论文标题
关键不稳定两级系统的量子相干性
Quantum Coherence of Critical Unstable Two-Level Systems
论文作者
论文摘要
我们通过采用Bloch-Sphere形式主义，详细研究不稳定的两级量子系统的动力学。通过为这种不稳定的量子系统采用Bloch-Vector表示，我们确定了一系列新颖的关键场景，其中所谓的能量水平和衰减宽度向量，$ {\ bf e} $和$ {\bfγ} $彼此之间是正性的e} |）$小于1。最显着的，我们发现关键的不稳定量子系统表现出非典型行为，例如连贯性 - 定义振荡，当在系统的适当定义的共同付款框架中进行分析时。在同一框架中，描述纯关键量子的单位bloch vector $ {\ bf b} $将在同等时间间隔内扫除不等的区域，同时围绕向量$ {\ bf e} $旋转。由于两级量子系统的能量差异，这些现象超出了通常的振荡模式。有趣的是，我们观察到这些新功能即使对于准关键的方案也将持续存在，其中vectors $ {\ bf e} $和$ {\bfγ} $彼此之间并不完美。讨论了我们的结果在量子信息和不稳定的介子中的应用 - 安段和其他系统。
We study in detail the dynamics of unstable two-level quantum systems by adopting the Bloch-sphere formalism of qubits. By employing the Bloch-vector representation for such unstable qubit systems, we identify a novel class of critical scenarios in which the so-called energy-level and decay-width vectors, ${\bf E}$ and ${\bfΓ}$, are orthogonal to one another, and the parameter $r = |{\bf Γ}|/(2|{\bf E}|)$ is less than 1. Most remarkably, we find that critical unstable qubit systems exhibit atypical behaviours like coherence--decoherence oscillations when analysed in an appropriately defined co-decaying frame of the system. In the same frame, a unit Bloch vector ${\bf b}$ describing a pure critical qubit will sweep out unequal areas during equal intervals of time, while rotating about the vector ${\bf E}$. These phenomena emerge beyond the usual oscillatory pattern due to the energy-level difference of the two-level quantum system. Interestingly enough, we observe that these new features will persist even for quasi-critical scenarios, in which the vectors ${\bf E}$ and ${\bfΓ}$ are not perfectly orthogonal to each other. Applications of our results to quantum information and to unstable meson--antimeson and other systems are discussed.
