Applications of exact solution for strongly interacting one dimensional bose-fermi mixture: low-temperature correlation functions, density profiles and collective modes

TL;DR

This paper provides an exact solution for a one-dimensional Bose-Fermi mixture, revealing detailed low-temperature correlation functions, density profiles, and collective modes, and challenges mean-field predictions about demixing.

Contribution

It applies the Bethe-ansatz technique to derive exact ground state energies and correlation functions, and predicts new collective oscillations in the strongly interacting regime.

Findings

No demixing occurs, contrary to mean-field predictions.

Prediction of low-lying collective oscillations due to counterflow.

Correlation functions exhibit significant temperature-dependent changes.

Abstract

We consider one dimensional interacting bose-fermi mixture with equal masses of bosons and fermions, and with equal and repulsive interactions between bose-fermi and bose-bose particles. Such a system can be realized in current experiments with ultracold bose-fermi mixtures.We apply the Bethe-ansatz technique to find the exact ground state energy at zero temperature for any value of interaction strength and density ratio between bosons and fermions. We use it to prove the absence of the demixing, contrary to prediction of a mean field approximation. Combining exact solution with local density approximation (LDA) in a harmonic trap, we calculate the density profiles and frequencies of collective modes in various limits. In the strongly interacting regime, we predict the appearance of low-lying collective oscillations which correspond to the counterflow of the two species. In the strongly interacting regime we use exact wavefunction to calculate the single particle correlation functions for bosons and fermions at low temperatures under periodic boundary conditions. We derive an analytical formula, which allows to calculate correlation functions at all distances numerically for a polynomial time in the system size. We investigate numerically two strong singularities of the momentum distribution for fermions at $k_f$ and $k_f+2k_b.$ We show, that in strongly interacting regime correlation functions change dramatically as temperature changes from 0 to a small temperature $\sim E_f/\gamma.$ A strong change of the momentum distribution in a small range of temperatures can be used to perform a thermometry at very small temperatures.