Quantum metrology at level anti-crossing

Abstract

We address parameter estimation in two-level systems exhibiting level anti-crossing and prove that universally optimal strategies for parameter estimation may be designed, that is, we may find a parameter independent measurement scheme leading to the ultimate quantum precision independently on the nature and the value of the parameter of interest. Optimal estimation may be achievable also at high temperature depending on the structure of the two-level Hamiltonian. Finally, we show that no improvement is achievable by dynamical strategies and discuss examples of applications.

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• Theoretical analysis of a nearly optimal analog quantum search
• Multi-outcome homodyne detection in a coherent-state light interferometer
• Adiabatic Quantum Estimation: A Numerical Study of the Heisenberg XX Model with Antisymmetric Exchange
• Multi-parameter Quantum Magnetometry with Spin States in coarsened measurement reference