Quantum mechanics boasts all sorts of delightfully odd features. There’s the fact that two separated particles can interact instantaneously, a phenomenon called quantum entanglement. (Einstein disparaged the theory, which he called “spooky action at a distance,” but there is significant evidence to support the theory of quantum entanglement.) And there’s another phenomenon called quantum superposition. This principle of quantum mechanics suggests that particles can exist in two separate locations at once.
Physicists from Stanford University have now demonstrated the superposition of a group of atoms over a greater distance than ever before: 54 centimeters, or about 1.77 feet. The largest distance ever achieved before this was less than a centimeter.
Quantum superposition is made even more perplexing by the fact that it can only occur when the particles are unobserved. Simply by observing a particle in two different quantum states, you cause what is known as wave function collapse and the particle again exists in only one state or the other (and in the case of superposition, only one physical location or the other). Therefore, measuring a particle in superposition is incredibly difficult.
The Stanford researchers used a cloud of 10,000 rubidium atoms cooled to near-absolute zero temperatures, called a Bose-Einstein condensate (BEC), to demonstrate superposition. The cloud of atoms, measuring a few millimeters across, was put into a 33-foot-tall chamber. Lasers were used to push the cloud up the chamber, a process that also separated the atoms into two quantum states. When the atoms fell back down to the bottom of the chamber, they returned to one quantum state and appeared to have arrived from two different heights 54 centimeters apart, confirming that they were in superposition at the top of the chamber. The BEC remained in superposition for about a second, four times longer than previous demonstrations.
It’s experiments like this one that can help create a new set of physical laws for the atomic world, principles that could lead to breakthroughs in fields like quantum computing and revolutionize our ability to process huge amounts of data. Until then, we can just enjoy the mind-blowing weirdness of spooky particles.