Secure communication over long distances requires robust encryption. While current encryption algorithms exist using classical methods, there are no unconditionally secure methods of distributing encryption keys classically. However, by exploiting the quantum nature of individual photons, quantum key distribution (QKD) can be proven as an unconditionally secure method for the distribution of encryption keys. Because QKD operates via the transmission and detection of single photons, there are major challenges for practical use in terms of both key generation rate and the maximum distance over which a secret key can be established.
To provide reliably secure communications, development of quantum optical devices for encrypted ground-to-space communications is a necessity. To support this, the current innovation is the development of an efficient, single-pass quantum optical waveguide source capable of backward quasi-phase-matched interactions for generation of high-purity photon pairs for use in an on-demand photon source to enable high-rate, long-distance encryption key distribution. The new devices will produce down-conversion entangled photon pairs with enhanced spectral properties and low attenuation, providing the key technology required for development of an ondemand heralded photon source. Furthermore, the waveguide-based technology is compact, robust, and power efficient for future deployment on space-based platforms to provide provably, unconditionally secure quantum encryption.
The basic idea is to array, cascade, or time multiplex the output from several parametric down-conversion sources. For each down-conversion source, the probability of attaining a photon pair is much less than one, but for the collection, the probability of at least one pair being produced approaches one. Heralding is used to determine which source has produced the pair, triggering a high-speed switch to route the heralded photon to the output.
To realize the current innovation, photon pair down-conversion sources for forward and backward QPM nonlinear interactions will be developed and manufactured. The new devices will produce down-conversion pairs with enhanced spectral properties and low attenuation, providing the key technology required for development of an ondemand heralded photon source.