PDF(Pubmed)
Abstract：
Transmon qubits are the predominant element in circuit-based quantum information processing, such as existing quantum computers, due to their controllability and ease of engineering implementation. But more than qubits, transmons are multilevel nonlinear oscillators that can be used to investigate fundamental physics questions. Here, they are explored as simulators of excited state quantum phase transitions (ESQPTs), which are generalizations of quantum phase transitions to excited states. We show that the spectral kissing (coalescence of pairs of energy levels) experimentally observed in the effective Hamiltonian of a driven SNAIL-transmon is an ESQPT precursor. We explore the dynamical consequences of the ESQPT, which include the exponential growth of out-of-time-ordered correlators, followed by periodic revivals, and the slow evolution of the survival probability due to localization. These signatures of ESQPT are within reach for current superconducting circuits platforms and are of interest to experiments with cold atoms and ion traps.
摘要：
发射子量子比特是基于电路的量子信息处理中的主要元素，比如现有的量子计算机，由于它们的可控性和易于工程实施。但不仅仅是量子比特，transmons是多级非线性振荡器，可用于研究基本物理问题。这里,它们被用作激发态量子相变(ESQPT)的模拟器，这是量子相变到激发态的推广。我们表明，在驱动的SNAIL-transmon的有效哈密顿量中实验观察到的光谱接吻（能级对的合并）是ESQPT前体。我们探讨了ESQPT的动态后果，其中包括非时间顺序相关器的指数增长，随后是周期性的复兴，以及由于本地化而导致的生存概率的缓慢演变。ESQPT的这些特征对于当前的超导电路平台是可以实现的，并且对冷原子和离子阱的实验感兴趣。
