Low-Loss, All-Fiber System Supports Coupling Between Distant Atoms

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TOKYO, April 3, 2019 — 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.

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 ( 

Published: April 2019
The term quantum refers to the fundamental unit or discrete amount of a physical quantity involved in interactions at the atomic and subatomic scales. It originates from quantum theory, a branch of physics that emerged in the early 20th century to explain phenomena observed on very small scales, where classical physics fails to provide accurate explanations. In the context of quantum theory, several key concepts are associated with the term quantum: Quantum mechanics: This is the branch of...
quantum optics
The area of optics in which quantum theory is used to describe light in discrete units or "quanta" of energy known as photons. First observed by Albert Einstein's photoelectric effect, this particle description of light is the foundation for describing the transfer of energy (i.e. absorption and emission) in light matter interaction.
An SI prefix meaning one billionth (10-9). Nano can also be used to indicate the study of atoms, molecules and other structures and particles on the nanometer scale. Nano-optics (also referred to as nanophotonics), for example, is the study of how light and light-matter interactions behave on the nanometer scale. See nanophotonics.
Research & TechnologyeducationAsia-PacificWaseda Universityfiber opticsOpticsquantumquantum opticsquantum communicationsCommunicationsquantum computingquantum electrodynamics systemnano

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