The work of researchers from Sweden’s KTH Royal Institute of Technology and Austria’s Johannes Kepler University Linz is making it possible to integrate optical switches and single-photon detectors in a single chip. Supported by the EU-funded S2QUIP project, the research team has helped to further the field of quantum computing by developing a new heat-free method for controlling single photons. The team’s work and findings are published in the journal ‘Nature Communications’. Current optical switches work by heating light guides inside a semiconductor chip. “This approach does not work for quantum optics,” remarks first author Samuel Gyger of S2QUIP project partner KTH Royal Institute of Technology in a news item posted on the ‘EurekAlert!’ website. “Because we want to detect every single photon, we use quantum detectors that work by measuring the heat a single photon generates when absorbed by a superconducting material. If we use traditional switches, our detectors will be flooded by heat, and thus not work at all,” Gyger goes on to explain. The heat generated by reconfigurable photonic circuits is therefore incompatible with heat-sensitive superconducting single-photon detectors, making the integration of these circuits and detectors on one chip difficult.
Removing heat from the optical switch equation
To solve this problem, the researchers developed an optical switch that’s reconfigured with microscopic electromechanical motion instead of heat. Single photons can therefore be controlled without the semiconductor chip heating up and incapacitating the single-photon detectors. This makes the switch compatible with the heat-sensitive detectors, therefore enabling their integration on a single chip. In addition to demonstrating the on-chip compatibility of reconfigurable photonic circuits and superconducting single-photon detectors, the researchers also demonstrated three key functionalities of photonic quantum technologies. These are reconfigurable routing of classical and quantum light, high-dynamic range detection of single photons and power stabilisation of optical excitation using a feedback loop. Their results showed that combining microelectromechanical systems and superconducting nanowire single-photon detectors “enables the on-chip integration of not only the main building blocks of quantum optics, but also devices for adaptive control, monitoring, and stabilization of classical and quantum optics,” the study reports. “Our technology will help to connect all building blocks required for integrated optical circuits for quantum technologies,” observes co-author Carlos Errando-Herranz of KTH Royal Institute of Technology in the ‘EurekAlert!’ article. “Quantum technologies will enable secure message encryption and methods of computation that solve problems today’s computers cannot. And they will provide simulation tools that enable us to understand fundamental laws of nature, which can lead to new materials and medicines.” The goal of S2QUIP (Scalable Two-Dimensional Quantum Integrated Photonics) is to bring about a paradigm shift in the development of scalable, cost-effective integrated-chip quantum light sources. The project ends in March 2022. For more information, please see: S2QUIP project website
S2QUIP, quantum, single-photon detector, optical switch, chip