Free-space quantum cryptography system

A system for quantum key delivery in a single-photon, free-space cryptography scheme comprising:

• a transmitter comprising two pairs of photon sources, each said photon source representing a specific photon polarization direction, a first said pair of photon sources representing a first polarization basis and a remaining said pair of photon sources representing a second polarization basis, said first polarization basis and said second polarization basis prepared as conjugate bases by one of being rotated with respect to each other and disposition of at least one retardation plate in a transmitter path of a photon emitted by at least one of said photon sources resulting in non-orthogonal polarization eigenstates, a transmitter polarizing beamsplitter corresponding to each said pair of photon sources whereby the polarizations of each said photon source of each said pair of photon sources are recombined, a transmitter non-polarizing beamsplitter whereby said recombined polarizations are combined for output to a receiver, and a photon output;
• and
• a receiver comprising a photon input, a receiver non-polarizing beamsplitter whereby said output from said transmitter is separated resulting in a random polarization basis selection, two pairs of photon receivers and a receiver polarizing beamsplitter corresponding to each said pair of photon receivers, said photon receivers and said receiver polarizing beamsplitters disposed inversely with respect to said photon sources and said receiver polarizing beamsplitters having been prepared as conjugate bases by one of being rotated with respect to each other and disposition of at least one retardation plate in a receiver path of a photon received by at least one of said photon receivers, said receiver in communication with said transmitter through a free-space channel.