Abstract
Experiments have reported the entanglement of two spatially separated macroscopic atomic ensembles at room temperature (Krauter et al 2011 Phys. Rev. Lett. 107 080503; Julsgaard et al 2001 Nature 413 400). We show how an Einstein–Podolsky–Rosen (EPR) paradox is realizable with this experiment. Our proposed test involves violation of an inferred Heisenberg uncertainty principle, which is a sufficient condition for an EPR paradox. This is a stronger test of nonlocality than entanglement. Our proposal would enable the first definitive confirmation of quantum EPR paradox correlations between two macroscopic objects at room temperature. This is a necessary intermediate step towards a nonlocal experiment with causal measurement separations. As well as having fundamental significance, the realization of an atomic EPR paradox could provide a resource for novel applications in quantum technology.
Highlights
Entangling two macroscopic atomic ensemblesThe experiments of Julsgaard et al [60], Krauter et al [61], Muschik et al [73] achieve entanglement of two macroscopic spatially separated atomic ensembles
Polzik and coworkers have made a pioneering step in the direction of realizing an EPR paradox between massive objects, in work that experimentally confirmed the entanglement of two macroscopic ensembles of gaseous atoms at room temperature [60, 61, 72, 73]
Our detailed analysis reveals that this is achievable within the limits of the parameters reported for the experiments, provided the appropriate conditional variances are measured. This is the first prediction of an EPR paradox for room temperature atoms, using a model that accounts for thermal effects
Summary
The experiments of Julsgaard et al [60], Krauter et al [61], Muschik et al [73] achieve entanglement of two macroscopic spatially separated atomic ensembles. Entanglement is achieved via a detuned polarized laser pulse, which is called the ‘entangling pulse’ This laser field is described by another set of spin operators, called the Stokes operators SX , SY , SZ. Following the theory of Duan et al [63], when the detuned ‘entangling’ pulse propagates through the first atomic ensemble, the outputs are given in terms of the inputs according to. The collective spin JAY + JBY is a constant of the motion, and the ensembles can be prepared via a second pulse (and by rotating the atomic spin) in a state with reduced fluctuation in JBY
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