【作者】 李芳；

【导师】 侯喜文；

【作者基本信息】 华中师范大学 ， 原子与分子物理， 2021， 硕士

【摘要】 量子相干和量子纠缠是量子物理中的两个重要特性,二者关系密切,它们在量子技术中扮演者重要的角色,如:量子通讯、量子加密、超密编码。在这篇论文里,我们分别研究了两种三量子比特XXZ模型的热相干和热纠缠,其中热相干用量子相对熵和l1 norm相干性来描述,纠缠用负性的两种平均量度来描述,探究这两种模型的热相干和纠缠特性,讨论它们之间的联系,比较它们的差异。首先,我们介绍了量子相干和量子纠缠的研究进展和它们的一些定义。然后,我们分别计算了线性和非线性三量子比特XXZ模型的热量子态,研究不同的温度,粒子耦合参数,以及磁场强度对量子相对熵(C1),l1 norm相干性(C2),以及纠缠负性的两种平均量度(N1)和(N2)的影响。结果表明:两种相干性量度具有一致的行为,说明它们都能很好地描述量子态的相干性。两种纠缠量度也具有一致的行为。在线性和非线性三比特模型中,相干性和负性呈现了一些类似的行为:当磁场强度增大时,或随着温度的升高,相干性和负性都趋于零;温度接近于零度时,随着磁场强度的变化,它们都会存在基态的跃迁;温度继续升高,相干性和负性的最大值减小,这说明高温破坏量子相干性和量子关联。但是,随着温度的增加,零负性在弱耦合的区域越来越大。在线性模型中,C1与C2的等级关系是不确定的,N1和N2的值有较小的差别。在非线性模型中,相干性的最大值满足C1<C2,而N1和N2的值是相同的。此外,存在量子相干性的参数范围比纠缠负性的范围要广。因此,我们可以得到,有量子纠缠,一定有量子相干性。但有量子相干性,不一定有量子纠缠。总之,我们探讨了两种模型的热量子相干性和负性,我们可以通过改变温度,耦合参数,以及磁场强度来调节热量子态的相干性和纠缠。这些能激发人们深入研究其它模型的量子相干性和纠缠。更多还原

【Abstract】 Quantum coherence and quantum entanglement are two important properties in quantum physics,and they are closely related.They play an important role in quantum technology,such as quantum communication,quantum encryption and superdense coding.In this paper,We study the thermal coherence and thermal entanglement of two kind of three qubits models,thermal coherence is described by quantum relative entropy and l1 normcoherence,entanglement is described as two average measures of negativeness,the thermal coherence and entanglement characteristics of the two models are explored,the relationship between them is discussed,and their differences are compared.Firstly,we introduce the research progress of quantum coherence and quantum entanglement and some of their definitions.Then,we calculate the quantum thermal states of linear and nonlinear three-qubit models respectively,and study the effects of different temperature,coupling parameters,and magnetic field strengths on the quantum relative entropy(C1)and l1 norm coherence(C2),as well as the two average measures of entanglement negativity(N1)和(N2).The results show that two coherence measures exhibit the same behavior,indicating that both measures are well to describe the coherence of quantum states.Two entanglement measures also exhibit the same behavior.In linear and nonlinear three-qubit models,coherence and negativity display some similar behaviors.For example,when the magnetic field intensity increases,or temperature increases,coherence and negativity tend to zero.If temperature is close to zero,with the change of magnetic field intensity,they all have the ground state transition.As temperature continues to increase,the maximum values of coherence and negativity decrease,indicating that high temperature destroys quantum coherence and correlation.However,as temperature increases,the region of zero negativity becomes larger and larger in the weak coupling.In the linear model,the hierarchy between C1 and C2 cannot be constructed,and the values of N1 and N2 have little difference.In the nonlinear model,the maximum value of coherence satisfies C1<C2,while the values of N1 and N2 are identical.In addition,the region of model parameters for the existence of quantum coherence is wider than that of entanglement negativity.Thus,we can conclude that if a quantum state is entanglement,it must be quantum coherence.However,the state that is quantum coherence is not entanglement.In summary,we have discussed quantum coherence and negativity of two three-qubit models,which can be adjusted by changing temperature,coupling parameters,and magnetic fields.We expect these could inspire the further investigation of quantum coherence and entanglement in other models.更多还原