The role of auxiliary stages in Gaussian quantum metrology

Danilo Triggiani, Paolo Facchi, Vincenzo Tamma*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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The optimization of the passive and linear networks employed in quantum metrology, the field that studies and devises quantum estimation strategies to overcome the levels of precision achievable via classical means, appears to be an essential step in certain metrological protocols achieving the ultimate Heisenberg-scaling sensitivity. This optimization is generally performed by adding degrees of freedom by means of auxiliary stages, to optimize the probe before or after the interferometric evolution, and the choice of these stages ultimately determines the possibility to achieve a quantum enhancement. In this work we review the role of the auxiliary stages and of the extra degrees of freedom in estimation schemes, achieving the ultimate Heisenberg limit, which employ a squeezed-vacuum state and homodyne detection. We see that, after the optimization for the quantum enhancement has been performed, the extra degrees of freedom have a minor impact on the precision achieved by the setup, which remains essentially unaffected for networks with a larger number of channels. These degrees of freedom can thus be employed to manipulate how the information about the structure of the network is encoded into the probe, allowing us to perform quantum-enhanced estimations of linear and non-linear functions of independent parameters.
Original languageEnglish
Article number345
Number of pages30
Issue number5
Publication statusPublished - 14 May 2022


  • quantum metrology
  • quantum sensing
  • distributed parameter
  • heisenberg limit
  • typicality
  • gaussian metrology
  • squeezing
  • estimation of functions


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