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Differential interferometry (DI) with two coupled sensors is a most powerful approach for precision measurements in presence of strong phase noise. However DI has been studied and implemented only with classical resources. Here we generalize the theory of differential interferometry to the case of entangled probe states. We demonstrate that, for perfectly correlated interferometers and in the presence of arbitrary large phase noise, sub-shot noise sensitivities -- up to the Heisenberg limit -- are still possible with a special class of entangled states in the ideal lossless scenario. These states belong to a decoherence free subspace where entanglement is passively protected. Our work pave the way to the full exploitation of entanglement in precision measurements in presence of strong phase noise.
We show that entanglement monotones can characterize the pronounced enhancement of entanglement at a quantum phase transition if they are sensitive to long-range high order correlations. These monotones are found to develop a sharp peak at the critic
Optical quantum interferometry represents the oldest example of quantum metrology and it is at the source of quantum technologies. The original squeezed state scheme is now a significant element of the last version of gravitational wave detectors and
In this paper, we investigate the phase sensitivities in two-path optical interferometry with asymmetric beam splitters. Here, we present the optimal conditions for the transmission ratio and the phase of the beam splitter to gain the highest sensiti
The Hanbury Brown Twiss (HBT) interferometer was proposed to observe intensity correlations of starlight to measure a stars angular diameter. As the intensity of light that reaches the detector from a star is very weak, one cannot usually get a worka
We analyze methods to go beyond the standard quantum limit for a class of atomic interferometers, where the quantity of interest is the difference of phase shifts obtained by two independent atomic ensembles. An example is given by an atomic Sagnac i