Without authentication, any form of communication is susceptible to a man-in-the-middle attack. You simply don't know who you are communicating with. This make

Without authentication, any form of communication is susceptible to a man-in-the-middle attack. You simply don't know who you are communicating with. This makes using QKD very hard to justify in practice. If you have exchanged a pre-shared key (which is required for authentication anyway), you can just use a symmetric stream cipher like AES for encrypting the communication. This is many orders of magnitude cheaper and faster than QKD and works independently of the communication medium. Also it doesn't look like AES is going to be broken anytime soon.