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Experimental long-lived entanglement of two macroscopic objects


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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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).

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