标题： 约瑟夫森结量子比特中异常非线性微波吸收的起源：二能级系统的神秘本质还是它们的动态相互作用？ 显示英文标题

标题： The origin of anomalous non-linear microwave absorption in Josephson junction qubits: mysterious nature of two level systems or their dynamic interaction?

摘要： 量子二能级系统（TLSs）在无定形和无序材料中低温下普遍存在，它们是超导约瑟夫森结量子比特退相干的原因，特别是因为它们在微波频率范围内吸收量子比特振荡的相干能量。 在具有氧化物界面的平面约瑟夫森谐振器中，这种吸收在非线性 regime 中表现出异常弱的损耗正切对场的依赖性，这与理论预期和无定形电介质中的观测结果相矛盾。 最近有人提出，这种异常吸收是由于 TLS 动态相互作用引起的。 在这里，我们表明这种相互作用不能导致观察到的损耗正切场依赖性，并提出了另一种解释，假设 TLS 偶极矩$p$按照特定的幂律分布$P(p) \propto 1/p^{3-\eta}$($0\leq \eta <1$)。这种假设确实导致了观察到的损耗正切行为。 幂律分布的假设得到了最近对单个 TLS 偶极矩的测量以及由于长程偶极-偶极相互作用导致 TLS 形成的理论模型的支持，从而将异常吸收与 TLS 本质这一长期存在的问题的可能解决方案联系起来。 显示英文摘要

摘要： Quantum two-level systems (TLSs) commonly found at low temperature in amorphous and disordered materials are responsible for decoherence in superconducting Josephson junction qubits particularly because they absorb energy of coherent qubit oscillations in the microwave frequency range. In planar Josephson resonators with oxide interfaces this absorption is characterized by an anomalously weak loss tangent dependence on the field in the non-linear regime that conflicts with the theoretical expectations and the observations in amorphous dielectrics. It was recently suggested that this anomalous absorption is due to TLS dynamic interactions. Here we show that such interactions cannot lead to the observed loss-tangent field dependence and suggest the alternative explanation assuming that TLS dipole moments $p$ are distributed according to the specific power law $P(p) \propto 1/p^{3-\eta}$ ($0\leq \eta <1$). This assumption, indeed, results in the observed loss tangent behavior. The hypothesis of a power law distribution is supported both by the recent measurements of individual TLS dipole moments and the theoretical model of TLS formation due to the long-range dipole-dipole interaction, thus connecting the anomalous absorption with the possible solution of the long-standing problem of the nature of TLSs.