Measuring the adiabatic Non-Hermitian Berry Phase in Feedback-Coupled Oscillators

Venerdì 21 gennaio 2022, con inizio alle ore 15:45, nell'ambito del ciclo di seminari del CMQT coordinato dal Prof. G. Falci, il Dott. Enrico Martello (University of Birmingham, UK), ha tenuto un seminario dal titolo Measuring the adiabatic Non-Hermitian Berry Phase in Feedback-Coupled Oscillators.

Il seminario si inserisce nella serie degli Alumni Colloquia, seminari tenuti da ex allieve ed allievi del DFA, oggi impegnati in attività di ricerca presso altre Università ed Enti di ricerca.

Abstract. The geometrical Berry phase is key to understanding the behaviour of quantum states under cyclic adiabatic evolution. When generalised to non-Hermitian systems with gain and loss, the Berry phase can become complex, and should modify not only the phase but also the amplitude of the quantum state. Here, we perform experimental measurements of the adiabatic non-Hermitian Berry phase, exploring a minimal two-site PT-symmetric Hamiltonian that is inspired by the Hatano-Nelson model. We realise this non-Hermitian model experimentally by mapping its dynamics to that of a pair of classical oscillators coupled by real-time measurement-based feedback. As we verify experimentally, the adiabatic non-Hermitian Berry phase is a purely geometrical effect that leads to significant amplification and damping of the amplitude also for non-cyclical paths within the parameter space even when all eigenenergies are real. This experiment demonstrates the importance of geometrical effects that are unique to non-Hermitian systems and paves the way towards the further studies of non-Hermitian and topological physics in synthetic metamaterials.