Negative Bogoliubov dispersion in exciton-polariton condensates

Abstract

Bogoliubov's theory states that self-interaction effects in Bose-Einstein condensates produce a characteristic linear dispersion at low momenta. One of the curious features of Bogoliubov's theory is that the new quasiparticles in the system are linear combinations of creation and destruction operators of the bosons. In exciton-polariton condensates, this gives the possibility of directly observing the negative branch of the Bogoliubov dispersion in the photoluminescence (PL) emission.Here we theoretically examine the PL spectra of exciton-polariton condensates taking into account of reservoir effects. At sufficiently high excitation densities, the negative dispersion becomes visible. We also discuss the possibility for relaxation oscillations to occur under conditions of strong reservoir coupling. This is found to give a secondary mechanism for making the negative branch visible.

Quantum Langevin model for nonequilibrium condensation

“…This result provides a theoretical explanation to the experimental observation [20] that a condensate can exhibit thermal-like features in the momentum distribution even in the absence of thermalising collisions. Given the qualitatively different shape of the collective excitation dispersion, we expect that a decisive insight in the equilibrium vs. non-equilibrium nature of a condensation process can be obtained by measuring dispersions from the luminescence spectra or via pump-andprobe spectroscopy [16,56,57,65].…”

“…Among the most interesting and non-trivial examples, we show in Fig.6 the photoluminescence spectrum for two cases of a negative detuning δ < 0 (left) and of finite photon-photon interactions λ > 0 (right): in both cases, photons are effectively interacting and the Bogoliubov transformation is expected to give spectral weight to the negative "ghost" branch of the Goldstone mode as well [57]. While this feature is clearly visible in the central panel, the effective interaction in the left panel is too weak to give an appreciable effect on this scale: the emitter-cavity detuning that is required for this purpose is in fact much larger than the amplification bandwidth of the emitters and therefore hardly compatible with condensation.…”

Dynamics and stability of dark solitons in exciton-polariton condensates

“…is the standard Bogoliubov dispersion relation for an equilibrium (atomic) condensate 3,4,28 . For a fixed k, Eq.…”

Stability of persistent currents in open dissipative quantum fluids

“…The gapped and diffusive character of the excitation spectra can be linked, respectively, to the underdamped and overdamped oscillations of the reservoir discussed in [41]. Figure 2 shows typical dispersion curves for the m = 0 in the gapped (a) and diffusive (c) regimes and the marginal case P 0 = γ c /γ R [ Fig.…”