近日，美国国家标准与技术研究院的R. W.Simmonds及其研究小组取得一项新进展。经过不懈努力，他们在静态解耦的两量子比特腔量子电动力学系统中实现了强参数色散位移。相关研究成果已于2023年6月26日在国际知名学术期刊《自然—物理学》上发表。

该研究小组共享了一个超导量子干涉器件（SQUID），将两个传输子量子比特与一个集总元件腔耦合。他们的设计平衡了互容和互感电路组件，使得两个量子比特与腔实现了静态解耦，并具有低磁通敏感性，从而提供了对抗退相干过程的保护。通过调节SQUID磁通的参数驱动，可以独立动态调节每个量子比特与腔之间的相互作用。

为了实际演示，研究人员对两个量子比特进行了脉冲参数色散读出。腔模式的色散频移符合理论预期的幅度和符号。这种参数化方法创造了一个可扩展且可调谐的腔量子电动力学框架，具备广泛的未来应用潜力。其中包括利用多量子比特宇称读出实现纠缠和错误纠正、实现状态和纠缠的稳定，以及实现参数逻辑门等功能。

据悉，腔量子电动力学（QED）结构中的量子比特通常在色散区域进行操作，这意味着腔的工作频率与量子比特的能级状态相互依赖。通过调节这些色散频移，可以提供额外的选择来进行量子测量或逻辑操作。

附：英文原文

Title: Strong parametric dispersive shifts in a statically decoupled two-qubit cavity QED system

Author: Noh, T., Xiao, Z., Jin, X. Y., Cicak, K., Doucet, E., Aumentado, J., Govia, L. C. G., Ranzani, L., Kamal, A., Simmonds, R. W.

Issue&Volume: 2023-06-26

Abstract: Qubits in cavity quantum electrodynamic (QED) architectures are often operated in the dispersive regime, in which the operating frequency of the cavity depends on the energy state of the qubit, and vice versa. The ability to tune these dispersive shifts provides additional options for performing either quantum measurements or logical manipulations. Here we couple two transmon qubits to a lumped-element cavity through a shared superconducting quantum interference device (SQUID). Our design balances the mutual capacitive and inductive circuit components so that both qubits are statically decoupled from the cavity with low flux sensitivity, offering protection from decoherence processes. Parametric driving of the SQUID flux enables independent, dynamical tuning of each qubit’s interaction with the cavity. As a practical demonstration, we perform pulsed parametric dispersive readout of both qubits. The dispersive frequency shifts of the cavity mode follow the theoretically expected magnitude and sign. This parametric approach creates an extensible, tunable cavity QED framework with various future applications, such as entanglement and error correction via multi-qubit parity readout, state and entanglement stabilization, and parametric logical gates.

DOI: 10.1038/s41567-023-02107-2

Source: https://www.nature.com/articles/s41567-023-02107-2