Fibre-Coupled GaSb Quantum Dot Tunable Single-Photon Sources for Field Deployed Quantum Key Distribution

• Applicant: Dr. Tobias Huber-Loyola
• Subject Area: Experimental Condensed Matter Physics ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 532770894

Quantum cryptography enables a theoretically provable security in contrast to the classical one, where security is based on mathematical complexity. The first proposed protocol for quantum key distribution (QKD) - the BB84 protocol, uses single photons to carry information. Since current on-demand single-photon (SP) sources (SPS) are either lacking efficiency or practicability, most QKD implementations so far use weak coherent pulses (WCP). These, however, require decoy states to detect possible attacks and cannot be extended to quantum repeater architectures, which limits their performance and applicability. To overcome this limitation, efficient on-demand SPSs emitting in the telecom spectral range are needed. Among different physical systems, quantum dot-based (QD) sources provide deterministic generation of the best quality SPs. They are compatible with semiconductor technology which makes them suitable for on-chip integrated and scalable solutions. Within the FiGAnti project we will explore an alternative material system for non-classical light sources operating in the telecom bands - Antimony-based QDs. The main goal of the project is to deploy single photons from a telecom (In)GaSb/AlGaSb QD device in an existing deployed fibre link for QKD demonstration. To achieve this goal, we will first understand the fundamental properties of the material and explore various photonic structures (circular Bragg grating resonators and photonic nanowire cavities) to engineer the SPS properties. The practical relevance of our SPSs will be increased by including strain-tuning of their emission energy, charge stabilisation and fibre pigtailing to obtain identical, scalable, compact and robust sources. Our testbed will allow us to optimise the exact transmission wavelength in view of trade-off between transmission loss and noise, and to determine the best achievable parameters using the proposed material platform. QD-based SPS will be benchmarked against commercial decoy state and discrete/continuous-variable QKD solutions.

• DFG Programme: Research Grants
• International Connection: Finland, France, Poland, Sweden
• Partner Organisation: Agence Nationale de la Recherche / The French National Research Agency
• Co-Investigator: Professor Dr. Sven Höfling
• Cooperation Partners: Professor Dr. Jean-Michel Gerard; Professor Dr. Mircea Guina; Dr. Anna Musial; Professor Dr. Valery Zwiller