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.
Highlights
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
Prohibits the exact knowledge of two noncommuting variables like xB and pB, since their measurement uncertainties are subject to the Heisenberg relation DxBDpB ! 12
EPR concluded that quantum mechanics is incomplete—under their assumptions that are today known as ‘local realism’
Summary
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. In a seminal publication[10], the EPR criterion was met by a twomode squeezed vacuum state generated by optical parametric down-conversion In this experiment, and in more recent investigations[11,12], continuous variables are represented by amplitude xA/B and phase pA/B quadratures, satisfying the commutation relation [xA/B, pA/B] 1⁄4 i. Continuous-variable entangled optical states have been applied for proof-of-principle quantum computation and communication tasks[7] Despite these advances with optical systems, an experimental realization of EPR correlations with massive particles is desirable, because of the similarity to the original EPR proposal and since massive particles may be more tightly bound to the concept of local realism[2,3]
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