Research

Research Interests

Condensed Matter Physics: Strongly correlated systems

Quantum Many-Body Physics / AMO Physics: Ultracold atoms, Open quantum systems, Non-Hermitian systems


Keywords

Fermionic superfluids, Tomonaga-Luttinger liquids, SU(N) symmetry, Nonequilibrium steady states, Lindblad master equation

Tools:

Effective field theory, Conformal field theory, Bethe ansatz, (Non-Hermitian) density-matrix renormalization group, (Time-dependent) generalized Gibbs ensemble

Research Activities

Non-Hermitian superconductivity (fermionic superfluids) (Phys. Rev. Lett. 123, 123601 (2019), Phys. Rev. B 109, L060501 (2024), arXiv:2406.16482)

Motivated by recent experimental advances in ultracold atoms, we have analyzed a non-Hermitian (NH) BCS Hamiltonian with a complex-valued interaction arising from inelastic scattering between fermions. We have first generalized the standard BCS theory to NH systems, finding unconventional phase transitions unique to NH systems: Superfluidity shows reentrant behavior with increasing dissipation as a consequence of exceptional points unique to NH systems.

     Dynamical phase transition in dissipative fermionic superfluids (Phys. Rev. Lett. 127, 055301 (2021))

We have predicted a new mechanism to induce collective excitations and a nonequilibrium phase transition of fermionic superfluids via a sudden switch-on of two-body loss, for which we have first extended the BCS theory to the dynamics under Lindblad equations. We have demonstrated that when dissipation is introduced to one of the two superfluids coupled via a Josephson junction, it gives rise to a nonequilibrium dynamical phase transition characterized by the vanishing dc Josephson current.

Universal properties of dissipative Tomonaga-Luttinger liquids (Phys. Rev. B 105, 205125 (2022))

We have demonstrated the universal properties of dissipative Tomonaga-Luttinger (TL) liquids by calculating correlation functions and performing finite-size scaling analysis of a NH XXZ spin chain as a prototypical model in one-dimensional(1D) open quantum many-body systems. We have used several analytical and numerical techniques: Effective field theory with bosonization, finite-size scaling approach in conformal field theory (CFT), Bethe-ansatz (BA) solution, and NH generalization of the density-matrix renormalization group (NH-DMRG). We have uncovered that the model in the massless regime with weak dissipation belongs to the universality class characterized by the complex-valued TL parameter, which is related to the complex generalization of the c=1 CFT.

Universal properties of dissipative TL liquids with SU(N) spin symmetry (Phys. Rev. B 107, 045110 (2023))

Motivated by recent experimental realizations of SU(N) Hubbard models, we have obtained universal scaling relations for dissipative TL liquids with SU(N) spin symmetry for both fermions and bosons, by using asymptotic BA solutions and CFT in 1D NH quantum many-body systems with SU(N) symmetry. We have uncovered that the spectrum of dissipative TL liquids with SU(N) spin symmetry is described by the sum of one charge mode characterized by a complex generalization of c=1 U(1) Gaussian CFT, and $N-1$ spin modes characterized by level-1 SU(N) Kac-Moody algebra with the conformal anomaly c=N-1, and thereby dissipation only affects the charge mode as a result of spin-charge separation in 1D NH quantum systems.

     Dissipation-induced nonreciprocal transport (Phys. Rev. Research 2, 043343 (2020))