Quantum experiments with human eyes as detectors based on cloning via stimulated emission

TL;DR

This paper demonstrates theoretically that human eyes can serve as effective detectors for multi-photon states produced by cloning single-photon qubits through stimulated emission, enabling feasible Bell experiments in micro-macro quantum systems.

Contribution

It introduces a novel approach showing human eyes can detect cloned multi-photon states with high fidelity, supporting micro-macro entanglement detection.

Findings

Human eyes can distinguish cloned multi-photon states with high efficiency.

Bell experiments with human detectors are feasible even with photon loss.

Micro-macro entanglement persists despite high photon loss.

Abstract

We show theoretically that the multi-photon states obtained by cloning single-photon qubits via stimulated emission can be distinguished with the naked human eye with high efficiency and fidelity. Focusing on the "micro-macro" situation realized in a recent experiment [F. De Martini, F. Sciarrino, and C. Vitelli, Phys. Rev. Lett. 100, 253601 (2008)], where one photon from an original entangled pair is detected directly, whereas the other one is greatly amplified, we show that performing a Bell experiment with human-eye detectors for the amplified photon appears realistic, even when losses are taken into account. The great robustness of these results under photon loss leads to an apparent paradox, which we resolve by noting that the Bell violation proves the existence of entanglement before the amplification process. However, we also prove that there is genuine micro-macro entanglement even for high loss.