Experimental Test of Entangled Histories

TL;DR

This paper experimentally creates and tests entangled history states of a single photon across three times, demonstrating quantum entanglement in the temporal domain using a GHZ-type scheme.

Contribution

It introduces a scheme to generate and measure entangled history states, specifically of the GHZ type, and experimentally verifies their entanglement.

Findings

Measured GHZ functional value of 0.656, confirming entangled histories.

Defined a GHZ functional with a maximum of 1 for ideal entangled history states.

Demonstrated that non-entangled history states have GHZ functional bounded by 1/16.

Abstract

We propose and demonstrate experimentally a scheme to create entangled history states of the Greenberger-Horne-Zeilinger (GHZ) type. In our experiment, the polarization states of a single photon at three different times are prepared as a GHZ entangled history state. We define a GHZ functional which attains a maximum value $1$ on the ideal GHZ entangled history state and is bounded above by $1/16$ for any three-time history state lacking tripartite entanglement. We have measured the GHZ functional on a state we have prepared experimentally, yielding a value of $0.656\pm 0.005$, clearly demonstrating the contribution of entangled histories.