We are currently experiencing a second quantum revolution in which quantum mechanics is moving from a laboratory curiosity to a real-world tool. Proof of this is the development of sophisticated quantum information networks. To continue advancing in this field, it is extremely important to have technologies based on the manipulation of light capable of addressing the challenges that currently exist and whose solutions have been elusive until now. This is the case for quantum frequency conversion and long-distance transport of single photons and entangled pairs of photons.
In an investigation led by David Novoa, Ikerbasque Researcher at the UPV/EHU, and published in the prestigious journal Science, a new type of micro-structured optical fiber is shown that, unlike the conventional fibers that bring the Internet to our homes, guides light into a hollow channel with extremely low attenuation. These types of optical fibers that are like "pipes for light" are unique in that their optical properties are reconfigurable when filled with gas at different pressures. This makes them highly versatile platforms, capable of operating in an unprecedented spectral range, from ultraviolet to infrared.
In this research they have filled the fiber with hydrogen (gas), since it is the lightest molecule in nature and, therefore, the one with the highest fundamental vibrational frequency. By means of what is known as the stimulated Raman effect, they are able to optically excite the molecules of the gaseous nucleus so that they oscillate precisely in sync. In the words of David Novoa, “it is in this molecular choreography where the beauty of our system lies: Quantum light sources (photons) are capable, under certain circumstances, of extracting the vibrational energy of these oscillating molecules to increase their own energy and thus change frequency (color)”.
This work demonstrates the application of a cutting-edge technology such as anti-resonant optical fibers, for the improvement of a critical process in quantum technologies related to light, such as quantum frequency conversion. Complex systems such as, for example, quantum networks are made up of different sub-systems whose optimum operating frequency does not usually coincide. That is why a technique capable of converting optical frequencies at the quantum level over a broad spectrum without affecting the properties of the original light sources would be extremely useful.
This research is the result of an international collaboration involving the Max-Planck Institute for the Science of Light and the Friedrich-Alexander Universität in Germany.