  In this project we examine several different quantum key distribution
protocols which we divide into ones utilizing qubits whose Hilbert spaces are
two dimensional and ones whose Hilbert space dimension is greater than two,
these units of data in quantum computers are known as qudits and in the papers
we'll examine are implemented using the orbital angular momentum of twisted
photons. In sections [3] and [4] the specific procedures of each protocol are
briefly described and followed by an examination of the theoretical and
experimental merits of each protocol. These merits are measured in the bit
error rate tolerance $e_b$, which quantifies the maximum channel noise and the
key rate $R$ which quantifies the rate at which data is transferred in the
protocol. In section [7] we present a unified view of all the relevant data for
the different protocols, and argue for the benefits and drawbacks of the
different protocols for different applications.
