EMphoQ – Generation of multiphoton states for quantum communication

Quantum technologies are among the key technologies of the 21st century. Quantum communication is of central importance for cybersecurity in the age of quantum computers. The distribution of quantum entanglement over long distances is a crucial resource for secure communication networks and distributed quantum information processing. It enables eavesdropping-proof information exchange using quantum keys, secure authentication using quantum tokens, and applications such as blind quantum computing. To realize such applications, concepts are being researched that are based on quantum memories for light or the generation of entangled multiphoton states, so-called photonic graph states. A key component for this are powerful light-matter interfaces that provide the necessary quantum optical functionalities.

The EMphoQ project aims to develop such an interface based on a resonator-coupled atom. It generates controlled entangled multiphoton states with high efficiency that can be directly coupled into optical fibers. To this end, a single rubidium atom is strongly coupled to the evanescent field of a fiber resonator and repeatedly excited by optimized pulse sequences. Thanks to fiber integration, EMphoQ enables the efficient generation of complex entangled photon states.

The implementation of EMphoQ will ensure that cybersecurity and ICT infrastructures benefit from the possibilities offered by widely available quantum communication. In the future, other fields of application, such as distributed quantum information processing, will also benefit significantly from the possibility of long-range entanglement distribution. EMphoQ thus makes an important contribution to strengthening Germany's technical sovereignty and the goals of the High-Tech Agenda Germany.