与腔场耦合的两个量子点中激子的纠缠动力学

利用共生纠缠度研究了单模腔场内两个耦合量子点中激子的纠缠动力学行为.结果表明:无论腔场初始制备于奇相干态还是偶相干态,两个量子点间直接耦合作用均能减弱激子的纠缠度.在腔场初始为奇相干态时,激子的纠缠度随场模强度的增加而减小;偶相干态时,激子的纠缠度呈现一个转折变化.此外,也研究了单模腔场内平均光子数与激子准最大相干纠缠态的关联.     

用W态实现量子隐形传态的腔QED方案

本文提出一个用类W态作为纠缠通道,采用不同于文献[19]的测量基来实现量子隐形传态的腔QED方案.在这个方案里,只需要利用原子和腔场通过J-C哈密顿量发生共振相互作用,一步就可制备纠缠通道.另外,通过原子与腔场的失谐作用,利用Bell态测量,可实现概率为100%的量子隐形传态.在目前的腔QED技术条件下,该方案是可以实现的.     

运动双原子与光场依赖强度耦合系统中的纠缠操纵与量子态制备

将Tavis-Cummings模型推广到同时考虑原子运动及与光场依赖强度耦合的情况.运用原子约化熵和Concurrence操纵了该系统在真空场、弱相干场和强相干场条件下,双原子-场之间以及双原子之间纠缠演化特性.以此为依据,选择双原子与场相互作用时间、选取双原子纠缠因子、调节场模结构参数,控制系统纯态概率幅和选择测量,制备了双原子-场W类态、双原子Bell态、Bell态原子保真态、光场的单光子态、双光子态及稳定的数态.实现了双原子Bell态突然产生及有限时间内的保持、Bell态原子周期量子回声的形成及其信息(态)持续保真.结果表明,该系统具有强大的量子信息功能,为量子信息处理的实验实现提供了物理载体和理论参数.     

远程制备双原子纠缠态

提出一种远程制备双原子纠缠态的方案,该方案基于两个原子与单模腔场的同时非共振相互作用.由于双粒子纠缠态比三粒子纠缠态容易制备,方案用两对双原子纠缠态作为量子通道.Alice 拥有的两个相同原子同时与一单模腔场非共振相互作用.Alice已知她要制备的纠缠态,她选择适当的相互作用时间、测量她所拥有的两个原子并通过经典通道通知Bob.Bob引入一个相同的辅助原子和一个单模腔场来实现方案.方案对腔场状态和腔损耗不敏感,基于当前的腔QED 技术,方案能在实验上实现.该方案有望在量子信息过程中有重要的应用价值.     

利用三原子W类纠缠态在腔量子电动力学体系中实现单原子态的远程制备

提出了两个利用三原子W类纠缠态作为量子通道.在腔量子电动力学(QED)体系中实现单原子态的远程制备方案:一个是接收者借助于原子与单模腔场之间的大失谐相互作用实现初始态重建,另一个则是接受者利用原子与单模腔场之间的共振相互作用完成远程态制备.两方案中都涉及到了一位发送者和两位接收者,发送者可以将被传送态远程制备到两位接收者中的任何一位的手中,而另一位接受者必须为其提供必要的协助.表明利用原子与腔场之间的大失谐相互作用的方法可以很好地克服腔场的消相干,降低对腔品质因子的要求;而利用共振相互作用的方法则无需引入辅助原子,操作简便.但不论采用何种方法,实现单原子远程态制备的总成功概率是相同的.     

利用Λ型原子与双模腔场的相互作用进行量子信息处理

利用Λ型三能级原子与一个两模腔场在两光子共振和单光子大失谐条件下的相互作用模型，给出了制备两个和三个远距离的腔场的纠缠态和如何实现一个量子比特的原子态的远距离转移、纠缠态的转移的方案；同时找到了一种不用进行Bell基测量而实现纠缠交换的方法；构造了实现量子交换门的操作.最后对实验的可行性进行了分析. 关键词： 量子信息处理 Λ型原子 双模腔场 相互作用     

利用V-型三能级原子与双模腔场的共振相互作用制备纠缠W态

提出了一种利用V-型三能级原子与双模腔场的共振相互作用制备多原子及多腔场纠缠W态的新方案,并用共生纠缠度研究了该模型中的纠缠演化和热纠缠现象.     

通过Raman相互作用制备三个腔场的W型纠缠相干态

通过对比分立变量量子信息过程和连续变量量子信息过程的差别,利用相干态比较容易获得的这个特点,提出一种方案制备三个腔场的W型纠缠相干态.方案基于Λ型三能级原子与单模腔场的简并Raman 相互作用.三个相同的腔初始分别处于相干态,三个相同的原子初始处于W型纠缠态,通过三个原子分别与三个腔的Raman相互作用、选择适当的相互作用时间并探测作用后的三个原子,三个腔场坍缩为W型纠缠相干态.在原子与腔的相互作用过程中原子不处于高能级,可以忽略原子的自发辐射,系统的相干性能够得到较好的维持.基于当前的腔量子电动力学技术,相信方案能在实验上实现.该方案制备的三个腔场W型纠缠相干态有望在连续变量量子信息过程中有重要的应用价值.文中将方案推广到制备n(n〉3)个腔场的W型纠缠相干态.     

与压缩真空库耦合的单模腔内三量子点中激子纠缠

研究了与压缩真空库场耦合的单模腔中三个量子点中激子间纠缠的动力学行为.结果表明：如果不考虑腔模与激子吸收，激子演化为纯的纠缠态.当腔场与一压缩真空库耦合时，激子间形成混合三模高斯纠缠态；在长时极限下，激子态为一稳定的混合三模高斯纠缠态.通过求解激子的特征函数，发现激子态的纯度与纠缠不仅依赖于腔场的初态，并且还与库的双光子关联强度密切相关. 关键词： 纠缠 纯度 压缩真空库 量子点     

V-型三能级原子与双模腔场模型中的纠缠交换方案

文章利用V-型三能级原子与双模腔场双光子共振相互作用,提出了一种纠缠交换的方案制备最大纠缠态,此方案不需要Bell基测量,只需对单个原子进行测量,就能实现初始没有直接相互作用的原子与腔场之间产生纠缠,合适选择原子与腔场之间的相互作用时间可获得具有最大保真度以及成功几率的最大纠缠态,另外,还讨论了该方案的实验可行性.     

Digraph states and their neural network representations

With the rapid development of machine learning, artificial neural networks provide a powerful tool to represent or approximate many-body quantum states. It was proved that every graph state can be generated by a neural network. Here, we introduce digraph states and explore their neural network representations (NNRs). Based on some discussions about digraph states and neural network quantum states (NNQSs), we construct explicitly an NNR for any digraph state, implying every digraph state is an NNQS. The obtained results will provide a theoretical foundation for solving the quantum many-body problem with machine learning method whenever the wave-function is known as an unknown digraph state or it can be approximated by digraph states.     

The simplex structure of the classical states of the quantum harmonic oscillator

It is shown that the convex set of classical states of the quantum harmonic oscillator is a simplex generated as the closed convex hull of the coherent states in the weak topology of the Banach space of trace class operators.     

非Lamb-Dicke近似下制备囚禁冷离子的振动相干态

根据非Lamb-Dicke近似下激光-离子相互作用动力学规律,讨论了如何利用一系列的激光脉冲来驱动冷离子,从而从运动基态出发获得一系列振动数态的宏观叠加态.具体研究了这些叠加态的Q函数、Wigner函数和它们的非经典特性,如压缩和反群聚效应等.结果表明,合适地调节各个所用激光的脉冲长度,所产生的叠加态能很好地逼近熟知的振动相干态. 关键词： Lamb-Dicke近似 叠加态 相干态 非经典特性     

Squeezed states of light as self-similar structures

A new approach to investigating a broad class of dynamic states for a quantum oscillator is suggested. It is based on an invariant transformation of the equation to a new time determined by the quantum dispersion of the corresponding state. The squeezed states of a quantum system generated by the ground-state wave function are constructed. In coordinate representation, these states are described by a self-similar wave function localized near a classical trajectory. The statistics of the squeezed state of light is analyzed in the single-mode approximation. The parametric excitation of squeezed states for a quantum harmonic oscillator is considered.     

Quantum Communication in Spin Chain with Multiple Spin Exchange Interaction

The transmission of quantum states in the anisotropic Heisenberg XXZ chain model with three-spin exchange interaction is studied. The average fidelity is used to evaluate the state transfer. It is found that quantum communication can be enhanced by the anisotropic coupling and multiple spin interaction. Such spin model can reduce the time required for the perfect state transmission where the fidelity is unity. The maximally entangled Bell states can be generated and separated from the whole quantum systems.     

A logical explanation for quarks

We construct a quantum logic which generates the usual quark states. It follows from this model that quarks can combine only in quark-antiquark pairs and quark (and antiquark) triples. The ground meson and baryon states are also generated and gluons are discussed.     

Dynamical violation of the superposition principle for open quantum systems

It is argued that the impossibility of observing coherent superpositions of certain macroscopically distinguishable quantum states is a combined effect of collective dissipation processes generated by an interaction of the N-particle system with external quantum fields and a “coarse-grained” character of real measurements. A simple model involving a quantum dynamical semigroup is discussed.     

Single-particle Entanglement and Its Application to Quantum Information Processing

Single-particle entanglement refers to entanglement produced with a single particle. It can be generated by illuminating a beam splitter with a single photon. We describe experimental schemes to realize quantum teleportation and quantum key distribution utilizing single-particle entanglement, and discuss the strengths and drawbacks of the schemes compared with the standard scheme utilizing two-photon polarization states. We show, in particular, that the quantum key distribution scheme based on single-particle entanglement is associated with a relatively high value of the bits of information transferred per particle sent and can thus be cost effective.     

Quasibound states in graphene quantum-dot nanostructures generated by concentric potential barrier rings

We study the quasibound states in a graphene quantum-dot structure generated by the single-, double-, and triple-barrier electrostatic potentials. It is shown that the strongest quasibound states are mainly determined by the innermost barrier. Specifically, the positions of the quasibound states are determined by the barrier height, the number of the quasibound states is determined by the quantum-dot radius and the angular momentum, and the localization degree of the quasibound states is influenced by the width of the innermost barrier, as well as the outside barriers. Furthermore, according to the study on the double- and triple-barrier quantum dots, we find that an effective way to generate more quasibound states with even larger energy level spacings is to design a quantum dot defined by many concentric barriers with larger barrier-height differences. Last, we extend our results into the quantum dot of many barriers, which gives a complete picture about the formation of the quasibound states in the kind of graphene quantum dot created by many concentric potential barrier rings.     

PREPARATION OF NONCLASSICAL STATES OF A CAVITY FIELD BASED ON A NONLINEAR JAYNES-CUMMINGS MODEL

It is proven in this paper that some kinds of nonclassical quantum states of the cavity field, such as Schr?dinger cat state (amplitude cat or phase cat), sub-Poissonian photon distribution and Fock state, etc., can be generated by conditional meas urements on atoms in the two-photon Jaynes-Cummings model with a Kerr-like medium. The nonlinear constant plays the key modulation role in the preparation of the quantum states, which gives a new controllable parameter for further experi mental researches in this field.