Observations of quantum entangled states and quantum critical behavior by using a precise probing method of microwave near-field

量子纠缠态在凝聚态物理和量子信息技术领域都变得至关重要。为了对这些态有一个完整的理解，我们研究了微波显微镜的发展来探测量子临界点附近的量子临界行为，并设计了超导腔谐振器来研究利用量子电动力学理论产生的量子纠缠态。我们发现，利用微波近场可以大大提高微波显微镜的空间分辨率，这是通过在腔体中插入金属针来实现的。我们还发现，这种金属针的插入对于在低温下精确控制约瑟夫森量子位和微波光子之间的耦合常数是有用的，这是产生量子纠缠态所必需的。

Quantum entangled states become essentially important in both regions of condensed matter physics and quantum information technology. Toward a complete understanding of such states, we study the development of a microwave microscope to probe the quantum critical behavior in the neighborhood of quantum critical point, and the design of a superconducting cavity resonator to investigate the quantum entangled states generated by using a quantum electrodynamics theory. We found that a spatial resolution of the microwave microscope is strongly enhanced by utilizing a microwave near-field, which is realized by the insertion of a metallic needle into a cavity resonator. We also found that such an insertion of the metallic needle is useful for a precise control of the coupling constant between the Josephson quantum bits and the microwave photons at low temperatures, which is required to create the quantum entangled states.