The Strange Quantum World That We Call Home

Today, after hours of trying to stick tiny copper wires to connected films of copper and aluminum on a piece of glass with a clay-like metal called indium (and failing miserably for much of the time), we finally were finished (not that we did a very good job--we probably destroyed the films in the process). The professor, a charming little Indian man with a deep fascination with the wonders of science, came in, commented brightly that we should take a picture of the thing (when I asked if that was because it was very good or very bad, he said that he would leave me with the benefit of the doubt), and said that he wanted to show us some quantum effects at low temperatures. It was getting late, and normally I would have left to go home around then, but I was highly interested. This could be the chance of a lifetime to see such things! So Melissa and I followed the professor into another lab, where an apparatus was set up with liquid helium to get very cold. The professor showed us the set-up, and told us how we could tell the temperature of the liquid helium by looking at the barometer and using a table to see how the temperature related to the pressure. You see, liquid helium at atmospheric pressure is 4.2 degrees Kelvin. But if you reduce the pressure, the boiling point goes down, so the liquid helium gets colder. The professor opened a valve, and the pressure and temperature started going down. The liquid helium was in a glass tube, which is apparently an old-fashioned technology that is rarely used anymore. So we were some of the few people who get to see liquid helium with their own eyes. We looked in through the glass, at the vigorously boiling helium. The professor told us to keep our eyes on the surface, because at a certain point the helium would experience a quantum effect--it would become "superfluid" in which every atom somehow "knows" what every other atom is doing, and goes into the same state. And indeed, as we watched, the temperature going down, 2.9 Kelvin...2.8 Kelvin...2.7 Kelvin...at that point, the helium stopped bubbling and shaking and became completely still. A post-doc with an Irish accent came in at some point, and he and the professor began talking about the wonder of it all. "it has no friction, so if you were to spin the container as it reached the superfluid point, the helium would keep spinning forever." They continued to muse about the strangeness of it all. If you have two such particles and you changed the momentum of one of them, the momentum of the other would change, faster than the speed of light, but rather instantaneously. Why? How? Sometimes it is difficult to tell the difference between physics and philosophy.

Submerged in the liquid helium, was a film of aluminum and copper similar to the one that we destroyed (as the professor said jokingly). Next, we were going to see the aluminum become a superconductor, with zero resistance. We went into a little chamber with device that held a pen over graph paper and moved it along, making a line that represented the resistance in the aluminum. The temperature continued to go down, 2.1 Kelvin...2.0 Kelvin...1.9 Kelvin...and suddenly the pen veered sharply, making the line go steeply down. At 1.6 Kelvin, it reached zero, and started going straight again. "It is now in the superconducting state," said the professor. He explained the mysteries of how superconductivity works; again, this had to do with electrons that "know" what the other one is doing without feeling a force. He commented on how amazing and mysterious it must have been for the people who discovered these effects. Finally, he had one more quantum effect to show us. He said we could go home and do it tomorrow, but we decided to stay a little longer to see it. This effect had to do with tunneling through a junction with two superconductors and a thin insulator in between. At a sufficiantly low temperature, strange things happened. The resistance for the tunneling electron pairs went to zero through the insulator, so that they could tunnel back and forth continuously without anything to stop them. Well, that was the end. The professor said that he had to do some measurements, we thanked him and left. But I still can't get over how amazing, awesome (using the real meaning of the word), and eerie it was.


-Philip