Bra-ket notation, or the Dirac notation, is a notation for complex vector spaces together with their dual space.
Looks like this:
A ket is of the form
Warning
Don’t confuse
with the vector. It is instead a unit vector.
A bra is of the form
Example
If
then
This notation is used ubiquitously in quantum mechanics.
We sometimes combine the bra and ket: the notation
Usage
We can write the length of the vector
We can also use the bra-ket notation to write the