Displacing entanglement back and forth between the micro and macro domains

TL;DR

This paper demonstrates the displacement of quantum entanglement from microscopic to macroscopic photon states and back, providing a new way to explore quantum theory at larger scales and potential applications in quantum sensing.

Contribution

It introduces a method to transfer and verify entanglement between micro and macro photon states, bridging the gap between quantum and classical regimes.

Findings

Successfully displaced entanglement to nearly a thousand photons

Re-displaced macro entanglement back to the micro level for verification

Shows potential for probing fundamental quantum questions and sensing applications

Abstract

Quantum theory is often presented as the theory describing the microscopic world, and admittedly, it has done this extremely well for decades. Nonetheless, the question of whether it applies at all scales and in particular at human scales remains open, despite considerable experimental effort. Here, we report on the displacement of quantum entanglement into the domain where it involves two macroscopically distinct states, i.e. two states characterised by a large enough number of photons to be seen, at least in principle, with our eyes and that could be distinguished using mere linear - coarse-grained - detectors with a high probability. Specifically, we start by the generation of entanglement between two spatially separated optical modes at the single photon level and subsequently displace one of these modes up to almost a thousand photons. To reliably check whether entanglement is preserved, the mode is re-displaced back to the single photon level and a well established entanglement measure, based on single photon detection, is performed. The ability to displace an entangled state from the micro to the macro domain and back again provides a fascinating tool to probe fundamental questions about quantum theory and holds potential for more applied problems such as quantum sensing.