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arXiv 0710.0285quant-phcond-mat.other
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具有产品状态的量子限制计量学

Quantum-limited metrology with product states

Sergio Boixo, Animesh Datta, Steven T. Flammia, Anil Shaji, Emilio Bagan, Carlton M. Caves

摘要:

研究了广义量子精密测量方案中n体系统初积态的性能,该方案涉及到非线性k体(k << n)哈密顿量中未知的耦合常数的估计.我们得到了参数估计的不确定性的理论下界。对于任意的初始状态,下界的尺度为1/n^k,对于初始乘积状态,它的尺度为1/n^(k-1/2)。我们表明,后者的缩放可以实现使用简单的,可分离的测量。我们详细分析的情况下,二次哈密顿量(k = 2),实现与玻色-爱因斯坦凝聚体。基于角动量相干态的演化,我们建立了一个简单的模型,解释了k = 2时的O(n^(-3/2))标度;该模型表明,二次哈密顿量产生的纠缠在增强的灵敏度标度中不起作用。我们证明了相位退相干不影响初始产物态的O(n^(-3/2))灵敏度标度。

英文摘要:

We study the performance of initial product states of n-body systems in generalized quantum metrology protocols that involve estimating an unknown coupling constant in a nonlinear k-body (k << n) Hamiltonian. We obtain the theoretical lower bound on the uncertainty in the estimate of the parameter. For arbitrary initial states, the lower bound scales as 1/n^k, and for initial product states, it scales as 1/n^(k-1/2). We show that the latter scaling can be achieved using simple, separable measurements. We analyze in detail the case of a quadratic Hamiltonian (k = 2), implementable with Bose-Einstein condensates. We formulate a simple model, based on the evolution of angular-momentum coherent states, which explains the O(n^(-3/2)) scaling for k = 2; the model shows that the entanglement generated by the quadratic Hamiltonian does not play a role in the enhanced sensitivity scaling. We show that phase decoherence does not affect the O(n^(-3/2)) sensitivity scaling for initial product states.

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