Friday, March 28, 2014

Large-Scale Quantum Superposition

Scientists have succeeded in creating the first basic quantum machine using a small visible paddle that resonates in a mixed quantum state of moving and not moving. The system works by having the paddle connected to a superconducting electrical circuit, cooling it down, and then carefully setting it to vibrate. In doing so, they have shown that it is possible to induce a quantum-mechanical ground state from a regularly-sized object previously thought to only obey the laws of classical physics. It is currently considered to be the largest object ever placed in a quantum superposition of states artificially as of August, 2009.

In general, the larger an object is, the harder it is for it to maintain a coherent quantum superposition of states. This peculiar idea is commonly illustrated by a famous thought experiment devised by physicist Erwin Schrödinger, which points out the surprising behavior of the quantum world if it could be readily applied to objects on a macroscopic level. In Schrödinger’s cat, a sealed box governs the state of a cat that's inside it through a quantum radioactive process which occurs randomly and controls whether a vial of poison gas within the box is effectively broken or left intact. Since there is no way of knowing the cat's condition without looking inside the box, the cat is proposed to be in a combined state of both alive and dead, just as a quantum object can be in multiple states at once. However, as soon as the box is opened and an observer becomes entangled with a specific outcome, the cat's quantum superposition of states immediately decoheres into one apparent result.

Amazingly, in the Many-Worlds Interpretation of quantum mechanics, developed by physicist Hugh Everett III, the universe itself is thought to exist in a quantum superposition of infinitely many states that each correspond to a different quantum "world," or parallel universe. These many worlds are similar to pocket universes existing within a unified multiverse but instead of them being far away from each other, they appear probabilistically within the same physical space. As a result, any event, no matter how small, may act as a point from which every possible future will diverge and exist within its very own timeline. This view allows both alive and dead states of the cat to persist simultaneously but only within separate realities, regardless of whichever one has been observed after the box is opened. Although moving and not moving states for a macroscopic object would normally be measured independently of one another as well, a small paddle is able to retain its combined state of motion through the use of an experimental setup that substantially delays the onset of decoherence. The achievement can be interpreted as a major step towards showing how the rules of quantum mechanics could also be applied to the movement of everyday objects.

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