We analyze the effects of quantum correlations, such as entanglement and discord, on the efficiency of phase estimation by studying four quantum circuits that can be readily implemented using NMR techniques. These circuits define a standard strategy of repeated single-qubit measurements, a classical strategy where only classical correlations are allowed, and two quantum strategies where nonclassical correlations are allowed. In addition to counting space (number of qubits) and time (number of gates) requirements, we introduce mixedness as a key constraint of the experiment.We compare the efficiency of the four strategies as a function of the mixedness parameter. We find that the quantum strategy gives ffiffiffiffi N p enhancement over the standard strategy for the same amount of mixedness. This result applies even for highly mixed states that have nonclassical correlations but no entanglement.
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机译：我们通过研究四个可以使用NMR技术轻松实现的量子电路，分析了纠缠和不和谐等量子相关性对相位估计效率的影响。这些电路定义了重复单量子位测量的标准策略，仅允许经典相关的经典策略以及允许非经典相关的两个量子策略。除了计算空间（qubit数）和时间（门数）需求外，我们还将混合性作为实验的关键约束条件。我们将这四种策略的效率作为混合性参数的函数进行了比较。我们发现，对于相同的混合量，量子策略比标准策略具有ffiffiffiffi N p增强。该结果甚至适用于具有非经典相关性但没有纠缠的高度混合状态。
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