Browsing by Subject "Dipolar droplets"

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Open Access
Temperature dependent density profiles and collective oscillations of dipolar droplets
(2019-09) Aybar, Enes
Dipolar droplets are a novel form of Bose gas that form in a regime where the mean field theory predicts collapse. In the literature, the beyond mean field e ects in the form of the Lee-Huang-Yang correction to the local chemical potential are used to explain the stability of these droplets. We employ the Hartree-Fock- Bogoliubov theory to include the beyond mean field terms in a systematic manner that also allows finite temperature calculations. In this thesis, we derive the modified Gross-Pitaevskii equation and the Bogoliubov-de Gennes equations, then solve the latter with a local density approximation and the former with a Gaussian variational anzats. We show that Hartree-Fock-Bogoliubov theory reproduces the zero temperature results found in the literature, and indicates that the density profile and the collective oscillation of dipolar droplets depend on the temperature. We find that experimentally relevant temperatures (T 100nK) may significantly alter the transition between low and high density phases, and change the collective oscillation frequencies of the system.
Open Access
Temperature-dependent density profiles of dipolar droplets
(American Physical Society, 2019) Aybar, Enes; Öktel, M. Özgür
Recently, trapped dipolar gases were observed to form high-density droplets in a regime where mean-field theory predicts collapse. These droplets present a form of equilibrium where quantum fluctuations are critical for stability. So far, the effect of quantum fluctuations has only been considered at zero temperature through the local chemical potential arising from the Lee-Huang-Yang correction. Here, we extend the theory of dipolar droplets to nonzero temperatures using Hartree-Fock-Bogoliubov theory (HFBT) and show that the equilibrium is strongly affected by temperature fluctuations. HFBT, together with local density approximation for excitations, reproduces the zero-temperature results and predicts that the condensate density can change dramatically even at low temperatures where the total depletion is small. In particular, we find that typical experimental temperatures (T∼100 nK) can significantly modify the transition between low-density and droplet phases.