A distinguishable single excited-impurity in a Bose–Einstein condensate

We investigate the properties of a distinguishable single excited state impurity pinned in the center of a trapped Bose–Einstein condensate in a one-dimensional harmonic trapping potential by changing the bare mass of the impurity and its interspecies interaction strength with the Bose–Einstein condensate. We model our system by using two coupled differential equations for the condensate and the single excited-impurity wave function, which we solve numerically. For equilibrium, we find that an excited-impurity induces two bumps or dips on the condensate for the attractive- or repulsive-interspecies coupling strengths, respectively. Afterwards, we show that the excited-impurity induced imprint upon the condensate wave function remains present during a time-of-flight expansion after having switched off the harmonic confinement. We also investigate shock-waves or gray-solitons by switching off the interspecies coupling strength in the presence of harmonic trapping potential. During this process, we found that the generation of gray bi-soliton or gray quad-solitons (four-solitons) depend on the bare mass of the excited-impurity in a harmonic trap. (letter)