We search for the optimal quantum pure states of identical bosonic particles for applications in quantum metrology, in particular in the estimation of a single parameter for the generic two-mode interferometric setup. We consider the general case in which the total number of particles is fluctuating around an average $N$ with variance $\Delta N^2$. By recasting the problem in the framework of classical probability, we clarify the maximal accuracy attainable and show that it is always larger than the one reachable with a fixed number of particles (i.e., $\Delta N=0$). In particular, for larger fluctuations, the error in the estimation diminishes proportionally to $1/\Delta N$, below the Heisenberg-like scaling $1/N$. We also clarify the best input state, which is a "quasi-NOON state" for a generic setup, and for some special cases a two-mode "Schr\"odinger-cat state" with a vacuum component. In addition, we search for the best state within the class of pure Gaussian states with a given average $N$, which is revealed to be a product state (with no entanglement) with a squeezed vacuum in one mode and the vacuum in the other.
|Titolo:||Two-mode bosonic quantum metrology with number fluctuations|
|Data di pubblicazione:||2015|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1103/PhysRevA.92.042115|
|Parole Chiave:||Quantum Physics; Quantum Physics; Mathematical Physics; Mathematics - Mathematical Physics|
|Appare nelle tipologie:||1.1 Articolo in rivista|