Experimental Tests

Foundational experiments test a defined physical or probabilistic hypothesis through measured data. This chapter connects coherence experiments, temporal correlations, precision null tests, and gravity-interface proposals without treating them as interchangeable “tests of quantum reality.” The recurring question is which assumptions turn an observation into a constraint.

Enter this chapter

Begin with Macroscopic Superpositions to distinguish branch populations from coherence. Follow it with the platform appropriate to the observable:

• Matter-Wave Interferometry measures spatial center-of-mass coherence.
• Superconducting Cat States measures coherence between oscillator branches.
• Optomechanical Tests separates cooling, nonclassical state preparation, and excess-noise bounds.

Then read Collapse-Model Tests for the translation from those measurements to a parameterized modification of dynamics. The physical coupling determines which platform is sensitive; “macroscopic” alone is not a coupling constant.

Three kinds of experimental inference

A witness certifies that observed data lie outside a specified set, such as separable states or a macrorealist probability model. A parameter bound excludes a region of a quantitative alternative. A null test examines a combination predicted to vanish after apparatus effects have been included. These forms can overlap, but each requires its own uncertainty analysis.

For example, an extra dephasing model predicts $V/V_0=e^{-\Gamma t}$. A lower confidence bound $r_{\min}$ on that ratio gives

$$\Gamma<-\frac{\ln r_{\min}}{t}.$$

This inference assumes the reference visibility $V_0$ is independently controlled. A fitted contrast deficit alone does not identify the mechanism that caused it.

The temporal tests introduce an additional issue: measuring earlier can disturb the later system. Leggett–Garg Tests explains the correlation protocols; Tests of Macrorealism isolates definite-value assumptions from noninvasiveness.

Precision and causality routes

Precision Tests of the Born Rule examines higher-order interference and detector linearity. Tests of Linearity considers state-dependent phase evolution and the composite-system rules a modified dynamics needs.

Tests of No-Signaling concerns locally accessible marginals, which must be distinguished from coincidence-selected data. A Bell violation can coexist with exact no-signaling; Bell-Test Experiments explains the spatial-correlation protocols and their historical development.

Gravity-Mediated Entanglement explains why a witness can constrain a mediator only after preparation, locality, and unwanted interaction channels have been specified. Its branch-phase calculation is a proposal model, not a claim of completed experimental certification.

A reading checkpoint

When reading an experimental paper, identify the measured quantity before reading its interpretation. Record the alternative’s equations, the detector response, accepted-trial definition, systematic controls, and statistical construction. Ask what a null result would exclude and what ordinary mechanism could imitate a positive result.

The Experimental Foundations Roadmap turns this into an investigation strategy. Dated examples in the chapter illustrate methods; a historical experiment’s quoted sensitivity is not automatically the strongest bound today.

References

• Bassi, A., et al., “Models of wave-function collapse, underlying theories, and experimental tests,” Reviews of Modern Physics 85, 471–527 (2013), arXiv:1204.4325 — dynamics modifications and experimental observables.
• Emary, C., Lambert, N., and Nori, F., “Leggett–Garg inequalities,” Reports on Progress in Physics 77, 016001 (2014), arXiv:1304.5133 — temporal tests and disturbance.