title: Satisfying the Einstein-Podolsky-Rosen criterion with massive particles.
abstract: In 1935, Einstein, Podolsky and Rosen (EPR) questioned the completeness of quantum mechanics by devising a quantum state of two massive particles with maximally correlated space and momentum coordinates. The EPR criterion qualifies such continuous-variable entangled states, where a measurement of one subsystem seemingly allows for a prediction of the second subsystem beyond the Heisenberg uncertainty relation. Up to now, continuous-variable EPR correlations have only been created with photons, while the demonstration of such strongly correlated states with massive particles is still outstanding. Here we report on the creation of an EPR-correlated two-mode squeezed state in an ultracold atomic ensemble. The state shows an EPR entanglement parameter of 0.18(3), which is 2.4 s.d. below the threshold 1/4 of the EPR criterion. We also present a full tomographic reconstruction of the underlying many-particle quantum state. The state presents a resource for tests of quantum nonlocality and a wide variety of applications in the field of continuous-variable quantum information and metrology.
authors.affiliation: Institut für Quantenoptik, Leibniz Universität Hannover, Welfengarten 1, D-30167 Hannover, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Peise
authors.affiliation: Institut für Quantenoptik, Leibniz Universität Hannover, Welfengarten 1, D-30167 Hannover, Germany.
authors.forename: I
authors.initials: I
authors.lastname: Kruse
authors.affiliation: Institut für Quantenoptik, Leibniz Universität Hannover, Welfengarten 1, D-30167 Hannover, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Lange
authors.affiliation: Institut für Quantenoptik, Leibniz Universität Hannover, Welfengarten 1, D-30167 Hannover, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Lücke
authors.affiliation: QSTAR, Largo Enrico Fermi 2, 50125 Firenze, Italy.|Istituto Nazionale di Ottica, INO-CNR, Largo Enrico Fermi 2, 50125 Firenze, Italy.|LENS, Via Nello Carrara 1, 50019 Sesto Fiorentino, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Pezzè
authors.affiliation: Institut for Fysik og Astronomi, Aarhus Universitet, Ny Munkegade 120, DK-8000 Århus C, Denmark.
authors.forename: J
authors.identifier: http://orcid.org/0000-0002-5782-3927
authors.initials: J
authors.lastname: Arlt
authors.affiliation: Institut für Quantenoptik, Leibniz Universität Hannover, Welfengarten 1, D-30167 Hannover, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Ertmer
authors.affiliation: Institut für Theoretische Physik, Leibniz Universität Hannover, Appelstraße 2, D-30167 Hannover, Germany.
authors.forename: K
authors.initials: K
authors.lastname: Hammerer
authors.affiliation: LENS, Via Nello Carrara 1, 50019 Sesto Fiorentino, Italy.
authors.forename: L
authors.initials: L
authors.lastname: Santos
authors.affiliation: QSTAR, Largo Enrico Fermi 2, 50125 Firenze, Italy.|Istituto Nazionale di Ottica, INO-CNR, Largo Enrico Fermi 2, 50125 Firenze, Italy.|LENS, Via Nello Carrara 1, 50019 Sesto Fiorentino, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Smerzi
authors.affiliation: Institut für Quantenoptik, Leibniz Universität Hannover, Welfengarten 1, D-30167 Hannover, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Klempt