In a pot, heat the sugar and water until the sugar has completely dissolved and the mixture starts to boil. Turn off the heat. Add the arugula and stir well, making sure the herbs are completely immersed in the liquid. Let sit for only 5–8 minutes, then strain. (If you let it sit for too long, the arugula turns brown and gets a funky “Brussels sprouts” aroma.) Funnel into a glass bottle (you can use a clean recycled bottle) and keep refrigerated.