Measuring the adiabatic non-Hermitian Berry phase in feedback-coupled oscillators
Measuring the adiabatic non-Hermitian Berry phase in feedback-coupled oscillators
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DOI：
10.1103/physrevresearch.5.l032026
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发表时间：
2022-05
影响因子：
4.2
通讯作者：
Yaashnaa Singhal;Enrico Martello;S. Agrawal;T. Ozawa;H. Price;B. Gadway
中科院分区：
文献类型：
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作者：
Yaashnaa Singhal;Enrico Martello;S. Agrawal;T. Ozawa;H. Price;B. Gadway
几何Berry相位是理解量子态在循环绝热演化下行为的关键。当推广到具有增益和损耗的非厄米系统时，Berry相位可以变得复杂，并且不仅应该修改状态的相位，而且还应该修改状态的振幅。在这里，我们进行的第一次实验测量的绝热非厄米Berry相位，探索一个最小的两个网站$\mathcal{PT}$-对称的哈密顿量，是由波多野-纳尔逊模型的启发。我们通过将其动态映射到一对基于实时测量的反馈耦合的经典振荡器的动态来实现这种非厄米模型。正如我们通过实验验证的那样，绝热非厄米Berry相位是一种纯粹的几何效应，即使当所有本征能量都是真实的时，该效应也会导致参数空间内的非循环路径的幅度的显著放大和阻尼。我们进一步观察到一个非厄米模拟的Aharonov-玻姆螺线管效应，观察放大和衰减时，包围一个区域的破$\mathcal{PT}$对称性，作为一个源的虚通量。该实验证明了非厄米特系统所特有的几何效应的重要性，并为进一步研究合成超材料中的非厄米特和拓扑物理铺平了道路。
The geometrical Berry phase is key to understanding the behaviour of quantum states under cyclic adiabatic evolution. When generalised to non-Hermitian systems with gain and loss, the Berry phase can become complex, and should modify not only the phase but also the amplitude of the state. Here, we perform the first experimental measurements of the adiabatic non-Hermitian Berry phase, exploring a minimal two-site $\mathcal{PT}$-symmetric Hamiltonian that is inspired by the Hatano-Nelson model. We realise this non-Hermitian model experimentally by mapping its dynamics to that of a pair of classical oscillators coupled by real-time measurement-based feedback. As we verify experimentally, the adiabatic non-Hermitian Berry phase is a purely geometrical effect that leads to significant amplification and damping of the amplitude also for non-cyclical paths within the parameter space even when all eigenenergies are real. We further observe a non-Hermitian analog of the Aharonov--Bohm solenoid effect, observing amplification and attenuation when encircling a region of broken $\mathcal{PT}$ symmetry that serves as a source of imaginary flux. This experiment demonstrates the importance of geometrical effects that are unique to non-Hermitian systems and paves the way towards the further studies of non-Hermitian and topological physics in synthetic metamaterials.