Measuring the adiabatic non-Hermitian Berry phase in feedback-coupled oscillators

Yaashnaa Singhal, Enrico Martello, Shraddha Agrawal, Tomoki Ozawa, Hannah Price, Bryce Gadway

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


The geometrical Berry phase is key to understanding the behavior of quantum states under cyclic adiabatic evolution. When generalized 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 state. Here, we perform the first 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 realize 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 noncyclical paths within the parameter space even when all eigenenergies are real. We further observe a non-Hermitian analog of the Aharonov-Bohm solenoid effect, observing amplification and attenuation when encircling a region of broken PT symmetry that serves as a source of imaginary flux. This experiment demonstrates the importance of geometrical effects that are unique to non-Hermitian systems and paves the way towards further studies of non-Hermitian and topological physics in synthetic metamaterials.

Original languageEnglish (US)
Article numberL032026
JournalPhysical Review Research
Issue number3
StatePublished - Jul 2023

All Science Journal Classification (ASJC) codes

  • General Physics and Astronomy

Cite this