Despite the high measurement fidelity that can now be reached, the dispersive qubit readout of circuit quantum electrodynamics is plagued by a loss of its quantum nondemolition character and a decrease in fidelity with increased measurement strength. In this work, we elucidate the nature of this dynamical process, which we refer to as transmon ionization. We develop a comprehensive framework which provides a physical picture of the origin of transmon ionization. This framework consists of three complementary levels of descriptions: a fully quantized transmon-resonator model, a semiclassical model where the resonator is treated as a classical drive on the transmon, and a fully classical model. Crucially, all three approaches preserve the full cosine potential of the transmon and lead to similar predictions. This framework identifies the multiphoton resonances responsible for transmon ionization. It also allows one to efficiently compute numerical estimates of the photon number threshold for ionization, which are in remarkable agreement with recent experimental results. The tools developed within this work are both conceptually and computationally simple, and we expect them to become an integral part of the theoretical underpinning of all circuit QED experiments. Published by the American Physical Society 2024

中文翻译：

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测量诱导的 Transmon 电离


尽管现在可以达到很高的测量保真度，但电路量子电动力学的色散量子比特读出受到其量子不破坏特性的损失和保真度随着测量强度的增加而降低的困扰。在这项工作中，我们阐明了这种动态过程的性质，我们称之为 transmon 电离。我们开发了一个全面的框架，提供了 transmon 电离起源的物理图片。该框架由三个互补的描述级别组成：一个完全量化的 transmon-resonator 模型，一个半经典模型，其中谐振器被视为 transmon 上的经典驱动器，以及一个完全经典模型。至关重要的是，这三种方法都保留了 transmon 的全部余弦电位，并导致了类似的预测。该框架确定了负责 transmon 电离的多光子共振。它还允许人们有效地计算电离光子数阈值的数值估计，这与最近的实验结果非常一致。这项工作中开发的工具在概念和计算上都很简单，我们希望它们成为所有电路 QED 实验理论基础的组成部分。 美国物理学会 2024 年出版