June 2021 Issue
Research Highlights

Innovative building blocks for the quantum internet:
All fiber platform for quantum photonic processing on tapered optical fibers

Research on quantum photonics is focused on the coherent control of individual quanta of light known as photons. Such control of light is an important step towards the realization of optical quantum networks and ultimately the so-called quantum internet.

Notably, single photons can be efficient carriers of quantum information, and they travel at the speed of light incurring the minimal of interaction with the medium through which they move. However, these same physical characteristics lead to difficulties in isolating (generation) and controlling (storage/retrieval/switching) single photons.

A solution to this problem is the development of means to control photons using atomic media. In this approach, one key requirement is to be able to confine atoms and photons to subwavelength dimensions, that is, within a single atom absorption cross-section to realize efficient light-matter interaction at the single quanta level. Therefore, there has been increasing interest in the strong confinement of photonic modes in nanophotonic waveguides and resonators that exhibit quantum electrodynamics (QED) effects.

Now, Kali Prasanna Nayak and colleagues at the University of Electro-Communications, Tokyo, are developing a unique all-fiber platform for quantum photonics applications using tapered subwavelength diameter waist optical nanofibers.

The key feature of the UEC optical nanofiber technology is that the optical field is tightly confined in the transverse direction while propagating over long distances as a guided mode and enabling strong interaction with the surrounding medium in the evanescent region. This characteristic has led to unique possibilities for manipulating single atoms (solid-state quantum emitters) and fiber-guided photons. Furthermore, implementing even moderate longitudinal confinement in nanofiber cavities has enabled the strong coupling regime of cavity QED where coherent light-matter interaction can be realized at the single quanta level.

Based on their achievements to-date, Nayak and colleagues are developing both quantum interfaces between trapped (laser-cooled) single atoms and fiber-guided photons using photonic crystal nanofiber cavities, and fiber-coupled quantum light sources using hybrid systems of single quantum dots deposited on nanofibers. These fiber-coupled quantum photonics platforms show promise as building blocks for optical quantum processors and can be easily integrated into optical quantum networks.

Schematic diagram of a nanofiber-based quantum interface. The nanofiber is located at the waist of a tapered single mode optical fiber. The nanofiber cavity (ONF Cavity) is formed by fabricating two photonic crystal (1-D PhC) Bragg mirrors on the nanofiber using femtosecond laser ablation. Single atoms are trapped and interfaced to the nanofiber cavity using a tightly focused optical dipole trap (single atom tweezer).


  • Authors: Kali P. Nayak, Mark Sadgrove, Ramachandrarao Yalla, Fam Le Kien and Kohzo Hakuta
  • Title of original paper: Nanofiber quantum photonics
  • Journal, volume, pages and year: J. Opt. 20, 073001 (2018).
  • Digital Object Identifier (DOI): 10.1088/2040-8986/aac35e
  • Affiliations: Department of Engineering Science, University of Electro-Communications.
  • Department website: http://kjk.office.uec.ac.jp/Profiles/56/0005533/prof_e.html