Put the chopped rhubarb in a glass container, like a Mason jar. Pour in enough sugar, so the rhubarb is completely buried by about 1/2 inch. Close the jar and shake well. Let this sit on the counter overnight.
The next day, all the sugar should have dissolved. Shake the jar to be certain. Add another 2 tablespoons of sugar to the jar and shake to dissolve. Repeat this process each day until, in the morning, you see sugar on the bottom of the jar that has not dissolved.
You can strain and use the syrup now, but you’ll get a pinker syrup if you leave the syrup to rest another week or so. If it’s hot in your kitchen, like hotter than 75°F, put the syrup in the fridge on Day 3.
When you’re ready, strain out the rhubarb. You can use it in rhubarb bread or muffins or pie, or as a garnish for drinks. Pour the syrup into a clean container and store in the fridge, where it will keep indefinitely.