# Entanglement, decoherence, and the measurement problem

## TL;DR

This paper clarifies that entangled states in quantum mechanics are superpositions of correlations rather than superpositions of macroscopic states, resolving the measurement problem through nonlocal coherence and standard quantum theory.

## Contribution

It demonstrates that the quantum measurement problem is resolved by understanding entanglement as superpositions of correlations, not states, eliminating the need for a collapse postulate.

## Key findings

- Entangled states are superpositions of correlations, not macroscopic superpositions.
- Nonlocal interferometry experiments support the correlation superposition view.
- Collapse arises naturally from entanglement and macroscopic registration, without extra postulates.

## Abstract

The entangled Schrodinger cat state obtained immediately upon measurement of a superposed two-state quantum system is often considered paradoxical because it appears to predict two macroscopically different outcomes, such as an alive and dead cat. However, nonlocal interferometry experiments testing momentum-entangled photon pairs over all phases demonstrate that the cat state does not fit this description and is not paradoxical. Both experiment and theory imply that it instead represents a superposition of two nonlocally coherent (i.e. phase-dependent) statistical correlations between its sub-systems. This is not paradoxical. Standard quantum theory rigorously predicts the experimentally-observed outcomes of this state. Neither sub-system is superposed; rather, the correlations between the states of the subsystems are superposed. This resolves the problem of definite outcomes. The nonlocal properties of entanglement then ensure that only one outcome occurs while the other outcome simultaneously does not occur, resolving a problem posed by Einstein in 1927. The single outcome that occurs then triggers an irreversible process leading to macroscopic registration of the outcome. This resolves the quantum measurement problem. Collapse occurs because of entanglement and does not require a special collapse postulate. Collapse is a consequence of standard quantum physics and the irreversible nature of the macroscopic registration.

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Source: https://tomesphere.com/paper/1904.04234