Physical manifestation of quantum fluctuations in Bose-Einstein condensates and their implications for superfluid flow

Chandra Raman, Roberto Onofrio, J. M. M. J. Vogels +2 more

Oleś, Bartłomiej

David C K Roberts, Yves Pomeau A

We calculate a force due to zero-temperature quantum fluctuations on a stationary object in a moving superfluid flow. We model the object by a localized potential varying only in the flow direction and model the flow by a three-dimensional weakly interacting Bose-Einstein condensate at zero temperature. We show that this force exists for any arbitrarily small flow velocity and discuss the implications for the stability of superfluid flow.

Wolfgang Ketterle

Chao Feng

This thesis examines the manifestation of the critical velocity for superfluidity in dilute gas Bose-Einstein condensates (BECs). Superfluidity is a macroscopic quantum phenomenon characterised by unique properties such as frictionless flow, high thermal conductivity and the presence of quantised vortices. Our study focuses on what is arguably the most well-known attribute: the ability for an object to move through a superfluid without experiencing a drag force when travelling below a threshold critical velocity.The Landau criterion for superfluidity predicts the critical velocity in a BEC is equal to the speed of sound, and this conclusion is supported by a large body of theoretical work. However, a number of experiments have observed lower critical velocities than theory predicts. In the first part of this thesis, we numerically model experiments on the superfluid critical velocity of an elongated, harmonically trapped Bose-Einstein condensate as reported by [P. Engels and C. Atherton, Phys. Rev. Lett. 99, 160405 (2007)]. These experiments swept a repulsive obstacle, formed by a optical dipole potential, through the long axis of a condensate at constant velocity. Their results found an increase in the resulting density fluctuations of the condensate above an obstacle velocity of v _ 0:3 mm s

Dr. Ali Khan

The study of exotic states of matter, particularly superfluids and Bose-Einstein condensates (BECs), has revolutionized our understanding of quantum mechanics in macroscopic systems. This article explores the thermodynamic properties of these states, focusing on their unique behavior at ultra-low temperatures. Superfluids exhibit zero viscosity and anomalous flow characteristics, while Bose-Einstein condensates, formed by cooling bosons to near absolute zero, present quantum phenomena on a macroscopic scale. This paper reviews key thermodynamic concepts, such as entropy, heat capacity, and chemical potential, as they apply to these exotic phases. Additionally, the relationship between quantum coherence and thermodynamic stability in superfluids and BECs is examined, along with the practical implications for quantum technologies.