A new generation of specialty optical fibers has been developed by physicists at the University of Bath in the UK to cope with the challenges of data transfer expected to arise in the future age of quantum computing. The cable networks used today to transmit information across the globe are likely to be sub-optimal for quantum communi­­cations, due to the solid cores of their optical fibers. Unlike regular optical fibers, the specialty fibers fabri­cated at Bath have a micro-structured core, consisting of a complex pattern of air pockets running along the entire length of the fiber.

“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. 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,” said Kristina Rusimova from the Department of Physics at Bath. Rusimova and her colleagues describe the state-of-the-art fibers, along with other recent and future developments in the emerging field of quantum computing. “Optical-fiber design and fabrication is at the forefront of the University of Bath Department of Physics research, and the optical fibers we are developing with quantum computers in mind are laying the foundations for the data transmission needs of tomorrow,” she adds.

Unlike the binary bits of classical computers, pairs of entangled photons can in fact exist as both a one and a zero at the same time, unleashing enormous amounts of compu­tational power. Cameron McGarry, until recently a physicist at Bath, said: “A quantum internet is an essential ingredient in delivering on the vast promises of such emerging quantum technology. “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.”

In a perspective, the researchers discuss the associated challenges of the quantum internet from the viewpoint of optical fiber techno­logy and present an array of potential solutions for scalability of a robust, wide-scale quantum network. This encompasses both the fibers that will be used for long-range communi­cation, and specialty fibers that will allow for quantum repeaters, integrated directly into the network in order to extend the distance over which this technology can operate. Specialty optical fibers can go beyond connecting nodes of a network to imple­menting quantum computation at the nodes themselves by acting as sources of entangled single photons, quantum wavelength converters, low-loss switches, or vessels for quantum memories.

McGarry said: “Unlike the optical fibers that are standardly used for telecommuni­cations, specialty fibers which are routinely fabricated at Bath have a micro-structured core, consisting of a complex pattern of air pockets running along the entire length of the fiber. 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.”

“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 postdoc Kerrianne Harrington. “Our per­spective describes the exciting advances of these novel fibers and how they could be beneficial to future quantum techno­logies.” Her colleague Alex Davis added: “It's the ability of fibers to tightly confine light and transport it over long distances that makes them useful. 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.”

Quantum advantage – the ability of a quantum device to perform a task more effi­ciently than a conventional computer – has yet to be conclusively demonstrated. The technological challenges identified in the perspective are likely to open new avenues of quantum research, and bring us closer to achieving this important milestone. The new optical fibers are expected to help lay the foundations for the quantum computers of tomorrow. (Source: U. Bath)

Reference: C. McGarry et al.: Microstructured optical fibers for quantum applications: Perspective, APL Quantum 1, 030901 (2024); DOI: 10.1063/5.0211055

Link: Centre for Photonics and Photonic Materials, Dept. of Physics, University of Bath, Bath, UK