What Is Quantum Entanglement?
Two quantum systems are entangled when their joint state cannot be written as a tensor product of individual states. A measurement on one system instantly determines the conditional state of the other, even if they are spatially separated.
The phenomenon was sharpened by Einstein, Podolsky and Rosen (1935) as the EPR paradox, formalised by Bell (1964) into testable inequalities, and confirmed experimentally by Aspect (1982) and many groups since — including the 2022 Nobel Prize for Aspect, Clauser and Zeilinger.
Crucially, entanglement does not allow faster-than-light signalling: the marginal distribution of outcomes at one site is unaffected by what is done at the other (no-signalling theorem). It does enable quantum teleportation, dense coding, device-independent QKD, and the speed-ups of quantum algorithms.
Recent research on this topic from arXiv
Preprints and papers indexed on arXiv.org. Links open the public abstract pages.
- On Quantum Entanglement and Nonlocality
Mafiz Uddin · 2025 ·arXiv:2506.00366v3
EPR showed that two particles emitted from a source can be entangled by a shared wavefunction where two non-commuting observables (position, momentum) can be simultaneously real, leading to a contradiction with quantum mechanics (two non-co... - Quantum entanglement
Ludmil Hadjiivanov, Ivan Todorov · 2015 ·arXiv:1506.04262v1
Expository paper providing a historical survey of the gradual transformation of the "philosophical discussions" between Bohr, Einstein and Schrödinger on foundational issues in quantum mechanics into a quantitative prediction of a new quant... - Spin Bath Decoherence of Quantum Entanglement
Zafer Gedik · 2005 ·arXiv:0505176v1
We study an analytically solvable model for decoherence of a two spin system embedded in a large spin environment. As a measure of entanglement, we evaluate the concurrence for the Bell states (Einstein-Podolsky-Rosen pairs). We find that w... - Quantum Entanglement under Lorentz Boost
Daeho Lee, Ee Chang-Young · 2003 ·arXiv:0308156v2
In order to understand the characteristics of quantum entanglement of massive particles under Lorentz boost, we first introduce a relevant relativistic spin observable, and evaluate its expectation values for the Bell states under Lorentz b...