Progress Report
Fault-tolerant Quantum Computing with Photonically Interconnected Ion Traps[6] Arranging individual trapped ions with junction traps
Progress until FY2024
1. Outline of the project
In the Moonshot Goal 6 project, we are developing a method to arrange ions of different elements in arbitrary sequences within an ion trap. This technology is essential for extending computation time and increasing the number of qubits.
While a 2D ion trap is suited for ion transport, 3D ion traps offer deeper and more stable confinement. In this study, we are developing a novel trap device using micro- fabricated 3D electrodes capable of simultaneously trapping and arranging Ca and Sr ions, with cooperative (sympathetic) cooling in mind.
2. Outcome so far
In FY2024, we continued the production of Y-junction-type 3D microfabricated ion trap. Due to difficulties in finding a domestic supplier capable of managing all fabrication steps, we divided the process into six parts and outsourced each stage. By March 2025, five of six steps had been completed, with final assembly underway.
- Procurement of high-purity alumina substrates
- Through-hole drilling of substrates using laser
- Ti/Au deposition via electron beam evaporation
- Patterning using picosecond laser processing
- Gold electroplating
- Electrode assembly (Ongoing)
We evaluated the slit widths in the laser-cut trap substrate, confirming fabrication accuracy within 5% tolerance (3.3% and 3.8% deviations at entry and exit, respectively as shown in Figure 1. A gold layer was then formed via electron beam deposition and electroplating, achieving a surface roughness of 0.32 μm.
The effect of the obtained processing characteristics on ion transport was then evaluated by numerical simulation. Figure 2 shows the trajectory of ions in the electrode model reflecting the processing characteristics. As can be seen, it was confirmed that ions can be captured at the center of the electrode. The increase in kinetic energy during the transport process from electrode 1 to electrode 5 was also quantitatively evaluated and found to be sufficiently smaller than the depth of the trapping potential, indicating that ion transport is expected to be stable even after taking processing errors into account.
As shown in Figure 3, the machining of the electrodes has been completed, and as soon as the assembly process is complete, they will be installed in the experimental apparatus and the experiment will begin.
3. Future plans
Once assembly is complete, we will begin experiments with Ca/Sr ion trapping and transport. By dynamically adjusting electrode voltages, we aim to achieve precise ion arrangement for quantum logic operations.
This research aligns with the Expo 2025 Osaka–Kansai theme of “Designing Future Society for Our Lives,” to contribute to the creation of a future society where quantum computing enables secure information processing, scientific breakthroughs, and innovations in daily life.