ICFO-Institut de Ciències Fotòniques, Mediterranean Technology Park, 08860 Castelldefels, Barcelona, Spain and Institute for Physics, University of Freiburg, Rheinstrasse 10, D-79104 Freiburg, Germany.
Phys Rev Lett. 2013 Sep 20;111(12):120401. doi: 10.1103/PhysRevLett.111.120401. Epub 2013 Sep 18.
Parameter estimation is of fundamental importance in areas from atomic spectroscopy and atomic clocks to gravitational wave detection. Entangled probes provide a significant precision gain over classical strategies in the absence of noise. However, recent results seem to indicate that any small amount of realistic noise restricts the advantage of quantum strategies to an improvement by at most a multiplicative constant. Here, we identify a relevant scenario in which one can overcome this restriction and attain superclassical precision scaling even in the presence of uncorrelated noise. We show that precision can be significantly enhanced when the noise is concentrated along some spatial direction, while the Hamiltonian governing the evolution which depends on the parameter to be estimated can be engineered to point along a different direction. In the case of perpendicular orientation, we find superclassical scaling and identify a state which achieves the optimum.
参数估计在从原子光谱和原子钟到引力波探测等领域都具有重要意义。在没有噪声的情况下，纠缠探针相对于经典策略提供了显著的精度增益。然而，最近的结果似乎表明，任何少量的实际噪声都会将量子策略的优势限制为最多一个乘法常数的改进。在这里，我们确定了一个相关的场景，在这个场景中，即使存在不相关的噪声，也可以克服这种限制并实现超经典的精度缩放。我们表明，当噪声集中在某个空间方向时，精度可以显著提高，而控制依赖于要估计的参数的演化的哈密顿量可以被设计为指向不同的方向。在垂直方向的情况下，我们发现了超经典的缩放，并确定了一个达到最优的状态。
