Speaker
Description
The non-Hermitian skin effect is one of the most remarkable topological features of non-conservative physics. It causes a macroscopic accumulation of states at the boundaries of a confined system, opening new ways for controlling waves in photonic, mechanical, and other non-Hermitian systems. This effect has recently been observed in nonlinear bosonic experiments with Bose-Einstein condensates of exciton polaritons [1] and ultracold quantum gases [2]. The underlying physics is captured by a mean-field Hamiltonian with a trapping potential and an imaginary gauge field. While prior work has examined the effect of the imaginary gauge field term on the condensate itself, the collective excitations on top of the condensate remained unexplored. Here, we develop a new theory for the Bogoliubov excitations in a non-Hermitian framework and systematically study their spectrum across different interaction regimes. By analysing the position expectation values, we find that while the repulsive interactions counter the localisation of the condensate due to the skin effect, the excitations remain strongly affected by the imaginary gauge field. As a consequence, in the presence of harmonic confinement, we predict a strong shift in the dipole oscillation frequency, which can be observed in experiments. This is in contrast to Hermitian systems, where this frequency is fixed by the trap frequency.
[1] Yow-Ming (Robin) Hu, M. Kròl, D. A. Smirnova, L. A. Smirnov, B. R. Fabricante, K. Winkler, M. Kamp, C. Schneider, S. Höfling, T. C. H. Liew, A. G. Truscott, E. A. Ostrovskaya, and E. Estrecho, arXiv preprint arXiv:2512.10146 (2025).
[2] J. Tao, E. D. Mercado-Gutierrez, M. Zhao, and I. B. Spielman, Phys. Rev. Lett. 136, 113401 (2026).
| I am the presenting author | Yes |
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