Single-Photon Non-Locality

Today’s society is based on the fast access to information. Getting a head start on information is key in business, finance, politics and security. Most of our information exchange is done via the internet. However, not only has the current structure of our internet its capacity limits but also data transfer is not secure. Therefore, we are in need to invest in a future network, capable of handling the massive data flow and allowing for secure data communication. The solution lies in quantum mechanics, making it possible to encode information on the smallest quanta of energy, a single light particle called photon. This not only reduces energy consumption for information transfer to the physical limit but also allows for totally secure data communication due to the principles of quantum mechanics (No-cloning theorem). Single and entangled photons, as well as highly efficient, low-noise single-photon detectors are important building blocks to realize such quantum networks. The project SiPhoN focused on investigating novel semiconductor nano-scale devices as quantum light sources and developing highly efficient single-photon detectors based on superconducting material in cooperation with the company Single Quantum B.V..

During the course of the project different types of solid-state quantum light sources have been investigated and their ability to emit photons on-demand after a trigger pulse was explored. In particular semiconductor nano-size structures, also referred to as artificial atoms, were used to generate deterministic single and entangled photons. The entanglement generation was verified by so called Bell tests, were the measurement of one of the entangled photons, instantaneously influences the measurement outcome of the other photon at a distant location. We were able to violate this Bell´s inequality for the first time with such nano-scale light sources. Furthermore, we were able to integrate such emitters in complex photonic circuits based on the mature silicon technology platform, enabling the first routing, filtering multiplexing, and demultiplexing of single photons on-chip. Our hybrid fabrication approach is platform independent and will allow for deterministic integration of quantum emitters in large scale photonic circuits. In parallel we worked together with the company Single Quantum B.V. to optimize their single-photon detectors. By carefully redesigning the resonator around the detector and optimizing the nanofabrication efficiencies close to unity have been achieved. This resulted in a new product with already over 25 sold detectors in the last two years with costumers in the academic and private sector.

Quantum light sources and detectors are key technologies for future quantum communication applications. Increasing the efficiency up to unity of both building blocks is of crucial importance to increase the possible communication range. This would allow for a practical implementations of secure communication in real world applications. Given the start of the European Quantum Flagship more investments in high-tech quantum devices, such as the detectors developed by Single Quantum B.V. will be made and the market for quantum tech will open up. Currently the quantum community has yet to decide on the most suitable candidate as the quantum light source of choice for quantum communication applications. The results obtained in the project SiPhoN on the source clearly pushed semiconductor quantum dots back into the spotlight and I expect them to have a bright future in the upcoming second quantum revolution.

Periodic Reporting for period 1 - SiPhoN (Single-Photon Non-Locality)

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