- #1
Talisman
- 95
- 6
If we have a ket ##|\psi\rangle = |x\rangle \otimes |y\rangle##, then what is the corresponding bra? It seems we want, for example:
$$\langle \psi | \psi \rangle =
\langle x|x \rangle \cdot \langle y|y \rangle =
\langle x| \langle y| |x\rangle|y\rangle$$
I.e., the bra is ##\langle x| \langle y|##. But I swear I've also seen it defined as ##\langle y| \langle x|##, i.e. the order of the systems is switched. Am I crazy, or is there a use for this?
Edit: it seems I'm not the only one.
$$\langle \psi | \psi \rangle =
\langle x|x \rangle \cdot \langle y|y \rangle =
\langle x| \langle y| |x\rangle|y\rangle$$
I.e., the bra is ##\langle x| \langle y|##. But I swear I've also seen it defined as ##\langle y| \langle x|##, i.e. the order of the systems is switched. Am I crazy, or is there a use for this?
Edit: it seems I'm not the only one.