Outline of Research and Development Items

This project aims to develop a new type of quantum computer hardware that can be scaled up and distributed, based on unique nanofiber cavity QED technology, and to realize a distributed fault-tolerant quantum computer with a large number of qubits. Using Ytterbium (Yb), a two-electron atom, we are developing nanofiber cavity QED hardware that maximizes its characteristics, and also working on technology development for scaling up compatible Yb atomic qubits.
The goal is to contribute to the development of fault-tolerant quantum computers using a new type of quantum computer hardware that can be scaled up and distributed, based on Dr. Aoki PM's unique nanofiber cavity QED technology, building upon the already successful development of the basic operation of Yb atomic array technology.

Overview of Research and Development Challenges Composing the Research and Development Item

In the development of nanofiber cavity QED quantum computers, it is necessary to implement a large-scale optical tweezer array of cooled Yb atoms adjacent to the nanofiber. Ideally, the qubit characteristics should include the ability to hold quantum information for a long time, along with an optical transition qubit that directly couples to the nanofiber cavity. Furthermore, unlike conventional optical tweezer array systems, it is necessary to efficiently couple atoms in the optical tweezer array with nanofibers whose spatial arrangement is predetermined. This requires not only a large-scale two-dimensional array but also a three-dimensional stacked array with spatial controllability in the depth direction, followed by the realization of layer-selective detection and manipulation. Therefore, the goal for FY2025, the research period, is to achieve "implementation of Yb atomic 3D stacked arrays and their layer-selective nuclear spin qubit manipulation," and for that purpose, the goal for FY2024 was set as the "realization of Yb isotope atomic arrays."

Progress and Research Results

First, to improve the performance of atomic arrays, we investigated the possibility of Yb isotope atomic arrays consisting of ¹⁷¹Yb atoms with nuclear spin 1/2 and ¹⁷⁴Yb atoms with a ¹S₀ (m=0)-³P₂ (m=0) optical transition robust to magnetic field fluctuations. Through previous research, as shown in the figure below, we succeeded in generating an Yb atomic hybrid atomic array system. After probabilistically introducing two isotopes randomly into the optical tweezer array, we succeeded for the first time in the world in deterministically generating a defect-free hybrid atomic array by applying the developed isotope-specific rearrangement algorithm.
In particular, in the realized Yb atomic hybrid atomic array system, we succeeded in verifying the possibility of crosstalk and confirmed that it is negligibly small.

The checkerboard-type defect-free 2D array system of dual Yb isotope atoms realized in this research is an unforeseen achievement that offers significant advantages for implementing quantum error correction using surface codes. Going forward, we will continue to explore the possibilities of this system, including the implementation of two-qubit gates.