Free Space Quantum Key Distribution using the Differential Phase Shift Protocol in Urban Daylight

Quantum key distribution exploits the principles of quantum mechanics to create and distribute cryptographic keys. The quantum communication channel can be either fiber-based or free space-based. Fiber-based quantum key distribution has evolved from lab demonstrations to commercially available systems, but its infrastructure dependency and limitations on achievable distance, due to optical fiber loss, do not allow for the realization of a global-scale quantum communication network. Free space quantum key distribution addresses this problem with features such as low loss, high data rates, and ease of deployment. This paper presents an experimental demonstration of free space quantum key distribution using the differential phase shift protocol in an urban location during daylight hours. We established a secure link, achieving a key rate of 10 kbps.