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arXiv quant-ph/0309091quant-ph
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先验信息:如何规避标准联合测量不确定度关系

Prior information: how to circumvent the standard joint-measurement uncertainty relation

Michael J. W. Hall

摘要:

互补原理以两种方式量化:通过一个通用的不确定性关系,有效的任意联合估计的任何两个观测量从一个给定的测量设置,并通过一个通用的不确定性关系,有效的最佳估计相同的两个观测量时,测量前的系统的状态是已知的。一个公式给出了任何给定的可观察的最佳估计,基于任意的测量数据和先验信息的状态的系统,概括和提供了一个更强大的解释以前的公式的“本地期望”和“弱值”的量子可观察。作为一个例子,位置X和动量P的正则联合测量对应于测量交换算子X_J=X+ X ',P_J= P-P',其中素变量指的是处于最小不确定状态的辅助系统。众所周知,Δ X_J Δ P_J >= hbar。在这里,它示出,给定_same_ physical实验设置,和测量之前的系统密度算子的知识,可以使X和P的改进的联合估计X_est和P_est。这些改进的估计不仅在统计上更接近X和P:它们满足Delta X_est Delta P_est >= hbar/4,其中在某些情况下可以实现相等。因此,可以比标准下限(后者对应于_no_ prior信息的限制)好四倍。其他应用包括外差检测正交的单模光场,和联合测量的基础上爱因斯坦-波多尔斯基-罗森相关。

英文摘要:

The principle of complementarity is quantified in two ways: by a universal uncertainty relation valid for arbitrary joint estimates of any two observables from a given measurement setup, and by a general uncertainty relation valid for the_optimal_ estimates of the same two observables when the state of the system prior to measurement is known. A formula is given for the optimal estimate of any given observable, based on arbitrary measurement data and prior information about the state of the system, which generalises and provides a more robust interpretation of previous formulas for ``local expectations'' and ``weak values'' of quantum observables. As an example, the canonical joint measurement of position X and momentum P corresponds to measuring the commuting operators X_J=X+X', P_J=P-P', where the primed variables refer to an auxilary system in a minimum-uncertainty state. It is well known that Delta X_J Delta P_J >= hbar. Here it is shown that given the_same_ physical experimental setup, and knowledge of the system density operator prior to measurement, one can make improved joint estimates X_est and P_est of X and P. These improved estimates are not only statistically closer to X and P: they satisfy Delta X_est Delta P_est >= hbar/4, where equality can be achieved in certain cases. Thus one can do up to four times better than the standard lower bound (where the latter corresponds to the limit of_no_ prior information). Other applications include the heterodyne detection of orthogonal quadratures of a single-mode optical field, and joint measurements based on Einstein-Podolsky-Rosen correlations.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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