Preheat sous vide to 83.9° C / 183° F.
Place the lemon pieces, salt, and sugar in a zip lock or vacuum seal bag, massage the salt into the lemons, ensuring that all the lemons are covered.
Seal and submerge the bag into the water bath, and cook for 60 minutes.
Remove the bag from the water bath and empty the contents into a glass jar.
Allow the lemons to sit for at least 60 minutes. If you can, refrigerate overnight before using for best results.
The preserved lemons will keep for several months, deeping in flavor.