共查询到20条相似文献,搜索用时 78 毫秒
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在非绝热近似下,研究了一维spin-Peierls系统中晶格量子涨落 对系统性质的影响,讨论了系统的二聚化相变、单粒子激发和双粒子束缚态. 结果表明,量子晶格涨落会抑制晶格的二聚化,破坏系统的spin-Peierls基态稳定性.在临界点,系统发生从二聚化spin-Peierls态向无能隙态的相变. 自旋声子耦合强度对束缚态能隙的影响比单粒子激发谱能隙显著.
关键词:
sin-Peierls系统
非绝热近似
玻色化
相图 相似文献
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针对Co(S1-xSex)2系统在x=0.11附近发生的铁磁金属到顺磁金属相变,制备了一系列不同Se替代浓度的多晶样品.通过对其结构和电阻率-温度ρ(T)关系的系统观测,结果发现,样品铁磁相变温度TC随着Se替代浓度x值的增加,以(1-x)1/2关系单调下降,其二级铁磁相变转变为一级相变;在临界浓度x=0.11附近,其ρ(T)关系由Fermi液体行为转变为非Fermi液体行为.作者认为,Co(S1-xSex)2系统在x=0.11附近发生的是一种量子相变,在该量子相变点附近零温度下的自旋量子涨落导致其ρ(T)关系的反常行为. 相似文献
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提出了一种利用原子系统的关联相位涨落调控量子干涉的方法。原子之间的碰撞以及原子与外界热库的耦合会导致原子能级产生随机的相位涨落。研究了不同能级的相位涨落的强度和他们之间的关联对原子相干性和量子干涉的影响。结果表明,正关联相位涨落可以增强相消量子干涉(探针光的吸收减弱),而反关联相位涨落可以增强相长量子干涉(吸收增强)。在特定条件下量子干涉消失,原子对探针光的响应由Autler-Townes分裂决定。最后,研究了耦合光Rabi频率对量子干涉的影响。当耦合光较弱时,可以利用原子能级的关联相位涨落有效地调控量子干涉;当耦合光很强时,量子干涉非常弱,可以被忽略。 相似文献
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基于电荷量子化的事实,运用最小平移算符Q∧的性质等,计算对应的相干态下介观金属环中电荷、电流及能量的量子涨落,研究影响量子涨落的因素.结果表明:计及电荷的离散性,在相干态下介观金属环中电荷、能量的量子涨落不为零,分别与电荷量子、相干态参量等因素有关;此外,能量的量子涨落还决定于金属环的电感、外磁通及其时间变化率的大小. 相似文献
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本文研究单模光场中N个二能级原子Dicke模型的有限温度特性和相变. 把原子赝自旋转换为双模费米算符, 用虚时路径积分方法推导出系统的配分函数, 对作用量变分求极值得到系统的热力学平衡方程, 及原子布居数期待值和平均光子数随原子-光场耦合强度变化的解析表达式. 重点研究了在量子涨落起主导作用的低温区, 由耦合强度变化产生的从正常相到超辐射相的相变, 指出该相变遵从Landau连续相变理论, 平均光子数可作为序参数, 零值表示正常相, 大于零则为超辐射相. 在零温极限下本文的结果和量子相变理论完全符合. 另外, 本文也讨论了系统的热力学性质, 比较有限温度相变和量子相变的异同. 发现, 在强耦合区低温稳定态的光子数和平均能量都和绝对零度的值趋于一致, 而超辐射相的熵则随耦合强度的增强迅速衰减为零. 相似文献
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针对介观电子谐振腔模型,在由电荷算符本征态构成的新Fock空间中,假设系统具有变换的对称性,通过求解Hamilton算符的本征值方程,给出系统的量子能谱关系.在电荷算符的Fock态下计算能量的量子涨落,分析和研究电子谐振腔的量子能谱性质.结果表明:类似于电荷的量子性,能谱明显地呈现出离散性,其大小决定于谐振腔的电参量、形状因子及栅极所加偏压等因素;而能量的量子涨落却仅与电荷量子、Planck常数以及系统自感有关. 相似文献
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Hong-Wei Li Yi-Bo Zhao Zhen-Qiang Yin Shuang Wang Zheng-Fu Han Wan-Su Bao Guang-Can Guo 《Optics Communications》2009,282(20):2533-0389
The number of transmitted signals in practical quantum key distribution (QKD) protocol is always finite. We discuss the security of decoy states QKD protocol with finite resources by considering the statistical fluctuation for the yield and error rate of the quantum state in different sources of pulses (signal sources and decoy sources). The number of exchanged quantum signals vs positive key generation rate is given with experiment results. 相似文献
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The very notion of a current fluctuation is problematic in the quantum context. We study that problem in the context of nonequilibrium
statistical mechanics, both in a microscopic setup and in a Markovian model. Our answer is based on a rigorous result that
relates the weak coupling limit of fluctuations of reservoir observables under a global unitary evolution with the statistics
of the so-called quantum trajectories. These quantum trajectories are frequently considered in the context of quantum optics,
but they remain useful for more general nonequilibrium systems. In contrast with the approaches found in the literature, we
do not assume that the system is continuously monitored. Instead, our starting point is a relatively realistic unitary dynamics
of the full system 相似文献
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基于相位调制偏振态QKD系统的量子信道校正发送方案 总被引:4,自引:1,他引:3
提出了一种基于相位调制偏振态QKD系统的量子信道校正发送的新方案—采用波导型相位调制器研制成电控连续可调光学相移器,它可随相位调制器输入电压的连续改变而产生连续的相移,从而控制输出的偏振态;在其前放置一个半波片,即可校正接收端偏振态量子态在信道中所发生的改变,从而保证信道传送密钥的可用性.通过理论推导和实验研究验证了基于相位调制偏振态QKD系统的量子信道校正发送方案的核心部件的可行性.由于本方案能实现高速调制(GHz),为解决光纤传输的偏振编码QKD系统中偏振态漂移问题提供了一种新的途径. 相似文献
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Out‐of‐Equilibrium Fluctuation‐Dissipation Relations Verified by the Electrical and Thermoelectrical AC‐Conductances in a Quantum Dot 下载免费PDF全文
Adeline Crépieux 《Annalen der Physik》2017,529(9)
The electrical and heat currents flowing through a quantum dot are calculated in the presence of a time‐modulated gate voltage with the help of the out‐of‐equilibrium Green function technique. From the first harmonics of the currents, we extract the electrical and thermoelectrical trans‐admittances and ac‐conductances. Next, by a careful comparison of the ac‐conductances with the finite‐frequency electrical and mixed electrical‐heat noises, we establish the fluctuation‐dissipation relations linking these quantities, which are thus generalized out‐of‐equilibrium for a quantum system. It is shown that the electrical ac‐conductance associated to the displacement current is directly linked to the electrical noise summed over reservoirs, whereas the relation between the thermoelectrical ac‐conductance and the mixed noise contains an additional term proportional to the energy step that the electrons must overcome when traveling through the junction. A numerical study reveals however that a fluctuation‐dissipation relation involving a single reservoir applies for both electrical and thermoelectrical ac‐conductances when the frequency dominates over the other characteristic energies. 相似文献
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《Physics letters. A》2020,384(25):126601
We investigate the quantum thermodynamical properties of localised relativistic quantum fields, and how they can be used as quantum thermal machines. We study the efficiency and power of energy transfer between the classical gravitational degrees of freedom, such as the energy input due to the motion of boundaries or an impinging gravitational wave, and the excitations of a confined quantum field. We find that the efficiency of energy transfer depends dramatically on the input initial state of the system. Furthermore, we investigate the ability of the system to extract energy from a gravitational wave and store it in a battery. This process is inefficient in optical cavities but is significantly enhanced when employing trapped Bose Einstein condensates. We also employ standard fluctuation results to obtain the work probability distribution, which allows us to understand how the efficiency is related to the dissipation of work. Finally, we apply our techniques to a setup where an impinging gravitational wave excites the phononic modes of a Bose Einstein condensate. We find that, in this case, the percentage of energy transferred to the phonons approaches unity after a suitable amount of time. These results give a quantitative insight into the thermodynamic behaviour of relativistic quantum fields confined in cavities. 相似文献
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The size dispersion and distributions of quantum dot nanoparticles (sizes from 2–5 nm) embedded in the active region of the intermediate band solar cells are important to reach the high efficiencies. An optimized size and regularity can increase the efficiency due largely to avoided non-radiative transitions which can originate from the fluctuations in the bandwidth of the intermediate layer. In this work, we propose all the energy band diagrams possible in the formation of such a cell. Five equivalent band diagrams of the cells with different size dispersions and regularity of quantum dots are considered and compared with the reported experimental profiles in the literature. Furthermore, the degree of the size fluctuation is considered by proposing a fluctuation degree for the band gap and sub-band gaps of the cell. These proposed profiles and the fluctuation theory are exploited to consider the experimental data reported in literature. The optimized size dispersion will increase the photocurrent of the cell. We believe that every quantum dot solar cell will fall into one of the proposed band diagrams. This approach gives foresight to the theoretical studies of such devices and expectation from the energy band structure and band widths since it considers the fluctuation of the band widths for the intermediate band separately. 相似文献
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On the basis of the existence of second and third moments of fluctuations, we prove a theorem about the Lie-algebraic structure
of fluctuation operators. This result gives insight into the quantum character of fluctuations. We illustrate the presence
of a Lie algebra of fluctuation operators in a model of the anharmonic crystal, and show the dependence of the Lie-algebra
structure on the fine structure of the fluctuation operator algebra. The result is also applied to construct the normal Goldstone
mode in the ideal Bose gas for Bose-Einstein condensation 相似文献
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马尔科夫量子主方程的确立将近半个世纪,它们经常被用于不可逆热力学的研究。然而,在
过去相当长的一段时间里,这些研究几乎只关注了系综平均的结果,量子系统的随机热力学一直未
受到重视。由于过去二十年里各种经典和量子涨落定理的发现,这种状况才有了明显地改变。在本
文中,我们采用两种不同的策略系统总结了当前对马尔科夫量子主方程的随机的热和功的理解。策
略之一是把量子系统和其周围的热库当成是一个封闭的量子系统,在含时总哈密顿量的控制下,这
个系统发生幺正演化,对该复合系统做两次能量投影测量得到的能量本征值之差被定义为热和功。
另一种策略是首先把量子主方程分解成随机的量子跳跃轨迹,然后在轨迹上定义随机的热和功。我
们以尽可能详尽的方式介绍这些重要的物理概念、数学技术以及不同描述层次的涨落定理。我们也
用模型具体地说明这些结论。 相似文献
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Atomistic Green function simulations of model 25 nm×25 nm Si MOSFETs predict strong fluctuation effects derived from mode fluctuations in the quantum transport through the inhomogeneous 2DEG channel caused by the spatial distribution of non-self-averaged discrete dopants. 相似文献