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Experimental long-lived entanglement of two macroscopic objects

Abstract

Entanglement is considered to be one of the most profound features of quantum mechanics1,2. An entangled state of a system consisting of two subsystems cannot be described as a product of the quantum states of the two subsystems3,4,5,6. In this sense, the entangled system is considered inseparable and non-local. It is generally believed that entanglement is usually manifest in systems consisting of a small number of microscopic particles. Here we demonstrate experimentally the entanglement of two macroscopic objects, each consisting of a caesium gas sample containing about 1012 atoms. Entanglement is generated via interaction of the samples with a pulse of light, which performs a non-local Bell measurement on the collective spins of the samples7. The entangled spin-state can be maintained for 0.5 milliseconds. Besides being of fundamental interest, we expect the robust and long-lived entanglement of material objects demonstrated here to be useful in quantum information processing, including teleportation8,9,10 of quantum states of matter and quantum memory.

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Figure 1: The experimental set-up, atomic level structure and the sequence of optical pulses.
Figure 2: Determination of the coherent spin state limit for entanglement.
Figure 3: Demonstration of the entangled spin state for two atomic samples.

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Acknowledgements

We gratefully acknowledge the contributions of J. Hald, J. L. Sørensen, C. Schori and A. Verchovski. We also thank I. Cirac, A. Kuzmich, A. Sørensen and P. Zoller for discussions.

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Correspondence to Eugene S. Polzik.

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Julsgaard, B., Kozhekin, A. & Polzik, E. Experimental long-lived entanglement of two macroscopic objects. Nature 413, 400–403 (2001). https://doi.org/10.1038/35096524

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