Resolution of gauge ambiguities in ultrastrong-coupling cavity quantum electrodynamics
Resolution of gauge ambiguities in ultrastrong-coupling cavity quantum electrodynamics
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DOI：
10.1038/s41567-019-0534-4
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发表时间：
2019-08-01
期刊：
影响因子：
19.6
通讯作者：
Nori, Franco
中科院分区：
文献类型：
--
作者：
Di Stefano, Omar;Settineri, Alessio;Nori, Franco
在量子电动力学中，规范的选择影响光-物质相互作用的形式。然而，规范不变性意味着所有的物理结果都应该独立于这种形式选择。Rabi模型是对两能级原子和量子化电磁场之间偶极耦合的一种广泛描述，在存在超强光-物质耦合的情况下，它似乎违反了这一原则，而这种耦合现在在许多物理系统中都是可以通过实验获得的。这种失败归因于物质系统的有限级截断，这是一种进入拉比模型推导的近似。在这里，我们确定了规范违反的来源，并提供了一种推导截断希尔伯特空间中产生规范不变物理结果的光-物质哈密顿量的一般方法，即使在极端光-物质相互作用状态下也是如此。这是通过补偿在构造有效哈密顿量时引入的非定域来实现的。在库仑规范中得到的量子拉比哈密顿量在形式上与标准的有很大的不同，但提供了与使用偶极规范得到的相同的物理结果。这些结果揭示了非微扰和极端相互作用体系中的规范不变性，并解决了量子Rabi和Dicke模型中规范模糊性引起的长期争议。
In quantum electrodynamics, the choice of gauge influences the form of light-matter interactions. However, gauge invariance implies that all physical results should be independent of this formal choice. The Rabi model, a widespread description for the dipolar coupling between a two-level atom and a quantized electromagnetic field, seemingly violates this principle in the presence of ultrastrong light-matter coupling, a regime that is now experimentally accessible in many physical systems. This failure is attributed to the finite-level truncation of the matter system, an approximation that enters the derivation of the Rabi model. Here, we identify the source of gauge violation and provide a general method for the derivation of light-matter Hamiltonians in truncated Hilbert spaces that produces gauge-invariant physical results, even for extreme light-matter interaction regimes. This is achieved by compensating the non-localities introduced in the construction of the effective Hamiltonians. The resulting quantum Rabi Hamiltonian in the Coulomb gauge differs significantly in form from the standard one, but provides the same physical results obtained by using the dipole gauge. These results shed light on gauge invariance in the non-perturbative and extreme-interaction regimes, and solve long-lasting controversies arising from gauge ambiguities in the quantum Rabi and Dicke models.