Actually proving this effect may be the real challenge. The easy part is creating entangled photons: just shoot light through a special, “downconverting” crystal that acts as a beam splitter; it produces separate yet linked rays. One ray illuminates the object, and the other serves as a reference. The returning and reference beams then are merged together (basically, by making them go through a splitter in reverse); the photons that were entangled should be more likely to recombine, or “upconvert.” But any experiment to prove that quantum illumination can boost the sensitivity of imaging has to use weak signals, and creating materials capable of upconverting faint beams with high efficiency is technically daunting, Kumar says. Still, Lloyd predicts experimental tests of this scheme might come later this year.
Besides boosting imaging sensitivity, the effect might confer benefits on quantum computing or quantum cryptography, Kumar suspects. “The quantum world is quite exotic and complex, and this shows there are surprises there that lurk around corners all the time,” he says.
Note: This article was originally printed with the title, "Quantum Afterlife".