极强耦合条件下电路QED系统中量子信息处理的研究

The coupling strength in circuit quantum electrodynamics (referred to as QED) system is comparable to or larger than the boson frequency due to the large dipole moments of the superconducting qubit and the small cavity-mode volumes of solid-state cavity. In the ultrastrong coupling regime, the ordinary rotating-wave approximation breaks down and the system shows a new physical picture. This project examines the quantum information processing based on the QED system in the ultrastrong coupling regime. The ultrastrong coupling between the multiple superconducting qubits and the transmission line resonator is investigated by means of a generalized rotating-wave approximation and Van Vleck perturbation method. The interaction between superconducting qubit and the transmission line resonator can be controlled by employing the technology of lithography and external driving field. The creation of multi-qubit entangled state can be obtained. The controllable coupling between the multiple superconducting qubits can be achieved by the control of qubit, transmission line resonator and the external driving field. The scheme of the ultrafast two-qubit gates is examined in the circuit QED system under ultrastrong coupling conditions. The available experimental parameters of the proposed scheme are given. The project intends to present the analytical solution of multiple superconducting qubits model system in ultrastrong coupling regime theoretically. Moreover, the analytical solution is used to construct ultrafast quantum logic gates and create the entangled states to achieve ultrafast quantum information processing. This project has important theoretical significance and potential applications.

由于超导量子比特大的偶极矩和固态腔小的腔模体积，电路量子电动力学(QED)系统中的耦合强度可以达到与玻色子频率可比拟甚至大于的程度。在这一极强耦合参数范围，传统的旋波近似不再适用，系统展现出一种新的物理图像。本项目拟研究极强耦合条件下电路QED系统中的量子信息处理。利用广义旋波近似和Van Vleck微扰理论等方法研究多个超导量子比特与传输线腔的极强耦合，利用光刻技术和外加驱动场技术控制超导量子比特与传输线腔相互作用，制备多比特纠缠态。通过对超导量子比特、传输线腔以及外加驱动场的控制，实现多个超导量子比特间的可控耦合。研究极强耦合条件下实现两比特超快量子逻辑门的方案，给出方案在实验上的可行性参数。本项目拟从理论上给出多个超导量子比特极强耦合模型系统的解析解，并将这些解析解用于构造超快量子逻辑门、制备纠缠态，实现超快的量子信息处理。本项目的研究内容具有重要的理论意义和潜在的应用价值。

由于超导量子比特大的偶极矩和固态腔小的腔模体积，电路量子电动力学(QED)系统中的耦合强度可以达到与玻色子频率可比拟甚至大于的程度。在这一极强耦合参数范围，传统的旋波近似不再适用，系统展现出一种新的物理图像。本项目研究极强耦合条件下电路QED系统中的量子信息处理，主要包括极强耦合条件下实现两超导量子比特超快控制相位门和iSWAP门以及超导量子比特纠缠态的制备和可控耦合。研究了由超导电荷量子比特和磁通量子比特通过大约瑟夫森结耦合的物理模型中的纠缠特性，研究了该方案中电荷比特和磁通比特的最大纠缠态的制备和保持，给出了方案在实验上的可行性参数，结果显示可制备宏观爱因斯坦-波多尔斯基-罗森（EPR）态和实现快速纠缠过程。研究了两超导电荷量子比特与压缩相干态相互作用的纠缠特性。研究结果对于理解和发展宏观量子纠缠、量子非定域性等量子力学基本原理具有重要的理论意义。

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