Low-Dimensional Stochastic Projected Gross-Pitaevskii Equation

TL;DR

This paper derives reduced-dimensional stochastic equations for superfluids in confined regimes, enabling accurate modeling of 1D or 2D superfluids immersed in 3D thermal clouds, with validation through numerical simulations.

Contribution

It introduces a rigorous projection formalism for deriving low-dimensional stochastic Gross-Pitaevskii equations applicable to confined superfluid systems.

Findings

Validated 1D theory against 3D simulations for oblate traps.

Established a consistent cutoff for the 1D stochastic equations.

Discussed extended validity for two-component systems with buffer gases.

Abstract

We present reduced-dimensional stochastic projected Gross-Pitaevskii equations describing regimes of confinement and temperature where a 1D or 2D superfluid is immersed in a 3D thermal cloud. The projection formalism provides both a formally rigorous and physically natural way to effect the dimensional reduction. The 3D form of the number-damping (growth) terms is unchanged by the dimensional reduction. Projection of the energy-damping (scattering) terms leads to modified stochastic equations of motion describing energy exchange with the thermal reservoir. The regime of validity of the dimensional reduction is investigated via variational analysis. Paying particular attention to 1D, we validate our variational treatment by comparing numerical simulations of a trapped oblate system in 3D with the 1D theory, and establish a consistent choice of cutoff for the 1D theory. We briefly discuss the scenario involving two-components with different degeneracy, suggesting that a wider regime of validity exists for systems in contact with a buffer-gas reservoir.