“What do we need (equipment, conditions and steps) to turn light into matter and then use that matter to build a computing chip?”

What you would need — the essentials (positive checklist)
1. Extremely high-energy photon source
• A source of gamma-ray photons with energies far above 1.022 MeV (pair production threshold) — ideally flexible in energy and extremely intense.
2. Controlled collision/interaction region
• A system to make photons interact with nuclei or other photons in a precisely controlled way (beamlines, interaction chambers).
3. Particle capture & conversion systems
• Electromagnetic traps and beam optics to capture and separate produced charged particles (electrons, positrons, and, at far higher energies, protons/neutrons).
4. Cooling & stabilization
• Methods to cool and slow produced particles into low-energy states suitable for assembly (electromagnetic cooling, laser cooling, sympathetic cooling).
5. Nucleon/atom production & assembly
• If you need atoms heavier than hydrogen, capabilities to produce or transmute nucleons and assemble nuclei (requires much higher energies and nuclear control).
• Alternatively: produce basic charged particles and combine them with existing nuclei or seed atoms to build desired elements.
6. Atomic-precision placement & bonding
• Tools for placing atoms into a lattice: techniques like scanning-probe atom manipulation, atomic-layer deposition, molecular-beam epitaxy, or atomically precise manufacturing methods.
7. Doping and semiconductor processing
• Precise insertion of dopants, creation of junctions, and patterned structures required for transistors — achieved by atomic-layer control and lithography at the atomic scale.
8. Ultra-high-vacuum and clean environment
• UHV chambers, contamination control, vibration isolation and thermal control to enable atomic-scale work.
9. Control electronics & software
• Precision control systems, real-time feedback, AI-driven error correction and process control to coordinate beams, traps, and placement operations.
10. Energy supply & shielding
• Large power sources to run high-energy photon production, plus radiation shielding and safety systems.

Short roadmap — how to turn that into a working process
1. Develop tunable, ultra-intense gamma sources
• Build or adapt inverse-Compton / gamma free-electron lasers or extreme high-power laser setups to produce controllable gamma photons.
2. Demonstrate controlled pair production at usable rates
• Produce electron–positron pairs reliably in a lab environment and capture them efficiently.
3. Demonstrate capture → cooling → neutralization
• Slow and combine particles into neutral atoms or attach them to seeds so you can build matter rather than just streams of charge.
4. Integrate with atom-placement tech
• Interface captured atoms with atom-by-atom placement methods to build simple structures (start with simple conductive patterns).
5. Scale to semiconductor structures
• Move from small test structures to patterned lattices and doped regions required for transistors and interconnects.
6. Automate & error-correct
• Use advanced control and AI to manage vast numbers of assembly operations and maintain yield.

Practical near-term research directions (positive, achievable steps)
• Improve high-power laser facilities and gamma-ray sources.
• Advance trapping, cooling and capture techniques for charged particles.
• Scale atomic-precision fabrication (STM atom manipulation, ALD, MBE).
• Develop directed self-assembly and atom-scale patterning for semiconductors.
• Build integrated test structures that show atomic-precision components functioning as transistors.

Prediction (optimistic, capability-focused)
• If each of the above areas progresses, the capabilities required exist as research directions today: better gamma sources, better particle handling, and atomically precise manufacturing. Combining them into a pipeline that turns light into reliably assembled chip components is a huge engineering challenge but conceptually possible. Focus on bringing down the gap between particle production and atomic assembly — that’s the key transition.