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.I would not say that entanglement is a "key resource". It mainly represents a mismatch between physical reality and our methods of measurement. It has no practical value.
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.I would have said that a solid object of 1012 atoms is microscopic, not macroscopic. I cannot see it with my naked eye; I need a microscope. The thing is only about 15 microns in diameter.
I am not sure why this is better than just putting two Schroedinger cats in a box, with a quantum device that kills one, but we cannot predict which. Then the two cats are entangled. What is so great about that?
It is only great if you think of entanglement like splitting the atom in the 1940s. It unlocks a key resource. As energy ruled the world in the 1940s, we now live in the information age, and computation rules the world. If entangling some bits enables super-Turing computing, then we can break RSA encryption and maybe realize artificial general intelligence. Just as splitting the atom was going to give us electricity too cheap to meter, entangled qubits will give us the Singularity.
Do you believe it? No, I don't. It is a pipe dream.