New technique developed for quantum cryptography applications

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Symbolic image (University of Paderborn, Besim Mazhiqi): Scientists at the Unive
Symbolic image (University of Paderborn, Besim Mazhiqi): Scientists at the University of Paderborn have developed a decoder that makes it possible to use special light properties for communication.

Paderborn scientists publish results in scientific journal

With the development of quantum computers, classical cryptography for secure communication threatens to become obsolete. Quantum cryptography, on the other hand, uses the laws of quantum mechanics to provide unrestricted security. One example is quantum key distribution, which allows two parties to secure a message using a random secret key. This is generated using quantum particles, usually photons. For this purpose, scientists are increasingly making use of an alphabet based on special properties of light particles, i.e. photons, namely their color composition. Until now, however, there has been no special device to decode the information. Scientists at the University of Paderborn have now developed such a decoder. They have published their results in the scientific journal -PRX Quantum-.

-Quantum key distribution protocols that use binary encodings are widely used. Nevertheless, their security and efficiency can be improved if a larger alphabet is used for coding. Here, the so-called temporal pulse modes are used, where the information is encoded in the color composition of the photons. A key distribution system based on these modes requires a multi-channel decoder capable of -reading- all the letters of an alphabet simultaneously. However, this device has not yet been realized-, explains Benjamin Brecht, a physicist at the University of Paderborn.

The Paderborn scientists have developed a so-called multi-output quantum pulse gate (mQPG). It separates the incoming letters into different output colors, which the physicists can detect with a spectrometer. They have also demonstrated a complete high-dimensional decoder based on the mQPG that enables encryption protocols based on single photons. -The versatility of the mQPG makes it a valuable resource for many quantum communication applications, in addition to opening up further possibilities for all temporal mode-based technologies-, Brecht said.

The research was funded by the German Federal Ministry of Education and Research (BMBF) in the QuantERA project -QuICHE-, in which the University of Paderborn is involved.

To the paper.