Multiparty multilevel energy-time entanglement

TL;DR

This paper introduces an improved multiparty energy-time entanglement scheme that overcomes limitations of previous setups, enabling reliable Bell tests and the preparation of complex entangled states.

Contribution

It extends a previous interferometric scheme to address postselection issues in multiparty energy-time entanglement experiments.

Findings

The new setup prevents local models from mimicking quantum predictions.

It enables the preparation of n-qubit GHZ and energy-time entangled states.

The scheme improves the reliability of multiparty Bell tests.

Abstract

Franson-like setups are inadequate for multiparty Bell experiments with energy-time entanglement because postselected events can depend on the local settings, and local models can exploit this feature to reproduce the quantum predictions, even in the case of ideal devices. We extend a previously introduced interferometric scheme [A. Cabello, et al., Phys. Rev. Lett. 102, 040401 (2009)] to solve this problem in the n-qubit and n-qunit cases. In addition, the proposed setups allow us to prepare and test n-qubit Greenberger-Horne-Zeilinger and $(\sum_{i=1}^n |i ... i>)/\sqrt{n}$ energy-time entangled states.