Toshiba Research Europe Ltd, a company belonging to the Toshiba group, achieved a quantum key data transmission speed of 1.02Mbps at a distance of 20km, which is 100 times faster than conventional speeds.

Also, a speed of 10.1Kbps was demonstrated at a transmission distance of 100km, according to the company. This was made possible by adopting an APD (avalanche photo diode), which is usually used for optical communication, as a single photon detector and enhancing the drive frequency of the detector to more than 100 times higher than the conventional frequency, the company said.

Previously, though it was possible to use an APD in a single photon detector, it was difficult to drive the detector at a high frequency due to afterpulse, a form of noise. Toshiba Research Europe improved the S/N ratio of the sensing signal by employing a self differential system, which is free from afterpulse, to make it possible to detect a single photon at a low gate voltage.