Abstract

Quantum metrology [1] aims at measuring physical parameters with the highest possible precision with respect to the number of employed resources. However, many techniques based on exploiting quantum resources, such as entanglement or squeezing, are extremely fragile with respect to losses [2]. An example is provided by the well-known case of N00N states [3,4], quantum superpositions of N photons propagating jointly in one of two interferometric arms leading to increased precision scaling as N in single-phase estimation. However, a small amount of losses suffices to reduce the precision to only $\sqrt{N}$ scaling, corresponding to the standard quantum limit. Thus, the implementations of quantum-enhancement schemes in realistic conditions are difficult to be achieved.

© 2015 IEEE