BBC: Researchers have been working to perfect secure communications via a technique called quantum key distribution. The method relies on the quantum mechanical properties of single photons to detect eavesdropping. However, producing single photons from the laser sources currently in use has not proven to be reliable—sometimes two or more photons can slip past. Any extra photons that get transmitted can pose a security risk because they could be intercepted en route without the intended recipient ever knowing. Now a more reliable method of generating single photons has been proposed by a group of researchers in Germany, whose results appear in the New Journal of Physics. They show that by using quantum dots, which are made of semiconductors, they can produce streams of single photons at rates as high as 95 000 bits per second and that can travel up to 500 meters. They are now working on quantum repeaters to increase the transmission range.