WO2021190349A1 - 基于超导量子比特和里德堡原子的纠缠态制备方法及装置 - Google Patents
基于超导量子比特和里德堡原子的纠缠态制备方法及装置 Download PDFInfo
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- the present invention relates to the field of quantum information technology, in particular to a method and device for preparing entangled states of superconducting qubits and Rydberg atoms through a thermally coupled cavity, which can be applied to a wide range of quantum information fields (including quantum storage, quantum communication and Quantum computing and other technical directions).
- Quantum interfaces or entanglements between different quantum systems are essential for realizing distributed quantum computing.
- Different experimental systems have their own advantages and disadvantages.
- superconducting qubits have fast operation speed and strong scalability, but they work in the microwave band and lack optical band transitions. They need the assistance of other quantum systems to interconnect with optical quantum networks.
- the cold atom system with both microwave band transition and optical band transition is one of the preferred systems. Therefore, the realization of quantum information exchange between superconducting quantum circuits and cold atom ensemble is very important for the realization of distributed superconducting quantum computers.
- a system that combines different experimental systems is called a composite system.
- the key to the research of a composite system is to realize the quantum interface or entanglement between different experimental systems.
- the Rydberg atom excites an electron of the atom to an orbit with a higher main quantum number, so it has a large electric dipole moment and is easy to interact with the outside world. Therefore, the research of superconducting qubit and cold atom composite system generally involves exciting cold atoms to the Rydberg state, and coupling the superconducting qubits and Rydberg atoms through a coupling cavity to realize the quantum interface between them. Or entanglement.
- the quantum interface or entanglement between superconducting qubits and cold atoms will realize composite atom-photon quantum gates, which will help the realization of atomic quantum storage and quantum converters.
- the superconducting qubit chip needs to be installed on the ⁇ 50mK platform of the dilution refrigerator, and is easily decohered by environmental influences. In order to reduce the adverse effects of background black body radiation and stray infrared light, it is usually shielded by multi-layer opaque shielding layer protect. In addition, multilayer magnetic shielding is required to protect from electromagnetic noise.
- Existing superconducting qubits and cold atom composite systems all install superconducting chips and trap cold atoms on the same refrigeration platform of the refrigerator.
- Transferring and trapping cold atoms near the superconducting qubit will inevitably destroy the radiation shielding and magnetic shielding, reducing the coherence of the superconducting qubit, not to mention the high-power laser required to excite cold atoms to the Rydberg state field.
- Installing superconducting chips and trapping Rydberg atoms on the same refrigeration platform will reduce the coherence of superconducting qubits, which is not conducive to quantum state transmission or entanglement.
- the non-local quantum interface or entanglement on different platforms has the disadvantages of low fidelity and slower speed compared with the local quantum state transmission. Therefore, it is necessary to propose a technical method that can realize superconducting qubits and The non-local quantum interface or entanglement between cold atoms does not affect the coherence of superconducting qubits; on the other hand, the fidelity and speed must reach the performance of the local system, which is higher than the realization of quantum networks or distributed quantum The calculated threshold.
- the present invention proposes a method and device for preparing entangled states based on superconducting qubits and Rydberg atoms.
- the experimental device has a simple structure and is under the existing experimental conditions. Feasibility is strong. And the speed of completing the preparation of the entangled state is fast and the fidelity is high.
- the present invention solves the above-mentioned problems through the following technical means:
- the present invention provides a method for preparing entangled states based on superconducting qubits and Rydberg atoms, which includes the following steps:
- the superconducting qubit is resonantly coupled with the selected mode of the superconducting transmission line cavity, and the two Rydberg states of the Rydberg atom are resonantly coupled with the superconducting planar waveguide cavity/superconducting planar LC resonant cavity to resonantly couple the superconducting plane Waveguide cavity/superconducting planar LC resonant cavity and superconducting transmission line cavity selected mode resonant coupling;
- ⁇ ri ⁇ r is the cavity mode frequency of the i-th cavity
- ⁇ qi ⁇ q is the frequency of the i-th qubit
- Respectively are the generation annihilation operators of the cavity modes of the superconducting transmission line cavity; with They are the annihilation operators of the cavity modes of the superconducting planar waveguide cavity or the superconducting planar LC resonator
- g 1 and g 2 are the coupling strength of the superconducting qubit and the superconducting transmission line cavity, and the Rydberg atoms and superconducting, respectively Coupling strength of planar waveguide cavity/superconducting planar LC cavity; Is the Pauli operator of the i-th qubit.
- the bare cavity cavity mode operator is described by the symmetry and antisymmetric superposition, namely with The two eigenmodes are simultaneously coupled with the superconducting qubit and the Rydberg qubit.
- each eigenmode is initially in equilibrium with the photon number distribution as Mixed state, Is the average number of photons per eigenmode at temperature T, and f i is the frequency of the i-th cavity; in order to reduce the adverse effects of thermal photons during the preparation of the entangled state, a strong qubit is introduced before the unconventional geometric quantum gate operation
- the driving field eliminates the adverse effects of thermal modes on the preparation of entangled states through the method of unconventional geometric quantum gates.
- the present invention also provides an entangled state preparation device based on superconducting qubits and Rydberg atoms, including a refrigeration platform ⁇ 50mK for a dilution refrigerator, a 1K refrigeration platform for a dilution refrigerator, a superconducting qubit, Tunable coupler, superconducting transmission line cavity, superconducting planar waveguide cavity/superconducting planar LC resonant cavity and Rydberg atoms;
- the superconducting qubit is installed on the refrigeration platform of the dilution refrigerator ⁇ 50mK; the coupling strength of the superconducting qubit and the superconducting transmission line cavity can be modulated by an adjustable coupler; one end of the superconducting transmission line cavity is fixed to the dilution refrigerator ⁇ 1 is coupled with superconducting qubit on the 50mK refrigeration platform, and the other end is fixed on the 1K refrigeration platform of the dilution refrigerator to couple with the superconducting planar waveguide cavity/superconducting planar LC cavity; superconducting planar waveguide cavity/superconducting planar LC The resonant cavity is installed on the 1K refrigeration platform of the dilution refrigerator to couple with Rydberg atoms;
- the refrigeration platform of the dilution refrigerator ⁇ 50mK is used to cool the superconducting qubit to maintain its superconducting state, and the 1K refrigeration platform is used to transfer, trap, prepare and manipulate Rydberg atoms.
- the superconducting qubit is a transmon superconducting qubit with a long coherence time.
- the Rydberg atom selects 87 Rb atoms with The two energy levels are used as qubits.
- the present invention does not need to trap and prepare Rydberg atoms on a refrigeration platform ⁇ 50mK, but on a 1K refrigeration platform, so it does not affect the coherence of superconducting qubits installed on a refrigeration platform ⁇ 50mK.
- the present invention adds two strong microwave driving fields to realize an unconventional geometric phase gate. This process is not sensitive to the thermal state and can further improve the fidelity of the preparation of the entangled state.
- the present invention realizes the preparation of the maximum entangled state, and has fast speed, high fidelity, and robustness to local random noise.
- the numerical simulation of the master equation of the present invention shows the preparation of entangled states between qubits, The fidelity and time can reach 0.99 and 50ns, which will promote the development of distributed superconducting quantum computing.
- the present invention uses a thermally coupled cavity. Although higher ambient temperature leads to a slightly higher population of thermal photons in the cavity, an increase in temperature will reduce the dielectric loss of the two-level system, thereby improving the quality factor of the superconducting resonator , And reduce the heating rate. In addition, the higher ambient temperature also provides greater cooling power and greater thermal conductivity than the millikelvin environment.
- Figure 1 is a schematic diagram of the structure of an entangled state preparation device based on superconducting qubits and Rydberg atoms in the present invention
- Figure 2 is a flow chart of the method for preparing entangled states based on superconducting qubits and Rydberg atoms in the present invention.
- Fig. 1 is a schematic structural diagram of an entangled state preparation device based on superconducting qubits and Rydberg atoms in the present invention.
- the entangled state preparation device based on superconducting qubits and Rydberg atoms includes a refrigeration platform of ⁇ 50mK of a dilution refrigerator, a 1K refrigeration platform of a dilution refrigerator, 2, a superconducting qubit, 3, Tuning coupler 4, superconducting transmission line cavity 5, superconducting planar waveguide cavity or superconducting planar LC resonant cavity 6, Rydberg atom 7.
- the superconducting qubit 3 is installed on the refrigeration platform 1 of the dilution refrigerator ⁇ 50mK; the coupling strength of the superconducting qubit 3 and the superconducting transmission line cavity 5 can be modulated by the adjustable coupler 4; the superconducting transmission line cavity 5 is fixed at one end Coupled with the superconducting qubit 3 on the refrigeration platform 1 of the dilution refrigerator ⁇ 50mK, and the other end is fixed on the 1K refrigeration platform 2 of the dilution refrigerator to couple with the superconducting planar waveguide cavity or the superconducting planar LC resonant cavity 6; The guide plane waveguide cavity or superconducting plane LC resonant cavity 6 is installed on the 1K refrigeration platform 2 of the dilution refrigerator to couple with the Rydberg atom 7.
- the basic working principle of the entangled state preparation device of the present invention based on superconducting qubits and Rydberg atoms is: the superconducting qubit 3 and the superconducting qubit 3 are realized by the superconducting transmission line cavity 5 and the superconducting planar waveguide cavity or the superconducting planar LC resonant cavity 6
- Preparation of non-local entangled states between Rydberg atoms 7, and the coupling strength J between superconducting coaxial cable 5 and superconducting planar waveguide cavity or superconducting planar LC resonator 6 is determined by processing before the experiment, and is determined by the tunable coupler 4 Adjust the coupling strength of the superconducting qubit 3 and the superconducting transmission line cavity 5, and adjust the coupling strength of the superconducting planar waveguide cavity or the superconducting planar LC resonator 6 and the Rydberg atom 7, when the specific relationship is satisfied By choosing a specific time to make the time evolution operator of Ry
- the refrigeration platform 1 of the dilution refrigerator ⁇ 50 mK is used to cool the superconducting qubit 3 to maintain its superconducting state, and the 1K refrigeration platform 2 is used to transfer, trap, prepare and manipulate Rydberg atoms 7.
- the superconducting qubit 3 is a transmon superconducting qubit with a long coherence time.
- the Rydberg atom 7 selects 87 Rb atoms with The two energy levels are used as qubits.
- g 1 is the coupling strength between the superconducting qubit and the superconducting transmission line cavity, which can be adjusted by a tunable coupler
- g 2 is the Rydberg qubit and the superconducting planar waveguide cavity or the superconducting planar LC resonance
- the coupling strength between the cavities can be adjusted by changing the angle ⁇ between the quantization axis of the atom and the electric field of the coupling cavity
- J represents the coupling strength between the two coupling cavities, which is determined by processing before the experiment.
- ⁇ ri ⁇ r is the cavity mode frequency of the i-th cavity
- ⁇ qi ⁇ q is the frequency of the i-th qubit
- Respectively are the generation annihilation operators of the cavity modes of the superconducting transmission line cavity; with They are the annihilation operators of the cavity modes of the superconducting planar waveguide cavity or the superconducting planar LC cavity
- g 1 and g 2 are the coupling strength of the superconducting qubit and the superconducting transmission line cavity, and the Rydberg atoms and superconducting, respectively Coupling strength of planar waveguide cavity/superconducting planar LC cavity
- the production annihilation operator of two decorated states can be described by the symmetry and antisymmetric superposition of two bare cavity mode operators, namely with The two eigenmodes are simultaneously coupled with the superconducting qubit and the Rydberg qubit.
- each eigenmode is initially in a balanced photon number distribution as Mixed state, Is the average number of photons per eigenmode at temperature T.
- the method of introducing a strong driving field into the two qubits to realize the unconventional geometric quantum gate before the operation of the SWAP gate eliminates the adverse effects of the thermal state during the preparation of the entangled state.
- the entangled state preparation device based on superconducting qubits and Rydberg atoms of the present invention realizes superconducting qubits placed on a refrigeration platform ⁇ 50mK and qubits of Rydberg atoms trapped near the 1K refrigeration platform through a thermal coupling cavity
- the long-range entanglement between entanglements can realize unconventional geometric quantum operations with the help of the driving field, which effectively eliminates the coupling between the qubit and the cavity mode, and can avoid the adverse effects of the cavity field thermal state on the entanglement process.
- the method of quantum state transmission includes the following steps: placing the superconducting qubit on a refrigeration platform ⁇ 50mK, and resonantly coupling with the standing wave mode selected by the superconducting NbTi coaxial cable; one end of the coaxial cable cavity is fixed at ⁇ 50mK on the refrigeration platform, the other end is fixed on the 1K refrigeration platform; the LC resonator is fixed on the 1K refrigeration platform, and resonantly coupled with the standing wave mode selected by the superconducting NbTi coaxial cable; adjust the superconducting qubit and superconducting transmission line coupling strength lumen g 1, and the Rydberg atoms and superconducting planar waveguide cavity (Rydberg atoms or LC resonator and a superconducting plane) coupling strength g 2, so that they transfer the superconducting wire lumen and super The coupling strength J between the guided planar waveguide cavity (or the superconducting transmission line cavity and the superconducting planar LC re
- the entangled state preparation device based on superconducting qubits and Rydberg atoms of the present invention utilizes an unconventional geometric quantum state transmission scheme, so the entangled state preparation speed is fast and the fidelity is high. As long as the coupling strength of the superconducting qubit, the Rydberg atom and the two coupling cavities meets a specific ratio, the specific time is selected so that the time evolution operator of the Rydberg atom and the superconducting bit state transfer is not affected by the thermal state. Sensitive, complete the entangled state preparation.
- the entangled state between the superconducting qubit and the Rydberg atom is prepared by the superconducting transmission line cavities fixed at the two ends on different refrigeration platforms. Before starting the quantum state transmission, a strong driving field is added to the two qubits to make the process correct The thermal state is not sensitive, which can further improve the fidelity of the entangled state preparation and greatly prevent the superconducting qubit from being disturbed. Based on this scheme, the fidelity and operating speed of the preparation of non-local entangled states of superconducting qubits and Rydberg atoms can reach the performance of existing local systems, providing a new technological basis for quantum networks and distributed quantum computing research .
- Figure 2 is a flow chart of the method for preparing entangled states based on superconducting qubits and Rydberg atoms in the present invention.
- the main idea of the present invention based on the preparation method of the entangled state of superconducting qubits and Rydberg atoms is to make the time evolution operator insensitive to thermal states by adjusting the coupling strength and selecting Rydberg atoms and superconducting bits at a specific time.
- the conditions complete the preparation of the entangled state.
- a strong driving field is added to realize unconventional geometric quantum gates, and the preparation of non-local entangled states between superconducting qubits and Rydberg atoms through two coupled cavities:
- Step 301 resonantly couple the superconducting qubit with the selected mode of the superconducting transmission line cavity, and at the same time resonantly couple the two Rydberg states of the Rydberg atom with the superconducting planar waveguide cavity, or resonantly couple the two Rydberg atoms of the Rydberg atom with the superconducting planar waveguide cavity.
- a Rydberg state is resonantly coupled with the superconducting planar LC resonator, and the superconducting planar waveguide cavity or the superconducting planar LC resonant cavity is resonantly coupled with the selected mode of the superconducting transmission line cavity;
- Step 302 adjusting the strength of the superconducting qubits coupled transmission lines and a superconducting cavity g 1, and the Rydberg atoms and superconducting planar waveguide cavity (Rydberg atoms or LC resonator and a superconducting plane) coupling strength g 2, Make the coupling strength J between them and the superconducting transmission line cavity and the superconducting planar waveguide cavity (or the superconducting transmission line cavity and the superconducting planar LC resonant cavity) satisfy Relationship;
- Step 303 Realize an unconventional geometric quantum gate with the help of two strong microwave driving fields
- step 304 a specific time is selected to make the time evolution operator of the Rydberg atom and the superconducting bit state insensitive to the thermal state to complete the preparation of the maximum entangled state.
- the invention can realize unconventional geometric quantum gates by means of the driving field added to the qubits, thereby realizing the generation of entangled states between the qubits.
- the phase factor of the evolution operator does not depend on the cavity state, the process is not sensitive to the thermal state.
- g 1 is the coupling strength between the superconducting qubit and the superconducting transmission line cavity, which can be adjusted by a tunable coupler
- g 2 is the Rydberg qubit and the superconducting planar waveguide cavity or the superconducting planar LC resonance
- the coupling strength between the cavities can be adjusted by changing the angle ⁇ between the quantization axis of the atom and the electric field of the coupling cavity
- J represents the coupling strength between the two coupling cavities, which is determined by processing before the experiment.
- ⁇ ri ⁇ r is the cavity mode frequency of the i-th cavity
- ⁇ qi ⁇ q is the frequency of the i-th qubit.
- They are the generation annihilation operators of the cavity modes of the superconducting transmission line cavity.
- g 1 and g 2 are the coupling strength of the superconducting qubit and the superconducting transmission line cavity, and the Rydberg atoms and superconducting, respectively Coupling strength of planar waveguide cavity/superconducting planar LC cavity; Is the Pauli operator of the i-th qubit.
- the bare cavity cavity mode operator is described by the symmetry and antisymmetric superposition, namely with The two eigenmodes are simultaneously coupled with the superconducting qubit and the Rydberg qubit.
- each eigenmode is initially in a balanced photon number distribution as Mixed state, Is the average number of photons per eigenmode at temperature T.
- the method of introducing a strong driving field into the two qubits to realize the unconventional geometric quantum gate before the operation of the SWAP gate eliminates the adverse effects of the thermal state during the preparation of the entangled state.
- the method for preparing the entangled state of superconducting qubits and Rydberg atoms is to adjust the coupling strength between the superconducting qubits, Rydberg atoms and two coupling cavities to meet a specific relationship and simultaneously add a strong driving field , Select a specific time to make the time evolution operator of Rydberg atoms and superconducting bits insensitive to the thermal state, and complete the preparation of the maximum entangled state; use the superconducting transmission line cavity fixed on the cooling platform ⁇ 50mK and 1K respectively.
- the coupling of superconducting planar waveguide cavity or superconducting planar LC resonant cavity realizes the preparation of non-local entangled states of superconducting qubits and Rydberg atoms, so the laser field and magnetic field required by Rydberg atoms can be reduced to superconducting qubits
- the influence of coherence; the driving field is introduced into the two-qubit system, and the unconventional geometric quantum gate is used to eliminate the bad influence
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Abstract
一种基于超导量子比特和里德堡原子的纠缠态制备方法及装置，将超导量子比特与超导传输线腔的选定模式共振耦合，同时将里德堡原子的两个里德堡态与超导平面波导腔/超导平面LC谐振腔共振耦合，将超导平面波导腔/超导平面LC谐振腔与超导传输线腔的选定模式共振耦合；调节超导量子比特和超导传输线腔的耦合强度g 1，以及里德堡原子和超导平面波导腔/超导平面LC谐振腔的耦合强度g 2，使它们与超导传输线腔和超导平面波导腔/超导平面LC谐振腔之间的耦合强度J满足（式I）的关系；借助两个强微波驱动场，实现非常规几何量子门，完成最大纠缠态的制备。可降低里德堡原子所需激光场和磁场以及辐射冷却超导同轴电缆对超导量子比特相干性的影响。
Description
本发明涉及量子信息技术领域，具体涉及一种通过热耦合腔实现超导量子比特和里德堡原子的纠缠态制备方法及装置，可以应用于广泛的量子信息领域(包括量子存储、量子通信以及量子计算等技术方向)。
不同量子体系(超导量子比特、囚禁离子、量子点、金刚石色心、冷原子、掺杂离子晶体、光子、声子等)之间的量子接口或纠缠对实现分布式量子计算至关重要。不同的实验体系有各自的优点和缺点，如超导量子比特的操作速度快、可扩展性强，但工作在微波波段，自身缺乏光学波段跃迁，需要其它量子体系辅助才能与光量子网络互联。同时具有微波波段跃迁和光学波段跃迁的冷原子体系是其中一种优选体系。因此，实现超导量子电路与冷原子系综的量子信息交换对实现分布式超导量子计算机的研究至关重要。结合不同实验体系的系统称为复合系统，复合系统的研究关键在于实现不同实验体系之间的量子接口或纠缠。里德堡原子是将原子的一个电子被激发到主量子数较高的轨道，因此具有大的电偶极矩，容易与外界相互作用。因此超导量子比特和冷原子复合系统的研究，一般是将冷原子激发到里德堡态，通过一个耦合腔去分别耦合超导量子比特和里德堡原子，从而实现它们之间的量子接口或纠缠。超导量子比特和冷原子间的量子接口或纠缠将实现复合原子-光子量子门，有助于原子的量子存储和量子转换器的实现。
超导量子比特芯片需要安装在稀释制冷机的≤50mK平台上，且容易受环境 影响退相干，为了减少背景黑体辐射和杂散红外光的不利影响，通常用多层不透光的屏蔽层屏蔽保护。此外，还需要多层磁屏蔽保护免受电磁噪声的影响。现有的超导量子比特和冷原子复合系统都是在制冷机的同一个制冷平台上安装超导芯片和囚禁冷原子。在超导量子比特附近转移和囚禁冷原子将不可避免地破坏辐射屏蔽和磁屏蔽，降低超导量子比特的相干性，更不用说将冷原子激发到里德堡态需要用到的高功率激光场。在同一个制冷平台安装超导芯片和囚禁里德堡原子，会降低超导量子比特的相干性，不利于量子态传输或纠缠。将超导芯片和里德堡原子放置在不同的制冷平台是解决超导量子比特的相干性受激光影响的途径之一，但是暂时缺乏非局域的超导量子比特和里德堡原子高保真度的量子接口或纠缠方案。
在不同平台的非局域量子接口或纠缠相对于局域的量子态传输存在着保真度低、速度较慢的缺点，因此有必要提出一种技术手段，一方面可以实现超导量子比特和冷原子之间非局域的量子接口或纠缠，从而不影响超导量子比特的相干性；另一方面保真度和速度要达到局域系统的性能，即高于实现量子网络或分布式量子计算的阈值。
发明内容
有鉴于此，为了解决现有技术中的上述问题，本发明提出一种基于超导量子比特和里德堡原子的纠缠态制备方法及装置，实验的装置结构简单，在现有的实验条件下可行性强。且完成纠缠态制备的速度快，保真度高。
本发明通过以下技术手段解决上述问题：
一方面，本发明提供一种基于超导量子比特和里德堡原子的纠缠态制备方法，包括如下步骤：
将超导量子比特与超导传输线腔的选定模式共振耦合，同时将里德堡原子的两个里德堡态与超导平面波导腔/超导平面LC谐振腔共振耦合，将超导平面波导腔/超导平面LC谐振腔与超导传输线腔的选定模式共振耦合；
调节超导量子比特和超导传输线腔的耦合强度g
1，以及里德堡原子和超导平面波导腔/超导平面LC谐振腔的耦合强度g
2，使它们与超导传输线腔和超导平面波导腔/超导平面LC谐振腔之间的耦合强度J满足
的关系；
借助两个强微波驱动场，实现非常规几何量子门，使量子比特之间产生有效的耦合；
选择特定的时间使得里德堡原子和超导比特态传输的时间演化算子对热态不敏感，完成最大纠缠态的制备。
进一步地，复合系统的哈密顿量在旋转波近似下表示为：
其中ω
ri＝ω
r是第i个腔的腔模频率，ω
qi＝ω
q是第i个量子比特的频率；
i＝1时对应超导量子比特的上升算符，i＝2时对应里德堡原子的上升算符；
和
分别为超导传输线腔的腔模的产生湮灭算符；
和
分别为超导平面波导腔或者超导平面LC谐振腔的腔模的产生湮灭算符；g
1和g
2分别为超导量子比特和超导传输线腔的耦合强度以及里德堡原子和超导平面波导腔/超导平面LC谐振腔的耦合强度；
为第i个量子比特的泡利算符。
进一步地，超导传输线腔和超导平面波导腔/超导平面LC谐振腔共振耦合，描述耦合腔系统的缀饰态是非简并的，分别是带有频率f
1＝f+J和f
2＝f-J的两个本征模式，其中f为超导传输线腔和超导平面波导腔的频率，J为两个耦合腔之间的耦合强度；两个缀饰态的产生湮灭算符用两个裸腔腔模算符的对称和反对称叠加来描述，即
和
两个本征模同时与超导量子比特和里德堡量子比特耦合。
进一步地，根据算符
和
重写复合系统的哈密顿量为H
r＝H
1+H
2，其中：
在强驱动极限Ω＞＞{g
i，J}中，得到
其中
由于H
1和H
2对易，演化算符可以分解为：
在t
n＝2nπ/J时演化算子对热态不敏感。
进一步地，每个本征模最初都处于平衡光子数分布为
的混合态，
是温度T时每个本征模的平均光子数，f
i为第i个腔的频率；为了减少纠缠态制备期间热光子的不利影响，在非常规几何量子门操作之前在量子比特中引入强驱动场，通过非常规几何量子门的方法消除热模对纠缠态制备的不良影响。
另一方面，本发明还提供一种基于超导量子比特和里德堡原子的纠缠态制备装置，包括稀释制冷机的≤50mK的制冷平台、稀释制冷机的1K制冷平台、超导量子比特、可调耦合器、超导传输线腔、超导平面波导腔/超导平面LC谐振腔以及里德堡原子；
其中超导量子比特安装在稀释制冷机的≤50mK的制冷平台上；超导量子比特与超导传输线腔的耦合强度可通过可调耦合器调制；超导传输线腔一端固定在稀释制冷机的≤50mK的制冷平台上1与超导量子比特耦合，另一端固定在稀释制冷机的1K制冷平台上与超导平面波导腔/超导平面LC谐振腔耦合；超导平面波导腔/超导平面LC谐振腔安装在稀释制冷机的1K制冷平台上与里德堡原子耦合；
通过超导传输线腔和超导平面波导腔/超导平面LC谐振腔实现超导量子比特和里德堡原子之间的非局域纠缠态制备，超导同轴电缆和超导平面波导腔/超导平面LC谐振腔之间的耦合强度J实验前加工确定，通过可调耦合器调节超导量子比特与超导传输线腔的耦合强度，同时调节超导平面波导腔/超导平面LC谐振腔和里德堡原子的耦合强度，当满足特定的关系
与选择特定的 时间使得里德堡原子和超导比特的时间演化算子对热态不敏感，可实现超导量子比特与里德堡原子之间的纠缠态制备。
进一步地，所述稀释制冷机的≤50mK的制冷平台用于给超导量子比特制冷以维持其超导态，1K制冷平台用于转移、囚禁、制备以及操控里德堡原子。
进一步地，所述超导量子比特为拥有长相干时间的transmon超导量子比特。
进一步地，借助于加在量子比特上的驱动场，实现非常规几何量子门，从而实现量子比特之间纠缠态的产生；在特定的时间点，由于演化算符的相位因子不依赖于腔态，因此该过程对热态不敏感。
进一步地，所述里德堡原子选择
87Rb原子的
和
两个能级作为量子比特。
本发明具有如下有益效果：
1、本发明不需要在≤50mK的制冷平台囚禁和制备里德堡原子，而是在1K制冷平台，因此不影响安装在≤50mK的制冷平台的超导量子比特的相干性。
2、本发明为了消除纠缠态制备期间热光子的不利影响，加入两个强微波驱动场实现非常规几何相位门，该过程对热态不敏感，可进一步提高纠缠态制备的保真度。
3、本发明实现了最大纠缠态的制备，并且速度快、保真度高、对局部随机噪声具有鲁棒性。
4、本发明对主方程的数值模拟表明量子比特之间纠缠态的制备，
的保真度和时间可达到0.99和50ns，这将促进分布式超导量子计算的发展。
5、本发明使用了热耦合腔，虽然较高的环境温度导致腔中的热光子布居略高，但温度升高会降低两能级系统的介质损耗，从而改善超导谐振器的品质因子，并降低加热速率。此外，与毫开尔文环境相比，更高的环境温度还提供了 更大的冷却功率和更大的导热系数。
为了更清楚地说明本发明实施例中的技术方案，下面将对实施例描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1为本发明基于超导量子比特和里德堡原子的纠缠态制备装置的结构示意图；
图2为本发明基于超导量子比特和里德堡原子的纠缠态制备方法的流程图。
以下通过特定的具体实例并结合附图说明本发明的实施方式，本领域技术人员可由本说明书所揭示的内容轻易地了解本发明的其它优点与功效。本发明亦可通过其它不同的具体实例加以施行或应用，本说明书中的各项细节亦可基于不同观点与应用，在不背离本发明的精神下进行各种修饰与变更。
实施例1
图1为本发明基于超导量子比特和里德堡原子的纠缠态制备装置的结构示意图。如图1所示，基于超导量子比特和里德堡原子的纠缠态制备装置，包括稀释制冷机的≤50mK的制冷平台1、稀释制冷机的1K制冷平台2、超导量子比特3、可调耦合器4、超导传输线腔5、超导平面波导腔或超导平面LC谐振腔6、里德堡原子7。
其中超导量子比特3安装在稀释制冷机的≤50mK的制冷平台1上；超导量子比特3与超导传输线腔5的耦合强度可通过可调耦合器4调制；超导传输线腔5一端固定在稀释制冷机的≤50mK的制冷平台1上与超导量子比特3耦合，另一端固定在稀释制冷机的1K制冷平台2上与超导平面波导腔或超导平面LC 谐振腔6耦合；超导平面波导腔或超导平面LC谐振腔6安装在稀释制冷机的1K制冷平台2上与里德堡原子7耦合。
本发明基于超导量子比特和里德堡原子的纠缠态制备装置的基本工作原理是：通过超导传输线腔5和超导平面波导腔或超导平面LC谐振腔6实现超导量子比特3和里德堡原子7之间的非局域纠缠态制备，超导同轴电缆5和超导平面波导腔或超导平面LC谐振腔6间的耦合强度J实验前加工确定，通过可调耦合器4调节超导量子比特3与超导传输线腔5的耦合强度，同时调节超导平面波导腔或超导平面LC谐振腔6和里德堡原子7的耦合强度，当满足特定的关系
与选择特定的时间使得里德堡原子和超导比特的时间演化算子对热态不敏感，可以实现超导量子比特3与里德堡原子7之间的纠缠态制备。
具体地，所述稀释制冷机的≤50mK的制冷平台1用于给超导量子比特3制冷以维持其超导态，1K制冷平台2用于转移、囚禁、制备以及操控里德堡原子7。
具体地，所述超导量子比特3为拥有长相干时间的transmon超导量子比特。
具体地，借助于加在量子比特上的驱动场，可以实现非常规几何量子门，从而实现量子比特之间纠缠态的产生。在特定的时间点，由于演化算符的相位因子不依赖于腔态，因此该过程对热态不敏感。
具体地，所述里德堡原子7选择
87Rb原子的
和
两个能级作为量子比特。
具体地，g
1是超导量子比特和超导传输线腔之间的耦合强度，可以通过可调耦合器来调节；g
2是里德堡量子比特和超导平面波导腔或超导平面LC谐振腔之间的耦合强度，可以通过改变原子的量子化轴与耦合腔的电场之间的角度θ来调节；J表示两个耦合腔之间的耦合强度，是实验前加工确定的。
具体地，复合系统的哈密顿量在旋转波近似下可以表示为(h＝1)：
其中ω
ri＝ω
r是第i个腔的腔模频率，ω
qi＝ω
q是第i个量子比特的频率；
i＝1时对应超导量子比特的上升算符，i＝2时对应里德堡原子的上升算符；
和
分别为超导传输线腔的腔模的产生湮灭算符；
和
分别为超导平面波导腔或者超导平面LC谐振腔的腔模的产生湮灭算符；g
1和g
2分别为超导量子比特和超导传输线腔的耦合强度以及里德堡原子和超导平面波导腔/超导平面LC谐振腔的耦合强度；
为第i个量子比特的泡利算符。
具体地，超导传输线腔和超导平面波导腔，或者和超导平面LC谐振腔共振耦合，描述耦合腔系统的缀饰态是非简并的，分别是带有频率f
1＝f+J和f
2＝f-J的两个本征模式，其中f为超导传输线腔和超导平面波导腔的频率，J为两个耦合腔之间的耦合强度。两个缀饰态的产生湮灭算符可以用两个裸腔腔模算符的对称和反对称叠加来描述，即
和
两个本征模同时与超导量子比特和里德堡量子比特耦合。
具体地，根据算符
和
重写复合系统的哈密顿量为：
具体地,为了纠缠态制备过程中热态的不利影响，我们采用了非常规几何量子门来实现超导量子比特与里德堡量子比特的纠缠。
具体地，对两个量子比特加入强微波驱动场，考虑共振驱动ω
d＝ω
q，在驱动频率的旋转坐标系中，系统的哈密顿量变为：
其中Ω是拉比频率。
具体地，在强驱动极限Ω＞＞{g
i，J}中，我们得到
其中
由此，由
得总演化算符
具体地,通过使用马格努斯公式，得到演化算子
在t
n＝2nπ/J时B＝0，腔模与量子比特的耦合被有效地去除，演化算符的相位因子不依赖于腔态，该过程对热态不敏感。
具体地，由于复合系统的两个耦合腔都固定在1K平台上，因此每个本征模最初都处于平衡光子数分布为
的混合态，
是温度T时每个本征模的平均光子数。为了消除纠缠态制备期间热光子的不利影响，在SWAP门操作之前在两量子比特中引入强驱动场实现非常规几何量子门的方法消除了纠缠态制备过程中热态的不良影响。
本发明的基于超导量子比特和里德堡原子的纠缠态制备装置，通过热耦合腔实现放置在≤50mK制冷平台上的超导量子比特与囚禁在1K制冷平台附近的里德堡原子量子比特之间的远程纠缠，借助驱动场实现非常规几何量子操作，有效消除量子比特与腔模的耦合，可以避免腔场热态对纠缠产生过程的不良影响。所述量子态传输的方法包括如下步骤：将超导量子比特放置在≤50mK的制冷平台上，并且与超导NbTi同轴电缆选定的驻波模式共振耦合；同轴电缆腔的一端固定在≤50mK的制冷平台上，另一端固定在1K制冷平台上；将LC谐振器固定在1K制冷平台上，并且与超导NbTi同轴电缆选定的驻波模式共振耦合； 调节超导量子比特和超导传输线腔的耦合强度g
1，以及里德堡原子和超导平面波导腔(或里德堡原子和超导平面LC谐振腔)的耦合强度g
2，使它们与超导传输线腔和超导平面波导腔(或超导传输线腔和超导平面LC谐振腔)之间的耦合强度J满足
的关系；借助于加在量子比特上的驱动场，可以实现非常规几何量子门，从而实现量子比特之间纠缠态的制备。在特定的时间点，由于演化算符的相位因子不依赖于腔态，因此该过程对腔模热态不敏感；选择特定的时间和参数使得里德堡原子和超导比特态传输的演化算子对热态不敏感，完成纠缠态的制备。
本发明的基于超导量子比特和里德堡原子的纠缠态制备装置，利用了非常规几何量子态传输的方案，因此纠缠态制备的速度快、保真度高。只要超导量子比特、里德堡原子以及两个耦合腔相互之间的耦合强度满足特定的比例，选择特定的时间使得里德堡原子和超导比特态传输的时间演化算子对热态不敏感，完成纠缠态制备。
通过两端固定在不同制冷平台的超导传输线腔实现超导量子比特和里德堡原子之间纠缠态制备，在开始量子态传输之前通过在两量子比特加入强的驱动场，使得该过程对热态不敏感，可以进一步提高纠缠态制备的保真度以及极大地防止超导量子比特被干扰。基于此方案超导量子比特和里德堡原子的非局域纠缠态制备的保真度和操作速度都可以达到现有局域系统的性能，为量子网络和分布式量子计算研究提供新技术基础。
实施例2
图2为本发明基于超导量子比特和里德堡原子的纠缠态制备方法的流程图。本发明基于超导量子比特和里德堡原子的纠缠态制备方法的主要思想是通过调节耦合强度及选择里德堡原子和超导比特在特定的时间使得时间演化算子中对热态不敏感的条件完成纠缠态制备。并且加入强驱动场实现非常规几何量子门，而且通过两个耦合腔实现超导量子比特和里德堡原子之间非局域纠缠态制备：
步骤301，将超导量子比特与超导传输线腔的选定模式共振耦合，同时将里德堡原子的两个里德堡态与超导平面波导腔共振耦合，或者将里德堡原子的两个里德堡态与超导平面LC谐振腔共振耦合，将超导平面波导腔或者超导平面LC谐振腔与超导传输线腔的选定模式共振耦合；
步骤302，调节超导量子比特和超导传输线腔的耦合强度g
1，以及里德堡原子和超导平面波导腔(或者里德堡原子和超导平面LC谐振腔)的耦合强度g
2，使它们与超导传输线腔和超导平面波导腔(或者超导传输线腔和超导平面LC谐振腔)之间的耦合强度J满足
的关系；
步骤303，借助两个强微波驱动场，实现非常规几何量子门；
步骤304，选择特定的时间使得里德堡原子和超导比特态传输的时间演化算子对热态不敏感即可完成最大纠缠态的制备。
本发明借助于加在量子比特上的驱动场，可以实现非常规几何量子门，从而实现量子比特之间纠缠态的产生。在特定的时间点，由于演化算符的相位因子不依赖于腔态，因此该过程对热态不敏感。
具体地，g
1是超导量子比特和超导传输线腔之间的耦合强度，可以通过可调耦合器来调节；g
2是里德堡量子比特和超导平面波导腔或超导平面LC谐振腔之间的耦合强度，可以通过改变原子的量子化轴与耦合腔的电场之间的角度θ来调节；J表示两个耦合腔之间的耦合强度，是实验前加工确定的。
具体地，复合系统的哈密顿量在旋转波近似下可以表示为(h＝1)：
其中ω
ri＝ω
r是第i个腔的腔模频率，ω
qi＝ω
q是第i个量子比特的频率。
i＝1时对应超导量子比特的上升算符，i＝2时对应里德堡原子的上升算符。
和
分别为超导传输线腔的腔模的产生湮灭算符。
和
分别为超导平面波导腔或者超导平面LC谐振腔的腔模的产生湮灭算符；g
1和g
2分别为超导量子比特和超导传输线腔的耦合强度以及里德堡原子和超导平面波导腔 /超导平面LC谐振腔的耦合强度；
为第i个量子比特的泡利算符。
具体地，超导传输线腔和超导平面波导腔/超导平面LC谐振腔共振耦合，描述耦合腔系统的缀饰态是非简并的，分别是带有频率f
1＝f+J和f
2＝f-J的两个本征模式，其中f为超导传输线腔和超导平面波导腔的频率，J为两个耦合腔之间的耦合强度；两个缀饰态的产生湮灭算符用两个裸腔腔模算符的对称和反对称叠加来描述，即
和
两个本征模同时与超导量子比特和里德堡量子比特耦合。
具体地，根据算符
和
重写复合系统的哈密顿量为：
具体地,为了纠缠态制备过程中热态的不利影响，我们采用了非常规几何量子门来实现超导量子比特与里德堡量子比特的纠缠。
具体地，对两个量子比特加入强微波驱动场，考虑共振驱动ω
d＝ω
q，在驱动频率的旋转坐标系中，系统的哈密顿量变为：
其中Ω是拉比频率。
具体地，在强驱动极限Ω＞＞{g
i，J}中，我们得到
其中
由此，由
得总演化算符
具体地,通过使用马格努斯公式，得到演化算子
在t
n＝2nπ/J时B＝0，腔模与量子比特的耦合被有效地去除，演化算符的相位因子不依赖于腔态，该过程对热态不敏感。
具体地，由于复合系统的两个耦合腔都固定在1K平台上，因此每个本征模最初都处于平衡光子数分布为
的混合态，
是温度T时每个本征模的平均光子数。为了消除纠缠态制备期间热光子的不利影响，在SWAP门操作之前在两量子比特中引入强驱动场实现非常规几何量子门的方法消除了纠缠态制备过程中热态的不良影响。
本发明给出的超导量子比特和里德堡原子的纠缠态制备方法是调节超导量子比特、里德堡原子和两个耦合腔相互之间的耦合强度满足特定关系同时并且加入强驱动场，选择特定的时间使得里德堡原子和超导比特的时间演化算子对热态不敏感，完成最大纠缠态的制备；利用两端分别固定在≤50mK和1K制冷平台的超导传输线腔与超导平面波导腔或超导平面LC谐振腔的耦合实现超导量子比特和里德堡原子的非局域纠缠态制备，因此可以降低里德堡原子所需激光场和磁场对超导量子比特相干性的影响；在两量子比特系统中引入驱动场，借助非常规几何量子门消除了热态的不良影响，进而为超导量子比特和里德堡原子之间快速的、高保真度的纠缠态制备提供了新技术。
以上所述实施例仅表达了本发明的几种实施方式，其描述较为具体和详细，但并不能因此而理解为对本发明专利范围的限制。应当指出的是，对于本领域的普通技术人员来说，在不脱离本发明构思的前提下，还可以做出若干变形和改进，这些都属于本发明的保护范围。因此，本发明专利的保护范围应以所附权利要求为准。
Claims (10)
- 一种基于超导量子比特和里德堡原子的纠缠态制备方法，其特征在于，包括如下步骤：将超导量子比特与超导传输线腔的选定模式共振耦合，同时将里德堡原子的两个里德堡态与超导平面波导腔/超导平面LC谐振腔共振耦合，将超导平面波导腔/超导平面LC谐振腔与超导传输线腔的选定模式共振耦合；调节超导量子比特和超导传输线腔的耦合强度g 1，以及里德堡原子和超导平面波导腔/超导平面LC谐振腔的耦合强度g 2，使它们与超导传输线腔和超导平面波导腔/超导平面LC谐振腔之间的耦合强度J满足的关系；
借助两个强微波驱动场，实现非常规几何量子门，使量子比特之间产生有效的耦合；选择特定的时间使得里德堡原子和超导比特态传输的时间演化算子对热态不敏感，完成最大纠缠态的制备。 - 如权利要求1所述的基于超导量子比特和里德堡原子的纠缠态制备方法，其特征在于，复合系统的哈密顿量在旋转波近似下表示为：
其中ω ri＝ω r是第i个腔的腔模频率，ω qi＝ω q是第i个量子比特的频率；i＝1时对应超导量子比特的上升算符，i＝2时对应里德堡原子的上升算符；
和
分别为超导传输线腔的腔模的产生湮灭算符；
和
分别为超导平面波导腔或者超导平面LC谐振腔的腔模的产生湮灭算符；g 1和g 2分别为超导量子比特和超导传输线腔的耦合强度以及里德堡原子和超导平面波导腔/超导平面LC谐振腔的耦合强度；
为第i个量子比特的泡利算符。
- 如权利要求2所述的基于超导量子比特和里德堡原子的纠缠态制备方法，其特征在于，超导传输线腔和超导平面波导腔/超导平面LC谐振腔共振耦 合，描述耦合腔系统的缀饰态是非简并的，分别是带有频率f 1＝f+J和f 2＝f-J的两个本征模式，其中f为超导传输线腔和超导平面波导腔的频率，J为两个耦合腔之间的耦合强度；两个缀饰态的产生湮灭算符用两个裸腔腔模算符的对称和反对称叠加来描述，即和
两个本征模同时与超导量子比特和里德堡量子比特耦合。
- 如权利要求3所述的基于超导量子比特和里德堡原子的纠缠态制备方法，其特征在于，根据算符和
重写复合系统的哈密顿量为H r＝H 1+H 2，其中：
在强驱动极限Ω＞＞{g i，J}中，得到其中
由于H 1和H 2对易，演化算符可以分解为：
在t n＝2nπ/J时演化算子对热态不敏感。 - 如权利要求1所述的基于超导量子比特和里德堡原子的纠缠态制备方法，其特征在于，每个本征模最初都处于平衡光子数分布为的混合态，
是温度T时每个本征模的平均光子数，f i为第i个腔的频率；为了减少纠缠态制备期间热光子的不利影响，在非常规几何量子门操作之前在量子比特中引入强驱动场，通过非常规几何量子门的方法消除热模对纠缠态制备的不良影响。
- 一种基于超导量子比特和里德堡原子的纠缠态制备装置，其特征在于：包括稀释制冷机的≤50mK的制冷平台、稀释制冷机的1K制冷平台、超导量子比特、可调耦合器、超导传输线腔、超导平面波导腔/超导平面LC谐振腔以及里德堡原子；其中超导量子比特安装在稀释制冷机的≤50mK的制冷平台上；超导量子比特与超导传输线腔的耦合强度可通过可调耦合器调制；超导传输线腔一端固定在稀释制冷机的≤50mK的制冷平台上1与超导量子比特耦合，另一端固定在稀释制冷机的1K制冷平台上与超导平面波导腔/超导平面LC谐振腔耦合；超导平面波导腔/超导平面LC谐振腔安装在稀释制冷机的1K制冷平台上与里德堡原子耦合；通过超导传输线腔和超导平面波导腔/超导平面LC谐振腔实现超导量子比特和里德堡原子之间的非局域纠缠态制备，超导同轴电缆和超导平面波导腔/超导平面LC谐振腔之间的耦合强度J实验前加工确定，通过可调耦合器调节超导量子比特与超导传输线腔的耦合强度，同时调节超导平面波导腔/超导平面LC谐振腔和里德堡原子的耦合强度，当满足特定的关系与选择特定的时间使得里德堡原子和超导比特的时间演化算子对热态不敏感，可实现超导量子比特与里德堡原子之间的纠缠态制备。
- 如权利要求6所述的基于超导量子比特和里德堡原子的纠缠态制备装置，其特征在于，所述稀释制冷机的≤50mK的制冷平台用于给超导量子比特制冷以维持其超导态，1K制冷平台用于转移、囚禁、制备以及操控里德堡原子。
- 如权利要求6所述的基于超导量子比特和里德堡原子的纠缠态制备装置，其特征在于，所述超导量子比特为拥有长相干时间的transmon超导量子比特。
- 如权利要求6所述的基于超导量子比特和里德堡原子的纠缠态制备装置，其特征在于，借助于加在量子比特上的驱动场，实现非常规几何量子门，从而实现量子比特之间纠缠态的产生；在特定的时间点，由于演化算符的相位因子不依赖于腔态，因此该过程对热态不敏感。
- 如权利要求6所述的基于超导量子比特和里德堡原子的纠缠态制备装置，其特征在于，所述里德堡原子选择 87Rb原子的和
两个能级作为量子比特。
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