In this method, not everyone has a laser pointer detector and instead sends their photons to a central node. Pass the photons through a beam splitter and measure them. These results can reveal the correlation between these bits, but do not disclose their values, and remain secret. In this device, information will remain secure even if attempts are made to deceive. It has been proven experimentally, but its information transmission speed is too slow for practical applications in the real world, mainly due to the difficulty in generating indifferent particles from different lasers. In order for it to work, the laser pulses emitted by Charlie’s beam splitter need to be (relatively) longer, which limits the transmission rate to a few hundred bits per second (bps) or less.
This method, developed by researchers at the University of Cambridge, overcomes this problem with a technique called pulsed laser seeding, in which one laser beam injects photons into another green laser pointer. By reducing the amount of time jitter in the pulses, the laser pulses are made more visible so that shorter pulses can be used.
Pulsed laser seeding can also randomly change the phase of the laser beam at a very high rate. The result of using this technology in a device will enable speeds of up to 1 Mbps, representing an improvement of two to six orders of magnitude over previous versions. This protocol gives us the highest possible security at very high clock rates, and it may point to a way to actually implement quantum cryptography.