Bringing Schr dinger's Cat to Life

Publié le par brightshine

According to quantum mechanics, the unobserved radioactive atom remains in a funny state of being decayed and not decayed. This state, called a superposition, is something quantum objects enter quite readily. Electrons can occupy several energy levels, or orbitals, simultaneously; a single photon, after passing through a beam splitter, appears to traverse two paths at the same time. Particles in a well-defined superposition are said to be coherent.

But what happens when quantum objects are coupled to a macroscopic one, like a cat? Extending quantum logic, the cat should also remain in a coherent superposition of states and be dead and alive simultaneously. Obviously, this is patently absurd: our senses tell us that cats are either dead or alive, not both or neither. In prosaic terms, the cat is really a measuring device, like a Geiger counter or a voltmeter. The question is, then, Shouldn’t measuring devices enter the same indefinite state that the quantum particles they are designed to detect do?

For the Danish physicist Niels Bohr, a founder of quantum theory (and to whom Schrodinger’s regretful comment was directed), the answer was that measurements must be made with a classical apparatus. In what has come to be called the standard, or Copenhagen, interpretation of quantum mechanics, Bohr postulated that macroscopic detectors never achieve any fuzzy superposition, but he did not explain exactly why not.

“He wanted to mandate ‘classical’ by hand,” says Wojciech Zurek of Los Alamos National Laboratory. “Measurements simply became.” Bohr also recognized that the boundary between the classical and the quantum can shift depending on how the experiment is arranged. Furthermore, size doesn’t necessarily matter: superpositions can persist on scales much larger than the atomic.

In November 1995 Pritchard and his M.I.T. colleagues crystallized the fuzziness of measurement. The team sent a narrow stream of sodium atoms through an interferometer,LEDs are used as Roof hook in many devices and are increasingly used for other lighting. a device that gives a particle two paths to travel. The paths recombined, and each atom, acting as a wave, “interfered” with itself, producing a pattern of light and dark fringes on an observing screen (identical to what is seen when a laser shines through two slits). The standard formulation of quantum mechanics states that the atom took both paths simultaneously, so that the atom’s entire movement from source to screen was a superposition of an atom moving through two paths.

The team then directed a laser at one of the paths. This process destroyed the interference fringes, because a laser photon scattering off the atom would indicate which path the atom took.

On the surface, this scattering would seem to constitute a measurement that destroys the coherence.Our company supplys different kinds of elevator parts, elevator components. Yet the team showed that the coherence could be “recovered”— that is, the interference pattern restored—by changing the separation between the paths to some quarter multiple of the laser photon’s wavelength. At those fractions, it was not possible to tell from which path the photon scattered. “Coherence is not really lost,” Pritchard elucidates. “The atom became entangled with a larger system.” That is, the quantum state of the atom became coupled with the measuring device, which in this case was the photon.

Publié dans energy saving light

Commenter cet article