Non-Hermitian quantum many-body physics in ultracold atoms subject to inelastic collisions

Masaya Nakagawa (U. Tokyo)

The effective description of open quantum systems by non-Hermitian Hamiltonians has recently led to an intense activity due to unique quantum phenomena that have no counterpart in closed Hermitian systems. While various quantum phenomena inherent in open systems have been discovered in single-particle non-Hermitian quantum mechanics, many-body physics with interparticle interactions largely remains unexplored. In this talk, we show that ultracold atoms subject to inelastic collisions provide a feasible platform for exploration of non-Hermitian quantum many-body physics described by complex-valued interactions. In particular, we discuss how non-Hermiticity alters two paradigmatic examples of quantum many-body effects: the Kondo effect [1] and magnetism in the Hubbard model [2]. First, we show that non-Hermiticity induces anomalous winding behavior of renormalization-group flows which is prohibited in Hermitian systems [1]. Second, we demonstrate that a finite lifetime of intermediate states in virtual spin-exchange processes stabilizes high-energy spin states, realizing magnetic correlations characterized by a negative absolute temperature [2].

References:
[1] M. Nakagawa, N. Kawakami, and M. Ueda, Phys. Rev. Lett. 121, 203001 (2018).
[2] M. Nakagawa, N. Tsuji, N. Kawakami, and M. Ueda, arXiv:1904.00154.