An Introduction to Quantum Computation and Communication by Rob Pike [PDF]
herpolhode.com
herpolhode.com
The two-slit experiment.
1. Single photon still produces interference pattern!
2. Ask which slit photon passes - pattern disappears
The interference pattern doesn't disappear "because we're looking", or "because we're asking", or "because we thought about finding the answer".
It disappears because in order to check which slit a photon passed through, we need some way of measuring that. To do so, we need some way to "see" the photon; to do that, we need to shine photons on it; and it is that which destroys the interference pattern.
The reason quantum mechanics is "weird" is because it (currently) is fundamentally impossible to invent a device to answer the question "which slit did the photon pass through?" without destroying the interference pattern.
However, that doesn't mean it disappears "because we're asking". The interference pattern is destroyed because our device, no matter what it is, will always interfere with the experiment (shining photon A at a photon B == "well obviously that would change the behavior of photon B"). Nothing more, nothing less.
There's no attempt with this to determine where photons are going, so you don't have the pesky issues of observation attempts messing with your photons.
http://en.wikipedia.org/wiki/Elitzur–Vaidman_bomb-tester
Here's an improved version that doesn't explode as often:
http://njsas.org/projects/light_polarization/Interaction-Fre...
In "real life" (meaning in the laboratory), measurement isn't some discrete process that can be isolated at a specific point in an experimental setup. Otherwise, there would be much better explanations for measurement in undergraduate physics curriculums.
In fact, even in top physics curriculums, the problem of measurement is barely treated at all, since the interpretation of measurement in quantum mechanics is a "philosophical" problem that apparently has no place in real physics, which instead must concern itself with mathematics that is phenomenologically accurate.
"A classical computer seems to need time exponential in n to predict precisely the behavior of a general quantum mechanical system of n particles. (Yet nature manages to do it in real time.)"
How could we know this from inside that system? For all we know it could take a billion [whatever unit is used to measure time outside of our dimension] to calculate each step, and it would still look fluid to us.
No really, read it. His writing style is very accessible. Ignore the formulas; read the words.
http://www.phy.mtu.edu/~sgowtham/PH4390/Week_02/IJTP_v21_p46...