# Quantum Foundations: State of the Field (October 2026)

Research dossier · v1 · updated 2026-10-30 · 3,333 words · 42 sources · 28 claims · verification: verified

This dossier surveys quantum foundations as of October 2026: loophole-free Bell tests, contextuality, extended Wigner's friend arguments and experimental bounds on spontaneous collapse models. The main takeaway is that nonlocality is well established under loophole-free conditions, while the measurement problem and the status of collapse models remain open.

## Contents

- Executive summary
- Background and core concepts
- Timeline of key milestones
- State of the art
  - Loophole-free Bell tests
  - Device-independent applications
  - Contextuality and nonlocality
  - Extended Wigner's friend arguments
  - Collapse models and experimental bounds
  - Quantitative benchmarks
- Open problems and active debates
- Major programs and players
- Outlook: what to watch (next 12-18 months)
- Key papers
- Glossary

## Sample findings

- Hensen et al. reported a loophole-free Bell violation using entangled electron spins in diamond separated by 1.3 km; a 2016 paper describes this as the first loophole-free evidence against local-realist theories.
- In 2015, one photonic test was reported as strong loophole-free (Shalm et al., with all relevant events spacelike separated) and another as significant-loophole-free (Giustina et al.), both violating local realism.

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