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The power of a control qubit in weak measurements

机译:弱测量中控制量子位的功效

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摘要

In the late 80s, a curious effect suggested by Aharanov, Albert and Vaidmanopened up new vistas regarding quantum measurements on weakly coupled systems.There, a combination of a "weak" finite interaction together with a "strong"post-selection measurement leads to an anomalous effect, namely the mean valueof a spin-1/2 particle in the $z-$direction lies outside the conventionalspectrum of $\pm$1. In this paper, we investigate the quantum control of the weak valueamplification of a qubit system coupled to a meter, via a secondnon-interacting qubit, initially quantum correlated with the first one. Ourresults show that for weak measurements, the control can be remotely realizedvia the post-selected state of the second qubit or the degree of squeezing ofthe meter. Additionally, in a step towards the study of the quantum control ofthe amplification, we can easily manipulate the degree of quantum correlationsbetween the initial correlated qubits. We find that the degree of Entanglementhas no effect on the quantum control of the amplification. However, we havefound a clear connection between the amplification and quantum discord likemeasurements as well as classical correlations between the qubits. Moreover, wegeneralize the analysis to two control qubits and we can conclude that thesingle control qubit scheme is more efficient. Lastly, we suggest an originalapplication of the amplification control protocol on the enhancement of thequantum measurement accuracy, e.g. measuring the relative phase of thepost-selected control qubit in a more precise way, as opposed to theno-amplification case
机译:在80年代后期,Aharanov,Albert和Vaidman提出的一种奇特的效果为弱耦合系统上的量子测量开辟了新的视野。在那里,“弱”有限相互作用与“强”后选择测量共同导致反常效应,即在$ z- $方向上自旋1/2粒子的平均值不在$ \ pm $ 1的常规频谱范围内。在本文中,我们研究了通过第二个非相互作用的量子位耦合到仪表的量子位系统的弱值放大的量子控制,该量子位最初与第一个量子位相关。我们的结果表明,对于较弱的测量,可以通过第二个qubit的后选择状态或仪表的挤压程度来远程实现控制。此外,在研究放大的量子控制的步骤中,我们可以轻松地控制初始相关量子位之间的量子相关程度。我们发现纠缠度对放大的量子控制没有影响。然而,我们已经发现了放大和量子不等式测量之间的明确联系,以及量子位之间的经典相关性。此外,将分析概括为两个控制量子位,可以得出结论:单个控制量子位方案更为有效。最后,我们建议扩增控制协议在提高量子测量精度方面的原始应用,例如与无放大情况相反,以更精确的方式测量后选控制量子位的相对相位

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