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两组份纠缠态光场是量子信息和量子计算的基本资源,随着研究的深入发展,为了完成更高效的量子信息处理,必须首先获得高纠缠度的两组份纠缠态光场。而通过操控实现纠缠光场纠缠度增加是目前提高纠缠光场质量的一个行之有效的办法。相干反馈控制由于不会带入额外噪声至光学参量系统的特点已经被实验证明可以用于压缩态光场压缩度的增强。理论计算增加了相干反馈系统的非简并光学参量放大器输出的两组份纠缠态光场的量子关联噪声与各系统参数的关系,并详细分析了各参数对相干反馈纠缠增强的影响,为进一步获得更高纠缠度的两组份纠缠态光场提供参考。 相似文献
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量子纠缠是执行量子计算和构建量子通信网络的关键资源,制备与操控纠缠态光场是实现量子信息处理的基础要素.本文提出了利用双端光学腔倍频产生四组份纠缠态的理论模型,从耦合波方程出发得到Ⅱ类倍频过程的传输矩阵,通过腔内自再现方程和输入输出传输矩阵理论研究了输出的两束倍频光的噪声特性;对于两束倍频光和两束基频泵浦场,利用多组份纠缠光场的充分必要判据PPT方法 (positivity under partial transposition criterion)分析了最小辛本征值与泵浦功率及分析频率之间的关系,研究结果表明基频泵浦光与倍频光之间存在四组份纠缠. 相似文献
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量子纠缠态是开展量子信息工作的核心资源。提出在一块光学超晶格中通过有注入信号的非简并光学参量振荡级联一个和频过程,可以产生不同频率的四组份连续变量纠缠态光场的可行实验方案。首先泵浦光和注入信号光通过差频过程产生闲置光。然后泵浦光和闲置光在同一块光学超晶格中通过级联和频过程产生和频光。根据多组份连续变量纠缠的判定方法,从理论上证明泵浦光、信号光、闲置光与和频光场之间的量子纠缠特性。四组份纠缠特性随泵浦功率的增大而减弱,另外选取较大的注入信号功率、级联非线性过程的耦合参数和泵浦光衰减常数可以得到较好的四组份纠缠光场。该实验方案只用到一块光学超晶格就可以产生四色连续变量纠缠态光场,实验装置简单。 相似文献
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非简并光学参量放大器产生的纠缠态光场是连续变量量子信息科学研究的重要资源。随着量子网络及量子计算的发展,需要更多组份纠缠态光场来完成对更复杂的量子信息的研究。一般的多组份纠缠态光场是将多个压缩态光场或者Einstein-Podolsky-Rosen(EPR)纠缠态光场通过不同的分束器阵列耦合而成,需要同时制备多个经典相干的EPR纠缠态光场。采用带楔角的非线性晶体,使非简并光学参量放大器的振荡阈值从原来的250mW降低至45mW,当注入腔内抽运光功率为23mW时,依然可以得到正交振幅及相位分量关联噪声分别低于量子噪声极限5.5dB的EPR纠缠态光场。在此基础上,可以使用一台激光器同时抽运多个非简并光学参量放大器来获得所希望的多组份纠缠态光场。 相似文献
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以一对工作在参量反放大状态的非简并光学参量放大器同时产生的两个正交振幅压缩相干态与两个正交位相压缩真空态光场为基础,经过不同位相关系的线性光学变换,可获得四组份纠缠态光场。我们将介绍实验原理和初步试验结果。 相似文献
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多组份纠缠是量子信息处理的重要资源,它的产生通常涉及到许多复杂的线性和非线性过程.本文从理论上提出了一种利用两个独立的四波混频过程和线性分束器产生真正的四组份纠缠的方案,其中,线性分束器的作用是将两个独立的四波混频过程联系起来.首先应用部分转置正定判据研究了强度增益对四组份纠缠的影响,结果表明,在整个增益区域内都存在真正的四组份纠缠,并且随着强度增益的增加,纠缠也在增强.然后研究了线性分束器的透射率对四组份纠缠的影响,发现只要线性分束器的透射率不为0或1,该系统也可以产生真正的四组份纠缠.最后,通过研究该系统可能存在的三组份纠缠和两组份纠缠来揭示该系统的纠缠结构.本文理论结果为实验上利用原子系综四波混频过程产生真正的四组份纠缠提供了可靠的方案. 相似文献
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It is impossible to perfectly duplicate an unknown entangled state while preserving inseparability, which is known as the entanglement no-cloning principle. Nevertheless, approximate cloning of entanglement is allowed by quantum mechanics. A universal entanglement cloning machine (UECM) duplicates an entangled state such that the quality of its entanglement replicas does not depend on the input. To duplicate entanglement shared between two parties, 1-to-N universal local entanglement cloning machine (ULECM) has already been proposed (Weedbrook, et al., Phys. Rev. A, 77, 052313 (2008)), which employs two local UECMs to copy each party of the entangled state. However, the ULECM can never preserve the inseparability in its replicas. Here, a 1-to-N universal global entanglement cloning machine (UGECM) that takes the entire entangled state as the input and then globally clone it to produce replicas is proposed. It is demonstrated that the UGECM outperforms the ULECM both in terms of the fidelity and the inseparability preservation. In addition, the UGECM is of more simple and easy structure, compared with the UGECM. Such a UGECM may find its new applications in quantum entanglement broadcasting. 相似文献
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Quantum metrology overcomes standard precision limits and has the potential to play a key role in quantum sensing. Quantum mechanics, through the Heisenberg uncertainty principle, imposes limits on the precision of measurements. Conventional bounds to the measurement precision such as the shot noise limit are not as fundamental as the Heisenberg limits, and can be beaten with quantum strategies that employ ‘quantum tricks’ such as squeezing and entanglement. Bipartite entangled quantum states with a positive partial transpose (PPT), i.e., PPT entangled states, are usually considered to be too weakly entangled for applications. Since no pure entanglement can be distilled from them, they are also called bound entangled states. We provide strategies, using which multipartite quantum states that have a positive partial transpose with respect to all bi-partitions of the particles can still outperform separable states in linear interferometers. 相似文献
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Quantum entanglement between two field modes can be achieved through the collective squeezing of the two respective modes. If single-mode squeezing is performed prior to such a two-mode squeezing, an enhancement of entanglement production can happen. Interestingly, the occurrence of this enhancement can be implicitly linked to the local classical dynamical behavior via the paradigm of quantum–classical correspondence. In particular, the entanglement generated through quantum chaos is found to be hardly enhanced by prior squeezing, since it is bounded by the saturation value of the maximally entangled Schmidt state with fixed energy. These results illustrate that entanglement enhancement via initial squeezing can serve as a useful indicator of quantum chaotic behaviour. 相似文献
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Effect of excess noise on continuous variable entanglement sudden death and Gaussian quantum discord 下载免费PDF全文
A symmetric two-mode Gaussian entangled state is used to investigate the effect of excess noise on entanglement sudden death and Gaussian quantum discord with continuous variables. The results show that the excess noise in the channel can lead to entanglement sudden death of a symmetric two-mode Gaussian entangled state, while Gaussian quantum discord never vanishes. As a practical application, the security of a quantum key distribution (QKD) scheme based on a symmetric two-mode Gaussian entangled state against collective Gaussian attacks is analyzed. The calculation results show that the secret key cannot be distilled when entanglement vanishes and only quantum discord exists in such a QKD scheme. 相似文献
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基于单-双模组合压缩真空态一定范围内能够获得压缩增强的效果,引入单-双模组合压缩热态(DSMST),讨论其纠缠性质.利用Weyl编序算符在相似变换下的不变性,简洁方便地导出了DSMST的纠缠度-负对数值,并给出了当热效应存在时保持纠缠的条件.研究表明:与通常的双模压缩态相比,随着参数的增加,DSMST的纠缠度增加.作为DSMST的应用,利用其实现相干态的量子隐形传输.结果表明:不同于纠缠度随压缩参数增加,保真度获得改善是有条件的,该条件恰好就是一正交分量涨落出现压缩增强的参数区域.此外,解析推导了有效隐形传输保真度(1/2)的条件. 相似文献
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双模纠缠态是量子信息领域一种重要的量子资源,本文基于四波混频过程从理论上提出了对双模纠缠态的单个模式(单模放大方案)和对双模纠缠态的两个模式(双模放大方案)的放大.利用光学分束器模型来模拟在光学传输过程中损耗引入的真空场噪声,利用部分转置正定判据分析了两种不同的放大方案中四波混频过程的增益对初始双模纠缠态的纠缠程度的影响.结果表明,在特定的损耗情况下,两个方案中初始双模纠缠态的纠缠度都随增益的增大而减小,直至消失,且双模放大方案中初始双模纠缠态纠缠消失得比单模放大方案中更快.本文的理论结果为实验上实现基于四波混频过程的双模纠缠态的放大奠定了理论基础. 相似文献
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We analyze the entanglement characteristics of three harmonic modes,which are the output fields from three cavities with an input tripartite entangled state at fundamental frequency.The entanglement properties of the input beams can be maintained after their frequencies have been up-converted by the process of second harmonic generation.We have calculated the parametric dependences of the correlation spectrum on the initial squeezing factor,the pump power,the transmission coefficient,and the normalized analysis frequency of cavity.The numerical results provide references to choose proper experimental parameters for designing the experiment.The frequency conversion of the multipartite entangled state can also be applied to a quantum communication network. 相似文献