Quantum probabilistic sampling of multipartite 60-qubit Bell inequality violations

TL;DR

This paper demonstrates that genuine multipartite Bell inequality violations for up to 60 qubits can be efficiently simulated using probabilistic phase-space methods, revealing faster-than-experimental sampling and contradictions with local realism.

Contribution

It introduces a novel probabilistic phase-space sampling approach for simulating large multipartite quantum states and Bell violations, surpassing experimental speed and confirming nonlocality.

Findings

Sampling can be exponentially faster than experiments.

Phase-space methods successfully simulate Bell violations in 60-qubit states.

The approach predicts contradictions with local realism in large quantum systems.

Abstract

We show that violation of genuine multipartite Bell inequalities can be obtained with sampled, probabilistic phase space methods. These genuine Bell violations cannot be replicated if any part of the system is described by a local hidden variable theory. The Bell violations are simulated probabilistically using quantum phase-space representations. We treat mesoscopically large Greenberger-Horne-Zeilinger (GHZ) states having up to 60 qubits, using both a multipartite SU(2) Q-representation and the positive P-representation. Surprisingly, we find that sampling with phase-space distributions can be exponentially faster than experiment. This is due to the classical parallelism inherent in the simulation of quantum measurements using phase-space methods. Our probabilistic sampling method predicts a contradiction with local realism of "Schr\"odinger-cat" states that can be realized as a GHZ spin state, either in ion traps or with photonic qubits. We also present a quantum simulation of the observed super-decoherence of the ion-trap "cat" state, using a phenomenological noise model.