Dr. Ugo Marzolino

Precision magnetometry exploiting excited state quantum phase transitions

Critical behaviour in phase transitions is a resource for enhanced precision metrology. The reason is that the so-called Fisher information is superextensive at critical points, and, at the same time, quantifies performances of metrological protocols. Therefore, preparing metrological probes at phase transitions provides enhanced precision in measuring the transition control parameter. I will focus on the Lipkin-Meshkov-Glick model that exhibits excited state quantum phase transitions at different magnetic fields. I will show numerical evidence of broad peaks for the Fisher information with superextensive scaling, which are explained by the Hamiltonian spectral properties. I will also propose metrological schemes for estimating the magnetic field in the Lipkin-Meshkov-Glick model with precision better than the shot-noise and comparable with the Heisenberg limit achieved by interferometric schemes with entangled states.