Quantum cryptography based on quantum-key distribution (QKD) is recognized as one of the most promising strategies to guarantee absolutely secure data communication. Among different quantum-key distribution (QKD) protocols, those based on entangled photon pairs are particularly attractive because of enhanced tolerance to losses and simplified analysis of the secure keys. In spite of impressive achievements, which include the implementation of satellite-based QKD, the maximum transmission rate is still modest, partly due to the intrinsic limitations of state-of-the-art sources of entangled photon pairs.

In this project, we aim to use for the first time semiconductor-based sources of polarization-entangled photon pairs to implement entangled-based QKD with transmission rates well beyond the state-of-the-art. To achieve this ambitious goal, we will make use of a JKU-patented technology, which has recently allowed us to obtain nearly perfectly entangled photon pairs from a special class of semiconductor quantum dots. Different from sources used so far, quantum dots have the potential of generating photon pairs at GHz rates and negligible probability of undesired simultaneous multi-pair generation.

The specific objectives of the project include the design and implementation of a proof-of-principle QKD system, which exclusively uses quantum-dot-photons for the generation of a secret key. The system will consist of a stationary quantum-dot source located in our lab and two sender/receiver units connected to the source via single-mode-fibers. This configuration will allow us to analyze the transmission in laboratory conditions and across the JKU campus. In order to ease the design and assembly of all necessary optical, electronic, and software components, we will apply design automation methods for selected tasks and simulation approaches for early validation. This shall allow us to converge rapidly to a fully functional bidirectional point-to-point QKD system.

By quantifying the performance (qubit error rates, overall transmission rates) of quantum-dot sources for entanglement-based QKD, this project shall guide further optimization of the sources, estimate their ultimate limits, and possibly open the way to “real-world” applications of quantum dots in quantum networks.

JKU PIs: Armando Rastelli, Robert Wille

Funding agency / scheme: LIT, State of Upper Austria / SEED

Funding period: 01.11.2019 – 31.10.2021