Dirac notation
? ? means “the probability amplitude that”
? particle arrives at x | particle leaves s ?
- The probability amplitude that a particle leaving s arrives at x
- A single complex number
- Read from right to left
- 2nd principle: ?x|s?12 = ?x|s?1 + ?x|s?2
- 3rd principle: ?x|s?1 = ?x|1??1|s?
Hint: Never add probability amplitudes for experiments that have different final states