Quantum entanglement is a phenomenon whereby systems cannot be described independently of each other, even though they may be separated by an arbitrarily large distance1. Entanglement has a solid theoretical and experimental foundation and is the key resource behind many emerging quantum technologies, including quantum computation, cryptography and metrology. Entanglement has been demonstrated for microscopic-scale systems, such as those involving photons2,3,4,5, ions6 and electron spins7, and more recently in microwave and electromechanical devices8,9,10. For macroscopic-scale objects8,9,10,11,12,13,14, however, it is very vulnerable to environmental disturbances, and the creation and verification of entanglement of the centre-of-mass motion of macroscopic-scale objects remains an outstanding goal. Here we report such an experimental demonstration, with the moving bodies being two massive micromechanical oscillators, each composed of about 1012 atoms, coupled to a microwave-frequency electromagnetic cavity that is used to create and stabilize the entanglement of their centre-of-mass motion15,16,17. We infer the existence of entanglement in the steady state by combining measurements of correlated mechanical fluctuations with an analysis of the microwaves emitted from the cavity. Our work qualitatively extends the range of entangled physical systems and has implications for quantum information processing, precision measurements and tests of the limits of quantum mechanics.
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We thank S. Paraoanu and I. Petersen for discussions. This work was supported by the Academy of Finland (contracts 250280, 308290 and 307757) and by the European Research Council (615755-CAVITYQPD). We acknowledge funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement number 732894 (FETPRO HOT). For this work, we used the facilities of the Micronova Nanofabrication Center and the Low Temperature Laboratory.
This file contains Supplementary Discussion, Supplementary Figures 1-10, Supplementary Tables 1-3, and additional references.