Occurrence of A-15 Phases

Three binary A-15 compounds (Zr₄Sn, Ta₃Sb, Ta₄Au) were reinvestigated and all three found to be superconducting below 1 ?K. Ternary compounds V₃(Al, X), (X=As, Ge, Au) were also investigated in the composition range where the A-15 structure is stable. The extrapolated superconducting transition temperature of the compound V₃Al, if it existed in the A-15 form, is ～ 17 ?K.     

Phases of atom-molecule vortex matter

We study ground state vortex configurations in a rotating atom-molecule Bose-Einstein condensate. It is found that the coherent coupling between the atomic and molecular condensates can render a pairing of atomic and molecular vortices into a composite structure that resembles a carbon dioxide molecule. Structural phase transitions of vortex lattices are also explored through different physical parameters including the rotational frequency of the system.     

Phases of the number-theoretic spin chain

We present numerical and analytical evidence for a first-order phase transition of the ferromagnetic spin chain with partition functionZ()=(–1)/() at the inverse temperature _cr=2.     

Phases of silicon at high pressure

X-ray diffraction studies are reported on silicon at pressures up to 250 kbar (25 GPa). A transition to the β-Sn structure (II) initiates at 112 ± 2 kbar and two phases (I + II) coexist to 125 ± 2 kbar. At 132 ± 2 kbar a new phase (V) initiates, and the transition is complete at 164 ± 5 kbar. This phase persists to 250 kbar. Its structure is tentatively assigned as primitive hexagonal with c/a = 0.941 ± 0.002 at 250 kbar. On release of pressure, the sequence is V → (V + II) (145 - 110 kbar) → II → (II + III) (108 - 85 kbar) → III, the last phase persisting to room pressure.     

Observable-Geometric Phases and Quantum Computation

This paper presents an alternative approach to geometric phases from the observable point of view. Precisely, we introduce the notion of observable-geometric phases, which is defined as a sequence of phases associated with a complete set of eigenstates of the observable. The observable-geometric phases are shown to be connected with the quantum geometry of the observable space evolving according to the Heisenberg equation. They are indeed distinct from Berry’s phase (Berry Proc. R. Soc. London Series A 392:45–57, 1984; Simon Phys. Rev. Lett. 51:2167–2170, 1983) as the system evolves adiabatically. It is shown that the observable-geometric phases can be used to realize a universal set of quantum gates in quantum computation. This scheme leads to the same gates as the Abelian geometric gates of Zhu and Wang (Phys. Rev. Lett. 89: 097902: 1–4, 2002, Phys. Rev. A 67: 022319: 1–9, 2003), but based on the quantum geometry of the observable space beyond the state space.

     

Aharonov-Anandan Phases in Lipkin-Meskov-Glick Model

In the system of several interacting spins, geometric phases have been researched intensively. However, the studies are mainly focused on the adiabatic case (Berry phase), so it is necessary for us to study the non-adiabatic counterpart (Aharonov and Anandan phase). In this paper, we analyze both the
non-degenerate and degenerate geometric phase of Lipkin-Meskov-Glick type model, which has many application in Bose-Einstein condensates and entanglement theory. Furthermore, in order to calculate degenerate geometric phases, the Floquet theorem and decomposition of operator are generalized. And the general formula is achieved.     

Theoretical Description of High-Pressure Phases of Semiconductors

First-principles ( ab initio ) electronic structure calculations allow detailed studies of the energetics of materials under high pressures. Here we illustrate some of the important themes using mainly examples from work on Si and Ge.     

Phases of wave functions and level repulsion

Avoided level crossings are associated with exceptional points which are the singularities of the spectrum and eigenfunctions, when considered as functions of a complex coupling parameter. It is shown that the wave function of one state changes sign but not the other, if the exceptional point is encircled in the complex plane. An experimental setup is suggested where this peculiar phase change could be observed. Received: 7 January 1999 / Received in final form: 15 March 1999     

具有全局对称性的强关联拓扑物态的规范场论

在有对称性保护的条件下,拓扑能带绝缘体等自由费米子体系的拓扑不变量可以在能带结构计算中得到.但是,为了得到强关联拓扑物质态的拓扑不变量,我们需要全新的理论思路.最典型的例子就是分数量子霍尔效应:其低能有效物理一般可以用Chern-Simons拓扑规范场论来计算得到;霍尔电导的量子化平台蕴含着十分丰富的强关联物理.本文将讨论存在于玻色和自旋模型中的三大类强关联拓扑物质态:本征拓扑序、对称保护拓扑态和对称富化拓扑态.第一类无需考虑对称性,后两者需要考虑对称性.理论上,规范场论是一种非常有效的研究方法.本文将简要回顾用规范场论来研究强关联拓扑物质态的一些研究进展.具体内容集中在"投影构造理论"、"低能有效理论"、"拓扑响应理论"三个方面.     

On Berry Phases Along Mixtures of States

Concepts connected with Berry's phase can be extended to curves and loops in state spaces defined by von Neumann algebras. This includes the important space of density operators.