Discrete-step evaporation of an atomic beam

TL;DR

This paper provides a theoretical framework for discrete-step evaporative cooling of atomic beams using radio-frequency antennas, analyzing flux, temperature, and phase-space density changes, and optimizing the process to achieve quantum degeneracy.

Contribution

It introduces a detailed theoretical model for evaporative cooling with multiple antennas and estimates the number needed to reach high phase-space density.

Findings

At least 30 antennas are required to increase phase-space density by a factor of 10^8.

The model predicts flux and temperature changes for each evaporation step.

Collision effects during propagation between antennas can be experimentally probed.

Abstract

We present a theoretical analysis of the evaporative cooling of a magnetically guided atomic beam by means of discrete radio-frequency antennas. First we derive the changes in flux and temperature, as well as in collision rate and phase-space density, for a single evaporation step. Next we show how the occurrence of collisions during the propagation between two successive antennas can be probed. Finally, we discuss the optimization of the evaporation ramp with several antennas to reach quantum degeneracy. We estimate the number of antennas required to increase the phase-space density by several orders of magnitude. We find that at least 30 antennas are needed to gain a factor $10^8$ in phase-space density.