Towards Distributed Quantum Computing with Photon-based Coupling between Distant Atoms
Distributed quantum computing has immense potential to revolutionize several sectors such as drugs and material development, finance, health and climate monitoring, and cybersecurity. Distinct features of this technology include large-scale quantum cimputing (that is, quantum computing with a much larger number of qubits than that employed in the current quantum computing hardware) and a full integration of quantum computers into a quantum network to realize a “quantum internet.”
Scientists working towards this goal use a prototypical experimental platform to understand and manipulate the quantum properties of photons and atoms. In this system, known as a “cavity-quantum electrodynamics (QED) system,” photons, the quanta of electromagnetic radiation, and atoms are confined within an optical resonator (cavity), where they interact with each other obeying the rules of quantum mechanics.
Integration of multiple cavity-QED systems with coherent, reversible coupling between each system is a critical requirement to make distributed quantum computing feasible. However, achieving a strong and efficient coupling of cavity-QED systems has been extremely challenging. To this end, a team of researchers led by Professor Takao Aoki from the Department of Applied Physics at Waseda University has now demonstrated a system consisting of two nanofiber cavity-QED systems that are 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 which 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.
The team showed that atom-photon and photon-photon interactions in this system generate five unique configurations or “normal modes.” They also demonstrated remote excitation of an individual normal mode and nonlocal saturation of atoms.
Further, the team performed experimental and theoretical investigation of the “cavity dark mode,” a configuration where two cavities coupled directly to the atoms did not show photonic excitation. Moreover, they showed that the coupling rate between atoms and photons is independent of the length of the connecting-fiber.
The team achieved a reversible interaction between atoms and delocalized photons separated by distances of up to two meters, leading to the generation of “dressed states” of distant atoms for the first time in any such system.
This study is a major stepping stone towards the physical realization of cavity QED-based distributed quantum computation that employs low-loss fiber channels to coherently connect a large number of cavity-QED systems. Furthermore, the proposed system provides a platform for the study of “many-body systems,” characterized by the collective behavior of a large number of interacting particles and could help realize quantum computers with unprecedented computing capabilities.
Link to the original journal articles:
https://www.nature.com/articles/s41467-019-08975-8
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.253603
About the author
Dr. Takao Aoki is a Professor of Applied Physics at the Faculty of Science and Engineering, School of Advanced Science and Engineering, Waseda University in Japan. Dr. Aoki received his Ph.D. from The University of Tokyo in Japan. His research focuses on quantum optics and atomic physics. His lab is currently working to build quantum computing hardware based on nanofiber cavity QED. He has authored over 46 articles with over 1,766 citations.
