The collapse postulate says measurement destroys unrealized quantum amplitudes. The unitary theory says those amplitudes persist — the measurement apparatus becomes entangled with the system, and the “unrealized” branches continue to exist in the joint state.
Adami, Giner, Lundeen, and Abrahao test this experimentally. They perform three or more consecutive measurements on single-photon quantum states and analyze the resulting joint density matrix. If collapse occurs at each measurement, the density matrix should show no coherence between different measurement outcomes. If unitary evolution continues, the coherence should be present.
The joint density matrix shows coherence. The pattern is consistent with unitary evolution, not collapse. The unrealized amplitudes from earlier measurements remain and influence the correlations observed in later measurements.
The control experiment confirms the interpretation: when decoherence is deliberately introduced between measurements — mimicking the environmental entanglement that standard quantum mechanics predicts should look like collapse — the coherence vanishes and the results match collapse-theory predictions. The decoherence acts as an effective collapse, reproducing the collapse phenomenology from purely unitary dynamics.
The experiment doesn't prove consciousness doesn't collapse the wave function or that many worlds is correct. It shows that within the laboratory, the unrealized amplitudes demonstrably persist through consecutive measurements and can be detected in the multi-measurement correlation structure. What “really happens” at measurement is still interpretation. What the joint density matrix shows is data.