For the rosemary simple syrup, combine ½ cup water and ½ cup granulated sugar in a small saucepan over medium heat. Bring to a simmer. Remove from heat and add 2 sprigs of rosemary. Allow to steep for 30 minutes. Drain and set aside. Cool completely before use. *If you choose to use sugared rosemary sprigs as a garnish, add additional springs to the steeping saucepan at the end of the 30 minute mark. Dip sprigs into syrup, place on a cooling rack and sprinkle with additional sugar. Allow to dry until hardened.
Fill a glass with ice. Pour gin over ice then stir in pomegranate juice and simple syrup.
Top with carbonated water and garnish with pomegranate arils and sugared rosemary sprig.