Schrodinger’s Cat
PPT Slide
The cat starts out waiting in a box. A single photon is shot through a two slit interference set up, and is detected on a screen, demonstrating its wave/quantum nature. Depending on where it hits, it does or does not release a giant stone block. We then observe two possible final states:
Schrodinger points out that we can wait as long as we like before “observing” the inside of the box, and that we cannot believe that there is really a superimposed state of “cat alive” and “cat dead” during all that time. (In practice, it is hard to keep a macroscopic object in a definite quantum state for a long time: h is so small that very tiny disturbances move it to a different quantum state, which then evolves away to a very different state rather quickly). There followed fifty years of argument about how we should “interpret” this. More interesting is the idea of applying this physical phenomenon.
The Quantum Bit: or “qubit” -- we can use the cat alive/cat dead state to represent one bit: cat alive = 1, cat dead =0. If I have 128 cats, I can represent 128 qubits.
Note that the answer has to be expressed in just the 128 bits I can observe. That is a trillion computations. If I could handle 256 cats, I could do a trillion trillion computations in the same time.
Einstein hated quantum mechanics, even though his Nobel Prize was for the Quantum, not Relativity. He came up with a number of paradoxes he threw to Bohr, who batted most of them quickly. One that troubled lots of serious people was Quantum Teleportation as people call it now. Idea:
Example of entangled states: photons with net polarization zero:
It has been experimentally demonstrated by several groups in the last year that you can use a pair of entangled states as a carrier to carry the properties of a third state to a different place, without observing them. This is the basic function of teleportation (as in StarTrek).
To encrypt, send a photon to the Remote Site, entangled with one at Home. (If the Enemy detects the entangled photon, it can’t be sent again, entangled, because of the Uncertainty Principle.) Then send the “message” photon, and read it by teleportantion with the entangled photon
Email: willis@nevis1.columbia.edu
Home Page: www.nevis.columbia.edu/~willis
Download presentation source