施例,可以在集成扩展的量子芯片中,利用与量子比特耦合的谐振腔和两个量子比特之间的耦合器读取两个量子比特。此外,根据本申请的实施例,也可以在与一个量子比特直接耦合的谐振腔发生故障时,利用与该量子比特耦合的相邻量子比特的谐振腔实现读取。
附图说明
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读取电路的结构示意图;
图3为本申请的一个实施例提供的读取方法的流程图。
附图标记说明:
1-读取信号线,2-谐振腔,3-量子比特,4-耦合器
21-第一谐振腔,22-第二谐振腔,23-第N谐振腔,
31-第一比特,32-第二比特,33-第N比特,
41-第一耦合器,42-第二耦合器。
具体实施方式
下面通过参考附图描述的实施例是示例性的,仅用于解释本申请,而不能解释为对本申请的限制。
以下详细描述仅是说明性的,并不旨在限制实施例和/或实施例的应用或使用。此外,它们无意受到前面的“背景技术”或“发明创造内容”部分或“具体实施方式”部分中呈现的任何明示或暗示信息的约束。
为使本申请实施例的目的、技术方案和优点更加清楚,现在参考附图描述一个或多个实施例。在整个说明书中,相似的附图标记用于指代相似的组件。在下面的描述中,出于解释的目的,阐述了许多具体细节,以便提供对一个或多个实施例的更透彻的说明。然而,很明显,在各种情况下,可以在没有这些具体细节的情况下实践一个或多个实施例,各个实施例在不矛盾的前提下可以相互结合和/或相互引用。
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。
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量子电路、半导体量子点、离子阱、金刚石空位、拓扑量子、光子等。
超导量子电路的量子计算是目前进展最快最好的一种固体量子计算实现方法。由于超导量子电路的能级结构可通过外加电磁信号进行调控,电路的设计定制的可控性强。得益于基于现有的成熟集成电路工艺,超导量子电路具有多数量子物理体系难以比拟的可扩展性。
在超导量子电路中,量子比特包括约瑟夫森结。约瑟夫森结是通过用非超导材料分离两个薄膜超导层而形成的结构。当温度降低到特定的低温温度,超导层实现超导,电子对可以从一个超导层通过非超导层隧穿到另一超导层。在量子比特中,约瑟夫森结(其用作非线性电感性器件)与一个或多个电容性器件并联形成非线性微波振荡器。量子比特具有由其中的电感和电容的值确定的谐振/跃迁频率。
量子比特读取的物理基础是色散读取,利用量子比特与腔的非线性耦合,将量子比特处理的信息以微波频率范围内的微波信号的形式被携带或传输,捕获、处理和分析微波信号即可其中编码的量子信息。读出电路即是与量子比特耦合的电路,用于捕获、读取和测量量子信息。
作为超导量子电路的一个示例,量子比特的结构包括单个对地的电容及一端接地、另一端与该电容连接的超导量子干涉装置。该电容常为十字型平行板电容。参见图1所示,十字型电容板Cq被接地平面(GND)包围。十字型电容板Cq与接地平面(GND)之间具有间隙。超导量子干涉装置squid的一端连接至十字型电容板Cq,另一端连接至接地平面(GND)。由于十字型电容板Cq 的第一端通常用于连接超导量子干涉装置squid,第二端用于与谐振腔等读取结构耦合,因此,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xy信号线和z信号线的空间。十字型电容板Cq的另外两端用于与相邻量子比特耦合。
按照一维链阵列排布利用这种结构的量子比特,以实现量子比特的集成扩展。相邻位置的量子比特形成耦合并且共用一条读取信号线(ReadOut Line)。读取的电路结构主要包括与待读取量子比特耦合的谐振腔、及与谐振腔耦合的读取信号线。每个量子比特通过独立的谐振腔与读取信号线的连接。基于各自的谐振腔、及与谐振腔耦合的读取信号线实现将量子比特的状态信息从量子比特到传输线的传递。
然而,申请人发现,这种读取机制有很大的限制性,包括但不限于以下两个方面。第一,读取的对象特定。仅能够通过谐振腔对直接耦合的量子比特进行读取,对于量子比特之间的耦合器等结构无法实现读取。第二,由于每个量子比特通过独立的谐振腔与读取信号线进行连接,因此,在由于工艺波动造成某一量子比特的读取电路发生故障时,无法实现读取。
为此,本申请提供一种读取电路、读取方法及量子计算机,以解决现有技术中的不足,它突破了相关技术中仅能通过与待读取元件直接耦合的谐振腔实现读取的限制。下文将结合附图2至附图3进行详细的描述介绍本申请的实施例。
图2为本申请的实施例提供的一种读取电路的结构示意图。
图3为本申请的一个实施例提供的读取方法的流程图。
需要说明的是,图2示意性的表示了读取信号线1、谐振腔2、量子比特3、频率可调谐的耦合器4的关系。例如,每一个量子比特3均具有独立配置的谐振腔2。谐振腔2与读取信号线耦合。相邻位置的量子比特3之间通过耦合器4建立耦合关系。谐振腔2包括第一谐振腔21、第二谐振腔22…….第N谐振腔23。量子比特3包括第一比特31、第二比特32…….第N比特33。耦合器4包括第一耦合器41、第二耦合器42…….第N耦合器43。图2中省略了部分元器件,例如,第二谐振腔22和第N谐振腔23之间的谐振腔等。
参照图2所示,并结合图1和图3所示,本申请的一个实施例提供了一 种读取电路,包括:与待读取元件耦合的传输元件;与所述传输元件耦合的谐振腔2;以及与所述谐振腔2耦合的读取信号线1。谐振腔2具有被配置为耦接到所述传输元件的第一端和被配置为耦接到所述读取信号线1的第二端。耦接的形式可以是电容性耦接或电感性耦接。在该读取电路中,待读取元件、传输元件、谐振腔2依次耦合,从而将待读取元件和谐振腔2间接的耦合连接,进而基于与谐振腔2耦合的读取信号线1实现对待读取元件的读取,从而突破了相关技术中仅能通过与待读取元件直接耦合的谐振腔2实现读取的限制。
在本申请的实施例中,传输元件为具有耦合连接作用的电元件。通过传输元件在待读取元件和谐振腔之间建立间接的耦合连接。应理解的是,传输元件可以具有被配置为耦接到所述待读取元件的第一端和被配置为耦接到所述谐振腔2的第二端。传输元件可以是与待读取元件耦合连接的量子比特3,待读取元件与量子比特3的耦合可以是两者相邻近直接形成耦合连接,也可以是通过其他电结构元件形成耦合连接。
在集成扩展的量子芯片中,可基于本申请实施例的方案,利用与量子比特3耦合的谐振腔2以及两个量子比特3之间的耦合器4实现对两个量子比特3的读取。也可基于本申请的方案,利用与一个量子比特3耦合的相邻量子比特3的谐振腔2实现对该一个量子比特3的读取,从而可以解决在与该一个量子比特直接耦合的谐振腔故障时无法对其读取的问题。
在一些实施例中,结合图2,第一比特31和第二比特32通过中第一耦合器41实现耦合。基于本申请的方案,针对第一比特31的读取电路可以包括:依次耦合的第一耦合器41、第二比特32、第二谐振腔22及读取信号线1。第一比特31与第一耦合器41耦合,第一耦合器41与第二比特32耦合,第二比特32与第二谐振腔22耦合,第二谐振腔22与读取信号线1耦合。具体的,利用读取信号线1使用色散读出(dispersive readout)技术原理来测量特定待读取元件(第一比特31)的状态信息。色散读出基于第一比特31与第二谐振腔22的色散相互作用,该色散位移引起第二谐振腔22的频率根据该第一比特31的状态而改变。第一比特31可以借助第一耦合器41、第二比特32实现与第二谐振腔22的间接耦合时,第二谐振腔22的频率根据该第一比特31的状态而改变。用微波脉冲探测第二谐振腔22,所反射的信号的相位和幅值被用 于区分该第一比特31的状态信息。
在另一些实施例中,所述读取电路可以具有多个依次耦合连接的所述传输元件。多个所述传输元件依次耦合连接形成传输链路。传输链路的一端与待读取元件耦合,另一端与谐振腔耦合,从而确保待读取元件通过该传输链路与谐振腔建立间接的耦合连接。基于这种耦合连接实现了对待读取元件的频谱读取。示例性的,第一比特31可以借助第一耦合器41、第二比特32、第二耦合器42……第N比特33依次耦合连接形成的传输链路,与第N谐振腔23形成间接耦合,第N谐振腔23的频率根据该第一比特31的状态而改变。用微波脉冲探测第N谐振腔23,所反射的信号的相位和幅值被用于区分该第一比特31的状态信息。
在本申请的一个实施例中,所述传输元件包括量子比特3。示例性的,在针对第一耦合器41读取时,可以借助第一比特31实现第一谐振腔21和第一耦合器41的间接耦合,或者可以借助第二比特32实现第二谐振腔22和第一耦合器41的间接耦合,从而可以用微波脉冲探测第一谐振腔21或者第二谐振腔22实现对第一耦合器41的读取。在另一个实施例中,所述传输元件也可以包括频率可调谐的耦合器4。例如,通过由量子比特3和耦合器形成的传输链路,实现第一耦合器41和第N谐振腔23的间接耦合,从而可以用微波脉冲探测第N谐振腔23实现对第一耦合器41的读取。
还有一些实施例中,所述传输元件包括量子比特3、及频率可调谐的耦合器4。示例性的,可以由多个量子比特3和多个耦合器4耦合连接形成该传输链路。在所述传输链路中所述量子比特3和所述耦合器4相间布置。频率可调谐的耦合器4能够控制相邻比特(第一比特31与第二比特32)之间的耦合,以便在读出期间或者在对量子比特3施加控制脉冲期间减少或者消除比特之间的微波串扰和/或频率冲突。调谐第一耦合器41的频率使得能够调节第一比特31与第二比特32之间的耦合强度,以允许第一比特31与第二比特32之间的耦合实现从弱耦合到强耦合的调节。
耦合器4的频率可以被调谐为与量子比特3的跃迁频率(量子比特谐振频率)相同或接近,或者可以被调谐为在距离量子比特3的频率范围的远端。当耦合器4的频率被调谐为与量子比特3的频率相同或接近时,耦合器4与量子 比特3谐振。当耦合器4的频率被调谐为与量子比特3的频率显著不同时,耦合器4与量子比特3不谐振。
在一些实施例中,所述待读取元件包括以下类型之一:量子比特3、频率可调谐的耦合器4。示例性的,所述耦合器4包括由具有至少两个约瑟夫森结并联形成的超导量子干涉器squid。可以理解的是,所述耦合器4配置有实现频率调谐的信号线。基于该信号线上施加的磁通信号可以调控所述耦合器4的频率。示例性的,所述量子比特3包括由具有至少两个约瑟夫森结并联形成的超导量子干涉器squid。可以理解的是,量子比特3配置有xy信号线和z信号线。
在一些实施例中,所述谐振腔2由共面波导传输线形成。示例性的,所述谐振腔2为半波长谐振腔或四分之一波长谐振腔。
本申请还提供一种针对如上所述读取电路的频谱读取方法。
参照图3所示,并可结合图1和图2所示,所述读取方法包括步骤S601至步骤S602。
步骤S601、在所述读取信号线1上施加测量微波信号,并获取所述谐振腔2响应的频谱。示例性的,获取的可以是频谱S21的曲线图。用微波脉冲探测谐振腔2。该微波脉冲通常处于接近对应于基态和激发态的谐振频率的中点的频率。所反射的信号的相位和幅值被用于区分该待读取元件的状态信息。步骤S602、调整所述待读取元件的第一频率以及所述传输元件的第二频率,确定色散频移值为最大时的所述频谱为目标频谱,该目标频谱即作为读取结果。
本申请实施例提供的针对如上所述读取电路的读取方法,它通过在所述读取信号线1上施加测量微波信号,并获取所述谐振腔2响应的频谱,然后调整所述待读取元件的第一频率以及所述传输元件的第二频率,将色散频移值为最大时的所述频谱确定为目标频谱,以实现对待读取元件的读取。本申请实施例的读取方法尤其适用于如下情形:在与量子比特3直接耦合的谐振腔2发生故障时,通过与该量子比特2耦合的相邻量子比特2所对应的谐振腔3实现读取。需要说明的是,该量子比特2与相邻量子比特2的耦合机制可以通过频率可调谐的耦合器4实现,也可以由频率可调谐的耦合器4、量子比特3依次耦合连接形成传输链路实现,其中,在该传输链路中所述量子比特3和所述耦合 器4相间布置。
在一些实施例中,在配置的信号线上施加磁通信号实现对所述第二频率的调整。示例性的,在所述传输元件包括以下类型之一:量子比特3、频率可调谐的耦合器4。示例性的,所述耦合器4包括由具有至少两个约瑟夫森结并联形成的超导量子干涉器squid。所述耦合器4配置有实现频率调谐的信号线,基于该信号线上施加的磁通信号可以调控所述耦合器4的频率。示例性的,所述量子比特3包括由具有至少两个约瑟夫森结并联形成的超导量子干涉器squid。量子比特3配置有实现频率调控的z信号线。
为提高读取的效率,快速得到目标频谱,可以将读取电路中近邻的量子比特3和谐振腔2的耦合强度调至最大。在一些实施例中,所述传输元件为量子比特3时,调整所述传输元件的第二频率的步骤可以包括:将所述第二频率调整至所述量子比特3的简并点。在另一些实施例中,所述传输元件为依次耦合连接的频率可调谐的耦合器4及量子比特3时,调整所述传输元件的第二频率的步骤,包括:将所述量子比特3的频率固定在简并点,并调整所述耦合器4的频率。在针对第一耦合器41读取时,读取电路包括依次耦合的第一比特31、第一谐振腔21和读取信号线1,可以将第一比特31的频率固定在简并点,从而将第一比特31与第一谐振腔21的耦合强度最大化,便于得到第一耦合器41的调制谱。在针对第一比特31的读取时,读取电路可以包括:依次耦合的第一耦合器41、第二比特32、第二谐振腔22及读取信号线1,可以将所述第二比特32的频率固定在简并点,并调整所述第一耦合器41的频率。
本申请实施例还提供了一种量子计算机,包括如上所述的读取电路。
这里需要指出的是:量子计算机具有上述结构的读取电路,且具有同上述读取电路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读取电路的描述而理解,为节约篇幅,这里不再赘述。
本申请实施例使用与集成电路制造所采用的相同或相似的处理技术(例如光刻、诸如溅射或化学气相沉积的材料沉积、以及诸如蚀刻或剥离的材料去除)来制造量子比特、谐振腔、传输元件和读取信号线。量子比特、谐振腔、传输元件和读取信号线中的每一个可以在相同的芯片(诸如相同的硅或蓝宝石 衬底或晶片)上形成/集成,并且在低于形成它们的超导材料的临界温度的温度下工作。超导材料的示例包括但不限于铝(例如1.2开尔文的超导临界温度)、铌(例如9.3开尔文的超导临界温度)和氮化钛(例如5.6开尔文的超导临界温度)。
在使用超导量子电路元件和/或超导经典电路元件(诸如,本文所述的电路元件)的量子计算系统的工作期间,超导电路元件在低温恒温器内被冷却到允许超导体材料表现超导特性的温度。
以上依据图式所示的实施例详细说明了本申请的构造、特征及作用效果,以上所述仅为本申请的较佳实施例,但本申请不以图面所示限定实施范围,凡是依照本申请的构想所作的改变,或修改为等同变化的等效实施例,仍未超出说明书与图示所涵盖的精神时,均应在本申请的保护范围内。

Claims (13)

  1. 一种读取电路,其特征在于,包括:
    与待读取元件耦合的传输元件,所述传输元件包括以下类型至少之一:量子比特、频率可调谐的耦合器;
    与所述传输元件耦合的谐振腔;以及
    与所述谐振腔耦合的读取信号线。
  2. 根据权利要求1所述的读取电路,其特征在于,所述读取电路具有多个依次耦合连接的所述传输元件。
  3. 根据权利要求1所述的读取电路,其特征在于,所述传输元件包括依次耦合连接的量子比特和频率可调谐的耦合器,且所述量子比特和所述耦合器相间布置。
  4. 根据权利要求1所述的读取电路,其特征在于,所述待读取元件包括以下类型之一:
    量子比特、频率可调谐的耦合器。
  5. 根据权利要求1或4所述的读取电路,其特征在于,所述耦合器包括由具有至少两个约瑟夫森结并联形成的超导量子干涉器。
  6. 根据权利要求1或4所述的读取电路,其特征在于,所述量子比特包括由具有至少两个约瑟夫森结并联形成的超导量子干涉器。
  7. 根据权利要求1-4任一项所述的读取电路,其特征在于,所述谐振腔由共面波导传输线形成。
  8. 根据权利要求6所述的读取电路,其特征在于,所述谐振腔为半波长谐振腔或四分之一波长谐振腔。
  9. 一种权利要求1-8中任一项读取电路的读取方法,其特征在于,包括:
    在所述读取信号线上施加测量微波信号,并获取所述谐振腔响应的频谱;
    调整所述待读取元件的第一频率以及所述传输元件的第二频率,确定色散频移值为最大的所述频谱为目标频谱。
  10. 根据权利要求9所述的读取方法,其特征在于,在配置的信号线上施加磁通信号实现对所述第二频率的调整。
  11. 根据权利要求9所述的读取方法,其特征在于,所述传输元件为量子比特时,调整所述传输元件的第二频率的步骤,包括:
    将所述第二频率调整至所述量子比特的简并点。
  12. 根据权利要求9所述的读取方法,其特征在于,所述传输元件为依次耦合连接的频率可调谐的耦合器及量子比特时,调整所述传输元件的第二频率的步骤,包括:
    将所述量子比特的频率固定在简并点,并调整所述耦合器的频率。
  13. 一种量子计算机,其特征在于,包括权利要求1-8中任一项所述的读取电路。
PCT/CN2023/086067 2022-05-27 2023-04-04 一种读取电路、读取方法及量子计算机 WO2023226598A1 (zh)

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CN115438794B (zh) * 2022-09-30 2023-09-05 本源量子计算科技(合肥)股份有限公司 一种量子计算电路及一种量子计算机
CN115511095B (zh) * 2022-10-11 2023-04-18 北京百度网讯科技有限公司 含耦合器超导量子比特结构的设计信息输出方法及装置
CN115632712B (zh) * 2022-11-30 2023-03-21 苏州浪潮智能科技有限公司 信号分离器以及量子比特状态的测量系统、方法和装置

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