Quantum technologies promise unparalleled computational power, leading to the development of new medicines and unbreakable cryptographic techniques for secure communications. But achieving seamless, low-loss integration between quantum network components and optical fibers for quantum data transmission is a formidable challenge. To support efficient data transfer between quantum computers in the future, researchers at the University of Bath are developing a new generation of optical fibers that feature a microstructured core. The microstructure consists of a complex pattern of air pockets running along the entire length of the fiber. Unlike traditional optical fibers, where light is guided in a silica core through total internal reflection, the guidance properties of these fibers are dictated and can be tailored by the design of the microstructured glass cladding that surrounds the core. The structure of the cladding depends on the guidance mechanism. The fiber core itself can be either solid or hollow. Optical fibers developed by University of Bath researchers feature microstructured glass cladding surrounding their core in order to tailor their functionality. Courtesy of the University of Bath/Cameron McGarry. “The pattern of these air pockets is what allows researchers to manipulate the properties of the light inside the fiber and create entangled pairs of photons, change the color of photons, or even trap individual atoms inside the fibers,” researcher Cameron McGarry said. The microstructured fibers provide a wide range of functionality. For example, the nonlinearity of solid core photonic crystal fibers would allow photon pairs to be generated directly inside optical fibers that could then be seamlessly spliced into conventional solid-core networks. Correlated photon-pair generation would enable the resource states required for many photonic implementations of quantum technology, including entangled pairs and the single photons that can be derived from them. Loss of quantum information as it travels over a distance could be reduced by transmitting it across mid- to long-range distances with hollow core fiber, which offers fast, low-latency data transfer. Coupling losses could be mitigated by integrating atomic vapors for storage and switching within the core of a hollow core fiber. The optical nonlinearity of solid core and gas-filled hollow core fibers could provide a valuable medium for quantum frequency conversion between the operating wavelengths of existing quantum photonic material architectures. The creation of photonic links between different wavelength bands is a key requirement for compatibility between processing nodes and memory technologies in future quantum networks. “The conventional optical fibers that are the workhorse of our telecommunications networks of today transmit light at wavelengths that are entirely governed by the losses of silica glass,” said researcher Kristina Rusimova. “However, these wavelengths are not compatible with the operational wavelengths of the single-photon sources, qubits, and active optical components that are required for light-based quantum technologies.” The researchers are exploring the types of fibers that would be needed for data transmission over a quantum internet, including the optical fibers that would be used for long-range communication and the specialty fibers that would allow for quantum repeaters integrated directly into the network to extend the distance over which the technology operates. “A quantum internet is an essential ingredient in delivering on the vast promises of such emerging quantum technology,” said McGarry. “Much like the existing internet, a quantum internet will rely on optical fibers to deliver information from node to node. These optical fibers are likely to be very different to those that are used currently and will require different supporting technology to be useful.” The team is also investigating how specialty optical fibers could be used to implement quantum computation at the nodes of a network by acting as sources of entangled single photons, quantum wavelength converters, low-loss switches, or vessels for quantum memories. “It’s the ability of fibers to tightly confine light and transport it over long distances that makes them useful,” sad researcher Alex Davis. “As well as generating entangled photons, this allows us to generate more exotic quantum states of light with applications in quantum computing, precision sensing, and impregnable message encryption.” The technological challenges of quantum data transmission, and the potential solutions identified by the University of Bath team, could open new avenues of quantum research. The team expects that the optical fibers it is fabricating will help lay the foundations for efficient data transmission across a wide-scale quantum network. “Researchers around the world are making rapid and exciting advancements in the capabilities of microstructured optical fibers in ways that are of interest to industry,” said researcher Kerrianne Harrington. “Our perspective describes the exciting advances of these novel fibers and how they could be beneficial to future quantum technologies.” The research was published in APL Quantum (www.doi.org/10.1063/5.0211055).
