Permanent magnet based Zeeman slower for lithium atoms

TL;DR

The paper presents a compact, maintenance-free Zeeman slower for $^7$Li based on a transverse-field Halbach magnet array, integrated with a 3D-printed structure to simplify mechanical support and vacuum compatibility. The design achieves a high flux of slow atoms by combining discrete Halbach magnets (136 in total) with pre-slow optical pumping and a well-defined magnetic-field trajectory, while allowing adjustable field profiles and easy assembly/disassembly. Key findings include a capture-field behavior around $B_{capt} \approx 115$–125 G, a linear dependence of the most-probable final velocity on detuning with a slope corresponding to the resonance condition, and substantial improvements in slow-atom flux due to optical pumping. The setup demonstrates robust operation and adaptability to other atomic species or slowly varying field configurations, offering a simpler alternative to electromagnet-based slowers without sacrificing performance.

Abstract

We describe the design, construction, and characterization of a permanent magnet based, transverse-field Zeeman slower for lithium atoms. We use off-the-shelf compact permanent bar magnets in the Halbach configuration to create a uniform magnetic field in the transverse direction. We develop a general approach for a mechanical structure that supports the spatial distribution of magnets using 3D printing technology. The approach allows for flexible assembly and dismantling of the magnetic field on the target vacuum system. Finally, we verify that the Zeeman slower supports a high flux of slow atoms in the region of magneto-optical trap.

Figures (8)

• Figure 1: Relevant energy spectrum of $^7$Li as a function of magnetic field. The two states used for the slowing mechanism are shown as thick blue lines. The primary excitations from our target ground state are indicated by straight arrows for $\sigma^+$/$\sigma^-$ polarized light. Spontaneous emission paths from these two excited states are represented by the wavy lines. The two possible ground states reached via a $\sigma^+\rightarrow\pi$ cycle are highlighted with dashed yellow lines. The inset zooms into the $F=1$ ground-state manifold and marks the transition from $m_F$ to $m_J^\prime$ states at $B_{turn}=143$ G (dashed red line). Apart from the illustrative axis break between the $2S_{1/2}$ and $2P_{3/2}$ manifolds, all data in the main figure is to scale (the hyperfine splitting in the $2P_{3/2}$ state is of the order of a few MHz and therefore not visible here.)
• Figure 2: Construction of the magnetic field profile: (a) ideal (dashed red line), calculated (solid green line) and measured (blue dotes) $\hat{y}$-component of the magnetic field profile along propagation axis of the Zeeman slower; (b) Velocity in resonance with the slowing laser along the Zeeman slower. The dashed lines mark the location at which the field crosses $B_{turn}$ and the corresponding velocity that interacts with the $\sigma^+$ component; (c1)-(c3) show the 3D printed mechanical structure that holds permanent magnets. The black arrows on the magnets in (c2) mark the magnetization axes; (d) shows to scale bar magnets position and orientation in a single Halbach leg of the Zeeman slower.
• Figure 3: Selected pictures of the Zeeman slower. (a) The top and bottom parts disassembled. (b) The complete structure, mounted at the designated height. (c) Separated layers of the bottom part showing the internal structure holding the magnets in place.
• Figure 4: Schematic representation of the experimental apparatus to demonstrate the performance of Zeeman slower. Atomic beam (light blue large arrow) originates from oven and propagates from right to left. It is collimated by the aperture tube and crosses the optical pumping region before entering the Zeeman slower deceleration region. The slowing laser beam (red large arrow) propagates from left to right and the probe laser beam is marked by a dark orange arrow which makes an angle $\beta$ with the atomic beam.
• Figure 5: The measured velocity profiles as a function of probe laser detuning (lower axis) and velocity (upper axis) for a number of slowing laser detunings. The initial Maxwell-Boltzmann distribution of velocities in the atomic beam is shown as a black solid line. The colored lines represent velocity profiles for different detunings as marked in the legend. The inset represent peaks of slow velocities. Vertical doted lines mark the ground state hyperfine splitting in lithium atoms. For the explanations of other features see text.