[Paper Review] Enhanced observation time of magneto-optical traps using micro-machined non-evaporable getter pumps

Rodolphe Boudot, J. P. McGilligan+6 more|arXiv (Cornell University)|Aug 3, 2020

Atomic and Subatomic Physics Research50 references33 citations

TL;DR

The paper demonstrates that laser-activated non-evaporable getter pumps (NEGs) dramatically extend magneto-optical trap (MOT) observation time, up to 10 minutes in a MEMS cell with a single NEG and over 4 days in a glass-blown cell with five NEGs, using passive pumping alone.

ABSTRACT

We show that micro-machined non-evaporable getter pumps (NEGs) can extend the time over which laser cooled atoms canbe produced in a magneto-optical trap (MOT), in the absence of other vacuum pumping mechanisms. In a first study, weincorporate a silicon-glass microfabricated ultra-high vacuum (UHV) cell with silicon etched NEG cavities and alumino-silicateglass (ASG) windows and demonstrate the observation of a repeatedly-loading MOT over a 10 minute period with a single laser-activated NEG. In a second study, the capacity of passive pumping with laser activated NEG materials is further investigated ina borosilicate glass-blown cuvette cell containing five NEG tablets. In this cell, the MOT remained visible for over 4 days withoutany external active pumping system. This MOT observation time exceeds the one obtained in the no-NEG scenario by almostfive orders of magnitude. The cell scalability and potential vacuum longevity made possible with NEG materials may enable inthe future the development of miniaturized cold-atom instruments.

Motivation & Objective

• Motivate miniaturization of vacuum systems for cold-atom devices by reducing dependence on active pumping.
• Demonstrate the effect of laser-activated NEGs on MOT observation time in microfabricated and glass-blown UHV cells.
• Quantify MOT decay dynamics and background pressure under passive pumping with NEGs.
• Assess scalability and longevity of NEG-based passive pumping for chip-scale atomic instruments.

Proposed method

• Fabricate MEMS MOT cell with embedded NEG cavities in silicon/ASG windows and activate a single NEG by laser heating.
• Operate a rubidium MOT with an alkali dispenser and monitor MOT fluorescence and loading curves.
• Turn off external ion pump after NEG activation to study passive-pumping performance.
• In a borosilicate glass-blown cell with five NEGs, sequentially activate NEGs and measure MOT decay and background pressure.
• Analyze MOT decay using exponential models to extract time constants for MOT and vacuum pressure dynamics.

Experimental results

Research questions

• RQ1 How much can MOT observation time be extended using laser-activated NEGs in MEMS and glass cells without active pumping?
• RQ2 How does NEG activation affect background pressure and Rb/Non-Rb gas dynamics over short and long timescales?
• RQ3 What is the relationship between the number of activated NEGs and vacuum longevity in passive-pumping regimes?
• RQ4 Can passive pumping with NEGs support MOTs for days in miniature vacuum environments?
• RQ5 What are the implications for scaling MEMS-based cold-atom sensors with NEG-based vacuum longevity?

Key findings

• A single laser-activated NEG extends MOT observation time in MEMS cells from ~10 s to >10 minutes.
• In a glass-blown cuvette cell with five NEGs, a MOT remains visible for more than 4 days under passive pumping.
• NEG activation increases the vacuum time constant, with final pressure rising more slowly and reaching new steady-states.
• MOT decay after NEG activation is best described by dual-exponential behavior before and after an initial period, with longer time constants (~11 s and ~109 s in MEMS; ~10 s and ~70 s in glass cell).
• MOT recovery occurs when the ion pump is reactivated, and subsequent NEG activations progressively improve the MOT atom number after pump cycles.
• Long-term measurements show MOT persistence beyond 3.5×10^5 s (over 4 days) in the five-NEG glass cell, despite He permeation considerations.