  We present a protocol for deterministic and highly efficient quantum
cryptography with entangled photon pairs in a 4x4-dimentional Hilbert space.
Two communicating parties, Alice and Bob first share a both polarization- and
path-entangled photon pair, and then each performs a complete Bell-state
measurement on their own photon in one of two complementary Bell-state bases.
It is demonstrated that each measurement in which both Alice and Bob register a
photon can build certain perfect correlation and generate 1.5 key bits on
average. The security of our protocol is guaranteed by the non-cloning theorem.
