<i>Colloquium</i>: The Einstein-Podolsky-Rosen paradox: From concepts to applications

TLDR

The Einstein–Podolsky–Rosen paradox, originally a thought experiment, has evolved into both continuous‑variable and discrete‑variable forms, with recent work linking it to entanglement, Bell’s theorem, and experimental demonstrations using laser‑based continuous‑variable setups. Experimental realizations employ continuous‑wave parametric amplifiers, optical‑fiber quantum solitons, and emerging massive‑particle schemes such as spin squeezing, atomic position entanglement, and ultracold‑atom quadrature entanglement. These advances enable practical quantum technologies, including key distribution, teleportation, and entanglement swapping.

Abstract

This Colloquium examines the field of the Einstein, Podolsky, and Rosen (EPR) gedanken experiment, from the original paper of Einstein, Podolsky, and Rosen, through to modern theoretical proposals of how to realize both the continuous-variable and discrete versions of the EPR paradox. The relationship with entanglement and Bell's theorem are analyzed, and the progress to date towards experimental confirmation of the EPR paradox is summarized, with a detailed treatment of the continuous-variable paradox in laser-based experiments. Practical techniques covered include continuous-wave parametric amplifier and optical fiber quantum soliton experiments. Current proposals for extending EPR experiments to massive-particle systems are discussed, including spin squeezing, atomic position entanglement, and quadrature entanglement in ultracold atoms. Finally, applications of this technology to quantum key distribution, quantum teleportation, and entanglement swapping are examined.