Projective measurements are sufficient for recycling nonlocality

TL;DR

This paper demonstrates that nonlocality can be recycled using only projective measurements without unsharp measurements or quantum ancillas, challenging previous assumptions and broadening experimental possibilities.

Contribution

It shows that standard projective measurements suffice for recycling nonlocality, revealing larger violations with non-maximally entangled states and emphasizing practical experimental relevance.

Findings

Nonlocality can be recycled with projective measurements alone.

Non-maximally entangled states allow larger sequential violations.

Recycling is possible with local randomness and projective measurements.

Abstract

Unsharp measurements are widely seen as the key resource for recycling the nonlocality of an entangled state shared between several sequential observers. Contrasting this, we here show that nonlocality can be recycled using only standard projective measurements, without using quantum ancillas. Focusing on the CHSH inequality, we determine the optimal trade-off in the Bell parameters for a maximally entangled two-qubit state in the presence of shared classical randomness. We then find that non-maximally entangled states make possible larger sequential violations, which contrasts the standard CHSH scenario. Furthermore, we show that nonlocality can be recycled even when only using projective measurements and local randomness. We discuss the implications of our results for experimental implementations of sequential nonlocality.