Quadrupole collective modes in trapped finite-temperature Bose-Einstein condensates

Area of Science:

• Atomic, Molecular & Optical Physics
• Quantum Gases
• Condensed Matter Physics

Background:

• Bose-Einstein condensates (BECs) exhibit unique quantum phenomena at ultralow temperatures.
• Quadrupole excitations in BECs are sensitive probes of their properties.
• An anomalous temperature dependence of the m=0 quadrupole mode frequency has been a persistent theoretical challenge.

Purpose of the Study:

• To investigate the anomalous temperature dependence of quadrupole excitations in trapped Bose-Einstein condensates.
• To resolve the long-standing theoretical problem concerning the m=0 mode frequency variation with temperature.
• To elucidate the underlying physical mechanisms responsible for the observed behavior.

Main Methods:

• Utilized finite-temperature simulations to model the behavior of trapped Bose-Einstein condensates.
• Focused on the specific case of the m=0 quadrupole excitation mode.
• Analyzed the interplay between the condensate and the surrounding thermal cloud during excitations.

Main Results:

• Explained the anomalous frequency variation by identifying the excitation of two distinct modes.
• These modes correspond to the coupled motion of the Bose-Einstein condensate and the thermal cloud.
• The relative amplitudes of these coupled modes were found to be sensitive to temperature and excitation frequency.

Conclusions:

• The anomalous behavior of the m=0 quadrupole mode is attributed to the coupled dynamics of the condensate and thermal cloud.
• Finite-temperature simulations provide a successful framework for understanding these complex excitations.
• The findings offer good agreement with experimental observations for specific drive frequencies.