Quantum entanglement from random measurements

TL;DR

This paper introduces a method to detect quantum entanglement using random measurements, enabling entanglement verification without shared reference frames and with minimal access to the system, suitable for practical experiments.

Contribution

It presents a novel entanglement detection technique based on random correlations that works without shared references and with limited measurement access.

Findings

Entanglement can be identified via squared correlations along random directions.

Detection is possible with only one qubit access per experimental run.

The method provides a state-independent entanglement witness.

Abstract

We show that the expectation value of squared correlations measured along random local directions is an identifier of quantum entanglement in pure states which can be directly experimentally assessed if two copies of the state were available. Entanglement can therefore be detected by parties who do not share a common reference frame and whose local reference frames, such as polarisers or Stern-Gerlach magnets, remain unknown. Furthermore, we also show that in every experimental run access to only one qubit from the macroscopic reference is sufficient to identify entanglement, violate a Bell inequality, and in fact observe all phenomena observable with macroscopic references. Finally, we provide a state-independent entanglement witness solely in terms of random correlations and emphasise how data gathered for a single random measurement setting per party reliably detects entanglement. This is only possible due to utilised randomness and should find practical applications in experimental confirmation of multi-photon entanglement or space experiments.