Entanglement in the Macro World

By linking the electrical currents of two superconductors large enough to be seen with the naked eye, researchers have extended the domain of observable quantum effects. Billions of flowing electrons in the superconductors can collectively exhibit a weird quantum property called entanglement, usually confined to the realm of tiny particles, scientists report in the Sept. 24 Nature.

That sounds pretty cool, though they don’t go into any details about why exposing the currents to microwaves would entangle them. If the microwaves were linearly polarized, and the current loops are acting as antennae, I can see this; linear polarization can be expressed as a superposition of right- and left-circular polarization, so that might do the trick.

However, I have some objections to the reporting.

After interacting in a certain way, objects become mysteriously linked, or entangled, so that what happens to one seems to affect the fate of the other.

This is ambiguous, so I’m not sure if it fall into the trap of the “doing something to one changes the other” error, but even ambiguous is bad. Entanglement means knowing the state of one tells you the state of the other. And the real kicker here is “mysteriously,” which implies that nobody knows what the heck is going on. There are unanswered questions in entanglement, as there are in all areas of science, but it’s not the same as scientists fumbling and bumbling around, saying, “OMG! WTF?” Entanglement is a prediction of quantum mechanics, and the fact that people are exploiting it shows that it’s not really Sphinx-y (terribly mysterious) at all. Physics ain’t easy, but there’s no need to hamstring the understanding of it by selling it as mysterious.

In the new study, researchers used a microwave pulse to attempt to entangle the electrical currents of the two superconductors. If the currents were quantum-mechanically linked, one current would flow clockwise at the time of measurement (assigned a value of 0), while the other would flow counterclockwise when measured (assigned a value of 1), Martinis says. On the other hand, the currents’ directions would be completely independent of each other if everyday, classical physics were at work.

This can’t be right. If they are independent of each other you expect the currents to have no correlation, so half the time they should be in the opposite direction — so simply measuring currents in the opposite direction is not an indication that they are entangled. That could hold only if classically you always expected them to be in the same direction. The indication that they are entangled is the much higher incidence of finding the opposite currents, as was observed.