What are $|+\rangle$ and $|-\rangle$?

On a view places, I've seen kets that look like this $$\left|+\right>$$ or this $$\left|-\right>$$ but I don't seem to find any explanation of this base online. Is it just a different notation for $$0$$ and $$1$$, or does it mean something else? Thanks for your help!

• $|\pm \rangle = \frac{1}{\sqrt 2} (|0\rangle \pm |1\rangle)$ – Sanchayan Dutta Feb 1 at 19:26
• Thanks a lot! Does this Notation have any particular name, as I was not able to find it? – Robinbux Feb 1 at 19:31

The set $$\{ \left|+\right>, \left|-\right> \}$$ is known as the polar basis. It easy to see that they are the result of applying the Hadamard transform $$H = \frac{1}{\sqrt{2}}\begin{pmatrix} 1 & 1 \\ 1 & -1 \end{pmatrix}$$ to the standard basis vectors of a one-dimensional Hilbert space: $$H\left|0\right> = \left| + \right>,$$ $$H\left|1\right> = \left| - \right>.$$ You can read more about them Hadamard transform here.