# Do I have some freedom when I define the quantum SHO ladder operators? [closed]

I tried to solve the quantum harmonic oscillator via the operator method. After doing it and looking up the solution I noticed that for some reason the ladder operators got an additional factor of (i) / (-i) in them. Is this just a (weird) convention? In my calculations I don't seem to need it and since only a product appears in the Hamiltonian it does not matter if there is an (i)*(-i)=1 in there or not.

My calculations are made with pencil - the extra (i) & (-i) is in blue.

Did I make some mistake or is really just a convention?

## closed as off-topic by ACuriousMind♦, Kyle Kanos, Neuneck, DanielSank, MartinAug 7 '15 at 13:06

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "Homework-like questions should ask about a specific physics concept and show some effort to work through the problem. We want our questions to be useful to the broader community, and to future users. See our meta site for more guidance on how to edit your question to make it better" – ACuriousMind, Kyle Kanos, Neuneck, Martin
If this question can be reworded to fit the rules in the help center, please edit the question.

• Please type all relevant information into the post. Posting pictures of calculation is discouraged. We much prefer you type in whatever you need. There are several reasons for this: 1) It avoids link rot, 2) it's easier to read, 3) you are much more likely to figure out what parts are actually relevant to your question, which leads to more focused questions and possibly you figuring it out yourself. – DanielSank Aug 5 '15 at 15:57
• It actually is even a bit more extreme than @BillN suggested: you have a quadratic Hamiltonian $\alpha^2 x^2 + \beta^2 p^2$, which is a Euclidean-norm $r^2$ acting on "distances" $\alpha x$ and $\beta p$. There's no reason that you can't choose some rotated axes in this space, like $\sqrt{1/2}(\alpha x \pm \beta p)$, to be your "quadratures" for the harmonic oscillator. In the end one dimensionless axis is $\hat a^\dagger + \hat a$ and the other is $i\hat a^\dagger - i \hat a$, your Hamiltonian is $\hbar\omega\left(\hat a^\dagger \hat a + \frac 12\right)$, and everything else is up in the air. – CR Drost Aug 5 '15 at 16:04
• I think "check-my-work" questions are not considered on topic here. – DanielSank Aug 6 '15 at 17:02
• I'm voting to close this question as off-topic because it is a check-my-work question. Please see if you can isolate a specific conceptual question. – DanielSank Aug 6 '15 at 17:03

So a difference in a factor of $i$ when defining the ladder operators is not unusual. Some people even call them $b$ and $b^\dagger$!