Thought you were big enough to escape quantum superposition? A recent demonstration by physicist Andrew Cleland and his colleagues at UC Santa Barbara suggests otherwise. Tiny particles have always been subject to quantum effects, but many physicists were skeptical those effects could be reproduced in larger objects. In an amazing leap, Cleland and his team succeeded in demonstrating quantum effects in an object with trillions of atoms, beating the previous record (fewer than 100 atoms) by a factor of over a billion!
Quantum mechanical experiments have long revealed that a particle can exist in a state of superposition, a state that seems to allow it to be in two contradictory states at once. It seems as if a particle can pass simultaneously through two slits, or be in a ground state and an excited state at once, or even take two wildly different paths through an experiment. There are many different explanations for such odd behavior (see below) but the important thing is that until now, these effects were unimaginably small.
According to a recent article in Nature, Cleland’s experiment began with a quartz-like wafer measuring .03 millimeters across, giant by quantum standards. The trick was to cool it down to within a tenth of a Kelvin of absolute zero, leaving the wafer with no energy left to vibrate. The experimenters verified that it was perfectly still, moving only when it was ‘pushed’ by a superconducting quantum circuit. Next the circuit was put into a superposition, simultaneously ‘pushing’ and ‘not pushing’. This superposition transferred from the circuit to the wafer. Thus, the wafer, as big as common house dust, existed in a quantum state of superposition, seeming to both vibrate and not vibrate. Wired reports that University of Vienna physicist Markus Aspelmeyer described the reaction of an audience of physicists to whom Cleland described the experiment’s design. “Dead silence — and then roaring applause,” he recalled.
While the particles’ (and by extension, the wafer’s) behavior may seem impossible, many philosophers have argued that this appearance is just an artifact of the common ‘Copenhagen’ interpretation of quantum mechanics. If you adopt one of several different interpretations, the absurdities disappear. Three prominent examples are de Broglie-Bohm theories, e.g. as developed by Shelly Goldstein, Ghirardi-Rimini-Weber theories, e.g. as developed by Roderich Tumulka, and Everett-many worlds theories, e.g. as developed by David Wallace. No matter which interpretation is correct, it will have to incorporate these new, exciting results.
By Hilary Greaves , Rutgers University
(Vol. 1, December 2006)
By RICHARD HEALEY