Figure 3: State tomography and phase relation.
From: Demonstration of entanglement-enhanced phase estimation in solid
(a) The state tomography result of a nuclear spin superposition state 
. (b) State tomography result of the electron–nuclear-entangled state 
. (c) Phase relation of an independent state. (d) Phase relation of an entangled state. Compared with independent state, the phase relation of entangled state has double frequency dependence on input phase, so a more precise phase estimation result can be achieved with entangled state.
