Models of light–matter interactions in quantum electrodynamics typically invoke the dipole approximation1,2, in which atoms are treated as point-like objects when compared to the wavelength of the electromagnetic modes with which they interact. However, when the ratio between the size of the atom and the mode wavelength is increased, the dipole approximation no longer holds and the atom is referred to as a ‘giant atom’2,3. So far, experimental studies with solid-state devices in the giant-atom regime have been limited to superconducting qubits that couple to short-wavelength surface acoustic waves4–10, probing the properties of the atom at only a single frequency. Here we use an alternative architecture that realizes a giant atom by coupling small atoms to a waveguide at multiple, but well separated, discrete locations. This system enables tunable atom–waveguide couplings with large on–off ratios3 and a coupling spectrum that can be engineered by the design of the device. We also demonstrate decoherence-free interactions between multiple giant atoms that are mediated by the quasi-continuous spectrum of modes in the waveguide—an effect that is not achievable using small atoms11. These features allow qubits in this architecture to switch between protected and emissive configurations in situ while retaining qubit–qubit interactions, opening up possibilities for high-fidelity quantum simulations and non-classical itinerant photon generation12,13. Superconducting giant atoms are realized in a waveguide by coupling small atoms to the waveguide at multiple discrete locations, producing tunable atom–waveguide coupling and enabling decoherence-free interactions.

中文翻译：

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具有超导人造巨原子的波导量子电动力学

量子电动力学中光与物质相互作用的模型通常会调用偶极子近似 1,2，其中与它们相互作用的电磁模式的波长相比，原子被视为点状物体。然而，当原子大小与模式波长之间的比率增加时，偶极子近似不再成立，原子被称为“巨原子”2,3。到目前为止，对巨原子状态下的固态器件的实验研究仅限于耦合到短波长表面声波 4-10 的超导量子位，仅在单一频率下探测原子的特性。在这里，我们使用另一种架构，通过将小原子耦合到多个但分离良好的离散位置的波导来实现巨原子。该系统可实现具有大开关比 3 的可调谐原子 - 波导耦合和可通过设备设计设计的耦合光谱。我们还展示了由波导中准连续模式光谱介导的多个巨原子之间的无退相干相互作用——这是使用小原子无法实现的效果11。这些特性允许该架构中的量子位在受保护和发射配置之间切换，同时保留量子位-量子位相互作用，为高保真量子模拟和非经典巡回光子生成开辟了可能性12,13。通过在多个离散位置将小原子耦合到波导，产生可调谐的原子-波导耦合并实现无退相干相互作用，从而在波导中实现超导巨原子。