Non-equilibrium dynamics of quantum-impurity systems close to quantum critical points

相干信息交换需要最少两个qbit。耦合到量子比特的费米环境不仅引起退相，而且还可以通过RKKY相互作用诱导有效的自旋-自旋耦合。另一个用于理解固体中电子耗散的范例系统是玻色-费米模型，其中附加的耗散玻色子浴耦合到电子子系统。这两类系统都可以表现出量子相变。对于这类量子系统在量子相变附近的实时非平衡动力学行为知之甚少，我们计划利用含时数值重整化群方法来研究量子相变附近两个量子杂质之间的退相和信息传递。我们特别感兴趣的问题热化系统与剩余杂质熵。我们想研究当接近临界耦合时，实时动态是如何变化的。相干振荡是否在强到足以引起基态变化的临界耦合处占优势？我们也将研究借由周期性地切换外加闸极电压来控制量子资讯传递的相关性。

The minimum of two qbits are required for coherent information exchange. A Fermionic environment coupled to the qbits causes not only dephasing but can also induce an effective spin-spin coupling via RKKY interaction. Another paradigm system for understanding dissipation of electrons in solids is the Bose-Fermi model where an additional dissipative Bosonic bath is coupled to the electronic subsystem. Both classes of systems can show quantum phase transitions. Little is known about the real-time dynamics out of equilibrium of such quantum systems close to the quantum phase transition.We plan to use the time-dependent numerical renormalization group approach to explore the dephasing and the information transfer between two quantum impurities close to the quantum phase transition. We are particularly interested in the question of thermalization in systems with residual impurity entropy. We want to investigate how the real-time dynamics changes when approaching the critical coupling. Do coherent oscillation prevail at the critical coupling which is strong enough to cause a change of ground state? We also will study the coherent control of the quantum information transfer by a periodic switching of the externally applied gate voltage.