Toshiba develops photo-detector able to secure optical communications News from E-InSiteToshiba Research Europe Ltd. (TREL) has developed a new type of very sensitivephoto-detector the company said is capable of detecting the faintest possible opticalsignals.
The device responds to individual photons, the smallest indivisible units (quantas) oflight, TREL said. The Cambridge, England-based subsidiary of Toshiba Corp. unveiled thephoton detector this week at the Conference on Lasers and Eltro-Optics in San Francisco.
At the heart of the device is a layer of quantum dots, tiny disks of a semiconductor,each measuring tens of nanometers in diameter and a few nanometers in height, TREL said.The electrons inside the dots display quantum properties not seen in larger pieces ofsemiconductor. TREL said their paper is the first report of quantum dots being used todetect individual visible, or near infrared phtons.
A photon incident upon the device liberates an electron trapped within one of the dots.Until now, it has been difficult to detect the tiny charge associated with this singleelectron, TREL said. The company's researchers have shown this can be achieved byintegrating the quantum dots inside a transistor structure, which was prepared incollaboration with the University of Cambridge.
The TREL team plans to apply the new device to the emerging field of quantumcommunication where data is sent along a conventional optical fibre encoded at the singlephoton level. By using single photons, two parties are able to detect if theircommunication has been intercepted or altered en route, TREL said. The security of thetechnique is guaranteed by fundamental laws of quantum mechanics, which require that aquantum state (a a single photon) cannot be measured without altering its properties in adetectable way.
"Advances in semiconductor nano-technology are creating devices with exciting newfunctionalities," said Dr. Andrew Shields, project leader. "The fact that atransistor containing quantum dots can detect individual photons is significant, becausesuch a structure is likely to have several important advantages over conventionaldetectors."
An important application of quantum communication is to allow two users of an opennetwork to form a secret cryptographic key that can subsequently be used to encrypt datasent between them, the company said. The technique could be of use in a range ofapplications where sensitive information is sent on an open network, such as e-commerce,banking and financial transactions.
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