Theory of cooling by flow through narrow pores

TL;DR

This paper explores novel cooling methods for dilution refrigerators using narrow channels that filter hot atoms, including effusion, quantum waveguides, and wall-limited diffusion, with recent nano-filter advances offering practical potential.

Contribution

It introduces and analyzes three innovative atom-filtering techniques for enhanced cooling in dilution refrigerators, emphasizing the feasibility of nano-scale channels.

Findings

Particle waveguide and wall-limited diffusion methods can achieve cooling.

Nano-filters show promise for practical implementation.

Channel dimensions smaller than mean-free path are effective.

Abstract

We consider the possibility of adding a stage to a dilution refrigerator to provide additional cooling by ``filtering out'' hot atoms. Three methods are considered: 1) Effusion, where holes having diameters larger than a mean-free path allow atoms to pass through easily; 2) Particle waveguide-like motion using very narrow channels that greatly restrict the quantum states of the atoms in a channel. 3) Wall-limited diffusion through channels, in which the wall scattering is disordered so that local density equilibrium is established in a channel. We assume that channel dimension are smaller than the mean-free path for atom-atom interactions. The particle waveguide and the wall-limited diffusion methods using channels on order of the de Broglie wavelength give cooling. Recent advances in nano-filters give this method some hope of being practical.