Quantum Sensing for Fusion Diagnostics

Quantum sensors, distinct from quantum computers, offer precision magnetometry and metrology that could sharpen future diagnostics on the Kronos machines.

A different quantum technology

Quantum sensing is separate from quantum computing and much closer to deployment. It uses quantum coherence, in atoms, defects, or superconducting circuits, to measure fields, time, and motion at fundamental precision limits. For fusion diagnostics the interesting cases are magnetometry (for the breeder's high-field environment) and ultra-stable frequency references.

# Quantum-limited phase sensing: N probes, coherence time T
standard quantum limit (independent probes):  d_phi ~ 1/sqrt(N)
Heisenberg limit (entangled probes):          d_phi ~ 1/N
# entanglement buys a sqrt(N) improvement in field/phase resolution
# NV-center magnetometry: shift ~ gamma_e * B  measured via spin readout

Candidate uses on the machines

• NV-center or atomic magnetometers as calibration references for magnetic diagnostics near the 16.84 T breeder magnets.
• Optically pumped and atomic clocks for high-stability timing of diagnostic acquisition.
• Quantum-enhanced interferometry for precision density or displacement metrology in specialized diagnostics.

Honest placement

Even quantum sensing must survive the fusion environment: intense 14 MeV neutron and gamma fields, strong background magnetic fields, and vibration. Many quantum sensors are sensitive to exactly these, so realistic use is as bench and calibration references or in shielded, low-radiation locations, not as primary in-vessel plasma diagnostics, which remain classical (interferometry, Thomson scattering, magnetic coils).

Kronos tracks quantum sensing as a nearer-term, lower-risk quantum technology than quantum computing, with concrete potential as a metrology backbone for the classical diagnostics constellation. It makes no operational claim today; it is a watch-and-benchmark item alongside the compute work, and it shares only the word 'quantum' with the materials-simulation program.