With visitors in the #lab, we often get the question: "How do the atoms initially get into the vacuum system?"
Let's look at it in this thread and discuss how one turns chunks of metal into cold gases
#quantumsensors #quantumtechnology #coldatoms #quantumFAQ #scicomm

Here, we'll treat the case for #ytterbium for our @VLBAI_Hannover but, very generally, our strategy is applicable to many other commonly used #species, e.g., #rubidium or #sodium (of course there are other ways to generate a lot of cold atoms)

I like to begin with the phrase "...so it always starts with a chunk of metal." In the image, you see #ytterbium nuggets conveniently bought from any chemicals supplier (it gets tricky if you want something other than natural isotope mix). We place the nuggets in our source oven.

An oven? Yes, just like any other oven, this one heats stuff. In our case, typical temperatures easily exceed 400°C. We need these high temperatures to vaporize enough ytterbium (remember, we want to generate a cold gas after all).

So at high enough temperatures, sufficient numbers of ytterbium are blazing around in the oven chamber. What's next? We form a beam using microtube array as a nozzle (see picture).

While the process in detail is a but more complex, intuitively, one can imagine these tubes selecting just the class of atoms going "straight to our #experiment chamber".

However, this beam of atoms is still very hot, i.e., its forward velocity with hundreds of meters per second is way too high to continue working with it. The way out was shown by @NIST @NobelPrize laureate Bill Phillips and is called "Zeeman slowing". https://en.wikipedia.org/wiki/William_Daniel_Phillips

At its heart, it makes the beam "face the headwind" of a counter-propagating #laser. Countless directed little kicks by resonant absorption of #photons and subsequent *undirected* kick during spontaneous emission (the latter do heat a little bit) slow the beam down - they cool it

Since changing velocities results in changing #Doppler shifts, an external magnetic field is designed such that it tunes a large fraction of atoms to always be on resonance with the counter-propagating laser beam.

In our case, this is done with what we call the #spaceship, an arrangement of permanent magnets surrounding the tube the atoms fly through.

And once everything worked out: there we are, with an atomic beam well below 50 m/s forward velocity, cold enough for subsequent trapping and cooling for our experiment (purple trace).

If you want to learn more, please have a look at our @arxiv preprint: https://arxiv.org/abs/2008.07498