A Localized Reality Appears To Underpin Quantum Circuits

TL;DR

This paper presents evidence that quantum circuit behavior can be explained by localized variables through weak values, suggesting a realistic underpinning for quantum mechanics despite entanglement.

Contribution

It introduces a localized account of quantum circuits using weak values, challenging the view that entangled states lack classical realism.

Findings

Weak values evolve only at local circuit elements.

Exchange interactions show classical-like evolution of weak values.

All-at-once models can generate weak values without state vectors.

Abstract

Although entangled state vectors cannot be described in terms of classically realistic variables, localized in space and time, any given entanglement experiment can be built from basic quantum circuit components with well-defined locations. By analyzing the (local) weak values for any given run of a quantum circuit, we present evidence for a localized account of any circuit's behavior. Specifically, even if the state is massively entangled, the weak values are found to evolve only when they pass through a local circuit element. They otherwise remain constant and do not evolve when other qubits pass through their circuit elements. A further surprise is found when two qubits are brought together in an exchange interaction, as their weak values then evolve according to a simple classical equation. The weak values are subject to both past and future constraints, so they can only be determined by considering the entire circuit "all-at-once", as in action principles. In the context of a few basic quantum gates, we show how an all-at-once model of a complete circuit could generate weak values without using state vectors as an intermediate step. Since these gates comprise a universal quantum gate set, this lends support to the claim that any quantum circuit can plausibly be underpinned by localized variables, providing a realistic, lower-level account of generic quantum systems.