Fate of the Bose polaron at finite temperature

Abstract

We consider an impurity immersed in a Bose-Einstein condensate with tunable boson-impurity interactions. Such a Bose polaron has recently been predicted to exhibit an intriguing energy spectrum at finite temperature, where the ground-state quasiparticle evenly splits into two branches as the temperature is increased from zero [Guenther et al., Phys. Rev. Lett. 120, 050405 (2018)]. To investigate this theoretical prediction, we employ a recently developed variational approach that systematically includes multi-body correlations between the impurity and the finite-temperature medium, thus allowing us to go beyond previous finite-temperature methods. Crucially, we find that the number of quasiparticle branches is simply set by the number of hole excitations of the thermal cloud, such that including up to one hole yields one splitting, two holes yields two splittings, and so on. Moreover, this effect is independent of the impurity mass. We thus expect that the exact ground-state quasiparticle will evolve into a single broad peak for temperatures T > 0, with a broadening that scales as T 3/4 at low temperatures and sufficiently weak boson-boson interactions. In the zero-temperature limit, we show that our calculated ground-state polaron energy is in excellent agreement with recent quantum Monte Carlo results and with experiments. arXiv:1910.02620v1 [cond-mat.quant-gas]

Static Impurities in a Weakly Interacting Bose Gas

“…The experimental progress in the field of ultra-cold atomic gases has recently lead to the observation [24] of Bose polarons at finite temperatures. This experiment confirmed previous theoretical predictions [25][26][27][28][29][30] about the breakdown of the quasi-particle picture description of Bose polarons in a close vicinity of the Bose-Einstein condensation (BEC) point.…”

Pump-probe spectroscopy of Bose polarons: Dynamical formation and coherence

“…It would be intriguing to utilize PPS at finite temperature [108,109] and also in higher dimensions to explore the timeresolved formation of quasiparticles. As further perspectives, PPS could be exploited to unravel recondensation dynamics [110,111] in excited bands of optical lattices and the dynamics of vibrational states of ultra-long-range Rydberg molecules [112,113] to infer their lifetime.…”

Emerging SYK physics in polaron system

“…For temperature higher than the critical one (T c = W 2 /g b with W the bandwidth) the non-Fermi-liquid feature, which is hidden by the instability at low temperature, will leads to incoherence between the electronic excitations. Note that the finite-temperature also affects the resonance structure of the polaron spectrum [6]. Also, the strong coupling, like in a strongly correlated metals, will largely reduce the critical temperature, and thus leads to the coherence to incoherence crossover, which also happen in the Dirac/Weyl semimetallic states.…”