If the rules of the tiny quantum world applied to ordinary objects, all sorts of strange things could happen: An object like a car or a person might be in two places at once, or two clocks could “entangle,” moving in synchrony as if they were physically conjoined even when miles apart. In June researchers at the National Institute of Standards and Technology (NIST) reported on their effort to see how far quantum behavior can be extended into the everyday realm.
First they coaxed a pair of beryllium ions to entangle, such that their physical properties remained bound together even when they were far apart. To do this, the scientists flashed lasers at a frequency that encouraged the ions to adopt complementary spin. Next the team split up the beryllium duo so that each was now matched with a magnesium ion, and those new pairs were moved to separate areas. The heavier magnesium ions helped cool and slow down the beryllium ions. Now the researchers could use lasers to transfer the entangled state of the beryllium ions to the motion of the new beryllium-magnesium pairs. Those pairs began to form two separate oscillating systems, analogous to a swinging pendulum or a vibrating weight on a spring. “We were motivated by pure curiosity to look at mechanical oscillators; no one had ever entangled them before,” says David Hanneke, a member of the NIST team.
The experiment will help scientists explore why small objects follow the weird rules of quantum mechanics but large ones do not—one of the greatest enigmas in physics. In this case, sets of oscillating ions can be made to act as if they are connected, even though equivalent human-scale objects, like pendulums and springs, “certainly don’t behave in this entangled way,” Hanneke says. “So where does the breakdown happen? It’s somewhere between four ions and a pendulum clock.”