Theoretical Quantum Physics Laboratory, RIKEN, Saitama 351-0198, Japan.
Department of Microtechnology and Nanoscience (MC2), Chalmers University of Technology, SE-412 96 Gothenburg, Sweden.
Phys Rev Lett. 2018 Apr 6;120(14):140404. doi: 10.1103/PhysRevLett.120.140404.
In quantum-optics experiments with both natural and artificial atoms, the atoms are usually small enough that they can be approximated as pointlike compared to the wavelength of the electromagnetic radiation with which they interact. However, superconducting qubits coupled to a meandering transmission line, or to surface acoustic waves, can realize "giant artificial atoms" that couple to a bosonic field at several points which are wavelengths apart. Here, we study setups with multiple giant atoms coupled at multiple points to a one-dimensional (1D) waveguide. We show that the giant atoms can be protected from decohering through the waveguide, but still have exchange interactions mediated by the waveguide. Unlike in decoherence-free subspaces, here the entire multiatom Hilbert space (2^{N} states for N atoms) is protected from decoherence. This is not possible with "small" atoms. We further show how this decoherence-free interaction can be designed in setups with multiple atoms to implement, e.g., a 1D chain of atoms with nearest-neighbor couplings or a collection of atoms with all-to-all connectivity. This may have important applications in quantum simulation and quantum computing.
在涉及自然和人工原子的量子光学实验中，与原子相互作用的电磁辐射的波长相比，原子通常小到可以近似为点状。然而，与蜿蜒的传输线或表面声波耦合的超导量子比特可以实现“巨型人工原子”，这些原子可以在相隔几个波长的多个点上与玻色子场耦合。在这里，我们研究了多个巨型原子在多个点与一维（1D）波导耦合的设置。我们表明，通过波导可以保护巨型原子不受退相干影响，但它们仍然通过波导具有交换相互作用。与无退相干子空间不同，这里整个多原子希尔伯特空间（N 个原子的 2^{N}个状态）都不受退相干影响。这对于“小”原子来说是不可能的。我们进一步展示了如何在具有多个原子的设置中设计这种无退相干相互作用，例如，实现具有最近邻耦合的原子一维链或具有全连接的原子集合。这在量子模拟和量子计算中可能有重要的应用。
