Quantum physics (quantum theory, quantum mechanics)

double slit expt., wave function
• light intensity at a point on screen I depends on number
of photons striking the point
number of photons probability P of finding photon there,
i.e
I P = |ψ| 2 , ψ = wave function
• probability to find photon at a point on the screen :
P = |ψ| 2 = |ψ 1 + ψ 2 | 2 =
|ψ 1 | 2 + |ψ 2 | 2 + 2 |ψ 1 | |ψ 2 | cosφ;
• 2 |ψ 1 | |ψ 2 | cosφ is “interference term”; factor cosφ due
to fact that ψs are complex functions
• wave function changes when experimental setup is changed
o by opening only one slit at a time
o by adding detector to determine which path photon took
o by introducing anything which makes paths distinguishable
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