Roton in a few-body dipolar system

TL;DR

This paper numerically investigates a 1D many-body bosonic system with short-range and dipolar interactions, revealing the transition from collective to single-particle-like states and identifying the roton excitation.

Contribution

It provides an exact numerical analysis of the transition between collective and single-particle states, including the roton, in a dipolar bosonic system beyond Bogoliubov theory.

Findings

Identification of the roton state in a 1D dipolar system

Smooth transition from collective to single-particle states

Analysis beyond Bogoliubov approximation

Abstract

We solve numerically exactly the many-body 1D model of bosons interacting via short-range and dipolar forces and moving in the box with periodic boundary conditions. We show that the lowest energy states with fixed total momentum can be smoothly transformed from the typical states of collective character to states resembling single particle excitations. In particular, we identify the celebrated roton state. The smooth transition is realized by simultaneous tuning short-range interactions and adjusting a trap geometry. With our methods we study the weakly interacting regime as well as the regime beyond the range of validity of the Bogoliubov approximation.