We demonstrate the existence of exact atypical many-body eigenstates in a class of disordered, interacting one-dimensional quantum systems that includes the Fermi-Hubbard model as a special case. These atypical eigenstates, which generically have finite energy density and are exponentially many in number, are populated by noninteracting excitations. They can exhibit Anderson localization with area-law eigenstate entanglement or, surprisingly, ballistic transport at any disorder strength. These properties differ strikingly from those of typical eigenstates nearby in energy, which we show give rise to diffusive transport as expected in a chaotic quantum system. We discuss how to observe these atypical eigenstates in cold-atom experiments realizing the Fermi-Hubbard model, and comment on the robustness of their properties.We demonstrate the existence of exact atypical many-body eigenstates in a class of disordered, interacting one-dimensional quantum systems that includes the Fermi-Hubbard model as a special case. These atypical eigenstates, which generically have finite energy density and are exponentially many in number, are populated by noninteracting excitations. They can exhibit Anderson localization with area-law eigenstate entanglement or, surprisingly, ballistic transport at any disorder strength. These properties differ strikingly from those of typical eigenstates nearby in energy, which we show give rise to diffusive transport as expected in a chaotic quantum system. We discuss how to observe these atypical eigenstates in cold-atom experiments realizing the Fermi-Hubbard model, and comment on the robustness of their properties.

arXiv:1811.07903Physical Review LettersJul 16, 201992 citations

Quantum phase transition and elementary excitations of a Bose-Fermi mixture in a one-dimensional optical lattice

Shi-Jian Gu, Junpeng Cao, Shu Chen +1 more

The mixture of the scalar bosonic and the spinless or polarized fermionic cold atoms in the one-dimensional optical lattice is studied. The system is modeled by the Bose-Fermi-Hubbard Hamiltonian, which shows different behavior from that of the Bose-Hubbard or the Fermi-Hubbard models. Because the $\text{SU}(1\ensuremath{\mid}1)$-supersymmetric Bethe ansatz solution gives an excellent approximation to this kind of mixed cold atomic systems, the ground-state properties of the system such as the densities of state in the momentum space are obtained based on the Bethe ansatz. If the number of bosons is equal to that of fermions and the filling factor is 1, it is found that there exists a critical on-site interaction ${U}_{c}$ . If $U<{U}_{c}$ , the ground state of the system is in the superfluid phase, while if $U>{U}_{c}$ , the ground state is in the insulating phase. The superfluid-insulator transition occurs at ${U}_{c}$ . From the analysis of the superfluid density, the value of the critical point is determined as ${U}_{c}=2.79256$ , which is larger than the ${U}_{c}=0$ for the Fermi-Hubbard model and smaller than the ${U}_{c}=3.28$ for the Bose-Hubbard model. The elementary excitations and effective Hamiltonian in the strong-coupling limit are also discussed.The mixture of the scalar bosonic and the spinless or polarized fermionic cold atoms in the one-dimensional optical lattice is studied. The system is modeled by the Bose-Fermi-Hubbard Hamiltonian, which shows different behavior from that of the Bose-Hubbard or the Fermi-Hubbard models. Because the $\text{SU}(1\ensuremath{\mid}1)$-supersymmetric Bethe ansatz solution gives an excellent approximation to this kind of mixed cold atomic systems, the ground-state properties of the system such as the densities of state in the momentum space are obtained based on the Bethe ansatz. If the number of bosons is equal to that of fermions and the filling factor is 1, it is found that there exists a critical on-site interaction ${U}_{c}$. If $U<{U}_{c}$, the ground state of the system is in the superfluid phase, while if $U>{U}_{c}$, the ground state is in the insulating phase. The superfluid-insulator transition occurs at ${U}_{c}$. From the analysis of the superfluid density, the value of the critical point is determined as ${U}_{c}=2.79256$, which is larger than the ${U}_{c}=0$ for the Fermi-Hubbard model and smaller than the ${U}_{c}=3.28$ for the Bose-Hubbard model. The elementary excitations and effective Hamiltonian in the strong-coupling limit are also discussed.

Physical Review BDec 14, 20093 citations

Transport properties of the infinite-dimensional Hubbard model

Thomas Pruschke, Mark Jarrell

Physica B Condensed MatterApr 1, 19943 citations

{U}_{c}

. If

U<{U}_{c}

, the ground state of the system is in the superfluid phase, while if

U>{U}_{c}

, the ground state is in the insulating phase. The superfluid-insulator transition occurs at

{U}_{c}

. From the analysis of the superfluid density, the value of the critical point is determined as

{U}_{c}=2.79256

, which is larger than the

{U}_{c}=0

for the Fermi-Hubbard model and smaller than the

{U}_{c}=3.28

for the Bose-Hubbard model. The elementary excitations and effective Hamiltonian in the strong-coupling limit are also discussed.