Optical EngineeringQuantum entanglement enables low-power optical communication to orbital ranges
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The signal intensity as a function of range is considered for optical communication systems that utilize time-coincident pairs (or larger sets) of photons for information encoding. Two systems are examined: one that generates pairs of photons that have an entangled quantum state, and another where the pairs of photons are generated from a pair of pulsed photon sources. The signal intensity as a function of range is analyzed as a qualitative first-order approximation for these two techniques. For the first time, to this author's knowledge, it is shown that pairs of photons that share a quantum state, and hence have highly correlated momenta, can produce communication systems that have a high degree of noise immunity and are useful for ranges significantly beyond the collimated range of the transmitter, which up until now has been considered the maximum range. As an example, it is shown that a transmitter with a 1-m aperture and a pair of pulsed photon sources will be effective for about 200 km, while a transmitter with the same aperture and a quantum-entangled photon source will have an effective range greater than 60,000 km.