Higher-Dimensional Quantum Cryptography

Paul G. Kwiat, Kevin T. McCusker and Bradley Christensen (University of Illinois at Urbana-Champaign)

 

In the vast majority of quantum cryptography experiments to date, one generates at most one random key bit per photon (and strictly speaking, half a bit per photon is much more common). Here we present current progress on a scheme which will eventually enable us to achieve over 10 random key bits per detected photon. The essential idea is to use pulsed position modulation (ppm) in which a photon appears in one of, e.g., 1024 time bins, from which one can extract 10 bits of randomness. In our initial implementation, we used hyperentangled photons, in which the correlated timing of the photon pairs is used to generate key material, while the polarization entanglement is used to check for the presence of an eavesdropper.