Laboratoire de Physique Théorique (IRSAMC), Université de Toulouse (UPS), Toulouse F-31062, France.
Nat Commun. 2011;2:223. doi: 10.1038/ncomms1220.
Quantum-enhanced measurements use quantum mechanical effects to enhance the sensitivity of the measurement of classical quantities, such as the length of an optical cavity. The major goal is to beat the standard quantum limit (SQL), that is, an uncertainty of order , where N is the number of quantum resources (for example, the number of photons or atoms used), and to achieve a scaling 1/N, known as the Heisenberg limit. So far very few experiments have demonstrated an improvement over the SQL. The required quantum states are generally highly entangled, difficult to produce, and very prone to decoherence. Here, we show that Heisenberg-limited measurements can be achieved without the use of entangled states by coupling the quantum resources to a common environment that can be measured at least in part. The method is robust under decoherence, and in fact the parameter dependence of collective decoherence itself can be used to reach a 1/N scaling.
量子增强测量利用量子力学效应来提高对经典量（如光腔长度）的测量灵敏度。主要目标是超越标准量子极限（SQL），即不确定性为 ，其中 N 是量子资源的数量（例如，使用的光子或原子的数量），并实现缩放 1/N，称为海森堡极限。到目前为止，很少有实验证明在 SQL 上有所改进。所需的量子态通常是高度纠缠的，难以产生，并且非常容易退相干。在这里，我们通过将量子资源耦合到至少可以部分测量的公共环境中，证明了无需使用纠缠态就可以实现海森堡极限测量。该方法在退相干下具有鲁棒性，实际上，集体退相干本身的参数依赖性可用于达到 1/N 缩放。
