Phase estimation with squeezed single photons. (arXiv:1802.02922v1 [quant-ph])

We address the performance of an interferometric setup in which a squeezed
single photon interferes at a beam splitter with a coherent state. Our analysis
in based on both the quantum Fisher information and the sensitivity when a
Mach-Zehnder setup is considered and the difference photocurrent is detected at
the output. We compare our results with those obtained feeding the
interferometer with a squeezed vacuum (with the same squeezing parameter of the
squeezed single photon) and a coherent state in order to have the same total
number of photons circulating in the interferometer. We find that for fixed
squeezing parameter and total number of photons there is a threshold of the
coherent amplitude interfering with the squeezed single photon above which the
squeezed single photons outperform the performance of squeezed vacuum (showing
the highest quantum Fisher information). When the difference photocurrent
measurement is considered, we can always find a threshold of the squeezing
parameter (given the total number of photons and the coherent amplitude) above
which squeezed single photons can be exploited to reach a better sensitivity
with respect to the use of squeezed vacuum states also in the presence of non
unit quantum efficiency.

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