Choi Jeong Ryeol
School of Electronic Engineering, Kyonggi University, Yeongtong-gu, Suwon 16227, Gyeonggi-do, Republic of Korea.
Nanomaterials (Basel). 2023 Aug 23;13(17):2395. doi: 10.3390/nano13172395.
Superconducting flux qubits have many advantages as a storage of quantum information, such as broad range tunability of frequency, small-size fabricability, and high controllability. In the flux qubit-oscillator, qubits are connected to SQUID resonators for the purpose of performing dispersive non-destructive readouts of qubit signals with high fidelity. In this work, we propose a theoretical model for analyzing quantum characteristics of a flux qubit-oscillator on the basis of quantum solutions obtained using a unitary transformation approach. The energy levels of the combined system (qubit + resonator) are analyzed in detail. Equally spaced each energy level of the resonator splits into two parts depending on qubit states. Besides, coupling of the qubit to the resonator brings about an additional modification in the split energy levels. So long as the coupling strength and the tunnel splitting are not zero but finite values, the energy-level splitting of the resonator does not disappear. We conclude that quantum nondemolition dispersive measurements of the qubit states are possible by inducing bifurcation of the resonator states through the coupling.
超导磁通量子比特作为量子信息的一种存储方式具有诸多优点，比如频率可调范围广、可制造小尺寸器件以及具有高度可控性。在磁通量子比特 - 振荡器中，量子比特连接到超导量子干涉器件（SQUID）谐振器上，以便对量子比特信号进行高保真的色散无损读出。在这项工作中，我们基于使用幺正变换方法得到的量子解，提出了一个用于分析磁通量子比特 - 振荡器量子特性的理论模型。详细分析了组合系统（量子比特 + 谐振器）的能级。谐振器的每个等间距能级根据量子比特状态分裂成两部分。此外，量子比特与谐振器的耦合会使分裂后的能级产生额外的变化。只要耦合强度和隧穿分裂不为零而是有限值，谐振器的能级分裂就不会消失。我们得出结论，通过耦合引起谐振器状态的分岔，可以实现对量子比特状态的量子无损色散测量。
