A team of scientists from Waseda University, the Japan Science and Technology Agency, and the University of Auckland developed an integrated, all-fiber coupled-cavities quantum electrodynamics (QED) system, in which a meter-long portion of conventional optical fiber seamlessly and coherently connects two nanofiber cavity-QED systems. A cavity-QED system is a system in which photons and atoms are confined within an optical resonator and interact with each other in a quantum-mechanical manner. Cavity-QED systems have been used as experimental platforms for helping scientists to better understand and manipulate the quantum properties of photons and atoms. This is an experimental device for an all-fiber, coupled-cavities QED system. Courtesy of Aoki Laboratory, Waseda University. Integrating multiple cavity-QED systems with coherent, reversible coupling between each system is necessary if these systems are to be used for quantum computation. Professor Takao Aoki and his team approached this challenge by demonstrating a system consisting of two nanofiber cavity-QED systems connected to each other in an all-fiber fashion. In each cavity, an ensemble of several tens of atoms interacts with the cavity field through the evanescent field of a nanofiber. Both ends of the nanofiber are connected to standard optical fibers through tapered regions and sandwiched by a pair of fiber-Bragg-grating mirrors. “Multiple resonators can be connected with minimal losses using additional, standard optical fiber, making the coherent, coupled dynamics of the two nanofiber cavity-QED systems possible,” Aoki said. With this low-loss, all-fiber system, the team was able to observe a reversible interaction between atoms and delocalized photons separated by distances of up to two meters — a first in any such quantum optical system, according to the team. “Our achievement is an important step towards the physical implementation of cavity-QED-based distributed quantum computation and a quantum network, where a large number of cavity-QED systems are coherently connected by low-loss fiber channels,” Aoki said. “In such systems, quantum entanglement over the whole network can be created deterministically, instead of probabilistically.” The system could also open the way for the study of many-body physics — the collective behavior of interacting particles in large numbers — with atoms and photons in a network of cavity-QED systems, including phenomena such as quantum phase transitions of light. The team is now making technical improvements to the setup to extend its work to the construction of a fiber network of coherently coupled, single-atom cavity-QED systems. This work will include reduction of uncontrolled losses in the cavities, active stabilization of the cavity resonance frequencies, and extension of the lifetimes of the atoms in the traps that hold them near the nanofibers. The research was published in Nature Communications (https://doi.org/10.1038/s41467-019-08975-8).
