转动诱发原子核量子相变的一种可能途径

基于微观IBM理论,提出转动诱导出玻色子量子相变的一种可能途径:一旦原子核在受到高能激发或作快速旋转时,假如外界提供的能量足以使玻色子完成拆对顺排,则核处于集体相与单粒子态的共存相,其特征是出现较密集的能谱;假如能量不足以完成拆对或顺排,可能发生两种情况之一,当核旋转达到某个临界转动频率ω_c时,或者一个高角动量的玻色子脱离“集体”而“游离”出来,或者发生一个高角动量的玻色子转变为一个低角动量的玻色子,核仍旧处于集体相;均会伴随出现光辐射,产生基态带的一条能级——相变信号.正是这类玻色子相变导致了原子核的量子相变.本物理图像统一了玻色子拆对顺排相变和退耦释放光子相变的描述.以¹⁰⁰Pd核的14⁺₁,14⁺₂和14⁺₃态的产生机理为例,对模型作了仔细说明.     

102Ru核振动到转动演化的微观研究

基于微观sdIBM-2方案和实验单粒子能量值, 在最普遍的哈密顿量下, 用两组不同的核子-核子等效相互作用参数, 分别很好地再现了¹⁰²Ru核的振动带能谱和转动带能谱及其演化过程. 微观和唯象的研究指认: 1) 这两种激发模式的共存区是能态8⁺₁—12⁺₁(即E_x=2.500—4.000 MeV); 态 8⁺_{1关键词： 微观sdIBM-2方案 形状演化 玻色子 102Ru核')" href="#">¹⁰²Ru核}     

原子核过渡区的量子相变

在相互作用玻色子模型(IBM) 基础上用O(6) 高阶项代替传统的SU(3) 四极-四极相互作用来研究原子核从振动到转动过渡区的量子相变行为。利用U(5)-SU(3) 和UQ 两种方案,在玻色子数分别为N = 8 和N = 20 不同情况下,研究了原子核的一些低激发态的能级比和电四极跃迁比。结果表明:随着玻色子数N 的增大,系统的量子相变行为得到加强;两种方案都可以用来描述从振动到转动过渡区的原子核的量子相变特征且O(6) 高阶项方案下量子相变行为更为明显。在此基础上,进一步应用这两种方案具体讨论了152Sm 核的低激发态能级和电四极跃迁性质并与实验数据进行对比分析。结果表明,用O(6) 高阶项可以更为合理地描述带内跃迁及不同带之间的带间跃迁性质。With the framework of Interacting Boson Model(IBM), transitional patterns from the spherical to the axially deformed limit of the IBM with a schematic Hamiltonian are studied by replacing the SU(3) quadrupole-quadrupole term with O(6) cubic interaction. But, we use the two schemes to investigate some energy ratios and B(E2) ratios for different bosons N = 8 and N = 20. The results show that with the increasing of the numbers of bosons, the transitional behaviors can be enhanced; the transitional behaviors are very similar in the two schemes. However, there are some distinctive differences for some quantities across the entire transitional region, such as energy levels and ratios, B(E2) values and ratios, and expectation values of the shape variables. Generally speaking, the transition is smoother and the nuclear shape is less well defined in the new scheme. Then we apply the two schemes to the critical point symmetry candidate, such as 152Sm, and find the overall fitting quality of the UQ scheme is better than that of the U(5)-SU(3) scheme, especially for the inter-band E2 transitions in 152Sm.     

156Gd基态SU(3)→O(6)相变的一种微观理解

γ射线能量自旋曲线指认156Gd核基态具有SU(3)和O(6)两种对称性。 基于微观sdIBM-max方案和单粒子能量实验值, 用两组核子之间的对作用、 四极对作用、 四极 四极作用的等效强度参数, 都很好地再现了这两种能谱及其演化过程。 计算结果揭示出对基态相变的一种新理解: SU(3)的基准态是低激发 低有序态, 而O(6)基准态则是高激发 高有序的, 它们有临界区6+1—8+1态; 当核退耦到临界区时, 高有序基准态释放多余的有序结构能, 导致低有序基准态重组, 实现减速旋转驱动高有序核向着低有序核过渡的量子相变。最后用156Gd核的势能曲面作了直观说明。 The γ ray energy over spin curves identifies that there are the SU(3) and O(6) symmetries in the ground states of the 156Gd nucleus; by means of the microscopic sdIBM max approach and signal particle experimental energies the spectra of those two symmetries and their transient process are successfully reproduced through two parameters of nucleon nucleon effective interaction with pairing plus quadrupole pairing plus quadrupole quadrupole forces. The calculated results reveal a new way to recognize ground states quantum phase transition, in which the basic state of the SU(3) symmetry is a low lying and low ordered state, while one of the O(6) are a high lying and high ordered state, their critical region is between 6+1—8+1 states, the high ordered basic state releases spare ordered structure energy, reducing rotation speed, thus causing the restructure of low ordered basic state and accomplishing the quantum phase transition from the high ordered phase into the low ordered phase, the shape phase transition takes place along the yrast line of nucleus when it de excited to the critical region. Because the structural phase transition takes place by no obvious charge of boson structure constants in the critical region it is a benignancy and calm transition with respect to its macroscopic behave. The potential energy surface of 156Gd nucleus has been illustrated to visualize.     

有限玻色子系统中的激发态量子相变

为了探讨原子核系统中存在激发态量子相变的可能性,在相互作用玻色子模型框架下对有限玻色子系统中的激发态量子相变现象进行唯象分析,特别是针对角动量和有限N效应如何影响U（5）-SU（3）和SU（3）-O（6）过渡区中的激发态量子相变行为进行了系统研究。结果表明,低角动量振动谱中的激发态量子相变特征在现实玻色子数情况下可以很好地保持,但随着角动量增加相变特征逐渐消失。In this work, a phenomenological analysis of the excited-state quantum phase transitions (ESQPTs) in the finite-N boson system has been carried out within the interacting boson model in order to reveal the possibility of finding ESQPTs in nuclear systems. Particularly, the angular momentum and finite-N effects on the ESQPTs in the U(5)-SU(3) and SU(3)-O(6) transitional regions have been systematically investigated. The results indicate that the main features of ESQPTs can be well preserved even at a realistic boson number for small angular momentum but will gradually disappear as the angular momentum increases.     

76Sr核yrast带结构演化的微观研究

对于发生在同一个原子核中的、从一种高有序激发模式向着另一种低有序激发模式演化的机理和物理图像,提出了一种新的理解:被布居到高角动量态的高有序激发核,以E2跃迁方式先行退耦到yrast带,再退耦到共存区时释放了结构能,诱发价核子对耦合强度改变,重新组合出低有序的激发模式基准态,实现了基准态结构的过渡.从微观上看,这是一种既温和而又平稳的转变.并以76 Sr核为例作了深入阐述.     

76Sr核yrast带结构演化的微观研究

对于发生在同一个原子核中的、从一种高有序激发模式向着另一种低有序激发模式演化的机理和物理图像,提出了一种新的理解：被布居到高角动量态的高有序激发核,以E₂跃迁方式先行退耦到yrast带,再退耦到共存区时释放了结构能,诱发价核子对耦合强度改变,重新组合出低有序的激发模式基准态,实现了基准态结构的过渡.从微观上看,这是一种既温和而又平稳的转变.并以⁷⁶Sr核为例作了深入阐述. 关键词： 量子相变 yrast带结构演化 微观sdIBM-2方案 76Sr核')" href="#">⁷⁶Sr核     

182Os核yrast带结构SU(3)→U(5)→SU(3)形状相变的有序性研究

对于发生在同一个原子核中的转动诱导发生基准态结构的量子相变,可以理解为一种从高有序激发模式向着低有序激发模式的演化：被布居到高角动量态的高有序激发核,以E2跃迁的方式先行退耦到yrast带,再退耦到共存区(或临界点)时释放了有序的结构能,诱发价核子对耦合强度改变,重新组合出低有序的激发模式基准态,实现了基准态结构的过渡.对核量子相变的这种描述,与朗道经典热相变理论之间有了某些相似的术语和物理内涵.本文把这种理解推广到了相继的二次相变中.以¹⁸²Os 核为例作了说明,并展 关键词： 量子相变 基态结构演化 F_max方案')" href="#">微观sdIBM-F_max方案 182Os核')" href="#">¹⁸²Os核     

102Ru核振动到转动演化的微观研究

基于微观sdIBM-2方案和实验单粒子能量值,在最普遍的哈密顿量下,用两组不同的核子.核子等效相互作用参数,分别很好地再现了102Ru核的振动带能谱和转动带能谱及其演化过程.微观和唯象的研究指认:1)这两种激发模式的共存区是能态81 -121 (即Ex=2.500-4.000 MeV);态81 是振动模式占据优势的能态,态121 是转动模式占据优势的能态,而状态101 则是两种模式的中立能态;2)态121 是141 态退耦到态101 辐射光子相变后的中间能态;3)从基态起直到201 态的yrast态全都是集体态,而以后出现的第一个拆对顺排态很可能就是中子h11/2的两准粒子态;4)这种结构的过渡不是很剧烈的,而是通过玻色子结构常数在过渡区中不大的改变来实现的.     

基于量子核函数算法的图像压缩研究

为了提高图像压缩的质量,提出量子核函数算法。首先采用自适应灰度阈值使图像归一化处理,用量子比特表示图像白色和黑色状态的出现概率;然后每个像素点的值被编码为量子角度向量;接着构造适应度函数的极小值获得高斯径向基核函数的最优核宽,在量子核影响半径以外的像素量子编码不再起引导作用;最后给出了算法流程。实验仿真显示本文算法的压缩重构效果清晰,PSNR最大,压缩时间最少。     

Intrinsic spin hall effect induced by quantum phase transition in HgCdTe quantum wells

The spin Hall effect can be induced by both extrinsic impurity scattering and intrinsic spin-orbit coupling in the electronic structure. The HgTe/CdTe quantum well has a quantum phase transition where the electronic structure changes from normal to inverted. We show that the intrinsic spin Hall effect of the conduction band vanishes on the normal side, while it is finite on the inverted side. By tuning the Cd content, the well width, or the bias electric field across the quantum well, the intrinsic spin Hall effect can be switched on or off and tuned into resonance under experimentally accessible conditions.     

Spin crossover: the quantum phase transition induced by high pressure

The relationship is established between the Berry phase and spin crossover in condensed matter physics induced by high pressure. It is shown that the geometric phase has topological origin and can be considered as the order parameter for such transition.     

Characterizing quantum phase transition by teleportation

In this paper we provide a novel way to explore the relation between quantum teleportation and quantum phase transition. We construct a quantum channel with a mixed state which is made from one dimensional quantum Ising chain with infinite length, and then consider the teleportation with the use of entangled Werner states as input qubits. The fidelity as a figure of merit to measure how well the quantum state is transferred is studied numerically. Remarkably we find the first-order derivative of the fidelity with respect to the parameter in quantum Ising chain exhibits a logarithmic divergence at the quantum critical point. The implications of this phenomenon and possible applications are also briefly discussed.     

Optically induced phase transition of excitons in coupled quantum dots

The weak classical light excitations in many semiconductor quantum dots have been chosen as important solid- state quantum systems for processing quantum information and implementing quantum computing. For strong classical light we predict theoretically a novel phase transition as a function of magnitude of this classical light from the deformed to the normal phases in resonance ease, and the essential features of criticality such as the scaling behaviour, critical exponent and universality are also present in this paper.     

The excitonic insulator route through a dynamical phase transition induced by an optical pulse

We consider a dynamical phase transition induced by a short optical pulse in a system prone to thermodynamical instability. We address the case of pumping to excitons whose density contributes directly to the order parameter. To describe both thermodynamic and dynamic effects on equal footing, we adopt a view of the excitonic insulator for the phase transition and suggest a formation of the Bose condensate for the pumped excitons. The work is motivated by experiments in donor–acceptor organic compounds with a neutral- ionic phase transition coupled to the spontaneous lattice dimerization and to charge transfer excitons. The double nature of the ensemble of excitons leads to an intricate time evolution, in particular, to macroscopic quantum oscillations from the interference between the Bose condensate of excitons and the ground state of the excitonic insulator. The coupling of excitons and the order parameter also leads to self-trapping of their wave function, akin to self-focusing in optics. The locally enhanced density of excitons can surpass a critical value to trigger the phase transformation, even if the mean density is below the required threshold. The system is stratified in domains that evolve through dynamical phase transitions and sequences of merging. The new circumstances in experiments and theory bring to life, once again, some remarkable inventions made by L.V. Keldysh.     

Geometric phase induced by quantum nonlocality

By analyzing an instructive example, for testing many concepts and approaches in quantum mechanics, of a one-dimensional quantum problem with moving infinite square-well, we define geometric phase of the physical system. We find that there exist three dynamical phases from the energy, the momentum and local change in spatial boundary condition respectively, which is different from the conventional computation of geometric phase. The results show that the geometric phase can fully describe the nonlocal character of quantum behavior.     

Dynamics of a quantum phase transition

We present two approaches to the dynamics of a quench-induced phase transition in the quantum Ising model. One follows the standard treatment of thermodynamic second order phase transitions but applies it to the quantum phase transitions. The other approach is quantum, and uses Landau-Zener formula for transition probabilities in avoided level crossings. We show that predictions of the two approaches of how the density of defects scales with the quench rate are compatible, and discuss the ensuing insights into the dynamics of quantum phase transitions.     

Disorder induced quantum phase transition in random-exchange spin-1/2 chains

We investigate the effect of quenched bond disorder on the anisotropic antiferromagnetic spin-1/2 (XXZ) chain as a model for disorder-induced quantum phase transitions. We find nonuniversal behavior of the average correlation functions for weak disorder, followed by a quantum phase transition into a strongly disordered phase with only short-range xy correlations. We find no evidence for the universal strong-disorder fixed point predicted by the real-space renormalization group, suggesting a qualitatively different view of the relationship between quantum fluctuations and disorder.