Two pendulums swing in sync, even though there is not a single string between them. One swings left, and the other moves right at the same instant. In the quantum world, this kind of coordination is called EPR steering, and it is stronger than ordinary entanglement: measuring the first pendulum immediately dictates how the second one moves.

In the lab, the role of the pendulums was played by two bits of crystal, each with the mass of a grain of salt. They were connected not by a string but by a superconducting qubit, a tiny electronic device that can be in two states at once. Two microwave signals made the qubit act as a shared metronome: it does not push the pieces one after another, but instead creates paired oscillations in both at once. The physicists measured the strength of the link and got a value of 0.90, whereas anything greater than 1 would have meant an ordinary, non-quantum connection. The confidence level of the result is 99%.

Two pendulums in Zurich swing in sync with no string, and this is not a trick but a quantum regularity. If we learn to control such a link, we could transmit mechanical motion from one piece to another without any contact.