共查询到20条相似文献,搜索用时 93 毫秒
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运用量子态变换的方法论证了两个qubit纯态中量子关联与纠缠的等价性.并利用三种带有横场的非线性相互作用模型研究了两个qubit体系中的量子关联.发现合适的横场对于最大量子关联态的获得、平均量子关联的提高都有着积极的作用.两个qubit体系获得最大量子关联时,不同模型,不同的横场,对应的量子态却各不相同. 相似文献
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利用Jaynes-Cummings模型,考虑场频率受微扰的情况,在旋波近似下研究了二能级原子与单模辐射场相互作用系统中量子态保真度的演化.利用数值计算方法给出量子态保真度随时间的演化曲线.研究了场频率随时间正弦函数形式变化对系统、光场和原子的量子态保真度演化的影响.结果表明:场频率随时间正弦函数形式变化对系统和光场的量子态保真度的演化的影响很小,但对原子的量子态保真度的演化有显著影响. 相似文献
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利用多光子J-C模型,考虑场频率随时间以正弦函数形式作小量变化,在旋波近似下,研究了二能级原子通过多光子跃迁与单模辐射场相互作用时的量子态保真度的演化。利用数值计算方法给出了量子态保真度随时间的演化曲线。研究结果表明:场频率随时间正弦函数形式的变化对系统和光场的量子态保真度的演化影响很小,但对原子的量子态保真度的演化具有显著的影响;原子的量子态保真度的演化受场频率变化的调制,场频率振荡的幅值u越大,调制作用越强,在场频率振荡的幅值u大于一定值后,量子态保真度将按场频率周期性的变化规律作周期性振荡;原子初始状态的分布对原子量子态保真度的演化也具有明显的影响。 相似文献
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通过对系统施加不同的非线性作用,利用量子关联的几何度量,研究了三个qubit体系中的两体量子关联.不同的非线性相互作用模型都能使系统产生最大值为0.1752的量子关联.z方向的横场对量子关联的优化有控制作用,对于三个模型,通过调节z方向的横场,系统能产生最大值为0.09645的平均量子关联.最佳组合的三个横场,不仅能够大幅度提高量子关联的振荡周期,使得两qubit长时间处于量子关联态,而且还能够提高两qubit的平均量子关联. 相似文献
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研究了量子态在一条均匀耦合的反铁磁自旋链中传输时, 信道中自旋激发数变化对其传输性质的影响. 利用信息流方法分析输出端粒子的算符演化动力学, 获得了量子态传输的平均保真度与信道自旋初态之间的关系. 结果表明, 平均保真度的大小只依赖于信道中自旋激发数的奇偶性. 通过比较在奇偶激发信道中获得的最大平均保真度, 构建了优化信道来提升量子态在自旋链中的传输质量. 进一步分析了纠缠在激发信道中的传输情况, 发现纠缠的传输质量不仅和信道中自旋激发的具体个数有关, 还取决于激发自旋的初始排列. 特别地, 当信道中自旋无激发或全部激发时, 纠缠传输的大小和持续时间都优于其他的激发信道. 上述研究结果有助于在实际系统中搭建适合量子态和纠缠传输的量子信道. 相似文献
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光场的量子存储不仅是构建量子计算机的重要基础,而且是实现量子中继和远距离量子通信的核心部分.由于存在不可避免的光学损耗,光学参量放大器产生的压缩真空态光场将变为压缩热态光场,不再是最小不确定态.因此,压缩热态光场的量子存储是实现量子互联网的关键.在原子系综中利用电磁诱导透明机制能够实现量子态在光场正交分量和原子自旋波之间的相互映射,即受控量子存储.本文根据量子存储的保真度边界,研究了实现压缩热态光场量子存储的条件.量子存储的保真度边界是通过经典手段能够达到的最大保真度,当保真度大于该边界时,就实现了量子存储.通过数值计算分析了不同情况下压缩热态光场的量子存储保真度边界,以及存储保真度随存储效率的变化关系,得到了实现量子存储的条件,为连续变量量子存储实验设计提供了直接参考. 相似文献
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廖湘萍等(Chin.Phys.B 23 020304,2014)指出弱测量和弱测量反转操作可以保护三个量子比特的纠缠,提高保真度.本文将弱测量方法推广至四个量子比特的情况,研究了几种典型四个量子比特量子态的演化.结果表明:在振幅阻尼通道中,弱测量方法能够有效地提高系统量子态的保真度.分析了影响量子态保真度的各种因素,对比了不同量子态的演化特征,划分了量子态保真度提高的敏感区域.最后,对弱测量方法抑制量子态衰减的内在机制做了合理的物理解释. 相似文献
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计算了三光子W态隐形传输令牌总线网的保真度.通过计算发现在整个量子网络通信过程中,对于给定的分析角θ,保真度仅与系数|a|2有关|随着分析角θ的增加,保真度出现最大值所对应的系数|a|2相应减小,取θ=π/4、π/2、3π/4时可使保真度达最大值1,此时对应的|a|2分别为0.724、0.5和0.276.对于给定的系数|a|,保真度仅与分析角θ有关|若|a|=0,则无论θ为何值,保真度始终为0|若|a|=|b|=0.707 1,则当θ=π/2、3π/2时保真度达最大值1. 相似文献
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Takeuchi M Ichihara S Takano T Kumakura M Yabuzaki T Takahashi Y 《Physical review letters》2005,94(2):023003
We propose a new method of spin squeezing of atomic spin, based on the interactions between atoms and off-resonant light which are known as paramagnetic Faraday rotation and the fictitious magnetic field of light. Since the projection process, squeezed light, or special interactions among the atoms are not required in this method, it can be widely applied to many systems. The attainable range of the squeezing parameter is zeta greater, similarS(-2/5), where S is the total spin, which is limited by additional fluctuations imposed by coherent light and the spherical nature of the spin distribution. 相似文献
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Squeezed spin states possess unique quantum correlation or entanglement and are significantly promising for advancing quantum information processing and quantum metrology. In recent back-to-back publications [C. Gross et al., Nature (London) 464, 1165 (2010) and Max F. Riedel et al., Nature (London) 464, 1170 (2010)], reduced spin fluctuations are observed leading to spin squeezing at -8.2 and -2.5 dB, respectively, in two-component atomic condensates exhibiting one-axis-twisting interactions. The noise reduction limit for the one-axis twisting scales as ∝1/N(2/3), which for a condensate with N~10(3) atoms is about 100 times below the standard quantum limit. We present a scheme using repeated Rabi pulses capable of transforming the one-axis-twisting spin squeezing into the two-axis-twisting type, leading to Heisenberg limited noise reduction ∝1/N or an extra tenfold improvement for N~10(3). 相似文献
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We investigate the dependence of the average parameter estimation precision (APEP), which is defined by the quantum Fisher information, on the polar angle of the initial coherent spin state |θ0,φ0〉 in a one-axis twisting model. Jin et al. [New J. Phys. 11 (2009) 073049] found that the spin squeezing sensitively depends on the polar angle θ0 of the initial coherent spin state. We show explicitly that the APEP is robust to the initial polar angle θ0 in the vicinity of π/2 and a near- Heisenberg limit 2IN in quantum single-parameter estimation may still be achieved for states created with the nonlinear evolution of the nonideal coherent spin states θ0- π/2. Based on this model, we also consider the effects of the collective dephasing on spin squeezing and the APEE 相似文献
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An effective one-axis passive packaging method for a D lens fiber collimator is presented and compared with the traditional five-axis active packaging method. The dependence of collimator insertion loss on the gap between fiber pigtail and lens is shown experimentally to verify the packaging tolerance. In case of a 20 mm working distance, a 10 μm gap tolerance is obtained for a D lens collimator to obtain an insertion loss of <0.3 dB. In addition, a 2000 h damp heat test was carried out to demonstrate the reliability of this effective packaging method. 相似文献
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Exact analytical solutions of the Landau-Lifshitz equation which may be treated as weak-bounded soliton-antisoliton states in the nonlinear dynamics of a one-axis ferromagnet are obtained. 相似文献
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讨论了银道面内的引力场强分布和太阳在银河系中所受引力与到银心距离r的关系,指出引力场强g并不是与r的平方成反比,这是由于银河系的大小和形状不能忽略造成的.强调了万有引力定律的适用条件. 相似文献
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The investigation was made of the dependence of the intensity of Tl, Ga, Mo, Mg, Mn, Sn, Bi, Ni, Zn, Pt and Au spectral lines and the plasma parameters (temperature T, electron concentration ne, degree of 6 ionnization α) from concentration of lithium additive. 相似文献
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SJ Rose 《Contemporary Physics》2013,54(2):109-121
In this paper we describe experiments conducted with high-power lasers that are attempting to replicate, for a very short time and in miniature, conditions found in the Sun. Experiments to date have reached conditions in the outer part of the Sun. To reach the Sun's centre requires compression of material to very much greater than solid density and heating to over ten million degrees. To achieve this, a new class of experiments and a new generation of high-power lasers are required. 相似文献
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We study the Cauchy problem for the Whitham modulation equations for increasing smooth initial data. The Whitham equations are a collection of one-dimensional quasi-linear hyperbolic systems. This collection of systems is enumerated by the genus g=0,1,2, ... of the corresponding hyperelliptic Riemann surface. Each of these systems can be integrated by the so-called hodograph transformation introduced by Tsarev. A key step in the integration process is the solution of the Tsarev linear overdetermined system. For each g>0, we construct the unique solution of the Tsarev system, which matches the genus g+1 and g–1 solutions on the transition boundaries. 相似文献